Sample records for early precambrian microfossils

  1. Carbon isotopic composition of individual Precambrian microfossils.

    House, C H; Schopf, J W; McKeegan, K D; Coath, C D; Harrison, T M; Stetter, K O


    Ion microprobe measurements of carbon isotope ratios were made in 30 specimens representing six fossil genera of microorganisms petrified in stromatolitic chert from the approximately 850 Ma Bitter Springs Formation, Australia, and the approximately 2100 Ma Gunflint Formation, Canada. The delta 13C(PDB) values from individual microfossils of the Bitter Springs Formation ranged from -21.3 +/- 1.7% to -31.9 +/- 1.2% and the delta 13C(PDB) values from microfossils of the Gunflint Formation ranged from -32.4 +/- 0.7% to -45.4 +/- 1.2%. With the exception of two highly 13C-depleted Gunflint microfossils, the results generally yield values consistent with carbon fixation via either the Calvin cycle or the acetyl-CoA pathway. However, the isotopic results are not consistent with the degree of fractionation expected from either the 3-hydroxypropionate cycle or the reductive tricarboxylic acid cycle, suggesting that the microfossils studied did not use either of these pathways for carbon fixation. The morphologies of the microfossils suggest an affinity to the cyanobacteria, and our carbon isotopic data are consistent with this assignment.

  2. Precambrian age of the Boston Basin: New evidence from microfossils

    Lenk, C.; Strother, P.K.; Kaye, C.A.; Barghoorn, E.S.


    A Vendian (Late Proterozoic Z) age has been determined for the Boston Basin by comparison of a microflora from the Cambridge Argillite with other late Precambrian assemblages. The microfossils, which include Bavlinella cf. faveolata, are preserved as petrifactions in pyrite. This age designation for the sedimentary rocks of the Boston Basin should allow for the reinterpretation of the structure of the basin and its regional correlations. Copyright ?? 1982 AAAS.

  3. Identifying early Earth microfossils in unsilicified sediments

    Javaux, Emmanuelle J.; Asael, Dan; Bekker, Andrey; Debaille, Vinciane; Derenne, Sylvie; Hofmann, Axel; Mattielli, Nadine; Poulton, Simon


    The search for life on the early Earth or beyond Earth requires the definition of biosignatures, or "indices of life". These traditionally include fossil molecules, isotopic fractionations, biosedimentary structures and morphological fossils interpreted as remnants of life preserved in rocks. This research focuses on traces of life preserved in unsilicified siliciclastic sediments. Indeed, these deposits preserve well sedimentary structures indicative of past aqueous environments and organic matter, including the original organic walls of microscopic organisms. They also do not form in hydrothermal conditions which may be source of abiotic organics. At our knowledge, the only reported occurrence of microfossils preserved in unsilicified Archean sediments is a population of large organic-walled vesicles discovered in shales and siltstones of the 3.2 Ga Moodies Group, South Africa. (Javaux et al, Nature 2010). These have been interpreted as microfossils based on petrographic and geochemical evidence for their endogenicity and syngeneity, their carbonaceous composition, cellular morphology and ultrastructure, occurrence in populations, taphonomic features of soft wall deformation, and the geological context plausible for life, as well as lack of abiotic explanation falsifying a biological origin. Demonstrating that carbonaceous objects from Archaean rocks are truly old and truly biological is the subject of considerable debate. Abiotic processes are known to produce organics and isotopic signatures similar to life. Spheroidal pseudofossils may form as self-assembling vesicles from abiotic CM, e.g. in prebiotic chemistry experiments (Shoztak et al, 2001), from meteoritic lipids (Deamer et al, 2006), or hydrothermal fluids (Akashi et al, 1996); by artifact of maceration; by migration of abiotic or biotic CM along microfractures (VanZuilen et al, 2007) or along mineral casts (Brasier et al, 2005), or around silica spheres formed in silica-saturated water (Jones and

  4. Structures of biogenic origin from Early Precambrian rocks of Euro-Asia.

    Lopuchin, A S


    Spheroidal microfossils mainly 20 to 100 mug in diameter and exhibiting granular surface textures have been recovered from Early Precambrian rocks by applying a new method of water separation in combination with thin chemical preparation. In contrast to the Acritarcha, these microfossils are characterized by a relatively low specific weight (close to one) and considerable fragility due to impregnation by mineral matter. They occur in Archean sediments of Hindustan, in rocks of the Baltic and Aldan Shields with ages of 3.0 to 3.5 billion (10-9) years, and in Proterozoic deposits in many regions of Euro-Asia. They commonly occur in great number in Precambrian sediments of West Africa, Australia and North America. These forms are here regarded as Menneria Lopuchin and are considered to be blue-green algae. Menneria resembles alga-like forms reported by Engel, Nagy and their co-workers from the Onverwacht Series and microfossils reported by Schopf and Barghoorn from the Fig Tree Series, both of the Swaziland System of southern Africa. In addition to spheroidal microfossils, ribbon-like and filiform microstructures are here reported from Archean deposits. The biogenic structures here described from the Early Precambrian of Euro-Asia are considered to have been photosynthetic and planktonic. Their progressive evolution, intensive production of organic matter, and biogeochemical role in concentration of rare elements is discussed.

  5. Microfossils and possible microfossils from the Early Archean Onverwacht Group, Barberton Mountain Land, South Africa.

    Walsh, M M


    There is widespread textural evidence for microbial activity in the cherts of the Early Archean Onverwacht Group. Layers with fine carbonaceous laminations resembling fossil microbial mats are abundant in the cherty metasediments of the predominantly basaltic Hooggenoeg and Kromberg Formations. In rare cases, filamentous microfossils are associated with the laminae. The morphologies of the fossils, as well as the texture of the encompassing laminae suggest an affinity to modern mat-dwelling cyanobacteria or bacteria. A variety of spheroidal and ellipsoidal structures present in cherts of the Hooggenoeg and Kromberg Formations resemble modern coccoidal bacteria and bacterial structures, including spores. The development of spores may have enabled early microorganisms to survive the relatively harsh surficial conditions, including the effects of very large meteorite impacts on the young Earth.

  6. Melanoidin and aldocyanoin microspheres: implications for chemical evolution and early precambrian micropaleontology.

    Kenyon, D H; Nissenbaum, A


    Two new classes of organic microspheres are described. One of them (melanoidin) is synthesized from amino acids and sugars in heated aqueous solutions. The other (aldocyanoin) is formed in aqueous solutions of ammonium cyanide and formaldehyde at room temperature. The general properties of these microspheres, including conditions of synthesis, size and shape, mechanical and pH stability, and solubility, are compared with corresponding properties of other "protocell" model systems. It is concluded that melanoidin and aldocyanoin microsphreres are plausible candidates for precellular units in the primitive hydrosphere. Since the bulk of the organic carbon in early Precambrian sediments is insoluble kerogen-melanoidin, it is suggested that some Precambrian "microfossils" may be abiotic melanoidin microspheres of the type described herein.

  7. Melanoidin and aldocyanoin microspheres - Implications for chemical evolution and early Precambrian micropaleontology

    Kenyon, D. H.; Nissenbaum, A.


    Two new classes of organic microspheres are described. One of them (melanoidin) is synthesized from amino acids and sugars in heated aqueous solutions. The other (aldocyanoin) is formed in aqueous solutions of ammonium cyanide and formaldehyde at room temperature. The general properties of these microspheres, including conditions of synthesis, size and shape, mechanical and pH stability, and solubility, are compared with corresponding properties of other protocell model systems. It is concluded that melanoidin and aldocyanoin microspheres are plausible candidates for precellular units in the primitive hydrosphere. Since the bulk of the organic carbon in early Precambrian sediments is insoluble kerogen-melanoidin, it is suggested that some Precambrian microfossils may be abiotic melanoidin microspheres.

  8. Pellet microfossils: Possible evidence for metazoan life in Early Proterozoic time.

    Robbins, E I; Porter, K G; Haberyan, K A


    Microfossils resembling fecal pellets occur in acid-resistant residues and thin sections of Middle Cambrian to Early Proterozoic shale. The cylindrical microfossils average 50 x 110 mum and are the size and shape of fecal pellets produced by microscopic animals today. Pellets occur in dark gray and black rocks that were deposited in the facies that also preserves sulfide minerals and that represent environments analogous to those that preserve fecal pellets today. Rocks containing pellets and algal microfossils range in age from 0.53 to 1.9 gigayears (Gyr) and include Burgess Shale, Greyson and Newland Formations, Rove Formation, and Gunflint Iron-Formation. Similar rock types of Archean age, ranging from 2.68 to 3.8 Gyr, were barren of pellets. If the Proterozoic microfossils are fossilized fecal pellets, they provide evidence of metazoan life and a complex food chain at 1.9 Gyr ago. This occurrence predates macroscopic metazoan body fossils in the Ediacaran System at 0.67 Gyr, animal trace fossils from 0.9 to 1.3 Gyr, and fossils of unicellular eukaryotic plankton at 1.4 Gyr.

  9. Africa and Precambrian biological evolution

    A. H. Knoll


    Full Text Available African sedimentary rocks and their contained fossils have played a fundamental role in the unravelling of Precambrian biological history. Various lines of evidence including stromatolites, filamentous and coccoidal microfossils, stable isotope ratios, organic carbon distribution, and oxide facies iron formation suggest that a complex prokaryotic ecosystem fueled by photosynthesis, and perhaps including aerobic photoautotrophs, existed as early as 3 500 m.y. ago. The primary sources of data on early Archean life are rock sequences in southern Africa and Australia. The diversity of later Archean (ca. 2 700 m.y. communities is attested to by abundant and varied stromatolites found in Zimbabwe. The extensive growth and consolidation of continents that heralded the Proterozoic Eon had profound effects on the earth’s biota. Primary productivity must have increased substantially, resulting in the establishment of an 02-rich atmosphere, and, subsequently, the radiation of aerobic respirers. Southern African sequences provide critical evidence bearing on this crust/atmosphere/biota interaction; however, the best known microfossils of this age come from North America. Upper Proterozoic sedimentary rocks abound in Africa. Stromatolites from northwestern Africa have been well studied; however, microfossil occurrences remain but sketchily described. Contemporaneous sequences from Scandinavia and Australia document the initial radiation of eukaryotes in the planktonic realm, as well as a terminal Precambrian episode of extinction among plankters. Early heterotrophic protists are known from several continents. The Nama Group of South West Africa/Namibia contains important evidence of early invertebrates. In general, Precambrian evolution can be viewed as a series of increasingly elevated biological plateaus connected by steps marking relatively short periods of evolutionary innovation and radiation. With each step, communities have increased in complexity

  10. Proterozoic and early Palaeozoic microfossils in the Karikkoselkä impact crater, central Finland

    Anneli Uutela


    Full Text Available The Karikkoselkä impact crater is located at Petäjävesi (Lat. 62°13.3' N, Long. 25°14.7' E, in central Finland. The crater is filled with impact-generated breccias and redeposited sedimentary rock yielding microfossils. The assemblage consists of Proterozoic, Cambrian and Ordovician acritarchs, cyanobacteria and green algae thoroughly mixed in the deposit. The late Ordovician acritarch Diexallophasis striatum indicates the maximum age of the impact event in the Keila Regional Stage, middle Caradocian in British Series, 458–449 Ma or later. A till sample overlying the sediments that infill the crater yields only Quaternary pollen and spores, indicating that the impact event occurred prior to the FennoscandianIce Age. The most likely palaeomagnetic age of 260–230 Ma (late Permian to early Triassic is neither excluded nor supported by the microfossil results. However, other palaeomagnetic ages are excluded leaving this the most likely age. This article presents new evidence of Proterozoic and early Palaeozoic deposits that covered central Finland.

  11. Microanalyzes of remarkable microfossils of the Late Mesoproterozoic-Early Neoproterozoic

    Cornet, Yohan; Beghin, Jérémie; Baludikay, Blaise; François, Camille; Storme, Jean-Yves; Compère, Philippe; Javaux, Emanuelle


    The Late Mesoproterozoic-Early Neoproterozoic is an important period to investigate the diversification of early eukaryotes [1]. Following the first appearance of red algae in the Late Mesoproterozoic, other (morphological or molecular) fossils of crown groups are recorded during the Early Neoproterozoic, including green algae, sponges, amoebozoa and possibly fungi. Other microfossils also includes unambiguous eukaryotes, including several distinctive forms for that time period, such as the acritarchs Cerebrosphaera buickii (˜820-720 Ma), Trachyhystrichosphaera aimika and T . botula (1100-720 Ma), and the multicellular eukaryotic problematicum taxon Jacutianema solubila (1100-?720 Ma). To further characterize the taxonomy of these microfossils and to test hypotheses about their possible relationships to crown groups, we combine analyzes of their morphology, wall ultrastructure and microchemistry, using optical microscopy, Scanning and Transmission Electron microscopy (SEM and TEM), as well as Raman and FTIR microspectroscopy respectively. Cerebrosphaera populations from the Svanbergfjellet formation, Spitsbergen, and from the Kanpa Formation, Officer Basin, Australia, include organic vesicles with dark and robust walls ornamented by cerebroid folds [2]. Our study shows the occurrence of complex tri- or bi-layered wall ultrastructures and a highly aromatic composition [3]. The genus Trachyhystrichosphaera includes various species characterized by the presence of a variable number of hollow heteromorphic processes [2]. Preliminary infrared microspectroscopy analyzes performed on two species, T. aimika and T. botula, from the 1.1 Ga Taoudeni Basin, Mauritania, and from the ˜1.1 - 0.8 Ga Mbuji-Mayi Supergroup, RDC, indicate a strong aliphatic and carbonyl composition of the wall biopolymer, with some differences linked to thermal maturity between the two locations. TEM is also performed to characterize the wall ultrastructure of these two species. Various morphotypes

  12. Fossil Microorganisms and Formation of Early Precambrian Weathering Profiles

    Rozanov, A. Yu; Astafieva, M. M.; Vrevsky, A. B.; Alfimova, N. A.; Matrenichev, V. A.; Hoover, R. B.


    Weathering crusts are the only reliable evidences of the existence of continental conditions. Often they are the only source of information about exogenous processes and subsequently about conditions under which the development of the biosphere occurred. A complex of diverse fossil microorganisms was discovered as a result of Scanning Electron Microscope investigations. The chemical composition of the discovered fossils is identical to that of the host rocks and is represented by Si, Al, Fe, Ca and Mg. Probably, the microorganisms fixed in rocks played the role of catalyst. The decomposition of minerals comprising the rocks and their transformation into clayey (argillaceous) minerals, most likely occurred under the influence of microorganisms. And may be unique weathering crusts of Early Precambrian were formed due to interaction between specific composition of microorganism assemblage and conditions of hypergene transformations. So it is possible to speak about colonization of land by microbes already at that time and about existence of single raw from weathering crusts (Primitive soils) to real soils.

  13. Microfossils' diversity from the Proterozoic Taoudeni Basin, Mauritania

    Beghin, Jérémie; Houzay, Jean-Pierre; Blanpied, Christian; Javaux, Emmanuelle


    palaeoecology (habitat diversity) of early eukaryotes, we are combining morphological, microchemical and ultrastructural studies of microfossils, with high-resolution palaeoenvironmental and palaeoredox characterization. References: Amard B. (1986) Microfossiles (Acritarches) du Protérozoïque supérieur dans les shales de la formation d'Atar (Mauritanie). Precambrian Research 31: 69-95. Blumenberg M, Thiel V, Riegel W, et al. (2012) Biomarkers of black shales formed by microbial mats, Late Mesoproterozoic (1.1 Ga) Taoudeni Basin, Mauritania. Precambrian Research 196-197: 113-127. Javaux EJ. (2011) Early eukaryotes in Precambrian oceans. Origins and Evolution of Life. An Astrobiological Perspective. Cambridge University Press, 414-449. Knoll AH, Javaux EJ, Hewitt D, et al. (2006) Eukaryotic organisms in Proterozoic oceans. Philosophical Transactions of the Royal Society B: Biological Sciences 361: 1023-1038.

  14. Evolution of Precambrian life in the Brazilian geological record

    Fairchild, Thomas Rich; Sanchez, Evelyn A. M.; Pacheco, Mírian Liza A. F.; de Moraes Leme, Juliana


    Precambrian rocks comprise nearly one-quarter of the surface of Brazil and range from Paleoarchean (ca. 3.6 Ga) to the latest Ediacaran (0.542 Ga) in age. Except for controversial phosphatized `embryo-like' microfossils like those from the lower Ediacaran Doushantuo Formation, China and complex rangeomorphs, Brazilian research has revealed all major categories of Precambrian life forms described elsewhere - microbialites, biomarkers, silicified microfossils, palynomorphs, vase-shaped microfossils, macroalgae, metazoans, vendobionts and ichnofossils - but the paleobiological significance of this record has been little explored. At least four occurrences of these fossils offer promise for increased understanding of the following aspects of Precambrian biospheric evolution: (i) the relationship of microbialites in 2.1-2.4 Ga old carbonates of the Minas Supergroup in the Quadrilátero Ferrífero, Minas Gerais (the oldest Brazilian fossils) to the development of the early oxygenic atmosphere and penecontemporaneous global tectonic and climatic events; (ii) the evolutionary and biostratigraphic significance of Mesoproterozoic to Ediacaran organic-walled microfossils in central-western Brazil; (iii) diversity and paleoecological significance of vase-shaped heterotrophic protistan microfossils in the Urucum Formation (Jacadigo Group) and possibly the Bocaina Formation (Corumbá Group), of Mato Grosso do Sul; and (iv) insights into the record of skeletogenesis and paleoecology of latest Ediacaran metazoans as represented by the abundant organic carapaces of Corumbella and calcareous shells of the index fossil Cloudina, of the Corumbá Group, Mato Grosso do Sul. Analysis of the Brazilian Precambrian fossil record thus holds great potential for augmenting paleobiological knowledge of this crucial period on Earth and for developing more robust hypotheses regarding possible origins and evolutionary pathways of biospheres on other planets.

  15. Precambrian Skeletonized Microbial Eukaryotes

    Lipps, Jere H.


    Skeletal heterotrophic eukaryotes are mostly absent from the Precambrian, although algal eukaryotes appear about 2.2 billion years ago. Tintinnids, radiolaria and foraminifera have molecular origins well back into the Precambrian yet no representatives of these groups are known with certainty in that time. These data infer times of the last common ancestors, not the appearance of true representatives of these groups which may well have diversified or not been preserved since those splits. Previous reports of these groups in the Precambrian are misinterpretations of other objects in the fossil record. Reported tintinnids at 1600 mya from China are metamorphic shards or mineral artifacts, the many specimens from 635-715 mya in Mongolia may be eukaryotes but they are not tintinnids, and the putative tintinnids at 580 mya in the Doushantou formation of China are diagenetic alterations of well-known acritarchs. The oldest supposed foraminiferan is Titanotheca from 550 to 565 mya rocks in South America and Africa is based on the occurrence of rutile in the tests and in a few modern agglutinated foraminifera, as well as the agglutinated tests. Neither of these nor the morphology are characteristic of foraminifera; hence these fossils remain as indeterminate microfossils. Platysolenites, an agglutinated tube identical to the modern foraminiferan Bathysiphon, occurs in the latest Neoproterozoic in Russia, Canada, and the USA (California). Some of the larger fossils occurring in typical Ediacaran (late Neoproterozoic) assemblages may be xenophyophorids (very large foraminifera), but the comparison is disputed and flawed. Radiolaria, on occasion, have been reported in the Precambrian, but the earliest known clearly identifiable ones are in the Cambrian. The only certain Precambrian heterotrophic skeletal eukaryotes (thecamoebians) occur in fresh-water rocks at about 750 mya. Skeletonized radiolaria and foraminifera appear sparsely in the Cambrian and radiate in the Ordovician

  16. Cyanobacterial evolution during the Precambrian

    Schirrmeister, Bettina E.; Sanchez-Baracaldo, Patricia; Wacey, David


    Life on Earth has existed for at least 3.5 billion years. Yet, relatively little is known of its evolution during the first two billion years, due to the scarceness and generally poor preservation of fossilized biological material. Cyanobacteria, formerly known as blue green algae were among the first crown Eubacteria to evolve and for more than 2.5 billion years they have strongly influenced Earth's biosphere. Being the only organism where oxygenic photosynthesis has originated, they have oxygenated Earth's atmosphere and hydrosphere, triggered the evolution of plants -being ancestral to chloroplasts- and enabled the evolution of complex life based on aerobic respiration. Having such a strong impact on early life, one might expect that the evolutionary success of this group may also have triggered further biosphere changes during early Earth history. However, very little is known about the early evolution of this phylum and ongoing debates about cyanobacterial fossils, biomarkers and molecular clock analyses highlight the difficulties in this field of research. Although phylogenomic analyses have provided promising glimpses into the early evolution of cyanobacteria, estimated divergence ages are often very uncertain, because of vague and insufficient tree-calibrations. Results of molecular clock analyses are intrinsically tied to these prior calibration points, hence improving calibrations will enable more precise divergence time estimations. Here we provide a review of previously described Precambrian microfossils, biomarkers and geochemical markers that inform upon the early evolution of cyanobacteria. Future research in micropalaeontology will require novel analyses and imaging techniques to improve taxonomic affiliation of many Precambrian microfossils. Consequently, a better understanding of early cyanobacterial evolution will not only allow for a more specific calibration of cyanobacterial and eubacterial phylogenies, but also provide new dates for the tree

  17. Early evolution of large micro-organisms with cytological complexity revealed by microanalyses of 3.4 Ga organic-walled microfossils.

    Sugitani, K; Mimura, K; Takeuchi, M; Lepot, K; Ito, S; Javaux, E J


    The Strelley Pool Formation (SPF) is widely distributed in the East Pilbara Terrane (EPT) of the Pilbara Craton, Western Australia, and represents a Paleoarchean shallow-water to subaerial environment. It was deposited ~3.4 billion years ago and displays well-documented carbonate stromatolites. Diverse putative microfossils (SPF microfossils) were recently reported from several localities in the East Strelley, Panorama, Warralong, and Goldsworthy greenstone belts. Thus, the SPF provides unparalleled opportunities to gain insights into a shallow-water to subaerial ecosystem on the early Earth. Our new micro- to nanoscale ultrastructural and microchemical studies of the SPF microfossils show that large (20-70 μm) lenticular organic-walled flanged microfossils retain their structural integrity, morphology, and chain-like arrangements after acid (HF-HCl) extraction (palynology). Scanning and transmitted electron microscopy of extracted microfossils revealed that the central lenticular body is either alveolar or hollow, and the wall is continuous with the surrounding smooth to reticulated discoidal flange. These features demonstrate the evolution of large micro-organisms able to form an acid-resistant recalcitrant envelope or cell wall with complex morphology and to form colonial chains in the Paleoarchean era. This study provides evidence of the evolution of very early and remarkable biological innovations, well before the presumed late emergence of complex cells.

  18. Morphotype disparity in the Precambrian

    Moore, Rachael; Reitner, Joachim; Braiser, Martin; Donoghue, Phil; Schirrmeister, Bettina


    Prokaryotes have dominated life on Earth for over 2 billion years. Throughout the Precambrian, prokaryotes acted as the major biological impetus for both large and small scale environmental changes. Yet, very little is known about the composition, diversity and evolution of ancient microbial communities due to poor preservation during the Precambrian period. Previous studies of fossils that date to this period relied mainly on light microscopy to identify microfossil morphology and abundance, with limited success. Here we present novel analyses of the microbial remains found in Precambrian stromatolites using Synchrotron Radiation x-Ray Tomographic Microscopy (SRXTM). Microfossils found in samples of three Precambrian deposits, 3.45 Ga Strelley Pool, Australia, 2.1 Ga Gunflint Chert, Canada, and 650 Ma Rasthof Cap Carbonate, Namibia, have been reconstructed in 3D. Based on four scans from each sample, we estimated size and abundance of spheroidal microfossils within those deposits. Our findings show that while cell abundance decreased towards the end of the Precambrian, the biovolume of microfossils within the host rock remained relatively constant. Additionally, both size and disparity increase through time. Constant biovolumes and yet different sizes for these three deposits, point towards a negative correlation of large cell size and cell abundance. This negative correlation indicates that the systems in which these prokaryotes lived may have been biolimited. Both, gas exchange and nutrient uptake in prokaryotes function via diffusion. Therefore, one would expect bacteria to evolve towards an increasing surface to volume ratio. Increased cell sizes, and hence decreased overall surface to volume ratio observed in our data, suggest the influence of other selective factors. Decreased abundance and increased cell size could potentially be associated to changes in nutrient availability and the occurrence of predation. As cells increased in size, more nutrients would

  19. Early Archean (approximately 3.4 Ga) prokaryotic filaments from cherts of the apex basalt, Western Australia: The oldest cellularly preserved microfossils now known

    Schopf, J. W.


    In comparison with that known from later geologic time, the Archean fossil record is miniscule: although literally hundreds of Proterozoic formations, containing more that 2800 occurrences of bona fide microfossils are now known, fewer than 30 units containing some 43 categories of putative microfossils (the vast majority of which are of questionable authenticity) have been reported from the Archean. Among the oldest known fossils are Early Archean filaments reported from cherts of the Towers Formation and the Apex Basalt of the 3.3-3.6 Ga-old Warrawoona Group of Western Australia. The paleobiologic significance of the Towers Formation microstructures is open to question: thin aggregated filaments are properly regarded as dubiomicrofossils (perhaps biogenic, but perhaps not); therefore, they cannot be regarded as firm evidence of Archean life. Although authentic, filamentous microfossiles were reported from a second Towers Formation locality, because the precise layer containing the fossiliferous cherts was not relocated, this discovery can neither be reconfirmed by the original collector nor confirmed independently by other investigators. Discovery of microfossils in bedded cherts of the Apex Basalt, the stratigraphic unit immediately overlying the Towers Formation, obviates the difficulties stored above. The cellularly preserved filaments of the Apex Basalt meet all of the criteria required of a bona fide Archean microfossils. Recent studies indicate that the Apex assemblage includes at least six morphotypes of uniseriate filaments, composed of barrel-shaped, discoidal, or quadrate cells and exhibiting rounded or conical terminal cells and medial bifurcated and paired half-cells that reflect the occurrence of prokaryotic binary cell division. Interestingly, the majority of these morphotypes are morphologically more similar to extant cyanobacteria than to modern filamentous bacteria. Prokaryotes seem clearly to have been hypobradytelic, and the evidence suggests

  20. A new plant assemblage (microfossil and megafossil) from the Lower Old Red Sandstone of the Anglo-Welsh Basin: its implications for the palaeoecology of early terrestrial ecosystems.

    Wellman; Habgood; Jenkins; Richardson


    Lower Old Red Sandstone deposits penetrated by a series of cored boreholes near Newport (South Wales) have been sedimentologically logged, and recovered plant assemblages (microfossil and megafossil) investigated. Sedimentological logging indicates that the deposits are typical of the extensive terrestrial-fluviatile floodplain deposits of the Anglo-Welsh Basin. Palynomorph assemblages have been recovered from a number of horizons and comprise entirely terrestrial forms (spores and phytodebris). They essentially represent a single assemblage, belonging to the middle subzone of the micrornatus-newportensis sporomorph assemblage biozone, and indicate an Early Devonian (mid-Lochkovian) age. The new biostratigraphical data enables correlation with other Lower Old Red Sandstone deposits of the Anglo-Welsh Basin, and the deposits are assigned to the lower part of the St. Maughan's Group. A plant megafossil/mesofossil assemblage recovered from one of the spore-bearing horizons includes a zosterophyll assigned to Zosterophyllum cf. fertile. This is the earliest reported zosterophyll from the Anglo-Welsh Basin. The new palynological/palaeobotanical data provide important information on the palaeoecology and palaeobiogeography of the vegetation of the southeastern margin of the Old Red Sandstone continent during Lochkovian times. Palaeogeographical variation in the distribution of plant microfossils and megafossils is interpreted as reflecting differences between the flora of the lowland floodplain and inland intermontaine basins, although this is to a certain extent overprinted by variation due to localized differences in environmental conditions.

  1. Early Precambrian Carbonate and Evapolite Sediments: Constraints on Environmental and Biological Evolution

    Grotzinger, John P.


    The work accomplished under NASA Grant NAG5-6722 was very successful. Our lab was able to document the occurrence and distribution of evaporite-to-carbonate transitions in several basins during Precambrian time, to help constrain the long-term chemical evolution of seawater.

  2. Precambrian oxygen levels estimated from the biochemistry and physiology of early eukaryotes

    Runnegar, Bruce


    (≤ 0.01 PAL O 2) which may have persisted until the end of the Precambrian. Unfortunately, these estimates of the minimal oxygen requirements of known Precambrian eukaryotes do little at this stage to constrain models for the growth of atmospheric oxygen during the Proterozoic. It is therefore unknown whether oxygen levels remained relatively low (< 0.1 PAL) until near the end of the Precambrian or climbed rapidly to near modern values after oceanic oxygen sinks were exhausted some 2 Ga ago.

  3. Precambrian clastic sedimentation systems

    Eriksson, P. G.; Condie, K. C.; Tirsgaard, H.; Mueller, W. U.; Altermann, W.; Miall, A. D.; Aspler, L. B.; Catuneanu, O.; Chiarenzelli, J. R.


    The unique and evolving nature of the Precambrian geological environment in many ways was responsible for significant differences between Precambrian clastic sedimentary deposits and their Phanerozoic-modern equivalents. Some form of plate tectonics, with rapid microplate collisions and concomitant volcanic activity, is inferred to have led to the formation of greenstone belts. Explosive volcanism promoted common gravity-flow deposits within terrestrial greenstone settings, with braided alluvial, wave/storm-related and tidal coastline sediments also being preserved. Late Archaean accretion of greenstone terranes led to emergence of proto-cratons, where cratonic and rift sedimentary assemblages developed, and these became widespread in the Proterozoic as cratonic plates stabilised. Carbonate deposition was restricted by the paucity of stable Archaean terranes. An Early Precambrian atmosphere characterised by greenhouse gases, including CO 2, in conjunction with a faster rotation of the Earth and reduced albedo, provide a solution to the faint young Sun paradox. As emergent continental crust developed, volcanic additions of CO 2 became balanced by withdrawal due to weathering and a developing Palaeoproterozoic microbial biomass. The reduction in CO 2, and the photosynthetic production of O 2, led to aerobic conditions probably being achieved by about 2 Ga. Oceanic growth was allied to atmospheric development, with approximately 90% of current ocean volume being reached by about 4 Ga. Warm Archaean and warm, moist Palaeoproterozoic palaeoclimates appear to have become more arid after about 2.3 Ga. The 2.4-2.3 Ga Huronian glaciation event was probably related to continental growth, supercontinent assembly and weathering-related CO 2 reduction. Despite many analogous features among both Precambrian and younger sedimentary deposits, there appear to be major differences as well. Two pertinent examples are rare unequivocal aeolian deposits prior to about 1.8 Ga and an

  4. Artificial microfossils - Experimental studies of permineralization of blue-green algae in silica.

    Oehler, J. H.; Schopf, J. W.


    A technique has been developed to artificially fossilize microscopic algae in crystalline silica under conditions of moderately elevated temperature and pressure. The technique is designed to simulate geochemical processes thought to have resulted in the preservation of organic microfossils in Precambrian bedded cherts. In degree of preservation and mineralogic setting, the artificially permineralized microorganisms are comparable to naturally occurring fossil algae.

  5. Microfossils as biosignatures

    Beraldi-Campesi, Hugo


    As technology advances, we have more possibilities to search for past life, looking for biosignatures in the rock record. Even when these biosignatures can be chemical compounds, the irrevocable evidence of past life would be life itself preserved as fossils. Besides the pure shape, extra information such as the paleoenvironment, biotic associations, and the age of the rocks, can be retrieved from fossils to understand their significance and the context in which they developed. However, much of that information is rarely well preserved, giving fossils a wide range for speculation. Furthermore, abiotic structures can sometimes be easily mistaken as fossils, leading to wrong interpretations. Depending on the mode of fossilization and the type of organism, more or fewer characteristics would be available for interpretation, and depending on the techniques used for observation, those characteristics would be more or less appreciated. In permineralized organisms, internal and external structures can be observable with simple techniques (e.g. thin sections), revealing basic anatomic features that can yield trusty identifications. An example of remarkable organisms with these characteristics is found in the North-East region of Sonora, Mexico. Cretaceous sequences (70-72 Ma old) from the Tarahumara Formation contain several chert horizons where palm roots, freshwater aquatic plants, pollen grains, flowers, seeds, small crustaceans, algae, and cyanobacteria (among others) are commonly found, reflecting the extense diversity existing at that time. One of the Formation's localities, the Huepac Chert, exhibits several stromatolitic horizons in close relation with black chert that harbors a number of permineralized microfossils. About 65 different morphotypes have been described and some have been identified as cyanobacteria, chlorophyceans, and diatoms. These comparisions allowed us to conclude that some had benthonic habits, being perhaps stromatolite constructors. Others

  6. Transitional changes in microfossil assemblages in the Japan Sea from the Late Pliocene to Early Pleistocene related to global climatic and local tectonic events

    Itaki, Takuya


    Many micropaleontological studies based on data from on-land sections, oil wells, and deep-sea drilling cores have provided important information about environmental changes in the Japan Sea that are related to the global climate and the local tectonics of the Japanese Islands. Here, major changes in the microfossil assemblages during the Late Pliocene to Early Pleistocene are reviewed. Late Pliocene (3.5-2.7 Ma) surface-water assemblages were characterized mainly by cold-temperate planktonic flora and fauna (nannofossils, diatoms, radiolarians, and planktonic foraminifera), suggesting that nutrient-rich North Pacific surface waters entered the Japan Sea via northern straits. The common occurrence of Pacific-type deep-water radiolarians during this period also suggests that deep water from the North Pacific entered the Japan Sea via the northern straits, indicating a sill depth >500 m. A weak warm-water influence is recognized along the Japanese coast, suggesting a small inflow of warm water via a southern strait. Nannofossil and sublittoral ostracod assemblages record an abrupt cooling event at 2.75 Ma that correlates with the onset of the Northern Hemisphere glaciation. Subsequently, cold intermediate- and deep-water assemblages of ostracods and radiolarians increased in abundance, suggesting active ventilation and the formation of the Japan Sea Proper Water, associated with a strengthened winter monsoon. Pacific-type deep-water radiolarians also disappeared around 2.75 Ma, which is attributed to the intermittent occurrence of deep anoxic environments and limited migration from the North Pacific, resulting from the near-closure or shallowing of the northern strait by a eustatic fall in sea level and tectonic uplift of northeastern Japan. A notable reduction in primary productivity from 2.3 to 1.3 Ma also suggests that the nutrient supply from the North Pacific was restricted by the near-closure of the northern strait. An increase in the abundance of subtropical

  7. Microfossils in Carbonaceous Meteorites

    Hoover, Richard B.


    Microfossils of large filamentous trichomic prokaryotes have been detected during in-situ investigations of carbonaceous meteorites. This research has been carried out using the Field Emission Scanning Electron Microscope (FESEM) to examine freshly fractured interior surfaces of the meteorites. The images obtained reveal that many of these remains are embedded in the meteorite rock matrix. Energy Dispersive X-Ray Spectroscopy (EDS) studies establish that the filamentous microstructures have elemental compositions consistent with the meteorite matrix, but are often encased within carbon-rich electron transparent sheath-like structures infilled with magnesium sulfate. This is consistent with the taphonomic modes of fossilization of cyanobacteria and sulphur bacteria, since the life habits and processes of these microorganisms frequently result in distinctive chemical biosignatures associated with the properties of their cell-walls, trichomes, and the extracellular polymeric substances (EPS) of the sheath. In this paper the evidence for biogenicity presented includes detailed morphological and morphometric data consistent with known characteristics of uniseriate and multiseriate cyanobacteria. Evidence for indigeneity includes the embedded nature of the fossils and elemental compositions inconsistent with modern biocontaminants.

  8. Cuatro Ciénegas Basin an analog of precambrian Earth and possible early mars scenario. (Invited)

    Souza, V.; Eguiarte, L. E.; Sierfert, J.


    In the present, the Cuatro Cienegas Basin (CCB) is in the Chihuahuan Desert in the state of Coahuila, Mexico. However, in the early Triasic, the sea penetrated the region of CCB with the opening of Pangea and became a continental wetland with the closing the western interior seaway only 35 million years ago. Its particular tectonics made of CCB a valley surrounded by high sierras that rose above the sea level 700 mt. All available molecular data lead us to suggest that these ancient marine microbial mats have persisted for a very long time and during all that time, the living microbial community evolved and diversified locally due to the rarity of migration and sex. The struggle for life in these structured communities generated uncountable new species that had to deal with the environment, the neighbors and most of all with the extreme lack of P. What for a long time represented the most successful community assemblage in the history of planet Earth, became mostly extinct in modern earth. The herbivores and the competition with algae left few relict communities in extreme environments such as CCB, Shark Bay and Guerrero Negro. Lets remember that stromatolite reefs have fossils as old as 3.6 billion years and that they became so successful that they changed the planet atmosphere producing the great oxygenation event. We also have data that at CCB these extensive microbialites are very patchy and differentiated both taxonomically and genetically, implying that, even though they may look as a continuum in the wetlands, each patch has been geographically isolated for a long time allowing each community to diverge in its composition. All these particularities of CCB arise because, due to its unusual geology, the valley floor was never buried, hence its marine sediment, with extensive microbial mats, always had sun and water, maintaining both the ancient lineages and the oligotrophic conditions that characterized early earth. The lack of P (less than 0.05 n

  9. New Data on Microfossils from Shungites

    Hoover, Robert B.; Rozanov, Alexei Yu.


    Shungites are pre-cambrian (2Gya) carbon-rich, silicate rocks known from deposits in the north-western part of lake Onega, near the city of Petrozavodsk in Karelia (North from St. Petersburg, Russia). Shungites are extremely rich in carbon, with carbon accounting for 98% in vein shungites. Shungites have been found to exhibit interesting optical, ultrasonic, thermal, mechanical, electrical properties and have recently been found to contain small amounts of C60 fullerene. Shungite rocks from Karelia have a characteristic globular structure and are chemically inert and metastable. As part of our ongoing search for biomarkers in ancient terrestrial rocks that are of potential significance to Astrobiology, we have conducted Environmental and Field Emission Scanning Electron Micrographs of freshly fractured interior surfaces of Shungites. We find them to contain indigenous miocrofossils, similar to cyanobacteria known from the phosphorites of Khubsugul, Mongolia. We describe this investigation and provide ESEM and FESEM images of biomorphic microstructures that we interpret as indigenous microfossils in Shungites.

  10. Oxygen isotope studies of early Precambrian granitic rocks from the Giants Range batholith, northeastern Minnesota, U.S.A.

    Viswanathan, S.


    Oxygen isotope studies of granitic rocks from the 2.7 b.y.-old composite Giants Range batholith show that: (1) ??(O18)quartz values of 9 to 10 permil characterize relatively uncontaminated Lower Precambrian, magmatic granodiorites and granites; (2) granitic rocks thought to have formed by static granitization have ??(O18)quartz values that are 1 to 2 permil higher than magmatic granitic rocks; (3) satellite leucogranite bodies have values nearly identical to those of the main intrusive phases even where they transect O18-rich metasedimentary wall rocks; (4) oxygen isotopic interaction between the granitic melts and their O18-rich wall rocks was minimal; and (5) O18/O18 ratios of quartz grains in a metasomatic granite are largely inherited from the precursor rock, but during the progression - sedimentary parent ??? partially granitized parent ??? metasomatic granite ??? there is gradual decrease in ??(O18)quartz by 1 to 2 permil. ?? 1974.

  11. Early Precambrian Crustal Evolution in the Northern Margin of the North China Craton: Constraints from Zircon U-Pb and Lu-Hf Isotopes

    LIU Shu-wen; Lü Yong-jun; LI Qiu-gen


    @@ Northern Hebei province, one of important Precambrian metamorphic areas, is located in the middle segment of northern margin of the North China Craton. Precambrian rocks in this area are subdivided into two units by the Chaiwopu-Dantazi ductile shear zone.

  12. SHRIMP zircon dating and LA-ICPMS Hf analysis of early Precambrian rocks from drill holes into the basement beneath the Central Hebei Basin, North China Craton

    Yusheng Wan; Runlong Fan; Huiyi Sun; Xianzheng Zhao; Zejiu Wang; Dunyi Liu; Alfred Kröner; Chunyan Dong; Hangqian Xie; Yuansheng Geng; Yuhai Zhang


    The Central Hebei Basin (CHB) is one of the largest sedimentary basins in the North China Craton, extending in a northeastesouthwest direction with an area of>350 km2. We carried out SHRIMP zircon dating, Hf-in-zircon isotopic analysis and a whole-rock geochemical study on igneous and metasedi-mentary rocks recovered from drill holes that penetrated into the basement of the CHB. Two samples of gneissic granodiorite (XG1-1) and gneissic quartz diorite (J48-1) have magmatic ages of 2500 and 2496 Ma, respectively. Their zircons also record metamorphic ages of 2.41e2.51 and w2.5 Ga, respec-tively. Compared with the gneissic granodiorite, the gneissic quartz diorite has higher SREE contents and lower Eu/Eu* and (La/Yb)n values. Two metasedimentary samples (MG1, H5) mainly contain w2.5 Ga detrital zircons as well as late Paleoproterozoic metamorphic grains. The zircons of different origins haveεHf (2.5 Ga) values and Hf crustal model ages ranging from 0 to 5 and 2.7 to 2.9 Ga, respectively. Therefore, w2.5 Ga magmatic and Paleoproterozoic metasedimentary rocks and late Neoarchean to early Paleoproterozoic and late Paleoproterozoic tectono-thermal events have been identified in the basement beneath the CHB. Based on regional comparisons, we conclude that the early Precambrian basement beneath the CHB is part of the North China Craton.

  13. Oxygen isotope perspective on crustal evolution on early Earth: A record of Precambrian shales with emphasis on Paleoproterozoic glaciations and Great Oxygenation Event

    Bindeman, I. N.; Bekker, A.; Zakharov, D. O.


    We present stable isotope and chemical data for 206 Precambrian bulk shale and tillite samples that were collected mostly from drillholes on all continents and span the age range from 0.5 to 3.5 Ga with a dense coverage for 2.5-2.2 Ga time interval when Earth experienced four Snowball Earth glaciations and the irreversible rise in atmospheric O2. We observe significant, downward shift of several ‰ and a smaller range of δ18 O values (7 to 9‰) in shales that are associated with the Paleoproterozoic and, potentially, Neoproterozoic glaciations. The Paleoproterozoic samples consist of more than 50% mica minerals and have equal or higher chemical index of alteration than overlying and underlying formations and thus underwent equal or greater degrees of chemical weathering. Their pervasively low δ18 O and δD (down to - 85 ‰) values provide strong evidence of alteration and diagenesis in contact with ultra-low δ18 O glacial meltwaters in lacustrine, deltaic or periglacial lake (sikussak-type) environments associated with the Paleoproterozoic glaciations. The δDsilicate values for the rest of Precambrian shales range from -75 to - 50 ‰ and are comparable to those for Phanerozoic and Archean shales. Likewise, these samples have similar ranges in δ13Corg values (-23 to - 33 ‰ PDB) and Corg content (0.0 to 10 wt%) to Phanerozoic shales. Precambrian shales have a large range of δ18 O values comparable to that of the Phanerozoic shales in each age group and formation, suggesting similar variability in the provenance and intensity of chemical weathering, except for the earliest 3.3-3.5 Ga Archean shales, which have consistently lower δ18 O values. Moreover, Paleoproterozoic shales that bracket in age the Great Oxidation Event (GOE) overlap in δ18 O values. Absence of a step-wise increase in δ18 O and δD values suggests that despite the first-order change in the composition of the atmosphere, weathering cycle was not dramatically affected by the GOE at ∼2

  14. The evolution and distribution of life in the Precambrian eon-Global perspective and the Indian record

    M Sharma; Y Shukla


    The discovery of Precambrian microfossils in 1954 opened a new vista of investigations in the field of evolution of life. Although the Precambrian encompasses 87% of the earth’s history, the pace of organismal evolution was quite slow. The life forms as categorised today in the three principal domains viz. the Bacteria, the Archaea and the Eucarya evolved during this period. In this paper, we review the advancements made in the Precambrian palaeontology and its contribution in understanding the evolution of life forms on earth. These studies have enriched the data base on the Precambrian life. Most of the direct evidence includes fossil prokaryotes, protists, advanced algal fossils, acritarchs, and the indirect evidence is represented by the stromatolites, trace fossils and geochemical fossils signatures. The Precambrian fossils are preserved in the form of compressions, impressions, and permineralized and biomineralized remains.

  15. Records of Precambrian Early Palaeozoic volcanic and sedimentary processes in the Central European Variscides: A review of SHRIMP zircon data from the Kaczawa succession (Sudetes, SW Poland)

    Kryza, Ryszard; Zalasiewicz, Jan


    The early, pre-orogenic stages of evolution in the Variscan belt, i.e. rifting processes, opening of sedimentary basins and associated igneous activities, are often obscure because many successions have yielded little or no biostratigraphic data, have a strong metamorphic overprint and are tectonically deformed and dislocated. The increasing application of SHRIMP zircon dating has provided useful constraints on magmatic and metamorphic processes, helped locate probable source areas for detritus within sedimentary successions and facilitated large-scale palaeogeographic correlations. This methodology has recently thrown considerable light on the age and relationships of the previously poorly constrained rock units of the Kaczawa Complex in the Polish West Sudetes. Thus, recent SHRIMP studies in the Kaczawa Mountains have yielded Early Ordovician ages of the initial rift type bimodal volcanic suites at the bottom part of the Kaczawa Succession: c. 503 Ma for metarhyodacites of crustal derivation, and c. 485 Ma for alkaline metatrachytes of mantle signature. These dates provide a firm temporal constraint on the initial rift magmatism interpreted as related to the continental break-up of the northern peripheries of Gondwana. New SHRIMP data from metavolcaniclastic and metasedimentary rocks of the Kaczawa Complex have yielded results that have provided significantly changed interpretations on their age and relationships. For instance, a siliciclastic sequence interpreted as belonging to the lower part of the Kaczawa Complex (the Gackowa Sandstones) and seemingly sourced (using an array of geochemical and mineralogical evidence) from nearby early Ordovician volcanic rocks has, surprisingly, yielded zircon ages not younger than Precambrian and thus this unit has tentatively been reinterpreted as a possible correlative of the Neoproterozoic Lusatian Graywackes. Felsic metavolcaniclastic rocks embedded in the carbonate succession of the Wojcieszów Limestone have yielded

  16. SHRIMP zircon dating and LA-ICPMS Hf analysis of early Precambrian rocks from drill holes into the basement beneath the Central Hebei Basin, North China Craton

    Yusheng Wan


    Full Text Available The Central Hebei Basin (CHB is one of the largest sedimentary basins in the North China Craton, extending in a northeast–southwest direction with an area of >350 km2. We carried out SHRIMP zircon dating, Hf-in-zircon isotopic analysis and a whole-rock geochemical study on igneous and metasedimentary rocks recovered from drill holes that penetrated into the basement of the CHB. Two samples of gneissic granodiorite (XG1-1 and gneissic quartz diorite (J48-1 have magmatic ages of 2500 and 2496 Ma, respectively. Their zircons also record metamorphic ages of 2.41–2.51 and ∼2.5 Ga, respectively. Compared with the gneissic granodiorite, the gneissic quartz diorite has higher ΣREE contents and lower Eu/Eu* and (La/Ybn values. Two metasedimentary samples (MG1, H5 mainly contain ∼2.5 Ga detrital zircons as well as late Paleoproterozoic metamorphic grains. The zircons of different origins have εHf (2.5 Ga values and Hf crustal model ages ranging from 0 to 5 and 2.7 to 2.9 Ga, respectively. Therefore, ∼2.5 Ga magmatic and Paleoproterozoic metasedimentary rocks and late Neoarchean to early Paleoproterozoic and late Paleoproterozoic tectono-thermal events have been identified in the basement beneath the CHB. Based on regional comparisons, we conclude that the early Precambrian basement beneath the CHB is part of the North China Craton.

  17. Martian "microfossils" in lunar meteorites?

    Sears, D W; Kral, T A


    One of the five lines of evidence used by McKay et al. (1996) for relic life in the Martian meteorite Allan Hills (ALH) 84001 was the presence of objects thought to be microfossils. These ovoid and elongated forms are similar to structures found in terrestrial rocks and described as "nanobacteria" (Folk, 1993; McBride et al., 1994). Using the same procedures and apparatus as McKay et al. (1996), we have found structures on internal fracture surfaces of lunar meteorites that cannot be distinguished from the objects described on similar surfaces in ALH 84001. The lunar surface is currently a sterile environment and probably always has been. However, the lunar and Martian meteorites share a common terrestrial history, which includes many thousands of years of exposure to Antarctic weathering. Although we do not know the origin of these ovoid and elongated forms, we suggest that their presence on lunar meteorites indicates that the objects described by McKay et al. (1996) are not of Martian biological origin.

  18. Proterozoic microfossils revealing the time of algal divergences

    Moczydlowska-Vidal, Malgorzata


    Proterozoic microfossils revealing the time of algal divergences Małgorzata Moczydłowska-Vidal Uppsala University, Department of Earth Sciences, Palaeobiology, Villavägen 16, SE 752 36 Uppsala, Sweden ( Morphological and reproductive features and cell wall ultrastructure and biochemistry of Proterozoic acritarchs are used to determine their affinity to modern algae. The first appearance datum of these microbiota is traced to infer a minimum age of the divergence of the algal classes to which they may belong. The chronological appearance of microfossils that represent phycoma-like and zygotic cysts and vegetative cells and/or aplanospores, respectively interpreted as prasinophyceaen and chlorophyceaen microalgae, is related to the Viridiplantae phylogeny. These divergence times differ from molecular clock estimates, and the palaeontological evidence suggests that they are older. The best examples of unicellular, organic-walled microfossils (acritarchs) from the Mesoproterozoic to Early Ordovician are reviewed to demonstrate features, which are indicative of their affinity to photosynthetic microalgae. The first indication that a microfossil may be algal is a decay- and acid-resistant cell wall, which reflects its biochemistry and ultrastructure, and probably indicates the ability to protect a resting/reproductive cyst. The biopolymers synthesized in the cell walls of algae and in land plants ("plant cells"), such as sporopollenin/algaenan, are diagnostic for photosynthetic taxa and were inherited from early unicellular ancestors. These preservable cell walls are resistant to acetolysis, hydrolysis and acids, and show diagnostic ultrastructures such as the trilaminar sheath structure (TLS). "Plant cell" walls differ in terms of chemical compounds, which give high preservation potential, from fungal and animal cell walls. Fungal and animal cells are fossilized only by syngenetic permineralization, whereas "plant cells" are fossilized as body

  19. Precambrian animal life: probable developmental and adult cnidarian forms from Southwest China

    Chen, Jun-Yuan; Oliveri, Paola; Gao, Feng; Dornbos, Stephen Q.; Li, Chia-Wei; Bottjer, David J.; Davidson, Eric H.


    The evolutionary divergence of cnidarian and bilaterian lineages from their remote metazoan ancestor occurred at an unknown depth in time before the Cambrian, since crown group representatives of each are found in Lower Cambrian fossil assemblages. We report here a variety of putative embryonic, larval, and adult microfossils deriving from Precambrian phosphorite deposits of Southwest China, which may predate the Cambrian radiation by 25-45 million years. These are most probably of cnidarian affinity. Large numbers of fossilized early planula-like larvae were observed under the microscope in sections. Though several forms are represented, the majority display remarkable conformity, which is inconsistent with the alternative that they are artifactual mineral inclusions. Some of these fossils are preserved in such high resolution that individual cells can be discerned. We confirm in detail an earlier report of the presence in the same deposits of tabulates, an extinct crown group anthozoan form. Other sections reveal structures that most closely resemble sections of basal modern corals. A large number of fossils similar to modern hydrozoan gastrulae were also observed. These again displayed great morphological consistency. Though only a single example is available, a microscopic animal remarkably similar to a modern adult hydrozoan is also presented. Taken together, the new observations reported in this paper indicate the existence of a diverse and already differentiated cnidarian fauna, long before the Cambrian evolutionary event. It follows that at least stem group bilaterians must also have been present at this time.

  20. Determining the Biogenicity of Microfossils in the Apex Chert, Western Australia, Using Transmission Electron Microscopy

    DeGregorio, B. T.; Sharp, T. G.


    For over a decade, the oldest evidence for life on this planet has been microfossils in the 3.5 Ga Apex Chert in Western Australia. Recently, the biogenicity of these carbon-rich structures has been called into question through reanalysis of the local geology and reinterpretation of the original thin sections. Although initially described as a stratiform, bedded chert of siliceous clasts, the unit is now thought to be a brecciated hydrothermal vein chert. The high temperatures of a hydrothermal environment would probably have detrimental effects to early non-hyperthermophilic life, compared to that of a shallow sea. Conversely, a hydrothermal origin would suggest that if the microfossils were valid, they might have been hyperthermophilic. Apex Chert controversy. The Apex Chert microfossils were originally described as septate filaments composed of kerogen similar in morphology to Proterozoic and modern cyanobacteria. However new thin section analysis shows that these carbonaceous structures are not simple filaments. Many of the original microfossils are branched and have variable thickness when the plane of focus is changed. Hydrothermal alteration of organic remains has also been suggested for the creation of these strange morphologies. Another point of contention lies with the nature of the carbon material in these proposed microfossils. Kerogen is structurally amorphous, but transforms into well-ordered graphite under high pressures and temperatures. Raman spectrometry of the carbonaceous material in the proposed microfossils has been interpreted both as partially graphitized kerogen and amorphous graphite. However, these results are inconclusive, since Raman spectrometry cannot adequately discriminate between kerogen and disordered graphite. There are also opposing views for the origin of the carbon in the Apex Chert. The carbon would be biogenic if the proposed microfossils are indeed the remains of former living organisms. However, an inorganic Fischer

  1. Manganese, Metallogenium, and Martian Microfossils

    Stein, L. Y.; Nealson, K. H.


    Manganese could easily be considered an abundant element in the Martian regolith, assuming that the composition of martian meteorites reflects the composition of the planet. Mineralogical analyses of 5 SNC meteorites have revealed an average manganese oxide concentration of 0.48%, relative to the 0.1% concentration of manganese found in the Earth's crust. On the Earth, the accumulation of manganese oxides in oceans, soils, rocks, sedimentary ores, fresh water systems, and hydrothermal vents can be largely attributed to microbial activity. Manganese is also a required trace nutrient for most life forms and participates in many critical enzymatic reactions such as photosynthesis. The wide-spread process of bacterial manganese cycling on Earth suggests that manganese is an important element to both geology and biology. Furthermore, there is evidence that bacteria can be fossilized within manganese ores, implying that manganese beds may be good repositories for preserved biomarkers. A particular genus of bacteria, known historically as Metallogenium, can form star-shaped manganese oxide minerals (called metallogenium) through the action of manganese oxide precipitation along its surface. Fossilized structures that resemble metallogenium have been found in Precambrian sedimentary formations and in Cretaceous-Paleogene cherts. The Cretaceous-Paleogene formations are highly enriched in manganese and have concentrations of trace elements (Fe, Zn, Cu, and Co) similar to modern-day manganese oxide deposits in marine environments. The appearance of metallogenium-like fossils associated with manganese deposits suggests that bacteria may be preserved within the minerals that they form. Additional information is contained in the original extended abstract.

  2. Precambrian Lunar Volcanic Protolife

    Jack Green


    Full Text Available Five representative terrestrial analogs of lunar craters are detailed relevant to Precambrian fumarolic activity. Fumarolic fluids contain the ingredients for protolife. Energy sources to derive formaldehyde, amino acids and related compounds could be by flow charging, charge separation and volcanic shock. With no photodecomposition in shadow, most fumarolic fluids at 40 K would persist over geologically long time periods. Relatively abundant tungsten would permit creation of critical enzymes, Fischer-Tropsch reactions could form polycyclic aromatic hydrocarbons and soluble volcanic polyphosphates would enable assembly of nucleic acids. Fumarolic stimuli factors are described. Orbital and lander sensors specific to protolife exploration including combined Raman/laser-induced breakdown spectrocsopy are evaluated.

  3. Evidence of Microfossils in Carbonaceous Chondrites

    Hoover, Richard B.; Rozanov, Alexei Y.; Zhmur, S. I.; Gorlenko, V. M.


    Investigations have been carried out on freshly broken, internal surfaces of the Murchison, Efremovka and Orgueil carbonaceous chondrites using Scanning Electron Microscopes (SEM) in Russia and the Environmental Scanning Electron Microscope (ESEM) in the United States. These independent studies on different samples of the meteorites have resulted in the detection of numerous spherical and ellipsoidal bodies (some with spikes) similar to the forms of uncertain biogenicity that were designated "organized elements" by prior researchers. We have also encountered numerous complex biomorphic microstructures in these carbonaceous chondrites. Many of these complex bodies exhibit diverse characteristics reminiscent of microfossils of cyanobacteria such as we have investigated in ancient phosphorites and high carbon rocks (e.g. oil shales). Energy Dispersive Spectroscopy (EDS) analysis and 2D elemental maps shows enhanced carbon content in the bodies superimposed upon the elemental distributions characteristic of the chondritic matrix. The size, distribution, composition, and indications of cell walls, reproductive and life cycle developmental stages of these bodies are strongly suggestive of biology' These bodies appear to be mineralized and embedded within the meteorite matrix, and can not be attributed to recent surface contamination effects. Consequently, we have interpreted these in-situ microstructures to represent the lithified remains of prokaryotes and filamentous cyanobacteria. We also detected in Orgueil microstructures morphologically similar to fibrous kerite crystals. We present images of many biomorphic microstructures and possible microfossils found in the Murchison, Efremovka, and Orgueil chondrites and compare these forms with known microfossils from the Cambrian phosphate-rich rocks (phosphorites) of Khubsugul, Northern Mongolia.

  4. Nutrient Limitation in the Precambrian

    Planavsky, N. J.; Lalonde, S.; Konhauser, K.; Lyons, T. W.


    We present Fe and P concentrations from distal hydrothermal sediments and iron formations through time in order to evaluate the evolution of the marine P reservoir. P concentrations appear to have been elevated in Precambrian oceans.

  5. Meteoritic Microfossils In Eltanin Impact Deposits

    Kyte, F. T.; Wollenburg, J.; Gersonde, R.; Kuhn, G.


    Introduction: We report the unique occurrence of microfossils composed largely of meteoritic ejecta particles from the late Pliocene (2.5 Ma) Eltanin impact event. These deposits are unique, recording the only known km- sized asteroid impact into a deep-ocean (5 km) basin. First discovered as in Ir anomaly in sediment cores that were collected in 1965, the deposits contain mm-sized shock-melted asteroidal material, unmelted meteorite fragments (named the Eltanin meteorite), and trace impact spherules. Two oceanographic expeditions by the FS Polarstern in 1995 and 2001 explored 80,000 square km of the impact region, mapping the distribution of meteoritic ejecta, disturbance of seafloor sediments by the impact, and collected 20 new cores with impact deposits in the vicinity of the Freeden Seamounts (57.3S, 90.5W). Analyses of sediment cores show that the impact disrupted sediments on the ocean floor, redepositing them as a chaotic jumble of sediment fragments overlain by a sequence of laminated sands, silts and clays deposited from the water column. Overprinted on this is a pulse of meteoritic ejecta, likely transported ballistically, then settled through the water column. At some localities, meteoritic ejecta was as much as 5 to 50 kg per square meter. This is the most meteorite-rich locality known on Earth. Results: Two cores were taken in a basin near the top of the Freeden Seamounts at a water depth of 2.7 km. Sediments in this shallow basin are compositionally different than those at all other sites as they contain abundant calcareous microfossils. In deeper water sites (4 to 5 km depth), higher pressures and CO2 concentrations cause dissolution of calcite and sediments contain siliceous (opal) microfossils or are barren. An exception to this is a few sites in the immediate vicinity of the seamounts that contain calcareous sediments that flowed off the seamounts after being disturbed by the impact. At the top of the seamounts, sediments with meteoritic ejecta

  6. Nanoscale analysis of pyritized microfossils reveals differential heterotrophic consumption in the ~1.9-Ga Gunflint chert.

    Wacey, David; McLoughlin, Nicola; Kilburn, Matt R; Saunders, Martin; Cliff, John B; Kong, Charlie; Barley, Mark E; Brasier, Martin D


    The 1.88-Ga Gunflint biota is one of the most famous Precambrian microfossil lagerstätten and provides a key record of the biosphere at a time of changing oceanic redox structure and chemistry. Here, we report on pyritized replicas of the iconic autotrophic Gunflintia-Huroniospora microfossil assemblage from the Schreiber Locality, Canada, that help capture a view through multiple trophic levels in a Paleoproterozoic ecosystem. Nanoscale analysis of pyritic Gunflintia (sheaths) and Huroniospora (cysts) reveals differing relic carbon and nitrogen distributions caused by contrasting spectra of decay and pyritization between taxa, reflecting in part their primary organic compositions. In situ sulfur isotope measurements from individual microfossils (δ(34)S(V-CDT) +6.7‰ to +21.5‰) show that pyritization was mediated by sulfate-reducing microbes within sediment pore waters whose sulfate ion concentrations rapidly became depleted, owing to occlusion of pore space by coeval silicification. Three-dimensional nanotomography reveals additional pyritized biomaterial, including hollow, cellular epibionts and extracellular polymeric substances, showing a preference for attachment to Gunflintia over Huroniospora and interpreted as components of a saprophytic heterotrophic, decomposing community. This work also extends the record of remarkable biological preservation in pyrite back to the Paleoproterozoic and provides criteria to assess the authenticity of even older pyritized microstructures that may represent some of the earliest evidence for life on our planet.

  7. Distribution and diagenesis of microfossils from the lower Proterozoic Duck Creek Dolomite, Western Australia

    Knoll, A. H.; Strother, P. K.; Rossi, S.


    Two distinct generations of microfossils occur in silicified carbonates from a previously undescribed locality of the Lower Proterozoic Duck Creek Dolomite, Western Australia. The earlier generation occurs in discrete organic-rich clasts and clots characterized by microquartz anhedra; it contains a variety of filamentous and coccoidal fossils in varying states of preservation. Second generation microfossils consist almost exclusively of well-preserved Gunflintia minuta filaments that drape clasts or appear to float in clear chalcedony. These filaments appear to represent an ecologically distinct assemblage that colonized a substrate containing the partially degraded remains of the first generation community. The two assemblages differ significantly in taxonomic frequency distribution from previously described Duck Creek florules. Taken together, Duck Creek microfossils exhibit a range of assemblage variability comparable to that found in other Lower Proterozoic iron formations and ferruginous carbonates. With increasing severity of post-mortem alteration, Duck Creek microfossils appear to converge morphologically on assemblages of simple microstructures described from early Archean cherts. Two new species are described: Oscillatoriopsis majuscula and O. cuboides; the former is among the largest septate filamentous fossils described from any Proterozoic formation.

  8. Controls on Precambrian sea level change and sedimentary cyclicity

    Eriksson, P. G.; Catuneanu, O.; Nelson, D. R.; Popa, M.


    second-order cycles of considerably longer duration than Phanerozoic examples, supporting less evolved tectonism affecting cratonic plates. It is possible that oceanic tectonic realms underwent more rapid and dynamic plate movements and arc generation, whereas early continental cratonic plates offered more stable platforms and may have been subject to slower migration rates. The wide range of controls on Precambrian sea level change, allied to their apparent variability (in rates and periodicity) through Precambrian time supports the conclusion that each order of cyclicity is relative and must be defined within the stratigraphic context of each individual case study. This underlines the importance of establishing a hierarchical order of cyclicity in sequence stratigraphic interpretations of Precambrian basins based on the relative importance of sequences rather than their temporal duration.

  9. Global Carbon Cycle of the Precambrian Earth

    Wiewióra, Justyna

    The carbon isotopic composition of distinct Archaean geological records provides information about the global carbon cycle and emergence of life on early Earth. We utilized carbon isotopic records of Greenlandic carbonatites, diamonds, graphites, marbles, metacarbonates and ultramafic rocks...... to investigate carbon fluxes between Precambrian Earth’s mantle and crust and to trace the evolution of life in the Eoarchaean oceans. The world’s desire for diamonds gives us a unique opportunity to obtain insight into the nature of metasomatic fluids affecting the subcratonic lithospheric mantle (SCLM) beneath...

  10. High CO2 levels in the Proterozoic atmosphere estimated from analyses of individual microfossils.

    Kaufman, Alan J; Xiao, Shuhai


    Solar luminosity on the early Earth was significantly lower than today. Therefore, solar luminosity models suggest that, in the atmosphere of the early Earth, the concentration of greenhouse gases such as carbon dioxide and methane must have been much higher. However, empirical estimates of Proterozoic levels of atmospheric carbon dioxide concentrations have not hitherto been available. Here we present ion microprobe analyses of the carbon isotopes in individual organic-walled microfossils extracted from a Proterozoic ( approximately 1.4-gigayear-old) shale in North China. Calculated magnitudes of the carbon isotope fractionation in these large, morphologically complex microfossils suggest elevated levels of carbon dioxide in the ancient atmosphere--between 10 and 200 times the present atmospheric level. Our results indicate that carbon dioxide was an important greenhouse gas during periods of lower solar luminosity, probably dominating over methane after the atmosphere and hydrosphere became pervasively oxygenated between 2 and 2.2 gigayears ago.

  11. Precambrian evolution of the climate system.

    Walker, J C


    Climate is an important environmental parameter of the early Earth, likely to have affected the origin and evolution of life, the composition and mineralogy of sedimentary rocks, and stable isotope ratios in sedimentary minerals. There is little observational evidence constraining Precambrian climates. Most of our knowledge is at present theoretical. Factors that must have affected the climate include reduced solar luminosity, enhanced rotation rate of the Earth, an area of land that probably increased with time, and biological evolution, particularly as it affected the composition of the atmosphere and the greenhouse effect. Cloud cover is a major uncertainty about the early Earth. Carbon dioxide and its greenhouse effect are the factors that have been most extensively studied. This paper presents a new examination of the biogeochemical cycles of carbon as they may have changed between an Archean Earth deficient in land, sedimentary rocks, and biological activity, and a Proterozoic Earth much like the modern Earth, but lacking terrestrial life and carbonate-secreting plankton. Results of a numerical simulation of this transition show how increasing biological activity could have drawn down atmospheric carbon dioxide by extracting sedimentary organic carbon from the system. Increasing area of continents could further have drawn down carbon dioxide by encouraging the accumulation of carbonate sediments. An attempt to develop a numerical simulation of the carbon cycles of the Precambrian raises questions about sources and sinks of marine carbon and alkalinity on a world without continents. More information is needed about sea-floor weathering processes.

  12. Microfossils of Cyanobacteria in Carbonaceous Meteorites

    Hoover, Richard B.


    During the past decade, Environmental and Field Emission Scanning Electron Microscopes have been used at the NASA/Marshall Space Flight Center to investigate freshly fractured interior surfaces of a large number of different types of meteorites. Large, complex, microfossils with clearly recognizable biological affinities have been found embedded in several carbonaceous meteorites. Similar forms were notably absent in all stony and nickel-iron meteorites investigated. The forms encountered are consistent in size and morphology with morphotypes of known genera of Cyanobacteria and microorganisms that are typically encountered in associated benthic prokaryotic mats. Even though many coccoidal and isodiametric filamentous cyanobacteria have a strong morphological convergence with some other spherical and filamentous bacteria and algae, many genera of heteropolar cyanobacteria have distinctive apical and basal regions and cellular differentiation that makes it possible to unambiguously recognize the forms based entirely upon cellular dimensions, filament size and distinctive morphological characteristics. For almost two centuries, these morphological characteristics have historically provided the basis for the systematics and taxonomy of cyanobacteria. This paper presents ESEM and FESEM images of embedded filaments and thick mats found in-situ in the Murchison CM2 and Orgueil cn carbonaceous meteorites. Comparative images are also provided for known genera and species of cyanobacteria and other microbial extremophiles. Energy Dispersive X-ray Spectroscopy (EDS) studies indicate that the meteorite filaments typically exhibit dramatic chemical differentiation with distinctive difference between the possible microfossil and the meteorite matrix in the immediate proximity. Chemical differentiation is also observed within these microstructures with many of the permineralized filaments enveloped within electron transparent carbonaceous sheaths. Elemental distributions of

  13. SIMS and NanoSIMS analyses of Mesoproterozoic individual microfossils indicating continuous oxygen-producing photosynthesis in Proterozoic Ocean

    Peng, X.; Guo, Z.; House, C. H.; Chen, S.; Ta, K.


    Well-preserved microfossils in the stromatolites from the Gaoyuzhuang Formation (~1500Ma), which is younger than the Gunflint Formation (~1880Ma) and older than the Bitter Springs Formation (~850Ma), may play key roles in systematizing information about the evolution of early life and environmental changes in the Proterozoic Ocean. Here, a combination of light microscopy (LM), scanning electron microscopy (SEM), focused ion beam (FIB), nano-scale secondary ion mass spectrometry (NanoSIMS) and secondary ion mass spectrometry (SIMS) were employed to characterize the morphology, elemental distributions and carbon isotope values of individual microfossils in the stromatolites from the Gaoyuahzuang Formation. Light microscopy analyses show that abundant filamentous and coccoid microfossils are exceptionally well preserved in chert. NanoSIMS analyses show that metabolically important elements such as 12C-, 13C-, 12C14N-, 32S-, and 34S- are concentrated in these microfossils and that the variations in the concentrations of these elements are similar, establishing the elemental distributions in incontestably biogenic microstructures. Carbon isotope (δ13C) values of individual microfossils range from -32.2‰ ± 0.9‰ to -23.3‰ ± 1.0‰ (weighted mean= -28.9‰ ± 0.1‰), consistent with carbon fixation via the Calvin cycle. The elevated δ13C values of the microfossils from Early-, Meso- to Late Proterozoic Era, possibly indicate decreasing CO2 and increasing O2 concentrations in the Proterozoic atmosphere. Our results, for the first time, provided the element distributions and cell specific carbon isotope values on convincing Mesoproterozoic cyanobacterial fossils, supporting continuous oxygen-producing photosynthesis in the Proterozoic Ocean.

  14. Chiral Biomarkers and Microfossils in Carbonaceous Meteorites

    Hoover, Richard B.


    Homochirality of the biomolecules (D-sugars of DNA and RNA and L-amino acids of proteins) is a fundamental property of all life on Earth. Abiotic mechanisms yield racemic mixtures (D/L=1) of chiral molecules and after the death of an organism, the enantiopure chiral biomolecules slowly racemize. Several independent investigators have now established that the amino acids present in CI1 and CM2 carbonaceous meteorites have a moderate to strong excess of the L-enantiomer. Stable isotope data have established that these amino acids are both indigenous and extraterrestrial. Carbonaceous meteorites also contain many other strong chemical biomarkers including purines and pyrimidines (nitrogen heterocycles of nucleic acids); pristine and phytane (components of the chlorophyll pigment) and morphological biomarkers (microfossils of filamentous cyanobacteria). Energy dispersive X-ray Spectroscopy (EDS) analysis reveals that nitrogen is below the detectability level in most of the meteorite filaments as well as in Cambrian Trilobites and filaments of 2.7 Gya Archaean cyanobacteria from Karelia. The deficiency of nitrogen in the filaments and the total absence of sugars, of twelve of the life-critical protein amino acids, and two of the nucleobases of DNA and RNA provide clear and convincing evidence that these filaments are not modern biological contaminants. This paper reviews the chiral, chemical biomarkers morphological biomarkers and microfossils in carbonaceous meteorites. This paper reviews chiral and morphological biomarkers and discusses the missing nitrogen, sugars, protein amino acids, and nucleobases as ?bio-discriminators? that exclude modern biological contaminants as a possible explanation for the permineralized cyanobacterial filaments found in the meteorites.

  15. Chiral biomarkers and microfossils in carbonaceous meteorites

    Hoover, Richard B.


    Homochirality of the biomolecules (D-sugars of DNA and RNA and L-amino acids of proteins) is a fundamental property of all life on Earth. Abiotic mechanisms yield racemic mixtures (D/L=1) of chiral molecules and after the death of an organism, the enantiopure chiral biomolecules slowly racemize. Several independent investigators have now established that the amino acids present in CI1 and CM2 carbonaceous meteorites have a moderate to strong excess of the L-enantiomer. Stable isotope data have established that these amino acids are both indigenous and extraterrestrial. Carbonaceous meteorites also contain many other strong chemical biomarkers including purines and pyrimidines (nitrogen heterocycles of nucleic acids); pristine and phytane (components of the chlorophyll pigment) and morphological biomarkers (microfossils of filamentous cyanobacteria). Energy dispersive X-ray Spectroscopy (EDS) analysis reveals that nitrogen is below the detectability level in most of the meteorite filaments as well as in Cambrian Trilobites and filaments of 2.7 Gya Archaean cyanobacteria from Karelia. The deficiency of nitrogen in the filaments and the total absence of sugars, of twelve of the life-critical protein amino acids, and two of the nucleobases of DNA and RNA provide clear and convincing evidence that these filaments are not modern biological contaminants. This paper reviews the chiral, chemical biomarkers morphological biomarkers and microfossils in carbonaceous meteorites. This paper reviews chiral and morphological biomarkers and discusses the missing nitrogen, sugars, protein amino acids, and nucleobases as "bio-discriminators" that exclude modern biological contaminants as a possible explanation for the permineralized cyanobacterial filaments found in the meteorites.

  16. Microfossils from loess of the Miaodao Islands, Bohai Sea



    Microfossils from the Malan Loess profiles, Miaodao Islands, have been quantitatively studied. The microfauna is composed mainly of benthic foraminifers together with a few planktonic foraminifers, ostracods, gastropods, bivalves and echinoid spines. With the exception of indigenous gastropods, benthic foraminifers, ostracods, bivalves and echinoid spines were transported from the north or northwest of the Bohai Sea in the glacial period by the prevailing winter monsoon, while planktonic foraminifers were probably driven from the Yellow Sea or even the northern East China Sea by southerly winds. The upward decrease of marine microfossil abundance and diversity in the Malan Loess profiles shows that the microfossil transportation occurred mainly at the beginning of the regression.

  17. Global Carbon Cycle of the Precambrian Earth

    Wiewióra, Justyna

    to investigate carbon fluxes between Precambrian Earth’s mantle and crust and to trace the evolution of life in the Eoarchaean oceans. The world’s desire for diamonds gives us a unique opportunity to obtain insight into the nature of metasomatic fluids affecting the subcratonic lithospheric mantle (SCLM) beneath...... derived from surface water. Partitioning of carbon between 13C-rich oxidized and 13C-poor reduced species indicates that life in the early ocean had to be well evolved before 3.8 Ga. Therefore, the Isua ultramafic rocks may be considered as an indirect biomarker for ancient life.......The carbon isotopic composition of distinct Archaean geological records provides information about the global carbon cycle and emergence of life on early Earth. We utilized carbon isotopic records of Greenlandic carbonatites, diamonds, graphites, marbles, metacarbonates and ultramafic rocks...

  18. Compaction of microfossil and clay-rich chalk sediments

    Fabricius, Ida Lykke


    The aim of this study was to evaluate the role of microfossils and clay in the compaction of chalk facies sediments. To meet this aim, chalk sediments with varying micro texture were studied. The sediments have been tested uniaxially confined in a stainless-steel compaction cell. The sediments are......: 1) Pure carbonate chalk with mudstone texture from Stevns Klint (Denmark), 2) Relatively pure chalk sediments with varying content of microfossils from the Ontong Java Plateau (Western Pacific), 3) Clay-rich chalk and mixed sediments from the Caribbean. The tested samples were characterised...... of microfossils and fine-grained silica and clay. Samples with relatively pure chalk mud supported texture compact along a common stress - matrix porosity trend. Microfossils thus have a passive role, apparently because they are supported by the chalk mud. Samples with fine-grained silica and clay can be modelled...

  19. Paleobiology of a Precambrian Shale: Geology, organic geochemistry, and paleontology are applied to the problem of detection of ancient life.

    Barghoorn, E S; Meinschein, W G; Schopf, J W


    Investigations have been made of crude oil, pristane, phytane, steranetype and optically active alkanes, porphyrins, microfossils, and the stable isotopes of carbon and of sulfur found in the Nonesuch shale of Precambrian age from Northern Michigan. These sediments are approximately 1 billion years old. Geologic evidence indicates that they were deposited in a nearshore deltaic environment. Porphyrins are found in the siltstones but not in the crude oils of the Nonesuch formation-evidence that these chemical fossils are adsorbed or absorbed and immobile. This immobility makes it highly unlikely that these porphyrins could have moved from younger formations into the Nonesuch sediments, and the widely disseminated particulate organic matters and fossils in this Precambrian shale are certainly indigenous.

  20. History and Evolution of Precambrian plate tectonics

    Fischer, Ria; Gerya, Taras


    Plate tectonics is a global self-organising process driven by negative buoyancy at thermal boundary layers. Phanerozoic plate tectonics with its typical subduction and orogeny is relatively well understood and can be traced back in the geological records of the continents. Interpretations of geological, petrological and geochemical observations from Proterozoic and Archean orogenic belts however (e.g., Brown, 2006), suggest a different tectonic regime in the Precambrian. Due to higher radioactive heat production the Precambrian lithosphere shows lower internal strength and is strongly weakened by percolating melts. The fundamental difference between Precambrian and Phanerozoic tectonics is therefore the upper-mantle temperature, which determines the strength of the upper mantle (Brun, 2002) and the further tectonic history. 3D petrological-thermomechanical numerical modelling experiments of oceanic subduction at an active plate at different upper-mantle temperatures show these different subduction regimes. For upper-mantle temperatures buckling and also lithospheric delamination and drip-offs. For upper-mantle temperatures > 250 K above the present day value no subduction occurs any more. The whole lithosphere is delaminating and due to strong volcanism and formation of a thicker crust subduction is inhibited. This stage of 200-250 K higher upper mantle temperature which corresponds roughly to the early Archean (Abbott, 1994) is marked by strong volcanism due to sublithospheric decompression melting which leads to an equal thickness for both oceanic and continental plates. As a consequence subduction is inhibited, but a compressional setup instead will lead to orogeny between a continental or felsic terrain and an oceanic or mafic terrain as well as internal crustal convection. Small-scale convection with plume shaped cold downwellings also in the upper mantle is of increased importance compared to the large-scale subduction cycle observed for present temperature

  1. Tectonic inheritance in the development of the Kivu - north Tanganyika rift segment of the East African Rift System: role of pre-existing structures of Precambrian to early Palaeozoic origin.

    Delvaux, Damien; Fiama Bondo, Silvanos; Ganza Bamulezi, Gloire


    The present architecture of the junction between the Kivu rift basin and the north Tanganyika rift basin is that of a typical accommodation zone trough the Ruzizi depression. However, this structure appeared only late in the development of the Western branch of the East African Rift System and is the result of a strong control by pre-existing structures of Precambrian to early Palaeozoic origin. In the frame of a seismic hazard assessment of the Kivu rift region, we (Delvaux et al., 2016) constructed homogeneous geological, structural and neotectonic maps cross the five countries of this region, mapped the pre-rift, early rift and Late Quaternary faults and compiled the existing knowledge on thermal springs (assumed to be diagnostic of current tectonic activity along faults). We also produced also a new catalogue of historical and instrumental seismicity and defined the seismotectonic characteristics (stress field, depth of faulting) using published focal mechanism data. Rifting in this region started at about 11 Ma by initial doming and extensive fissural basaltic volcanism along normal faults sub-parallel to the axis of the future rift valley, as a consequence of the divergence between the Nubia and the Victoria plate. In a later stage, starting around 8-7 Ma, extension localized along a series of major border faults individualizing the subsiding tectonic basins from the uplifting rift shoulders, while lava evolved towards alkali basaltic composition until 2.6 Ma. During this stage, initial Kivu rift valley was extending linearly in a SSW direction, much further than its the actual termination at Bukavu, into the Mwenga-Kamituga graben, up to Namoya. The SW extremity of this graben was linked via a long oblique transfer zone to the central part of Lake Tanganyika, itself reactivating an older ductile-brittle shear zone. In the late Quaternary-early Holocene, volcanism migrated towards the center of the basin, with the development of the Virunga volcanic massif

  2. Drifting organisms in the Precambrian sea

    Milton, D.J.


    Drag marks in the Upper Precambrian Winnall Beds of central Australia were made by semibuoyant flexible objects at least 15 centimeters long, which presumably were algae. This find extends the range of such marks into the Precambrian era and supplements the discovery of microflora in the same sedimentary sequence.

  3. Reproductive cyst and operculum formation in the Cambrian-Ordovician galeate-plexus microfossils

    Agic, Heda; Moczydlowska, Malgorzata; Canfield, Donald Eugene


    Unicellular organic-walled microfossils from the Cambrian-Ordovician transition in Estonia (ca. 490-480million years ago) exhibit rare characters reflecting their function as reproductive algal cysts. The studied assemblages record the evolutionary history of phytoplankton in the early Palaeozoic......-organisms. Due to strong morphological and ecological similarities between galeate fossils and dasycladalean cysts, and the antiquity of this algal order, galeates may be positioned within green algae, more specifically Dasycladales. The unique morphology of the operculum-bearing microbiota would have required...

  4. Genuine modern analogues of Precambrian stromatolites from caldera lakes of Niuafo'ou Island, Tonga.

    Kazmierczak, Józef; Kempe, Stephan


    Calcareous or dolomitic, often secondarily silicified, laminated microbial structures known as stromatolites are important keys to reconstruct the chemical and biotic evolution of the early ocean. Most authors assume that cyanobacteria-associated microbialitic structures described from Shark Bay, Western Australia, and Exuma Sound, Bahamas, represent modern marine analogues for Precambrian stromatolites. Although they resemble the Precambrian forms macroscopically, their microstructure and mineralogical composition differ from those characterizing their purported ancient counterparts. Most Precambrian stromatolites are composed of presumably in situ precipitated carbonates, while their assumed modern marine analogues are predominantly products of accretion of grains trapped and bound by microbial, predominantly cyanobacterial, benthic mats and biofilms and only occasionally by their physicochemical activity. It has therefore been suggested that the carbonate chemistry of early Precambrian seawater differed significantly from modern seawater, and that some present-day quasi-marine or non-marine environments supporting growth of calcareous microbialites reflect the hydrochemical conditions controlling the calcification potential of Precambrian microbes better than modern seawater. Here we report the discovery of a non-marine environment sustaining growth of calcareous cyanobacterial microbialites showing macroscopic and microscopic features resembling closely those described from many Precambrian stromatolites.

  5. Beyond the Burgess Shale: Cambrian microfossils track the rise and fall of hallucigeniid lobopodians.

    Caron, Jean-Bernard; Smith, Martin R; Harvey, Thomas H P


    Burgess Shale-type deposits are renowned for their exquisite preservation of soft-bodied organisms, representing a range of animal body plans that evolved during the Cambrian 'explosion'. However, the rarity of these fossil deposits makes it difficult to reconstruct the broader-scale distributions of their constituent organisms. By contrast, microscopic skeletal elements represent an extensive chronicle of early animal evolution--but are difficult to interpret in the absence of corresponding whole-body fossils. Here, we provide new observations on the dorsal spines of the Cambrian lobopodian (panarthropod) worm Hallucigenia sparsa from the Burgess Shale (Cambrian Series 3, Stage 5). These exhibit a distinctive scaly microstructure and layered (cone-in-cone) construction that together identify a hitherto enigmatic suite of carbonaceous and phosphatic Cambrian microfossils--including material attributed to Mongolitubulus, Rushtonites and Rhombocorniculum--as spines of Hallucigenia-type lobopodians. Hallucigeniids are thus revealed as an important and widespread component of disparate Cambrian communities from late in the Terreneuvian (Cambrian Stage 2) through the 'middle' Cambrian (Series 3); their apparent decline in the latest Cambrian may be partly taphonomic. The cone-in-cone construction of hallucigeniid sclerites is shared with the sclerotized cuticular structures (jaws and claws) in modern onychophorans. More generally, our results emphasize the reciprocal importance and complementary roles of Burgess Shale-type fossils and isolated microfossils in documenting early animal evolution.

  6. High-temperature, acid-hydrolyzed remains of Polytrichum (Musci, Polytrichaceae) resemble enigmatic Silurian-Devonian tubular microfossils.

    Kodner, R B; Graham, L E


    Gametophytes and sporophyte components of two species of the evolutionarily early-divergent moss Polytrichum were separately subjected to high-temperature acid hydrolysis, and remains were examined by fluorescence microscopy and scanning electron microscopy. Remains included fragments of capsule, seta, leaves, stems, and calyptra. Cell walls of all remains were autofluorescent in violet and UV excitation, suggesting occurrence of resistant polyphenolic compounds. Calyptras of both species dissociated into smooth- walled, acutely branched filamentous associations of tubular cells with distinctively thickened cell junctions. In these aspects and measurements of wall dimensions made from SEMs, the hydrolysis-resistant Polytrichum calyptra remains were similar to several tubular microfossils described from Silurian and Lower Devonian deposits, whose provenance is unknown or ascribed to fungi. Our data suggest the possibility that at least some ancient tubular microfossils might have originated from Polytrichum-like early mosses. They add to increasing evidence that bryophytes left microfossil evidence for their presence millions of years earlier than is indicated by their macrofossil record.

  7. Petrographic approach to the study of organic microfossils from the Irati Subgroup (Permian, Paraná Basin, Brazil)

    Calça, Cléber Pereira; Fairchild, Thomas R.


    Early diagenetic chert, infrequently exploited in Phanerozoic micropaleontology, was examined for organic-walled microfossils in petrographic thin sections of silicified dolostones from diverse levels and localities of the Assistência Formation (Permian, Paraná Basin) in the state of São Paulo, Brazil. In contrast to previous palynological studies of this formation, the use of thin sections allowed direct observation in three dimensions of common palynomorphs, as well as benthic microbial mats preserved in situ in various stages of their life cycles and degradation. As in palynological residues from the more well-known shale of this formation, the chert contains wind-dispersed pollen grains and phytoclasts derived from terrestrial sources and planktonic cryptarchs (unornamented coccoidal unicellular or colonial palynomorphs). However, only in the chert is it possible to see much more delicate microfossils, such as abundant cyanobacteria of the in situ benthic microbiota as well as chlorophycean microalgae of the microphytoplankton. Post-depositional processes affecting the formation have destroyed all but the most resistant organic remains in the other lithologies, such that only rare, degraded pollen grains are seen in the unsilicified dolostone of the formation, and in the shale the vast majority of microfossils have been compacted to flattened disks. On the other hand, early silicification not only preserved organic remains at an incipient stage of decomposition but also impeded significant further degradation due to compaction, recrystallization, and oxidation. Thus, the petrographic study of such chert can complement traditional palynological investigations in Phanerozoic rocks by furnishing hitherto unavailable information, especially with regard to benthic organic microfossils and fragile organic-walled phytoplankton normally absent from organic residues.

  8. Experimental mineralization of crustacean eggs leads to surprising tissue conservation: new implications for the fossilization of Precambrian-Cambrian embryos


    Phosphatized globular microfossils from the Ediacaran and Lower Cambrian of South China represent an impressive record of early animal evolution and development, however their affinity based on putative embryonic metazoan, bacterial and inorganic features is strongly debated. Understanding key processes and conditions that cause exceptional egg and embryo preservation and fossilization are therefore crucial for a reliable interpretation of their phylogenetic position. Taphonomic experime...

  9. Iron in Precambrian rocks: implications for the global oxygen budget of the ancient Earth.

    Kump, L R; Holland, H D


    Banded iron formations (BIF) are prominent in sediments older than 2 Ga. However, little is known about the absolute abundance of BIF in Archean and Early Proterozoic sediments, and the source of the Fe is still somewhat uncertain. Also unknown is the role that Fe may have played in the maintenance of low oxygen pressures in the Archean and Early Proterozoic atmosphere. An analysis of the chemical composition of Precambrian rocks provides some insight into the role of Fe in Precambrian geochemical cycles. The Fe content of igneous rocks is well correlated with their Ti content. Plots of Fe vs. Ti in Precambrian sandstones and graywackes fall very close to the igneous rock trend. Plots of Fe vs. Ti in Precambrian shales also follow this trend but show a definite scatter toward an excess of Fe. Phanerozoic shales and sandstones lie essentially on the igneous rock trend and show surprisingly little scatter. Mn/Ti relations show a stronger indication of Precambrian Mn loss, perhaps due to weathering under a less oxidizing early atmosphere. These data show that Fe was neither substantially added to nor significantly redistributed in Archean and early Proterozoic sediments. Enough hydrothermal Fe was added to these sediments to increase the average Fe content of shales by at most a factor of 2. This enrichment would probably not have greatly affected the near-surface redox cycle or atmospheric oxygen levels. Continued redistribution of Fe and mixing with weathered igneous rocks during the recycling of Precambrian sediments account for the excellent correlation of Fe with Ti in Phanerozoic shales and for the similarity between their Fe/Ti ratio and that of igneous rocks.

  10. Occurrence of helically coiled microfossil Obruchevella in the Owk Shale of the Kurnool Group and its significance

    Mukund Sharma; Yogmaya Shukla


    The present study reports occurrence of helically coiled microfossil Obruchevella Reitlinger from the Owk Shale of the Kurnool Group from the peninsular India. The age of the Kurnool Group is poorly constrained due to the absence of direct radiometric dating and meager palaeobiological data. Occurrence of Obruchevella is considered as a typical Vendian marker genus recorded mostly from close to the Precambrian–Cambrian boundary successions. Hence, the present assemblage is important to ascertain the age of the basin. In the Owk Shale, four species of Obruchevella, viz., O. delicata, O. parva, O. minor and O. valdaica are recorded as organic walled microfossils. Among them O. valdaica is the largest in terms of size parameters. On the global scale, the recovered species occur in the Late Neoproterozoic to Early Cambrian sediments. Therefore, the occurrence of microfossil Obruchevella in the Owk Shale and known burrow structures in the Narji Limestone suggest Ediacaran age close to the Cambrian for the Kurnool Basin and challenges the recently assigned esoproterozoic age of the basin.

  11. Stratigraphic scale the Lower Precambrian of Russia

    Anisimova, Svetlana; Bogdanov, Yuri


    The quality of state geological maps depends on the quality of the combined serial legends, which are based on the adopted stratigraphic scheme of the General stratigraphic scale, regional and local stratigraphic schemes. The main task of the General stratigraphic scale is the temporal correlation of stratigraphic units of regional schemes and the age of their boundaries. For the Precambrian age determination is based on paleontological and geochronological methods. Currently, work is being carried out to update the stratigraphic framework of the formations of the upper Proterozoic (Riphean and Vendian). Relatively less studied is the stratigraphy of the lower Precambrian. To the bottom are Precambrian structurally-material complexes of Archean and lower Proterozoic rocks, crystalline basement of ancient platforms and also included in the fold belts. The solution to the problems of stratigraphy of the lower Precambrian is possible only by creating and improving regional stratigraphic schemes. Such work should be based on the study of stratotype sections and references of boundaries in the model regions of the lower Precambrian. The current General stratigraphic scale of the lower Precambrian of Russia (RGSS) consists of the Lower Archean (Sami) and the Upper Archean (Lopi) and lower Proterozoic (Karelian) Eonotam. Archaea is divided into two Eonotam in Russian General stratigraphic scale, in the International Chronostratigraphic Chart (ICC) - three units, designated as Eon. The age of the boundary between Eonotam and Eon the same (3200 million years). The same and the age of the boundary between the Archean and the Proterozoic. The RGSS of the Precambrian, based on the comprehensive study of typical sections and analysis of isotopic Dating of different methods. Stratotype reference sections of the districts of Karelia and the Kola Peninsula represent different types of sections, the time (geochronological) correlation which was the basis for the regional scheme

  12. A pan-Precambrian link between deglaciation and environmental oxidation

    Raub, T.J.; Kirschvink, J.L.


    Despite a continuous increase in solar luminosity to the present, Earth’s glacial record appears to become more frequent, though less severe, over geological time. At least two of the three major Precambrian glacial intervals were exceptionally intense, with solid evidence for widespread sea ice on or near the equator, well within a “Snowball Earth” zone produced by ice-albedo runaway in energy-balance models. The end of the first unambiguously low-latitude glaciation, the early Paleoproterozoic Makganyene event, is associated intimately with the first solid evidence for global oxygenation, including the world’s largest sedimentary manganese deposit. Subsequent low-latitude deglaciations during the Cryogenian interval of the Neoproterozoic Era are also associated with progressive oxidation, and these young Precambrian ice ages coincide with the time when basal animal phyla were diversifying. However, specifically testing hypotheses of cause and effect between Earth’s Neoproterozoic biosphere and glaciation is complicated because large and rapid True Polar Wander events appear to punctuate Neoproterozoic time and may have episodically dominated earlier and later intervals as well, rendering geographic reconstruction and age correlation challenging except for an exceptionally well-defined global paleomagnetic database.

  13. Possible ctenophoran affinities of the Precambrian "sea-pen" Rangea.

    Dzik, Jerzy


    The Namibian Kuibis Quartzite fossils of Rangea are preserved three-dimensionally owing to incomplete collapse of the soft tissues under the load of instantaneously deposited sand. The process of fossilization did not reproduce the original external morphology of the organism but rather the inner surface of collapsed organs, presumably a system of sacs connected by a medial canal. The body of Rangea had tetraradial symmetry, a body plan shared also by the White Sea Russian fossil Bomakellia and possibly some other Precambrian frond-like fossils. They all had a complex internal anatomy, smooth surface of the body, and radial membranes, making their alleged colonial nature unlikely. Despite a different style of preservation, the Middle Cambrian Burgess Shale frond-like Thaumaptilon shows several anatomical similarities to Rangea. The body plan of the Burgess Shale ctenophore Fasciculus, with its numerous, pinnately arranged comb organs, is in many respects transitional between Thaumaptilon and the Early Cambrian ctenophore Maotianoascus from the Chengjiang fauna of South China. It is proposed that the irregularly distributed dark spots on the fusiform units of the petaloid of Thaumaptilon represent a kind of macrocilia and that the units are homologous with the ctenophoran comb organs. These superficial structures were underlain by the complex serial organs, well represented in the fossils of Rangea. The Precambrian "sea-pens" were thus probably sedentary ancestors of the ctenophores.

  14. The nature and origin of nucleus-like intracellular inclusions in Paleoproterozoic eukaryote microfossils.

    Pang, K; Tang, Q; Schiffbauer, J D; Yao, J; Yuan, X; Wan, B; Chen, L; Ou, Z; Xiao, S


    The well-known debate on the nature and origin of intracellular inclusions (ICIs) in silicified microfossils from the early Neoproterozoic Bitter Springs Formation has recently been revived by reports of possible fossilized nuclei in phosphatized animal embryo-like fossils from the Ediacaran Doushantuo Formation of South China. The revisitation of this discussion prompted a critical and comprehensive investigation of ICIs in some of the oldest indisputable eukaryote microfossils-the ornamented acritarchs Dictyosphaera delicata and Shuiyousphaeridium macroreticulatum from the Paleoproterozoic Ruyang Group of North China-using a suite of characterization approaches: scanning electron microscopy (SEM), transmission electron microscopy (TEM), and focused ion beam scanning electron microscopy (FIB-SEM). Although the Ruyang acritarchs must have had nuclei when alive, our data suggest that their ICIs represent neither fossilized nuclei nor taphonomically condensed cytoplasm. We instead propose that these ICIs likely represent biologically contracted and consolidated eukaryotic protoplasts (the combination of the nucleus, surrounding cytoplasm, and plasma membrane). As opposed to degradational contraction of prokaryotic cells within a mucoidal sheath-a model proposed to explain the Bitter Springs ICIs-our model implies that protoplast condensation in the Ruyang acritarchs was an in vivo biologically programmed response to adverse conditions in preparation for encystment. While the discovery of bona fide nuclei in Paleoproterozoic acritarchs would be a substantial landmark in our understanding of eukaryote evolution, the various processes (such as degradational and biological condensation of protoplasts) capable of producing nuclei-mimicking structures require that interpretation of ICIs as fossilized nuclei be based on comprehensive investigations.

  15. The Precambrian crustal structure of East Africa

    Tugume, Fred Alex

    In this thesis, the Precambrian crustal structure of East African is investigated along with the crustal structures of three Cenozoic rift basins located in the western branch of the East African Rift System (EARS). In the first part of the thesis, P-wave receiver functions are modeled using the H-k method to obtain new insights about the bulk composition and thickness of the crust for Precambrian terrains throughout East Africa. The average crustal thickness for all but one of the terrains is between 37 and 39 km. An exception is the Ubendian terrain, which has an average crustal thickness 42 km. In all terrains, the average Poisson's ratio is similar, ranging from 0.25 to 0.26, indicating a bulk crustal composition that is felsic to intermediate. The main finding of this study is that crustal structure is similar across all terrains, which span more than 4.0 Ga of earth history. There is no discernable difference in the crustal thicknesses and Poisson's ratios between the Archean and Proterozoic terrains, or between the Proterozoic terrains, unlike the variability in Precambrian crustal structure found in many other continents. In the second part of the thesis, a joint inversion of Rayleigh wave phase and group velocities and receiver functions was used to investigate the shear wave velocity structure of the crust and uppermost mantle beneath the Precambrian terrains of East Africa. In comparison with other areas of similar age in southern and western Africa where the same joint inversion method has been applied, I find that while there is little difference in the mean shear wave velocities for the entire crust across all of the Precambrian terrains, and also few differences in the thickness of the crust, there exists substantial variability in lower crustal structure. This variability is reflected primarily in the thickness of the lower crustal layers with shear wave velocities ≥ 4.0 km/s. This variability is found both within terrains of the same age (i

  16. Precambrian Secular Evolution of Oceanic Nickel Concentrations: An Update

    Konhauser, K.; Pecoits, E.; Peacock, C.; Robbins, L. J.; Kappler, A.; Lalonde, S.


    Iron formations (IF) preserve a history of Precambrian oceanic elemental abundance that can be exploited to address nutrient limitations on early biological productivity. In 2009 we reported that secular trends in IF Ni/Fe ratios record a reduced flux of Ni to the oceans ca. 2.7 billion years ago, which we attribute to decreased eruption of Ni-rich ultramafic rocks1. We determined that dissolved Ni concentrations may have reached ~400 nM throughout much of the Archean, but dropped below ~200 nM by 2.5 Ga and to modern day values (~9 nM) by ~550 Ma. As Ni is a key metal cofactor in several enzymes of methanogens, its decline would have stifled their activity in the ancient oceans and disrupted the supply of biogenic methane. Here we provide an updated compilation of Ni concentrations and Ni/Fe ratios in Precambrian iron formations based on a greatly expanded (>3 fold) dataset. We frame our rock record compilation in the context of new experiments examining the partitioning and mobility of Ni during simulated diagenesis of Ni-doped iron formation mineral precursors, as well as a fresh look at Ni-Fe scaling relationships in IF vs. modern Fe-rich chemical sediments. While its potential effects on atmospheric oxygenation remains to be fully resolved2, our new results reaffirm the Paleoproterozoic Ni famine, whereby the enzymatic reliance of methanogens on a diminishing supply of volcanic Ni links mantle cooling to the trajectory of Earth surface biogeochemical evolution. Konhauser KO, et al. (2009) Oceanic nickel depletion and a methanogen famine before the Great Oxidation Event. Nature 458: 750-753. Kasting JE (2013) What caused the rise of atmospheric O2? Chemical Geology 362: 13-25.

  17. Hydrogen sulphide release to surface waters at the Precambrian/Cambrian boundary.

    Wille, Martin; Nägler, Thomas F; Lehmann, Bernd; Schröder, Stefan; Kramers, Jan D


    Animal-like multicellular fossils appeared towards the end of the Precambrian, followed by a rapid increase in the abundance and diversity of fossils during the Early Cambrian period, an event also known as the 'Cambrian explosion'. Changes in the environmental conditions at the Precambrian/Cambrian transition (about 542 Myr ago) have been suggested as a possible explanation for this event, but are still a matter of debate. Here we report molybdenum isotope signatures of black shales from two stratigraphically correlated sample sets with a depositional age of around 542 Myr. We find a transient molybdenum isotope signal immediately after the Precambrian/Cambrian transition. Using a box model of the oceanic molybdenum cycle, we find that intense upwelling of hydrogen sulphide-rich deep ocean water best explains the observed Early Cambrian molybdenum isotope signal. Our findings suggest that the Early Cambrian animal radiation may have been triggered by a major change in ocean circulation, terminating a long period during which the Proterozoic ocean was stratified, with sulphidic deep water.

  18. Early precambrian asteroid impact-triggered tsunami: excavated seabed, debris flows, exotic boulders, and turbulence features associated with 3.47-2.47 Ga-old asteroid impact fallout units, Pilbara Craton, Western Australia.

    Glikson, Andrew Y


    Pioneering studies of Precambrian impact fallout units and associated tsunami deposits in the Hamersley Basin, Pilbara Craton, Western Australia, by B.M. Simonson and S.W. Hassler, document a range of tsunami deposits associated with impact fallout units whose impact connection is identified by associated microtektites and microkrystites (condensation spherules). The impact connection of these particles is demonstrated by iridium anomalies, unique platinum group elements patterns, and Ni-rich mineral phases. Densely packed tsunami-transported fragments and boulders overlie microkrystite units of the >2629 +/- 5 Ma top Jeerinah Impact Layer (JIL). Tsunami events closely follow spherule settling associated with the 2561 +/- 8 Ma Spherule Marker Bed SMB-1 and SMB-2 impact events, Bee Gorge Member, Wittenoom Formation. The two impact cycles are separated by a stratigraphically consistent silicified black siltstone, representing a "Quiet Interval." The SMB turbidites display turbulence eddies, climbing ripples, conglomerate pockets, slumps, and waterlogged sediment deformation features. Consequences of tsunami in the probably contemporaneous Carawine Dolomite (Pb-Pb carbonate ages of approximately 2.56-2.54 Ga), eastern Hamersley Basin, include sub-autochthonous below-wave base excavation and megabrecciation of sea floor substrata, resulting in a unique 10-30-m-thick spherule-bearing megabreccia marker mapped over a nearly 100-km north-south strike distance in the east Hamersley Basin. The field relations suggest a pretsunami settling of the bulk of the spherules. Tsunami wave effects include: (1). dispersal of the spherule-rich soft upper sea floor sediments as a subaqueous mud cloud and (2). excavation of consolidated substrata below the soft sediment zone. Excavation and megabrecciation included injection of liquefied spherule-bearing microbreccia into dilated fractures in the disrupted underlying carbonates. Near-perfect preservation of the spherules within the

  19. Principal stages in evolution of precambrian organic world: Communication 2. The late proterozoic

    Sergeev, V. N.; Semikhatov, M. A.; Fedonkin, M. A.; Vorob'eva, N. G.


    A new suggested model outlining the evolution of the organic world from the mid-Early Proterozoic (˜2.0 Ga) to the Early Cambrian is based on data characterizing the relevant chert-embedded and compression-preserved organic-walled microbiotas, impressions of soft-bodied multicellular organisms, and biomarkers. Critical analysis of overall paleontological data resulted in the distinguishing of seven successive assemblages of Proterozoic micro- and macrofossils. Being of global geographic range, the assemblages correspond to the major stages in evolution of the organic world and typify global units which are termed the Labradorian (˜2.0-1.65 Ga), Anabarian (1.65-1.2 Ga), Turukhanian (1.2-1.03 Ga), Uchuromayan (1.03-0.85 Ga), Yuzhnouralian (0.85-0.635 Ga), Amadeusian (0.635-0.56 Ga), and Belomorian (0.56-0.535 Ga). Characteristic of the Labradorian unit are microfossil assemblages of the Gunflint type including remains of morphologically bizarre prokaryotic microorganisms: star-like Eoastrion, umbrella-shaped Kakabekia, dumbbell-shaped Xenothrix, and some others. Fine-grained siliciclastic deposits of the same age yield the oldest remains of millimeter-sized eukaryotes: spherical to ribbon-like Chuaria and Tawuia. Microfossils prevailing in shallow-water carbonate facies of the Anabarian unit are akinetes of nostocalean cyanophyceae Archaeoellipsoides and entophysalidacean cyanobacteria Eoentophysalis, whereas acanthomorphic acritarchs Tappania and Shuiyousphaeridium dominate the assemblages of open-shelf facies, where they are associated with the first-found rare macroscopic multicellular fossils Horodyskia. The distinguishing feature of the next Turukhanian unit is the first occurrence of filamentous red alga Bangiomorpha and the stalked cyanobacterium Polybessurus. The Uchuromayan unit is characterized by the appearance and worldwide radiation of structurally complicated eukaryotic microorganisms, primarily of acanthomorphic acritarchs Trachyhystrichosphaera and

  20. Siliceous microfossils as late Quaternary paleo-environmental indicators at Braamhoek wetland, South Africa

    Finné, M.; Norström, E.; Risberg, J.; Scott, L.


    phytolith indices (Iph and Ic) interpreted as indicators of climatic change, show periods of increased wetness and possibly minor temperature fluctuations during the late Quaternary. The fossil diatom record infer changes in past moisture conditions. Unlike the modern wetland, which is dominated by benthic and aerophilic diatoms, the late Pleistocene-early Holocene wetland favoured growth of planktonic species requiring deeper water. Abundance of planktonic diatoms suggests three main phases of greater water depth than today at c.13.6 ka, 11.3 ka and 10.4-10.0 ka. As part of a multi-proxy comparison, siliceous microfossil indications of past fluctuations in humidity in the Braamhoek wetland generally accord with the results from previous studies of pollen, charcoal fragments and stable isotopes in the same core.

  1. Microfossils from Cerro Prieto geothermal wells, Baja California, Mexico

    Cotton, M.L.; Vonder Haar, S.


    To aid in a paleoenvironmental and age reconstruction of the Cerro Prieto reservoir system, 59 samples of well cuttings were analyzed for microfossils. The cuttings were obtained at depths from 351 to 3495 m in 14 geothermal wells in the Cerro Prieto field, Baja California, Mexico. We found foraminifera in 6 samples, ostracodes in 19 samples, and nannoplankton as coccoliths in 24 samples. Other groups, such as molluscs, insects, fish skeletal parts, and plant material were occasionally present. Detailed interpretations are not possible at this time because of poor preservation of samples. This is primarily due to causes: dissolution by geothermal fluids that reach 350{sup 0}C, and the extensive mixing of filled Cretaceous forms (reworked from the Colorado Plateau region) with Tertiary species during drilling. Further studies of ostracodes and foraminifera from colder portions of the wells are needed. The abundant and well-preserved ostracodes indicate marine to brackish water environments that correspond, in part, to lagoonal or estuarine facies. The presence of the mid-Tertiary (15-My-old) marine foraminifera, Cassigerinela chipolensis, in wells M-11 and M-38, 350 to 500 m deep, is perplexing. These are not laboratory contaminates and, as yet, have not been found in the drilling mud. If further studies confirm their presence at Cerro Prieto, established ideas about the opening of the Gulf of California and about Pacific Coast mid-Tertiary history will need to be rewritten.

  2. Microfossils from Cerro Prieto geothermal wells, Baja California, Mexico

    Cotton, M.L.; Haar, S.V.


    To aid in a paleonenvironmental and age reconstruction of the Cerro Prieto reservoir system, 59 samples of well cuttings were analyzed for microfossils. The cuttings were obtained at depths from 351 to 3495m in 14 geothermal wells in the Cerro Prieto field, Baja California, Mexico. Foraminifera was found in 6 samples, ostracodes in 19 samples and mannoplankton as coccoliths in 24 samples. Other groups, such as molluscus, insects, fish skeletal parts, and plant material were occasionally present. Detailed interpretations at this time cannot be made because of poor preservation of samples. This is primarily due to causes: dissolution by geothermal fluids that reach 350/sup 0/C, and the extensive mixing of filled Cretaceous forms (reworked from the Colorado Plateau region) with Tertiary species during drilling. Further studies of ostracodes and foraminifera from colder portions of the wells are needed. The abundant and well-preserved ostracodes indicate marine to backish water inviroments that correspond in part, to lagoonal or estuarine facies. The presence of the mid-Tertiary (15-m.y.-old) marine foraminifera, Cassigerinela chipolensis, in wells M-11 and M-38, 350 to 500m deep, is perplexing. These are not laboratory contaminates and, as yet have not been found in the drilling mud. If further studies confirm their presence at Cerro Prieto, established ideas about the opening of the Gulf of California and about Pacific Coast mid-Tertiary history will need to be rewritten.

  3. Calcareous microfossil-based orbital cyclostratigraphy in the Arctic Ocean

    Marzen, Rachel; DeNinno, Lauren H.; Cronin, Thomas M.


    Microfaunal and geochemical proxies from marine sediment records from central Arctic Ocean (CAO) submarine ridges suggest a close relationship over the last 550 thousand years (kyr) between orbital-scale climatic oscillations, sea-ice cover, marine biological productivity and other parameters. Multiple paleoclimate proxies record glacial to interglacial cycles. To understand the climate-cryosphere-productivity relationship, we examined the cyclostratigraphy of calcareous microfossils and constructed a composite Arctic Paleoclimate Index (API) "stack" from benthic foraminiferal and ostracode density from 14 sediment cores. Following the hypothesis that API is driven mainly by changes in sea-ice related productivity, the API stack shows the Arctic experienced a series of highly productive interglacials and interstadials every ∼20 kyr. These periods signify minimal ice shelf and sea-ice cover and maximum marine productivity. Rapid transitions in productivity are seen during shifts from interglacial to glacial climate states. Discrepancies between the Arctic API curves and various global climatic, sea-level and ice-volume curves suggest abrupt growth and decay of Arctic ice shelves related to climatic and sea level oscillations.

  4. Calcareous microfossil-based orbital cyclostratigraphy in the Arctic Ocean

    Marzen, Rachel E.; DeNinno, Lauren H.; Cronin, Thomas M.


    Microfaunal and geochemical proxies from marine sediment records from central Arctic Ocean (CAO) submarine ridges suggest a close relationship over the last 550 thousand years (kyr) between orbital-scale climatic oscillations, sea-ice cover, marine biological productivity and other parameters. Multiple paleoclimate proxies record glacial to interglacial cycles. To understand the climate-cryosphere-productivity relationship, we examined the cyclostratigraphy of calcareous microfossils and constructed a composite Arctic Paleoclimate Index (API) "stack" from benthic foraminiferal and ostracode density from 14 sediment cores. Following the hypothesis that API is driven mainly by changes in sea-ice related productivity, the API stack shows the Arctic experienced a series of highly productive interglacials and interstadials every ∼20 kyr. These periods signify minimal ice shelf and sea-ice cover and maximum marine productivity. Rapid transitions in productivity are seen during shifts from interglacial to glacial climate states. Discrepancies between the Arctic API curves and various global climatic, sea-level and ice-volume curves suggest abrupt growth and decay of Arctic ice shelves related to climatic and sea level oscillations.

  5. Patterns of sedimentation in the Precambrian

    Eriksson, Patrick G.; Catuneanu, Octavian; Sarkar, Subir; Tirsgaard, Henrik


    The principle of uniformitarianism may be applied to Precambrian basin evolution and to the sedimentary record as a whole. The major difference in the Precambrian Eon lay in variability of rates and intensities of processes controlling weathering, erosion, transport, deposition, lithification, and diagenesis. This paper examines Precambrian sedimentation patterns within the larger framework of Earth evolution. Pre-rock record sedimentation probably comprised deep water oceanic realms within which meteoritic and cometary impact events generated very large tsunamis, resulting in very coarse volcaniclastic detritus combined with fine dust settling out of suspension, all reworked by marine current systems and localised turbidites. From c. 4 to 3.2 Ga, greenstone belts provided the predominant settings for the thin passive margin carbonates, BIF, stromatolitic evaporites, pelites and quartzites, and lesser synorogenic turbidites, conglomerates, and sandstones that accompanied the volcanic and volcaniclastic rocks typical of these settings. Common palaeoenvironments were high gradient alluvial fans, low sinuosity braided rivers, and relatively shallow marine settings, subject to wave and tidal action, and turbidity currents. Although continental crustal growth continued largely through greenstone belts until c. 2.7 Ga, the Witwatersrand basin (c. 3.0-2.7 Ga; Kaapvaal craton, South Africa) reflects initial stabilisation of the oldest craton, with an epeiric sea accumulating largely fluvial detritus subject to tidal (inland) and storm-wave (craton-marginal) reworking within a retroarc foreland basin setting. Neoarchaean-Palaeoproterozoic sedimentation is discussed within a framework of two global "superevents", at c. 2.7 Ga and 2.2-1.8 Ga, each encompassing major changes in Earth's evolution related to the supercontinent cycle, mantle superplumes, peaks in crustal growth rates, and significant biochemical changes within the atmosphere-hydrosphere system. Concomitant

  6. The late Precambrian greening of the Earth.

    Knauth, L Paul; Kennedy, Martin J


    Many aspects of the carbon cycle can be assessed from temporal changes in the (13)C/(12)C ratio of oceanic bicarbonate. (13)C/(12)C can temporarily rise when large amounts of (13)C-depleted photosynthetic organic matter are buried at enhanced rates, and can decrease if phytomass is rapidly oxidized or if low (13)C is rapidly released from methane clathrates. Assuming that variations of the marine (13)C/(12)C ratio are directly recorded in carbonate rocks, thousands of carbon isotope analyses of late Precambrian examples have been published to correlate these otherwise undatable strata and to document perturbations to the carbon cycle just before the great expansion of metazoan life. Low (13)C/(12)C in some Neoproterozoic carbonates is considered evidence of carbon cycle perturbations unique to the Precambrian. These include complete oxidation of all organic matter in the ocean and complete productivity collapse such that low-(13)C/(12)C hydrothermal CO(2) becomes the main input of carbon. Here we compile all published oxygen and carbon isotope data for Neoproterozoic marine carbonates, and consider them in terms of processes known to alter the isotopic composition during transformation of the initial precipitate into limestone/dolostone. We show that the combined oxygen and carbon isotope systematics are identical to those of well-understood Phanerozoic examples that lithified in coastal pore fluids, receiving a large groundwater influx of photosynthetic carbon from terrestrial phytomass. Rather than being perturbations to the carbon cycle, widely reported decreases in (13)C/(12)C in Neoproterozoic carbonates are more easily interpreted in the same way as is done for Phanerozoic examples. This influx of terrestrial carbon is not apparent in carbonates older than approximately 850 Myr, so we infer an explosion of photosynthesizing communities on late Precambrian land surfaces. As a result, biotically enhanced weathering generated carbon-bearing soils on a large

  7. Sr isotopic chemostratigraphy of Precambrian carbonate rocks in the Amderma Rise, Pai-Khoi Ridge

    Kuznetsov, A. B.; Starikova, E. V.; Maslov, A. V.; Konstantinova, G. V.


    The Sr and C isotopic compositions of Precambrian carbonate rocks are determined for Amderma Rise, in the northeastern margin of Pai-Khoi Ridge. Based on the Sr isotopic chemostratigraphy, it is established for the first time that the Amderma Formation is referred to the Early Vendian, while the Morozovsk Formation is Late Riphean in age. This conclusion along with detailed mapping proves that the Precambrian "section" of the Amderma Rise is a series of tectonic plates combined in a nonchronostratigraphic order. Volcanic and sedimentary rocks of the Morozovsk and Sokolninsk formations make up the allochthon proper, while carbonate rocks of the Amderma Formation make up the para-autochthon. The high values of δ13C (up to +9.5‰) identified in limestones of both formations suggest a considerable distance of the Pai-Khoi paleobasin from the passive margin of the Baltic Region upon facies similarity to the Laurentia active margins.

  8. A Precambrian proximal ejecta blanket from Scotland

    Amor, Kenneth; Hesselbo, Stephen P.; Porcelli, Don; Thackrey, Scott; Parnell, John


    Ejecta blankets around impact craters are rarely preserved onEarth. Although impact craters are ubiquitous on solid bodiesthroughout the solar system, on Earth they are rapidly effaced,and few records exist of the processes that occur during emplacementof ejecta. The Stac Fada Member of the Precambrian Stoer Groupin Scotland has previously been described as volcanic in origin.However, shocked quartz and biotite provide evidence for high-pressureshock metamorphism, while chromium isotope values and elevatedabundances of platinum group metals and siderophile elementsindicate addition of meteoritic material. Thus, the unit isreinterpreted here as having an impact origin. The ejecta blanketreaches >20 m in thickness and contains abundant dark green,vesicular, devitrified glass fragments. Field observations suggestthat the deposit was emplaced as a single fluidized flow thatformed as a result of an impact into water-saturated sedimentarystrata. The continental geological setting and presence of groundwatermake this deposit an analogue for Martian fluidized ejecta blankets.

  9. Theoretical constraints on oxygen and carbon dixoide concentrations in the Precambrian atmosphere

    Kasting, James F.


    Theoretical arguments which bear on the time histories of atmospheric oxygen and carbon dioxide during the Precambrian are reviewed and extended. It is shown that reasonably tight constraints can be placed on atmospheric pCO2 during the early and late Proterozoic, based on the observation that parts of the earth were glaciated at those times. It is demonstrated that an upper bound on early Proterozoic pO2 can be derived from a simple box model of the atmosphere-ocean system.

  10. Experimental mineralization of crustacean eggs: new implications for the fossilization of Precambrian-Cambrian embryos

    Hippler, D.; Hu, N.; Steiner, M.; Scholtz, G.; Franz, G.


    Phosphatized globular microfossils from the Ediacaran and lower Cambrian of South China represent an impressive record of early animal evolution and development. However, their phylogenetic affinity is strongly debated. Understanding key processes and conditions that cause exceptional egg and embryo preservation and fossilization are crucial for a reliable interpretation of their phylogenetic position. We conducted phosphatization experiments on eggs of the marbled crayfish Procambarus that indicate a close link between early mineralization and rapid anaerobic decay of the endochorional envelope. Our experiments replicated the different preservational stages of degradation observed in the fossil record. Stabilization of the spherical morphology was achieved by pre-heating of the eggs. Complete surface mineralization occurred under reduced conditions within one to two weeks, with fine-grained brushite (CaHPO4 · 2H2O) and calcite. The mechanisms of decay, preservation of surface structures, and mineral replacement in the experiment were likely similar during fossilization of Cambrian embryos.

  11. Electron microscopy reveals unique microfossil preservation in 1 billion-year-old lakes

    Saunders, M.; Kong, C.; Menon, S.; Wacey, D.


    Electron microscopy was applied to the study of 1 billion-year-old microfossils from northwest Scotland in order to investigate their 3D morphology and mode of fossilization. 3D-FIB-SEM revealed high quality preservation of organic cell walls with only minor amounts of post-mortem decomposition, followed by variable degrees of morphological alteration (folding and compression of cell walls) during sediment compaction. EFTEM mapping plus SAED revealed a diverse fossilizing mineral assemblage including K-rich clay, Fe-Mg-rich clay and calcium phosphate, with each mineral occupying specific microenvironments in proximity to carbonaceous microfossil cell walls.

  12. Microfossils of filamentous prokaryotes in CI1 and CM2 meteorites

    Hoover, Richard B.


    Field Emission Scanning Electron Microscopy (FESEM) studies of recently obtained samples of Orgueil, Ivuna and Murchison meteorites have provided further evidence for the existence of indigenous filamentous microfossils embedded in the mineral matrix of CI1 and CM2 carbonaceous meteorites. Energy Dispersive X-ray Spectroscopy (EDS) spot data and 2-D elemental X-ray maps establish that the nitrogen and sulphur content of the forms found in the meteorites are dramatically different from modern prokaryotic and eukaryotic cells. These results are interpreted as providing additional evidence for the existence of a complex suite of indigenous microfossils in carbonaceous meteorites.

  13. Testing the survival of microfossils in an artificial martian sedimentary meteorite: the STONE 6 Experiment

    Foucher, Frédéric; Westall, Frances; Brandstaetter, Franz; Demets, Rene; Parnell, John; Cockell, Charles; Edwards, Howell; Jean-Michel, B.; Brack, André; Kurat, Gero

    Conditions on early Mars during the Noachian (-4.5 to -3.5 Ga) were possibly suitable for the emergence of life [1,3] even though water bodies were probably not permanent and could have been destroyed by frequent impacts. Since Mars does not appear to have had plate tectonics, the remains of this hypothetic life could be found within Noachian sediments. In addition to proving the existence of extraterrestrial life, such a discovery would be very helpful for studies related to the origin and early evolution of life on Earth. Indeed, although life most likely appeared on Earth before 4 Ga ago, no suitable (i.e. well-preserved) rocks containing traces of life older than 3.5 billion years exist; older rocks are either too metamorphosed or have been destroyed by plate tectonics. Because of the harsh conditions on Noachian Mars compared to those of the early Earth, the martian organisms are likely to have remained in a very primitive state of evolution and will thus be very difficult to observe in situ. One way to investigate potential traces of life in martian rocks would be to study sedimentary meteorites from Mars. However, all the 54 martian meteorites found so far are volcanic rocks [4]. Is this because sedimentary rocks do not survive the original impact to escape Mars, or the stresses of entry into the Earth's atmosphere? In order to test the latter effects, a series of experiments were devised to test the survivability of different types of sediments during Earth atmosphere entry, the STONE experiments. In particular, the present experiment STONE 6 tested a Noachian sedimentary analogue that consisted of a 3.45 Ga-old silicified volcanic sand containing ancient traces of life [5]. The volcanic sand (chert) from the Pilbara, Australia, containing organic microfossils [6] was embedded in the heat shield of a FOTON space capsule that underwent atmospheric entry on the 26th September, 2007. After landing, the first observation was the white colour of the fusion crust

  14. Biomineral formation as a biosignature for microbial activities Precambrian cherts

    Rincón Tomás, Blanca; Mühlen, Dominik; Hoppert, Michael; Reitner, Joachim


    In recent anoxic sediments manganese(II)carbonate minerals (e.g., rhodochrosite, kutnohorite) derive mainly from the reduction of manganese(IV) compounds by microbial anaerobic respiration. Small particles of rhodochrosite in stromatolite-like features in the Dresser chert Fm (Pilbara supergroup, W-Australia), associated with small flakes of kerogen, account for biogenic formation of the mineral in this early Archaean setting. Contrastingly, the formation of huge manganese-rich (carbonate) deposits requires effective manganese redox cycling, also conducted by various microbial processes, mainly requiring conditions of the early and late Proterozoic (Kirschvink et al., 2000; Nealson and Saffrani 1994). However, putative anaerobic pathways like microbial nitrate-dependent manganese oxidation (Hulth et al., 1999), anoxygenic photosynthesis (Johnson et al., 2013) and oxidation in UV light may facilitate manganese cycling even in a reducing atmosphere. Thus manganese redox cycling might have been possible even before the onset of oxygenic photosynthesis. Hence, there are several ways how manganese carbonates could have been formed biogenically and deposited in Precambrian sediments. Thus, the minerals may be suitable biosignatures for microbial redox processes in many respects. The hyperthermophilic archaeon Pyrobaculum islandicum produces rhodochrosite during growth on hydrogen and organic compounds and may be a putative model organism for the reduction of Mn(IV). References Hulth S, Aller RC, Gilbert F. (1999) Geochim Cosmochim Acta, 63, 49-66. Johnson JE, Webb SM, Thomas K, Ono S, Kirschvink JL, Fischer WW. (2013) Proc Natl Acad Sci USA, 110, 11238-11243. Kirschvink JL, Gaidos EJ, Bertani LE, Beukes NJ, Gutzmer J, Maepa LN, Steinberger LE. (2000) Proc Natl Acad Sci USA, 97, 1400-1405. Nealson KH, Saffarini D. (1994). Annu Rev Microbiol, 48, 311-343.

  15. New estimates of global CH4 and C2H6 production in the Precambrian crust

    Sutcliffe, Chelsea N.; Lacrampe-Couloume, Georges; Ballentine, Chris J.; Sherwood Lollar, Barbara


    Saline fracture fluids found deep within the Precambrian shield possess isotopic and geochemical signatures consistent with prolonged water rock interaction. Noble gas-derived residence times of these fluids, on the order of millions to billions of years, highlight their significance as an ancient deep hydrosphere (Lippmann-Pipke et al., 2011; Holland et al., 2013). With mM concentrations of dissolved gases such as H2 and hydrocarbons, these fracture fluids are energy rich and capable of sustaining microbial communities of H2-utilizing methanogens and sulphate reducers (Lin et al., 2006). Globally, Precambrian rocks constitute over 70% of the volume of the continental crust (Goodwin, 1996) and represent a substantial under-investigated source of such dissolved gases. Recent calculations of global H2 production from these Precambrian Shield rocks, including both hydration reactions and radiolysis, doubles previous estimates to an increased rate of 0.4-2.3 x 1011 mol/yr (Sherwood Lollar et al., 2014). This has important consequences for hydrocarbon production, reflected in the high abundance of CH4 and C2H6 in dissolved fracture gases, up to 80 and 10 vol %, respectively. Given the long residence times of these fluids, hydrocarbon production could have persisted on geological timescales. To date, production from this source has not been incorporated into models of evolution of the early atmosphere. Additionally, the quantification of abiotic sources of methane and ethane in the analogous terrestrial Precambrian crust could contribute to our understanding of the origin of the episodic traces of methane recently detected on Mars (Webster et al., 2014). Investigating the origin of these gases has important implications for the global carbon cycle, as well as the distribution of life in the terrestrial deep subsurface and on other planets. We examine the isotopic evolution of these fracture fluids in the Canadian Shield and provide the first attempts to estimate methane

  16. Microfossils, carbonate lysocline and compensation depth in surface sediments of the northeastern South China Sea

    Chen Ronghua; Xu Jian; Meng Yi; Wang Dongjun; Liu Chuanlian; Huang Baoqi; Zhang Fuyuan


    Based on the quantitative analyses of abundance of planktonic foraminifera, benthic foraminifera, calcareous nannofossils, the ratios of calcareous to siliceous microfossils, and the determination of carbonate contents in the surface sediments of the northeastern South China Sea, it has been found that the carbonate contents, the abundance of planktonic foraminifera and calcareous nannoplankton, and the ratio of calcareous microfossils decrease rapidly while the ratio of the benthic foraminifera to the total foraminiferal fauna, specific value of siliceous microfossils, and the percentage of the agglutinated tests in the benthic foraminiferal fauna increase with the water depth. The results indicate that the microfossils abundance and ratio, and the carbonate content are closely related to the carbonate lysocline and carbonate compensation depth (CCD) in the study area. In addition, the carbonate lysocline and the CCD are different between the southern and northern parts of the South China Sea. Both the lysocline and the CCD are deeper in the south with 2 600 and 3 600 m than in the north with 2 200 and 3 400 m,respectively.

  17. The potential of vertebrate microfossils for marine to non-marine correlation in the Late Jurassic

    Detlev Thies; Alexander Mudroch; Susan Turner


    Fish (cartilaginous: elasmobranch and bony: osteichthyan actinopterygian) and reptile (crocodile) microfossils comprising scales and teeth have been examined from a series of limestone samples in the Upper Jurassic of France and Germany to gauge the possibilities of using them for correlation between fully marine and hypo- or hyper-saline (non-marine) deposits.

  18. Middle Triassic (Anisian Limestones from Bled, Northwestern Slovenia: Microfacies and Microfossils

    Erik Flügel


    Full Text Available Microfacies types (predominantly intrabioclastic grainstones and microfossils (predominantly dasycladacean algae and diverse foraminifera characterize the Anisian carbonates near Bled (Castle Hill and in the area westnorthwest of Bled as subtidal to intertidal shelf sediments deposited in the irmer part ofthe Julian carbonate platform. The age of the carbonates is Middle Anisian (Pelsonian according to the biozonation based on foraminifera and dasycladaceans.

  19. Biogenic silica microfossils in sediments of the Permian - Carboniferous Unayzah Formation, Saudi Arabia

    Garming, J.F.L.; Franks, S.G.; Cremer, H.; Abbink, O.A.


    Biogenic silica particles (BSPs) have been discovered in sediments of the Permian - Carboniferous Unayzah Formation of Saudi Arabia. The BSPs are extracted from sediments that are generally barren of macro- or microfossils. BSPs have been found in the Basal Khuff Clastics (BKC), and the Unayzah A, B

  20. Facilitating Identification of Poorly Preserved Marine Microfossils through 3D Printing

    Christensen, R. V.; Robinson, M. M.; Sessa, J.


    The Paleocene-Eocene Thermal Maximum (PETM) was a period of sudden and intense global warming that occurred 56 Myr, and is widely considered a possible analogue for future climatic changes. Marine microfossils are important proxies used in the reconstruction of PETM paleoenvironments and paleoclimate. The correct species-level identification of foraminifera and pteropod specimens is necessary to understand ocean temperature, chemistry, nutrient availability, and ecosystem structure during this hyperthermal event. During periods of extreme or rapid environmental perturbations foraminifera can be poorly preserved. Pteropod identification is equally challenging as aragonitic shells are vulnerable to changing ocean acidity and often only internal molds are left to be identified. The macroscopic rendering of the internal and external test morphology of marine microfossils via 3D printing allows for a more experiential species-recognition education, especially of difficult to identify specimens. A selected microfossil specimen is scanned using computerized tomography (CT), creating x-ray slices of the specimen that are then processed into a digital model. The digitized fossil can then be analyzed using 3D software and subsequently printed using a wide variety of materials. The magnified model can be easily manipulated in a student's hand, and thus can be studied in a more visible and tactile way than traditional methods allow. This invaluable teaching tool physically manifests what was previously limited to textbook images and illustrations or the view field of a microscope. We show the step-by-step 3-D printing process of several PETM marine microfossil specimens from CT scans and demonstrate their advantage over 2-D SEM images for learning to identify microfossils to the species level. In addition, we provide samples to demonstrate the utility of 3-D models in identifying poorly preserved foraminifer specimens and species of pteropods from internal molds.

  1. Micro Raman spectroscopy of carbonaceous material in microfossils and meteorites: improving a method for life detection.

    Bower, D M; Steele, A; Fries, M D; Kater, L


    The identification of biosignatures in Earth's ancient rock record and detection of extraplanetary life is one of the primary goals in astrobiology. Intrinsic to this goal is the improvement of analytical techniques and protocols used to identify an unambiguous signal of life. Micro Raman spectroscopy is a nondestructive method that allows for in situ identification of a wide range of minerals and compounds. The use of D (∼1350 cm(-1)) and G (∼1580 cm(-1)) band parameters to infer the biogenicity of carbonaceous materials in fossils has become a commonly used analytical tool, but carbonaceous compounds from different sources often share the same spectroscopic characteristics. Microfossil studies do not always take into consideration a nonbiological source for the carbon in their samples and therefore still rely on morphology as the primary mode of identification. Comprehensive studies that consider all carbon sources are typically done on metasediments, coals, or meteorites, and the results are not clearly applicable to microfossil identification. In this study, microfossils from a suite of sedimentary rock samples of various ages were analyzed with micro Raman spectroscopy to investigate the nature and provenance of carbonaceous material. To further constrain D- and G-band carbon characteristics, micro Raman analyses were also performed on well-characterized meteorite samples as abiological controls. The results appear to show a correlation of precursor carbonaceous material with D-band parameters and thermal history with G-band parameters. This systematic study lays the groundwork for improving the use of the G- and D-band trends as useful indicators of the origin of carbon in microfossils. Before unambiguous biosignatures can be established, further work characterizing the carbonaceous material in microfossils of different ages, thermal histories, and host rock compositions is needed.

  2. On the issue of the Precambrian basement of the Arctic shelf

    Vernikovsky, Valery A.; Korago, Evgeny A.; Proskurnin, Vasily F.; Sobolev, Nikolay N.


    Many researchers of the geological structures of the Russian Arctic concluded that the basements of the terranes composing the Arctic shelf and continental slopes have a Precambrian age. It is assumed that these terranes are actually fragments of the ancient Arctida paleocontinent [Zonenshain, Natapov, 1987] that broke up as a result of rifting and its separate plates and terranes either were overlain by continental margins sediments or included in the fold belts in the periphery of the ocean. In the western part of the Russian Arctic, a Grenvillian and Mesoproterozoic basement was demonstrated for Svalbard, Novaya Zemlya and Taimyr Peninsula, and at least a Neoproterozoic basement was established for structures in the basement of Severnaya Zemlya archipelago. In the eastern part of the Russian Arctic, such proofs were almost nonexistent. In recent years, new information was obtained concerning the continental nature and Precambrian age of the basement crust of the New Siberian Islands and De Long archipelagos as well as probably the Mendeleev Ridge. For the New Siberian Islands and De Long archipelagos, a whole series of geochronological evidence was obtained in addition to geological data (horizontally bedding Early Paleozoic passive continental margin sediments (Cambrian, Ordovician) at Bennett Island). In magmatic and tuffaceous-sedimentary rocks of Henrietta and Zhokhov islands we discovered zircons that had formed from magmatic crystallization in the Late Neoproterozoic. New U-Pb data for zircons from rocks of these islands do not contradict isotopic dating obtained earlier by other methods - Ar/Ar and Sm/Nd in different laboratories. Considering different closure temperatures for isotopic systems, these new results complement each other. On the islands of the eastern sector of the Russian Arctic, a Neoproterozoic complex of rocks is most certainly established in the basement of the mesozoides of Vrangel Island. Here were discovered metamorphosed volcanics

  3. Molecular preservation of 1.88 Ga Gunflint organic microfossils as a function of temperature and mineralogy

    Alleon, Julien; Bernard, Sylvain; Le Guillou, Corentin; Marin-Carbonne, Johanna; Pont, Sylvain; Beyssac, Olivier; McKeegan, Kevin D.; Robert, François


    The significant degradation that fossilized biomolecules may experience during burial makes it challenging to assess the biogenicity of organic microstructures in ancient rocks. Here we investigate the molecular signatures of 1.88 Ga Gunflint organic microfossils as a function of their diagenetic history. Synchrotron-based XANES data collected in situ on individual microfossils, at the submicrometre scale, are compared with data collected on modern microorganisms. Despite diagenetic temperatures of ~150-170 °C deduced from Raman data, the molecular signatures of some Gunflint organic microfossils have been exceptionally well preserved. Remarkably, amide groups derived from protein compounds can still be detected. We also demonstrate that an additional increase of diagenetic temperature of only 50 °C and the nanoscale association with carbonate minerals have significantly altered the molecular signatures of Gunflint organic microfossils from other localities. Altogether, the present study provides key insights for eventually decoding the earliest fossil record.

  4. Anoxic and oxic phototrophic primary production during the Precambrian

    Ebey-Honeycutt, Christina Marie; Bjerrum, Christian J.; Canfield, Donald Eugene


    of the mixed layer often lies above the base of the photic zone . Thus, an ecosystem model for the Precambrian should reflect the net primary production (NPP) of oxygenic phototrophs in the mixed layer and anoxygenic phototrophs below (NPPox and NPPred, respectively). Satelite data and a vertically generalized...


    Klootwijk, C.T.


    Klootwijk, C.T., 1974. Palaeomagnetic data from the Precambrian Gwalior Traps, Central India. Tectonophysics, 21: 181-195. From alternating-field and thermal demagnetization studies on two dolerite “Traps” in the Gwalior Series (Central India), dated at 1830 f200 m.y., three different palaeomagnetic

  6. The palaeoecologic and biostratigraphic evaluation of Middle Miocene freshwater sediments and microfossils near Denkendorf (Bavaria)

    Pirkenseer, C.; Reichenbacher, B.


    Isolated freshwater sediments that partially cover the Jurassic limestones of the Swabian and Franconian Alb represent the northernmost expansion of the Molasse sediments. These sediments represent the analogue to the Brackish Molasse and part of the Upper Freshwater Molasse (Ottnangian to Badenian). Samples of six drillcores from the vicinity of Denkendorf (Franconian Alb, Bavaria) yielded ostracods of the superfamily Cypridoidea, frequent oogonia of charophytes, otoliths of the family Gobiidae, teeth of several taxa of micromammals as well as abundant material of amphibians, reptiles and gastropods. The sediments show a general trend from basal, more clastic influenced deposits to uniformly developed marly sediments with freshwater carbonate intercalations. The acme of microfossil occurrences is associated with the latter section. The palaeoecologic analysis characterises the environment as structured littoral zone (e.g. Pseudocandona steinheimensis, Gyraulus sp., Planorbarius sp., Rana ridibunda, Triturus sp.) of a larger oligo- to mesotrophic (Chara spp., Nitellopsis spp.) low-energy freshwater system under a warm subtropical to tropical climate (Diplocynodon cf. D. styriacus, Channa sp.). The cooccurrence of suboxia- and oligotrophy-tolerant species like Palaeocarassius sp. and Channa sp. may indicate short intervals of regional depletion of oxygene and raise of nutrient content. Mediocypris candonaeformis and Gobius latiformis represent relict species of the preceding Brackwassermolasse. Terrestrial elements include Proboscidea (phalanx), Cervidae (astragalus), land turtles (Testudo sp.) and gastropods (Clausiliidae, Pupillidae, Cepaea sp.). The occurrence of Jurassic xenoclasts and bean iron ore indicate the presence of a tributary system. The faunal and floral assemblages show close affinities to other localities of the Molasse Basin (e.g., Sandelzhausen). In accordance with the depositional history this indicates a palaeogeographic connection with the

  7. Digital database of microfossil localities in Alameda and Contra Costa Counties, California

    McDougall, Kristin; Block, Debra


    The eastern San Francisco Bay region (Contra Costa and Alameda Counties, California) is a geologically complex area divided by faults into a suite of tectonic blocks. Each block contains a unique stratigraphic sequence of Tertiary sediments that in most blocks unconformably overlie Mesozoic sediments. Age and environmental interpretations based on analysis of microfossil assemblages are key factors in interpreting geologic history, structure, and correlation of each block. Much of this data, however, is distributed in unpublished internal reports and memos, and is generally unavailable to the geologic community. In this report the U.S. Geological Survey microfossil data from the Tertiary sediments of Alameda and Contra Costa counties are analyzed and presented in a digital database, which provides a user-friendly summary of the micropaleontologic data, locality information, and biostratigraphic and ecologic interpretations.

  8. Reconnaissance geology and geochronology of the Precambrian of the Granite Mountains, Wyoming

    Peterman, Zell E.; Hildreth, Robert A.


    Rb-Sr and K-Ar mineral ages are obtained on rocks of the metamorphic complex and on the granite. These ages range from about 2,400 to 1,420 million years and are part of a regional pattern of lowered mineral ages of Precambrian W rocks of southern Wyoming. A major discontinuity in these mineral ages occurs along a line extending from the northern Laramie Range, through the northern part of the Granite Mountains, to the southeastern Wind River Mountains. North of this line, Rb-Sr and K-Ar biotite ages are 2,300 million years or greater, whereas to the south, the biotite ages decrease drastically over a short distance, to a common range of 1,600-1,400 million years. We suggest that these lowered ages represent regional cooling below the 300 0 C isotherm as a consequence of uplift and erosion of the large crustal block occurring south of the age discontinuity. In this interpretation, the westerly-trending age discontinuity would be a zone of major crustal dislocation that resulted from vertical tectonics in late Precambrian X or early Precambrian Y time.

  9. Iron minerals within specific microfossil morphospecies of the 1.88 Ga Gunflint Formation

    Lepot, Kevin; Addad, Ahmed; Knoll, Andrew H.; Wang, Jian; Troadec, David; Béché, Armand; Javaux, Emmanuelle J.


    Problematic microfossils dominate the palaeontological record between the Great Oxidation Event 2.4 billion years ago (Ga) and the last Palaeoproterozoic iron formations, deposited 500-600 million years later. These fossils are often associated with iron-rich sedimentary rocks, but their affinities, metabolism, and, hence, their contributions to Earth surface oxidation and Fe deposition remain unknown. Here we show that specific microfossil populations of the 1.88 Ga Gunflint Iron Formation contain Fe-silicate and Fe-carbonate nanocrystal concentrations in cell interiors. Fe minerals are absent in/on all organically preserved cell walls. These features are consistent with in vivo intracellular Fe biomineralization, with subsequent in situ recrystallization, but contrast with known patterns of post-mortem Fe mineralization. The Gunflint populations that display relatively large cells (thick-walled spheres, filament-forming rods) and intra-microfossil Fe minerals are consistent with oxygenic photosynthesizers but not with other Fe-mineralizing microorganisms studied so far. Fe biomineralization may have protected oxygenic photosynthesizers against Fe2+ toxicity during the Palaeoproterozoic.

  10. Saturated hydrocarbon biomarkers in oils of Late Precambrian age from Eastern Siberia

    Fowler, M.G.; Douglas, A.G.


    Large quantities of petroleum derived from source rocks of Late Precambrian-Early Cambrian age have been discovered in the Lena-Tunguska region of Eastern Siberia over the last twenty-five years. The authors have examined three oils, with presumed Late-Precambrian (Vendian) source rocks, from this region for C/sub 15/ + saturated hydrocarbon biomarkers using gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). The results show these oils to have many characteristics in common with other oils of similar age from Eastern Siberia and Oman. Amongst the compounds detected in the three oils analyzed were: (1) n-alkanes which show a marine-derived distribution, (2) centrally branched monomethyl alkanes, (3) acyclic isoprenoids (pr/ph < 1), (4) tricyclic and tetracyclic terpanes, (5) hopanes, (6) C/sub 29/ unrearranged steranes, and (7) C/sub 30/ nuclear methylated steranes. All of these compounds with the exception of the 4-methylsteranes (which on current biochemical knowledge are unexpected in oils of this age), can be assigned a prokaryotic source. This and other evidence such as the lack of diasteranes suggest microorganisms were the major contributors to organic matter deposited as part of a carbonate source rock.

  11. The lunar nodal tide and the distance to tne Moon during the Precambrian era

    Walker, J. C. G.; Zahnle, K. J.


    The origin and early evolution of life on Earth occurred under physical and chemical conditions distinctly different from those of the present day. The broad goal of this research program is to characterize these conditions. One aspect involves the dynamics of the Earth-Moon system, the distance of the Moon from the Earth, and the length of the day. These have evolved during the course of Earth history as a result of the dissipation of tidal energy. As the moon has receded the amplitude of oceanic tides has decreased while the increasing length of the day should have influenced climate and the circulation of atmosphere and ocean. A 23.3 year periodicity preserved in a 2500 million year old banded iron-formation was interpreted as reflecting the climatic influence of the lunar nodal tide. The corresponding lunar distance would then have been approx. 52 Earth radii. The influence of the lunar nodal tide is also apparent in rocks with an age of 680 million years B.P. The derived value for lunar distance 2500 million years ago is the only datum on the dynamics of the Earth-Moon system during the Precambrian era of Earth history. The implied development of Precambrian tidal friction is in accord with more recent paleontological evidence as well as the long term stability of the lunar orbit.

  12. A key role for green rust in the Precambrian oceans and the genesis of iron formations

    Halevy, I.; Alesker, M.; Schuster, E. M.; Popovitz-Biro, R.; Feldman, Y.


    Iron formations deposited in marine settings during the Precambrian represent large sinks of iron and silica, and have been used to reconstruct environmental conditions at the time of their formation. However, the observed mineralogy in iron formations, which consists of iron oxides, silicates, carbonates and sulfides, is generally thought to have arisen from diagenesis of one or more mineral precursors. Ferric iron hydroxides and ferrous carbonates and silicates have been identified as prime candidates. Here we investigate the potential role of green rust, a ferrous-ferric hydroxy salt, in the genesis of iron formations. Our laboratory experiments show that green rust readily forms in early seawater-analogue solutions, as predicted by thermodynamic calculations, and that it ages into minerals observed in iron formations. Dynamic models of the iron cycle further indicate that green rust would have precipitated near the iron redoxcline, and it is expected that when the green rust sank it transformed into stable phases within the water column and sediments. We suggest, therefore, that the precipitation and transformation of green rust was a key process in the iron cycle, and that the interaction of green rust with various elements should be included in any consideration of Precambrian biogeochemical cycles.

  13. Uinta Arch Project: investigations of uranium potential in Precambrian X and older metasedimentary rocks in the Unita and Wasatch ranges, Utah and Colorado

    Graff, P.J.; Sears, J.W.; Holden, G.S.


    This study is part of the United States Department of Energy's National Uranium Resource Evaluation Program to understand the geologic setting, amount, and availability of uranium resources within the boundaries of the United States. The systematic study of Precambrian quartz-pebble conglomerates and areas that may contain such conglomerates is an integral part of DOE's resource evaluation program, because deposits of world-wide importance occur in such terrains in Canada and South Africa, and because terrains similar to those producing uranium from quartz-pebble conglomerates exist elsewhere in the United States. Because of the ready availability of Tertiary sandstone and Colorado Plateau-type uranium deposits, large areas of Precambrian rocks in the US have not been fully assessed for uranium potential. Thus, the Uinta Arch Project was undertaken to assess the favorability of Precambrian metasedimentary rocks in northern Utah for deposits of uranium in Precambrian quartz-pebble conglomerates. Rocks of interest to this study are the thick, clastic sequences within the Uinta Arch that are considered to be of Early Proterozoic age. The Uinta Arch area is known to contain rocks which generally fit the lithologic characteristics that are understood to limit the occurrence of Precambrian fossil placers. However, detailed geology of these rocks and their exact fit to the model described for uraniferous conglomerates was not known. The primary goal of the Uinta Arch Project was to determine how well these Precambrian rocks resemble known deposits and to describe the favorability of placer uranium deposits.

  14. Microfossils from the Neoarchean Campbell Group, Griqualand West Sequence of the Transvaal Supergroup, and their paleoenvironmental and evolutionary implications

    Altermann, W.; Schopf, J. W.


    The oldest filament- and colonial coccoid-containing microbial fossil assemblage now known is described here from drill core samples of stromatolitic cherty limestones of the Neoarchean, approximately 2600-Ma-old Campbell Group (Ghaap Plateau Dolomite, Lime Acres Member) obtained at Lime Acres, northern Cape Province, South Africa. The assemblage is biologically diverse, including entophysalidacean (Eoentophysalis sp.), probable chroococcacean (unnamed colonial coccoids), and oscillatoriacean cyanobacteria (Eomycetopsis cf. filiformis, and Siphonophycus transvaalensis), as well as filamentous fossil bacteria (Archaeotrichion sp.); filamentous possible microfossils (unnamed hematitic filaments) also occur. The Campbell Group microorganisms contributed to the formation of stratiform and domical to columnar stromatolitic reefs in shallow subtidal to intertidal environments of the Transvaal intracratonic sea. Although only moderately to poorly preserved, they provide new evidence regarding the paleoenvironmental setting of the Campbell Group sediments, extend the known time-range of entophysalidacean cyanobacteria by more than 400 million years, substantiate the antiquity and role in stromatolite formation of Archean oscillatoriacean cyanobacteria, and document the exceedingly slow (hypobradytelic) evolutionary rate characteristic of this early evolving prokaryotic lineage.

  15. Analysis of a Precambrian resonance-stabilized day length

    Bartlett, Benjamin C


    Stromatolite data suggest the day length throughout much of the Precambrian to be relatively constant near 21 hours; this period would have been resonant with the semidiurnal atmospheric tide. At this point, the atmospheric torque would have been nearly maximized, being comparable in magnitude but opposite in direction to the lunar torque, halting Earth's angular deceleration, as suggested by Zahnle and Walker [1987]. Computational simulations of this scenario indicate that, depending on the atmospheric $Q$-factor, a persistent increase in temperature larger than ~10K over a period of time less than $10^7$ years will break resonance, such as the deglaciation following a snowball event near the end of the Precambrian. The resonance was found to be relatively unaffected by other forms of climate fluctuation (thermal noise). Our model provides a simulated day length over time that matches existing records of day length, though further data is needed.

  16. The evolution of the oceanic redox state through Precambrian times

    Kurzweil, Florian


    The oceanic redox state distinctly changed during the Precambrian eon. Entirely anoxic oceans in earliest Earth history first became mildly oxygenated in some shallow marine areas during the late Archean. The areal extension of such ‘oxygen oases’ may have triggered atmospheric oxygenation during the subsequent Great Oxidation Event around 2.4 billion years ago. In the aftermath of the Great Oxidation Event and the proposed oxygen ‘overshoot’ during the following Lumagundi Jatuli Event oxygen...

  17. Microfossil assemblage characteristics in Core B10 and implication for paleoenvironmental evolution in the southern Yellow Sea


    Microfossil assemblage and pollen zone characteristics in Core B10 recorded the history of environmental changes in the southern Yellow Sea since Würm Subinterglaciation. Environmental variations reflected by these glacial and interglacial sediments coincide with general characteristics of paleoenvironmental and sedimentary changes in the Yellow Sea. In the section of 550-520 cm, microfossil foraminifera have low abundance and diversity, and pollens are composed mainly of those of herbaceous vegetation, indicating climate change during Würm Subinterglaciation. In the section of 520-140 cm, the changes from a few microfossils to no microfossils reflect the sedimentary environment variation from coastal to terrestrial facies. Paleoclimate reflected by pollen also underwent the changes from conifer-broadleaf mixed forest to grassland, indicating the climate changes from temperate and cool type to warm and dry one. In the section of 140-0 cm, the general microfossil characteristics are the gradual increase in abundance with most species being neritic species, the major pollen being ligneous pollen and the rapid increase in small Hystrichosphaera content, which indicates that the air temperature increased and the sea level gradually rose.

  18. Thermal maturity of Tasmanites microfossils from confocal laser scanning fluorescence microscopy

    Hackley, Paul C.; Kus, Jolanta


    We report here, for the first time, spectral properties of Tasmanites microfossils determined by confocal laser scanning fluorescence microscopy (CLSM, using Ar 458 nm excitation). The Tasmanites occur in a well-characterized natural maturation sequence (Ro 0.48–0.74%) of Devonian shale (n = 3 samples) from the Appalachian Basin. Spectral property λmax shows excellent agreement (r2 = 0.99) with extant spectra from interlaboratory studies which used conventional fluorescence microscopy techniques. This result suggests spectral measurements from CLSM can be used to infer thermal maturity of fluorescent organic materials in geologic samples. Spectra of regions with high fluorescence intensity at fold apices and flanks in individual Tasmanites are blue-shifted relative to less-deformed areas in the same body that have lower fluorescence intensity. This is interpreted to result from decreased quenching moiety concentration at these locations, and indicates caution is needed in the selection of measurement regions in conventional fluorescence microscopy, where it is common practice to select high intensity regions for improved signal intensity and better signal to noise ratios. This study also documents application of CLSM to microstructural characterization of Tasmanites microfossils. Finally, based on an extant empirical relation between conventional λmax values and bitumen reflectance, λmax values from CLSM of Tasmanites microfossils can be used to calculate a bitumen reflectance equivalent value. The results presented herein can be used as a basis to broaden the future application of CLSM in the geological sciences into hydrocarbon prospecting and basin analysis.

  19. Using modern ferruginous habitats to interpret Precambrian banded iron formation deposition

    Koeksoy, Elif; Halama, Maximilian; Konhauser, Kurt O.; Kappler, Andreas


    Early Earth processes are typically identified through the study of mineralogical, elemental and isotopic features in the rock record, including Precambrian banded iron formations (BIF). However, post-depositional processes often obscure the primary geochemical signals, making the use of BIF as proxies for paleo-seawater and the paleo-biosphere potentially imprecise. Thus, alternative approaches are required to complement the information gained from the rock record in order to fully understand the distinctive biogeochemical processes on ancient Earth. Simulating these conditions in the laboratory is one approach, but this approach can never fully replicate the complexity of a natural environment. Therefore, finding modern environments with a unique set of geochemical and microbiological characteristics to use as analogues for BIF depositional environments can provide invaluable information. In this review, we provide an overview of the chemical, physical and biological parameters of modern, ferruginous lakes that have been used as analogue BIF environments.

  20. Microfossils in the Ordovician erratic boulders from South-western Finland

    Nõlvak, J.


    Full Text Available Chitinozoans, ostracods and acritarchs found in four glacially transported limestone boulders from the south-western coast of Finland have been studied in order to test the usefulness of these microfossil groups in age determinations. Also rare specimens of conodonts, inarticulated brachiopods and foraminifers were found. Baltic limestone (or Östersjö limestone was the most problematic, because only fossils with calcitic or phosphatic shells are preserved. It is concluded that the boulders identified correlate with the Uhaku and Rakvere stages of the Middle Ordovician.

  1. The microfossils in phosphate deposit in Doushantuo stage, Sinian System, Weng'an, Guizhou Province


    The aim of this study is to discuss the microfossils in phosphate deposit in the Doushantuo stage, Sinian System, Weng'an, Guizhou Province. Based on the detailed observation in morphology and microstructures, it is considered that those acritarchs with interior spicules probably belong to sponge animals. However, some explanations for a part of soft-tissue are still contrioversial. The reliable conclusion still needs more evidence to study. The scientific significance of this study and the key questions for further studies are suggested here.

  2. Early Holocene environmental change, the presence and disappearance of early Mesolithic habitation near Zutphen (The Netherlands)

    Bos, J.A.A.; Geel, B. van; Groenewoudt, B.J.; Lauwerier, R.C.G.M


    The Early Holocene landscape near Zutphen (The Netherlands) is reconstructed by means of microfossil, macroremain and bone analyses. In this area early Mesolithic sites were found on a river dune along a former river channel. AMS14C dating provided a detailed chronology for the sites and river chann

  3. The investigation of microfossils in ancient rocks: the comparison of different techniques

    Astafieva, M.


    Traditionally microfossils in ancient Archaean - Proterozoic (AR-PR1) silicified rocks were investigated in thin sections and macerates (preparations obtained by the chemical decomposition of rocks) by polarized optical microscopy. These methods produced great results and greatly changed the investigation of ancient rocks and our mental picture of world. Among these achievements, the modern concepts concerning the evolution of the Earth's biosphere evolution and processes of sedimentation are the most important. Pioneers in this research included E. S. Barghoorn,[2], J. W. Schopf[9], J. F. Banfield[1], K. H. Nealson[1], A. H. Knoll[7], B. V. Timofeev[10] and many others. Another method of studying ancient rocks and the microfossils contained within them is the method of examining freshly fractured interior surfaces of rock chips using the Scanning Electron Microscope (SEM). The wide application of this method began with the study of microfossils in the ancient phosphorites of Khubsugul (the Lower Cambrian, Tommotian stage, Mongolia) [8, 15]. It is possible to say that the investigation of fresh phosphorites chips in the SEM gave rise to a new epoch in the understanding of many problems such as, for example, the rate of fossilization[3, 5, 4] the possibility of bacterial preservation in different types of sedimentary rocks and meteorites [6, 11, 13, 14, 12] and, finally, the resolution of many interesting questions of bacterial paleontology. The method of the SEM study of fresh chips has many advantages over the prior techniques (e.g., the study of thin sections and macerates). While working with thin sections we are dealing with thin (0.003mm) smooth (polished) rock surfaces. So, we have little opportunity to trace mutual relations (interrelationships) of the microfossils encountered and the host rock. While preparing macerates (i.e. while dissolving host rock by strong acids) we can usually only observe the separate microorganism fragments without the knowledge

  4. Cenozoic macroevolution in the deep-sea microfossil record: can we let go of species richness?

    Hannisdal, Bjarte; Liow, Lee Hsiang


    The deep-sea microfossil record is an outstanding resource for the study of macroevolutionary changes in planktonic groups. Studies of plankton evolution and its possible link to climate changes over the Cenozoic have typically targeted apparent trends in species richness. However, most species are rare, and fossil richness is particularly vulnerable to the imperfections (incompleteness, reworking, age and taxonomic errors) of existing microfossil occurrence databases. Here we use an alternative macroevolutionary quantity: Summed Common Species Occurrence Rate (SCOR). By focusing on the most commonly occurring species, SCOR is decoupled from species richness, robust to preservation/sampling variability, yet sensitive to relative changes in the overall abundance of a group. Numerical experiments are used to illustrate the sampling behavior of SCOR and its relationship to (sampling-standardized) species richness. We further show how SCOR estimated from the NEPTUNE database (ODP/DSDP) can provide a new perspective on long-term evolutionary and ecological changes in major planktonic groups (e.g. coccolithophores and forams). Finally, we test possible linkages between planktonic SCOR records and proxy reconstructions of climate changes over the Cenozoic.

  5. Tectonics of Precambrian basement of the Tarim craton

    GUO; Zhaojie; (


    [1]Jia Chengzao, Tectonic Characteristics and Petroleum, Tarim Basin, China (in Chinese), Beijing: Petroleum Industry Press, 1997, 29?/FONT>92.[2]Huang, T. K., Ren, J. S., Jiang, C. F. et al., The Geologic Evolution of China (in Chinese), Beijing: Geological Publishing House, 1980.[3]Che, Z. C., Liu, L., Liu, H. F. et al., Discovery and occurrence of high-pressure meta-pelitic rocks from Altun Mountain areas, Xinjiang Uygur Autonomous Region, Chinese Science Bulletin, 1995, 40(23): 1988.[4]An Yin, Nie Shangyou, A phanerozoic palinspastic reconstruction of China and its neighboring regions, in The Tectonic Evolution of Asia (eds. An Yin, Harrison, T. M.), London: Cambridge University Press, 1996, 442-485.[5]Sobel, E. R., Arnaud, N., A possible middle Paleozoic suture in the Altyn Tagh, NW China, Tectonics, 1999, 18(1): 67.[6]Xu, Z. Q., Yang, J. S., Zhang, J. X. et al., A comparison between the tectonic units on the two sides of the Altun sinistral strike-slip fault and the mechanism of lithospheric shearing, Acta Geologica Sinica (in Chinese with English abstract), 1999, 73(3): 193.[7]Guo, Z., J., Zhang, Z. C., Wang, J. J., Sm-Nd isochron age of ophiolite along northern margin of Altun Tagh Mountain and its significance, Chinese Science Bulletin, 1999, 44(5): 456.[8]Liu, L., Che, Z. C., Wang, Y. et al., The evidence of Sm-Nd isochron age for the early Paleozoic ophiolite in Mangya area, Altun Mountains, Chinese Science Bulletin, 1998, 43(15): 754.[9]Xinjiang Bureau of Geology and Mineral Resources, Regional Geology of Xinjiang Uygur Autonomous Region (in Chinese with English abstract), Beijing: Geological Publishing House, 1993, 555-557.[10]Gansu Bureau of Geology and Mineral Resources, Regional Geology of Gansu Province (in Chinese with English abstract), Beijing: Geological Publishing House, 1989.[11]Hu, A. Q., Rogers, G., Discovery of 3.3 Ga Archean rocks in North Tarim Block of Xinjiang, Western China, Chinese Science

  6. Bedded Precambrian iron deposits of the Tobacco Root Mountains, southwestern Montana

    James, H.L.


    Bedded deposits of iron-formation are minor components of the thoroughly metamorphosed and deformed Precambrian rocks that make up the core of the Tobacco Root Mountains. The rocks are Archean in age; they predate a major Precambrian orogeny that affected all of southwestern Montana about 2,750 m.y. ago. The principal bed of iron-formation occurs within a metasedimentary sequence that has dolomite marble at the base and rests on quartzofeldspathic gneiss of uncertain origin. The stratigraphic thickness of the preserved part of the metasedimentary group cannot readily be established because of structural complexities, including both thickening and attenuation, but it probably does not exceed 300 m. The true (original) thickness of the iron-formation is even more difficult to determine because of the structural incompetence of the rock, but it ranges from 15 to 30 m. All the rocks, with the exception of a few younger Precambrian (Proterozoic Y) diabase dikes, are metamorphosed to amphibolite or hornblende granulite facies. The iron-formation typically consists of quartz and magnetite, with subordinate amounts of iron silicates, mainly hypersthene, garnet, clinopyroxene, and grunerite. The principal deposits of iron-formation are in the Copper Mountain area, an area of about 13 km 2 in the west-central part of the Tobacco Root range that has been mapped in some detail. The structure consists of an early set of tight isoclinal folds, trending north-south and overturned to the east, that are deformed by later crossfolds that trend and plunge northwest. The most prominent belt of iron-formation is on a tight anticlinal buckle within the northsouth-trending Ramshorn syncline, a major structure of the first fold set. This belt of iron-formation is estimated to contain about 63 million t of potential low-grade ore (taconite) to a depth of 100 m. The rock contains about 35 weight percent Fe, mostly in the form of magnetite. Iron-formation occurs in many other localities in

  7. Global database of paleocurrent trends through the Phanerozoic and Precambrian.

    Brand, Leonard; Wang, Mingmin; Chadwick, Arthur


    Paleocurrents are sedimentological features contained in all sedimentary deposits, enabling the direction of movement of the sediment and the containing fluid at the time of deposition to be determined. This database contains paleocurrent directions and other relevant associated data from published sources and theses and dissertations for the entire Phanerozoic and Precambrian for all continents. Such information may be of general interest to sedimentologists and will be of specific interest in sedimentary basin analysis, and to petroleum geologists and mineralogists seeking source areas. Paleocurrents may also be useful in plate reconstructions and in testing the timing of global tectonic events.

  8. Microfossil measures of rapid sea-level rise: Timing of response of two microfossil groups to a sudden tidal-flooding experiment in Cascadia

    Horton, B.P.; Milker, Yvonne; Dura, T.; Wang, Kelin; Bridgeland, W.T.; Brophy, Laura S.; Ewald, M.; Khan, Nicole; Engelhart, S.E.; Nelson, Alan R.; Witter, Robert C.


    Comparisons of pre-earthquake and post-earthquake microfossils in tidal sequences are accurate means to measure coastal subsidence during past subduction earthquakes, but the amount of subsidence is uncertain, because the response times of fossil taxa to coseismic relative sea-level (RSL) rise are unknown. We measured the response of diatoms and foraminifera to restoration of a salt marsh in southern Oregon, USA. Tidal flooding following dike removal caused an RSL rise of ∼1 m, as might occur by coseismic subsidence during momentum magnitude (Mw) 8.1–8.8 earthquakes on this section of the Cascadia subduction zone. Less than two weeks after dike removal, diatoms colonized low marsh and tidal flats in large numbers, showing that they can record seismically induced subsidence soon after earthquakes. In contrast, low-marsh foraminifera took at least 11 months to appear in sizeable numbers. Where subsidence measured with diatoms and foraminifera differs, their different response times may provide an estimate of postseismic vertical deformation in the months following past megathrust earthquakes.

  9. Metamorphism of siliceous dolomites in the high-grade Precambrian of Rogaland, SW Norway

    Sauter, P.C.C.


    In the Precambrian granulite facies terrain of Rogaland, SW Norway, some small occurrences of marbles are present. They are mainly exposed at three locations A, Band C, at increasing distance from the anorthositic and monzonitic intrusions. The Precambrian basement in Rogaland has undergone several

  10. Hematite-coated microfossils: primary ecological fingerprint or taphonomic oddity of the Paleoproterozoic?

    Shapiro, R S; Konhauser, K O


    Microfossils belonging to the 1.88-billion-year-old 'Gunflint-biota' are preserved as carbonaceous and hematitic filaments and spheres that are believed to represent ancient chemolithoautotrophic Fe(II) oxidizing bacteria that grew above a chemocline where ferruginous seawater upwelled into shallow, oxygenated waters. This 'biological' model posits that hematite formed during burial from dewatering of the precursor ferric oxyhydroxides that encrusted Fe(II)-oxidizing bacteria. Here, we present an alternate 'taphonomic' model in which iron-rich groundwaters discharged into buried stromatolites; thus, the mineralization reactions are more informative of diagenetic processes than they are for primary marine conditions. We sampled centimeter-scale columnar stromatolites from both the lower and upper stromatolite horizons of the Biwabik and Gunflint formations, across a range of metamorphic gradients including unaltered to prehnite-pumpellyite taconite, supergene altered ore, and amphibolite-pyroxene grade contact-metamorphic zones. Fossils are rare to very rare and comprise curved filaments that exist in clusters with similar orientations. The filaments from throughout the Biwabik are similar to well-preserved carbonaceous Gunflintia from Ontario. Spheres of Huroniospora are also found in both formations. Microfossils from the least altered sections are preserved as carbon. Prehnite-pumpellyite samples are composed of either carbon or hematite (Fe2 O3 ). Within the contact aureole, filaments are densely coated by magnetite (Fe3 O4 ); the highest grade samples are secondarily oxidized to martite. The consistency in stromatolite microstructure and lithofacies throughout the metamorphic grades suggests they formed under similar environmental conditions. Post-depositional alteration led to replacement of the carbon by iron oxide. The facies association, filament distribution, and lack of branching and attached spherical cells argue against Gunflintia being a direct

  11. Composite synvolcanic intrusions associated with Precambrian VMS-related hydrothermal systems

    Galley, Alan G.


    Large subvolcanic intrusions are recognized within most Precambrian VMS camps. Of these, 80% are quartz diorite-tonalite-trondhjemite composite intrusions. The VMS camps spatially associated with composite intrusions account for >90% of the aggregate sulfide tonnage of all the Precambrian, intrusion-related VMS camps. These low-alumina, low-K, and high-Na composite intrusions contain early phases of quartz diorite and tonalite, followed by more voluminous trondhjemite. They have a high proportion of high silica (>74% SiO2) trondhjemite which is compositionally similar to the VMS-hosting rhyolites within the volcanic host-rock successions. The quartz-diorite and possibly tonalite phases follow tholeiitic fractionation trends whereas the trondhjemites fall within the composition field for primitive crustal melts. These transitional M-I-type primitive intrusive suites are associated with extensional regimes within oceanic-arc environments. Subvolcanic composite intrusions related to the Archean Sturgeon Lake and Noranda, and Paleoproterozoic Snow Lake VMS camps range in volume from 300 to 1,000 km3. Three have a sill morphology with strike lengths between 15 and 22 km and an average thickness between 1,500 and 2,000 m. The fourth has a gross stock-like shape. The VMS deposits are principally restricted to the volcanic strata above the strike length of the intrusions, as are areally extensive, thin exhalite units. The composite intrusions contain numerous internal phases which are commonly clustered within certain parts of the composite intrusion. These clusters underlie eruptive centers surrounded by areas of hydrothermal alteration and which contain most of the VMS deposits. Early quartz-diorite and tonalite phases appear to have intruded in rapid succession. Evidence includes gradational contacts, magma mixing and disequilibrium textures. They appear to have been emplaced as sill-dike swarms. These early phases are present as pendants and xenoliths within later

  12. New data on the trace metal composition of the planktonic foraminifera microfossils of the Atlantic Ocean

    Demina, L. L.; Oskina, N. S.


    This paper reports new data on the trace metal composition of planktonic foraminifer shells from surface sediments and cores (fraction >0.1 mm) in the central part of the Atlantic Ocean. This investigation has made it possible to identify a considerable accumulation of trace elements from water due to calcite entering into the crystal lattice under biomineralization and adsorption on the shell surface and pores, despite the fact that the shells are depleted in trace elements relative to pelagic clays. The trace element content in planktonic foraminifer microfossils is characterized by temporal variability, which is the most pronounced in long cores (Holocene-Upper Pleistocene) and reflects the sedimentation paleoenvironment in the ocean.

  13. De novo active sites for resurrected Precambrian enzymes

    Risso, Valeria A.; Martinez-Rodriguez, Sergio; Candel, Adela M.; Krüger, Dennis M.; Pantoja-Uceda, David; Ortega-Muñoz, Mariano; Santoyo-Gonzalez, Francisco; Gaucher, Eric A.; Kamerlin, Shina C. L.; Bruix, Marta; Gavira, Jose A.; Sanchez-Ruiz, Jose M.


    Protein engineering studies often suggest the emergence of completely new enzyme functionalities to be highly improbable. However, enzymes likely catalysed many different reactions already in the last universal common ancestor. Mechanisms for the emergence of completely new active sites must therefore either plausibly exist or at least have existed at the primordial protein stage. Here, we use resurrected Precambrian proteins as scaffolds for protein engineering and demonstrate that a new active site can be generated through a single hydrophobic-to-ionizable amino acid replacement that generates a partially buried group with perturbed physico-chemical properties. We provide experimental and computational evidence that conformational flexibility can assist the emergence and subsequent evolution of new active sites by improving substrate and transition-state binding, through the sampling of many potentially productive conformations. Our results suggest a mechanism for the emergence of primordial enzymes and highlight the potential of ancestral reconstruction as a tool for protein engineering.

  14. Late Precambrian oxygenation; inception of the clay mineral factory.

    Kennedy, Martin; Droser, Mary; Mayer, Lawrence M; Pevear, David; Mrofka, David


    An enigmatic stepwise increase in oxygen in the late Precambrian is widely considered a prerequisite for the expansion of animal life. Accumulation of oxygen requires organic matter burial in sediments, which is largely controlled by the sheltering or preservational effects of detrital clay minerals in modern marine continental margin depocenters. Here, we show mineralogical and geochemical evidence for an increase in clay mineral deposition in the Neoproterozoic that immediately predated the first metazoans. Today most clay minerals originate in biologically active soils, so initial expansion of a primitive land biota would greatly enhance production of pedogenic clay minerals (the "clay mineral factory"), leading to increased marine burial of organic carbon via mineral surface preservation.

  15. 用于早前寒武纪岩石Ar-Ar法定年的K-Ar法年龄国家二级标准物质——ZMT04白云母的定值结果%The certified results of ZMT04 muscovite reference material utilized for 40Ar/39Ar isotopic geochronological research on Early precambrian rocks in China.

    桑海清; 王非; 龚俊峰; 周晶


    desirable for any relatively old sample.In that occasion,if the neutron flux monitor is much younger than the unknown age sample,the 40 Ar/39Ar ratio in standard may become very small,approaching a smaller limit value (≈3).Therefore,it is quite necessary to prepare an old age standard for the flux monitor of the 40 Ar-39 Ar method,especially for isotopic geochronological research on Early Precambrian rocks and meteorites.ZMT04 muscovite as K-Ar age geostandard of China,were separated from a pegmatite dike which occurs at Tianpishan area,in the southwest of Zhuozi County,Inner Mongolia of China.The pegmatite consists of muscovite,quartz and minor zircon,sphere etc.About 1080g of pure ZMT04 muscovite was obtained at the (10 × 1 × 0.02)mm fraction.The purity is about 100%.Following mixing,the ZMT04 muscovite was divided into 14 jars about 77g each.Each jar sample was further subdivided into14 aliquots about 5.51g each (total 196 aliquots).One aliquot (prefixed C) was retained for control analysis of K and 40Ar*,the other 13 aliquot of the same jar remain to be used fo interlabortory work.40Ar-39 Ar age spectrum of ZMT04 muscovite indicats that the muscovite has remained undisturbed since its crystallisation.The plateau age age is 1823 ± 15Ma.Thirteen stepwise hating Ar isotopic data of the muscovite give a 40Ar/39Ar isochron age of 1824 ± 15Ma and the initial 40Ar/36Ar ration of 288 ± 16,and the MSWD in the 40Ar/36Ar-39Ar/36Ar isochron diagram is 2.10.This age may represent the crystallization time of the muscovite in the pegmatite dike.The homogeneity tests and the certification analyses of 40Ar* and K in ZMT04 muscovite were performed according to the rules from the International Standard Organization (ISO) Guid 35 (1985) and primary referenc material technique of China (1994).During the homogeneity tests the analyses of K and 40Ar* in 77-600 hornblende,Hb3gr hornblende and BSP-1 hornblend were done and the results are almost coincident with their mean value

  16. Precambrian plate tectonic setting of Africa from multidimensional discrimination diagrams

    Verma, Sanjeet K.


    New multi-dimensional discrimination diagrams have been used to identify plate tectonic setting of Precambrian terrains. For this work, nine sets of new discriminant-function based multi-dimensional discrimination diagrams were applied for thirteen case studies of Precambrian basic, intermediate and acid magmas from Africa to highlight the application of these diagrams and probability calculations. The applications of these diagrams indicated the following results: For northern Africa: to Wadi Ghadir ophiolite, Egypt indicated an arc setting for Neoproterozoic (746 ± 19 Ma). For South Africa: Zandspruit greenstone and Bulai pluton showed a collision and a transitional continental arc to collision setting at about Mesoarchaean and Neoarchaean (3114 ± 2.3 Ma and 2610-2577 Ma); Mesoproterozoic (1109 ± 0.6 Ma and 1100 Ma) ages for Espungabera and Umkondo sills were consistent with an island arc setting. For eastern Africa, Iramba-Sekenke greenstone belt and Suguti area, Tanzania showed an arc setting for Neoarchaean (2742 ± 27 Ma and 2755 ± 1 Ma). Chila, Bulbul-Kenticha domain, and Werri area indicated a continental arc setting at about Neoproterozoic (800-789 Ma); For western Africa, Sangmelima region and Ebolowa area, southern Cameroon indicated a collision and continental arc setting, respectively for Neoarchaean (∼2800-2900 Ma and 2687-2666 Ma); Finally, Paleoproterozoic (2232-2169 Ma) for Birimian supergroup, southern Ghana a continental arc setting; and Paleoproterozoic (2123-2108 Ma) for Katiola-Marabadiassa, Côte d'Ivoire a transitional continental arc to collision setting. Although there were some inconsistencies in the inferences, most cases showed consistent results of tectonic settings. These inconsistencies may be related to mixed ages, magma mixing, crustal contamination, degree of mantle melting, and mantle versus crustal origin.

  17. Hydrology of some deep mines in Precambrian rocks

    Yardley, D.H.


    A number of underground mines were investigated during the summer of 1975. All of them are in Precambrian rocks of the Lake Superior region. They represent a variety of geologic settings. The purpose of the investigations was to make a preliminary study of the dryness, or lack of dryness of these rocks at depth. In other words, to see if water was entering the deeper workings through the unmined rock by some means such as fracture or fault zones, joints or permeable zones. Water entering through old mine workings extending to, or very near to the surface, or from the drilling equipment, was of interest only insofar as it might mask any water whose source was through the hanging or footwall rocks. No evidence of running, seeping or moving water was seen or reported at depths exceeding 3,000 feet. At depths of 3,000 feet or less, water seepages do occur in some of the mines, usually in minor quantities but increased amounts occur as depth becomes less. Others are dry at 2,000 feet of depth. Rock movements associated with extensive mining should increase the local secondary permeability of the rocks adjoining the mined out zones. Also most ore bodies are located where there has been a more than average amount of faulting, fracturing, and folding during the geologic past. They tend to cluster along crustal flows. In general, Precambrian rocks of similar geology, to those seen, well away from zones that have been disturbed by extensive deep mining, and well away from the zones of more intense geologic activity ought to be even less permeable than their equivalents in a mining district.

  18. Stratified precambrian rocks (sedimentary ) beneath the midcontinent region of the US

    Hauser, E.C.


    A thick sequence of layered rocks occurs beneath the Phanerozoic platform strata which blanket the US midcontinent. Observed on COCORP deep reflection data in southern Illinois and Indiana and in SW Oklahoma and adjacent Texas, this sequence is locally 1--3 times as thick as the overlying Paleozoic cover, but the origin of this sequence and its ultimate lateral extent are unknown. However, the occurrences of Precambrian layered rocks on both the COCORP profiles and reprocessed industry seismic reflection data from the region lie within regions of generally low amplitude and low frequency aeromagnetic anomaly, suggesting an even greater distribution. Unmetamorphosed Precambrian sedimentary rocks have been recovered from drill holes in southwest Ohio and adjacent northern Kentucky and southwesternmost Indiana. These Precambrian sedimentary rocks lie above and may be part of an underlying package of strongly layered rocks imaged on a short and shallow seismic profile in southwest Ohio. These Precambrian sedimentary rocks were originally viewed as part of a late Precambrian (Keweenawan ) rift; however, in light of Grenville foreland structures seen on the COCORP profile to the north in west central Ohio, these Precambrian strata may (1) be part of a heretofore unrecognized Grenville foreland basin, or (2) indicate that unmetamorphosed Precambrian sedimentary material may be an important constituent of the layered rocks observed on COCORP beneath southern Illinois and Indiana.

  19. Stratified precambrian rocks (sedimentary?) beneath the midcontinent region of the US. Final technical report

    Hauser, E.C.


    A thick sequence of layered rocks occurs beneath the Phanerozoic platform strata which blanket the US midcontinent. Observed on COCORP deep reflection data in southern Illinois and Indiana and in SW Oklahoma and adjacent Texas, this sequence is locally 1--3 times as thick as the overlying Paleozoic cover, but the origin of this sequence and its ultimate lateral extent are unknown. However, the occurrences of Precambrian layered rocks on both the COCORP profiles and reprocessed industry seismic reflection data from the region lie within regions of generally low amplitude and low frequency aeromagnetic anomaly, suggesting an even greater distribution. Unmetamorphosed Precambrian sedimentary rocks have been recovered from drill holes in southwest Ohio and adjacent northern Kentucky and southwesternmost Indiana. These Precambrian sedimentary rocks lie above and may be part of an underlying package of strongly layered rocks imaged on a short and shallow seismic profile in southwest Ohio. These Precambrian sedimentary rocks were originally viewed as part of a late Precambrian (Keweenawan?) rift; however, in light of Grenville foreland structures seen on the COCORP profile to the north in west central Ohio, these Precambrian strata may (1) be part of a heretofore unrecognized Grenville foreland basin, or (2) indicate that unmetamorphosed Precambrian sedimentary material may be an important constituent of the layered rocks observed on COCORP beneath southern Illinois and Indiana.

  20. Precambrian phosphatized embryos and larvae from the Doushantuo Formation and their affinities, Guizhou (SW China)

    CHEN Junyuan; CHI Huimei


    Weng,an phosphates of the Precambrian Doushantuo Formation, Guizhou (southwestern China) preserve a large number of exquisite biological structures, which are mostly micro-spherical and represent seaweeds, acritarchs and developing eggs related to various groups of metazoans. Here is a report of a variety of developing eggs and larvae, which are most probably of Cnidarian affinity. The eggs examined in the study are composed of early cleavage embryos and two-layered gastrulae. The early cleavage embryos are radial and total cleavage with equal-size blastomeres. The gastrulae mostly bear a large archenteron, which is filled with yolk-degrading organic matter. Ovoid to fusiform planula-like larvae identified in thin sections under light microscope are mostly mouthless and their gastrovascular cavity is filled with possible yolk-degrading organic matter. They are likely representatives of non-feeding larva. The uncommon planula-like structures are hollow, with each having a mouth-like structure on its narrow end. We interpret them as feeding larva. Study of these embryos with possible Cnidarian affinities shed new insight on the origin of metazoans.

  1. Precambrian uranium-bearing quartz-pebble conglomerates: exploration model and United States resource potential

    Houston, R.S.; Karlstrom, K.E.


    Uranium has been discovered in fluvial quartz-pebble conglomerates in most of the Precambrian shield areas of the world, including the Canadian, African, South American, Indian, Baltic, and Australian shields. Occurrences in these and other areas are shown. Two of these occurrences, the Huronian supergroup of Canada and the Witwatersrand deposit of South Africa contain 20 to 30 percent of the planet's known uranium reserves. Thus it is critical that we understand the origin of these deposits and develop exploration models that can aid in finding new deposits. Inasmuch as these uranium-bearing conglomerates are confined almost entirely to rocks of Precambrian age, Part I of this review begins with a discussion of Precambrian geology as it applies to the conglomerates. This is followed by a discussion of genetic concepts, a discussion of unresolved problems, and finally a suggested exploration model. Part II summarizes known and potential occurrences of Precambrian fossil placers in the world and evaluates them in terms of the suggested exploration model. Part III discusses the potential for important Precambrian fossil-placer uranium deposits in the United States and includes suggestions that may be helpful in establishing an exploration program in this country. Part III also brings together new (1975-1978) data on uranium occurrences in the Precambrian of the Wyoming Province. Part IV is a complete bibliography of Precambrian fossil placers, divided according to geographical areas. In total, this paper is designed to be a comprehensive review of Precambrian uranium-bearing fossil placers which will be of use to uranium explorationists and to students of Precambrian geology.

  2. The environmental response of Middle Ordovician large organic walled microfossils from the Goldwyer and Nita Formations, Canning Basin, Western Australia.

    Winchester-Seeto, T; Foster, C; O'Leary, T


    Middle Ordovician large organic walled microfossils (chitinozoans, scolecodonts, hydrozoans and foraminiferal linings) were recovered from the upper Goldwyer and lower Nita formations, Canning Basin, Western Australia, from three cores (WMC Santalum 1A, Kunzea 1 and Acacia 2). Petrophysical logs of these cores reveal an overall upward shallowing supersequence, overprinted by numerous transgression/regression couplets that can be correlated over 100km.Analysis of the abundance of the microfossils with respect to the gamma log signatures reveals that both chitinozoan abundance and diversity decrease as water depth shallows; however, the opposite is not always true and other factors probably intervene. Scolecodonts show an increase in abundance in transgressions, while hydrozoans and foraminiferal linings show no consistent response to trangressive or regressive phases. Cyathochitina hunderumensis tends to dominate chitinozoan assemblages where there is a transgression, while species of Belonechitina replace Cy. hunderumensis in regressive phases.

  3. SIMS U-Pb zircon age of a tuff layer in the Meishucun section, Yunnan, southwest China: Constraint on the age of the Precambrian-Cambrian boundary


    Determination of the age of the Precambrian-Cambrian boundary is critical in understanding early evolution of life on Earth. SIMS U-Pb zircon analyses of the Bed 5 tuff layer of the Meishucun section were carried out closely following the guidance of cathodoluminescence images, and the majority of analyses were conducted on the oscillatory zircon grains. Thirteen measurements yield a highly reliable Concordia U-Pb age of 536.7 ± 3.9 Ma for the Bed 5 horizon. A grand mean of 206Pb/238U age of 535.2± 1.7 Ma (MSWD = 0.53) is calculated based on 13 concordant SIMS measurements of this study and 4 nano-SIMS measurements of Sawaki et al., which is the best estimate of the deposition age of the tuff layer within Bed 5 in the Meishucun section. This age has provided a robust age constraint on the significant Precambrian-Cambrian boundary strata in southern China, which independently suggested the placement of the Precambrian-Cambrian boundary at the bottom of the Xiaowaitoushan Member (Marker A).

  4. Search for supernova produced {sup 60}Fe in Earth's microfossil record

    Ludwig, Peter; Bishop, Shawn; Chernenko, Valentyna; Faestermann, Thomas; Fimiani, Leticia; Gomez, Jose; Hain, Karin; Korschinek, Gunther [Technische Univ. Muenchen, Garching (Germany). Physik-Department; Egli, Ramon [Central Institute for Meteorology and Geodynamics, Vienna (Austria)


    The detection of supernova debris on Earth can be achieved by use of accelerator mass spectrometry (AMS) to search for radionuclides like {sup 60}Fe. This long-lived isotope (T{sub 1/2}=2.6 Myr) is produced in massive stars and is expected to be present in the debris of type II supernovae. The discovery of {sup 60}Fe in a ferromanganese crust from the Pacific ocean (Knie et al., 2004) was interpreted as the input of a supernova explosion about 2.2 Myr ago. Currently, several projects are aiming for the confirmation of the signature of {sup 60}Fe in terrestrial and lunar samples. In this talk, the search for this {sup 60}Fe signature in Earth's microfossil record is presented. The sample material for this study is marine sediment from the eastern equatorial Pacific. A specific kind of secondary (formed in situ) magnetite mineral contained in the sample material are magnetofossils, which are the remains of magnetotactic bacteria, which are the target for extraction. The chemical extraction technique used to produce AMS samples has been characterized using newly developed magnetic analysis methods and has been shown to be extremely selective towards secondary magnetite. The AMS samples produced in this way are uniquely suited for the search for supernova {sup 60}Fe. Preliminary AMS results are presented.

  5. Early Life on Earth and the Search for Extraterrestrial Biosignatures

    Oehler, Dorothy Z.; House, Christopher


    In the last 2 years, scientists within the ARES Directorate at JSC have applied the technology of Secondary Ion Mass Spectrometry (SIMS) to individual organic structures preserved in Archean (approximately 3 billion years old) sediments on Earth. These organic structures are among the oldest on Earth that may be microfossils - structurally preserved remnants of ancient microbes. The SIMS work was done to determine the microfossils' stable carbon isotopic composition (delta C-13 values). This is the first time that such ancient, potential microfossils have been successfully analyzed for their individual delta C-13 values. The results support the interpretation that these structures are remnants of early life on Earth and that they may represent planktonic organisms that were widely distributed in the Earth's earliest oceans. This study has been accepted for publication in the journal Geology.

  6. Uranium Isotope Ratios in Modern and Precambrian Soils

    DeCorte, B.; Planavsky, N.; Wang, X.; Auerbach, D. J.; Knudsen, A. C.


    Uranium isotopes (δ238U values) are an emerging paleoredox proxy that can help to better understand the redox evolution of Earth's surface environment. Recently, uranium isotopes have been used to reconstruct ocean and atmospheric redox conditions (Montoya-Pino et al., 2010; Brennecka et al., 2011; Kendall et al., 2013; Dahl et al., 2014). However, to date, there have not been studies on paleosols, despite that paleosols are, arguably better suited to directly tracking the redox conditions of the atmosphere. Sedimentary δ238U variability requires the formation of the soluble, oxidized form of U, U(VI). The formation of U(VI) is generally thought to require oxygen levels orders of magnitude higher than prebiotic levels. Without significant U mobility, it would have been impossible to develop isotopically distinct pools of uranium in ancient Earth environments. Conversely, an active U redox cycle leads to significant variability in δ238U values. Here we present a temporally and geographically expansive uranium isotope record from paleosols and modern soils to better constrain atmospheric oxygen levels during the Precambrian. Preliminary U isotope measurements of paleosols are unfractionated (relative to igneous rocks), possibly because of limited fractionation during oxidation (e.g., {Wang, 2015 #478}) or insufficient atmospheric oxygen levels to oxidize U(IV)-bearing minerals in the bedrock. Further U isotope measurements of paleosols with comparison to modern soils will resolve this issue.

  7. Glacial sedimentation in the late precambrian bebedouro formation, Bahia, Brazil

    Montes, A. S. L.; Gravenor, C. P.; Montes, M. L.


    The possibility that diamictites of the Late Precambrian Bebedouro Formation of northern Bahia, Brazil, are glacial in origin has been based on the areal extent, diversity of the lithology of the stones and the presence of outsize dropstones in rhythmites. More detailed studies on the diamictites show that some of the stones are faceted and their shapes are typical of those developed by glacial transport. Additionally, a small abraded pavement is described and garnets found in the matrix of the diamictite have chattermark trails. Taken in aggregrate, these observations suggest a glacial origin for the Bebedouro Formation. In the study area, the texture of the diamictites range from stone-rich to siltstones containing sporadic stones. The stone-rich diamictites are commonly found in layers, up to a metre in thickness, separated by poorly laminated siltstone. The Formation probably was deposited in a large lake or sea and the layered diamictites are debris flows which were derived from uneven piles of glacial debris deposited on the floor of the lake or sea.

  8. Experimental mineralization of crustacean eggs leads to surprising tissue conservation: new implications for the fossilization of Precambrian-Cambrian embryos

    Hippler, D.; Hu, N.; Steiner, M.; Scholtz, G.; Franz, G.


    Phosphatized globular microfossils from the Ediacaran and Lower Cambrian of South China represent an impressive record of early animal evolution and development, however their affinity based on putative embryonic metazoan, bacterial and inorganic features is strongly debated. Understanding key processes and conditions that cause exceptional egg and embryo preservation and fossilization are therefore crucial for a reliable interpretation of their phylogenetic position. Taphonomic experiments on eggs of the marbled crayfish indicate a close link between early mineralization and rapid anaerobic decay of the endochorional envelope, producing different preservational stages of degradation resembling the various decay stages observed in the fossil record. Stabilization of the spherical morphology was achieved by pre-heating of the eggs. Complete surface mineralization occurred under reduced conditions within one to two weeks, with fine-grained brushite (CaHPO4·2H2O) over calcite as the dominating mineral phase. Although the endochorional envelope was not preserved, experiments resulted in exceptional preservation of the embryonic tissue at the cellular level. Thus our findings suggest that the mechanisms of decay, preservation of surface structures, and mineral replacement in the experiment and during fossilization of Cambrian embryos were likely operating at a similar rationale.

  9. Experimental mineralization of crustacean eggs leads to surprising tissue conservation: new implications for the fossilization of Precambrian-Cambrian embryos

    D. Hippler


    Full Text Available Phosphatized globular microfossils from the Ediacaran and Lower Cambrian of South China represent an impressive record of early animal evolution and development, however their affinity based on putative embryonic metazoan, bacterial and inorganic features is strongly debated. Understanding key processes and conditions that cause exceptional egg and embryo preservation and fossilization are therefore crucial for a reliable interpretation of their phylogenetic position. Taphonomic experiments on eggs of the marbled crayfish indicate a close link between early mineralization and rapid anaerobic decay of the endochorional envelope, producing different preservational stages of degradation resembling the various decay stages observed in the fossil record. Stabilization of the spherical morphology was achieved by pre-heating of the eggs. Complete surface mineralization occurred under reduced conditions within one to two weeks, with fine-grained brushite (CaHPO4·2H2O over calcite as the dominating mineral phase. Although the endochorional envelope was not preserved, experiments resulted in exceptional preservation of the embryonic tissue at the cellular level. Thus our findings suggest that the mechanisms of decay, preservation of surface structures, and mineral replacement in the experiment and during fossilization of Cambrian embryos were likely operating at a similar rationale.

  10. Constraining the origin and prevalence of biological N2 fixation in the Precambrian

    Stüeken, Eva; Buick, Roger; Guy, Bradley; Koehler, Matthew


    Nitrogen is an essential nutrient for all life on Earth; however, atmospheric N2, the largest nitrogen reservoir at the Earth's surface, is chemically inert and only accessible to some prokaryotic microbes that possess a nitrogenase enzyme. Prior to the origin of this metabolism, bioavailable nitrogen may have been derived from hydrothermal activity, lightning or photochemical reactions, but these sources are minor today and probably became limiting with the expansion of the biosphere. The origin of biological N2 fixation was therefore of paramount importance for early evolution. Geochemical and phylogenetic data, however, suggest that this event may have been delayed until the early Proterozoic, possibly by the lack of dissolved Mo, an essential co-factor in nitrogenase. Here we show new nitrogen isotopic data from low-grade sedimentary rocks of the Soanesville Group (~3.2 Ga, Western Australia), the Witwatersrand Supergroup (~2.9 Ga, South Africa), and the lower Fortescue Group (~2.75 Ga, Western Australia), with a total mean of 0.0 ± 1.2 ‰ relative to atmospheric N2. These values are inconsistent with abiotic sources of fixed nitrogen and difficult to reconcile with alternative nitrogenase enzymes that do not depend on Mo. Instead it is most likely that Mo-based nitrogenase had already evolved and was widespread in the mid-Archean. Combined with a literature database of δ15N values through time, our results suggest that other forms of fixed nitrogen became available in the late Archean and persisted throughout the Paleoproterozoic. In the Mesoproterozoic ocean, fixed nitrogen was likely restricted to shallow waters, while offshore environments were dominated by Mo-based N2 fixation. This basinal gradient likely disappeared in the Neoproterozoic. In conclusion, biological N2 fixation is a much more ancient metabolism than previously proposed and Mo has been bioavailable in at least small amounts throughout the Precambrian.

  11. Mass Independent Fractionation of Hg Isotopes Preserved in the Precambrian

    Thibodeau, A. M.; Bergquist, B. A.; Kah, L. C.; Ono, S.; Ghosh, S.; Hazen, R. M.


    Mercury (Hg) is a photochemically active, redox-sensitive, chalcophilic metal with complex biogeochemistry that displays a wide range of mass-dependent (MDF) and mass-independent (MIF) stable isotopic fractionation. In the past decade, Hg isotopes have emerged as important tracers of both the sources and cycling of Hg in the modern environment. However, their utility as environmental proxies in ancient rocks remains largely unexplored. The potential of Hg isotopes to inform Precambrian environments derives from the observation that Hg isotopes with odd atomic mass numbers (199Hg and 201Hg) undergo large MIF by the magnetic isotope effect (MIE) and smaller MIF through the nuclear volume effect (NVE). Small MIF produced via NVE has been observed for numerous transformations and is characterized by MIF ratios (Δ199Hg/Δ201Hg) of about 1.6. Large Hg-MIF driven by MIE has been observed during photochemical transformations and is characterized by Δ199Hg/Δ201Hg ratios between 1 and 1.3. This MIF signal is sensitive to a range of environmental conditions, including the amount and type of solar radiation, the presence and type of complexing organic ligands, and the Hg/dissolved organic carbon (DOC) ratio. Thus, it is hoped that Hg-MIF signals may indirectly record changes in atmospheric composition or seawater chemistry if preserved in marine sedimentary records. Previous work has clearly demonstrated that Hg-MIF signals are preserved in Archean and Paleoproterozoic marine shales and massive sulfide deposits. Here, we present evidence that such signals are also preserved in marine shales of mid-Proterozoic age, including the ~1.3 Ga Sulky formation (Dismal Lakes Group, NW Arctic), the ~1.45 Ga Greyson Shale (Belt Basin, Montana), and the ~1.5 Ga Katalsy formation (Kypry Group, Eastern European Platform). We observe that the Greyson shale and shales within the Sulky formation yield negative Hg-MIF with Δ199Hg/Δ201Hg ratios close to 1 and that Kaltasy group sediments

  12. Chromium Isotopes Record Fluctuations in Precambrian Biospheric Oxygenation

    Frei, R.; Gaucher, C.; Poulton, S. W.; Canfield, D. E.


    There is a direct relationship between life, oxygen, and the surface chemistry of the Earth. Geochemical data suggest that oxygenation of the Earth's atmosphere occurred in two broad steps, near the beginning and the end of the Proterozoic Eon (2500 to 542 million years ago), but the details of this history are unclear. The geochemical behaviour of chromium (Cr) is highly sensitive to the redox state of the surface environment as oxidative weathering processes produce the oxidised hexavalent [Cr(VI)] form. Oxidation of reduced trivaltent [Cr(III)] chromium on land is accompanied by an isotopic fractionation, leading to enrichment of the mobile hexavalent form in the heavier isotope. The fractionated Cr isotope signature is then tranfered by riverine transport to the sea. Here, we use Cr stable isotopes from banded iron formations (BIFs) to track the presence of Cr(VI) in Precambrian oceans, providing a time-resolved picture of the oxygenation history of Earth’s atmosphere-hydrosphere system. Fractionated Cr isotopes indicate the accumulation of Cr(VI) in ocean surface waters ~2.8 to 2.6 billion years (Gyr) ago and a likely transient elevation in atmospheric and surface ocean oxygen prior to the first great rise of oxygen 2.45-2.2 Gyr ago (the Great Oxidation Event; GOE). In contrast, Cr isotopes in ~1.88 Gyr old BIFs are not fractionated, indicating a major decline in atmospheric oxygen and demonstrating that the GOE did not lead to a unidirectional stepwise increase in atmospheric oxygen. In the late Neoproterozoic, ~800 to 542 million years (Myr) ago, we observe strong positive fractionations in Cr isotopes (δ53Cr up to +4.9 ‰) providing independent support for increased surface oxygenation at this time. This may have stimulated rapid evolution of macroscopic multicellular life. Our chromium isotope data thus provide new insights into the oxygenation history of the Earth, and highlight its use as a powerful redox tracer in aquatic systems.

  13. Fluctuations in Precambrian atmospheric oxygenation recorded by chromium isotopes

    Frei, Robert; Gaucher, Claudio; Poulton, Simon W.; Canfield, Don E.


    Geochemical data suggest that oxygenation of the Earth's atmosphere occurred in two broad steps. The first rise in atmospheric oxygen is thought to have occurred between ~2.45 and 2.2Gyr ago, leading to a significant increase in atmospheric oxygen concentrations and concomitant oxygenation of the shallow surface ocean. The second increase in atmospheric oxygen appears to have taken place in distinct stages during the late Neoproterozoic era (~800-542Myr ago), ultimately leading to oxygenation of the deep ocean ~580Myr ago, but details of the evolution of atmospheric oxygenation remain uncertain. Here we use chromium (Cr) stable isotopes from banded iron formations (BIFs) to track the presence of Cr(VI) in Precambrian oceans, providing a time-resolved picture of the oxygenation history of the Earth's atmosphere-hydrosphere system. The geochemical behaviour of Cr is highly sensitive to the redox state of the surface environment because oxidative weathering processes produce the oxidized hexavalent [Cr(VI)] form. Oxidation of reduced trivalent [Cr(III)] chromium on land is accompanied by an isotopic fractionation, leading to enrichment of the mobile hexavalent form in the heavier isotope. Our fractionated Cr isotope data indicate the accumulation of Cr(VI) in ocean surface waters ~2.8 to 2.6Gyr ago and a likely transient elevation in atmospheric and surface ocean oxygenation before the first great rise of oxygen 2.45-2.2Gyr ago (the Great Oxidation Event). In ~1.88-Gyr-old BIFs we find that Cr isotopes are not fractionated, indicating a decline in atmospheric oxygen. Our findings suggest that the Great Oxidation Event did not lead to a unidirectional stepwise increase in atmospheric oxygen. In the late Neoproterozoic, we observe strong positive fractionations in Cr isotopes (δ53Cr up to +4.9‰), providing independent support for increased surface oxygenation at that time, which may have stimulated rapid evolution of macroscopic multicellular life.

  14. Microfossils, biomolecules and biominerals in carbonaceous meteorites: implications to the origin of life

    Hoover, Richard B.


    Environmental and Field Emission Scanning Electron Microscopy (ESEM and FESEM) investigations have shown that a wide variety of carbonaceous meteorites contain the remains of large filaments embedded within freshly fractured interior surfaces of the meteorite rock matrix. The filaments occur singly or in dense assemblages and mats and are often encased within carbon-rich, electron transparent sheaths. Electron Dispersive X-ray Spectroscopy (EDS) spot analysis and 2D X-Ray maps indicate the filaments rarely have detectable nitrogen levels and exhibit elemental compositions consistent with that interpretation that of the meteorite rock matrix. Many of the meteorite filaments are exceptionally well-preserved and show evidence of cells, cell-wall constrictions and specialized cells and processes for reproduction, nitrogen fixation, attachment and motility. Morphological and morphometric analyses permit many of the filaments to be associated with morphotypes of known genera and species of known filamentous trichomic prokaryotes (cyanobacteria and sulfur bacteria). The presence in carbonaceous meteorites of diagenetic breakdown products of chlorophyll (pristane and phytane) along with indigenous and extraterrestrial chiral protein amino acids, nucleobases and other life-critical biomolecules provides strong support to the hypothesis that these filaments represent the remains of cyanobacteria and other microorganisms that grew on the meteorite parent body. The absence of other life-critical biomolecules in the meteorites and the lack of detectable levels of nitrogen indicate the filaments died long ago and can not possibly represent modern microbial contaminants that entered the stones after they arrived on Earth. This paper presents new evidence for microfossils, biomolecules and biominerals in carbonaceous meteorites and considers the implications to some of the major hypotheses for the Origin of Life.

  15. Microfossils and biomolecules in carbonaceous meteorites: possibility of life in water-bearing asteroids and comets

    Hoover, Richard B.


    It is well established that carbonaceous meteorites contain water, carbon, biogenic elements and a host of organic chemicals and biomolecules. Several independent lines of evidence indicate that the parent bodies of the CI1 and CM2 carbonaceous meteorites are most probably the C-type asteroids or cometary nuclei. Several of the protein amino acids detected in the meteorites exhibit chirality and have an excess of the L-enantiomer -- such as in the amino acids present in the proteins of all known life forms on Earth. Isotopic studies have established that the amino acids and nucleobases in the CI1 and CM2 carbonaceous meteorites are both indigenous and extraterrestrial. Optical and Scanning Electron Microscopy studies carried out by researchers during the past half century have revealed the presence of complex biogenic microstructures embedded in the rock-matrix of many of carbonaceous meteorites similar to extinct life-forms known as acritarchs and hystrichospheres. Carbonaceous meteorites also contain a wide variety of large filaments that exhibit the complex morphologies and correct size ranges of known genera and species of photosynthetic microorganisms such as cyanobacteria and diatoms. However, EDAX investigations have shown that these carbon-rich filaments typically have nitrogen content below the level of detection (hair and teeth of Pleistocene Mammoths. Hence, the absence of detectable nitrogen in the filaments provides direct evidence that they do not represent recent biological contaminants that invaded these meteorite stones after they were observed to fall to Earth. The spectral and fluorescence properties of pigments found in several species of terrestrial cyanobacteria which are similar to some microfossils found in carbonaceous meteorites may provide valuable clues to help search for evidence for biomolecules and life on the icy moons of Jupiter and Saturn, asteroids and comets.

  16. Paleosols in laterite and silcrete profiles Evidence from the South East Margin of the Australian Precambrian Shield

    Firman, J. B.


    Laterite and silcrete profiles are common in the arid and semi-arid areas of the Australian Precambrian Shield - a vast planar surface masked by the regolith. Much of the geological history of the shield subsequent to its early development is recorded in ancient cover rocks and younger basin sediments which occur in important stratigraphic sequences, particularly on the margins of the shield. Within these sequences, stratigraphically associated or as companion materials, weathering zones and paleosols were developed which individually and as assemblages of layers and horizons record the history of weathering and of soil formation since the Proterozoic. Laterite and silcrete profiles are seen to be assemblages of paleosols, stratigraphically associated deposits and companion materials which were formed in response to changes in groundwater conditions at particular times in the past. The paleosols record the evolution of the regolith: Older weathering zones and bleached rocks were features of successive landscapes after the early Palaeozoic; ferruginous mottling, ferricrete and silcrete pans were formed after the early Cainozoic; ferricretes and mottled clay paleosols - some of which have been described as "laterite" - were formed during and after the Pliocene. Materials in laterite and silcrete profiles are overlain in places by calcretes formed after the early Pleistocene and by younger soils. The assemblages are distinctive and are characteristic of particular morpholithogical provinces.

  17. Paleoproterozoic mojaveprovince in northwestern Mexico? Isotopic and U-Pb zircon geochronologic studies of precambrian and Cambrian crystalline and sedimentary rocks, Caborca, Sonora

    Lang, Farmer G.; Bowring, S.A.; Matzel, J.; Maldonado, G.E.; Fedo, C.; Wooden, J.


    Whole-rock Nd isotopic data and U-Pb zircon geochronology from Precambrian crystalline rocks in the Caborca area, northern Sonora, reveal that these rocks are most likely a segment of the Paleoproterozoic Mojave province. Supporting this conclusion are the observations that paragneiss from the ??? 1.75 Ga Bamori Complex has a 2.4 Ga Nd model age and contains detrital zircons ranging in age from Paleo- proterozoic (1.75 Ga) to Archean (3.2 Ga). Paragneisses with similar age and isotopic characteristics occur in the Mojave province in southern California. In addition, "A-type" granite exposed at the southern end of Cerro Rajon has ca 2.0 Ga Nd model age and a U-Pb zircon age of 1.71 Ga, which are similar to those of Paleoproterozoic granites in the Mojave province. Unlike the U.S. Mojave province, the Caborcan crust contains ca. 1.1 Ga granite (Aibo Granite), which our new Nd isotopic data suggest is largely the product of anatexis of the local Precambrian basement. Detrital zircons from Neoproterozoic to early Cambrian miogeoclinal arenites at Caborca show dominant populations ca. 1.7 Ga, ca. 1.4 Ga, and ca. 1.1 Ga, with subordinate Early Cambrian and Archean zircons. These zircons were likely derived predominately from North American crust to the east and northeast, and not from the underlying Caborcan basement. The general age and isotopic similarities between Mojave province basement and overlying miogeoclinal sedimentary rocks in Sonora and southern California is necessary, but not sufficient, proof of the hypothesis that Sonoran crust is allochthonous and was transported to its current position during the Mesozoic along the proposed Mojave-Sonora megashear. One viable alternative model is that the Caborcan Precambrian crust is an isolated, autochthonous segment of Mojave province crust that shares a similar, but not identical, Proterozoic geological history with Mojave province crust found in the southwest United States ?? 2005 Geological Society of America.

  18. Lunar nodal tide and distance to the moon during the Precambrian

    Walker, J. C. G.; Zahnle, K. J.


    The first direct determination of the lunar distance in the Precambrian is presented. A 23.3 + or - 0.3 yr periodicity preserved in 2500 Myr BP Australian banded iron formation is interpreted as reflecting the climatic influence of the lunar nodal tide, which has been detected with its modern 18.6-yr periodicity in some modern climate records. The lunar distance at 2500 Myr BP would then have been about 52 earth radii. The implied history of precambrian tidal friction is in accord with both the more recent paleontological evidence and the long-term stability of the lunar orbit. The length of the Milankovitch cycles that modulate the ice ages today also evolve with the earth-moon system. Their detection in the Precambrian sedimentary record would then permit an independent determination of the lunar distance.

  19. Continental velocity through Precambrian times: The link to magmatism, crustal accretion and episodes of global cooling

    J.D.A. Piper


    Full Text Available Quasi-integrity of continental crust between Mid-Archaean and Ediacaran times is demonstrated by conformity of palaeomagnetic poles to near-static positions between ∼2.7–2.2 Ga, ∼1.5–1.2 Ga and ∼0.75–0.6 Ga. Intervening data accord to coherent APW loops turning at “hairpins” focused near a continental-centric location. Although peripheral adjustments occurred during Early Proterozoic (∼2.2 Ga and Grenville (∼1.1 Ga times, the crust retained a low order symmetrical crescent-shaped form constrained to a single global hemisphere until break-up in Ediacaran times. Conformity of palaeomagnetic data to specific Eulerian parameters enables definition of a master Precambrian APW path used to estimate the root mean square velocity (vRMS of continental crust between 2.8 and 0.6 Ga. A long interval of little polar movement between ∼2.7 and 2.2 Ga correlates with global magmatic shutdown between ∼2.45 and 2.2 Ga, whilst this interval and later slowdown at ∼0.75–0.6 Ga to velocities of <2 cm/year correlate with episodes of widespread glaciation implying that these prolonged climatic anomalies had an internal origin; the reduced input of volcanically-derived atmospheric greenhouse gases is inferred to have permitted freeze-over conditions with active ice sheets extending into equatorial latitudes as established by low magnetic inclinations in glaciogenic deposits. vRMS variations through Precambrian times correspond to the distribution of U-Pb ages in orogenic granitoids and detrital zircons and demonstrate that mobility of continental crust has been closely related to crustal tectonism and incrementation. Both periods of near-stillstand were followed by rapid vRMS recording massive heat release from beneath the continental lid at ∼2.2 and 0.6 Ga. The first coincided with the Lomagundi-Jatuli isotopic event and led to prolonged orogenesis accompanied by continental flooding and reconfiguration of the crust on the Earth

  20. Multiple High-Frequency Carbon Isotope Excursions Across the Precambrian-Cambrian Boundary: Implications for Correlations and Environmental Change

    Smith, E. F.; Macdonald, F. A.; Schrag, D. P.; Laakso, T.


    The GSSP Precambrian-Cambrian boundary in Newfoundland is defined by the first appearance datum (FAD) of Treptichnus pedum, which is considered to be roughly coincident with the FAD of small shelly fossils (SSFs) and a large negative carbon isotope excursion. An association between the FAD of T. pedum and a negative carbon isotope excursion has previously been documented in Northwest Canada (Narbonne et al., 1994) and Death Valley (Corsetti and Hagadorn, 2000), and since then has been used as an chronostratigraphic marker of the boundary, particularly in siliciclastic poor sections that do not preserve T. pedum. Here we present new high-resolution carbon isotope (δ13C ) chemostratigraphy from multiple sections in western Mongolia and the western United States that span the Ediacaran-Cambrian transition. High-resolution sampling (0.2-1 m) reveals that instead of one large negative excursion, there are multiple, high-frequency negative excursions with an overall negative trend during the latest Ediacaran. These data help to more precisely calibrate changes in the carbon cycle across the boundary as well as to highlight the potential problem of identifying the boundary with just a few negative δ13C values. We then use a simple carbon isotope box model to explore relationships between phosphorous delivery to the ocean, oxygenation, alkalinity, and turnovers in carbonate secreting organisms. Corsetti, F.A., and Hagadorn, J.W., 2000, Precambrian-Cambrian transition: Death Valley, United States: Geology, v. 28, no. 4, p. 299-302. Narbonne, G.M., Kaufman, A.J., and Knoll, A.H., 1994, Integrated chemostratigraphy and biostratigraphy of the Windermere Supergroup, northwestern Canada: Implications for Neoproterozoic correlations and the early evolution of animals: Geological Society of America Bulletin, v. 106, no. 10, p. 1281-1292.

  1. A geological synthesis of the Precambrian shield in Madagascar

    Tucker, Robert D.; Roig, J.Y.; Moine, B.; Delor, C.; Peters, S.G.


    Available U–Pb geochronology of the Precambrian shield of Madagascar is summarized and integrated into a synthesis of the region’s geological history. The shield is described in terms of six geodynamic domains, from northeast to southwest, the Bemarivo, Antongil–Masora, Antananarivo, Ikalamavony, Androyan–Anosyan, and Vohibory domains. Each domain is defined by distinctive suites of metaigneous rocks and metasedimentary groups, and a unique history of Archean (∼2.5 Ga) and Proterozoic (∼1.0 Ga, ∼0.80 Ga, and ∼0.55 Ga) reworking. Superimposed within and across these domains are scores of Neoproterozoic granitic stocks and batholiths as well as kilometer long zones of steeply dipping, highly strained rocks that record the effects of Gondwana’s amalgamation and shortening in latest Neoproterozoic time (0.560–0.520 Ga). The present-day shield of Madagascar is best viewed as part of the Greater Dharwar Craton, of Archean age, to which three exotic terranes were added in Proterozoic time. The domains in Madagascar representing the Greater Dharwar Craton include the Antongil–Masora domain, a fragment of the Western Dharwar of India, and the Neoarchean Antananarivo domain (with its Tsaratanana Complex) which is broadly analogous to the Eastern Dharwar of India. In its reconstructed position, the Greater Dharwar Craton consists of a central nucleus of Paleo-Mesoarchean age (>3.1 Ga), the combined Western Dharwar and Antongil–Masora domain, flanked by mostly juvenile “granite–greenstone belts” of Neoarchean age (2.70–2.56 Ga). The age of the accretionary event that formed this craton is approximately 2.5–2.45 Ga. The three domains in Madagascar exotic to the Greater Dharwar Craton are the Androyan–Anosyan, Vohibory, and Bemarivo. The basement to the Androyan–Anosyan domain is a continental terrane of Paleoproterozoic age (2.0–1.78 Ga) that was accreted to the southern margin (present-day direction) of the Greater Dharwar Craton in pre

  2. Fluctuations in Precambrian atmospheric oxygenation recorded by chromium isotopes.

    Frei, Robert; Gaucher, Claudio; Poulton, Simon W; Canfield, Don E


    Geochemical data suggest that oxygenation of the Earth's atmosphere occurred in two broad steps. The first rise in atmospheric oxygen is thought to have occurred between approximately 2.45 and 2.2 Gyr ago, leading to a significant increase in atmospheric oxygen concentrations and concomitant oxygenation of the shallow surface ocean. The second increase in atmospheric oxygen appears to have taken place in distinct stages during the late Neoproterozoic era ( approximately 800-542 Myr ago), ultimately leading to oxygenation of the deep ocean approximately 580 Myr ago, but details of the evolution of atmospheric oxygenation remain uncertain. Here we use chromium (Cr) stable isotopes from banded iron formations (BIFs) to track the presence of Cr(VI) in Precambrian oceans, providing a time-resolved picture of the oxygenation history of the Earth's atmosphere-hydrosphere system. The geochemical behaviour of Cr is highly sensitive to the redox state of the surface environment because oxidative weathering processes produce the oxidized hexavalent [Cr(VI)] form. Oxidation of reduced trivalent [Cr(III)] chromium on land is accompanied by an isotopic fractionation, leading to enrichment of the mobile hexavalent form in the heavier isotope. Our fractionated Cr isotope data indicate the accumulation of Cr(VI) in ocean surface waters approximately 2.8 to 2.6 Gyr ago and a likely transient elevation in atmospheric and surface ocean oxygenation before the first great rise of oxygen 2.45-2.2 Gyr ago (the Great Oxidation Event). In approximately 1.88-Gyr-old BIFs we find that Cr isotopes are not fractionated, indicating a decline in atmospheric oxygen. Our findings suggest that the Great Oxidation Event did not lead to a unidirectional stepwise increase in atmospheric oxygen. In the late Neoproterozoic, we observe strong positive fractionations in Cr isotopes (delta(53)Cr up to +4.9 per thousand), providing independent support for increased surface oxygenation at that time, which may

  3. The contribution of the Precambrian continental lithosphere to global H2 production.

    Lollar, Barbara Sherwood; Onstott, T C; Lacrampe-Couloume, G; Ballentine, C J


    Microbial ecosystems can be sustained by hydrogen gas (H2)-producing water-rock interactions in the Earth's subsurface and at deep ocean vents. Current estimates of global H2 production from the marine lithosphere by water-rock reactions (hydration) are in the range of 10(11) moles per year. Recent explorations of saline fracture waters in the Precambrian continental subsurface have identified environments as rich in H2 as hydrothermal vents and seafloor-spreading centres and have suggested a link between dissolved H2 and the radiolytic dissociation of water. However, extrapolation of a regional H2 flux based on the deep gold mines of the Witwatersrand basin in South Africa yields a contribution of the Precambrian lithosphere to global H2 production that was thought to be negligible (0.009 × 10(11) moles per year). Here we present a global compilation of published and new H2 concentration data obtained from Precambrian rocks and find that the H2 production potential of the Precambrian continental lithosphere has been underestimated. We suggest that this can be explained by a lack of consideration of additional H2-producing reactions, such as serpentinization, and the absence of appropriate scaling of H2 measurements from these environments to account for the fact that Precambrian crust represents over 70 per cent of global continental crust surface area. If H2 production via both radiolysis and hydration reactions is taken into account, our estimate of H2 production rates from the Precambrian continental lithosphere of 0.36-2.27 × 10(11) moles per year is comparable to estimates from marine systems.

  4. Early

    Kamel Abd Elaziz Mohamed


    Conclusion: Early PDT is recommended for patients who require prolonged tracheal intubation in the ICU as outcomes like the duration of mechanical ventilation length of ICU stay and hospital stay were significantly shorter in early tracheostomy.

  5. Reactivation of precambrian faults on the southwestern continental margin of India: Evidence from gravity anomalies

    Subrahmanyam, V.; Ramana, M.V.; Rao, D.G.

    Gravimetric and bathymetric studies on the southwestern continental margin of India confirm the extension of onshore NW-SE-, NNW-SSE-, N-S-, NE-SW-, ENE-WSW- and E-W-trending lineaments of Precambrian age over a considerable distance...

  6. Precambrian mega lineaments across the Indian sub-continent - Preliminary evidence from offshore magnetic data

    Subrahmanyam, V.; Subrahmanyam, A.S.; Murthy, K.S.R.; Murty, G.P.S.; Sarma, K.V.L.N.S.; SuneetaRani, P.; Anuradha, A.

    continental block between 10°45`N and 12°30`N exhibit distinct character compared to the adjoining northern and southern blocks. The study revealed the presence of two Precambrian mega lineaments over a stretch of 750–800 km running in east-west direction...

  7. Precambrian crustal structure in Africa and Arabia : Evidence lacking for secular variation

    Tugume, Fred; Nyblade, Andrew; Julia, Jordi; Meijde, van der Mark


    We review the thickness and shear wave velocity structure of Precambrian crust in Africa and Arabia, where over 90% of the landmass is comprised of Archean and Proterozoic terranes, and examine the data for evidence of secular variation. The data come from many published 1D shear wave velocity profi

  8. 贵州瓮安陡山沱组球状化石元素地球化学浅析%Preliminary Analysis on the Elemental Geochemistry of Doushantuo Spherical Microfossils from the Weng'an Biota in South China

    唐烽; 高林志; 尹崇玉; 王约


    The Ediacaran Doushantuo Formation in Weng'an and Fuquan areas of the Guizhou Provincein southern China hosts high-grade phosphorus ore deposits and exceptionally well-preserved phosphaticmicrofossils that are commonly less than 1 mm in diameter. Earlier studies attributed these fossils to algaeor acritarchs. In the last decade, researchers found that the spherical microfossils, in a large proportion,show metazoan embryonic development features with early cleavage stages. Thus these sphericalmicrofossils have been considered as diploblast or triploblast embryos and resting eggs of early animals.However, reliable fossils similar to blastula, gastrula embryos, fossils of larvae after hatching, andparticularly, the corresponding body fossils of these animal embryos have never been found in the relevantstrata. This phenomenon challenges the interpretation that these globular microfossils are animal embryos.Because the major uncertainty on these fossils is whether they are animals or plants, a detailed geochemicalanalyses across the fossils may help to reveal the differences (between animal and plant) in the compositionof cell membrane / wall and cell inclusions, the pattern of physiological metabolism, and the phosphatizedmechanisms in particular depositional environments. On this basis and in combination with morphologicalcomparison with the Cambrian microfossils and modern metazoan embryos, elemental geochemistry acrossthe spherical microfossils ("embryos") of the Weng' an biota may provide new information for betterunderstanding the genetic affinity of the Doushantuo globular fossils. In this paper, the author analyzesthe microfossils collected from Weng' an and Fuquan areas in Guizhou by electron probe micro-analyzer(EPMA) to obtain trace elemental geochemistry across the globular fossils. For comparison purposes, twotypes of fossils have been analyzed, including fossils with tumor-like outer wall and those with polygonalplate-shaped outer wall. Comparing results

  9. Raman Imaging Spectroscopy of a Putative Microfossil from the ∼3.46 Ga Apex Chert: Insights from Quartz Grain Orientation.

    Bower, D M; Steele, A; Fries, M D; Green, O R; Lindsay, J F


    The utility of nondestructive laser Raman for testing the biogenicity of microfossil-like structures in ancient rocks is promising, yet results from deposits like the ∼3.46 Ga Apex chert remain contentious. The essence of the debate is that associated microstructures, which are not purported to be microfossils, also contain reduced carbon that displays Raman D- and G-band peaks similar to those seen in the purported microfossils. This has led to the hypothesis that all features including reported microfossils are due to compression of nonfossil carbon during crystal growth around quartz spherulites or more angular crystals. In this scenario, the precursor to this macromolecular carbon may or may not have been of biogenic origin, while the arcuate and linear features described would be pseudofossils. To test this hypothesis, we have undertaken 2-D micro-Raman imaging of the Eoleptonema apex holotype and associated features using instrumentation with a high spatial and spectral resolution. In addition to this, we utilized the ratio of two Raman active quartz mode intensities (I129/I461) to assess quartz grain orientation and grain-splitting artifacts. These data lead us to conclude that the holotype of Eoleptonema apex is a sheet-shaped pseudofossil that appears to be a carbon infilled intragranular crack; therefore other holotypes should be carefully reexamined for syngenicity.

  10. Carbonaceous matter and putative microfossils of the mid-Archean Kromberg type-section re-visited, Barberton Greenstone Belt, South Africa

    McLoughlin, Nicola; Grosch, Eugene


    Silicified seafloor sediments of the Kromberg Formation from the Onverwacht Group of the Barberton greenstone belt (BGB), South Africa, have been argued to contain some of the world's oldest preserved carbonaceous microfossils. Previous studies of these cherts have reported filamentous, spheroidal and ellipsoidal microfossils in thin-section (Walsh 1992); and bacteriomorph like structures in HF-etched samples (Westall et al. 2001). These microtextural studies however, lack supporting in-situ geochemical data, and are hampered to some degree by re-mobilisation of the carbonaceous matter (Van Zuilen et al. 2007). In light of these concerns, and ongoing debates surrounding carbonaceous remains in other Archean cherts (e.g., W Australia), further in-situ data from the Kromberg is required to positively identify carbonaceous matter of biogenic origin. New data will also help to address outstanding questions regarding the relative contribution of benthic versus planktonic microorganisms, and the putative microbial metabolisms involved. This study focuses on surface samples and drill core from the Barberton Scientific Drilling Programme, (BSDP, Grosch et al. 2009) from the southeastern limb of the Onverwacht anticline of the BGB. We sampled the Footbridge chert and a second chert horizon in drill core KD1 of the BSDP in the upper Kromberg Fm; and surface outcrops of two black cherts from the lower Kromberg Fm. Sedimentological logging reveals horizons rich in volcaniclastics with interbedded finely laminated grey-black chert, also intrusive black cherts, and sulphide rich horizons. The TOC of the sampled cherts is 1.24 to 5.40 wt%. Preliminary bulk carbon isotope values range from δ13C -21.1 to -35.3o values that are consistent with organic matter produced by anoxygenic photosynthesis. Microfabrics preserved in the Kromberg cherts include, primary wispy-laminated carbonaceous films suggesting compaction of early carbonaceous laminae. Also large composite carbonaceous

  11. Control of Precambrian basement deformation zones on emplacement of the Laramide Boulder batholith and Butte mining district, Montana, United States

    Berger, Byron R.; Hildenbrand, Thomas G.; O'Neill, J. Michael


    What are the roles of deep Precambrian basement deformation zones in the localization of subsequent shallow-crustal deformation zones and magmas? The Paleoproterozoic Great Falls tectonic zone and its included Boulder batholith (Montana, United States) provide an opportunity to examine the importance of inherited deformation fabrics in batholith emplacement and the localization of magmatic-hydrothermal mineral deposits. Northeast-trending deformation fabrics predominate in the Great Falls tectonic zone, which formed during the suturing of Paleoproterozoic and Archean cratonic masses approximately 1,800 mega-annum (Ma). Subsequent Mesoproterozoic to Neoproterozoic deformation fabrics trend northwest. Following Paleozoic through Early Cretaceous sedimentation, a Late Cretaceous fold-and-thrust belt with associated strike-slip faulting developed across the region, wherein some Proterozoic faults localized thrust faulting, while others were reactivated as strike-slip faults. The 81- to 76-Ma Boulder batholith was emplaced along the reactivated central Paleoproterozoic suture in the Great Falls tectonic zone. Early-stage Boulder batholith plutons were emplaced concurrent with east-directed thrust faulting and localized primarily by northwest-trending strike-slip and related faults. The late-stage Butte Quartz Monzonite pluton was localized in a northeast-trending pull-apart structure that formed behind the active thrust front and is axially symmetric across the underlying northeast-striking Paleoproterozoic fault zone, interpreted as a crustal suture. The modeling of potential-field geophysical data indicates that pull-apart?stage magmas fed into the structure through two funnel-shaped zones beneath the batholith. Renewed magmatic activity in the southern feeder from 66 to 64 Ma led to the formation of two small porphyry-style copper-molybdenum deposits and ensuing world-class polymetallic copper- and silver-bearing veins in the Butte mining district. Vein orientations

  12. Palaeoclimatology: evidence for hot early oceans?

    Shields, Graham A; Kasting, James F


    The oxygen isotopes in sedimentary cherts (siliceous sediments) have been used to argue that the Precambrian oceans were hot--with temperatures of up to 70 degrees C at 3.3 Gyr before present. Robert and Chaussidon measure silicon isotopes in cherts and arrive at a similar conclusion. We suggest here that both isotope trends may be caused by variations in seawater isotope composition, rather than in ocean temperatures. If so, then the climate of the early Earth may have been temperate, as it is today, and therefore more consistent with evidence for Precambrian glaciations and with constraints inferred from biological evolution.

  13. Hf Isotope Composition and REE Pattern of Zircons from Early Precambrian Metamorphic Rocks in the Daqing Mountains, Inner Mongolia%内蒙古大青山地区早前寒武纪变质岩的锆石Hf同位素组成和稀土模式

    董春艳; 刘敦一; 万渝生; 徐仲元; 王伟; 颉颃强


    This paper reports Hf isotope and REE composition of zircons from metamorphic rocks in the Daqing Mountains, Inner Mongolia. Detrital zircons from two meta - sedimentary rock samples have [n(176Hf)/n(177Hf)]c, tDM1(Hf) and tDM2(Hf) ranging from 0. 281079~0. 281502, 2548~3000 Ma and 2612 ~ 3153 Ma and from 0. 280916 ~0. 281451, 2533 ~ 2717 Ma and 2600 ~ 3404 Ma, respectively. The eHf (t) and tym (Hf) of magmatic zircon from one meta-gabbro sample range from-5. 45 -6.68 and 2319-2647 Ma, respectively. These indicate that late Neoarhcaean - early Palaeoproterozoic tectono-magmatic events occurred in the Daqing Mountains and adjacent areas, with both mantle addition and crustal recycling. Metamorphic zircon rims commonly show young tDM2 (Hf) when comparing with detrital and magmatic zircon cores, suggesting that Lu-Hf compositions of the rocks and minerals were changed during metamorphic processes. Metamorphic zircon rims are similar in REE pattern to adjacent detrital and magmatic cores, but commonly being lower in total REE content. Most of the metamorphic rims are smaller than 0. 1 in Th/U ratio, being quite different from the cores which Th/U ratios are generally higher than 0. 5. It is speculated that metamorphic fluid was high in w(176Hf)/w(177Hf) ratio and U and low in Th and REE and played an important role in metamorphic zircon formation.%本文报道了内蒙古大青山地区早前寒武纪变质岩石的锆石Hf同位素和稀土组成.两个古元古代晚期(1.9~2.1 Ga)变质碎屑沉积岩样品中碎屑锆石的[n(176Hf)/n(177Hf)]c、tDM1(Hf)和tDM2(Hf)分别为0.281079~0.281502、2548~3000 Ma、2612~3153 Ma和0.280g16~0.281451、2533~2717 Ma、2600~3404 Ma;一个古元古代早期(2.37 Ga)变质辉长岩样品中岩浆锆石的εHf(t)和tDM1(Hf)分别为1.50~6.68和2449~2647 Ma,表明大青山及邻区在新太古代晚期-古元古代早期存在强烈的构造岩浆热事件,既有地幔添加又有壳内再循环作用.三个样

  14. Mo Isotopes Record Destabilization of a Stratified Ocean at the Precambrian-Cambrian Boundary

    Wille, M.; Nägler, T. F.; Schröder, S.; Lehmann, B.; Kramers, J. D.


    Here we present Mo isotope signatures in black shales from two sample sets (Ara group, Oman and Yangtze Platform, China) which were deposited at and shortly after the Precambrian-Cambrian boundary (PC-C). At the first view, the overall Mo isotopic signatures (delta98/95Mo) of the Early Cambrian black shales is 1.2 permil below recent ocean water, similar to the signature found in Mesoproterozoic shales (Arnold et al. 2004), indicating a larger proportion of Mo sedimentation under strongly euxinic conditions compared to recent oceans. A chemically stratified ocean with sulfidic deep waters and modestly oxygenated surface waters as proposed by Canfield (1998) for the Paleoproterozoic and Mesoproterozoic ocean, and Jiang et al. (2007) reported Carbon isotope data from the Ediacaran Yangtze platform (635-542 Ma) to be consistent with long-term deep ocean anoxia/euxinia. A stratified ocean therefore provides a plausible scenario to explain our new PC-C Mo isotope data. On closer inspection, a transient Mo isotopic signal following immediately after the PC-C boundary in both sample sets indicates a short but intense global non-steady state situation. In particular, a short term, drastic decrease of the Mo ocean inventory to almost zero is required to reconcile the observed Mo isotope data. Combined with the extreme Mo enrichment, found in the Chinese sulfide marker bed at the PC-C boundary, this signal has to be explained with a non-uniformitarian Mo scavenging mechanism. We put forward the hypothesis of mixing of oxidized, i.e. Mo rich surface waters with upwelling euxinic bottom water masses of the stratified ocean, as H2S is the most efficient Mo scavenging reagent. This scenario not only explains the transient isotopic signal, it can also be responsible for the sudden extinction of the Ediacaran fauna by H2S poisoning. In contrast, mass extinction scenarios like bolide impact, flood basalt eruptions or methane release, do not provide a direct explanation for the

  15. On the origin and evolution of thermophily: reconstruction of functional precambrian enzymes from ancestors of Bacillus.

    Hobbs, Joanne K; Shepherd, Charis; Saul, David J; Demetras, Nicholas J; Haaning, Svend; Monk, Colin R; Daniel, Roy M; Arcus, Vickery L


    Thermophily is thought to be a primitive trait, characteristic of early forms of life on Earth, that has been gradually lost over evolutionary time. The genus Bacillus provides an ideal model for studying the evolution of thermophily as it is an ancient taxon and its contemporary species inhabit a range of thermal environments. The thermostability of reconstructed ancestral proteins has been used as a proxy for ancient thermal adaptation. The reconstruction of ancestral "enzymes" has the added advantages of demonstrable activity, which acts as an internal control for accurate inference, and providing insights into the evolution of enzymatic catalysis. Here, we report the reconstruction of the structurally complex core metabolic enzyme LeuB (3-isopropylmalate dehydrogenase, E. C. from the last common ancestor (LCA) of Bacillus using both maximum likelihood (ML) and Bayesian inference. ML LeuB from the LCA of Bacillus shares only 76% sequence identity with its closest contemporary homolog, yet it is fully functional, thermophilic, and exhibits high values for k(cat), k(cat)/K(M), and ΔG(‡) for unfolding. The Bayesian version of this enzyme is also thermophilic but exhibits anomalous catalytic kinetics. We have determined the 3D structure of the ML enzyme and found that it is more closely aligned with LeuB from deeply branching bacteria, such as Thermotoga maritima, than contemporary Bacillus species. To investigate the evolution of thermophily, three descendents of LeuB from the LCA of Bacillus were also reconstructed. They reveal a fluctuating trend in thermal evolution, with a temporal adaptation toward mesophily followed by a more recent return to thermophily. Structural analysis suggests that the determinants of thermophily in LeuB from the LCA of Bacillus and the most recent ancestor are distinct and that thermophily has arisen in this genus at least twice via independent evolutionary paths. Our results add significant fluctuations to the broad

  16. From a collage of microplates to stable continental crust - an example from Precambrian Europe

    Korja, Annakaisa


    Svecofennian orogen (2.0-1.7 Ga) comprises the oldest undispersed orogenic belt on Baltica and Eurasian plate. Svecofennian orogenic belt evolved from a series of short-lived terrane accretions around Baltica's Archean nucleus during the formation of the Precambrian Nuna supercontinent. Geological and geophysical datasets indicate W-SW growth of Baltica with NE-ward dipping subduction zones. The data suggest a long-lived retreating subduction system in the southwestern parts whereas in the northern and central parts the northeasterly transport of continental fragments or microplates towards the continental nucleus is also documented. The geotectonic environment resembles that of the early stages of the Alpine-Himalayan or Indonesian orogenic system, in which dispersed continental fragments, arcs and microplates have been attached to the Eurasian plate margin. Thus the Svecofennian orogeny can be viewed as proxy for the initial stages of an internal orogenic system. Svecofennian orogeny is a Paleoproterozoic analogue of an evolved orogenic system where terrane accretion is followed by lateral spreading or collapse induced by change in the plate architecture. The exposed parts are composed of granitoid intrusions as well as highly deformed supracrustal units. Supracrustal rocks have been metamorphosed in LP-HT conditions in either paleo-lower-upper crust or paleo-upper-middle crust. Large scale seismic reflection profiles (BABEL and FIRE) across Baltica image the crust as a collage of terranes suggesting that the bedrock has been formed and thickened in sequential accretions. The profiles also image three fold layering of the thickened crust (>55 km) to transect old terrane boundaries, suggesting that the over-thickened bedrock structures have been rearranged in post-collisional spreading and/or collapse processes. The middle crust displays typical large scale flow structures: herringbone and anticlinal ramps, rooted onto large scale listric surfaces also suggestive

  17. Iron Isotopes in Lake Pavin (French Massif Central): A Window to the Precambrian Ocean

    Busigny, V.; Jézéquel, D.; Louvat, P.; Viollier, E.; Michard, G.


    Consequences and timing of ocean oxygenation are still debated. It is generally considered that early ocean was anoxic and passed through a stratified state (oxic at the surface and anoxic in the deeper part) before being completely oxidized. Stratified ocean may have persisted more than 1Ga, thus representing an important period of the Earth history. The Fe isotope record in Precambrian sediments may provide constraints on the ocean evolution but a major question is what do the rocks tell us about the water column? This is an indirect way to get information and the geochemical signal may be modified later by diagenesis and metamorphism. The study of present stratified water body associated with sediments may help to decipher the isotopic signal from old sediments. Unlike marine complex environments, smaller and well-defined ecosystems such as lake can be useful to understand element transfer and processes. Lake Pavin is characterized by the presence of two stratified layers. The upper layer (mixolimnion) extends from the surface to 60m depth, and is oxidized. The deeper layer (monimolimnion), which extends from 70 to 92m depth, is permanently anoxic and separated from the mixolimnion by the mesolimnion where a drastic dissolved Fe gradient exists. In lake Pavin, Fe is oxidized and precipitated as Fe(III) in the mixolimnion. It is then dissolved in the deep layers (60 to 92m) and within the sediments and accumulates as aqueous Fe(II). Fe(II) either diffuses towards the mixolimnion or reacts with sulfides or phosphates to form FeS colloids and secondary minerals such as pyrite, vivianite or siderite. In order to characterize Fe isotope fractionations in this system, we measured Fe content and isotopic composition of aqueous Fe(II) along a vertical profile at different depths from the oxic-anoxic interface to the bottom of the lake. Fe content increases with depth, from less than 2 μmol/L above 60m depth to more than 1200 μmol/L at the bottom of the lake. δ56Fe

  18. Diamond drilling for geologic information in the middle Precambrian basins in the western portion of northern Michigan. Final report

    Trow, J.


    Between September 26, 1977, and May 11, 1978, six initially vertical holes probed a total of 9896 feet (1109 feet or 11.2% in overburden, 155 feet or 1.6% in Precambrian Y mafic dikes, 8386 feet or 84.7% in Precambrian X Goodrich Quartzite and Michigamme Formation, and 246 feet or 2.5% in Precambrian W basement lithologies). In addition to normal examination of core, logging, and storing of core, the holes were extensively logged geophysically, acidized core was tested for phosphate content by ammonium molybdate, splits from five out of every thirty feet of core were subjected to chemical scrutiny, thin sections of all lithologies were examined, and radiometric determinations of geologic age were made for confirmation of Precambrian W basement which was encountered in each of the three basins in Marquette County.

  19. Isotopic chronology and geological events of Precambrian complex in Taihangshan region

    刘树文; 梁海华; 赵国春; 华永刚; 简安华


    There are five major geological events in Precambrian complex, Taihangshan region determined by researching into geology and isotopic chronology of the complex. Basaltic magma erupted and quartz-dioritic to tonalitic magma intruded in earlier neo-Archaean, which formed horn-blende-plagiogneiss of Fuping gneiss complex and metamorphic mafic rock enclaves in TTG gneiss complex. Granulite fades metamorphism and emplacement of biotite-plagiogneiss occurred in late neo-Archaean. Extension and uplifting from the end of neo-Archaean to Paleoproterozoic era formed Chengnanzhuang large extensional deformation zones and metamorphic mafic veins emplaced into the deformation zones. Remobilization of Precambrian complex and tectonic uplifting in late Paleoproterozoic era formed Longquanguan ductile shear zone and emplacement of Nanying gneiss. Occurrence of regional granite pegmatite at the end of Paleoproterozoic era means the end of the Luliang movement.

  20. Isotopic chronology and geological events of Precambrian complex in Taihangshan region


    There are five major geological events in Precambrian complex, Taihangshan region determined by researching into geology and isotopic chronology of the complex. Basaltic magma erupted and quartz-dioritic to tonalitic magma intruded in earlier neo-Archaean, which formed hornblende-plagiogneiss of Fuping gneiss complex and metamorphic mafic rock enclaves in TTG gneiss complex. Granulite facies metamorphism and emplacement of biotite-plagiogneiss occurred in late neo-Archaean. Extension and uplifting from the end of neo-Archaean to Paleoproterozoic era formed Chengnanzhuang large extensional deformation zones and metamorphic mafic veins emplaced into the deformation zones. Remobilization of Precambrian complex and tectonic uplifting in late Paleoproterozoic era formed Longquanguan ductile shear zone and emplacement of Nanying gneiss. Occurrence of regional granite pegmatite at the end of Paleoproterozoic era means the end of the Lliang movement.

  1. Radon emissions related to the granitic Precambrian shield in southern Brazil.

    Fianco, Ana C B; Roisenberg, Ari; Bonotto, Daniel M


    The equivalent uranium (eU) activity concentration was analysed in selected granite samples at several sites in Porto Alegre, Southern Brazil, to obtain information on the radon ((222)Rn) generation by the aquifer rock matrices. Radon analyses of ground water and soil samples were also performed. Several samples exhibited a dissolved (222)Rn activity concentration exceeding the World Health Organization maximum limit of 100 Bq l(-1). The dissolved radon content in ground waters from the Fractured Precambrian Aquifer System exhibited a direct significant correlation with the eU in the rock matrices, which is a typical result of water-rock interactions. Variation in the soil's porosity was confirmed as an important factor for (222)Rn release, as expected, due to its gaseous nature. Thus, although the calcic-alkaline to alkaline Precambrian granitoid rocks of the study area are important reservoirs for underground resources, they can release high amounts of radon gas into the liquid phase.

  2. Comparative Study of Modern Stromatolites in Coastal Lagoa Salgada and Lagoa Vermehla, Brazil: Analogues for Precambrian Environmental Evolution

    Vasconcelos, C.; Lundberg, R.; Bahniuk, A.; Och, L.; McKenzie, J. A.


    Ancient microbial processes continue to be active in isolated modern lacustrine environments. As these unique environments can serve as analogues for Precambrian systems, biogeochemical studies in modern lakes or lagoons can be used to develop a better understanding of microcosms thriving on the early Earth. We study the biogeochemical processes associated with modern stromatolite formation in two distinctly different lagoons (lagoas in Portuguese) located in a special semi-arid microclimate within the tropical region along the central Brazilian coast. Although the stromatolites in both lagoons are characterized by high-Mg calcite to dolomite precipitation, the aqueous geochemistry is very different. Lagoa Salgada, Brazil contains fresh to brackish water feed by meteoric ground waters and has low sulfate concentrations, whereas Lagoa Vermehla, Brazil is brackish to hypersaline as a result of recharge with altered marine water and has sulfate concentrations greater than normal sea water. The average oxygen isotope composition of the in situ stromatolites reflects the different hydrology of the lakes: δ18O values of Lagoa Salgada stromatolites average -1.5 ‰, while the δ18O values of Lagoa Vermehla stromatolites average 1.5 ‰. Furthermore, the average carbon isotope composition of the stromatolites mirrors the prominent microbial process active in the lakes: δ13C values of Lagoa Salgada stromatolites average 10 to 20 ‰, while the δ13C values of Lagoa Vermehla stromatolites average -2.5 ‰. These dissimilar δ13C values indicate the importance of different microbial processes as the main carbon source for the carbonate incorporated into the laminae, that is, methanogenesis vs. sulfate reduction, respectively. In fact, using microbiologic and genomic techniques, the molecular characterization of the microbial mats from which the discrete laminae develop is consistent with this geochemical observation. We propose that a comparative study of the Lagoa Salgada

  3. REE Geochemical Evolution and Its Significance of Early Precambrian Metamorphic Terrain,Wuyang,Henan

    陈衍景; 富士谷; 等


    The supracrustal rocks of the Wuyang metamorphic terrain are divided into the Zhao anzhuang,Tieshanmiao and Yangshuwan Formations.These three Formations were dated at 3000-2550Ma,2550-2300Ma and 2300-2200Ma,respectively.∑REE and La/Yb)n of the Zhao anzhuang Formation volcanic rocks are obviously higher than those of the Tiesanmiao Formation equivalents,suggesting a sedimentary gap(2550 Ma boundary)between these two formations,The Zhao'anzhuang Formation is older than the Tieshanmiao Formation.The sediments of these two Formations show no obvious differences in REE and are generally characterized by low ∑REE and positive Eu anomalies.On the contrary,the sediments of the Yangshuwan Formation are characterized by high ∑REE and negative Eu anomalies.Detailed discussions demonstrate that the Yangshuwan Formation was deposited in an oxidizing environment whereas the other two formations were formed in a reducing environment.At the end of the evolution of the Tieshanmiao Formation about 2300 Ma ago,the sedimentary environment was transformed from reducing to oxidizing .On the basis of the SHAB (soft/hard acid and base)theory,an oxidation-reduction model for sedimentary REE evolution has been established .It is proposed that the mantle tends to become gradually depleted in REE.especially in LREE,and the indices ∑REE and La/Yb) n of mantle-dervived volcanic rocks also tend to become lower and lower.

  4. Tectonic Evolution of an Early Precambrian High-Pressure Granulite Belt in the North China Craton


    A large-scale high-pressure granulite belt (HPGB), more than 700 km long, is recognized within the metamorphic basement of the North China craton. In the regional tectonic framework, the Hengshan-Chengde HPGB is located in the central collision belt between the western block and eastern block, and represents the deep crustal structural level. The typical high-pressure granulite (HPG) outcrops are distributed in the Hengshan and Chengde areas. HPGs commonly occur as mafic xenoliths within ductile shear zones, and underwent multipile deformations. To the south, the Hengshan-Chengde HPGB is juxtaposed with the Wutai greenstone belt by several strike-slip shear zones. Preliminary isotopic age dating indicates that HPGs from North China were mainly generated at the end of the Neoarchaean, assocaited with tectonic assembly of the western and esatern blocks.

  5. Charnockite Formation and Early Precambrian Crust Evolution in Yishui Area, Shandong Province, China


    Charnockite and granulite in Yishui area, Shandong Province are located in the middle part of the Tancheng-Lujiang fault zone, eastern China. Field studies have shown that the charnockites, derived from the adjacent granulites, are classified as three types: enderbite, garnet-enderbite and hypersthene-trondhjemite. In addition, two generations of minerals are present in the charnockites: the relic minerals such as garnet, hypersthene and clinopyroxene, and the neocrystallized minerals such as plagioclase and K-feldspar. The relic minerals occurring in the granulite facies stage were affected by the later partial melting. The relic minerals, irregular and usually ragged in shape, occupy the interstitial positions in the neocrystalline minerals. The neocrystalline minerals are usually euhedral-subhedral crystals. The study of petrology, mineralogy and geochemistry of charnokites concludes that the enderbite was formed by the anatexis of the two-pyroxene plagioclase granulite, that the garnet-enderbite was formed by the anatexis of sillimanite garnet gneiss, and that the hypersthene-trondhjemite was formed by the anatexis of the leucocratic two-pyroxene plagioclase granulite. The U-Pb dating of the zircon indicates that the formation of the charnockite and granulite was related to the Archean-Proterozoic upwelling of a mantle plume (hot spot)around 2 500 Ma, in Yishui area, Shandong Province.

  6. Eukaryotic stromatolite builders in acid mine drainage: Implications for Precambrian iron formations and oxygenation of the atmosphere?

    Brake, S.S.; Hasiotis, S.T.; Dannelly, H.K.; Connors, K.A. [Indiana State University, Terre Haute, IN (United States). Dept. of Geography, Geology & Anthropology


    Biological activity of Euglena mutabilis, an acidophilic, photosynthetic protozoan, contributes to the formation of Fe-rich stromatolites in acid mine drainage systems. E. mutabilis is the dominant microbe in bright green benthic mats (biofilm), coating drainage channels at abandoned coal mine sites in Indiana. It builds biolaminates through phototactic and aerotactic behavior, similar to prokaryotes, by moving through precipitates that periodically cover the mats. E. mutabilis also contributes to formation of Fe-rich stromatolites by (1) intracellularly storing Fe compounds released after death, contributing to the solid material of stromatolites and acting as nucleation sites for precipitation of authigenic Fe minerals, and (2) generating 02 via photosynthesis that further facilitates precipitation of reduced Fe, any excess 02 not consumed by Fe precipitation being released to the atmosphere. Recognition of E. mutabilis-dominated biofilm in acidic systems raises a provocative hypothesis relating processes involved in formation of Fe-rich stromatolites by E. mutabilis to those responsible for development of Precambrian stromatolitic Fe formations and oxygenation of the early atmosphere.

  7. Big insights from tiny peridotites: Evidence for persistence of Precambrian lithosphere beneath the eastern North China Craton

    Liu, Jingao; Rudnick, Roberta L.; Walker, Richard J.; Xu, Wen-liang; Gao, Shan; Wu, Fu-yuan


    Previous studies have shown that the eastern North China Craton (NCC) lost its ancient lithospheric mantle root during the Phanerozoic. The temporal sequence, spatial extent, and cause of the lithospheric thinning, however, continue to be debated. Here we report olivine compositions, whole-rock Re-Os isotopic systematics, and platinum-group element abundances of small ( 92) lithospheric mantle is largely absent. Osmium isotopic data suggest the Wudi peridotites experienced melt depletion primarily during the Paleoproterozoic (~ 1.8 Ga), although an Archean Os model age for one xenolith indicates incorporation of a minor component of Archean lithospheric mantle. These data suggest that a previously unrecognized Paleoproterozoic orogenic event removed and replaced the original Archean lithospheric mantle beneath the sedimentary basin at the southern edge of the Bohai Sea. By contrast, the Fuxin peridotites, entrained in Cretaceous basalts that crop out along the northern edge of the eastern NCC, document the coexistence of both ancient (≥ 2.3 Ga) and modern lithospheric mantle components. Here, the original Late Archean-Early Paleoproterozoic lithospheric mantle was, at least partially, removed and replaced prior to 100 Ma. Combined with literature data, our results show that removal of the original Archean lithosphere occurred within Proterozoic collisional orogens, and that replacement of Precambrian lithosphere during the Mesozoic may have been spatially associated with the collisional boundaries and the strike-slip Tan-Lu fault, as well as the onset of Paleo-Pacific plate subduction.

  8. Biogenicity of an Early Quaternary iron formation, Milos Island, Greece.

    Chi Fru, E; Ivarsson, M; Kilias, S P; Frings, P J; Hemmingsson, C; Broman, C; Bengtson, S; Chatzitheodoridis, E


    A ~2.0-million-year-old shallow-submarine sedimentary deposit on Milos Island, Greece, harbours an unmetamorphosed fossiliferous iron formation (IF) comparable to Precambrian banded iron formations (BIFs). This Milos IF holds the potential to provide clues to the origin of Precambrian BIFs, relative to biotic and abiotic processes. Here, we combine field stratigraphic observations, stable isotopes of C, S and Si, rock petrography and microfossil evidence from a ~5-m-thick outcrop to track potential biogeochemical processes that may have contributed to the formation of the BIF-type rocks and the abrupt transition to an overlying conglomerate-hosted IF (CIF). Bulk δ(13) C isotopic compositions lower than -25‰ provide evidence for biological contribution by the Calvin and reductive acetyl-CoA carbon fixation cycles to the origin of both the BIF-type and CIF strata. Low S levels of ~0.04 wt.% combined with δ(34) S estimates of up to ~18‰ point to a non-sulphidic depository. Positive δ(30) Si records of up to +0.53‰ in the finely laminated BIF-type rocks indicate chemical deposition on the seafloor during weak periods of arc magmatism. Negative δ(30) Si data are consistent with geological observations suggesting a sudden change to intense arc volcanism potentially terminated the deposition of the BIF-type layer. The typical Precambrian rhythmic rocks of alternating Fe- and Si-rich bands are associated with abundant and spatially distinct microbial fossil assemblages. Together with previously proposed anoxygenic photoferrotrophic iron cycling and low sedimentary N and C potentially connected to diagenetic denitrification, the Milos IF is a biogenic submarine volcano-sedimentary IF showing depositional conditions analogous to Archaean Algoma-type BIFs.

  9. Quantifying Precambrian crustal extraction: the root is the answer

    Abbott, Dallas; Sparks, David; Herzberg, Claude; Mooney, Walter; Nikishin, Anatoly; Zhang, Yu Shen


    We use two different methods to estimate the total amount of continental crust that was extracted by the end of the Archean and the Proterozoic. The first method uses the sum of the seismic thickness of the crust, the eroded thickness of the crust, and the trapped melt within the lithospheric root to estimate the total crustal volume. This summation method yields an average equivalent thickness of Archean crust of 49±6 km and an average equivalent thickness of Proterozoic crust of 48± 9 km. Between 7 and 9% of this crust never reached the surface, but remained within the continental root as congealed, iron-rich komatiitic melt. The second method uses experimental models of melting, mantle xenolith compositions, and corrected lithospheric thickness to estimate the amount of crust extracted through time. This melt column method reveals that the average equivalent thickness of Archean crust was 65±6 km, and the average equivalent thickness of Early Proterozoic crust was 60±7 km. It is likely that some of this crust remained trapped within the lithospheric root. The discrepancy between the two estimates is attributed to uncertainties in estimates of the amount of trapped, congealed melt, overall crustal erosion, and crustal recycling. Overall, we find that between 29 and 45% of continental crust was extracted by the end of the Archean, most likely by 2.7 Ga. Between 51 and 79% of continental crust was extracted by the end of the Early Proterozoic, most likely by 1.8-2.0 Ga. Our results are most consistent with geochemical models that call upon moderate amounts of recycling of early extracted continental crust coupled with continuing crustal growth (e.g. McLennan, S.M., Taylor, S.R., 1982. Geochemical constraints on the growth of the continental crust. Journal of Geology, 90, 347-361; Veizer, J., Jansen, S.L., 1985. Basement and sedimentary recycling — 2: time dimension to global tectonics. Journal of Geology 93(6), 625-643). Trapped, congealed, iron-rich melt

  10. Hydrogen isotopes as a tracer of the Precambrian hydrosphere

    Pope, Emily Catherine; Rosing, Minik Thorleif; Bird, Dennis K.

    Oceanic serpentinites and hydrous silicate minerals that are formed in subduction-related volcanic and hydrothermal environments obtain their hydrogen isotope composition (δD) from seawater-derived fluids, and thus may be used to calculate secular variation in δDSEAWATER. Hydrogen isotope...... is constrained by the hydrogen isotope composition of the minerals at Isua. We developed a first-order mass balance model of δDSEAWATER evolution delimited by δD of Isua serpentine and fuchsite and that of modern seawater. The ca. 25‰ change in δDSEAWATER can be accounted for by the development of the modern...... account for the remainder of the observed isotopic shift in seawater. This estimate is consistent with independent approximations of atmospheric methane concentrations in the early Archean, and is within an order of magnitude of the amount of hydrogen escape required to oxidize the continents before...

  11. Matching 30 years of ecosystem monitoring with a high resolution microfossil record of chironomid eggs and Cladocera from Lake Mývatn, Iceland

    Hauptfleisch, Ulf; Einarsson, Arni; Andersen, Thorbjørn Joest


    1. Monitoring of the ecosystem of Lake My´vatn, Iceland, since 1975 has revealed extreme fluctuations in important food web components, such as chironomids and cladocerans, with amplitudes of several orders of magnitude and a period of 5–8 years. This study uses sediment cores from the lake...... to examine if the food web fluctuations appear in the microfossil record of the sediment. 2. Dating was achieved by means of a combination of 137Cs and volcanic tephra and was fine-tuned by wiggle-matching of chironomid microfossil and monitoring data. 3. Cladocera exuviae and chironomid egg capsules...... record of chironomid eggs and of the exuviae of three of seven cladocerans: Alonella nana, Alona rectangula and Eurycercus lamellatus, which also had the most extreme fluctuations in the monitoring data (3–4 orders of magnitude). Chydorus sphaericus, and to some extent Alona quadrangularis and Acroperus...

  12. Formation and evolution of Precambrian continental crust in South China

    ZHENG YongFei; ZHANG ShaoBing


    The occurrence of zircons with U-Pb ages of ~3.8 Ga and Hf model ages of ~4.0 Ga in South China suggests the existence of the Hadean crustal remnants in South China. Furthermore, a detrital zircon with a U-Pb age as old as 4.1 Ga has been found in Tibet. This is the oldest zircon so far reported in China. These results imply that continental crust was more widespread than previously thought in the late Hadean, but its majority was efficiently reworked into Archean continental crust. On the basis of available zircon U-Pb age and Hf isotope data, it appears that the growth of continental crust in South China started since the early Archean, but a stable cratonic block through reworking did not occur until the Paleoproterozoic. Thus the operation of some form of plate tectonics may occur in China continents since Eoarchean. The initial destruction of the South China craton was caused by intensive magmatic activity in association with the assembly and breakup of the supercontinent Rodinia during the Neoproterozoic. However, most of the Archean and Paleoproterozoic crustal materials in South China do not occur as surface rocks, but exist as sporadic crustal remnants. Nevertheless, the occurrence of Neoproterozoic magmatism is still a signature to distinguish South China from North China.

  13. Palaeotemperature trend for Precambrian life inferred from resurrected proteins.

    Gaucher, Eric A; Govindarajan, Sridhar; Ganesh, Omjoy K


    Biosignatures and structures in the geological record indicate that microbial life has inhabited Earth for the past 3.5 billion years or so. Research in the physical sciences has been able to generate statements about the ancient environment that hosted this life. These include the chemical compositions and temperatures of the early ocean and atmosphere. Only recently have the natural sciences been able to provide experimental results describing the environments of ancient life. Our previous work with resurrected proteins indicated that ancient life lived in a hot environment. Here we expand the timescale of resurrected proteins to provide a palaeotemperature trend of the environments that hosted life from 3.5 to 0.5 billion years ago. The thermostability of more than 25 phylogenetically dispersed ancestral elongation factors suggest that the environment supporting ancient life cooled progressively by 30 degrees C during that period. Here we show that our results are robust to potential statistical bias associated with the posterior distribution of inferred character states, phylogenetic ambiguity, and uncertainties in the amino-acid equilibrium frequencies used by evolutionary models. Our results are further supported by a nearly identical cooling trend for the ancient ocean as inferred from the deposition of oxygen isotopes. The convergence of results from natural and physical sciences suggest that ancient life has continually adapted to changes in environmental temperatures throughout its evolutionary history.

  14. Optimization of the Acetic Acid method for microfossil extraction from lithified carbonate rocks: Examples from the Jurassic and Miocene of Saudi Arabia

    Chan, Septriandi; Malik, Muhammad; Kaminski, Michael; Babalola, Lamidi


    We report the first ever use of the acetic acid processing method for the extraction of microfossils from indurated limestones in Saudi Arabia. Two different limestone samples from Middle Jurassic and Middle Miocene formation in Saudi Arabia were tested under different concentrations of acid from 50% to 100% and with processing times from 2 hours to 10 hours, in an attempt to optimize the processing methodology. The recovery of acid residues shows a similar trend for both Jurassic and Miocene samples. The weight percentage of residue particle size > 1 mm decreases as acid concentration increases, especially in the 50 to 80% acid concentration range, and the weight percentage of the smallest size particles >0.063 mm increases as acid concentration increases. The small fraction of residue between 0.50 - 0.063 mm was split into 3 g subsamples and picked for microfossils in order to assess their preservation. All concentrations of acetic acid tested show promising results for both the Jurassic Dhruma and Miocene Dam formation carbonates. Higher acid concentrations with longer reaction times yield better recovery than higher concentrations with less reaction time. Based on our experiment, we recommended a 60% concentration of acetic acid to be the optimal concentration for use on routine micropaleontological samples of Saudi Arabian carbonate rocks. By lowering the concentration of acetic acid from 80% to 60%, the consumption of acid is reduced without compromising the recovery of microfossils, and the sample can be processed in a more environmentally friendly manner.

  15. Micro-scale Complexity in Iron-Sulfide Phases in Precambrian Sedimentary Rocks Determined by Synchrotron Microprobe Spectroscopy

    Webb, S.; Johnson, J. E.; Slotznick, S. P.; Roach, C.; Fischer, W. W.


    The record of sedimentary pyrite forms the foundation for most isotope records working to define the coupled evolution and behavior of the ancient iron and sulfur cycles. In order to assess the strengths and limitations of records derived from pyrite-rich rocks (e.g. iron speciation, sulfur isotope ratios), we need to understand more about the processes that form and alter sedimentary pyrite. From samples of the Archean/early Proterozoic Transvaal and middle Proterozoic Belt Supergroups, petrography reveals that what might operationally be called sedimentary pyrite has complex textures that hint at a rich process history of sulfur mineralization. A common limitation of virtually all proxy measurements employed to date is that they operate on 'bulk' samples, typically gram-sized or larger pieces. As such, they lose the ability to relate geochemistry to petrography at the scale of mineral grains. Many of the sedimentary pyrites in the Transvaal Supergroup exhibit complex redox and electronic structures of S and Fe, with crystals of pyrite, pyrrhotite, and sulfate-bearing minerals throughout. Parallel application of multiple techniques on the same samples across micron bases spatial scales, provide an opportunity to diagnose issues resulting from post-depositional alteration of sedimentary rocks. We have integrated light and electron microscopy for petrography, electron microprobe and synchrotron XRF for elemental composition, synchrotron X-ray spectroscopy for redox and chemical state, and secondary ion mass spectrometry (SIMS) for isotopic composition. The coupling of these tools allows in essence "images" of the proxy data at the micrometer scale, giving a wide array of textural and mineralogical information designed to inform and untangle the complicated histories of these early Precambrian rocks.

  16. Beyond the Burgess Shale: Cambrian microfossils track the rise and fall of hallucigeniid lobopodians

    Caron, Jean-Bernard; Smith, Martin R.; Harvey, Thomas H. P.


    Burgess Shale-type deposits are renowned for their exquisite preservation of soft-bodied organisms, representing a range of animal body plans that evolved during the Cambrian ‘explosion’. However, the rarity of these fossil deposits makes it difficult to reconstruct the broader-scale distributions of their constituent organisms. By contrast, microscopic skeletal elements represent an extensive chronicle of early animal evolution—but are difficult to interpret in the absence of corresponding w...

  17. High resolution integrated study of microfossil assemblages in Sapropel S1, S3 and S5: preliminary results

    Negri, Alessandra; Morigi, Caterina; Sangiorgi, Francesca; Keller, Joerg


    The Eastern Mediterranean late Neogene to Quaternary sedimentary record is characterized by the widespread and distinctly periodical occurrence of organic carbon-rich layers, called sapropels. The deposition of sapropels is related to significant changes in climate, in the pattern of water circulation and in the biogeochemical cycles. The primary cause triggering the formation of sapropels has been debated ever since their discovery: productivity in the surface waters and organic matter preservation at the sea-floor due to hypoxia or anoxia have been indicated as the two major contributing factors operating either separately or combined. Moreover, each sapropel seems to have its own peculiar feature, likely attributed to the different climate forcing and the different response of productivity and preservation to the water column parameters. Here we present preliminary data from core M25/4 12, located in the Ionian Sea, containing a continuous record of the sapropels deposited in the last 330 ka (S1 to S10, excluding S2). We analysed the microfossil assemblages in sapropels S1 (10 ka BP), S3 (80 ka BP) and S5 (125 ka BP) at a multi-centennial time resolution to get insights into the climatic and oceanographical features leading to their deposition and the role of productivity and preservation.

  18. Sedimentary Features and Implications for the Precambrian Non-stromatolitic Carbonate Succession: A Case Study of the Mesoproterozoic Gaoyuzhuang Formation at the Qiangou Section in Yanqing County of Beijing

    MEI Mingxiang


    In the long Precambrian period, stromatolitic carbonate successions were very common.However, the non-stromatolitic carbonate succession that is marked by subtidal deposits shows a sharp contrast to the stromatolitic carbonate succession. Both the non-stromatolitic and the stromatolitic carbonate successions are important clues for the further understanding of the evolving carbonate world of the Precambrian. The Mesoproterozoic Gaoyuzhuang Formation at the Qiangou section in northwestern suburb of Beijing is a set of more than 1000 m-thick carbonate strata that can be divided into four members (or subformations), in which a non-stromatolitic carbonate succession marked by the scarcity of stromatolites makes up the third member of the formation. This non-stromatolitic carbonate succession can further be subdivided into three third-order sequences that are marked by the regular succession of sedimentary facies. In third-order sequences, a lot of subtidal carbonate meter-scale cycles made up of medium-bedded leiolite limestones and thin-bedded marls constitute their transgressive system tracts (TSTs) and the early high-stand system tracts (EHSTs), a lot of meterscale cycles made up by thin-bedded limestones and marls constitute their condensed sections (CSs),and thick-bedded to massive dolomitic limestones or lime dolomites make up the late high-stand system tracts (LHSTs). The particularly non-stromatolitic carbonate succession making up the third member of the Mesoproterozoic Gaoyuzhuang Formation at the Qiangou section might be the representative of the non-stromatolitic carbonate succession of the Precambrian because of its special lithological features and particular sedimentary structures, and its general sedimentary features are helpful and meaningful for the further understanding of the evolution rules of the sophisticate and evolving carbonate world of the Precambrian. The time scale of the Gaoyuzhuang Formation is deduced as that from 1600 Ma to 1400 Ma

  19. Hydrogen Isotopes as a Tracer of the Precambrian Hydrosphere (Invited)

    Pope, E. C.; Rosing, M. T.; Bird, D. K.


    Oceanic serpentinites and hydrous silicate minerals that are formed in subduction-related volcanic and hydrothermal environments obtain their hydrogen isotope composition (δD) from seawater-derived fluids, and thus may be used to calculate secular variation in δDSEAWATER. Hydrogen isotope compositions of serpentine and fuchsite from the ca. 3.8 Ga Isua supracrustal belt in West Greenland range from -99 to -53‰, and -115 to -61‰, respectively. The highest values indicate that Eoarchean seawater had a δD that was at most 25 × 5‰ lower than modern oceans. Deuterium-poor water is potentially sequestered from oceans over geologic time by continental growth, large-scale glaciation events, biologically mediated hydrogen escape to space, and subduction of water that is chemically bound in alteration minerals of the ocean crust. The extent to which any of these fluxes have occurred since the Eoarchean is constrained by the hydrogen isotope composition of the minerals at Isua. We developed a first-order mass balance model of δDSEAWATER evolution delimited by δD of Isua serpentine and fuchsite and that of modern seawater. The ca. 25‰ change in δDSEAWATER can be accounted for by the development of the modern cryosphere (9‰), continental growth (as much as 10‰ if continents grew continuously from 0% to 100% of their modern volume since 3.8 Ga) and hydrogen escape to space before the rise of an oxygen-rich atmosphere. ~1.0 × 0.8 x 1022 mol of elemental hydrogen released to space via biogenic methanogenesis would account for the remainder of the observed isotopic shift in seawater. This estimate is consistent with independent approximations of atmospheric methane concentrations in the early Archean, and is within an order of magnitude of the amount of hydrogen escape required to oxidize the continents before the rise of atmospheric oxygen. Volatile ingassing to the mantle at subduction zones and outgassing in arcs and mid-ocean ridges are apparently equivocal

  20. Precambrian tectonic evolution of the Tarim Block, NW China: New geochronological insights from the Quruqtagh domain

    Shu, L. S.; Deng, X. L.; Zhu, W. B.; Ma, D. S.; Xiao, W. J.


    The Tarim Block is an important tectonic unit to understand the Proterozoic tectonic framework of the Central Asian Orogenic Belt and the supercontinent Rodinia. The granitic, dioritic, gabbroic intrusive rocks and volcanic-volcanoclastic rocks are widely distributed in the Quruqtagh domain of NE-Tarim. The precise ages of these rocks and their tectonic implications in this part of the world are not well understood. This paper reports geochronological data of gabbro, diorite and granitic rocks from Quruqtagh. LA ICPMS U-Pb zircon ages suggest that numerous of gabbroic and granitic rocks were mainly crystallized at ca. 800 Ma. New geochronological data from the magmatic zircons of gabbro, granite and paragneiss can be preliminarily divided into four groups, which are (1) 2469 ± 12 Ma or 2470 ± 24 Ma, (2) 933 ± 11 Ma to 1048 ± 19 Ma, (3) 806 ± 8 Ma, 798 ± 7 Ma, 799 ± 24 Ma, 698 ± 51 Ma (lower intercept age of the paragneiss), and (4) 1930 Ma (upper intercept age of the paragneiss), respectively. These age data are consistent with four tectono-thermal events that took ever place in the Tarim Block. The 93 U-Pb age data (seven for average Concordia age from seven igneous plutons, 86 for xenocrystic and metamorphic ones) from eight samples can be divided into four evolutionary stages: 2360-2550 Ma (peak of 2510 Ma), 1800-2020 Ma (peak of 1870 Ma), 860-1140 Ma (peak of 920 Ma) and 680-840 Ma (peak of 800 Ma), respectively. The age peak of 2500 Ma, consistent with characteristic period of a global building-continent event, indicates that the late Neoarchean-early Paleoproterozoic magmatism had been ever taken place in Tarim. Two peaks at 1870 Ma and 920 Ma, being two assembly periods of the middle Paleoproterozoic Columbia and the Neoproterozoic Rodinia supercontinents, suggest that Tarim had connections with both Columbia and Rodinia, whereas structural evidence of these two events is absent in Tarim. Notable peak of 800 Ma is interpreted as a response to the

  1. Mineralogical and isotopic indicators of palaeoclimatological conditions during Precambrian time, Aldan Shield, Siberia

    Guliy, Vasyl


    Sedimentary sulfates in Precambrian rocks are direct evidences that free oxygen was important component in the atmosphere-hydrosphere system at that time and may be reflections of evaporate deposition in old sedimentary basins. Rocks with sulfates were early identified in the Fedorovskaya Formation of the Aldan Shield (V. Vinogradov et al., 1975). Geological works in different sectors of the Aldan Shield reveal presence of anhydrite, barite, gypsum and celestine in metamorphic sedimentary rocks of the Fedorovskaya Formation. The rocks are metamorphosed to the granulite and amphibolite faces, and their U-Pb age is 1.8 - 2.0 Ga. Carbon and oxygen isotope compositions of different sectors confirm that each of these carbonate rocks represents a clearly defined and isotopically distinct sedimentary facies. Anhydrite, gypsum and celestine were collected from the borehole cores of the Seligdar, Mustolaakh, Birikeen and Chukurdan apatite deposits. Samples of barites came from outcrops of the Hematitovoe deposits. All these minerals commonly are heterogeneous and composed of several generations. First generations of anhydrite form concordant layers, lenses or segregations in marbles, gneisses and geologically oldest sulfate-bearing apatite-carbonate rocks underlying the Seligdar ore body. Last generations of the sulfates form pods and branching veinlets in the apatite-bearing carbonate rocks of the Seligdar deposit with a thickness of 1.5 - 5 cm, and veins up to 3 - 5 m thick. Fine-grained and platy gypsum, white and pink in color, predominates over anhydrite, which concentrates toward the axial portions of the veins and forms aggregates of tabular burred crystals of lilac color. At the Mustolaakh, Birikeen and Chukurdan deposits sulfates were sporadically found in borehole cores as separated nets and clear late veins. Three generations of barite occur in barite-quarts-hematite ores. First generations of the minerals are smaller in size (1 - 2 mm), scattered in the ores

  2. Postglacial environmental succession of Nettilling Lake (Baffin Island, Canadian Arctic) inferred from biogeochemical and microfossil proxies

    Narancic, Biljana; Pienitz, Reinhard; Chapligin, Bernhard; Meyer, Hanno; Francus, Pierre; Guilbault, Jean-Pierre


    Nettilling Lake (Baffin Island, Nunavut) is currently the largest lake in the Canadian Arctic Archipelago. Despite its enormous size, this freshwater system remains little studied until the present-day. Existing records from southern Baffin Island indicate that in the early postglacial period, the region was submerged by the postglacial Tyrell Sea due to isostatic depression previously exerted by the Laurentide Ice Sheet. However, these records are temporally and spatially discontinuous, relying on qualitative extrapolation. This paper presents the first quantitative reconstruction of the postglacial environmental succession of the Nettilling Lake basin based on a 8300 yr-long high resolution sedimentary record. Our multi-proxy investigation of the glacio-isostatic uplift and subsequent changes in paleosalinity and sediment sources is based on analyses of sediment fabric, elemental geochemistry (μ-XRF), diatom assemblage composition, as well as on the first diatom-based oxygen isotope record from the eastern Canadian Arctic. Results indicate that the Nettilling Lake basin experienced a relatively rapid and uniform marine invasion in the early Holocene, followed by progressive freshening until about 6000 yr BP when limnological conditions similar to those of today were established. Our findings present evidence for deglacial processes in the Foxe Basin that were initiated at least 400yrs earlier than previously thought.

  3. Reservoir uncertainty, Precambrian topography, and carbon sequestration in the Mt. Simon Sandstone, Illinois Basin

    Leetaru, H.E.; McBride, J.H.


    Sequestration sites are evaluated by studying the local geological structure and confirming the presence of both a reservoir facies and an impermeable seal not breached by significant faulting. The Cambrian Mt. Simon Sandstone is a blanket sandstone that underlies large parts of Midwest United States and is this region's most significant carbon sequestration reservoir. An assessment of the geological structure of any Mt. Simon sequestration site must also include knowledge of the paleotopography prior to deposition. Understanding Precambrian paleotopography is critical in estimating reservoir thickness and quality. Regional outcrop and borehole mapping of the Mt. Simon in conjunction with mapping seismic reflection data can facilitate the prediction of basement highs. Any potential site must, at the minimum, have seismic reflection data, calibrated with drill-hole information, to evaluate the presence of Precambrian topography and alleviate some of the uncertainty surrounding the thickness or possible absence of the Mt. Simon at a particular sequestration site. The Mt. Simon is thought to commonly overlie Precambrian basement granitic or rhyolitic rocks. In places, at least about 549 m (1800 ft) of topographic relief on the top of the basement surface prior to Mt. Simon deposition was observed. The Mt. Simon reservoir sandstone is thin or not present where basement is topographically high, whereas the low areas can have thick Mt. Simon. The paleotopography on the basement and its correlation to Mt. Simon thickness have been observed at both outcrops and in the subsurface from the states of Illinois, Ohio, Wisconsin, and Missouri. ?? 2009. The American Association of Petroleum Geologists/Division of Environmental Geosciences. All rights reserved.

  4. Advancing Precambrian palaeomagnetism with the PALEOMAGIA and PINT(QPI) databases

    Veikkolainen, Toni H.; Biggin, Andrew J.; Pesonen, Lauri J.; Evans, David A.; Jarboe, Nicholas A.


    State-of-the-art measurements of the direction and intensity of Earth's ancient magnetic field have made important contributions to our understanding of the geology and palaeogeography of Precambrian Earth. The PALEOMAGIA and PINT(QPI) databases provide thorough public collections of important palaeomagnetic data of this kind. They comprise more than 4,100 observations in total and have been essential in supporting our international collaborative efforts to understand Earth's magnetic history on a timescale far longer than that of the present Phanerozoic Eon. Here, we provide an overview of the technical structure and applications of both databases, paying particular attention to recent improvements and discoveries.

  5. National Uranium Resource Evaluation. Volume 1. Summary of the geology and uranium potential of Precambrian conglomerates in southeastern Wyoming

    Karlstrom, K.E.; Houston, R.S.; Flurkey, A.J.; Coolidge, C.M.; Kratochvil, A.L.; Sever, C.K.


    A series of uranium-, thorium-, and gold-bearing conglomerates in Late Archean and Early Proterozoic metasedimentary rocks have been discovered in southern Wyoming. The mineral deposits were found by applying the time and strata bound model for the origin of uranium-bearing quartz-pebble conglomerates to favorable rock types within a geologic terrane known from prior regional mapping. No mineral deposits have been discovered that are of current (1981) economic interest, but preliminary resource estimates indicate that over 3418 tons of uranium and over 1996 tons of thorium are present in the Medicine Bow Mountains and that over 440 tons of uranium and 6350 tons of thorium are present in Sierra Madre. Sampling has been inadequate to determine gold resources. High grade uranium deposits have not been detected by work to date but local beds of uranium-bearing conglomerate contain as much as 1380 ppM uranium over a thickness of 0.65 meters. This project has involved geologic mapping at scales from 1/6000 to 1/50,000 detailed sampling, and the evaluation of 48 diamond drill holes, but the area is too large to fully establish the economic potential with the present information. This first volume summarizes the geologic setting and geologic and geochemical characteristics of the uranium-bearing conglomerates. Volume 2 contains supporting geochemical data, lithologic logs from 48 drill holes in Precambrian rocks, and drill site geologic maps and cross-sections from most of the holes. Volume 3 is a geostatistical resource estimate of uranium and thorium in quartz-pebble conglomerates.

  6. Microfossils and molecular records in oil shales of the Songliao Basin and implications for paleo-depositional environment


    Several oil shale beds, over 10 m thick, occur at the base of the first member of the Upper Cretaceous Qingshankou Formation (K2qn1) in the Songliao Basin. They act both as excellent source rocks for conventional oil and as potential oil deposit for shale oil production. Here we combine micropaleon-tology with organic geochemistry to investigate the paleo-depositional environment and organic source characteristics of the oil shales and black shales. Our results indicate that algal remains are dominant microfossils in K2qn1 oil shales, and their relatively high abundance suggests a major algal thriving event during the oil shale deposition. The presence of fresh water and brackish water species, Sentusidinium, Vesperopsis and Nyktericysta, and marine or brackish water deltaic and lagoonal species such as Kiokansium and Dinogymniopsis demonstrate that this paleo-continental lake was influenced by marine transgressions at the time of K2qn1 oil shale formation. The extremely low pristine/phytane ratios, relatively high abundance of gammacerane and 4-methyl steranes, and low δ 13C values of C14-C37 n-alkanes in the oil shale organic extracts indicate the deposition of oil shales in anoxic and highly stratified water columns and the significant contribution of lacustrine algae to sedimentary organic matter. High molecular-weight paraffinic hydrocarbons with unusually high abundance of nC43, nC45, and nC47 may be related to special algal species associated with marine transgression events. The giant water body of Songliao paleo-lake and the change in the organic and chemical environment (such as nutrition source and water column salinity) associated with seawater transgression into the lake are among the most important reasons for oil shales in the Songliao Basin being different from mudstone and oil shale in other rifted basins.

  7. Ultra-high geomagnetic field reversal frequency around the Precambrian-Cambrian transition ?

    Pavlov, V.; Gallet, Y.; Shatsillo, A.; Kouznetsov, N.


    Magnetostratigraphic investigations carried out in Siberia have shown that the middle Cambrian was marked by an extremely high geomagnetic field reversal frequency of about 7 to 10 rev./Myr. The results available for the Lower Cambrian are more uncertain but they may indicate an even higher reversal frequency, which could thus reveal a very unstable nature of the geomagnetic field at this time. Recent magnetostratigraphic results also suggest that the geomagnetic reversal frequency has been extraordinarily high at the end of the Precambrian, thus in agreement with the Lower Cambrian data. We will present a review of these data, and will further describe new results we have obtained from Late Ediacaran-Nemakit-Daldynian sections of the south-western Siberian platform (Enisey range, Teya and Chapa rivers valleys). All these data provide consistent evidences for an ultra-high geomagnetic field reversal frequency, and thus for the exceptional nature of the geomagnetic field, around the Precambrian-Cambrian transition. We will also discuss a number of hypotheses which could explain a temporary destabilization of the geomagnetic field.

  8. A palaeotemperature curve for the Precambrian oceans based on silicon isotopes in cherts.

    Robert, François; Chaussidon, Marc


    The terrestrial sediment record indicates that the Earth's climate varied drastically in the Precambrian era (before 550 million years ago), ranging from surface temperatures similar to or higher than today's to global glaciation events. The most continuous record of sea surface temperatures of that time has been derived from variations in oxygen isotope ratios of cherts (siliceous sediments), but the long-term cooling of the oceans inferred from those data has been questioned because the oxygen isotope signature could have been reset through the exchange with hydrothermal fluids after deposition of the sediments. Here we show that the silicon isotopic composition of cherts more than 550 million years old shows systematic variations with age that support the earlier conclusion of long-term ocean cooling and exclude post-depositional exchange as the main source of the isotopic variations. In agreement with other lines of evidence, a model of the silicon cycle in the Precambrian era shows that the observed silicon isotope variations imply seawater temperature changes from about 70 degrees C 3,500 million years ago to about 20 degrees C 800 million years ago.

  9. Estimating the distribution of strontium isotope ratios (87Sr/86Sr in the Precambrian of Finland

    Lars Kaislaniemi


    Full Text Available A method to estimate the 87Sr/86Sr ratio of a rock based on its age and Rb/Sr ratio is presented. This method, together with data from the Rock Geochemical Database of Finland (n=6544 is used to estimate the 87Sr/86Sr ratios in the Precambrian of Finland and in its different major units. A generalization to cover the whole area of Finland is achieved by smoothing of estimation points. The estimation method is evaluated by comparing its results to published Rb-Sr isotope analyses (n=138 obtained on the Finnish Precambrian. The results show correspondence to different geological units of Finland,but no systematic difference between Archaean and younger areas is evident. Evaluation of the method shows that most of the estimates are reliable and accurate to be used as background material for provenance studies in archaeology, paleontology and sedimentology. However, some granitic rocks may have large (>1.0 % relative errors.Strontium concentration weighted average of the estimates differs only by 0.001 from the average 87Sr/86Sr ratio (0.730 of the rivers on the Fennoscandian shield.

  10. Origin and microfossils of the oil shale of the Green River formation of Colorado and Utah

    Bradley, W.H.


    The Green River formation of Colorado and Utah is a series of lakebeds of middle Eocene age that occupy two broad, shallow, simple, structural basins--the Piceance Creek basin in northwestern Colorado and the Uinta basin in northeastern Utah. The ancient lakes served as a basin for the accumulation of tremendous quantities of aquatic organisms. The predominance of microscopic fresh-water algae and protozoa over the remains of land plants, pollens and spores suggests that the greater part of the organic matter was derived from microorganisms that grew in the lakes. The pollens and spores were carried into the lakes by wind. Fish, mollusks, crustaceans, and aquatic insect larvae were also plentiful; and turtles, crocodiles, birds, small camels, and insects may have contributed to the organic matter. The ancient lakes apparently were shallow and had a large area, compared with depth. The abundance of organisms and the decaying organic matter produced a strongly reducing environment. Mechanical and chemical action, such as the mastication and digestion of the organic material by bottom-living organisms, caused disintegration of the original organic matter. When the residue was reduced to a gelatinous condition, it apparently resisted further bacterial decay, and other organisms accidently entombed in the gel were protected from disintegration. An accumulation of inorganic material occurred simultaneously with the disintegration of the organic ooze, and the entire mass became lithified. After most of the oil shale was deposited, the lake reverted nearly to the conditions that prevailed during its early stage, when the marlstone and low-grade oil shale of the basal member were formed. The streams in the vicinity of the lake were rejuvenated and carried great quantities of medium- to coarse-grained sand into the basin and formed a thick layer over the lakebeds.

  11. Anoxygenic growth of cyanobacteria on Fe(II) and their associated biosignatures: Implications for biotic contributions to Precambrian Banded Iron Formations

    Parenteau, M.; Jahnke, L. L.; Cady, S. L.; Pierson, B.


    Banded Iron Formations (BIFs) are widespread Precambrian sedimentary deposits that accumulated in deep ocean basins or shallow platformal areas with inputs of reduced iron (Fe(II)) and silica from deep ocean hydrothermal activity. There is debate as to whether abiotic or biotic mechanisms were responsible for the oxidation of aqueous Fe(II) and the subsequent accumulation of ferric iron (Fe(III)) mineral assemblages in BIFs. Biotic Fe(II) oxidation could have occurred indirectly as a result of the photosynthetic production of oxygen by cyanobacteria, or could have been directly mediated by anoxygenic phototrophs or chemolithotrophs. The anoxygenic use of Fe(II) as an electron donor for photosynthesis has also been hypothesized in cyanobacteria, representing another biotic mechanism by which Fe(II) could be oxidized in BIFs. This type of photoferrotrophic metabolism may also represent a key step in the evolution of oxygenic photosynthesis. Members of our group have speculated that an intermediate reductant such as Fe(II) could have acted as a transitional electron donor before water. The widespread abundance of Fe(II) in Archean and Neoproterozoic ferruginous oceans would have made it particularly suitable as an electron donor for photosynthesis. We have been searching for modern descendants of such an ancestral "missing link" cyanobacterium in the phototrophic mats at Chocolate Pots, a hot spring in Yellowstone National Park with a constant outflow of anoxic Fe(II)-rich thermal water. Our physiological ecology study of the Synechococcus-Chloroflexi mat using C-14 bicarbonate uptake and autoradiography experiments revealed that the cyanobacteria grow anoxygenically using Fe(II) as an electron donor for photosynthesis in situ. An initial set of similar experiments substituting C-13 bicarbonate as the tracer was used to characterize labeling of the community lipid biomarker signature and confirm the C-14 results. Under light conditions with and without Fe(II), the C

  12. Four magnetite generations in the Precambrian Varena Iron Ore deposit, SE Lithuania, as a result of rock-fluid interactions

    Skridlaite, Grazina; Prusinskiene, Sabina; Siliauskas, Laurynas


    Iron ores in Precambrian crystalline basement of the Varena area, SE Lithuania, were discovered during the detail geological-geophysical exploration in 1982-1992. They are covered with 210-500 m thick sediments. The Varena Iron Ore deposit (VIOD) may yield from 71 to 219.6 million tons of iron ore according to different economic evaluations (Marfin, 1996). They were assumed to be of metasomatic and hydrothermal origin, however several other hypotheses explaining the VIOZ origin, e.g. as a layered mafic or carbonatite intrusions were also suggested. Magnetites of the VIOD were thoroughly investigated by the Cameca SX100 microprobe at the Warsaw University and by the Quanta 250 Energy Dispersive Spectroscopy (EDS) at the Nature Research Centre in Vilnius, Lithuania. Four generations of magnetite were distinguished in the studied serpentine-magnetite ores (D8 drilling) and were compared with the earlier studied and reference magnetites. The earliest, spinel inclusion-rich magnetite cores (Mag-1) have the highest trace element contents (in wt%): Si (0.032), Al (0.167-0.248), Mg (0.340-0.405), Ti (0.215-0.254), V (0.090-0.138) etc. They might have formed during an early metamorphism and/or related skarn formation. Voluminous second magnetite (Mag-2) replacing olivine, pyroxenes, spinel and other skarn minerals at c. 540o C (Magnetite-Ilmenite geothermometer) has much lower trace element abundances, probably washed out by hydrothermal fluids. The latest magnetites (Mag-3 and Mag-4) overgrow the earlier ones and occur near or within the sulfide veins (Mag-4). As was observed from microtextures, the Mag-3 and Mag-4 have originated from the late thermal reworking by dissolution-reprecipitation processes. To imply an origin of the studied magnetites, they were compared to the earlier studied magmatic-metamorphic (1058 drilling), presumably skarn (982 drilling) magnetites from the studied area and plotted in the major magnetite ore type fields according to Dupuis and Beaudoin

  13. Helium and neon isotope geochemistry of some ground waters from the Canadian Precambrian Shield

    Bottomley, D. J.; Ross, J. D.; Clarke, W. B.


    Ground waters in a Precambrian granitic batholith at the Whiteshell Nuclear Research Establishment (WNRE) in Pinawa, Manitoba contain between 5 × 10 -5 and 10 -1 cc STP/g H 2O of radiogenic helium-4 but have relatively uniform 3He/ 4He ratios of between 0.6 × 10 -8 and 2.3 × 10 3. The highest helium samples also contain radiogenic 21,22Ne produced by (α, n) or ( n,α) reactions with other isotopes. As much as 1.8 × 10 -9ccSTP/ gH2O of excess 21Ne and 3.8 × 10 -9ccSTP/ gH2O of excess 22Ne have been measured. Helium and 21Ne ages of these ground waters, calculated on the basis of known crustal production rates of 4He and 21Ne, are unreasonably high (up to 2 × 10 5 years) and incompatible with the 14C ages and other isotopic and hydrogeologic data. Uranium enrichment in the flow porosity of the granite may dominate 4He and 21,22Ne production in this granite and mask the contributions from more typical U and Th concentrations in the rock matrix. At the Chalk River Nuclear Laboratories in Ontario helium concentrations in ground waters in a Precambrian monzonitic gneiss range from 1.5 × 10 -7 to 8.7 × 10 -4ccSTP/ gH2O with the 3He/ 4He ratios ranging from 2.0 × 10 -3 to 1.5 × 10 -7. The highest helium concentrations may be attributable to the presence of a thick uraniferous pegmatite vein and yield helium ages more than two orders of magnitude higher than the 14C ages. Application of He age dating equations to ground waters from Precambrian granitic rocks requires knowledge of the nature of uranium and thorium enrichment in the subsurface in order to select appropriate values for porosity and uranium and thorium concentration in the rock.

  14. The Dr H.M.E. Schürmann collection : Precambrian and other crystalline rocks and minerals

    Zwaan, J.C.


    The Dr H.M.E. Schürmann collection is stored at the National Museum of Natural History in Leiden, The Netherlands. It mainly consists of Precambrian rocks, but also includes other crystalline rocks and minerals, which were collected from all over the world. In order to provide a quick reference to

  15. Crustal structure of the Bighorn Mountains region: Precambrian influence on Laramide shortening and uplift in north-central Wyoming

    Worthington, Lindsay L.; Miller, Kate C.; Erslev, Eric A.; Anderson, Megan L.; Chamberlain, Kevin R.; Sheehan, Anne F.; Yeck, William L.; Harder, Steven H.; Siddoway, Christine S.


    The crustal structure of north-central Wyoming records a history of complex lithospheric evolution from Precambrian accretion to Cretaceous-Paleogene Laramide shortening. We present two active source P wave velocity model profiles collected as part of the Bighorn Arch Seismic Experiment in 2010. Analyses of these velocity models and single-fold reflection data, together with potential field modeling of regional gravity and magnetic signals, constrain crustal structure and thickness of the Bighorn region. We image a west dipping reflection boundary and model a sharp magnetic contact east of the Bighorn Arch that together may delineate a previously undetected Precambrian suture zone. Localized patches of a high-velocity, high-density lower crustal layer (the "7.× layer") occur across the study area but are largely absent beneath the Bighorn Arch culmination. Moho topography is relatively smooth with no large-scale offsets, with depths ranging from ~50 to 37 km, and is largely decoupled from Laramide basement topography. These observations suggest that (1) the edge of the Archean Wyoming craton lies just east of the Bighorn Mountains, approximately 300 km west of previous interpretations, and (2) Laramide deformation localized in an area with thin or absent 7.× layer, due to its relatively weak lower crust, leading to detachment faulting. Our findings show that Precambrian tectonics in northern Wyoming may be more complicated than previously determined and subsequent Laramide deformation may have been critically dependent on laterally heterogeneous crustal structure that can be linked to Precambrian origins.

  16. The Dr H.M.E. Schürmann collection : Precambrian and other crystalline rocks and minerals

    Zwaan, J.C.


    The Dr H.M.E. Schürmann collection is stored at the National Museum of Natural History in Leiden, The Netherlands. It mainly consists of Precambrian rocks, but also includes other crystalline rocks and minerals, which were collected from all over the world. In order to provide a quick reference to l

  17. How great was the Great Oxidation Event? Observations from the behavior of redox-sensitive elements in Precambrian glacial tillites

    Gaschnig, R. M.; Rudnick, R. L.; McDonough, W. F.


    The Great Oxidation Event (GOE) is considered a watershed event in the development of the Earth's biosphere, in which global atmospheric oxygen levels exceeded ~2 ppmv for the first time. This event occurred during the early Paleoproterozoic Huronian glacial interval and is defined by the disappearance of mass independent sulfur isotope fractionation. In the Huronian Supergroup in Ontario, this sulfur isotopic marker occurs between the lower two of the three glacial tillites present (Papineau et al., 2007). This implies that the youngest Huronian tillite (the Gowganda Formation) was deposited in a distinctively more oxic Earth surface environment. Here, we present data for redox sensitive transition metals in Precambrian glacial tillites, which indicate that oxic weathering of the continents remained insignificant in the immediate aftermath of the GOE, during the second half of the Huronian glaciation. Glacial tillites deposited around the world by continental ice sheets during the Mesoarchean (~2.9 Ga), Paleoproterozoic (~2.4-2.2 Ga), Neoproterozoic (~0.7-0.6 Ga), and Paleozoic (~0.3 Ga) were analyzed for their trace element compositions (n = 120). Mesoarchean and Paleoproterozoic tillites show significant differences from younger tillites in both absolute abundances of redox sensitive transition metals and abundances relative to elements with similar compatibilities. Transition metal abundances in all Mesoarchean and Paleoproterozoic tillites are either similar to or are higher than those in the average upper continental crust, whereas these elements are depleted in Neoproterozoic and younger tillites. Moreover, Mo, V and Cr are preferentially enriched in Mesoarchean and Paleoproterozoic tillites relative to elements of similar incompatibility, whereas a complementary depletion is seen in Neoproterozoic and younger tillites. We attribute these depletions of Mo, V, and Cr to their significantly enhanced solubility during weathering in the presence of an oxic

  18. Analysis of lineament swarms in a Precambrian metamorphic rocks in India

    Tapas Acharya; Sukumar Basu Mallik


    Addressing the geologic significance of lineaments and their correlation with joints/fractures is still unclear. The present study attempts to analyse the lineament swarms developed in a Precambrian metamorphic terrain in India using both unfiltered and filtered techniques. The unfiltered analysis technique shows that the major lineament and fracture trends are oriented along EW and NS directions respectively, thus failing to provide any correlation between them. The application of domain-based filtering techniques identifies a highly predominant fracture-correlated lineaments in mica schist constituting the EW trending shear zone in the area. This correlation is not evident in the areas north and south of the shear zone, where the lineaments are consistently oriented along the foliation planes of the rocks and are designated as ‘foliation correlated’. The present analysis indicates that the fracture frequency and the strain history may have played significant roles for the formation of fracture-correlated lineaments in the metamorphic terrain.

  19. Silicon isotope composition of diagenetic quartz: A record of Precambrian weathering

    Pollington, A. D.; Kozdon, R.; Valley, J. W.


    The genesis of quartz cements, which modify the porosity and permeability of many sedimentary rocks, is widely studied to determine the origin, flux, pathways and timing of water-rich fluids. Stable isotope ratios provide evidence of fluid/rock interactions. So called 'non-traditional stable isotope' ratios such as silicon may record processes such as chemical weathering, whereas aqueous fluid dominates the source of oxygen during precipitation. Silicon may be derived internally to a rock such as from pressure solution or recrystallization, or introduced by fluids. Silicon isotope ratios of diagenetic quartz reflect the source of dissolved chemical components; if δ30Si values of overgrowth quartz (OQ) and neighboring detrital quartz (DQ) are similar, the cations may be locally sourced from detrital grains. Alternatively, if the δ30Si of overgrowth quartz is significantly different than that of nearby detrital grains, then the silicon in those overgrowths is dominated by material derived from outside the formation. Here we present high-resolution in situ silicon isotope data, measured by secondary ion mass spectrometry from 10 μm spots, for the Mt Simon Sandstone, the basal Cambrian unit in the Midcontinent of North America. Silicon and oxygen isotope ratios have been measured in detrital quartz grains and quartz overgrowths from outcrops and deeply buried samples from drill core. Overgrowths from drill cores and most outcrops studied have δ30Si values close to 0‰ NBS-28, which is the same as values measured for adjacent detrital grains and δ18O values between 18 and 33‰ VSMOW, reflecting different temperatures of precipitation. However, in multiple samples from an outcrop on the Wisconsin Dome, adjacent to the Precambrian-Cambrian unconformity, quartz overgrowths have a wide range of δ30Si, with values as low as -5.4‰ and paired δ18O values as low as 18.5‰. Using the high spatial resolution afforded by SIMS analyses, we have measured isotopic

  20. Sampling of brine in cores of Precambrian granite from northern Illinois

    Couture, Rex A.; Seitz, Martin G.; Steindler, Martin J.


    The composition of groundwater in deep-seated rocks is of great interest, both geochemically and in connection with the disposal of radioactive waste. However, sampling of deep-seated groundwater is expensive and often difficult. We describe here a simple technique for the elution of pore fluid (groundwater) from cores of igneous rocks, and we describe brine eluted from a core of Precambrian granite from Northern Illinois drill hole UPH-3. The brine is predominantly NaCl and CaCl2, with a Ca/Na mole ratio of about 0.05 to 0.1. From analysis of soluble chloride in a crushed sample the chloride concentration in the pore water is estimated as 2.3 M. The brine is similar to brine in the Illinois Basin, and it was probably derived from the overlying sediments.

  1. Ore-Bearing Formations of the Precambrian in South China and Their Prospects

    HE Jurui; WANG Aiguo; RUI Xingjian; LI Chunhai


    In the Precambrian System of the Yangtze and Cathaysian plates six ore-bearing formations can be identified: the Cu-Pb-Zn-bearing formations in volcanic rocks of marine facies of the Neoarchean-Paleoproterozoic, CuAu-bearing formations and Pb-Zn-bearing formations in volcanic rocks of marine facies of the Mesoproterozoic, Pb-Znbearing formations in volcaniclastic rock and carbonate rock of the Neoproterozoic, Fe-Mn-bearing formations in the volcaniclastic rock of the Neoproterozoic, and Ni-Cr-serpentine-bearing formations in ophiolite and ultrabasic rock of the Meso- and Neoproterozoic. They were mostly formed in the marginal rift valleys of the Yangtze and Cathaysian plates,where occur stratabound and stratiform ore deposits, thermal deposits and porphyry polymetallic deposits. The six regions with ore-bearing formations have good prospects for ore deposits.

  2. Seismic anisotropy of Precambrian lithosphere: Insights from Rayleigh wave tomography of the eastern Superior Craton

    Petrescu, Laura; Darbyshire, Fiona; Bastow, Ian; Totten, Eoghan; Gilligan, Amy


    The thick, seismically fast lithospheric keels underlying continental cores (cratons) are thought to have formed in the Precambrian and resisted subsequent tectonic destruction. A consensus is emerging from a variety of disciplines that keels are vertically stratified, but the processes that led to their development remain uncertain. Eastern Canada is a natural laboratory to study Precambrian lithospheric formation and evolution. It comprises the largest Archean craton in the world, the Superior Craton, surrounded by multiple Proterozoic orogenic belts. To investigate its lithospheric structure, we construct a frequency-dependent anisotropic seismic model of the region using Rayleigh waves from teleseismic earthquakes recorded at broadband seismic stations across eastern Canada. The joint interpretation of phase velocity heterogeneity and azimuthal anisotropy patterns reveals a seismically fast and anisotropically complex Superior Craton. The upper lithosphere records fossilized Archean tectonic deformation: anisotropic patterns align with the orientation of the main tectonic boundaries at periods ≤110 s. This implies that cratonic blocks were strong enough to sustain plate-scale deformation during collision at 2.5 Ga. Cratonic lithosphere with fossil anisotropy partially extends beneath adjacent Proterozoic belts. At periods sensitive to the lower lithosphere, we detect fast, more homogenous, and weakly anisotropic material, documenting postassembly lithospheric growth, possibly in a slow or stagnant convection regime. A heterogeneous, anisotropic transitional zone may also be present at the base of the keel. The detection of multiple lithospheric fabrics at different periods with distinct tectonic origins supports growing evidence that cratonization processes may be episodic and are not exclusively an Archean phenomenon.

  3. Petrography and geochemistry of precambrian rocks from GT-2 and EE-1

    Laughlin, A.W.; Eddy, A.


    During the drilling of GT-2 and EE-1, 27 cores totaling about 35 m were collected from the Precambrian section. Samples of each different lithology in each core were taken for petrographic and whole-rock major- and trace-element analyses. Whole-rock analyses are now completed on 37 samples. From these data four major Precambrian units were identified at the Fenton Hill site. Geophysical logs and cuttings were used to extrapolate between cores. The most abundant rock type is an extremely variable gneissic unit comprising about 75% of the rock penetrated. This rock is strongly foliated and may range compositionally from syenogranitic to tonalitic over a few centimeters. The bulk of the unit falls within the monzogranite field. Interlayered with the gneiss is a ferrohastingsite-biotite schist which compositionally resembles a basaltic andesite. A fault contact between the schist and gneiss was observed in one core. Intrusive into this metamorphic complex are two igneous rocks. A leucocratic monzogranite occurs as at least two 15-m-thick dikes, and a biotite-granodiorite body was intercepted by 338 m of drill hole. Both rocks are unfoliated and equigranular. The biotite granodiorite is very homogeneous and is characterized by high modal contents of biotite and sphene and by high K/sub 2/O, TiO/sub 2/, and P/sub 2/O/sub 5/ contents. Although all of the cores examined show fractures, most of these are tightly sealed or healed. Calcite is the most abundant fracture filling mineral, but epidote, quartz, chlorite, clays or sulfides have also been observed. The degree of alteration of the essential minerals normally increases as these fractures are approached. The homogeneity of the biotite granodiorite at the bottom of GT-2 and the high degree of fracture filling ensure an ideal setting for the Hot Dry Rock Experiment.

  4. Isotopic and multi-proxy continental records in the Precambrian rocks, Aldan Shield, Russian Federation

    Guliy, Vasyl


    Clay minerals and hematite from paleo-weathering profiles, observed on and within Precambrian rocks of the apatite deposits, have been investigated from the view-points of geology, mineralogy, pedology. Weathering phenomena have been recognized in the Fedorovskaya and Gorbyliakhskaya Formations of the Precambrian Aldan Shield. Two complexes that differ in rock composition and structure are involved in the geological sections of the deposits. The lower complex (basement) is a stratum (up to 500m) of interlayered gneisses, schists and apatite-bearing carbonate and calc-silicate rocks. The upper complex (up to 200m) is a blanket-like residual deposit intensely crushed and strongly altered formations of the basement. Clay minerals (hydromica, vermiculite, chlorite, illite, and kaolinite) are predominantly developed in the upper complex of the deposits, whereas in the lower complex they occur dissipated as separate crystals and grains or concentrated in layers and nests mainly in the apatite-carbonate rocks. The carbonate rocks are typically medium-grained, massive, mottled or banded, and red-brown in color. Their oxidized character is expressed by high Fe3+/Fe2+ ratio. The banded structure is due to throughgoing bands a few millimeters to several decimeters in thickness. Some of the mottled rocks contain pocket-like isolation and thin beds rich in clay, hematite (after magnetite), and rounded apatite and seem to be of paleo-carstic origin. The isotopic data for the carbonates from coexisting poor and rich in clay minerals bands are similar to those under- and overlaying massive carbonates. It is consistent with the proposed model of simultaneous chemogenic and detrital deposition and intra-formational erosion during weathering processes.

  5. Oxygen isotope study of Precambrian granites from the Illinois Deep Hole Project

    Shieh, Yuch-Ning


    Seventeen whole rock samples and 27 mineral separates from the Precambrian granites in drill cores UPH-1, -2, and -3 have been analyzed. The δ180 values for quartz remain exceedingly uniform (δ =7.6-8.6‰) throughout the entire length of the three cores and are indicative of their primary igneous values. The δ180 for the feldspars are also uniform for samples located 70 m or deeper below the unconformity (δ =6.0-6.9‰) However, in the upper 70 m of the granite body, a gradual upward increase of δ180 in the feldspars is observed (to 8.8‰). Similarly Δ18 quartz-feldspar show typical plutonic values (1.4-2.1) in the main part of the Precambrian sections except in the upper 70 m, where ΔQ-F become progressively smaller upward until a reversed fractionation (negative ΔQ-F) is observed in samples several meters below the unconformity. The increase of δ180 in the feldspars is interpreted as a result of hydrothermal alteration of the granites at low temperatures (probably between 110°-260°C). The source of the hydrothermal fluid responsible for the alteration most likely derived from the formation waters in the upper Cambrian-Ordovician sedimentary rocks overlying the unconformity. The alteration occurred at least 135-200 m.y, ago when there was also a lead mobilization event. The relative low primary 18O/16O ratios in the granites suggest that the granites may have derived from partial melting of low -180 metamorphic rocks in the lower crust.

  6. Influence of Earth crust composition on continental collision style in Precambrian conditions: Results of supercomputer modelling

    Zavyalov, Sergey; Zakharov, Vladimir


    A number of issues concerning Precambrian geodynamics still remain unsolved because of uncertainity of many physical (thermal regime, lithosphere thickness, crust thickness, etc.) and chemical (mantle composition, crust composition) parameters, which differed considerably comparing to the present day values. In this work, we show results of numerical supercomputations based on petrological and thermomechanical 2D model, which simulates the process of collision between two continental plates, each 80-160 km thick, with various convergence rates ranging from 5 to 15 cm/year. In the model, the upper mantle temperature is 150-200 ⁰C higher than the modern value, while the continental crust radiogenic heat production is higher than the present value by the factor of 1.5. These settings correspond to Archean conditions. The present study investigates the dependence of collision style on various continental crust parameters, especially on crust composition. The 3 following archetypal settings of continental crust composition are examined: 1) completely felsic continental crust; 2) basic lower crust and felsic upper crust; 3) basic upper crust and felsic lower crust (hereinafter referred to as inverted crust). Modeling results show that collision with completely felsic crust is unlikely. In the case of basic lower crust, a continental subduction and subsequent continental rocks exhumation can take place. Therefore, formation of ultra-high pressure metamorphic rocks is possible. Continental subduction also occurs in the case of inverted continental crust. However, in the latter case, the exhumation of felsic rocks is blocked by upper basic layer and their subsequent interaction depends on their volume ratio. Thus, if the total inverted crust thickness is about 15 km and the thicknesses of the two layers are equal, felsic rocks cannot be exhumed. If the total thickness is 30 to 40 km and that of the felsic layer is 20 to 25 km, it breaks through the basic layer leading to

  7. Geology of Precambrian rocks and isotope geochemistry of shear zones in the Big Narrows area, northern Front Range, Colorado

    Abbott, Jeffrey T.


    Rocks within the Big Narrows and Poudre Park quadrangles located in the northern Front Range of Colorado are Precambrian metasedimentary and metaigneous schists and gneisses and plutonic igneous rocks. These are locally mantled by extensive late Tertiary and Quaternary fluvial gravels. The southern boundary of the Log Cabin batholith lies within the area studied. A detailed chronology of polyphase deformation, metamorphism and plutonism has been established. Early isoclinal folding (F1) was followed by a major period of plastic deformation (F2), sillimanite-microcline grade regional metamorphism, migmatization and synkinematic Boulder Creek granodiorite plutonism (1.7 b.y.). Macroscopic doubly plunging antiformal and synformal structures were developed. P-T conditions at the peak of metamorphism were probably about 670?C and 4.5 Kb. Water pressures may locally have differed from load pressures. The 1.4 b.y. Silver Plume granite plutonism was post kinematic and on the basis of petrographic and field criteria can be divided into three facies. Emplacement was by forcible injection and assimilation. Microscopic and mesoscopic folds which postdate the formation of the characteristic mineral phases during the 1.7 b.y. metamorphism are correlated with the emplacement of the Silver Plume Log Cabin batholith. Extensive retrograde metamorphism was associated with this event. A major period of mylonitization postdates Silver Plume plutonism and produced large E-W and NE trending shear zones. A detailed study of the Rb/Sr isotope geochemistry of the layered mylonites demonstrated that the mylonitization and associated re- crystallization homogenized the Rb87/Sr 86 ratios. Whole-rock dating techniques applied to the layered mylonites indicate a probable age of 1.2 b.y. Petrographic studies suggest that the mylonitization-recrystallization process produced hornfels facies assemblages in the adjacent metasediments. Minor Laramide faulting, mineralization and igneous activity

  8. EBSD characterization of pre-Cambrian deformations in conglomerate pebbles (Sierra de la Demanda, Northern Spain)

    Puelles, Pablo; Ábalos, Benito; Fernández-Armas, Sergio


    Pre-Cambrian and unconformable earliest Cambrian rocks from the Sierra de la Demanda (N Spain) exhibit field and microstructural relationships that attest to orogenic events recorded by concealed basement rocks. Neoproterozoic foliated slates ("Anguiano Schists") crop out under up to 300 m thick, unfoliated quartz-rich conglomerates ("Anguiano Conglomerates") and quartzites which are stratigraphically ca. 600 m below the oldest, paleontologically dated, pre-trilobitic Cambrian layers (likely older than 520 Ma). The Anguiano Conglomerates contain mm to cm grainsized well-rounded pebbles of various types including monocrystalline quartz, detrital zircon and tourmaline-bearing sandstones, black cherts and metamorphic poly-crystalline quartz aggregates. The undeformed matrix is made of much smaller (diagenetically overgrown) monocrystaline quartz grains and minor amounts of accesory zircon, tourmaline and mica. Black chert pebbles exhibit microstructural evidence of brittle deformation (microfaults and thin veins of syntaxial fibrous quartz). These and the fine-grained sandstone pebbles can also exhibit ductile deformations (microfolds with thickened hinges and axial planar continuous foliations), too. Polycrystalline quartz pebbles exhibit a variety of microstructures that resulted from syn-metamorphic ductile deformations. These are recognisable under the petrographic microscope and include continuous foliations, quartz shape fabrics, various types of subgrain or recrystallized new grain microtextures, and lattice preferred orientations (LPOs). Conventional characterization of quartz fabrics (after oriented structural sections) is challenged in conglomerate pebble thin sections by the difficulty of unraveling in them the complete structural reference framework provided by foliation (whose trace can be unraveled) and lineation orientation (which cannot be directly identified). Quartz in various metamorphic polycrystalline pebbles was studied with the Electron Back

  9. Study of fractures in Precambrian crystalline rocks using field technique in and around Balarampur, Purulia district, West Bengal, India

    Monalisa Mitra; Tapas Acharya


    Location of recharge zone in Precambrian crystalline rock is still unclear. The present study attempts to perform a detailed analysis of the joints/fractures developed in a Precambrian metamorphic terrain in and around Balarampur in Purulia district of West Bengal, India using bedrock data. The analysis shows that the orientations of major fracture trends are variable along with varying lithological units and structural affinities. The application of lithology-based analysis technique identifies highly predominant fracture frequency and fracture aperture in mica schist and phyllite in the area. This property is not evident in the granite gneiss and epidiorite. The moderate to high fracture permeability value is also associated with the fractures occurring in the shear zone. Mica schist and phyllite associated with the shear zone may represent a permeable recharge zone in the region.

  10. Aeromagnetic signatures of Precambrian shield and suture zones of Peninsular India

    Mita Rajaram; S.P. Anand


    In many Precambrian provinces the understanding of the tectonic history is constrained by limited exposure and aeromagnetic data provide information below the surface cover of sediments, water, etc. and help build a tectonic model of the region. The advantage of using the aeromagnetic data is that the data set has uniform coverage and is independent of the accessibility of the region. In the present study, available reconnaissance scale aeromagnetic data over Peninsular India are analyzed to understand the magnetic signatures of the Precambrian shield and suture zones thereby throwing light on the tectonics of the region. Utilizing a combination of differential reduction to pole map, analytic signal, vertical and tilt derivative and upward continuation maps we are able to identify magnetic source distribution, tectonic elements, terrane boundaries, suture zones and metamorphic history of the region. The mag-netic sources in the region are mainly related to charnockites, iron ore and alkaline intrusives. Our analysis suggests that the Chitradurga boundary shear and Sileru shear are terrane boundaries while we interpret the signatures of Palghat Cauvery and Achankovil shears to represent suture zones. Processes like metamorphism leave their signatures on the magnetic data:prograde granulites (charnockites) and retrograde eclogites are known to have high susceptibility. We find that charnockites intruded by alkali plutons have higher magnetization compared to the retrogressed charnockites. We interpret that the Dharwar craton to the north of isograd representing greenschist to amphibolite facies transition, has been subjected to metamorphism under low geothermal conditions. Some recent studies suggest a plate tectonic model of subductionecollisioneaccretion tectonics around the Palghat Cauvery shear zone (PCSZ). Our analysis is able to identify several west to east trending high amplitude magnetic anomalies with deep sources in the region from Palghat Cauvery shear to

  11. Mechanisms of iron-silica aqueous interaction and the genesis of Precambrian iron formation

    Chemtob, S. M.; Catalano, J. G.; Moynier, F.; Pringle, E. A.


    Iron formations (IFs), Fe- and Si-rich chemical sediments common in Precambrian successions, preserve key information about the compositional, biological, and oxidative evolution of the Precambrian ocean. Stable Si isotopes (δ30Si) of IF have been used to infer paleo-oceanic composition, and secular variations in δ30Si may reflect ancient biogeochemical cycles. The δ30Si of primary Fe-Si precipitates that formed IF depends not only on the δ30Si of aqueous silica but also on the precipitation mechanism. Multiple formation mechanisms for these primary precipitates are plausible. Aqueous Si may have adsorbed on newly precipitated iron oxyhydroxide surfaces; alternatively, Fe and Si may have coprecipitated as a single phase. Here we explore variations in the Si isotope fractionation factor (ɛ) with Fe-Si aqueous interaction mechanism (adsorption vs. coprecipitation). In adsorption experiments, sodium silicate solutions (pH 8.1, 125-2000 µM Si) were reacted with iron oxide particles (hematite, ferrihydrite, goethite, and magnetite) for 24 to 72 hours. Resultant solutions had δ30Si between 0 and +6‰. Calculated ɛ varied significantly with oxide mineralogy and morphology. For ferrihydrite, ɛ = -1.7‰; for hematite, ɛ = -2 to -5‰, depending on particle morphology. Apparent ɛ decreased upon surface site saturation, implying a smaller isotope effect for polymeric Si adsorption than monomeric adsorption. In coprecipitation experiments, solutions of Na-silicate and Fe(II) chloride (0.4-10 mM) were prepared anaerobically, then air-oxidized for 3 days to induce precipitation. At low Si concentrations, magnetite formed; near silica saturation, lepidocrocite and ferrihydrite formed. The Si isotope fractionation factor for coprecipitation was within the range of ɛ observed for adsorption (ɛ = -2.3 ± 1.0‰). These results indicate that the mechanism of Fe-Si interaction affects ɛ, presumably due to varying silicate coordination environments. These isotopic

  12. Aeromagnetic signatures of Precambrian shield and suture zones of Peninsular India

    Mita Rajaram


    Full Text Available In many Precambrian provinces the understanding of the tectonic history is constrained by limited exposure and aeromagnetic data provide information below the surface cover of sediments, water, etc. and help build a tectonic model of the region. The advantage of using the aeromagnetic data is that the data set has uniform coverage and is independent of the accessibility of the region. In the present study, available reconnaissance scale aeromagnetic data over Peninsular India are analyzed to understand the magnetic signatures of the Precambrian shield and suture zones thereby throwing light on the tectonics of the region. Utilizing a combination of differential reduction to pole map, analytic signal, vertical and tilt derivative and upward continuation maps we are able to identify magnetic source distribution, tectonic elements, terrane boundaries, suture zones and metamorphic history of the region. The magnetic sources in the region are mainly related to charnockites, iron ore and alkaline intrusives. Our analysis suggests that the Chitradurga boundary shear and Sileru shear are terrane boundaries while we interpret the signatures of Palghat Cauvery and Achankovil shears to represent suture zones. Processes like metamorphism leave their signatures on the magnetic data: prograde granulites (charnockites and retrograde eclogites are known to have high susceptibility. We find that charnockites intruded by alkali plutons have higher magnetization compared to the retrogressed charnockites. We interpret that the Dharwar craton to the north of isograd representing greenschist to amphibolite facies transition, has been subjected to metamorphism under low geothermal conditions. Some recent studies suggest a plate tectonic model of subduction–collision–accretion tectonics around the Palghat Cauvery shear zone (PCSZ. Our analysis is able to identify several west to east trending high amplitude magnetic anomalies with deep sources in the region from

  13. State of stress, permeability, and fractures in the Precambrian granite of northern Illinois

    Haimson, Bezalel C.; Doe, Thomas W.


    In situ fracture logging, permeability tests, and stress measurements have been conducted in UPH 3, a 1600-m-deep hole drilled into the Precambrian granitic basement of northern Illinois. Two major fracture zones are revealed, which cannot be discerned in UPH 2, a similarly deep hole about 1 km away. The segments of the UPH 3 core that were oriented indicate the existence of three sets of subvertical joints striking at N55°E, N40°W and E-W. These sets correspond to surface and shallow borehole joint directions in the Precambrian and Paleozoic rock of southern Wisconsin as well as other areas of the Midwest. The permeability values in UPH 3 display an overall reduction with depth from about 10-4 darcy at 700 m to 10-8-10-9 darcy at 1600 m. Permeability is highest in the zones of greatest fracturing, one of which occurs near the top of the granite and is probably related to fractures which were formed when the granite was at the surface in late Paleozoic times. Permeability reduction with depth is consistent with previous laboratory and field results in crystalline rocks. Hydrofracturing measurements in UPH 3 reveal a compressional stress field with the largest stress horizontal and oriented at N48°E (±30°). Based on linear regression of 13 test results in the depth range of 686-1449 m, the greatest horizontal stress has a magnitude of [20.5+(0.023×depth(m))] MPa. The least horizontal compression has a value of [8.7+(0.019×depth(m))] MPa. The vertical stress, based on density measurements, is given by [-1.3+(0.026xdepth(m))] MPa. Both magnitudes and directions support previous results in the technically stable Great Lakes region of the midcontinent. However, a mb = 4.4 earthquake did occur in 1972 some 90 km south of UPH 3, at a depth of 13 km. The focal mechanism solution revealed strike slip motion with the pressure axis horizontal and trending northeast, in accord with our measured stress directions and relative magnitudes but not predicted from a

  14. An REU Project on the Precambrian Rocks of Yellowstone National Park: Some lessons learned

    Henry, D.; Mogk, D. W.; Mueller, P. A.; Foster, D. A.


    An NSF-funded REU project (2011-2013), based in Yellowstone National Park (YNP), was designed to characterize the geology, geochemistry and geochronology of Precambrian rocks in northern YNP. Over two field seasons two cadres of 12 students (12 women and 12 men) were chosen from small-to-large state universities and private colleges. REU students participated in three major activities constituting a complete research experience: Field studies involved geologic mapping and sampling of Precambrian basement; formulation of testable research questions by smaller working groups; and mapping and sampling projects to address research questions; Analytical studies, sample preparation immediately followed field work with petrographic analysis at students' home institutions and a week-long visit to analytical laboratories to conduct follow-up studies by small research groups during the academic year (Univ. Florida - geochemistry and geochronology; Univ. Minnesota - EMPA analysis); Communicating results, each working group submitted an abstract and collectively presented 13 posters at the 2011 and 2012 GSA Rocky Mountain sectional meetings. We used directed discovery to engage students in a community of practice in the field and found that a long apprenticeship (2-3 weeks) is optimal for novice-master interactions in exploring natural setting. Initial group hikes were used to normalize methods and language of the discipline. Students developed a sense of ownership of the overall project and assumed personal responsibility for directed research projects. Training was provided to: guide students in selection and appropriate use of tools; develop sampling strategies; discuss communal ethics, values, and expectations; develop efficient work habits; stimulate independent thinking; and engage decision-making. It was important to scaffold the field experience to students' level of development to lead to mastery. Analytical activities were designed from rock to analysis so that each

  15. Carbon isotope discrepancy between precambrian stromatolites and their modern analogs: Inferences from hypersaline microbial mats of the sinai coast

    Schidlowski, Manfred


    The isotopic composition of organic carbon from extant stromatolite-type microbial ecosystems is commonly slanted toward heavy δ13 C values as compared to respective compositions of average organic matter (including that from Precambrian stromatolites). This seems the more enigmatic as the bulk of primary producers from benthic microbial communities are known to fix carbon via the C3 pathway normally entailing the sizable fractionations of the RuBP carboxylase reaction. There is reason to believe that the small fractionations displayed by aquatic microorganisms result from the limitations of a diffusion-controlled assimilatory pathway in which the isotope effect of the enzymatic reaction is largely suppressed. Apart from the diffusion-control exercised by the aqueous environment, transport of CO2 to the photosynthetically active sites will be further impeded by the protective slime (polysaccharide) coatings commonly covering microbial mats in which gas diffusivities are extremely low. Ineffective discrimination against13C becomes, however, most pronounced in hypersaline environments where substantially reduced CO2 solubilities tend to push carbon into the role of a limiting nutrient (brine habitats constitute preferential sanctuaries of mat-forming microbenthos since the emergence of Metazoan grazers ˜ 0.7 Ga ago). As the same microbial communities had been free to colonize normal marine environments during the Precambrian, the CO2 concentration effect was irrelevant to the carbon-fixing pathway of these ancient forms. Therefore, it might not surprise that organic matter from Precambrian stromatolites displays the large fractionations commonly associated with C3 photosynthesis. Increased mixing ratios of CO2 in the Precambrian atmosphere may have additionally contributed to the elimination of the diffusion barrier in the carbon-fixing pathways of ancient mat-forming microbiota.

  16. Phylogenomic Methods to Guide Paleontological Searches for the Early Cyanobacteria

    Blank, C. E.


    Phylogenomic methods can help paleontologists target their searches for early microbial microfossils and potentially help them better interpret the early fossil record. In this study, the deep-branching relationships in the cyanobacteria were resolved using whole genome sequences, multiple genes for taxa lacking genomes, and intein presence/absence in the DnaE protein. Once a framework tree was produced, characters were mapped onto the tree. Characters included morphology (unicellular vs. filamentous), habitat (marine vs. freshwater), metabolism (use of sulfide as electron donor, nitrogen fixation), presence/absence of complex morphological traits (akinetes, heterocysts, hormogonia), salt tolerance, and thermal tolerance. It was found that the earliest cyanobacteria were unicellular coccoids, with cell diameters cyanobacteria to freshwater deposits (lakes, streams) and to small diameter coccoids (not mats, not filaments). The earliest "cyanobacterial" microfossils (Eosynechococcus and Eoentophysalis) are large-diameter coccoids found in shallow marine platform carbonates. Because these cells have large diameters, if they were cyanobacteria one would also expect to see their sister taxa in the fossil record (i.e., large-diameter filamentous forms with sheaths, also akinetes). Because these are not found until 2.0 Ga (and akinetes until 1.5 Ga), this suggests that these earliest microfossils are not cyanobacteria. There are several instances in the cyanobacterial tree where ancestors with low salt tolerance gave rise to lineages that grow in brackish, marine, and/or hypersaline environments. This suggests that either the cyanobacteria first originated on continents and later colonized more saline environments, or that the cyanobacteria first originated in shallow "seas" that were not very saline but gradually became more saline by about 2.0 Ga. Because the continents were likely harsh environments (due to lack of an ozone layer and increased chemical and physical

  17. The Precambrian Structure of the Estancia Basin, Central New Mexico: New Seismic Images of the Mazatzal Province

    Elebiju, O. O.; Miller, K. C.; Andronicos, C. L.


    The Estancia Basin, located between the Manzano Mountains and Pedernal Hills, in central New Mexico, provides an excellent location for studying the effects of Proterozoic structural grain on subsequent Phanerozoic tectonic events. The Estancia Basin lies within the Proterozoic Mazatzal province. In recent years, the National Science Foundation Continental Dynamics Program within the Rocky Mountains Project, (CD-ROM) group has been examining the boundary between the two broad northeast-trending tectonically-mixed Paleoproterozoic terranes in New Mexico: the Yavapai province to the north and the Mazatzal province to the south. Reflection data collected as part of the CD-ROM effort image a portion of the Mazatzal province at a location 100 km east of the Estancia Basin. In an effort to contribute to a deeper understanding of the CD-ROM seismic image and regional Precambrian geology, we are analyzing ten seismic reflection profiles, well-logs, magnetic and gravity data from the Estancia basin area. The seismic data show numerous dipping reflections within the Precambrian basement that may represent prominent Precambrian ductile shear zones similar to those exposed in the adjacent Manzano Mountains and Pedernal Hills. An earlier study that focused on the Paleozoic evolution of the Estancia Basin, by Barrow and Keller (1994) also noted these same reflectors and that a prominent gravity low observed in the vicinity of the basin could not be fully explained by the Paleozoic geology. We present a new interpretation of these data.

  18. Phenotypic comparisons of consensus variants versus laboratory resurrections of Precambrian proteins.

    Risso, Valeria A; Gavira, Jose A; Gaucher, Eric A; Sanchez-Ruiz, Jose M


    Consensus-sequence engineering has generated protein variants with enhanced stability, and sometimes, with modulated biological function. Consensus mutations are often interpreted as the introduction of ancestral amino acid residues. However, the precise relationship between consensus engineering and ancestral protein resurrection is not fully understood. Here, we report the properties of proteins encoded by consensus sequences derived from a multiple sequence alignment of extant, class A β-lactamases, as compared with the properties of ancient Precambrian β-lactamases resurrected in the laboratory. These comparisons considered primary sequence, secondary, and tertiary structure, as well as stability and catalysis against different antibiotics. Out of the three consensus variants generated, one could not be expressed and purified (likely due to misfolding and/or low stability) and only one displayed substantial stability having substrate promiscuity, although to a lower extent than ancient β-lactamases. These results: (i) highlight the phenotypic differences between consensus variants and laboratory resurrections of ancestral proteins; (ii) question interpretations of consensus proteins as phenotypic proxies of ancestral proteins; and (iii) support the notion that ancient proteins provide a robust approach toward the preparation of protein variants having large numbers of mutational changes while possessing unique biomolecular properties. © 2014 Wiley Periodicals, Inc.

  19. The keystone species of Precambrian deep bedrock biosphere belong to Burkholderiales and Clostridiales

    Purkamo, L.; Bomberg, M.; Kietäväinen, R.; Salavirta, H.; Nyyssönen, M.; Nuppunen-Puputti, M.; Ahonen, L.; Kukkonen, I.; Itävaara, M.


    The bacterial and archaeal community composition and the possible carbon assimilation processes and energy sources of microbial communities in oligotrophic, deep, crystalline bedrock fractures is yet to be resolved. In this study, intrinsic microbial communities from six fracture zones from 180-2300 m depths in Outokumpu bedrock were characterized using high-throughput amplicon sequencing and metagenomic prediction. Comamonadaceae-, Anaerobrancaceae- and Pseudomonadaceae-related OTUs form the core community in deep crystalline bedrock fractures in Outokumpu. Archaeal communities were mainly composed of Methanobacteraceae-affiliating OTUs. The predicted bacterial metagenomes showed that pathways involved in fatty acid and amino sugar metabolism were common. In addition, relative abundance of genes coding the enzymes of autotrophic carbon fixation pathways in predicted metagenomes was low. This indicates that heterotrophic carbon assimilation is more important for microbial communities of the fracture zones. Network analysis based on co-occurrence of OTUs revealed the keystone genera of the microbial communities belonging to Burkholderiales and Clostridiales. Bacterial communities in fractures resemble those found from oligotrophic, hydrogen-enriched environments. Serpentinization reactions of ophiolitic rocks in Outokumpu assemblage may provide a source of energy and organic carbon compounds for the microbial communities in the fractures. Sulfate reducers and methanogens form a minority of the total microbial communities, but OTUs forming these minor groups are similar to those found from other deep Precambrian terrestrial bedrock environments.

  20. The Trans-Rocky Mountain Fault System - A Fundamental Precambrian Strike-Slip System

    Sims, P.K.


    Recognition of a major Precambrian continental-scale, two-stage conjugate strike-slip fault system - here designated as the Trans-Rocky Mountain fault system - provides new insights into the architecture of the North American continent. The fault system consists chiefly of steep linear to curvilinear, en echelon, braided and branching ductile-brittle shears and faults, and local coeval en echelon folds of northwest strike, that cut indiscriminately across both Proterozoic and Archean cratonic elements. The fault system formed during late stages of two distinct tectonic episodes: Neoarchean and Paleoproterozoic orogenies at about 2.70 and 1.70 billion years (Ga). In the Archean Superior province, the fault system formed (about 2.70-2.65 Ga) during a late stage of the main deformation that involved oblique shortening (dextral transpression) across the region and progressed from crystal-plastic to ductile-brittle deformation. In Paleoproterozoic terranes, the fault system formed about 1.70 Ga, shortly following amalgamation of Paleoproterozoic and Archean terranes and the main Paleoproterozoic plastic-fabric-producing events in the protocontinent, chiefly during sinistral transpression. The postulated driving force for the fault system is subcontinental mantle deformation, the bottom-driven deformation of previous investigators. This model, based on seismic anisotropy, invokes mechanical coupling and subsequent shear between the lithosphere and the asthenosphere such that a major driving force for plate motion is deep-mantle flow.

  1. The keystone species of Precambrian deep bedrock biosphere belong to Burkholderiales and Clostridiales

    L. Purkamo


    Full Text Available The bacterial and archaeal community composition and the possible carbon assimilation processes and energy sources of microbial communities in oligotrophic, deep, crystalline bedrock fractures is yet to be resolved. In this study, intrinsic microbial communities from six fracture zones from 180–2300 m depths in Outokumpu bedrock were characterized using high-throughput amplicon sequencing and metagenomic prediction. Comamonadaceae-, Anaerobrancaceae- and Pseudomonadaceae-related OTUs form the core community in deep crystalline bedrock fractures in Outokumpu. Archaeal communities were mainly composed of Methanobacteraceae-affiliating OTUs. The predicted bacterial metagenomes showed that pathways involved in fatty acid and amino sugar metabolism were common. In addition, relative abundance of genes coding the enzymes of autotrophic carbon fixation pathways in predicted metagenomes was low. This indicates that heterotrophic carbon assimilation is more important for microbial communities of the fracture zones. Network analysis based on co-occurrence of OTUs revealed the keystone genera of the microbial communities belonging to Burkholderiales and Clostridiales. Bacterial communities in fractures resemble those found from oligotrophic, hydrogen-enriched environments. Serpentinization reactions of ophiolitic rocks in Outokumpu assemblage may provide a source of energy and organic carbon compounds for the microbial communities in the fractures. Sulfate reducers and methanogens form a minority of the total microbial communities, but OTUs forming these minor groups are similar to those found from other deep Precambrian terrestrial bedrock environments.

  2. Isotopic characterization of the Precambrian carbonate aquifers under the city of Bangui (Central African Republic)

    Huneau, Frederic; Djebebe-Ndjiguim, Chantal-Laure; Foto, Eric; Ito, Mari; Celle-Jeanton, Helene; Garel, Emilie; Mabingui, Joseph


    The city of Bangui, the capital of the Central African Republic, is located on the right bank of the Ubangi River which is the northernmost tributary of the Congo River. From its foundation in 1889 this city has always suffered from serious problems of water management. This is related to the specificity of the site configuration (steep hills surrounding a large swampy flat valley poorly drained) and to the urbanisation process responsible for the waterproofing of soils and the associated increased runoff processes under tropical humid condition.This paper presents the results of a geochemical and isotopic survey carried out in 2011 aiming at evaluating the type and chemical quality of the groundwater resources of the Bangui region. By combining geological, hydrogeochemical and isotopic data it appears that the underground of Bangui seems favourable to the development of a secured and sustainable water supply from groundwater provided that the conditions of exploitation would be constrained by the local authorities. The deep fractured (and locally kastified) Precambrian carbonate aquifers known as Bimbo and Fatima formations are identified as target resources considering the relatively good quality of the resource from the chemical point of view, and the semi-confined structure of the aquifer preventing the mixing with shallow aquifers already strongly impacted by domestic and industrial pollutions.

  3. Precambrian paleontology and acrochrons of the biosphere evolution: On the theory of the expanding biosphere

    Sokolov, B. S.


    What is pre-life? We have no idea, since it is hidden in chemical molecules that conceal its future genetic potential. From the biological standpoint, a prokaryotic cyanobacteria cell represents a culmination of biochemical evolution. Its appearance on the Earth marked the starting point of the formation of the first biogeocoenosis on the planet, i.e., the onset of its biosphere. After having started, approximately 4.0-3.7 Ga ago, biosphere evolution has continued uninterrupted on the Earth. Its whole course is reflected in the geochronological record of the stratisphere, the stratified shell of the Earth. In the stratigraphic sense, this record comprises the Archean, Proterozoic (i.e., Karelian and Riphean), and Phanerozoic (i.e., Paleozoic, Mesozoic, and Cenozoic). They correspond to acrochrons, i.e., the main stages in biosphere evolution. According to the Precambrian paleontology, the first three acrochrons represent a pre-Vendian stage in the evolution of unicellular prokaryotic and eukaryotic organisms that terminated in the Riphean with the appearance of their colonial communities. The true metacellular structure of tissue Metaphyta and Metazoa started forming only in the Late Neoproterozoic (Late Riphean). The Vendian Period was marked by a radiation of macrotaxonomic diversity with the appearance of the main multicellular types of the Phanerozoic organization level. Therefore, the last acrochron (lasting from approximately 650 Ma ago) should be considered as corresponding to the Vendian-Phanerozoic period. The Cambrian explosion corresponds to the mass expansion of skeletal Metazoa.

  4. Age and significance of Precambrian Basement Samples from northern Illinois and adjacent states

    Hoppe, W. J.; Montgomery, C. W.; van Schmus, W. R.


    Geochronologic results are reported for 12 localities where deep drilling has penetrated Precambrian basement in Iowa, Illinois, Indiana, Michigan, and Kentucky. For the northern Illinois deep drill holes UPH 1 and UPH 3, a zircon U-Pb age of 1463±10 m.y. was obtained. Rb-Sr data for these samples indicate mild disturbance of this system but are not interpreted in terms of any specific younger event. U-Pb ages for other localities fall in the interval 1450-1510 m.y. and indicate that this was a major period of igneous activity throughout the southern Great Lakes region. Rb-Sr results indicate that alteration was ubiquitous and that most ages in the range 1100-1400 m.y. probably represent disturbed systems. The results obtained so far tend to support interpretations in which Kentucky, Indiana, and Illinois are primarily underlain by a rhyolite and epizonal granite terrane that is 1450-1500 m.y. old; older Proterozoic rocks may be absent or more deeply buried.

  5. Is the outcrop topology of dolerite dikes of the Precambrian Singhbhum Craton fractal?

    Nibir Mandal; Atin Kumar Mitra; Santanu Misra; Chandan Chakraborty


    In the Precambrian Singhbhum Craton of eastern India, newer dolerite dikes occur profusely with varying outcrop lengths. We have analysed the nature of their length-size and orientation distributions in relation to the theory of fractals. Two orientational sets of dikes (NW–SE and NE–SW) are present. Both the sets show strongly non-power-law size distributions, as reflected in nonlinear variations in logarithmic space. We analyzed thousands of data, revealing that polynomial functions with a degree of 3 to 4 are the best representatives of the non-linear variations. Orientation analysis shows that the degree of dispersions from the mean trend tends to decrease with increasing dike length. The length-size distributions were studied by simulating fractures in physical models. Experimental fractures also show a non-power-law distribution, which grossly conforms to those of the dolerite dikes. This type of complex size distributions results from the combined effects of nucleation, propagation and coalescence of fractures.

  6. Microbial co-occurrence patterns in deep Precambrian bedrock fracture fluids

    Purkamo, Lotta; Bomberg, Malin; Kietäväinen, Riikka; Salavirta, Heikki; Nyyssönen, Mari; Nuppunen-Puputti, Maija; Ahonen, Lasse; Kukkonen, Ilmo; Itävaara, Merja


    The bacterial and archaeal community composition and the possible carbon assimilation processes and energy sources of microbial communities in oligotrophic, deep, crystalline bedrock fractures is yet to be resolved. In this study, intrinsic microbial communities from groundwater of six fracture zones from 180 to 2300 m depths in Outokumpu bedrock were characterized using high-throughput amplicon sequencing and metagenomic prediction. Comamonadaceae-, Anaerobrancaceae- and Pseudomonadaceae-related operational taxonomic units (OTUs) form the core community in deep crystalline bedrock fractures in Outokumpu. Archaeal communities were mainly composed of Methanobacteriaceae-affiliating OTUs. The predicted bacterial metagenomes showed that pathways involved in fatty acid and amino sugar metabolism were common. In addition, relative abundance of genes coding the enzymes of autotrophic carbon fixation pathways in predicted metagenomes was low. This indicates that heterotrophic carbon assimilation is more important for microbial communities of the fracture zones. Network analysis based on co-occurrence of OTUs revealed possible "keystone" genera of the microbial communities belonging to Burkholderiales and Clostridiales. Bacterial communities in fractures resemble those found in oligotrophic, hydrogen-enriched environments. Serpentinization reactions of ophiolitic rocks in Outokumpu assemblage may provide a source of energy and organic carbon compounds for the microbial communities in the fractures. Sulfate reducers and methanogens form a minority of the total microbial communities, but OTUs forming these minor groups are similar to those found in other deep Precambrian terrestrial bedrock environments.

  7. Crustal uplift of the Precambrian cratons due to metamorphism in crustal rocks under infiltration of mantle fluids

    Artyushkov, Eugene; Chekhovich, Peter; Korikovsky, Sergey; Massonne, Hans-Joachim


    Precambrian cratons cover about 70% of the total area of the continents. During the last several million years cratonic areas underwent rapid uplift, from 100-200 m in East Europe to 1000-1500 m Southern Africa. Shortening of the Precambrian crust terminated half a billion years ago or earlier and this popular mechanism cannot be applied to its recent uplift. Large thickness of cratonic mantle lithosphere, 100-200 km in most regions, together with its low density precludes delamination of this layer and magmatic underplating as possible causes of recent uplift. It cannot be precluded that in some cratonic regions recent uplift occurred due to delamination of the lower part of mantle lithosphere with the density increased by metasomatism. Even a small uplift of ≥ 100-200 m would require delamination of a thick layer of mantle lithosphere. As a result a temperature drop of > 200 C would arise at the base of the lithosphere producing a shear wave velocities drop of > 2%. According to the seismic tomography data such a drop in VS is observed only in some regions with the Precambrian lithosphere, e.g., in Northeastern Africa. Spatial distribution of the Precambrian cratons is quite different from that predicted by the main models of dynamic topography in the mantle. Moreover, many uplifted blocks are bounded by steep slopes hundreds of meters to one kilometer high and only tens of kilometers wide. Such slopes could not have been formed by bending of thick cratonic lithosphere under the forces acting from below. Their recent formation indicates rock expansion within the crust at shallow depth comparable with the slope width. Rocks formed at the pressure P ˜ 0.5-1.0 GPa are widespread on the Precambrian cratons. This indicates that during their lifetime a layer of rocks ˜ 15-30 km thick has been removed from the crustal surface by denudation. As a result rocks which were initially located in the lower crust emerged to the middle or upper crust. Due to metamorphic

  8. Thermal-mechanical Numerical Models of Evolution For Different Precambrian Collisional Zones

    Parphenuk, O.

    Precambrian continental shields such as the Anabar, Baltic and Canadian, are the structurally stable areas for at least the last 1.6 Ga. Deeply eroded structures of the shields formed in the process of multistage tectonic evolution including horizontal shortening and collision by overthrusting expose at the surface middle to the lower crustal rocks uplifted along the faults from the depths 20-40 km. Thermal-mechanical model of horizontal shortening and continental crust formation in collisional zones is developed and applied to the modelling of thermal and dynamic evolution of different Archean and Proterozoic structures. The thermal structure of the lithosphere subjected to compression and shortening resulted in crustal thickening determines in large scale the further tectonic and thermal evolution of collisional zones. The lithospheric exten- sion in orogenic structures can be the possible reaction to the increase of vertical stress due to the uplift and crustal roots formation. But the number of examples exist of the areas which did not experience post-orogenic extension: the collisional structures of the Anabar Shield, the Kapuskasing structural zone of the Canadian Shield etc. The numerical modelling of the process of brittle overthrusting in the upper crust and the lower crustal viscous flow demonstrated the possibility of different structural forma- tions with thickened upper crust, uplift at the surface and progressively increasing erosion level of the rocks exumated from different depths. The thermal and rheolog- ical conditions are discussed for the formation and preservation of crustal roots. The topography of the uplift and crustal roots strongly depends on the number of param- eters, the most important of which are the viscosity values and contrast for the lower crust and lithospheric upper mantle, the initial dip angle of fault, the rate of shortening and erosion, the thermal regime of the region.

  9. Iodine-to-calcium ratios in carbonates suggest a primary origin for the Precambrian Lomagundi and Shuram carbon isotope excursions

    Hardisty, D. S.; Lu, Z.; Planavsky, N. J.; Osburn, M. R.; Bekker, A.; Lyons, T. W.


    Systematic increases in iodine-to-calcium ratios (I/Ca) in carbonates from both the Precambrian Lomagundi and Shuram carbonate carbon isotope (δ13Ccarb) excursion intervals suggest primary origins for these events. Iodate (IO3-), the oxidized iodine species, is the exclusive species incorporated into carbonates. The high redox sensitivity of IO3- to deoxygenation requires highly oxidizing fluids for IO3- production, making I/Ca in platform carbonates a simple indicator of the presence of oxidizing fluids in the surface ocean. Similarly, redox sensitivity makes the proxy host susceptible to diagenetic iodine loss during carbonate recrystallization in reducing pore fluids. Recent work has shown carbonates to experience near-complete iodine loss during dolomitization in the Permian, and work from our group evaluating modern and recent carbonates demonstrate the potential for diagenetic iodine loss during carbonate recrystallization. In some cases, however, such as meteoric aragonite-to-calcite transitions, oxidizing pore fluids have the potential to buffer IO3- concentrations, causing negligible alteration to primary I/Ca despite negative shifts in δ13Ccarb. These results highlight that diagenetic alterations to I/Ca and δ13Ccarb need not always be coupled, but importantly, no observed scenario promotes post-depositional addition of iodine to carbonates. This means that, independent of δ13Ccarb, systematic, stratigraphic increases in I/Ca ratios observed in the carbonate record are most easily interpreted as resulting from depositional controls such as surface ocean redox or shifts in the total marine iodine reservoir. From this, increasing I/Ca ratios coincident with rising and falling δ13Ccarb trends for the Paleoproterozic Lomagundi and Neoproterozoic Shuram events, respectively, support suggestions of a primary origin for the δ13Ccarb excursions. Significant increase in I/Ca in dolomites deposited during the Lomagundi excursion, rising from blank values in

  10. Laboratory Simulation of an Iron(II)-rich Precambrian Marine Upwelling System to Explore the Growth of Photosynthetic Bacteria.

    Maisch, Markus; Wu, Wenfang; Kappler, Andreas; Swanner, Elizabeth D


    A conventional concept for the deposition of some Precambrian Banded Iron Formations (BIF) proceeds on the assumption that ferrous iron [Fe(II)] upwelling from hydrothermal sources in the Precambrian ocean was oxidized by molecular oxygen [O2] produced by cyanobacteria. The oldest BIFs, deposited prior to the Great Oxidation Event (GOE) at about 2.4 billion years (Gy) ago, could have formed by direct oxidation of Fe(II) by anoxygenic photoferrotrophs under anoxic conditions. As a method for testing the geochemical and mineralogical patterns that develop under different biological scenarios, we designed a 40 cm long vertical flow-through column to simulate an anoxic Fe(II)-rich marine upwelling system representative of an ancient ocean on a lab scale. The cylinder was packed with a porous glass bead matrix to stabilize the geochemical gradients, and liquid samples for iron quantification could be taken throughout the water column. Dissolved oxygen was detected non-invasively via optodes from the outside. Results from biotic experiments that involved upwelling fluxes of Fe(II) from the bottom, a distinct light gradient from top, and cyanobacteria present in the water column, show clear evidence for the formation of Fe(III) mineral precipitates and development of a chemocline between Fe(II) and O2. This column allows us to test hypotheses for the formation of the BIFs by culturing cyanobacteria (and in the future photoferrotrophs) under simulated marine Precambrian conditions. Furthermore we hypothesize that our column concept allows for the simulation of various chemical and physical environments - including shallow marine or lacustrine sediments.

  11. Stratigraphic and microfossil evidence for a 4500-year history of Cascadia subduction zone earthquakes and tsunamis at Yaquina River estuary, Oregon, USA

    Graehl, Nicholas A; Kelsey, Harvey M.; Witter, Robert C.; Hemphill-Haley, Eileen; Engelhart, Simon E.


    The Sallys Bend swamp and marsh area on the central Oregon coast onshore of the Cascadia subduction zone contains a sequence of buried coastal wetland soils that extends back ∼4500 yr B.P. The upper 10 of the 12 soils are represented in multiple cores. Each soil is abruptly overlain by a sandy deposit and then, in most cases, by greater than 10 cm of mud. For eight of the 10 buried soils, times of soil burial are constrained through radiocarbon ages on fine, delicate detritus from the top of the buried soil; for two of the buried soils, diatom and foraminifera data constrain paleoenvironment at the time of soil burial.We infer that each buried soil represents a Cascadia subduction zone earthquake because the soils are laterally extensive and abruptly overlain by sandy deposits and mud. Preservation of coseismically buried soils occurred from 4500 yr ago until ∼500–600 yr ago, after which preservation was compromised by cessation of gradual relative sea-level rise, which in turn precluded drowning of marsh soils during instances of coseismic subsidence. Based on grain-size and microfossil data, sandy deposits overlying buried soils accumulated immediately after a subduction zone earthquake, during tsunami incursion into Sallys Bend. The possibility that the sandy deposits were sourced directly from landslides triggered upstream in the Yaquina River basin by seismic shaking was discounted based on sedimentologic, microfossil, and depositional site characteristics of the sandy deposits, which were inconsistent with a fluvial origin. Biostratigraphic analyses of sediment above two buried soils—in the case of two earthquakes, one occurring shortly after 1541–1708 cal. yr B.P. and the other occurring shortly after 3227–3444 cal. yr B.P.—provide estimates that coseismic subsidence was a minimum of 0.4 m. The average recurrence interval of subduction zone earthquakes is 420–580 yr, based on an ∼3750–4050-yr-long record and seven to nine interearthquake

  12. Petrochemical Characteristics and Age of Rare Metal (Ta-Nb Mineralization in Precambrian Pegmatites, Komu, Nigeria



    Full Text Available The Precambrian pegmatites of Komu area intrude semi discordantly older rock types, such as biotite gneiss, amphibolites and pelitic schists. The pegmatites occur as near flat lying bodies. This study aims at elucidating the geological setting, petrography, geochemical features and age of mineralization of these pegmatite bodies, with a view to classifying them and knowing their economic potential. The petrographic analysis shows that the pegmatite samples contain mainly quartz (35%, plagioclase (15%, microcline (10% and muscovite (12% with accessories like tourmaline, tantalum, niobium and illmeno-rutiles. Geochemical analysis of the muscovites extracted from pegmatites show that these rocks are enriched in silica (>60% and Al2O3 (>12% and depleted in Fe2O3, MgO and TiO2. Trace element analysis shows that the pegmatites contain rare metals with moderately high Ta, Nb, Sn, Rb, Li and Cs values and depleted in Ti, Ba and Zr. Elemental ratios indicate low ratios of K/Cs, Th/U and K/Rb. Variation plots of Ta/(Ta+Nb versus Mn/ (Mn+Fe show that the pegmatites plot in the complex (beryl subtype field. The Na/K versus Sn, Nb, Rb variation plots show that the pegmatites of Komu area are mineralized and compare favourably with those of other mineralized pegma-tite areas like Egbe and Ijero in southwestern Nigeria. The variation plots of Ta versus K/Cs, and Ta/W versus Cs, also confirm rare metal mineralization of Komu pegmatites, which plot over the mineralized line of Beus and Gordiyenko. The K/Rb versus Rb, Cs and Sn plots indicate low K/Rb ratios indicating moderate differentiation. The Rare Earth Elements (REE show high heavy REE values and lower light REE values with prominent positive Ce anomaly and negative Eu anomaly from normalized chondrite plots. K/Ar dating of the age of mineralization of muscovites extracted from the pegmatite yielded late Pan-African ages between 502.8±13Ma and 514.5±13.2Ma. This period represents the cooling ages of the

  13. Abiogenic and Microbial Controls on Volatile Fatty Acids in Precambrian Crustal Fracture Waters

    McDermott, J. M.; Heuer, V.; Tille, S.; Moran, J.; Slater, G.; Sutcliffe, C. N.; Glein, C. R.; Hinrichs, K. U.; Sherwood Lollar, B.


    Saline fracture waters within the Precambrian Shield rocks of Canada and South Africa have been sequestered underground over geologic timescales up to 1.1-1.8 Ga [1, 2]. These fluids are rich in H2 derived from radiolysis and hydration of mafic and ultramafic rocks [1, 2, 3] and host a low-biomass, low-diversity microbial ecosystem at some sites [2]. The abiogenic or biogenic nature of geochemical processes has important implications for bioavailable carbon sources and the role played by abiotic organic synthesis in sustaining a chemosynthetic deep biosphere. Volatile fatty acids (VFAs) are simple carboxylic acids that may support microbial communities in such environments, such as those found in terrestrial [4] and deep-sea [5] hot springs. We present abundance and δ13C analysis for VFAs in a spectrum of Canadian Shield fluids characterized by varying dissolved H2, CH4, and C2+ n-alkane compositions. Isotope mass balance indicates that microbially mediated fermentation of carbon-rich graphitic sulfides may produce the elevated levels of acetate (39-273 μM) found in Birchtree and Thompson mine. In contrast, thermodynamic considerations and isotopic signatures of the notably higher acetate (1.2-1.9 mM), as well as formate and propionate abundances (371-816 μM and 20-38 μM, respectively) found at Kidd Creek mine suggest a role for abiogenic production via reduction of dissolved inorganic carbon with H2 for formate, and oxidation of C2+ n-alkanes for acetate and propionate, along with possible microbial cycling. VFAs comprise the bulk of dissolved and total organic carbon in the mines surveyed, and as such represent a potential key substrate for life. [1] Holland et al. (2013) Nature 497: 367-360. [2] Lin et al. (2006) Science 314: 479-482. [3] Sherwood Lollar et al. (2014) Nature 516: 379-382. [4] Windman et al. (2007) Astrobiology 7(6): 873-890. [5] Lang et al. (2010) Geochim. Cosmochim. Acta 92: 82-99.

  14. Carbon isotope fluctuations in Precambrian carbonate sequences of several localities in Brazil



    Full Text Available Carbon isotope fluctuations in Precambrian sedimentary carbonates between 2.8 Ga and 0.60 Ga in Brazil are examined in this study. The carbonate facies of the BIF of the 2.8 Ga-old Carajás Formation, state of Pará in northern Brazil, has rather homogeneous delta13C (-5 o/ooPDB, compatible with carbonatization of a silicate protolith by a CO2-rich fluid from mantle degassing. The Paleoproterozoic Gandarela Formation, state of Minas Gerais, displays a narrow delta13C variation (-1.5 to +0.5 o/oo compatible with carbon isotope signatures of carbonates deposited around 2.4 Ga worldwide. The Fecho do Funil Formation has probably recorded the Lomagundi delta13C positive anomaly (+6.4 to +7.1 o/ooPDB. The magnesite-bearing carbonates of the Orós mobile belt, state of Ceará, exhibit carbon isotope fluctuation within the range for carbonates deposited at 1.8 Ga. The C-isotope record of the Frecheirinha Formation, northwestern state of Ceará, shows negative delta13C values in its lower portion (-2 o/oo and positive values up section (+1 to +3 o/oo, which suggests this sequence is a cap carbonate deposited after a glacial event around 0.95 Ga. The Jacoca and Acauã sedimentary carbonate Formations, state of Sergipe, NE Brazil, show carbon isotope fluctuations very similar to each other (average around -5 o/oo, compatible with a deposition around 0.76 Ga. The younger Olho D'Água carbonate Formation, however, also in the state of Sergipe, displays negative delta13C values at the lower portion of the Formation, changing dramatically up section to positive values as high as +10 o/oo, a characteristic compatible with a Sturtian cap carbonate deposited around 0.69 Ga. On the light of the C isotope data discussed in this study, it seems that delta13C fluctuations in Paleoproterozoic carbonates in Brazil are within the range found globally for metasedimentary carbonates of this age. Carbon isotope data proved to be very useful in establishing relative

  15. Chemostratigraphies of carbon, oxygen and strontium isotopes and oxygen contents across the Precambrian-Cambrian boundary

    Komiya, T.; Sawaki, Y.; Ishikawa, T.


    The Precambrian-Cambrian (PC-C) boundary is one of the most important intervals for evolution of life. However, the scarcity of well-preserved outcrops through the boundary makes it ambiguous to decode change of the surface environment and biological evolution. In south China, strata through the PC-C boundary are continuously exposed and contain many fossils, suitable for study of environmental and biological change. In addition, we conducted excavations at four sites of Three Gorge area to obtain continuous and fresh samples. We measured the delta13C, delta18O and 87Sr/86Sr values of the drill core samples and REE compositions of fresh carbonate rocks, respectively. We identified two positive and two negative isotope excursions of delta13Ccarb within this interval: a moderate increase from 0 to +2 permil and a subsequent dramatic drop to -7 permil at the PC-C boundary, and a continuous increase to +5 permil at the upper part of the Nemakit-Daldynian (ND) stage and the subsequent sharp decrease to -9 permil just below the basal Tommotian unconformity, respectively. The continuous pattern of the delta13C shift is irrespective of lithotype and is comparable to fragmented records of other sections within and outside of the Yangtze Platform, indicating that the profile represents global change of seawater chemistry. A chemostratigraphy of 87Sr/86Sr ratios of the drilled samples also displays a smooth curve and its large positive anomaly just below the PC-C boundary. The estimate of oxygen content of seawater from REE composition of carbonate minerals shows significant decreases around PC-C and ND-Tommotian boundaries, respectively. The combination of chemostratigraphies of delta13C, 87Sr/86Sr and pO2 indicates that the 87Sr/86Sr excursions preceded the delta13C negative excursion at PC-C boundary, and suggests that global regression or formation of the Gondwana supercontinent, evident in increase of influx of continental materials, caused biological depression together

  16. New material of microfossils from the Ediacaran Doushantuo Formation in the Zhangcunping area,Yichang, Hubei Province and its zircon SHRIMP U-Pb age

    LIU PengJu; YIN ChongYu; GAO LinZhi; TANG Feng; CHEN ShouMing


    The Zhangcunping area is located at the north limb of the Huangling anticline in Yichang, Hubei Province. Here, the sedimentary succession of the Ediacaran Doushantuo Formation is similar with that in the Weng'an area, Guizhou Province. A large number of new microfossils (mainly acanthoacritarchs) from the Doushantuo Formation in this area are reported in this paper. The fossil assemblage shows similarity as the phosphatized biota of the Doushantuo Formation at Wang'an, Guizhou Province and the silicified biota of the Doushantuo Formation at the Yangtze Gorges, which suggests that the Zhangcunping area is a key for correlation of the Doushantuo Formation between the Weng'an area,Guizhou Province and the Yangtze Gorges. Besides, a new zircon SHRIMP U-Pb age (614.0±7.6 Ma) is first obtained from a horizon underneath the exposed surface in the middle of the Doushantuo Formation in the Zhangcunping area. This age not only provides a new datum for subdivision of the Ediacaran Doushantuo Formation, but also indicates that the age of the exposed surface in the middle of the Doushantuo Formation in the Yangtze Platform should be posterior to 614.0±7.6 Ma. Due to the horizon of the Weng'an biota situated above the exposed surface, the age of the Wang'an biota should be posterior to 614.0±7.6 Ma as well.

  17. 植物微体遗存分析在第四纪环境研究中的应用:综述与展望%Application of plant microfossils in Quaternary environmental research:a review and perspective

    张继效; 徐海


    以孢粉、植硅体等为代表的植物微体遗存由于其分布广泛,容易保存,可反映母体植物类型的优点,在第四纪环境研究中得到了广泛应用。本文介绍了植物微体遗存的概念、常见类型,以及它们的提取方法和原理,综述了利用植物微体遗存重建古环境的传统方法和近年来发展的几种古植被与古气候定量重建方法,最后简述了植物微体遗存在年代测定、稳定同位素分析研究上的应用进展与实例。文末指出了现有研究方法的问题与不足,并对今后的多代用指标的综合研究提出了展望。%Background, aim, and scope Plant microfossils, such as sporopollen, phytoliths, starch grains and charcoals, have been widely used in Quaternary environmental research due to their features of huge quantity, wide distribution and easy preservation. However, review articles on plant microfossils in China so far have not been systematic and comprehensive enough. In this paper, key types, extraction methods and application examples in Quaternary environmental research of plant microfossils are reviewed and analyzed, and the prospects on integrated multi-proxy studies are proposed.Materials and methods Ferns spores and pollen of seed plants are collectively referred to as sporopollen, and they can be identiifed and categorized in different parent plants by comparing their morphologies. By analyzing the types and composition ratios of sporopollen in sedimentary strata, the vegetation composition, precipitation and temperature in the historical period may become available. Some plants such as grasses can form a type of silica-plant microfossils called phytolith, which can be preserved in the soil after its death. Different plants can form distinct or similar forms of phytolith, so phytolith can also be used in Quaternary research. Similarly, starch grains of different plants have their own characteristics and are a basis for the


    李勇; 张兴亮; 郭俊峰; 丁莲芳; 韩健; 舒德干


    在用醋酸浸泡处理采自贵州瓮安新元古代陡山沱组磷酸质岩石样品时,获得大量微体动物骨骼化石.文中重点报道部分管柱状微体化石,即:Sinoquadraticus poratus gen. et sp. nov.和 Sinoquadraticus wenganensis gen. et sp. nov..并对Sinocyclocylicus的部分特征进行补充.%In 1992 Xue et al. reported some skeletal fossils, including one genus and two species, from the Neoprotorozoic Doushantuo Formation at Weng'an, Guizhou, and assigned them to Echinodermata. In this paper, new materials of phosphatized cylindrical and tabulate microfossils, including a new genus and two new species, are described from the same layer and locality. It provides us much more evidence not only to display the Neoproterozoic biodiversity, but also to explore the origin and the early evolution of biomineralization.

  19. Deep 3-D seismic reflection imaging of Precambrian sills in the crystalline crust of Alberta, Canada

    Welford, Joanna Kim


    Using deep 3-D seismic reflection datasets collected by the Canadian petroleum exploration industry in southwestern and northwestern Alberta, the Head-Smashed-In and Winagami Precambrian sill complexes within the crystalline upper crust, previously identified on Lithoprobe 2-D multichannel reflection lines, are investigated to determine their 3-D geometries and reflective characteristics. During seismic processing of the dataset in southwestern Alberta, a recently developed wavelet-based method, Physical Wavelet Frame Denoising, is applied and shown to successfully suppress ground roll contamination while preserving low frequency signals from deeper structures. A new 3-D empirical trace interpolation scheme, DSInt, is developed to address the problem of spatial aliasing associated with 3-D data acquisition. Results from applying the algorithm to both datasets are comparable to available interpolation codes while allowing for greater flexibility in the handling of irregular acquisition geometries and interpolated trace headers. Evidence of the Head-Smashed-In reflector in southwestern Alberta is obtained using a dataset acquired to 8 s TWTT (approx. 24 km depth). From locally coherent, discontinuous pockets of basement reflectivity, the dataset appears to image the tapering western edge of the deep reflections imaged by Lithoprobe. A statistical approach of tracking reflectivity is developed and applied to obtain the spatial and temporal distribution of reflections. Simple 1-D forward modelling results reveal that the brightest reflections likely arise from a 50 to 150 m thick body of high density/high velocity material although variations in the amplitudes and lateral distribution of the reflections indicate that the thickness of the sills is laterally variable. Thus, the results are consistent with imaging the tapering edge of the sill complex. Clear evidence of the Winagami reflection sequence in northwestern Alberta, emerges from the second dataset acquired to 5

  20. 40Ar/39Ar dating of exceptional concentration of metals by weathering of Precambrian rocks at the Precambrian–Cambrian boundary

    Parnell, John; Mark, Darren F.; Frei, Robert


    The sub-Cambrian surface, including diverse metalliferous deposits, shows evidence of intense weathering of Precambrian rocks to form supergene-enriched ores and metalliferous placers, followed by widespread peneplanation. Much of the metal would have been flushed to the Cambrian ocean during pen...

  1. Paleo-hydrological changes in the Chew Bahir area during the past 50 ka inferred from isotope signatures in aquatic microfossils

    Junginger, Annett


    A major challenge in paleo-anthropology is to understand the impact of climatic changes on human evolution. The Hominin Sites and Paleo-lakes Drilling Project (HSPDP) is currently meeting that challenge by providing records that cover the last 3.7 Ma of paleoenvironmental change all located in close proximity to key paleo-anthropological findings in East Africa. One of the cored climatic archives comes from the Chew Bahir basin in southern Ethiopia, where duplicate sediment cores provide valuable insights about East African environmental variability during the last 550 ka. The lake basins in the eastern branch of the East African Rift System today contain mainly shallow and alkaline lakes. However, paleo-shorelines in the form of wave cut notches, shell beds, and beach ridges are common morphological evidences for deep freshwater lakes that have filled the basins up to their overflow level during pronounced humid episodes, such as the African Humid Period (15-5 ka). Unfortunately, further back in time, many of those morphological features disappear due to erosion and the estimation of paleo-water depths depend merely on qualitative proxies from core analyses. We here present a method that shows high potential to translate qualitative proxy signals from sediment core analyses to quantitative climate signals in the Ethiopian Rift. The method aims at water level reconstruction in the Chew Bahir basin using strontium isotope ratios (87Sr/86Sr, SIR) in lacustrine microfossils. SIR reflect the lithology of the drained catchment. SIR have changed pronouncedly when higher elevated paleo-lakes Abaya, Chamo and Awassa were overflowing into paleo-lake Chew Bahir. This new method may help to quantify paleo-lake levels beyond the past 20 ka and may also detect migrational barriers or routes due to the occurrence of synchronous large, connected and deep paleo-lakes.

  2. The Rae craton of Laurentia/Nuna: a tectonically unique entity providing critical insights into the concept of Precambrian supercontinental cyclicity

    Bethune, K. M.


    Forming the nucleus of Laurentia/Nuna, the Rae craton contains rocks and structures ranging from Paleo/Mesoarchean to Mesoproterozoic in age and has long been known for a high degree of tectonic complexity. Recent work strongly supports the notion that the Rae developed independently from the Hearne; however, while the Hearne appears to have been affiliated with the Superior craton and related blocks of 'Superia', the genealogy of Rae is far less clear. A diagnostic feature of the Rae, setting it apart from both Hearne and Slave, is the high degree of late Neoarchean to early Paleoproterozoic reworking. Indeed, following a widespread 2.62-2.58 Ga granite bloom, the margins of Rae were subjected to seemingly continuous tectonism, with 2.55-2.50 Ga MacQuoid orogenesis in the east superseded by 2.50 to 2.28 Ga Arrowsmith orogenesis in the west. A recent wide-ranging survey of Hf isotopic ratios in detrital and magmatic zircons across Rae has demonstrated significant juvenile, subduction-related crustal production in this period. Following break-up at ca. 2.1 Ga, the Rae later became a tectonic aggregation point as the western and eastern margins transitioned back to convergent plate boundaries (Thelon-Taltson and Snowbird orogens) marking onset of the 2.0-1.8 Ga assembly of Nuna. The distinctive features of Rae, including orogenic imprints of MacQuoid and Arrowsmith vintage have now been identified in about two dozen cratonic blocks world-wide, substantiating the idea that the Rae cratonic family spawned from an independent earliest Paleoproterozoic landmass before its incorportation in Nuna. While critical tests remain to be made, including more reliable ground-truthing of proposed global correlations, these relationships strongly support the notion of supercontinental cyclicity in the Precambrian, including the Archean. They also challenge the idea of a globally quiescent period in the early Paleoproterozoic (2.45-2.2 Ga) in which plate tectonics slowed or shut down.

  3. Large-scale fluctuations in Precambrian atmospheric and oceanic oxygen levels from the record of U in shales

    Partin, C. A.; Bekker, A.; Planavsky, N. J.; Scott, C. T.; Gill, B. C.; Li, C.; Podkovyrov, V.; Maslov, A.; Konhauser, K. O.; Lalonde, S. V.; Love, G. D.; Poulton, S. W.; Lyons, T. W.


    The atmosphere-ocean system experienced a progressive change from anoxic to more oxidizing conditions through time. This oxidation is traditionally envisaged to have occurred as two stepwise increases in atmospheric oxygen at the beginning and end of the Proterozoic Eon. Here, we present a study of the redox-sensitive element, uranium, in organic-rich shales to track the history of Earth's surface oxidation at an unprecedented temporal resolution. Fluctuations in the degree of uranium enrichment in organic-rich shales suggest that the initial rise of atmospheric oxygen ~2.4 billion yr ago was followed by a decline to less oxidizing conditions during the mid-Proterozoic. This redox state persisted for almost 1 billion yr, ending with a second oxygenation event in the latest Neoproterozoic. The U record tracks major fluctuations in surface oxygen level and challenges conventional models that suggest the Earth underwent a unidirectional rise in atmospheric oxygen during the Precambrian.

  4. Precambrian accretionary history and phanerozoic structures-A unified explanation for the tectonic architecture of the nebraska region, USA

    Carlson, M.P.


    The Phanerozoic history in Nebraska and adjacent regions contains many patterns of structure and stratigraphy that can be directly related to the history of the Precambrian basement rocks of the area. A process is proposed that explains the southward growth of North America during the period 1.8-1.6 Ga. A series of families of accretionary events during the Proterozoic emplaced sutures that remained as fundamental basement weak zones. These zones were rejuvenated in response to a variety of continental stress events that occurred during the Phanerozoic. By combining the knowledge of basement history with the history of rejuvenation during the Phanerozoic, both the details of Proterozoic accretionary growth and an explanation for the patterns of Phanerozoic structure and stratigraphy is provided. ?? 2007 The Geological Society of America. All rights reserved.

  5. A New Morphological Phylogeny of the Ophiuroidea (Echinodermata Accords with Molecular Evidence and Renders Microfossils Accessible for Cladistics.

    Ben Thuy

    Full Text Available Ophiuroid systematics is currently in a state of upheaval, with recent molecular estimates fundamentally clashing with traditional, morphology-based classifications. Here, we attempt a long overdue recast of a morphological phylogeny estimate of the Ophiuroidea taking into account latest insights on microstructural features of the arm skeleton. Our final estimate is based on a total of 45 ingroup taxa, including 41 recent species covering the full range of extant ophiuroid higher taxon diversity and 4 fossil species known from exceptionally preserved material, and the Lower Carboniferous Aganaster gregarius as the outgroup. A total of 130 characters were scored directly on specimens. The tree resulting from the Bayesian inference analysis of the full data matrix is reasonably well resolved and well supported, and refutes all previous classifications, with most traditional families discredited as poly- or paraphyletic. In contrast, our tree agrees remarkably well with the latest molecular estimate, thus paving the way towards an integrated new classification of the Ophiuroidea. Among the characters which were qualitatively found to accord best with our tree topology, we selected a list of potential synapomorphies for future formal clade definitions. Furthermore, an analysis with 13 of the ingroup taxa reduced to the lateral arm plate characters produced a tree which was essentially similar to the full dataset tree. This suggests that dissociated lateral arm plates can be analysed in combination with fully known taxa and thus effectively unlocks the extensive record of fossil lateral arm plates for phylogenetic estimates. Finally, the age and position within our tree implies that the ophiuroid crown-group had started to diversify by the Early Triassic.

  6. Application Of Recent (2008-2013) Lunar Probe Instrumentation To The Exploration For Precambrian Protolife In Volcanic Vents

    Green, Jack


    Selected recent and future lunar probes have instruments suitable for the exploration of Precambrian protolife. Fumaroles contain the ingredients for protolife. With available energy including flow charging and charge separation, amino acids and related compounds could evolve into ATP. Fischer-Tropsch reactions in hydrothermal clay could create lipid micelles as reaction chambers. Fumarolic polyphosphates and tungsten catalysts could contribute to precambrian protolife evolution . The floors of Alphonsus and Lavoisier M exhibit dark mounds which could be buried fumaroles at fracture intersections. Chang'e-1 could define regolith thickness at these mounds with microwave radiometry. The MoonLITE penetrometer could likely identify hydrothermal products in these mounds using X-ray fluorescence spectrometry. Regarding polar craters which may host volcanic ices, intermittent illumination of selected crater floors warmed to 220 K may create a transient tenuous atmosphere of COS, H2S, CO2, CO, HCl and CH4 which could be analyzed by near infrared spectrometry (NIMS) of SELENE or Chandrayaan-1. Prior to the 2009 impact of a polar crater by LCROSS (of the LRO mission), the Soviet LEND mission may detect water using epithermal neutrons. The impact plume proposed in the LCROSS mission at a polar crater could be analyzed by NIMS for fumarolic fluids similar the the NIMS analyses of Callisto and Ganymede moons of Jupiter. The possible identification of cyanogen in the LCROSS impact plume would support the CN2 spectrogram at Aristarchus by Kozyrev in 1969. In the Aristarchus region, lunar dawn during periods of maximum orbital flexing may accentuate release of Rn, Ar and protolife gases. These gases could possibly by identified by the Chang'e-1 gamma/x ray spectrometer, NIMS and the neutral mass spectrometer of the LADEE mission. Microwave spectrometry and radar on the LEO mission as well as LROC (LRO mission) could also be directed at verified lunar transient sites.

  7. Uranium potential of precambrian rocks in the Raft River area of northwestern Utah and south-central Idaho. Final report

    Black, B.A.


    A total of 1214 geochemical samples were collected and analyzed. The sampling media included 334 waters, 616 stream sediments, and 264 rocks. In addition, some stratigraphic sections of Elba and Yost Quartzites and Archean metasedimentary rock were measured and sampled and numerous radiation determinations made of the various target units. Statistical evaluation of the geochemical data permitted recognition of 156 uranium anomalies, 52 in water, 79 in stream sediment, and 25 in rock. Geographically, 68 are located in the Grouse Creek Mountains, 43 in the Raft River Mountains, and 41 in the Albion Range. Interpretation of the various data leads to the conclusion that uranium anomalies relate to sparingly and moderately soluble uraniferous heavy minerals, which occur as sparse but widely distributed magmatic, detrital, and/or metamorphically segregated components in the target lithostratigraphic units. The uraniferous minerals known to occur and believed to account for the geochemical anomalies include allanite, monazite, zircon, and apatite. In some instances samarskite may be important. These heavy minerals contain uranium and geochemically related elements, such as Th, Ce, Y, and Zr, in sufficient quantities to account for both the conspicuous lithologic preference and the generally observed low amplitude of the anomalies. The various data generated in connection with this study, as well as those available in the published literature, collectively support the conclusion that the various Precambrian W and X lithostratigraphic units pre-selected for evaluation probably lack potential to host important Precambrian quartz-pebble conglomerate uranium deposits. Moreover it is also doubted that they possess any potential to host Proterozoic unconformity-type uranium deposits.

  8. Micromechanical modeling of healed crack orientations as a paleostress indicator: Application to Precambrian granite from Illinois and Wisconsin

    Wang, Herbert F.


    We have used a micromechanical, four-grain model to simulate intragranular cracks produced during primary cooling of a granitic pluton in a horizontally anisotropic stress field. The orientations of vertical, intragranular cracks were obtained using the criterion that they are perpendicular to the maximum principal tensile stress when it exceeds the local tensile strength. The preferred orientation was always parallel to the maximum regional compressive stress direction. The sharpness of the distribution peak increases with the ratio of the maximum to minimum horizontal stress. We applied the model results to new and previous data on Precambrian granites from Wisconsin and Illinois. Our new data are healed crack orientations and fluid inclusion properties in unoriented granite core from Illinois borehole UPH-2. The fluid inclusion measurements and isotopic age dates indicate that most healed cracks were formed during the primary cooling of the pluton. The fluid inclusion characteristics and shape of the crack orientation distribution were almost identical to those previously determined for UPH-3, 1 km away (Kowallis et al., 1987), suggesting that the preferred orientation of healed cracks in granite from UPH-2 is the same as for UPH-3 (N25°+/-5°). The orientation distribution from the micromechanical model for a stress ratio of 4 is very similar to the healed crack orientation distribution measured in several Precambrian granites from the midcontinent region. We conclude that healed crack orientations are useful indicators of the paleostress field and that they may be used as a tool for orienting core in stable, structurally simple regions.

  9. Natural evidence for chemical and early biological evolution

    Kvenvolden, K. A.


    Oparin (1924) and Haldane (1929) have independently hypothesized that life arose under reducing conditions through an evolutionary sequence of events involving increasingly complex organic substances. The natural evidence for this hypothesis of chemical evolution is considered, giving particular attention to tangible samples which have been chemically analyzed in earth-bound laboratories. It is found that meteorites provide naturally occurring evidence in support of chemical evolution, but not of biological evolution. Studies on the early Precambrian Swaziland Sequence and the Bulawayan System of southern Africa provide evidence for very early biological evolution.

  10. Early Life on Earth: the Ancient Fossil Record

    Westall, F.


    The evidence for early life and its initial evolution on Earth is lin= ked intimately with the geological evolution of the early Earth. The environment of the early Earth would be considered extreme by modern standards: hot (50-80=B0C), volcanically and hydrothermally active, a= noxic, high UV flux, and a high flux of extraterrestrial impacts. Habitats = for life were more limited until continent-building processes resulted in= the formation of stable cratons with wide, shallow, continental platforms= in the Mid-Late Archaean. Unfortunately there are no records of the first appearance of life and the earliest isotopic indications of the exist= ence of organisms fractionating carbon in ~3.8 Ga rocks from the Isua greenst= one belt in Greenland are tenuous. Well-preserved microfossils and micro= bial mats (in the form of tabular and domical stromatolites) occur in 3.5-= 3.3 Ga, Early Archaean, sedimentary formations from the Barberton (South Afri= ca) and Pilbara (Australia) greenstone belts. They document life forms that = show a relatively advanced level of evolution. Microfossil morphology inclu= des filamentous, coccoid, rod and vibroid shapes. Colonial microorganism= s formed biofilms and microbial mats at the surfaces of volcaniclastic = and chemical sediments, some of which created (small) macroscopic microbi= alites such as stromatolites. Anoxygenic photosynthesis may already have developed. Carbon, nitrogen and sulphur isotopes ratios are in the r= ange of those for organisms with anaerobic metabolisms, such as methanogenesi= s, sulphate reduction and photosynthesis. Life was apparently distribute= d widely in shallow-water to littoral environments, including exposed, evaporitic basins and regions of hydrothermal activity. Biomass in t= he early Archaean was restricted owing to the limited amount of energy t= hat could be produced by anaerobic metabolisms. Microfossils resembling o= xygenic photosynthesisers, such as cyanobacteria, probably first occurred in

  11. Provenance and tectonic setting of siliciclastic rocks associated with the Neoproterozoic Dahongliutan BIF: Implications for the Precambrian crustal evolution of the Western Kunlun orogenic belt, NW China

    Hu, Jun; Wang, He; Wang, Min


    The Late Neoproterozoic Dahongliutan BIF is associated with siliciclastic rocks in the Tianshuihai terrane of the Western Kunlun orogenic belt (WKO), NW China. The sedimentary rocks have various weathering indices (e.g., CIA = 57-87, PIA = 61-96 and Th/U = 4.85-12.45), indicative of varying degrees of weathering in the source area. The rocks have trace element ratios, such as Th/Sc = 0.60-1.21 and Co/Th = 0.29-1.67, and light rare earth element (LREE) enriched chondrite-normalized REE patterns, suggesting that they were mainly sourced from intermediate and felsic rocks. Available U-Pb ages of detrital zircon from these rocks reveal that the detrital sources may have been igneous and metamorphic rocks from the WKO and the Tarim Block. Our study suggests that the Dahongliutan BIF and hosting siliciclastic rocks may have deposited in a setting transitional from a passive to active continental margin, probably related to the Late Neoproterozoic-Early Cambrian seafloor spreading and subduction of the Proto-Tethys Ocean. U-Pb dating of 163 detrital zircons defines five major age populations at 2561-2329 Ma, 2076-1644 Ma, 1164-899 Ma, 869-722 Ma and 696-593 Ma. These age groups broadly correspond to the major stages of supercontinent assembly and breakup events widely accepted for Columbia, Rodinia and Gondwana. Some zircons have TDM2 model ages of 3.9-1.8 Ga and negative εHf(t) values, suggesting that the Archean to Paleoproterozoic (as old as Eoarchean) crustal materials were episodically reworked and incorporated into the late magmatic process in the WKO. Some Neoproterozoic zircons have TDM2 model ages of 1.47-1.07 Ga and 1.81-1.53 Ga and positive εHf(t) values, indicating juvenile crustal growth during the Mesoproterozoic. Our new results, combined with published data, imply that both the Tianshuihai terrane in the WKO and the Tarim Block share the same Precambrian tectonic evolution history.

  12. Revision of species of Minerisporites, Azolla and associated plant microfossils from deposits of the Upper Palaeocene and Palaeocene/Eocene transition in the Netherlands, Belgium and the USA.

    Batten, D J.; Collinson, M E.


    Species of the megaspore genus Minerisporites Potonié, megaspore apparatuses of species of the water fern Azolla Lamarck, and some associated organic-walled microfossils recovered from deposits of the Upper Palaeocene and Palaeocene/Eocene transition in the southern part of the Netherlands and neighbouring Belgium are redescribed on the basis of an examination of specimens under scanning and transmission electron microscopes. Originally studied about 40 years ago by S.J. Dijkstra, the re-examination has enabled emended diagnoses to be produced for six taxa: Minerisporites glossoferus (Dijkstra) Tschudy, M. mirabilis (Miner) Potonié, M. mirabilissimus (Dijkstra) Potonié, Azolla schopfii Dijkstra, A. teschiana Florschütz, and A. velus (Dijkstra) Jain and Hall. In addition, a revised description is provided for massulae of Salvinia Séguier that were originally thought to be megaspores and, hence, named by Dijkstra as Triletes? exiguus. The gross morphology and construction of the exospore of the species of Minerisporites are similar, but nevertheless sufficiently distinct for them to be maintained as separate taxa. Monolete microspores are preserved in hollows in the reticulate surface of some of the specimens of M. mirabilissimus. This is consistent with the presumed isoetalean affinity of Minerisporites. An apparent stratigraphic morphocline from M. glossoferus to M. mirabilis, suggested previously, is confirmed following our reassessment of their characteristics. The species of Azolla are all multi-floated, but they differ from each other in several ways, in particular with respect to the ultrastructure of the megaspore wall. They are also distinct from all other species that have been considered in sufficient detail for satisfactory comparisons to be made. The massulae of A. teschiana are described for the first time. The floats in A. velus are attached to the proximal part of the megaspore only by suprafilosal hairs. There are no maniculae. It is argued that

  13. Paleoenvironmental implications of novel C 30 steranes in Precambrian to Cenozoic Age petroleum and bitumen

    McCaffrey, Mark A.; Michael Moldowan, J.; Lipton, Paul A.; Summons, Roger E.; Peters, Kenneth E.; Jeganathan, Alwarsamy; Watt, David S.


    Petroleums and bitumens from Early Proterozoic (≈ 1800 Ma) to Miocene (≈ 15 Ma) age marine strata contain 24-isopropylcholestanes, a novel group of C 30 steroids. The abundance of these compounds, relative to 24- n-propylcholestanes, varies with source rock age. Late Proterozoic (Vendian) and Early Cambrian oils and/or bitumens from Siberia, the Urals, Oman, Australia, and India have a high ratio of 24-isopropylcholestanes to 24- n-propylcholestanes (≥1), while younger and older samples have a lower ratio (≤0.4). Temporal changes in this parameter may reflect the relative abundance of certain Porifera (sponges) and certain marine algae through time. Geochemical indicators such as this, which can constrain the source rock age of a migrated oil, are useful in source rock identification during petroleum exploration.

  14. Drill-hole data, drill-site geology, and geochemical data from the study of Precambrian uraniferous conglomerates of the Medicine Bow Mountains and Sierra Madre of southeastern Wyoming

    Karlstrom, K.E.; Houston, R.S.; Schmidt, T.G.; Inlow, D.; Flurkey, A.J.; Kratochvil, A.L.; Coolidge, C.M.; Sever, C.K.; Quimby, W.F.


    This volume is presented as a companion to Volume 1: The Geology and Uranium Potential of Precambrian Conglomerates in the Medicine Bow Mountains and Sierra Madre of Southeastern Wyoming; and to Volume 3: Uranium Assessment for Precambrian Pebble Conglomerates in Southeastern Wyoming. Volume 1 summarized the geologic setting and geologic and geochemical characteristics of uranium-bearing conglomerates in Precambrian metasedimentary rocks of southeastern Wyoming. Volume 3 is a geostatistical resource estimate of U and Th in quartz-pebble conglomerates. This volume contains supporting geochemical data, lithologic logs from 48 drill holes in Precambrian rocks of the Medicine Bow Mountains and Sierra Madre, and drill site geologic maps and cross-sections from most of the holes.

  15. Geochronology of Precambrian granites and associated U-Ti-Th mineralization, northern Olary province, South Australia

    Ludwig, K. R.; Cooper, J.A.


    Proterozoic granitoids and metamorphic rocks in the Olary province of the Willyama block of South Australia host ore-grade amounts of U-Th-Ti and U-Fe-Ti-Th minerals. U-Pb-Th isotope analyses on zircons from all granitoids associated with the Crocker Well brannerite deposit indicate that these granitoids were intruded within a short time span, close to the 1579.2??1.5 m.y. age of the brannerite-bearing host-rock. Though the early Paleozoic Delamerian orogeny was intense in this region, the zircon isotopic systems remained unaffected; rather, the best-defined zircon chords on concordia plots show a welldefined lower intercept of 43.8??6.5 Ma, which can only be associated with early Tertiary block faulting. Pb-U-Th isotope analyses on brannerite from the Crocker Well deposit and davidite from the Mt. Victoria deposit and the Radium Hill deposit yield badly scattered and discordant apparent ages that suggest a primary age at least as old as the age of the Crocker Well granitoids, followed by a severe disturbance in the early Paleozoic. ?? 1984 Springer-Verlag.

  16. A Geophysical Study in Grand Teton National Park and Vicinity, Teton County, Wyoming: With Sections on Stratigraphy and Structure and Precambrian Rocks

    Behrendt, John Charles; Tibbetts, Benton L.; Bonini, William E.; Lavin, Peter M.; Love, J.D.; Reed, John C.


    An integrated geophysical study - comprising gravity, seismic refraction, and aeromagnetic surveys - was made of a 4,600-km2 area in Grand Teton National Park and vicinity, Wyoming, for the purpose of obtaining a better understanding of the structural relationships in the region. The Teton range is largely comprised of Precambrian crystalline rocks and layered metasedimentary gneiss, but it also includes granitic gneiss, hornblende-plagioclase gneiss, granodiorite, and pegmatite and diabase dikes. Elsewhere, the sedimentary section is thick. The presence of each system except Silurian provides a chronological history of most structures. Uplift of the Teton-Gros Ventre area began in the Late Cretaceous; most of the uplift occurred after middle Eocene time. Additional uplift of the Teton Range and downfaulting of Jackson Hole began in the late Pliocene and continues to the present. Bouguer anomalies range from -185 mgal over Precambrian rocks of the Teton Range to -240 mgal over low-density Tertiary and Cretaceous sedimentary rocks of Jackson Hole. The Teton fault (at the west edge of Jackson Hole), as shown by steep gravity gradients and seismic-refraction data, trends north-northeast away from the front of the Teton Range in the area of Jackson Lake. The Teton fault either is shallowly inclined in the Jenny Lake area, or it consists of a series of fault steps in the fault zone; it is approximately vertical in the Arizona Creek area. Seismic-refraction data can be fitted well by a three-layer gravity model with velocities of 2.45 km per sec for the Tertiary and Cretaceous rocks above the Cloverly Formation, 3.9 km per sec for the lower Mesozoic rocks, and 6.1 km per sec for the Paleozoic (limestone and dolomite) and Precambrian rocks. Gravity models computed along two seismic profiles are in good agreement (sigma=+- 2 mgal) if density contrasts with the assumed 2.67 g per cm2 Paleozoic and Precambrian rocks are assumed to be -0.35 and -0.10 g per cm2 for the 2

  17. Genesis of the Precambrian copper-rich Caraiba hypersthenite-norite complex, Brazil

    Oliveira, E. P.; Tarney, J.


    Caraiba, the largest Brazilian copper deposit under exploitation, consists mostly of disseminated and remobilised bornite and chalcopyrite hosted in early Proterozoic norite and hypersthenite. The mafic igneous complex comprises multiple intrusions of dykes, veins and breccias of norites and hypersthenites, with minor proportions of amphibolised gabbronorite and peridotite xenoliths transported by the magma from deeper levels in the lithosphere. The country rocks are high-grade gneisses, granulites and metasediments. Compositions of plagioclase(An60-40) and orthopyroxene(En70-60) fall in a narrow range similar to the Koperberg Suite from the Okiep copper district, South Africa, and to that in many massif-type anorthosites. Whole-rock major and trace element geochemistry indicate a parental magma enriched in Fe, LREE, P, K, and Cu. Negative Nb anomalies on multi-element plots and fractionated REE patterns, along with sulphide sulphur isotopes in the range δ34S = -1.495 to + 0.643‰, suggest a primary mantle lithosphere source, although a lower crustal source for the gabbronorite and peridotite xenoliths cannot be excluded. Geochronological and field evidence indicate that both norite and hypersthenite are likely to have been emplaced during a major sinistral transcurrent (partly transpressional) shearing event associated with the waning stage of evolution of the early Proterozoic Salvador-Curaçá orogen.

  18. Provenance of Precambrian Fe- and Al-rich Metapelites in the Yenisey Ridge and Kuznetsk Alatau, Siberia: Geochemical Signatures

    Igor I. LIKHANOV; Vladimir V. REVERDATTO


    Major, trace and rare earth element contents of Fe- and Al-rich metapelites from the Korda (Yenisey Ridge) and Amar (Kuznetsk Alatau) formations were determined to examine the nature, origin and evolution of their protoliths. Results indicate that these rocks are the redeposited and metamorphosed products of Precambrian kaolinitic weathering crusts, while the geochemical distinctions between the studied metapelites are determined by different weathering conditions in the source area and tectonic settings. The protolith of the Korda Formation metapelites was produced by erosion products of the post-Archean granitoid rocks, which accumulated under humid climate conditions in shallow-water basins along the continental margin. The geochemical characteristics of the deeper primary deposits of the Amar Formation suggest that volcanogenic material of mafic composition derived from an island-arc environment had a major role in supplying the erosion zone.These results agree with lithofacies data and with the geodynamic reconstruction of the evolution of the Yenisey Ridge and Kuznetsk Alatau during the Mesoproterozoic and Neoproterozoic, respectively.It was shown that REEs had limited mobility during contact metamorphism. The coherent mobility of REEs during collisional metamorphism may be attributed both to mineral reactions responsible for modal changes and to local chemical heterogeneity inherited from the initial protolith.

  19. The South India Precambrian crust and shallow lithospheric mantle: Initial results from the India Deep Earth Imaging Experiment (INDEX)

    S S Rai; Kajaljyoti Borah; Ritima Das; Sandeep Gupta; Shalivahan Srivastava; K S Prakasam; K Sivaram; Sudesh Kumar; Rishikesh Meena


    We present here the most comprehensive study of the thickness and composition (/ ratio) of the South India Precambrian crust and the nature of shallower mantle inferred from analysis of teleseismic receiver functions from 70 broad-band seismic stations operated as a part of the India Deep Earth Imaging Experiment (INDEX). South India could be broadly divided into regions with thin crust (32–38 km) and thick crust (38–54 km). Thin crust domains include the East Dharwar Craton (EDC), Cuddapah basin and Madurai/Kerala Khondalite Block. The thicker crust domain includes the Western Dharwar Craton (WDC) and northern part of Southern Granulite Terrain. The WDC shows progressive increase in thickness from 38 km in north to 46–54 km in south, compared to an almost flat Moho beneath the EDC. Compositionally, most of the crustal domains are felsic to intermediate (/ ∼ 1.69–1.75) except the mid Archean block in the southern WDC where it is mafic (/ < 1.81). Considering erosion depth in the WDC, we argue for Himalaya like ∼70 km thick crust beneath it during the Archean. Variation in crustal thickness does not have a first-order influence on regional topography in South India and suggests significant role for the crustal composition. We also present evidence of mid-lithospheric low velocity at ∼85–100 km beneath South India.

  20. Theoretical constraints on oxygen and carbon dioxide concentrations in the Precambrian atmosphere

    Kasting, J. F.


    Simple (one-dimensional) climate models suggest that carbon dioxide concentrations during the Archean must have been at least 100-1000 times the present level to keep the Earth's surface temperature above freezing in the face of decreased solar luminosity. Such models provide only lower bounds on CO2, so it is possible that CO2 levels were substantially higher than this and that the Archean climate was much warmer than today. Periods of extensive glaciation during the early and late Proterozoic, on the other hand, indicate that the climate at these times was relatively cool. To be consistent with climate models CO2 partial pressures must have declined from approximately 0.03 to 0.3 bar around 2.5 Ga ago to between 10(-3) and 10(-2) bar at 0.8 Ga ago. This steep decrease in carbon dioxide concentrations may be inconsistent with paleosol data, which implies that pCO2 did not change appreciably during that time. Oxygen was essentially absent from the Earth's atmosphere and oceans prior to the emergence of a photosynthetic source, probably during the late Archean. During the early Proterozoic the atmosphere and surface ocean were apparently oxidizing, while the deep ocean remained reducing. An upper limit of 6 x 10(-3) bar for pO2 at this time can be derived by balancing the burial rate of organic carbon with the rate of oxidation of ferrous iron in the deep ocean. The establishment of oxidizing conditions in the deep ocean, marked by the disappearance of banded iron formations approximately 1.7 Ga ago, permitted atmospheric oxygen to climb to its present level. O2 concentrations may have remained substantially lower than today, however, until well into the Phanerozoic.

  1. Atmospheric oxygen levels in the precambrian: a review of isotopic and geological evidence

    Lambert, I. B.; Donnelly, T. H.


    The significant change in the sulfur isotope record in the early Proterozoic implies global scale oxidation of the previously reduced and sulfate-poor hydrosphere. Changes in the nature/abundance of uranium, iron and manganese deposits are consistent with the evolution of significant oxygen levels in the atmosphere in this period. It is suggested that global oxidation occurred in the early Proterozoic as a result of widespread development of sedimentary environments favourable for the proliferation of phytosynthetic organisms, coupled with steadily decreasing availability of ferrous iron, an important oxygen buffer, because of generally declining igneous and hydrothermal activity. There is a predominance of positive δ34S values for sulfides in Proterozoic carbonaceous strata and sediment-hosted mineral deposits, although the uncommonly preserved evaporitic sulfate deposits do not provide evidence of unusual 34S-enrichment in contemporaneous seawater. These data can be explained in terms of a supercontinent on which there was extensive sedimentation in major intracratonic troughs and platforms. This model is consistent with geological and palaeomagnetic data for this era. In the many sedimentary basins which had only occasional, or no, access to the open ocean, variably 34S-enriched sulfides accumulated by high rates and high degrees of biological sulfate reduction, and also by hydrothermal processes. Pyrite in Proterozoic open marine strata should have had mainly variable negative δ34S values, but few examples of such sequences occur in the geological record for this era. Late Proterozoic carbonates (ca. 900-600 m.y.) from different regions are characterised by mainly positive δ13C values. These are explained as the result of long-term global oceanic anoxia, which may have been a function of prolonged crustal stability preceding continental dispersion around the Proterozoic-Cambrian boundary. Significant rises in atmospheric oxygen levels would have resulted

  2. Fe isotope fractionation during Fe(II) oxidation by the marine photoferrotroph Rhodovulum iodosum in the presence of Si - Implications for Precambrian iron formation deposition

    Wu, Wenfang; Swanner, Elizabeth D.; Kleinhanns, Ilka C.; Schoenberg, Ronny; Pan, Yongxin; Kappler, Andreas


    The iron (Fe) isotopic composition of Precambrian iron formations (IFs), besides providing geological context through its mineralogical properties, was suggested to function as a biosignature that can be used to infer a potential microbial role in the formation of the deposited Fe minerals. Anoxygenic phototrophic Fe(II)-oxidizing bacteria (photoferrotrophs), capable of oxidizing Fe(II) anoxically using light energy, were potentially involved in Fe(II) oxidation in anoxic or suboxic Precambrian oceans. The effect of Si on Fe isotopic fractionation between aqueous Fe(II) and Fe-Si-co-precipitates has been investigated before. However, it is currently unknown how stable Fe isotopes are fractionated during enzymatic Fe(II) oxidation under marine hydrogeochemical conditions, and particularly how the presence of Si affects the Fe isotope composition and the isotopic exchange among different Fe phases. We therefore studied Fe isotope fractionation during Fe(II) oxidation by the marine photoferrotroph Rhodovulum iodosum in simulated Precambrian seawater amended with 1 mM dissolved Si. Our results show that the change in the Fe isotope compositions over time for both the initial aqueous Fe(II) (Feaq) and the Fe(III) precipitates (Feppt) follow a Rayleigh distillation model. Moreover, the fractionation (ε56Feppt-aq) determined independently from either δ56Feaq or δ56Feppt data resulted in a value of 2.3 ± 0.3 (2SD, N = 6). This value differs from the fractionation factor determined previously for Fe(II) oxidation by R. iodosum in the absence of Si, where the fractionation calculated from δ56Feaq (i.e. 0.96-1.18) was different from that calculated from δ56Feppt (1.96-1.98). This difference was attributed to isotopic exchange processes with soluble and sorbed Fe species. The present study suggests that Si present in Precambrian oceans retards Fe isotopic exchange, likely through combined effects of complexation of dissolved Fe species by Si and sorption of Si to Fe

  3. 前寒武纪科马提岩研究概况%Research Survey of Precambrian Komatiite

    胡刚; 缪向亮; 聂晓亮; 李牟; 刘茜; 刘莉茗


    科马提岩是前寒武纪绿岩的重要组成部分,对探讨前寒武纪地球演化历史、壳—幔演化及岩石成因等方面有着重要的意义。科马提岩来源于地幔的镁铁质、超镁铁质火山熔岩,具有流动熔岩的结构构造,其化学成分表现为SiO246%~53%, MgO>9%, CaO/Al2O3>1, K2O<0.9%, TiO2<0.9%, F/F+M比值低, TiO2含量低, MgO、 Ni、 Cr含量高。且不同产地的科马提岩具有不同的化学组成,主要分为贫铝科马提岩、富铝科马提岩、钛富集型科马提岩与镁铁质富镁的科马提岩。目前主流的成因模式为Jarvis G.T, Campbell I.H等先后提出的热地幔柱模式,认为科马提岩为地幔柱引起的高温熔融形成的。%Komatiite is an important component of the Precambrian greenstone,that has important significance to explore the Precambrian earth evolution history,crust-mantle evolution and rock formation,etc.Komatiite is derived from the man-tle mafic,super mafic volcanic lava,and has lava flow structure.The chemical composition expression SiO246%~53%, MgO>13 9%,CaO/Al2 O3 >1,K2 O<0.9%,TiO2 <0.9%,F/F+M ratio is low,low content of TiO2 ,high content of MgO style,Ni and Cr.Komatiite in different regions has different chemical composition,mainly divided into poor alumi-num komatiite,rich aluminum komatiite,enrichment of titanium type komatiite and mafic rich magnesium komatiite.The cause mode of the current mainstream,is by Jarvis G.T,Campbell I.H successively put forward the hot mantle plume model,such as consider komatiite for mantle plume caused by high temperature melt.

  4. Contemporary Rigidity of Precambrian and Paleosoic Platform on the Area of Poland on the Base of GPS Data

    Kontny, B.; Grzempowski, P.; Bogusz, J.; Jarosinski, M.; Klos, A.


    Now it became obvious in the world literature that Cenozoic intraplate deformations of the Northwestern Eurasia were connected with the Alpine plate collision. However, relations of the Cenozoic intraplate deformations with the contemporary spreading in the north and transcontinental shears along the Tornquist line and Urals must be taken into account as well. On the contrary, in East Europe, periods of the activity being coincident with those in the Caucasus and the phases of the Red Sea opening. It is also evidence that the southern East European craton belongs to the Periarabian collision area. A compression axis orientation was sub latitudinal there, this allows suggestion that the deformations were originated under pressure of the adjacent Urals. According to some authors the present view of unity and rigidity of the Cenozoic Eurasian plate is correct only at the first approximation. In reality, the Eurasian plate represented a time varying kaleidoscope of sub plates that moved at different velocities from the Atlantic-Arctic spreading axis. Contemporary image of the intraplate deformation can be verified on the basis of observations of permanent stations GPS at present. Density the IGS and EPN station on the North-East Eurasian area isn't sufficient to the credible estimation of geokinematics parameters of every sub plates (platforms). But national networks of the GBAS stations, as for example a Polish network ASG-EUPOS, are ensuring the much higher density of measuring stations (average distance between stations of the c 70 km). Stations are located on both sides of the Teisseyre - Tornquist zone, both on East-European Precambrian platform (East European Craton) as well as on West-European Paleozoic platform. Three-year period of permanent GPS observation on ASG-EUPOS stations enabled the estimation of the velocities of the stations with the sufficing accuracy for the geodynamic purposes. It gave the possibility of the evaluation of contemporary rigidity of

  5. Abiotic and biotic controls on methane formation down to 2.5 km depth within the Precambrian Fennoscandian Shield

    Kietäväinen, Riikka; Ahonen, Lasse; Niinikoski, Paula; Nykänen, Hannu; Kukkonen, Ilmo T.


    Despite a geological history characterised by high temperature and pressure processes and organic carbon deprived crystalline bedrock, large amounts of hydrocarbons are found in deep groundwaters within Precambrian continental shields. In many sites, methane comprises more that 80% of the dissolved gas phase reaching concentrations of tens of mmol l-1. In this study, we used isotopic methods to study the carbon isotope systematics and sources of crustal methane within the Fennoscandian Shield. The main study sites were the Outokumpu Deep Drill Hole and the Pyhäsalmi mine in Finland, both of which allow groundwater sampling down to 2.5 km depth and have been previously studied for their groundwater chemistry and microbiology. We show that the differences in the amount and isotopic composition of methane are related to the availability of carbon sources as well as processes behind the incorporation of hydrogen and carbon via abiotic and biotic pathways into hydrocarbon molecules. Supported by previously reported occurrences and isotopic data of deep groundwater methane in lithologically different locations in Finland and Sweden, we show that methane formation is controlled by microbial methanogenesis and abiotic reactions, as well as lithology with the metasedimentary environments being the most favourable for methane occurrence. Rather than a thermogenic relic, crustal methane within the Fennoscandian Shield is more likely the result of low temperature formation from ancient organic compounds or their inorganic intermediates such as graphite. Such crustal gases are characterised by the lack of major amounts of C2+ hydrocarbons and 13C-rich methane. Further, microbiological and isotopic geochemical evidence suggest that microbial methane is more common at depths shallower than 1.5 km.

  6. On the possibility of life on early Mars

    Oberbeck, V. R.; Fogleman, G.


    Prebiotic reactants, liquid water, and temperatures low enough for organic compounds to be stable are requirements for the origination of life as we know it. Prebiotic reactants and sufficiently low temperatures were present on Mars before liquid water vanished. Early in this time period, however, large planetesimal impacts may have periodically sterilized Mars, pyrolyzed organic compounds, and interrupted chemical origination of life. However, the calculated time interval between such impacts on Mars was larger just before liquid water vanished 3.8 Gyr (billion years) ago than it was on earth just before life originated. Therefore, there should have been sufficient time for life to originate on Mars. Ideal sites to search for microfossils are in the heavily cratered terrain of Upper Noachian age. Craters and channels in this terrain may have been the sites of ancient lakes and streams that could have provided habitats for the first microorganisms.

  7. Geochemical evidence for subduction in the early Archaean from quartz-carbonate-fuchsite mineralization, Isua Supracrustal Belt, West Greenland

    Pope, Emily Catherine; Rosing, Minik Thorleif; Bird, Dennis K.

    Quartz, carbonate and fuchsite (chromian muscovite) is a common metasomatic assemblage observed in orogenic gold systems, both in Phanerozoic convergent margin settings, and within supracrustal and greenstone belts of Precambrian rocks. Geologic and geochemical observations in younger orogenic...... systems suggest that ore-forming metasomatic fluids are derived from subduction-related devolitilization reactions, implying that orogenic Au-deposits in Archaean and Proterozoic supracrustal rock suites are related to subduction-style plate tectonics beginning early in Earth history. Justification...

  8. Potential Effects of Climate Changes on Aquatic Systems: Laurentian Great Lakes and Precambrian Shield Region

    Magnuson, J. J.; Webster, K. E.; Assel, R. A.; Bowser, C. J.; Dillon, P. J.; Eaton, J. G.; Evans, H. E.; Fee, E. J.; Hall, R. I.; Mortsch, L. R.; Schindler, D. W.; Quinn, F. H.


    increase but many complex reactions of the phytoplankton community to altered temperatures, thermocline depths, light penetrations and nutrient inputs would be expected. Zooplankton biomass would increase, but, again, many complex interactions are expected.Generally, the thermal habitat for warm-, cool- and even cold-water fishes would increase in size in deep stratified lakes, but would decrease in shallow unstratified lakes and in streams. Less dissolved oxygen below the thermocline of lakes would further degrade stratified lakes for cold water fishes. Growth and production would increase for fishes that are now in thermal environments cooler than their optimum but decrease for those that are at or above their optimum, provided they cannot move to a deeper or headwater thermal refuge. The zoogeographical boundary for fish species could move north by 500-600 km; invasions of warmer water fishes and extirpations of colder water fishes should increase. Aquatic ecosystems across the region do not necessarily exhibit coherent responses to climate changes and variability, even if they are in close proximity. Lakes, wetlands and streams respond differently, as do lakes of different depth or productivity. Differences in hydrology and the position in the hydrological flow system, in terrestrial vegetation and land use, in base climates and in the aquatic biota can all cause different responses. Climate change effects interact strongly with effects of other human-caused stresses such as eutrophication, acid precipitation, toxic chemicals and the spread of exotic organisms. Aquatic ecological systems in the region are sensitive to climate change and variation. Assessments of these potential effects are in an early stage and contain many uncertainties in the models and properties of aquatic ecological systems and of the climate system.


    M. I. Kuz’min


    Full Text Available The paper provides a review of early stages of development the Solar System and the geological history of Earth with reference to the latest data on the origin of the Solar System and the formation of the first continental rocks and results of studies of zircon, the oldest mineral so far dated on Earth. The formation of the Solar System from a gas-and-dust nebula is estimated to have begun 4.568 billion years ago. Ice was formed 1.5 million years later; it concentrated at the periphery of the system and served as the material for the largest planets, Jupiter and Saturn. In the central areas of the system, asteroids with diameters of about 10 km were formed. Their small bodies were composed of the basic material of the solar nebula, as evidenced by carbonaceous chondrite, CI, which composition is similar to the composition of the Sun, with the exception of hydrogen, helium, and volatile components that served as the main material for peripheral planets of the Solar System. Due to collision and partial merger of such small bodies, the formation of embryos of the terrestrial planets was initiated. Gravity made such embryos to cluster into larger bodies. After 7 million years, large asteroids and planet Mars were formed. It took 11 million years to form Planet Earth with a mass of 63 %, and 30 million years to form 93 % of its mass. Almost from the beginning of the formation of the Earth, short-lived radionuclides, 26Al and 60Fe, caused warming up of the small planetary bodies which led to the formation of their cores. During the initial stages, small magma reservoirs were formed, and molten iron particles gathered in the centres of the planetary bodies. As suggested by the ratio of 182W/184W, the major part of the core was formed within 20 million years, while its full mass accumulated completely within the next 50 million years. In 30–40 million years after the creation of the Solar System, the Earth collided with a cosmic body which mass was

  10. Characterization of the physiology and cell-mineral interactions of the marine anoxygenic phototrophic Fe(II) oxidizer Rhodovulum iodosum--implications for Precambrian Fe(II) oxidation.

    Wu, Wenfang; Swanner, Elizabeth D; Hao, Likai; Zeitvogel, Fabian; Obst, Martin; Pan, Yongxin; Kappler, Andreas


    Anoxygenic phototrophic Fe(II)-oxidizing bacteria (photoferrotrophs) are suggested to have contributed to the deposition of banded iron formations (BIFs) from oxygen-poor seawater. However, most studies evaluating the contribution of photoferrotrophs to Precambrian Fe(II) oxidation have used freshwater and not marine strains. Therefore, we investigated the physiology and mineral products of Fe(II) oxidation by the marine photoferrotroph Rhodovulum iodosum. Poorly crystalline Fe(III) minerals formed initially and transformed to more crystalline goethite over time. During Fe(II) oxidation, cell surfaces were largely free of minerals. Instead, the minerals were co-localized with EPS suggesting that EPS plays a critical role in preventing cell encrustation, likely by binding Fe(III) and directing precipitation away from cell surfaces. Fe(II) oxidation rates increased with increasing initial Fe(II) concentration (0.43-4.07 mM) under a light intensity of 12 μmol quanta m(-2) s(-1). Rates also increased as light intensity increased (from 3 to 20 μmol quanta m(-2) s(-1)), while the addition of Si did not significantly change Fe(II) oxidation rates. These results elaborate on how the physical and chemical conditions present in the Precambrian ocean controlled the activity of marine photoferrotrophs and confirm the possibility that such microorganisms could have oxidized Fe(II), generating the primary Fe(III) minerals that were then deposited to some Precambrian BIFs. © 2014 Federation of European Microbiological Societies. Published by John Wiley & Sons Ltd. All rights reserved.

  11. What lies beneath: geophysical mapping of a concealed Precambrian intrusive complex along the Iowa–Minnesota border

    Drenth, Benjamin J.; Anderson, Raymond R.; Schulz, Klaus J.; Feinberg, Joshua M.; Chandler, Val W.; Cannon, William F.


    Large-amplitude gravity and magnetic highs over northeast Iowa are interpreted to reflect a buried intrusive complex composed of mafic–ultramafic rocks, the northeast Iowa intrusive complex (NEIIC), intruding Yavapai province (1.8–1.72 Ga) rocks. The age of the complex is unproven, although it has been considered to be Keweenawan (∼1.1 Ga). Because only four boreholes reach the complex, which is covered by 200–700 m of Paleozoic sedimentary rocks, geophysical methods are critical to developing a better understanding of the nature and mineral resource potential of the NEIIC. Lithologic and cross-cutting relations interpreted from high-resolution aeromagnetic and airborne gravity gradient data are presented in the form of a preliminary geologic map of the basement Precambrian rocks. Numerous magnetic anomalies are coincident with airborne gravity gradient (AGG) highs, indicating widespread strongly magnetized and dense rocks of likely mafic–ultramafic composition. A Yavapai-age metagabbro unit is interpreted to be part of a layered intrusion with subvertical dip. Another presumed Yavapai unit has low density and weak magnetization, observations consistent with felsic plutons. Northeast-trending, linear magnetic lows are interpreted to reflect reversely magnetized diabase dikes and have properties consistent with Keweenawan rocks. The interpreted dikes are cut in places by normally magnetized mafic–ultramafic rocks, suggesting that the latter represent younger Keweenawan rocks. Distinctive horseshoe-shaped magnetic and AGG highs correspond with a known gabbro, and surround rocks with weaker magnetization and lower density. Here, informally called the Decorah complex, the source body has notable geophysical similarities to Keweenawan alkaline ring complexes, such as the Coldwell and Killala Lake complexes, and Mesoproterozoic anorogenic complexes, such as the Kiglapait, Hettasch, and Voisey’s Bay intrusions in Labrador. Results presented here suggest that

  12. 微生物参与前寒武纪条带状铁建造沉积的研究进展%Microbial mineralization in Precambrian banded iron formations

    吴文芳; 李一良; 潘永信


    地球演化早期太古代和早元古代大规模的条带状铁建造(BIF)是目前世界上最重要的铁矿资源.已有的稳定同位素组成、分子化石以及岩石磁学性质等证据支持早期微生物广泛参与了BIF的形成.本文评述了微生物参与BIF形成过程中铁搬运和沉淀及其同位素分馏、生物标志物和岩石磁学证据.深入地研究BIF成矿中的微生物矿化贡献,有助于解释BIF形成机制,反演前寒武纪大气-海洋环境演化,以及理解地球早期生命的过程.%Late Achaean to Palaeoproterozoic deposition of banded iron formations ( BIF) is the most important iron ore resource on Earth. As evident by stable isotopes compositions, fossil molecule, rock magnetic properties , microorganisms such as cyanobacteria, iron-oxidizing and iron-reducing bacteria are suggested to have participated in the deposition of BIF. In this review, we briefly introduced the global distribution of BIF and the environments of early Precambrian Earth; then we went through the recent studies on bacterial mineralization related to the deposition of banded iron, including oxygenic/anoxygenie photosynthesis and dissimilatory iron reduction. Finally,we proposed some challenges and prospectives. We suggest three approaches to understand the microbial mediated deposition of BIF; Searching for organic and inorganic signatures of bacterial mineralization, investigating the microbial participation in modern iron deposition in aquatic environments comparable to the microbial process of BIF, and laboratory microbial mineralization simulation, aiming at promoting the research on BIF formation mechanism.

  13. Abiologic silicon isotope fractionation between aqueous Si and Fe(III)-Si gel in simulated Archean seawater: Implications for Si isotope records in Precambrian sedimentary rocks

    Zheng, Xin-Yuan; Beard, Brian L.; Reddy, Thiruchelvi R.; Roden, Eric E.; Johnson, Clark M.


    Precambrian Si-rich sedimentary rocks, including cherts and banded iron formations (BIFs), record a >7‰ spread in 30Si/28Si ratios (δ30Si values), yet interpretation of this large variability has been hindered by the paucity of data on Si isotope exchange kinetics and equilibrium fractionation factors in systems that are pertinent to Precambrian marine conditions. Using the three-isotope method and an enriched 29Si tracer, a series of experiments were conducted to constrain Si isotope exchange kinetics and fractionation factors between amorphous Fe(III)-Si gel, a likely precursor to Precambrian jaspers and BIFs, and aqueous Si in artificial Archean seawater under anoxic conditions. Experiments were conducted at room temperature, and in the presence and absence of aqueous Fe(II) (Fe(II)aq). Results of this study demonstrate that Si solubility is significantly lower for Fe-Si gel than that of amorphous Si, indicating that seawater Si concentrations in the Precambrian may have been lower than previous estimates. The experiments reached ˜70-90% Si isotope exchange after a period of 53-126 days, and the highest extents of exchange were obtained where Fe(II)aq was present, suggesting that Fe(II)-Fe(III) electron-transfer and atom-exchange reactions catalyze Si isotope exchange through breakage of Fe-Si bonds. All experiments except one showed little change in the instantaneous solid-aqueous Si isotope fractionation factor with time, allowing extraction of equilibrium Si isotope fractionation factors through extrapolation to 100% isotope exchange. The equilibrium 30Si/28Si fractionation between Fe(III)-Si gel and aqueous Si (Δ30Sigel-aqueous) is -2.30 ± 0.25‰ (2σ) in the absence of Fe(II)aq. In the case where Fe(II)aq was present, which resulted in addition of ˜10% Fe(II) in the final solid, creating a mixed Fe(II)-Fe(III) Si gel, the equilibrium fractionation between Fe(II)-Fe(III)-Si gel and aqueous Si (Δ30Sigel-aqueous) is -3.23 ± 0.37‰ (2σ). Equilibrium

  14. Geochemical interpretation of the Precambrian basement and overlying Cambrian sandstone on Bornholm, Denmark: Implications for the weathering history

    Zhou, Lingli; Friis, Henrik; Yang, Tian; Nielsen, Arne Thorshøj


    A geochemical study of the Precambrian basement granites from the Borggård borehole on Bornholm, Denmark, suggests that the granites were moderately weathered (Chemical Index of Alteration-CIA = 66-71) during subaerial exposure in a humid climate. The microcline is well preserved, whereas plagioclase was thoroughly altered to clay minerals (Plagioclase Index of Alteration-PIA = 93-99) which is likely due to its original Ca-rich composition. The primary Fe-Ti accessory minerals were oxidized to hematite and anatase. Evidence from REE distribution patterns and immobile element ratios, e.g. Zr/Hf and Nb/Ta, between the weathered basement granite from the Borggård borehole and regional granitoids on Bornholm, constrains the Svaneke Granite as the original basement lithology. A tau (τ) mass transport model (assuming immobile Ti) was applied to quantify the mass transfer during weathering of the basement granite. The results show a depletion of major elements in the following order: Na > Ca > Mg > Si; Al and Ti are immobile and stay constant; K shows sample dependent enrichment or depletion; Fe is slightly enriched. The Cambrian sandstone overlying the basement in the Borggård borehole, assigned to the Gadeby Member of the Nexø Formation, is feldspathic litharenite-litharenite in composition. Provenance indicators including (Gd/Yb)N, Zr/Hf and Nb/Ta ratios and petrological features indicate that source material was derived from both weathered and fresh basement granite of intermediate composition. The Gadeby Member equivalents in Germany, the basal lower Cambrian Adlergrund Konglomerat Member (AKM) in the offshore G-14 well north of Rügen, and the approximately coeval Lubmin Sandstein Formation (LSF) from the Loissin-1 borehole, mainland Germany, must have been sourced from a basement with compositions comparable to the intermediate group of the regional granitoids on Bornholm. The source materials for the AKM (CIA = 71-72, PIA = 94-96), the Gadeby Member in the

  15. Cognitive Factors that Impact Learning in the Field: Observations from an REU Project on Precambrian Rocks of Yellowstone National Park

    Henry, D.; Mogk, D. W.; Goodwin, C.


    Field work requires cognitive processing on many different levels, and constitutes a powerful and important learning environment. To be effective and meaningful, the context of field work must be fully understood in terms of key research questions, earlier published work, regional geology, geologic history, and geologic processes. Scale(s) of observation and sample selection methods and strategies must be defined. Logistical decisions must be made about equipment needed, points of access, and navigation in the field. Professional skills such as field note-taking, measuring structural data, and rock descriptions must be employed, including appropriate use of field tools. Interpretations of geologic features in the field must be interpreted through recall of concepts from the geologic knowledge base (e.g. crystallization history of igneous rocks interpreted through phase diagrams). Field workers need to be able to self-monitor and self-regulate their actions (metacognitively), and make adjustments to daily plans as needed. The results of field work must be accurately and effectively communicated to other geoscientists. Personal and professional ethics and values are brought to bear as decisions are made about whether or not the work has been satisfactorily completed at a field site. And, all of this must be done against a back drop of environmental factors that affect the ability to do this work (e.g. inclement weather, bears, impassable landscapes). The simultaneous relevance of all these factors creates a challenging, but rewarding environment for learning on many different scales. During our REU project to study the Precambrian rocks in the back country of Yellowstone National Park (YNP), we considered these cognitive factors in designing our project curriculum. To reduce the "novelty space" of the project a website was developed that described the project goals and expected outcomes, introduced primary literature, and alerted students about the physical demands

  16. Geochemical evolution of the banded iron formations of the Voronezh Crystalline Massif in the early Precambrian: Sources of matter and geochronological constraints

    Savko, K. A.; Bazikov, N. S.; Artemenko, G. V.


    The banded iron formations (BIFs) of the Voronezh Crystalline Massif occur at three stratigraphic levels: Mesoarchean, Neoarchean, and Paleoproterozoic. In comparison with Paleoproterozoic BIFs, the Archean BIFs are enriched in TiO2, Al2O3, Cr, Ni, and REEs. All the BIFs are characterized by positive Eu anomalies, absence of Ce anomalies, and predominance of HREEs over LREEs. The Paleoproterozoic BIFs show no evidence of clastic or hydrothermal contamination. The low Ni/Fe ratios indicate that the BIFs are younger than 2.7 Ga and their formation was followed by a sharp drop of the level of the mantle Ni supply. On the other hand, very low (iron accumulation—no later than the Great Oxidation Event of ~2.47 Ga.

  17. The Precambrian Singo Igneous Complex (SIC), Uganda Revealed As a Mineralized Nested Ring Complex Using High Resolution Airborne Radiometric and Magnetic Data.

    Atekwana, E. A.; LePera, A.; Abdelsalam, M. G.; Katumwehe, A. B.; Achang, M.


    We used high-resolution radiometrics and aeromagnetic data to investigate the Precambrian Singo Igneous Complex (SIC) in Uganda. The SIC covers an area of about 700 km² and is host to hydrothermally formed economic minerals such as Gold and Tungsten. The distribution of the ore deposits is not well known and current mine workings are limited to the western margins of the complex. Our objectives were to (1) provide a detailed geological map of the SIC and surrounding, (2) investigate relationships between preserved intrusive bodies and Precambrian tectonic structures to provide insight into emplacement of the complex, (3) examine links between magma emplacement, discontinuities and hydrothermal alteration (4) generate two-dimensional (2-D) and three-dimensional (3-D) models of the complex to understand its subsurface geometry, (5) investigate the relationship between the structure of the SIC and mineral occurrences as an aid to future exploration programs. Edge enhancement filters such as the analytical signal, vertical and tilt derivatives were applied to the magnetic data. In addition, 2-D and 3-D models were produced using Geosoft's GM-SYS 2-D and Voxi modules. The filtered data provided unprecedented structural details of the complex and revealed the following: (1) the edge of the SIC is characterized by higher magnetic susceptibility and Thorium content than its interior, (2) the SIC is characterized by eight to nine nested ring complexes with diameters ranging from 2.5 to 14 km, (3) the 3-D inversion suggests near vertical walls for the ring complexes extending to a depth of about 7 km, (4) the SIC was emplaced within a Precambrian folded basement and was traversed by numerous NW-trending dykes and (5) present day mining activities are concentrated within the folded basement units although occurrences of Tungsten and Gold are found associated with the highly magnetized edge of the ring complexes. We interpret the highly magnetized edges of the nested ring

  18. Nature of the Precambrian metamorphic blocks in the eastern segment of Central Tianshan:Constraint from geochronology and Nd isotopic geochemistry

    LIU; Shuwen; GUO; Zhaojie; ZHANG; Zhicheng; LI; Qiugen; ZH


    Granitoid gneisses are widespread in Precambrian metamorphic blocks of eastern segment of the Central Tianshan Tectonic Zone, and they have intrusive contact relationships with their metamorphic sedimentary country rocks of Proterozoic Xingxingxia and Kawabulag groups. Zircon U-Pb ages from a granodioritic gneiss (IW11-1) and a parametamorphic schist (W05-9) are determined at the Weiya area. Euhedral prismatic zircons from the granodioritic gneiss (IW11-1) provide U-Pb isotopic discordia intercept ages of 1218±17 Ma and 426±26 Ma, respectively, and euhedral prismatic zircons from the parametamorphic schist (W05-9) display U-Pb isotopic discordia intercept ages of 1216±74 Ma and 290±15 Ma, respectively. A whole-rock Sm-Nd isotopic isochron is determined in augen granitoid gneiss samples at the Ganggou-Kumishi area and we obtain the isochron age of 1142±120 Ma, and its εNd(t) = -4.3. These geochronological data suggest that these Precambrian metamorphic basement blocks within eastern segment of the Central Tianshan Tectonic Zone can be produced during 1140-1220 Ma, and occur a nearly homochronous metamorphism. Integrated to these geochronological data, Nd depleted mantle model ages (TDM) and epsilon Nd(t) values of these granitoid gneiss samples indicate that they can derive from mixing in various scales both magmas from mantle and crust sources at a late Mesoproterozoic active continental margin tectonic environment. Similarity in geochronology, Sm-Nd isotopic geochemistry between Weiya-Xingxingxia, Pargangtag and Ganggou-Kumishi areas suggests that they could be a bigger uniform metamorphic basement block, which could be formed by the assembly of the supercontinent Rodinia and be separated by late geological processes.

  19. Hydrogeologic Controls on Episodic H2 Release from Precambrian Fractured Rocks-Energy for Deep Subsurface Life on Earth and Mars

    Sherwood Lollar, B.; Voglesonger, K.; Lin, L.-H.; Lacrampe-Couloume, G.; Telling, J.; Abrajano, T. A.; Onstott, T. C.; Pratt, L. M.


    Dissolved H2 concentrations up to the mM range and H2 levels up to 9-58% by volume in the free gas phase are reported for groundwaters at sites in the Precambrian shields of Canada and Finland. Along with previously reported dissolved H2 concentrations up to 7.4 mM for groundwaters from the Witwatersrand Basin, South Africa, these findings indicate that deep Precambrian Shield fracture waters contain some of the highest levels of dissolved H2 ever reported and represent a potentially important energy-rich environment for subsurface microbial life. The δ 2H isotope signatures of H2 gas from Canada, Finland, and South Africa are consistent with a range of H2-producing water-rock reactions, depending on the geologic setting, which include both serpentinization and radiolysis. In Canada and Finland, several of the sites are in Archean greenstone belts characterized by ultramafic rocks that have under-gone serpentinization and may be ancient analogues for serpentinite-hosted gases recently reported at the Lost City Hydrothermal Field and other hydrothermal seafloor deposits. The hydrogeologically isolated nature of these fracture-controlled groundwater systems provides a mechanism whereby the products of water-rock interaction accumulate over geologic timescales, which produces correlations between high H2 levels, abiogenic hydrocarbon signatures, and the high salinities and highly altered δ 18O and δ 2H values of these groundwaters. A conceptual model is presented that demonstrates how periodic opening of fractures and resultant mixing control the distribution and supply of H2 and support a microbial community of H2-utilizing sulfate reducers and methanogens.

  20. Early Silurian Foraminifera from Gondwana - an early origin of the multichambered globothalamids?

    Kaminski, Michael


    Early Silurian foraminifera until now have been regarded to consist of simple single-chambered monothalamids and two-chambered tubothalamids with an agglutinated wall. Although pseudo-multichambered agglutinated foraminifera first appeared in the mid-Ordovician (Kaminski et al. 2009), the origin of true multichambered forms was not believed to have taken place until the early or middle Devonian at the earliest (Holcová, 2002). New discoveries from the Lower Silurian Qusaiba Shale Member in Saudi Arabia point to an earlier origin of the multichambered globothalamid Foraminifera than the currently accepted estimate of 350 Ma (Pawlowski et al. 2003). The agglutinated foraminiferal genera Ammobaculites and Sculptobaculites have been recovered from dark graptolite-bearing claystones of Telychian age, from the transitional facies between the Qusaiba and Sharawa Members of the Qasim Formation at the type locality near Qusaiba town, Saudi Arabia. The multichambered lituolids occur as rare components in a foraminiferal assemblage consisting mostly of monothalamids. This new finding revises our understanding of the early evolution of the multichambered globothalamid foraminifera. The fossil record now shows that the globothalamids were already present in Gondwana by 435 m.y. Holcová, K. 2002. Silurian and Devonian foraminifers and other acid-resistant microfossils from the Barrandian area. Acta Musei Nationalis Pragae, Series B, Historia Naturalis, 58 (3-4), 83-140. Kaminski, M.A., Henderson, A.S., Cetean, C.G. & Waskowska-Oliwa, A. 2009. A new family of agglutinated foraminifera: the Ammolagenidae n.fam., and the evolution of multichambered tests. Micropaleontology, 55 (5), 487-494. Pawlowski, J., Holzmann, M., Berney, C., Fahrni, J.F., Gooday, Aj., Cedhagen, T., Habura, A., & Bowser, SS. 2003. The evolution of early Foraminifera. Proceedings of the National Academy of Sciences, 100 (20), 11494-11498

  1. Early-middle Eocene birds from the Lillebaelt Clay Formation of Denmark

    Lindow, Bent Erik Kramer


    The marine Lillebaelt Clay Formation of central Denmark is of early-middle Eocene age (late Ypresian - middle Lutetian; microfossil zones NP 13-NP 15). Over 20 bird fossils collected by amateur palaeontologists have been acquired through the Danish national ‘Danekrae' fossil treasure trove...... legislation. The fossils are preserved in clay ironstone concretions and almost two-thirds are isolated skulls preserved three-dimensionally. Bird fossils of this age and degree of preservation are rare in an international context. The fossils indicate a very diverse assemblage consisting of both marine...... and terrestrial forms. These include at least one pelagornithid or 'pseudo-toothed bird'; two or three taxa with charadriiform affinities (shorebirds and allies); a massive, narrow-beaked psittaciform (parrots and allies); a large rallid (rail) and one lithornithid (extinct, volant palaeognaths). The Lillebaelt...

  2. Preliminary study of Precambrian integration with tectonic events in brazilian sedimentary basins (Updated); Estudo preliminar de integracao do Pre-Cambriano com os eventos tectonicos das bacias sedimentares brasileiras (Atualizacao)

    Cordani, Umberto G. [Universidade de Sao Paulo (USP), SP (Brazil). Inst. de Geociencias. Centro de Pesquisas Geocronologicas], Email:; Neves, Benjamim Bley de Brito [Universidade de Sao Paulo (USP), SP (Brazil). Inst. de Geociencias. Dept. de Mineralogia e Geotectonica], Email:; Thomaz Filho, Antonio [Universidade do Estado do Rio de Janeiro (UERJ), RJ (Brazil). Fac. de Geologia. Dept. de Estratigrafia e Paleontologia], Email:


    The article 'Preliminary study of Precambrian integration with tectonic events in Brazilian sedimentary basins,' by U. G. Cordani, B. B. Brito-Neves, R. A. Fuck, R. Porto, A. Thomaz-Filho and F. M. B. da Cunha, was published in PETROBRAS Petroleum Technical Science Series (Serie Ciencia Tecnica Petroleo da PETROBRAS) in 1984 and is being reissued by PETROBRAS Geosciences Bulletin. Naturally, the work requires many updates in the light of geosciences' progress in Brazil over the past 26 years. In these comments, numerous reflections have been addressed at short notice, but nevertheless considered appropriate, to occupy space conceded by the publishers for an assessment of the original work. In principle, only the latest summaries and newer published items on the topic have been consulted and commented. For this reason, it was decided to 'overlook' a number of important references on this issue, apologizing to the authors of omitted relevant works. The study, conducted in the early '80s, was based on the knowledge at the time regarding the tectonic evolution of the South American basement; an examination of PETROBRAS subsurface data in Brazilian sedimentary basins and the study of the Company's core samples obtained from perforations which reached the basement. Since then, great advances have been made in understanding the Brazilian territory tectonic evolution and important geophysical data collected regarding its sedimentary basins. On the other hand, there are virtually no recent perforations of the interior Cratonic basins. Moreover, in the marginal and offshore basins, many wells have not reached the basement. Therefore, in these comments, we sought to review the original study's interpretations and confirm the relevant geological knowledge added in recent decades, in the range of the original work. In this article, we try to follow the same structural sequence of the original text, giving the reader a better understanding

  3. Assessing the fidelity of marine vertebrate microfossil δ18O signatures and their potential for palaeo-ecological and -climatic reconstructions

    Roelofs, Brett; Barham, Milo; Cliff, John; Joachimski, Michael; Martin, Laure; Trinajstic, Kate


    Conodont biogenic apatite has become a preferred analytical target for oxygen isotope studies investigating ocean temperature and palaeoclimate change in the Palaeozoic. Despite the growing application in geochemical based palaeoenvironmental reconstructions, the paucity or absence of conodont fossils in certain facies necessitates greater flexibility in selection of robust oxygen bearing compounds for analysis. Microvertebrates offer a potential substitute for conodonts from the middle Palaeozoic. Microvertebrate bioapatite is particularly advantageous given a fossil record extending to the present with representatives across freshwater to fully marine environments, thus widening the scope of oxygen isotope studies on bioapatite. However, significant tissue heterogeneity within vertebrates and differential susceptibility of these tissues to diagenetic alteration have been raised as potential problems affecting the reliability of the oxygen isotope ratios as palaeoclimate proxies. Pristine microvertebrate and co-occurring conodont fossils from the Late Devonian and Early Carboniferous of the Lennard Shelf, Canning Basin, Western Australia, were analysed using bulk (gas isotope ratio mass spectrometry) and in-situ (secondary ion mass spectrometry) methodologies, with the latter technique allowing investigation of specific tissues within vertebrate elements. The δ18Oconodont results may be interpreted in terms of palaeolatitudinally and environmentally sensible palaeotemperatures and provide a baseline standard for comparison against δ18Omicrovertebrate values. Despite an absence of obvious diagenetic influences, GIRMS of microvertebrate denticles yielded δ18O values depleted by 2-4 ‰ relative to co-occurring conodonts. SIMS analysis of hypermineralised tissues in both scales and teeth produced δ18O values comparable with those of associated conodonts. The susceptibility of porous phosphatic fossil tissues to microbial activity, fluid interaction and

  4. The simulated silicification of bacteria--new clues to the modes and timing of bacterial preservation and implications for the search for extraterrestrial microfossils.

    Toporski, Jan K W; Steele, Andrew; Westall, Frances; Thomas-Keprta, Kathie L; McKay, David S


    Evidence of microbial life on Earth has been found in siliceous rock formations throughout the geological and fossil record. To understand the mechanisms of silicification and thus improve our search patterns for evidence of fossil microbial life in rocks, a series of controlled laboratory experiments were designed to simulate the silicification of microorganisms. The bacterial strains Pseudomonas fluorescens and Desulphovibrio indonensis were exposed to silicifying media. The experiments were designed to determine how exposure time to silicifying solutions and to silicifying solutions of different Si concentration affect the fossilization of microbial biofilms. The silicified biofilms were analyzed using transmission electron microscopy (TEM) in combination with energy-dispersive spectroscopy. Both bacterial species showed evidence of silicification after 24 h in 1,000 ppm silica solution, although D. indonensis was less prone to silicification. The degree of silicification of individual cells of the same sample varied, though such variations decreased with increasing exposure time. High Si concentration resulted in better preservation of cellular detail; the Si concentration was more important than the duration in Si solution. Even though no evidence of amorphous silica precipitation was observed, bacterial cells became permineralized. High-resolution TEM analysis revealed nanometer-sized crystallites characterized by lattice fringe-spacings that match the (10-11) d-spacing of quartz formed within bacterial cell walls after 1 week in 5,000 ppm silica solution. The mechanisms of silicification under controlled laboratory conditions and the implication for silicification in natural environments are discussed, along with the relevance of our findings in the search for early life on Earth and extraterrestrial life.

  5. The Simulated Silicification of Bacteria- New Clues to the Modes and Timing of Bacterial Preservation and Implications for the Search for Extraterrestrial Microfossils

    Toporski, Jan K. W.; Steele, Andrew; Westall, Frances; Thomas-Keprta, Kathie L.; McKay, David S.


    Evidence of microbial life on Earth has been found in siliceous rock formations throughout the geological and fossil record. To understand the mechanisms of silicification and thus improve our search patterns for evidence of fossil microbial life in rocks, a series of controlled laboratory experiments were designed to simulate the silicification of microorganisms. The bacterial strains Pseudomonas fluorescens and Desulphovibrio indonensis were exposed to silicifying media. The experiments were designed to determine how exposure time to silicifying solutions and to silicifying solutions of different Si concentration affect the fossilization of microbial biofilms. The silicified biofilms were analyzed using transmission electron microscopy (TEM) in combination with energy-dispersive spectroscopy. Both bacterial species showed evidence of silicification after 24 h in 1,000 ppm silica solution, although D. indonensis was less prone to silicification. The degree of silicification of individual cells of the same sample varied, though such variations decreased with increasing exposure time. High Si concentration resulted in better preservation of cellular detail; the Si concentration was more important than the duration in Si solution. Even though no evidence of amorphous silica precipitation was observed, bacterial cells became permineralized. High-resolution TEM analysis revealed nanometer-sized crystallites characterized by lattice fringe-spacings that match the {10-11} d-spacing of quartz formed within bacterial cell walls after 1 week in 5,000 ppm silica solution. The mechanisms of silicification under controlled laboratory conditions and the implication for silicification in natural environments are discussed, along with the relevance of our findings in the search for early life on Earth and extraterrestrial life.

  6. Paleoenvironmental implications of novel C[sub 30] steranes in Precambrian to Cenozoic age petroleum and bitumen

    McCaffrey, M.A.; Lipton, P.A. (Chevron Petroleum Technology Company, La Habra, CA (United States)); Moldowan, J.M. (Cheveron Petroleum Technology Company, Richmond, CA (United States) Stanford Univ., CA (United States)); Summons, R.E. (Australian Geological Survey Organization, Canberra City (Australia)); Peters, K.E. (Chevron Overseas Petroleum Inc., San Ramon, CA (United States) Mobil Exploration and Producing Technical Center, Dallas, TX (United States)); Jeganathan, A.; Watt, D.S. (Univ. of Kentucky, Lexington, KY (United States))


    Petroleums and bitumens from Early Proterozoic ([approx] 1800 Ma) to Miocene ([approx] 15 Ma) age marine strata contain 24-isopropylcholestanes, a novel group of C[sub 30] steroids. The abundance of these compounds, relative to 24-n-propylcholestanes, varies with source rock age. Late Proterozoic (Vendian) and Early Cambrian oils and/or bitumens from Siberia, the Urals, Oman, Australia, and India have a high ratio of 24-isopropylcholestanes to 24-n-propylcholestanes ([ge] 1), while younger and older samples have a low ratio ([le]0.4). Temporal changes in this parameter may reflect the relative abundance of certain Porifera (sponges) and certain Marine algae through time. Geochemical indicators such as this, which can constrain the source rock age of a migrated oil, are useful in source rock identification during petroleum exploration.

  7. Implications of the Precambrian Non-stromatolitic Carbonate Succession Making up the Third Member of Mesoproterozoic Gaoyuzhuang Formation in Yanshan Area of North China

    Mei Mingxiang


    A particular non-stromatolitic carbonate succession making up the third member of the the Mesoproterozoic occurring at ca. 1 450 Ma besides other three events of the Proterozoic,respectively, occurred at ca. 2 000 Ma, ca. 1 000 Ma, and ca. 675 Ma. The forming duration of this non-stromatolitic carbonate succession can be generally correlative to that of a similar depositional succession in North America, i.e. a non-stromatolitic carbonate succession made up by the Helena Formation of the Belt Supergroup, which suggests that the stromatolite decline occurring at ca. 1 450 significance for the further understanding of Precambrian sedimentology. The Mesoproterozoic Gaoyuzhuang Formation in Yanshan area is a set of more than 1 000 m thick carbonate strata that can subformation) is marked by a set of stromatolitic dolomites overlying a set of transgressive sandstones; leiolite and laminite limestones and is characterized by the development of molar-tooth structures in dolomites of stromatolitic reefs or lithoherms. Sequence-stratigraphic divisions at two sections, i.e. the member of the Mesoproterozoic Gaoyuzhuang Formation is developed in the Yanshan area of North China, in which lots of grotesque matground structures (wrinkle structures and palimpsest ripples) are developed in beds of leiolite limestone at the Qiangou Section and lotsof molar-tooth structures are developed in beds of leiolite limestone at the Jixian Section. The time scale of the Gaoyuzhuang Formation is deduced as 200 Ma (from 1 600 Ma to 1 400 Ma). The duration of an obvious hiatus between the Gaoyuzhuang thus the forming duration of the Gaoyuzhuang Formation is thought as 100 Ma (1 500 Ma to 1 400 Ma). Furthermore, the age of the subface of the third member of the Gaoyuzhuang Formation that is just in the mid position of the Gaoyuzhuang Formation can be deduced as about 1 450 Ma, which is the basis to infer a stromatolite decline of the Mesoproterozoic occurring at ca. 1 450 Ma. Importantly

  8. Towards a palaeoecological model of the Mesoproterozoic Taoudeni Basin, Mauritania, Northwestern Africa: implications for early eukaryote evolution

    Beghin, Jérémie; Guilbaud, Romain; Poulton, Simon W.; Gueneli, Nur; Brocks, Jochen J.; Storme, Jean-Yves; Blanpied, Christian; Javaux, Emmanuelle J.


    The mid-Proterozoic rock record preserves a relatively moderate diversity of early eukaryotes, despite the early evolution of fundamental features of the eukaryotic cell. Common hypotheses involve the redox state of stratified oceans with oxic shallow waters, euxinic mid-depth waters, and anoxic and ferruginous deep waters during this time period. Mid-Proterozoic eukaryotes would have found suitable ecological niches in estuarine, fluvio-deltaic and coastal shallow marine environments near nutrient sources, while N2-fixing photoautotrophs bacteria would have been better competitors than eukaryotic algae in nutrient-poor niches. Here, we present the first palaeoecological model of the late Mesoproterozoic Taoudeni Basin, Mauritania, Northwestern Africa. Previous palaeontological studies in the basin reported stromatolites, a low diversity of microfossils - including one species of presumed eukaryotes: verrucae-bearing acritarch - and biomarkers of anoxygenic phototrophic purple and green sulfur bacteria, cyanobacteria and microaerophilic methanotrophs. However, no biomarkers diagnostic for crown group eukaryotes were reported so far. In addition to exceptionally well preserved microbial mats showing chain-like aggregates of pyrite grains, we observed a total of sixty-two morphotaxa including nine presumed prokaryotes, thirty-five possible prokaryotes or eukaryotes, fifteen unambiguous species of eukaryotes - ornamented and process-bearing acritarchs, multicellular morphotaxon, putative VSMs, large budding vesicles, and vesicles with a sophisticated excystment structure: the pylome - and three remains of structured kerogen. Here, we combined the geological context (sedimentological features and lithofacies), iron speciation (n = 156) - with the aim of reconstructing palaeoredox environmental conditions -, and microfossils quantitative analysis (n = 61). Sediments were deposited under shallow waters in pericratonic (western basin) and epicratonic (eastern basin

  9. Tidal control on gas flux from the Precambrian continental bedrock revealed by gas monitoring at the Outokumpu Deep Drill Hole, Finland

    Kietäväinen, Riikka; Ahonen, Lasse; Wiersberg, Thomas; Korhonen, Kimmo; Pullinen, Arto


    Deep groundwaters within Precambrian shields are characteristically enriched in non-atmospheric gases. High concentrations of methane are frequently observed especially in graphite bearing metasedimentary rocks and accumulation of hydrogen and noble gases due to water-rock interaction and radioactive decay within the U, Th and K containing bedrock takes place. These gases can migrate not only through fractures and faults, but also through tunnels and boreholes, thereby potentially mobilizing hazardous compounds for example from underground nuclear waste repositories. Better understanding on fluid migration may also provide tools to monitor changes in bedrock properties such as fracture density or deterioration and failure of engineered barriers. In order to study gas migration mechanisms and variations with time, we conducted a gas monitoring campaign in eastern Finland within the Precambrian Fennoscandian Shield. At the study site, the Outokumpu Deep Drill Hole (2516 m), spontaneous bubbling of gases at the well head has been on-going since the drilling was completed in 2005, i.e. over a decade. The drill hole is open below 39 m. In the experiment an inflatable packer was placed 15 cm above the water table inside the collar (Ø 32.4 cm), gas from below the packer was collected and the gas flow in the pipe line carefully assisted by pumping (130 ml/min). Composition of gas was monitored on-line for one month using a quadrupole mass spectrometer (QMS) with measurement interval of one minute. Changes in the hydraulic head and in situ temperature were simultaneously recorded with two pressure sensors which were placed 1 m apart from each other below the packer such that they remained above and below the water table. In addition, data was compared with atmospheric pressure data and theoretical effect of Earth tides at the study site. Methane was the dominant gas emanating from the bedrock, however, relative gas composition fluctuated with time. Subsurface derived gases

  10. Neoproterozoic diamictite-bearing sedimentary rocks in the northern Yili Block and their constraints on the Precambrian evolution of microcontinents in the Western Central Asian Orogenic Belt

    He, Jingwen; Zhu, Wenbin; Zheng, Bihai; Wu, Hailin; Cui, Xiang; Lu, Yuanzhi


    The origin and tectonic setting of Precambrian sequences in the Central Asian Orogenic Belt (CAOB) have been debated due to a lack of high resolution geochronological data. Answering this question is essential for the understanding of the tectonic framework and Precambrian evolution of the blocks within the CAOB. Here we reported LA-ICP-MS detrital zircon U-Pb ages and in-situ Hf isotopic data for Neoproterozoic sedimentary cover in the northern Yili Block, an important component of the CAOB, in order to provide information on possible provenance and regional tectonic evolution. A total of 271 concordant U-Pb zircon ages from Neoproterozoic sedimentary cover in the northern Yili Block define three major age populations of 1900-1400 Ma, 1300-1150 Ma and 700-580 Ma, which are quite different from cratons and microcontinents involved in the CAOB. Although it is not completely consistent with the local basement ages, an autochthonous provenance interpretation is more suitable. Some zircon grains show significant old Hf model ages (TDMC; 3.9-2.4 Ga) and reveal continental crust as old as Paleoarchean probably existed. Continuous Mesoproterozoic zircon age populations exhibit large variations in the εHf(t) ratios, suggesting the long-time involvement of both reworked ancient crust and juvenile material. Similar Mesoproterozoic evolution pattern is identified in many continental terranes involved in the CAOB that surround the Tarim Craton. Based on our analysis and published research, we postulate that the northern Yili Block, together with Chinese Central Tianshan, Kyrgyz North Tianshan and some other microcontinents surrounding the Tarim Craton, once constituted the continental margin of the Tarim Craton in the Mesoproterozoic, formed by long-lived accretionary processes. Most of the late Neoproterozoic zircons exhibit significant positive εHf(t) ratios, suggesting the addition of juvenile crust. It is consistent with the tectonic event related to the East Africa

  11. Episodic Growth and Multiple Modification of Precambrian Lower Crust in the Southeastern Margin of North China Craton: Petrologic,Geochronological and Hf-isotopic Evidences%华北克拉通东南缘前寒武纪下地壳的幕式生长与多期改造:岩石学、年代学和Hf同位素证据

    刘贻灿; 王安东


    The early Precambrian is regarded to be a crucial stage for continental crust formation. The Precambrian lower-crustal rocks in the southeastern margin of North China Craton occur as the exposed metamorphic basement (named as the Wuhe metamorphic complex) and xenoliths in the Mesozoic dioritic to monzodioritic porphyry. These rocks provide an excellent natural laboratory to study formation and evolution of the Precambrian lower crust in the region. Integrated investigations on metamorphic petrology, petrologic geochemistry, Hf-isotope and zircon U-Pb geochronology of the rocks suggested that the Precambrian lower crust beneath the studied region experienced an episodic growth and multiple modification history. Intensive tectono-thermo events and metamorphic overprinting mainly occurred at several peaks, such as 2. 5-2. 6, 2. 1, 1. 8-1. 9 Ga and 390, 176 Ma. For the 2. 5-2. 6 Ga lower-crustal rocks, some of them with high radiogenic Pb-isotopic compositions, which were similar to those formed at 2. 1 Ga subduction-related arc setting and underwent 1. 8 Ga high-pressure granulite-facies metamorphism, suffered from high-pressure granulite-facies metamorphism at 2.1 Ga and (or) 1. 8-1. 9 Ga, and subsequent metamorphic overprinting at 390 Ma and 176 Ma; however, others had low radiogenic Pb-isotopic compositions for typical Precambrian lower-crustal rocks, and formed at 2. 55-2. 64 Ga and underwent 2. 48-2. 49 Ga peak metamorphism of granulite-facies without record of post-peak metamorphic overprint at 2. 1 Ga and (or) 1. 8-1. 9 Ga. Therefore, they formed simultaneously, but probably located at different crustal levels and escaped from subsequent metamorphic overprinting, strongly depending on their formation depths. The 2. 7- 2. 8 Ga ages defined by inherited zircons and depleted mantle zircon-Hf model ages could record an earlier crustal growth episode in the area.%早前寒武纪被认为是大陆地壳形成的重要时期.华北克拉通东南缘前寒武纪下地




    Full Text Available The family Fasciellaceae was created as a group of red algae. It was emended as a tribe Fascielleae of incertae sedis algae, and related to the tribe Calcifolieae Shuysky emend. Vachard & Cózar. The tribes Fascielleae and Calcifolieae both constitute the family Calcifoliaceae emend. This family is actually a homogeneous group, and could be more or less closely related with some questionable Moravamminales and Aoujgaliales: Claracrustaceae, Labyrinthoconaceae and Donezellaceae. All these microfossils were successively considered as green algae, red algae, "phylloid" algae, or fibres of calcispongia. The genera included in Fascielleae are: Fasciella, Praedonezella, and ?Kulikaella. The genera Calcifolium, Falsocalcifolium and Frustulata are included in the Calcifolieae. The phylogeny of the Calcifoliaceae is reconstructed. Thus, the family appears to be ancestrally linked, in the early Mississippian and even earlier in the Devonian, to Kulikaella, Stacheoidella, Pseudostacheoides, Pokorninella and Precorninella. The Calcifoliaceae are important for the zonation of the Late Mississippian-earliest Pennsylvanian (early Bashkirian interval (Asbian to Siuransky in the carbonate platform facies from western Palaeotethys and Ural Oceans.

  13. Fourier transform infrared and electron spin resonance examinations of kerogen from the Gunflint stromatolitic cherts (Middle Precambrian, Ontario, Canada and related materials



    Full Text Available Kerogen occurrences in stromatolitic cherts from the Middle Precambrian Gunflint Formation and related rocks have been investigated by the use of elemental analysis, Fourier transform infrared and electron spin reconance spectroscopies. Particular attention was paid to the structural properties of the Schreiber kerogen to allow comparison with biologically controlled kerogens from Paleozoic carbonaceous rocks. The low atomic H/C ratios (0.5 of the Schreiber kerogen indicates that this material has reached a high level of maturity. The Fourier transform infrared/electron spin resonance examinations revealed that the Schreiber kerogen contains predominantly aromatic/polyaromatic structures similar to those found in mature kerogens from Paleozoic carbonaceous rocks. The evidence from this organogeochemical comparison indicates that the Schrei-ber kerogen and mature kerogens from Paleozoic/Mesozoic carbonaceous rocks have sufficient similarity to suggest a similar origin. Consequently, this work gives strong support to the hypothesis that if the Schreiber kerogen is of biotic origin than it is derived from the remnants of various microbial organisms (mainly phytoplanktons including a minor contribution of subtidal (stromatolite-building cyanobacteria.

  14. Sm—Nd and Zircon U—Pb Isotopic Constraints on the Age of Formation of the Precambrian Crust in Southeast China

    李献华; 赵振华; 等


    Nd model ages(TDM) of the Pre-Mesozoic crustal rock samples from Southeast China range from 1.2 to 3.5Ga.Two age peaks of 1.4Ga and 1.8 Ga are observed in the histogram of TDM model ages.Available U-Pb zircon inheritance ages are concentrated around 1.2-1.4Ga,1.8Ga and 2.5Ga,respectively.The combined use of Sm-Nd and U-Pb zircon inheritance ages suggests that the formation of the Precambrian curst is of episodic character.The oldest crustal nucleus may have been formed during the Late Archean(2.5Ga or older?).A rapid production of the crust took place 1.8 Ga ago,consistent with the global crust formation event at 1.7-1.9Ga.Another important episode of the addition of juvenile crustal material from the mantle in Southeast China took place 1.2-1.4Ga ago,during which the pre-existing crust was strongly reworked and/or remelted.

  15. Geochemistry of sericite deposits at the base of the Paleoproterozoic Aravalli Supergroup, Rajasthan, India: Evidence for metamorphosed and metasomatised Precambrian Paleosol

    B Sreenivas; A B Roy; R Srinivasan


    Fine grained sericite deposits occur at the interface between Archean Mewar Gneiss Complex and the Proterozoic Aravalli Supergroup independent of shearing. They show a gradational contact with the basement granites and gneisses and a sharp contact with the overlying quartz pebble conglomeratic quartzites. Rip-up clasts of these sericite schists are found in the overlying conglomerates. The sericite schists are rich in sericite towards the top and contain chlorite towards the base. The sericite in these schists was formed by metasomatic alteration of kyanite and not from the feldspars of the basement granitoids and gneisses. Uni-directional variations of SiO2 and Al2O3, high Al2O3 content (>30%), positive correlation between Al2O3 and TiO2 , Ti/Al and Ti/Zr ratios, high pre-metasomatic chemical indices of alteration (>90), and enrichment of heavy rare earth elements relative to the parent granites and gneisses — all these chemical characteristics combined with field evidence suggest that the sericite schists are formed from a paleosol protolith, which developed on Archean basement between 2.5 and ∼2.1 Ga in the Precambrian of Rajasthan. The superimposed metasomatic alteration restricts the use of Fe2+/Ti and Fe3+/Ti ratios of these paleosols for interpretation of PO2 conditions in the atmosphere.

  16. EBSD microfabric study of pre-Cambrian deformations recorded in quartz pebbles from the Sierra de la Demanda (N Spain)

    Ábalos, B.; Puelles, P.; Fernández-Armas, S.; Sarrionandia, F.


    We describe a new method for the reorientation of lattice preferred orientation data in the absence of a pre-constrained kinematic reference frame. The method enables us to present conventional quartz fabric diagrams after measurements taken from rock sections with a general orientation with respect to foliation and lineation. A microstructural and Electron Back-Scattered Diffraction (EBSD) study of quartz pebbles in early Cambrian conglomerates following this method permit us to recognize a variety of fabrics that resulted from syn-metamorphic ductile deformation under variable temperatures up to 650 °C. The likely source area of the conglomerates was a Proterozoic basement. Candidates for source rock correlations include Neoproterozoic units similar to those outcropping in the northern Iberian Massif, Neoproterozoic medium- to high-grade metamorphic rocks as those outcropping in SW Iberia, or a Neoarchean to Mesoproterozoic concealed basement.

  17. Gravity analysis of the Precambrian basement topography associated with the northern boundary of Ghadames Basin (southern Tunisia)

    Dhaoui, Mohamed; Gabtni, Hakim; Jallouli, Chokri; Jleilia, Ali; Mickus, Kevin Lee; Turki, Mohamed Moncef


    Gravity data were analyzed to determine the structural development of the northern boundary of the Ghadames Basin in southern Tunisia. The Ghadames Basin which also occurs in eastern Algeria and northwestern Libya is one of the most prolific hydrocarbon producers in North Africa with several of the largest oil fields occurring along its northern boundary. The Ghadames Basin was formed during a series of tectonic events ranging from the Early Paleozoic to the Early Cenozoic. These tectonic events produced a basin in southern Tunisia that has a complex basement configuration which is not completely known. A residual gravity anomaly map constructed using polynomial trend surfaces, and vertical and horizontal gravity derivative maps indicate that the northern boundary contains a series of maxima and minima anomalies that trend in two prominent directions: northeast-southwest and east-west. The horizontal and vertical derivative gravity anomaly maps indicate that the width of the basement structures range between 10 and 20 km in width. Three-dimensional (3D) Euler deconvolution and 3D forward modeling constrained by well data, one seismic reflection profile and remote sensing data confirm the width of the basement structures and indicates that the depth of basin varies between 1.5 and 5 km, with deeper sections in general more numerous in the southern sections of the boundary. The gravity analysis constrained by the seismic reflection profile and well data implies that the basement topography may have been formed during the Pan African and/or late Mesozoic rifting. However, additional seismic reflection and well data are needed to confirm this conclusion. The discovery of the numerous basement structures suggests that there may exist additional hydrocarbon traps within the northern boundary of the Ghadames Basin.



    Since 1992, the siliciclastic Fortune Head section(southeastern Newfoundland, Canada) and the base of the Trichophycus pedium trace fossil zone have together served as the Precambrian-Cambrian(PreC-C) boundary global stratotype section and point(GSSP). However, the fact that the Fortune Head section consists mainly of siliciclastic rocks makes it difficult to correlate this section with boundary sections consisting mainly of carbonate rocks, which contain abundant small shelly fossils(SSFs) and can also be correlated using stable carbon isotope data. We propose that a predominantly carbonate section near the town of Dahai, eastern Yunnan Province, southwestern China, be designated a supplementary stratotype for the PreC-C boundary GSSP, for the following reasons:(1) the Dahai section is continuous, consisting of the Neoproterozoic Baiyanshao and Daibu members conformably overlain by the Early Cambrian Zhongyicun and Dahai members and Shiyantou Formation; (2) the Early Cambrian units contain abundant SSFs representing four assemblage zones; (3) the Dahai section can be correlated with numerous other sections using stable C isotopic chemostratigraphy; (4) the famous Meishucun section, located not far from Dahai, contains both abundant SSFs and trace fossils and can be readily correlated with the SSF-rich Dahai section. We further propose that the base of the Cambrian System be placed at the base of the first SSF assemblage zone(the Anabarites-Protohertzina Zone), which in the Dahai section coincides with the base of Bed 11.%1992年,全球前寒武系与寒武系界线层型剖面和层型点确定在加拿大纽芬兰东南幸运角剖面,并以遗迹化石带Trichophycus pedium的底作为前寒武系与寒武系的分界点。但是,幸运角剖面主要是以硅质碎屑岩相为主,难以与含有丰富小壳化石和具有可对比的稳定同位素资料的碳酸盐相界线剖面进行对比。为此,提出我国云南会泽大海附近的一条以

  19. Camian microfossils from Bevško

    Tea Kolar-Jurkovšek


    Full Text Available In the section west of Bevško with prevailing platy limestone the fossil microfauna was studied. The association consists of foraminifers, ostracods,conodonts and fish remains. Determined microfauna is characterized by the conodont element Neogondolella polygnathiformis indicating the Carnian stage.

  20. Precambrian ophiolites of arabia: geologic settings, UPb geochronology, Pb-isotope characteristics, and implications for continental accretion

    Pallister, J.S.; Stacey, J.S.; Fischer, L.B.; Premo, W.R.


    Disrupted ophiolites occur in linear belts up to 900 km long between microplates that collided during the late Proterozoic to form the Arabian Shield. UPb zircon ages and Pb-isotope data from these ophiolitic rocks help constrain the history of accretion of the Arabian Shield and thereby contribute to the definition of its microplates and terranes. Terranes of the central and western Arabian Shield are generally thought to represent intraoceanic island arcs that range in age from about 900 to 640 Ma; however, a region of the eastern Arabian Shield contains rocks of Early Proterozoic age and may represent an exotic continental fragment entrained between the arc complexes. Ophiolites of the Yanbu suture (northwestern shield), dated by UPb (zircon) and SmNd (mineral isochron) methods, yield model ages of 740-780 Ma. These are among the oldest well-dated rocks in the northwestern Arabian Shield. Ages from the Jabal al Wask complex overlap with ages of adjacent arc rocks. This overlap in age supports geologic and geochemical evidence that the Wask complex represents a fragment of back-arc oceanic lithosphere formed during arc magmatism. Older ages of about 780 Ma for gabbro from the Jabal Ess ophiolite suggest that the ophiolite is either a fragment of fore-arc oceanic crust or oceanic basement on which an arc was built. Gabbro samples from ophiolites of the Bir Umq suture (west-central Arabian Shield) yield zircons with ages of 820-870 Ma and $ ??1250 Ma. The 820-870 Ma dates overlap with ages of the oldest nearby arc rocks; this favors an intra-arc or near-arc paleotectonic setting. The older zircons suggest that middle or early Proterozoic crustal material, possibly derived from the Mozambique belt of Africa, was present during back- or intra-arc magmatism. Plagiogranite from the Bir Tuluhah ophiolitic complex at the nothern end of the 900 km-long Nabitah mobile belt was dated by the zircon UPb method at ??? 830 Ma. This date is in the range of the oldest dated arc

  1. The origin of novel features by changes in developmental mechanisms: ontogeny and three-dimensional microanatomy of polyodontode scales of two early osteichthyans.

    Qu, Qingming; Sanchez, Sophie; Zhu, Min; Blom, Henning; Ahlberg, Per Erik


    Recent advances in synchrotron imaging allow us to study the three-dimensional (3D) histology of vertebrate fossils, including microfossils (e.g. teeth and scales) of early jawed vertebrates. These microfossils can often be scanned at submicron resolution (propagation phase-contrast synchrotron X-ray microtomography (PPC-SRµCT), and 3D models of internal canal systems and buried odontodes were created from the scans. Based on these new data, we review the evolutionary origin of cosmine and its associated pore-canal system, which has been long recognized as a synapomorphy of sarcopterygians. The first odontode that appeared during growth shows almost identical morphology in the two scales, but the second odontode of the Psarolepis scale shows a distinctive morphology with several pores on the surface. It is suggested that a shift from ridge-like odontode to pore-bearing odontode was the key step in the origin of cosmine, which was then elaborated further in more-derived sarcopterygians. We perform a detailed comparison between the two scales and propose a primary homology framework to generate microanatomical characters, which can be used in the phylogenetic analysis of early osteichthyans when more 3D data become available. Our results highlight the importance of 3D data for the study of histology and ontogeny of the dermal skeleton of early jawed vertebrates, especially scales of the polyodontode type. The traditional microvertebrate collection is not only useful for biostratigraphic studies, but also preserves invaluable biological information about the growth of vertebrate hard tissues. Today, we are only beginning to understand the biological meaning of the new 3D data. The increasing availability of such data will enable, and indeed require, a complete revision of traditional palaeohistological studies on early vertebrates. © 2016 Cambridge Philosophical Society.

  2. Oxygen isotope exchange kinetics of mineral pairs in closed and open systems: Applications to problems of hydrothermal alteration of igneous rocks and Precambrian iron formations

    Gregory, R.T.; Criss, R.E.; Taylor, H.P.


    heat-balance constraints, we can utilize the 18O 16O data on natural mineral assemblages to calculate the kinetic rate constants (k's) and the effective diffusion constants (D's) for mineral-H2O exchange: these calculated values (kqtz ??? 10-14, kfeld ??? 10-13-10-12) agree with experimental determinations of such constants. In nature, once the driving force or energy source for the external infiltrating fluid phase is removed, the disequilibrium mineral-pair arrays will either: (1) remain "frozen" in their existing state, if the temperatures are low enough, or (2) re-equilibrate along specific closed-system exchange vectors determined solely by the temperature path and the mineral modal proportions. Thus, modal mineralogical information is a particularly important parameter in both the open- and closed-system scenarios, and should in general always be reported in stable-isotopic studies of mineral assemblages. These concepts are applied to an analysis of 18O 16O systematics of gabbros (Plagioclase-clinopyroxene and plagioclase-amphibole pairs), granitic plutons (quartz-feldspar pairs), and Precambrian siliceous iron formations (quartz-magnetite pairs). In all these examples, striking regularities are observed on ??-?? and ??-?? plots, but we point out that ??-?? plots have many advantages over their equivalent ??-?? diagrams, as the latter are more susceptible to misinterpretation. Using the equations developed in this study, these regularities can be interpreted to give semiquantitative information on the exchange histories of these rocks subsequent to their formation. In particular, we present a new interpretation indicating that Precambrian cherty iron formations have in general undergone a complex fluid exchange history in which the iron oxide (magnetite precursor?) has exchanged much faster with low-temperature (< 400??C) fluids than has the relatively inert quartz. ?? 1989.

  3. A Neoarchean subduction recorded by the Eastern Hebei Precambrian basement, North China Craton: Geochemical fingerprints from metavolcanic rocks of the Saheqiao-Shangying-Qinglong supracrustal belt

    Guo, Rongrong; Liu, Shuwen; Bai, Xiang; Wang, Wei


    The Saheqiao-Shangying-Qinglong supracrustal belt (SSQB) in the northern Eastern Hebei Precambrian basement (EHPB) is located in the northern margin of the Eastern Block (EB) of the North China Craton (NCC). The Shangying terrane constitutes the middle segment of the SSQB and contains primarily metamorphic volcanics and plutonic tonalitic gneisses. The metamorphic volcanics mainly consist of pyroxene plagioclase amphibolites, garnet plagioclase amphibolites, biotite plagioclase amphibole gneisses, and amphibole plagioclase gneisses. Zircon U-Pb-Lu-Hf isotopic analyses reveal that the metavolcanic rocks from the Shangying terrane crystallized at ∼2506-2613 Ma with TDM (Hf) values of ∼2541-2944 Ma. These metamorphic volcanic rocks are subdivided into four groups based on their lithological and chemical features. Group I consists chiefly of tholeiites that are characterized by slightly light rare earth element (LREE) depleted patterns and flat multi-element spider diagrams, which are similar to back-arc basin basalt (BABB)-like rocks and were derived from the partial melting of the depleted mantle. The tholeiites in Group II have slightly fractionated rare earth element (REE) patterns without Nb anomalies, exhibit an affinity to Nb-enriched basalt (NEB)-like rocks, and were produced by the partial melting of HFSE-enriched mantle peridotites. Group III is composed of slightly LREE-enriched tholeiites with negative Nb-Ta anomalies that resemble island arc tholeiites. Group IV comprises calc-alkaline basalts and andesites with highly enriched LREEs and evident Nb, Ta and Ti depletions that are geochemically similar to the products of island arcs. The island arc tholeiites and calc-alkaline basalt-andesites originated from the partial melting of sub-arc mantle peridotites that were previously metasomatized by slab-derived fluids/melts with the fractional crystallization of ferromagnesian minerals. Collectively, the BABB-like rocks, the NEBs, arc tholeiites and calc

  4. Geophysically inferred structural and lithologic map of the precambrian basement in the Joplin 1 degree by 2 degrees Quadrangle, Kansas and Missouri

    McCafferty, Anne E.; Cordell, Lindrith E.


    This report is an analysis of regional gravity and aeromagnetic data that was carried out as part of a Conterminuous United States Mineral Assessment Program (CUSMAP) study of the Joplin 1° X 2° quadrangle, Kansas and Missouri. It is one in a series of reports representing a cooperative effort between the U.S. Geological Survey, Kansas Geological Survey, and Missouri Department of Natural Resources, Division of Geology and Land Survey. The work presented here is part of a larger project whose goal is to assess the mineral resource potential of the Paleozoic sedimentary section and crystalline basement within the quadrangle. Reports discussing geochemical, geological, and various other aspects of the study area are included in this Miscellaneous Field Studies Map series as MF-2125-A through MF-2125-E. Geophysical interpretation of Precambrian crystalline basement lithology and structure is the focus of this report. The study of the crystalline basement is complicated by the lack of exposures due to the presence of a thick sequence of Phanerozoic sedimentary cover. In areas where there are no outcrops, the geologist must turn to other indirect methods to assist in an understanding of the basement. Previous investigations of the buried basement in this region used available drill hole data, isotope age information, and regional geophysical data (Sims, 1990; Denison and others, 1984; Bickford and others, 1986). These studies were regional in scope and were presented at state and multistate scales. The work documented here used recently collected detailed gravity and aeromagnetic data to enhance the regional geologic knowledge of the area. Terrace-density and terrace-magnetization maps were calculated from the gravity and aeromagnetic data, leading directly to inferred physical-property (density and magnetization) maps. Once these maps were produced, the known geology and drill-hole data were reconciled with the physical-property maps to form a refined structural and

  5. Precambrian supercontinents, glaciations, atmospheric oxygenation, metazoan evolution and an impact that may have changed the second half of Earth history

    Grant M. Young


    Full Text Available In more than 4 Ga of geological evolution, the Earth has twice gone through extreme climatic perturbations, when extensive glaciations occurred, together with alternating warm periods which were accompanied by atmospheric oxygenation. The younger of these two episodes of climatic oscillation preceded the Cambrian “explosion” of metazoan life forms, but similar extreme climatic conditions existed between about 2.4 and 2.2 Ga. Over long time periods, changing solar luminosity and mantle temperatures have played important roles in regulating Earth's climate but both periods of climatic upheaval are associated with supercontinents. Enhanced weathering on the orogenically and thermally buoyed supercontinents would have stripped CO2 from the atmosphere, initiating a cooling trend that resulted in continental glaciation. Ice cover prevented weathering so that CO2 built up once more, causing collapse of the ice sheets and ushering in a warm climatic episode. This negative feedback loop provides a plausible explanation for multiple glaciations of the Early and Late Proterozoic, and their intimate association with sedimentary rocks formed in warm climates. Between each glacial cycle nutrients were flushed into world oceans, stimulating photosynthetic activity and causing oxygenation of the atmosphere. Accommodation for many ancient glacial deposits was provided by rifting but escape from the climatic cycle was predicated on break-up of the supercontinent, when flooded continental margins had a moderating influence on weathering. The geochemistry of Neoproterozoic cap carbonates carries a strong hydrothermal signal, suggesting that they precipitated from deep sea waters, overturned and spilled onto continental shelves at the termination of glaciations. Paleoproterozoic (Huronian carbonates of the Espanola Formation were probably formed as a result of ponding and evaporation in a hydrothermally influenced, restricted rift setting. Why did metazoan

  6. Permian, Jurassic and Early Cretaceous palynofloral assemblages from subsurface sedimentary rocks in Chuperbhita Coalfield, Rajmahal Basin, India.

    Tripathi, A


    The results of a palynological analysis of the sedimentary sequence of Borehole RCH-151, Chuperbhita Coalfield, Rajmahal Basin, Bihar are presented here. The borehole penetrated the Rajmahal Formation (comprising two traps sandwiching an intertrappean bed), the thinly represented Dubrajpur Formation and in its lower part, the Coal Measures. The coal-bearing interval is associated with Scheuringipollenites barakarensis, Faunipollenites varius, Densipollenites indicus, Gondisporites raniganjensis and Densipollenites magnicorpus Assemblage Zones. The presence of these biostratigraphic units indicates correlation with the Barakar Formation (Early Permian) and the Barren Measures and Raniganj Formations (both Late Permian). This is the first record, in the Chuperbhita Coalfield, of Late Permian strata, which appear to represent a condensed sequence. Prior to the present study, the Permian succession was thought to have been associated entirely with the Barakar Formation. The overlying Dubrajpur Formation yielded a distinct spore-pollen assemblage (in association with the first report of dinoflagellate, Phallocysta), which is assigned to the newly identified Callialasporites turbatus palynozone of latest Early to early Middle Jurassic age. The diverse spore-pollen flora of the intertrappean bed (Rajmahal Formation) incorporates several age marker taxa, viz. Undulatisporites, Leptolepidites, Klukisporites, Ruffordiaspora, and Coptospora. The assemblages from intertrappean beds are correlated with the Ruffordiaspora australiensis palynozone of Australia. Thus the palynodating indicates Permian, latest Early to early Mid-Jurassic and Early Cretaceous age for the strata studied. This is the first record of definite Jurassic microfossils from the non-marine sequence of Rajmahal Basin, India.

  7. Relationship between Precambrian North Korean Peninsula and the North China Craton: Evidence from LA-ICP-MS U-Pb ages of detrital zircons from Neoproterozoic tillites of North Korea and Southern North China Craton

    Hu, B.; Zhai, M.; Peng, P.; Zhang, Y.; Wu, J.; Jia, X.; Zhang, H.; Lei, W.; Zhuang, G.


    Relationship between Precambrian Korean Peninsula and the North China Craton (NCC) is focus of attention. There are Neoproterozoic tillites in Phyongnam Basin, Nangrim massif, North Korea (NK) and Southern NCC. Nangrim massif was regarded as a part of the NCC according to similar Precambrian basements between Nangrim massif and Longgang massif in the Northeast NCC. But the comparation of Neoproterozoic rocks is lacked between NK and NCC. Detrital zircon LA-ICP-MS U-Pb ages of 2 pebbly phyllite samples of Pirangdong Series in Phyongnam Basin and 2 argillaceous cemented mix-conglomeate samples of Luoquan Series in Southern NCC was analyzed in this research. Detrital zircon ages of pebbly phyllites of Pirangdong Series distribute mainly at 1.85 Ga, 1.8 Ga, 1.6 Ga, 1.4 Ga and 1.2 Ga. A small number of them are at 3.2 Ga, 2.6 - 2.5 Ga, 2.3 Ga, 2.1 Ga and 900 - 860 Ma. Detrital zircon ages of mix-conglomeates of Luoquan Series mainly focus on 2.5 Ga, 2.2 Ga, 2.0 Ga, 1.8 Ga and 1.6 Ga. Minor of them distribute at 1.12 Ga. The similar age distribution of Pirangdong and Luoquan Series of 2.6 - 2.5 Ga, 2.1 - 2.0 Ga, 1.85 - 1.8 Ga and 1.6 Ga corresponds to Precambrian significant tectonic- magmatic- thermal events of the NCC, which indicates that the Precambrian basement rocks of the NCC are main provenances of both Pirangdong and Luoquan Series. This also confirm that the Phyongnam Basin is a part of Neoproterozoic sedimentary covers of the NCC. It is worth to mention that 1.2 - 1.0 Ga and 900 - 850 Ma magmatic rocks in the NCC are seldom reported which relate to the assemblage and breakup of Rodinia Supercontinent. whereas they crop out widely in the South China Craton (SCC) and was always regarded as a mark distingusing the two craton. 1.2 - 1.0 Ga and 900 - 850 Ma zircon ages preserved in sedimentary rocks not only in North Korea and Southern NCC but also in Northeast NCC and East NCC provide data to compare Neoproterozoic strata between NCC and SCC and important clues to

  8. Detrital zircon geochronology and Nd isotope geochemistry of an early Paleozoic succession in Korea:

    Lee, Yong Il; Choi, Taejin; Lim, Hyoun Soo; Orihashi, Yuji


    This study reports the results of an analysis of U-Pb ages of detrital zircons and Nd isotope compositions from the well-established lower Paleozoic platform succession developed on the Precambrian gneiss and metasedimentary rocks in South Korea. The three stratigraphic units in the basal part of the succession are the Jangsan, Myeonsan, and Myobong Formations. The unfossiliferous Jangsan (white­to­pink quartz sandstone) and Myeonsan (dark-gray ilmenite-rich sandstone/shale) Formations are in fault contact and are generally considered to be coeval (Early Cambrian). Both formations are also generally considered to be conformably overlain by the dark­ gray, fossiliferous, fine-grained Myobong Formation (late Early-early Middle Cambrian). We here report U-Pb ages of detrital zircons and Nd isotopic data from the Jangsan, Myeonsan, and Myobong Formations. The Jangsan and Myeonsan Formations provide Archean-Paleoproterozoic U-Pb ages, but the former is characterized by Archean Sm-Nd model ages and the latter by late Paleoproterozoic Sm-Nd model ages, which is indicative of a significant change in provenance. This suggests that the Jangsan Formation predates the Myeonsan Formation. The Myobong Formation provides dominantly Meso- to Neoproterozoic U-Pb ages and Sm-Nd model ages that are slightly younger than those of the Myeonsan Formation. Contrary to the conventional wisdom, the combined evidence of unconformable contact and marked changes in zircon U-Pb ages and Nd isotopic compositions suggests that the Myobong Formation overlies the Jangsan and Myeonsan Formations unconformably. Considering the metamorphic age of the immediately underlying Precambrian basement metasediments (0.8 to 0.9 Ga), this stratigraphic relationship strongly suggests that the Jangsan Formation may be Neoproterozoic in age and that the Myeonsan Formation may be latest Neoproterozoic to Early Cambrian and calls for reevaluation of Precambrian-Paleozoic history of the Korean Peninsula. The

  9. Early clerkships

    Kamalski, Digna M. A.; Ter Braak, Edith W. M. T.; Ten Cate, Olle Th. J.; Borleffs, Jan C. C.


    Background: Early clinical experience is being introduced in innovative, vertically integrated undergraduate medical curricula. While in many cases, this early clinical experience is limited to the presence of patients during lectures, in Utrecht students gain 'hands on' experience of daily clinical

  10. Regional trends in evaporation loss and water yield based on stable isotope mass balance of lakes: The Ontario Precambrian Shield surveys

    Gibson, J. J.; Birks, S. J.; Jeffries, D.; Yi, Y.


    Stable isotopes of water, oxygen-18 and deuterium, were measured in water samples collected from a network of 300 lakes sampled in six ∼100 km2 blocks (centred at 49.72°N, 91.46°W; 48.49°N, 91.58°W; 50.25°N, 86.62°W; 49.78°N, 83.98°W; 48.24°N, 85.49°W; 47.73, 84.52°W) within Precambrian shield drainages in the vicinity of Lake Superior, northern Ontario, Canada. Additional sampling was also conducted within the Turkey Lakes watershed (47.03°N, 84.38°W), a research basin situated in the Algoma region located 50 km north of Sault Saint Marie, Ontario. The studies were undertaken to gain a better understanding of hydrology and geochemistry of watersheds in the region in order to better predict acid sensitivity of lakes. The main objective of this paper is to describe the hydrologic variations observed based on stable isotope results. Evaporative isotopic enrichment of lake water was found to be systematic across the region, and its deviation from the isotopic composition of precipitation was used to estimate the evaporation/inflow to the lakes as well as runoff (or water yield) based on a simple isotope mass balance model. The analysis illustrates significant variability in the water yield to lakes and reveals a pattern of positively skewed distributions in all six widely spaced blocks, suggesting that a high proportion of lakes have relatively limited runoff whereas relatively few have greater runoff. Such basic information on the drainage structure of an area can be valuable for site-specific hydrologic assessments but also has significant implications for critical loads assessment, as low runoff systems tend to be less buffered and therefore are more sensitive to acidification. Importantly, the Turkey Lakes sampling program also suggests that isotope-based water yield is comparable in magnitude to hydrometric gauging estimates, and also establishes that uncertainty related to stratification can be as high as ±20% or more for individual lakes

  11. Micrometer-scale chemical and isotopic criteria (O and Si) on the origin and history of Precambrian cherts: Implications for paleo-temperature reconstructions

    Marin-Carbonne, Johanna; Chaussidon, Marc; Robert, François


    Oxygen and silicon isotopes in cherts have been extensively used for the reconstruction of seawater temperature during the Precambrian. These reconstructions have been challenged because cherts can have various origins (hydrothermal, sedimentary, volcanic silicification) and their isotopic compositions might have been reset by metamorphic fluid circulation. Existing criteria used to assess the pristine sedimentary origin of a chert are based on petrography (criterion #1: chert is composed mostly of microquartz); on the bulk oxygen isotopic composition (criterion #2: bulk δ18O has to be close enough to the maximum δ18O value previously measured in other cherts of the same age); and on the presence of a large δ18O range at the micrometer scale (criterion #3: δ18O range of ˜10‰ at ˜2 μm). However, these criteria remain incomplete in determining precisely the origin and degree of preservation of ancient cherts. We report in situ Si and O isotope compositions and trace element concentrations in seven chert samples ranging from 1.88 to 3.5 Ga in age. Correlations between δ30Si and Al2O3 (and K2O, TiO2) reveal that microquartz is of three different origins, i.e. diagenetic, hydrothermal or silicification. Moreover, chert samples composed mostly of diagenetic microquartz show a large range of δ30Si at the micrometer scale (1.7-4.5‰), consistent with the large range of δ18O previously found in the Gunflint diagenetic cherts. We propose two further quantitative criteria to assess the origin, state of preservation and diagenetic history of cherts. Criterion #4 uses trace element concentrations coupled with δ30Si to ascribe the origin of cherts among three possible end-members (diagenetic, hydrothermal, and silicified). Criterion #5 is the presence of a large range of δ30Si in pure diagenetic microquartz. In the seven samples analyzed in this study, only one (from the Gunflint Iron formation at 1.88 Ga) passes all the criteria assessed here and can be used for

  12. Mineralogical and microfabric characteristics of magnetite in the Wuyang Precambrian BIFs, southern North China Craton: Implications for genesis and depositional processes of the associated BIFs

    Li, Hongzhong; Zhai, Mingguo; Zhang, Lianchang; Yang, Zhijun; Kapsiotis, Argyrios; Zhou, Yongzhang; He, Junguo; Wang, Changle; Liang, Jin


    Precambrian Banded Iron Formations (BIFs) are widely distributed in the North China Craton (NCC). Among them, the Wuyang BIFs located in the southern margin of NCC occur in the Late Archaean Tieshanmiao Formation and can be subdivided in two different sub-types: (i) quartz-magnetite BIFs (QMB), consisting of magnetite, fine-microcrystalline quartz and minor calcite and (ii) pyroxene-magnetite BIFs (PMB), composed of pyroxene, fine-microcrystalline quartz and subordinate feldspars. Both sub-types display apparent discrepancies in terms of petrography and mineral composition. As shown in Electron BackScattered Diffraction (EBSD) images and micrographs, magnetite grains from the QMB range in size from tens up to hundreds of μm, whereas magnetite crystals from the PMB can be up to a few tens of μm across. The X-ray diffraction (XRD) structural data indicate that magnetite from both BIF sub-types is equiaxed (cubic) and was generated by sedimentary metamorphic processes. The cell parameters of magnetite in the QMB are a = b = c = 8.396 Å and Z = 8, which deviate slightly from these of magnetite in the PMB: a = b = c = 8.394 Å and Z = 8. The analytical results of Raman spectroscopy analysis revealed micro-structural signatures of both magnetite (Raman shifts near 552 cm-1 and 673 cm-1) and hematite (Raman shifts near 227 cm-1, 295 cm-1 and 413 cm-1). In magnetite from both QMB and PMB, the crystallinity degree is similar for magnetite micro-structures but varies significantly for hematite micro-structures. Oxygen fugacity (fO2) conditions fluctuated during the recrystallization of magnetite in the QMB, whereas no evident variation of fO2 occurred during the formation of magnetite in the PMB. Analytical results of laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) show that the Si, Al and Mg abundances are higher in magnetite from the QMB, whereas the Ti and Mn contents are more elevated in magnetite from the PMB. Magnetite composition also

  13. Research progress of Precambrian iron formations abroad and some problems deserving further discussion%国外前寒武纪铁建造的研究进展与有待深入探讨的问题

    王长乐; 张连昌; 刘利; 代堰锫


    Iron formation (IF), formed during the early Precambrian period, is an iron-rich (TFe> 15%) and siliceous chemical sedimentary rock. It consists chiefly of iron oxides (magnetite and hematite) and quartz. According to its petrographic features, IF can be classified into two types: Banded Iron Formation (BIF) and Granular Iron Formation (GIF); BIF can also be further divided into Algoma type related to volcanic rocks and Superior type related to fine clastic-carbonate rocks on the basis of sedimentary environment. IF began its production at 3.8 Ga, mainly occurred from 2.8 Ga to 1.8 Ga, continuously disappeared after 1.8 Ga, and reappeared in small amounts at about 0.8 Ga because of the Snowball Event. Algoma type BIF was dominantly pro-duced in Meso-Neoarchean, whereas Superior-type BIF was much more common in Paleoproterozoic. The former, mainly formed before cratonization, was closely related to marine volcanic activity and continental accretion while the latter, mainly formed after cratonization, was related to stable craton basins and increasing atmospheric oxygen content. Algoma-type iron deposits are often characterized by smaller-size in terms of single ore body, lower grade and multilayer development, whereas the Superior-type ones have features of larger-size single ore bodies, higher grade and fairly stable layers. Due to extensive production and unrepeatable nature of IF, the research on IF has not only economic value but also important scientific significance. The research trend of IF seems to further focus on such problems as the relationship between IF and early tectonic (mantle plumes and early plate tectonics) evolution, the composition and evolution of hydrosphere and atmosphere, the activity of early organisms in the earth, the genesis of IF and the regularity of its temporal and spatial distribution.%形成于早前寒武纪的铁建造,是一种富铁[ω(TFe)>15%]的硅质化学沉积岩,其主要矿物组成是铁氧化物(磁铁矿和赤

  14. Zircon geochronology of Xingxingxia quartz dioritic gneisses:Implications for the tectonic evolution and Precambrian basement affinity of Chinese Tianshan orogenic belt%星星峡石英闪长质片麻岩的锆石年代学:对天山造山带构造演化及基底归属的意义

    贺振宇; 张泽明; 宗克清; 王伟; 于飞


    protoliths are speculated to be quartz dioritic. Zircon grains from two collected samples have similar internal structures identified on the cathodoluminescence (CL) images, which is characterized by CL-dark, homogeneous rims surrounding the oscillatory zoning cores with rare inherited inner cores. Zircon U-Pb dating results indicate that their protoliths were formed in Early Paleozoic time at ~425Ma, and were metamorphosed during Early Carboniferous at approximately 320 ~360Ma. The inherited zircon cores yield a wide age range of ca. 1381 ~ 1743Ma. The crystallization zircons from the protolith show positive and varying εHf(t) values (from 0. 9 to 17. 8) , and the inherited zircon cores give tDM2 model ages of 1. 54 Ga to 2. 44Ga. The quartz dioritic gneisses are characterized by marked positive Rb, Ba, Th and K anomalies and depletion in Nb, Ta and Ti on the primitive mantle-normalized spider diagrams. Through integration of these new data with the previous results of Precambrian basements, high-grade metamorphic rocks, ophiolitic melanges and igneous rocks from the Tianshan orogen, we suggest that : 1) the Precambrian crustal basements in the Tianshan orogen don' t have much affinity with the Tarim Block, and are inferred to be formed through a magmatic arc accretionary orogen along the margins of Baltica during the Mesoproterozoic; 2) the eastern segment of Central Tianshan was an active continental margin during the Early Paleozoic, due to the subduction of the South Tianshan Ocean; 3) the closure of the South Tianshan Ocean may be synchronous in its eastern and western segments.

  15. Origin of Mesozoic and Tertiary granite in the western United States and implications for Pre-Mesozoic crustal structure: 2. Nd and Sr isotopic studies of unmineralized and Cu- and Mo-mineralized granite in the Precambrian Craton

    Farmer, G. Lang; Depaolo, Donald J.


    In the Cordilleran region of the western United States, Mesozoic and Tertiary peraluminous granitic rocks display regional variations in initial 143Nd/144Nd (ɛNd); ɛNd = -10 to -12 in southern Arizona, - 17 to -19 in the northern Great Basin (NGB), and -30 in the northern Rocky Mountains. Initial 87Sr/86Sr values are between 0.710 and 0.721 and show no regional pattern. Metaluminous granitic rocks have a wider range of ɛNd values extending from values similar to those of the peraluminous granites to much higher values. The 87Sr/86Sr values are mostly fairly low, between 0.705 and 0.710 except in the NGB where values as high as 0.7157 are observed. No systematic differences between the ɛNd or 87Sr/86Sr values of Cu- or Mo-mineralized and Unmineralized granite were discerned, except for Cu-mineralized granite in eastern Nevada and Mo-mineralized granite in Colorado, which have ɛNd values higher (˜0) and lower ( ˜-10.0), respectively, than Unmineralized granite in the same region. Comparison to ɛNd values of exposed Precambrian rock suggests that the peraluminous granite, and the Mo granite in Colorado, were derived exclusively from felsic Precambrian basement rocks and that the regional variations in the ɛNd values reflect the regional variation in the average crustal age. The Nd data confirm that the Precambrian basement underlying the NGB and eastern California is isotopically distinct from Precambrian crust in the remainder of the western United States. The similarity between the ɛNd values of peraluminous granite and Precambrian crust also suggests that the high 147Sm/144Nd (>0.13) and the low total light rare earth element (LREE) abundances characteristic of peraluminous granite in southern Arizona were imposed during the chemical evolution of the magmas. Metaluminous granite are interpreted to have formed via mixing of mantle-derived magma and large proportions of low 87Sr/86Sr (granulite facies) lower crust, except in the eastern NGB where the mantle

  16. Early literacy

    Jensen, Anders Skriver


    This paper discusses findings from the Danish contribution to the EASE project, a European research project running from 2008 to 2010 on early literacy in relation to the transition from childcare to school. It explores a holistic, inclusive approach to early literacy that resists a narrow...... and schools. The paper also draws on Gee’s (2001, 2003, 2004, 2008) sociocultural approach to literacy, and Honneth’s (2003, 2006) concept of recognition. Emphasizing participation and recognition as key elements, it claims that stakeholders in early liter- acy must pay attention to how diverse early literacy...... opportunities empower children, especially when these opportunities are employed in a project-based learning environ- ment in which each child is able to contribute to the shared literacy events....

  17. 甘肃敦煌水峡口地区前寒武纪岩石的锆石U-Pb年龄、Hf同位素组成及其地质意义%Zircon geochronology and Lu-Hf isotope compositions for Precambrian rocks of the Dunhuang complex in Shuixiakou area, Gansu Province

    赵燕; 第五春荣; 孙勇; 朱涛; 王洪亮


    Dunhuang block is located in the southeast of Tarim Craton,and the research of Precambrian Dunhuang complex is of great significance in investigating the formation and evolution of the crust of Dunhuang block,as well as its tectonic relationship with the North China Craton and Yangtze Craton.Dunhuang complex,in Shuixiakou area,Gansu Province,mainly consists of tonaliticgranodioritic gneisses,granitic gneisses and metamorphosed supracrustal rocks.The age of 2561 ± 16Ma and 2510 ± 22Ma respectively for the tonalitic and the granitic gneisses by LA-ICP-MS U-Pb dating of zircons confirm the existence of Archean rocks in Dunhuang complex,LA-ICP-MS U-Pb dating of zircons yielded a metamorphic age of 1806-± 14Ma for the amphibolite,and its parent magma probably derived from the partial melting of ancient lithospheric mantle.Based on the integration of our study and the available data,we put forward that Dunhuang complex has experienced a metamorphism during the Late Paleoproterozoic (1.80 ~ 1.85Ga).The analysis of Hf isotopes of zircons indicates that ~ 2.5Ga is a major period of crustal growth in Dunhuang block during the Neoarchean,while the ~ 1.8Ga tectonic-thermal event represent a reworking period of ancient crust.The above data show that the formation and evolution of Dunhuang block is similar with the North China Craton during Early Precambrian,and they are involved in the global collision-orogenic event during Columbia Period.%敦煌杂岩位于塔里木克拉通的东部,探寻和研究其中的早前寒武纪地质体对于探讨敦煌地块早前寒武纪地壳的形成和演化及其构造归属等问题具有重要的意义.甘肃敦煌水峡口地区的敦煌杂岩主要由英云闪长质片麻岩、花岗闪长质片麻岩以及表壳岩石组成.利用LA-ICP-MS锆石U-Pb定年方法测得水峡口英云闪长片麻岩和花岗片麻岩原岩的形成年龄分别为2561±16Ma和2510±22Ma,确证了在敦煌杂岩中存在太古宙岩石.此外,还

  18. Palaeomagnetism of Precambrian dyke swarms in the North China Shield: The ˜1.8 Ga LIP event and crustal consolidation in late Palaeoproterozoic times

    Piper, John D. A.; Jiasheng, Zhang; Huang, Baochung; Roberts, Andrew P.


    The North China Shield (NCS) is cut by a laterally-extensive dyke swarm emplaced at 1.78-1.76 Ga when an extensional regime succeeded regional metamorphism and completion of cratonisation by ˜1.85 Ga. Palaeomagnetic study of these dykes and adjoining metamorphic country rocks identifies a dominant shallow axis comprising a contiguous population with NE to N declinations and rare opposite polarity. Dykes with NE shallow magnetic declination (A1, D/ I = 36/-1°) recognised from previous study and emplaced in granulite terranes in the north are displaced by more northerly declinations (A2, D/ I = 8/2°) in lower grade metamorphic terranes to the south. Contact tests indicate a primary cooling-related origin to these magnetisations although tests are in part ambiguous because magnetisations in the granulite basement are comparable. Petrologic and rock magnetic considerations imply that magnetisation of the dykes occurred during uplift from depths as deep as 20 km following the peak of metamorphism at ˜1.85 Ga. A temporal migration A2 → A1 is implied by the higher crustal level and earlier acquisition of the former, and the deeper source and later acquisition of the latter. A third population of dyke magnetisations (A3, D/ I = 18/43°) is distributed towards steeper inclinations and close to the Mesozoic-Recent palaeofield. These are either partial or complete overprints of A1-A2 magnetisations with greater degrees of alteration indicated by demagnetisation and thermomagenetic spectra, or are much younger dykes of Mesozoic-Tertiary age. A minority fourth (later Precambrian but presently undated) dual polarity population has a magnetisation (11 dykes, D/ I = 108/7°) with contact tests indicating a primary cooling-related origin. The ˜1.78-1.76 Ga time of emplacement of the dominant dyke swarms in this study is widely represented by contemporaneous igneous rocks in other major shields linked to major Large Igneous Province (LIP)-related events. The new definition of

  19. Mass Independent Fractionation of Sulphur Isotopes in Precambrian Sedimentary Rocks: Indicator for Changes in Atmospheric Composition and the Operation of the Global Sulphur Cycle

    Peters, M.; Farquhar, J.; Strauss, H.


    mass independent fractionation of sulphur isotopes. In Palaeoproterozoic sediments of the Brockman Iron Fm., just prior to the proposed Great Oxidation Event, we determined predominantly negative Δ33S values between -1.07 and +0.08 ‰, which is atypical for sulphides. We interpret this negative MIF signal as a product of microbial reduction of atmospheric sulphate with an original negative MIF signature. This observation may indicate a higher concentration of sulphate in the ocean. Mass independent sulphur isotope data presented here provide a deeper insight into the major steps in atmospheric evolution and the Precambrian sulfur cycle. Ohmoto, H., Watanabe, Y., Ikemi, H. (2005) Geochim. Cosmochim. Acta 69, A 450 (abstr.). Pavlov, A.A., Kasting, J.F., Brown, L.L. (2001) JGR 106, 23267-23287.

  20. Early maize (Zea mays L.) cultivation in Mexico: dating sedimentary pollen records and its implications.

    Sluyter, Andrew; Dominguez, Gabriela


    A sedimentary pollen sequence from the coastal plain of Veracruz, Mexico, demonstrates maize cultivation by 5,000 years ago, refining understanding of the geography of early maize cultivation. Methodological issues related to bioturbation involved in dating that record combine with its similarity to a pollen sequence from the coastal plain of Tabasco, Mexico, to suggest that the inception of maize cultivation in that record occurred as much as 1,000-2,000 years more recently than the previously accepted 7,000 years ago. Our analysis thereby has substantive, theoretical, and methodological implications for understanding the complex process of maize domestication. Substantively, it demonstrates that the earliest securely dated evidence of maize comes from macrofossils excavated near Oaxaca and Tehuacán, Mexico, and not from the coastal plain along the southern Gulf of Mexico. Theoretically, that evidence best supports the hypothesis that people in the Southern Highlands domesticated this important crop plant. Methodologically, sedimentary pollen and other microfossil sequences can make valuable contributions to reconstructing the geography of early maize cultivation, but we must acknowledge the limits to precision that bioturbation in coastal lagoons imposes on the dating of such records.

  1. Reconstruction of early Cambrian ocean chemistry from Mo isotopes

    Wen, Hanjie; Fan, Haifeng; Zhang, Yuxu; Cloquet, Christophe; Carignan, Jean


    The Neoproterozoic-Cambrian transition was a key time interval in the history of the Earth, especially for variations in oceanic and atmospheric chemical composition. However, two conflicting views exist concerning the nature of ocean chemistry across the Precambrian-Cambrian boundary. Abundant geochemical evidence suggests that oceanic basins were fully oxygenated by the late Ediacaran, while other studies provide seemingly conflicting evidence for anoxic deep waters, with ferruginous conditions [Fe(II)-enriched] persisting into the Cambrian. Here, two early Cambrian sedimentary platform and shelf-slope sections in South China were investigated to trace early Cambrian ocean chemistry from Mo isotopes. The results reveal that early Cambrian sediments deposited under oxic to anoxic/euxinic conditions have δ98/95Mo values ranging from -0.28‰ to 2.29‰, which suggests that early Cambrian seawater may have had δ98/95Mo values of at least 2.29‰, similar to modern oceans. The heaviest and relatively homogeneous δ98/95Mo values were recorded in siltstone samples formed under completely oxic conditions, which is considered that Mn oxide-free shuttling was responsible for such heavy δ98/95Mo value. Further, combined with Fe species data and the accumulation extent of Mo and U, the variation of δ98/95Mo values in the two studied sections demonstrate a redox-stratified ocean with completely oxic shallow water and predominantly anoxic (even euxinic) deeper water having developed early on, which eventually became completely oxygenated. This suggests that oceanic circulation at the time became reorganized, and such changes in oceanic chemistry may have been responsible for triggering the "Cambrian Explosion" of biological diversity.

  2. Paleobiological Perspectives on Early Eukaryotic Evolution

    Knoll, Andrew H.


    Eukaryotic organisms radiated in Proterozoic oceans with oxygenated surface waters, but, commonly, anoxia at depth. Exceptionally preserved fossils of red algae favor crown group emergence more than 1200 million years ago, but older (up to 1600–1800 million years) microfossils could record stem group eukaryotes. Major eukaryotic diversification ∼800 million years ago is documented by the increase in the taxonomic richness of complex, organic-walled microfossils, including simple coenocytic and multicellular forms, as well as widespread tests comparable to those of extant testate amoebae and simple foraminiferans and diverse scales comparable to organic and siliceous scales formed today by protists in several clades. Mid-Neoproterozoic establishment or expansion of eukaryophagy provides a possible mechanism for accelerating eukaryotic diversification long after the origin of the domain. Protists continued to diversify along with animals in the more pervasively oxygenated oceans of the Phanerozoic Eon. PMID:24384569

  3. Distinguishing major lithologic types in rocks of precambrian age in central Wyoming using multilevel sensing, with a chapter on possible economic significance of iron formation discovered by use of aircraft images in the Granite Mountains of Wyoming

    Houston, R. S. (Principal Investigator)


    The author has identified the following significant results. Information obtained by remote sensing from three altitude levels: ERTS-1 (565 miles), U-2 (60,000 feet), and C-130 aircraft (15,000 feet) illustrates the possible application of multilevel sensing in mineral exploration. Distinction can be made between rocks of greenstone belts and rocks of granite-granite gneiss areas by using ERTS-1 imagery in portions of the Precambrian of central Wyoming. Study of low altitude color and color infrared photographs of the mafic terrain revealed the presence of metasedimentary rocks with distinct layers that were interpreted as amphibolite by photogeologic techniques. Some of the amphibolite layers were found to be iron formation when examined in the field. To our knowledge this occurrence of iron formation has not been previously reported in the literature.

  4. Zircon U-Pb geochronology, geochemistry and its geological implications for the Precambrian granitoids in Zhongtiao Mountain, Shanxi Province%中条山前寒武纪花岗岩地球化学、年代学及其地质意义

    张瑞英; 张成立; 第五春荣; 孙勇


    涉及华北克拉通基底拼合的时、空演化近年已成为华北克拉通研究的热点之一.开展对华北克拉通中部带中条山前寒武纪涑水杂岩中非TTG质花岗岩的研究有可能为讨论这一问题提供重要信息.涑水杂岩中非TTG质的花岗岩以横岭关、解州黑云二长花岗岩和烟庄钾长花岗岩为代表,岩相学、地球化学和LA-ICP-MS锆石U-Pb定年结果显示,横岭关和解州黑云二长花岗岩具有相似的岩相学、地球化学特征和几乎一致的形成年龄(锆石年龄分别为2609±31Ma和2620±14Ma),表明它们属于同一期岩浆活动的产物.烟庄钾长花岗岩形成于古元古代(2351±37Ma).横岭关、解州黑云二长花岗岩锆石εHf(t)值分别为-2.3~+4.8和+4.4~ +7.6,对应的模式年龄分别为2791~ 3222Ma和2628 ~2823Ma.新太古代横岭关和解州黑云二长花岗岩属于高钾钙碱性Ⅰ型花岗岩,源自~2.7Ga的TTG岩石和下地壳镁铁质岩石部分熔融混合而成.烟庄钾长花岗岩中锆石的εHf(t)值为-1.8~ +7.8,对应的模式年龄为2408~2996Ma,类似低Sr、Yb的喜马拉雅型花岗岩,其成因与地壳加厚引起陆壳熔融相关.综合前人及本项研究成果发现,华北克拉通中部带在2.8~ 1.8Ga这一长达10亿年的地壳演化过程中,并不存在明显的地壳生长“幕式”特点,而显示出小频率持续脉冲生长的特点,表明华北的东部、西部和中部带在晚太古代末之前已经是统一的陆块.%The geometry and timing of amalgamation of the North China Craton ( NCC ) have been controversial. The research on the Precambrian Sushui Complex in Zhongtiao Mountain, located in the Trans-North China Orogen, can provide important information for Early Precambrian geological evolution of the NCC. This paper concentrates mainly on the Henglingguan, Xiezhou and Yanzhuang granites, which are the representative components of cala-alkaline granitoids of the Precambrian Sushui

  5. Precambrian crustal contribution to the Variscan accretionary prism of the Kaczawa Mountains (Sudetes, SW Poland): evidence from SHRIMP dating of detrital zircons

    Kryza, Ryszard; Zalasiewicz, Jan; Mazur, Stanisław; Aleksandrowski, Paweł; Sergeev, Sergey; Larionov, Alexander


    SHRIMP dating of detrital zircons from sandstones of the Gackowa Formation (Kaczawa Complex, Sudetes, SW Poland) indicates input from late (550-750 Ma) and early Proterozoic to Archaean sources (˜2.0-3.4 Ga, the latter being the oldest recorded age from the Sudetic region). These dates preclude within-terrane derivation from seemingly correlatory acid volcanic rocks of early Palaeozoic age. Rather, they indicate provenance from Cadomian and older rocks that currently form part of other, geographically distant terranes; the most likely source identified to date is the Lusatian Block in the Saxothuringian Zone. Hence, the Gackowa Formation may be late Proterozoic rather than early Palaeozoic in depositional age, possibly coeval with the late Proterozoic (pre-Cadomian) greywackes of Lusatia, being subsequently tectonically interleaved with early Palaeozoic volcanic rocks into the Kaczawa accretionary prism during the Variscan orogeny. However, correlation with the lithologically similar early Ordovician Dubrau Quartzite of Saxothuringia, and so assignation to the early Paleozoic (post-Cadomian) rift succession deposited at the northern margin of Gondwana, cannot yet be precluded.

  6. Early Holocene groundwater table fluctuations in relation to rice domestication in the middle Yangtze River basin, China

    Liu, Tao; Liu, Yan; Sun, Qianli; Zong, Yongqiang; Finlayson, Brian; Chen, Zhongyuan


    The early Holocene environmental amelioration stimulated the trajectory of Neolithic farming cultures and specific geographic settings played a role in determining the nature of these cultures. Using microfossil evidence, the present study reveals that the fluctuations of the groundwater table substantially influenced rice domestication in the Dongting Lake area of the middle Yangtze River basin in the early Holocene. Our 14C-dated sediment core taken from the Bashidang (BSD) Neolithic site contains evidence that the site was a floodplain prior to human occupation ca. 8600 years ago. Poaceae, which contained wild rice (Oryza sp.) as indicated by combined pollen and phytolith evidence, and low counts of freshwater algae indicated a moist site condition. The area then gradually evolved into wetlands as the water table rose, in response to the increasing monsoon precipitation during the early Holocene. This favored rice domestication, assisted by firing and clearing, that continued to flourish for several hundred years. Finally, rice domestication declined during the late stage of the Pengtoushan culture, accompanied by evidence of the expansion of wetlands reflecting the effects of a rising groundwater table that had caused the cessation of rice farming at the Bashidang site after ca. 8000-7900 cal yr BP. This study shows that there are local effects at particular sites that may differ from the trend at the regional scale, necessitating a careful interpretation of the available evidence.

  7. Siderophilic Cyanobacteria: Implications for Early Earth.

    Brown, I. I.; Mummey, D.; Sarkisova, S.; Shen, G.; Bryant, D. A.; Lindsay, J.; Garrison, D.; McKay, D. S.


    Of all extant environs, iron-depositing hot springs (IDHS) may exhibit the greatest similarity to late Precambrian shallow warm oceans in regards to temperature, O2 gradients and dissolved iron and H2S concentrations. Despite the insights into the ecology, evolutionary biology, paleogeobiochemistry, and astrobiology examination of IDHS could potentially provide, very few studies dedicated to the physiology and diversity of cyanobacteria (CB) inhabiting IDHS have been conducted. Results. Here we describe the phylogeny, physiology, ultrastructure and biogeochemical activity of several recent CB isolates from two different greater Yellowstone area IDHS, LaDuke and Chocolate Pots. Phylogenetic analysis of 16S rRNA genes indicated that 6 of 12 new isolates examined couldn't be placed within established CB genera. Some of the isolates exhibited pronounced requirements for elevated iron concentrations, with maximum growth rates observed when 0.4-1 mM Fe(3+) was present in the media. In light of "typical" CB iron requirements, our results indicate that elevated iron likely represents a salient factor selecting for "siderophilicM CB species in IDHS. A universal feature of our new isolates is their ability to produce thick EPS layers in which iron accumulates resulting in the generation of well preserved signatures. In parallel, siderophilic CB show enhanced ability to etch the analogs of iron-rich lunar regolith minerals and impact glasses. Despite that iron deposition by CB is not well understood mechanistically, we recently obtained evidence that the PS I:PS II ratio is higher in one of our isolates than for other CB. Although still preliminary, this finding is in direct support of the Y. Cohen hypothesis that PSI can directly oxidize Fe(2+). Conclusion. Our results may have implications for factors driving CB evolutionary relationships and biogeochemical processes on early Earth and probably Mars.

  8. A micropalaeontological and palynological insight into Early Carboniferous floodplain environments

    Bennett, Carys; Kearsey, Timothy; Davies, Sarah; Millward, David; Marshall, John; Reeves, Emma


    Romer's Gap, the interval following the end Devonian mass extinction, is traditionally considered to be depauperate in tetrapod and fish fossils. A major research project (TW:eed -Tetrapod World: early evolution and diversification) focusing on the Tournaisian Ballagan Formation of Scotland is investigating how early Carboniferous ecosystems rebuilt following the extinction. A multi-proxy approach, combining sedimentology, micropalaeontology and palynology, is used to investigate the different floodplain environments in which tetrapods, fish, arthropods and molluscs lived. The formation is characterised by an overbank facies association of siltstone, sandstone and palaeosols, interbedded with dolostone and evaporite units, and cut by fluvial sandstone facies associations of fining-upwards conglomerate lags, cross-bedded sandstone and rippled siltstone. Macrofossils are identified from 326 horizons within a 520 metre thick Ballagan Formation field section at Burnmouth, near Berwick-upon-Tweed, Scottish Borders. Common fauna are ostracods, bivalves, arthropods, sarcopterygians, dipnoans, acanthodians, tetrapods and chondrichthyans. Quantitative microfossil picking of the three sedimentary rock types in which tetrapods occur was undertaken to gain further insight into the palaeoecology. The sediments are; 1) laminated grey siltstones, deposited in floodplain lakes; 2) sandy siltstones, grey siltstones with millimetre size clasts. 71% of these beds overlie palaeosols or desiccated surfaces and are formed in small-scale flooding events; 3) conglomerates, mostly lags at the base of thick sandstones, with centimetre sized siltstone, sandstone and dolostone clasts. Grey siltstones contain a microfauna of common plant fragments, megaspores and sparse actinopterygian and rhizodont fragments. Sandy siltstones have the highest fossil diversity and contain microfossil fragments of plants, megaspores, charcoal, ostracods, actinopterygians, rhizodonts, eurypterids and rarer non




    他地区的裂谷盆地之生物地层,岩相,古环境重建,孔隙度和渗透率预测,盆地勘探和盆地建模开辟了一个新窗口.%Over 200 core samples from 2 wells in the Gialo High of the Sirt Basin,Libya,have been conducted for micropaleontological study.A number of silicified marine microfossils are discovered for the first time in the Nubian Sandstones that have been long considered as terrestrial origin prior to Neocomian.Silicified fossils show that in Gialo area the Nubian Sandstones moderately-severely cemented and recrystallized with silica are characterized by subtidal supertidal deposits with low amplitudes of sea-level fluctuations.The main body of the Nubian Sandstones is dated as Albian using silicified microfossils and nannofossils,although little Aptian deposits might exist in the lowermost part of Well I.Four types of silicified microfossils have been recognized.Type Ⅰ bearing calcareous cortex,is partially replaced by amorphous silica with distinct original features of fossils,Type Ⅱ is completely replaced by amorphous silica and has moderately preserved interior and exterior features on smooth surface,Type Ⅲ is replaced by microcrystalline quartzes with poorly preserved features on surface,and Type Ⅳ is replaced by megacrystalline quartzes without marked interior and exterior features.These silicified microfossils are considered to be formed during different stages of diagenesis.Type Ⅲ and Ⅳ (particularly Type Ⅳ) are associated with severe cementation of silica in the coarse sandstones.Well primarily developed interstitial conduits between sand grains may allow a large volume of silicaborne fluid flow to travel around,which yields more severe precipitation,cementation and recrystallization of silica than in finely grained deposits.Fossil silicification in the Gialo High appears to be linked to the regional and local tectonic and hydrothermal activities due to frequent occurrences of faulting and volcanisms

  10. Early Neogene unroofing of the Sierra Nevada de Santa Marta along the Bucaramanga -Santa Marta Fault

    Piraquive Bermúdez, Alejandro; Pinzón, Edna; Bernet, Matthias; Kammer, Andreas; Von Quadt, Albrecht; Sarmiento, Gustavo


    Plate interaction between Caribbean and Nazca plates with Southamerica gave rise to an intricate pattern of tectonic blocks in the Northandean realm. Among these microblocks the Sierra Nevada de Santa Marta (SNSM) represents a fault-bounded triangular massif composed of a representative crustal section of the Northandean margin, in which a Precambrian to Late Paleozoic metamorphic belt is overlain by a Triassic to Jurassic magmatic arc and collateral volcanic suites. Its western border fault belongs to the composite Bucaramanga - Santa Marta fault with a combined left lateral-normal displacement. SE of Santa Marta it exposes remnants of an Oligocene marginal basin, which attests to a first Cenoizoic activation of this crustal-scale lineament. The basin fill consists of a sequence of coarse-grained cobble-pebble conglomerates > 1000 m thick that unconformably overlay the Triassic-Jurassic magmatic arc. Its lower sequence is composed of interbedded siltstones; topwards the sequence becomes dominated by coarser fractions. These sedimentary sequences yields valuable information about exhumation and coeval sedimentation processes that affected the massif's western border since the Upper Eocene. In order to analyse uplifting processes associated with tectonics during early Neogene we performed detrital zircon U-Pb geochronology, detrital thermochronology of zircon and apatites coupled with the description of a stratigraphic section and its facies composition. We compared samples from the Aracataca basin with analog sequences found at an equivalent basin at the Oca Fault at the northern margin of the SNSM. Our results show that sediments of both basins were sourced from Precambrian gneisses, along with Mesozoic acid to intermediate plutons; sedimentation started in the Upper Eocene-Oligocene according to palynomorphs, subsequently in the Upper Oligocene a completion of Jurassic to Cretaceous sources was followed by an increase of Precambrian input that became the dominant

  11. 华北克拉通前寒武纪BIF铁矿研究:进展与问题%Study of the Precambrian BIF-iron deposits in the North China Craton: Progresses and questions

    张连昌; 翟明国; 万渝生; 郭敬辉; 代堰锫; 王长乐; 刘利


    为低氧或缺氧环境,而铕正异常可能指示BIFs为热水沉积成因,其机制可能为海水对流循环从新生镁铁质-超镁铁质洋壳中淋滤出F(e)和Si等元素,在海底排泄沉淀成矿,而条带状构造的形成可能归咎于成矿流体的脉动式喷溢.但对于BIF铁矿的物质来源、成矿条件和机制、富铁矿成因、华北克拉通不发育苏比利尔湖型铁矿的原因等方面,仍需深入研究.%It is shown that regular patterns can be established for the distribution of BIF-iron deposits in the North China Craton ( NCC). Large scale BIF-iron deposits mainly exist in some greenstone-belts areas such as Anshan-Benxi, eastern Hebei, Huoqiu-Wuyang, Wutai, western Shandong and Guyang etc; formation ages of BIF in the NCC cover a wide range from Paleoarchean to Early Paleoproterozoic, among which Late Neoarchean is the peak period (2. 52 ~2. 56Ga) ; BIF can be divided into two types, Algoma and Superior Lake. Most BIFs occurring in Neoarchean greenstone belts in the NCC belong to the former while only the Paleoproterozoic Yuanjiacun iron deposit in the Lvliang area has typical characteristics similar to Superior-type BIF. Five specific types for BIFs in the NCC can be divided on the basis of their occurrences in greenstone belts successions and their relations with rock assembly: 1 ) amphibolites ( or hornblende plagioclase gneiss) and magnetite quartzite association; 2) amphibolites, biotite leptynite, mica quartz schist, and magnetite quartzite association; 3 ) biotite leptynite ( or biotite quartz schist) and magnetite quartzite association; 4) biotite leptynite, sericite chlorite schist, biotite quartz schist and magnetite quartzite association; and 5) amphibolites (gneiss) , marble and magnetite quartzite association. The formation era of BIFs in the NCC is in accordance with magmatic activity in Early Precambrian, but there is some deviation from the peak period of crustal growth of the NCC, due to Neoarchean intense

  12. The Tendaguru formation of southeastern Tanzania, East Africa: An alternating Late Jurassic to Early Cretaceous palaeoenvironment of exceptional status

    Sames, B.


    Dinosaur remains have inspired considerable scientific interest in the Tendaguru formation of southeastern Tanzania during the 20th century; however, this formation is exceptional in many other respects. The Late Jurassic to Early Cretaceous deposits of the Tendaguru formation in the southwestern Tethys are unique because they represent a marginal marine palaeoenvironment with nonmarine faunal and floral content. It is a threefold succession of marginal marine to terrestrial, carbonate-siliciclastic sediments with cyclic character, consisting of three transgressive-regressive cycles. Revisitation of the type locality (the Tendaguru, a hill approximately 60km northwest of the town of Lindi) by a German-Tanzanian expedition in summer 2000 (Heinrich et al., 2001) resulted in a new standard section (hitherto unpublished, the informal terminology is indicated by the use of lower case in Tendaguru formation), a refined environmental model (Aberhan et al., 2002) and many new insights towards its geology (with evidence of event-sedimentation, Bussert and Aberhan, 2004), biostratigraphy and a better understanding of the Tendaguru palaeo-ecosystems and the palaeoclimate. Within the scope of the designation of a new standard section at the type locality, calcareous microfossils (ostracods, charophytes) have been described to supplement the ongoing discussion about the age and palaeoecology of the Tendaguru formation (Sames, 2008). Although only a few unevenly distributed layers across the section produced calcareous microfossils, the results are very promising. A total of 40 ostracode and 2 charophyte taxa could be distinguished. The non-marine part of the ostracod fauna provides an important contribution to the documentation of Purbeck/Wealden-type nonmarine palaeoenvironments and its microfaunas and -floras previously unknown from East Africa. The marine faunal part belongs to a relatively endemic southern (Gondwana) fauna. Together with other fossil groups, the

  13. Micropaleontology and palaeoclimate during the early Cretaceous in the Lishu depression, Songliao basin, Northeast China

    Wei Yan


    Full Text Available Diverse and abundant microfossils, such as palynomorphs, algae and Ostracoda, were collected from lower Cretaceous strata of Lishu depression, located in southeastern Songliao basin, and were identified and classified in order to provide relevant, detailed records for paleoclimate research. The early Cretaceous vegetation and climate of southeastern Songliao basin have been inferred from the analysis of palynomorph genera, algae and Ostracoda of the LS1 and SW110 wells. The lower Cretaceous strata include, in ascending stratigraphic order, the Shahezi, Yingcheng and Denglouku formations. Palynological assemblages for each formation, based on biostratigraphic and statistical analyses, provide an assessment of their longitudinal variations. During deposition of the Shahezi Formation, the climate was mid-subtropical. Vegetation consisted of coniferous forest and herbage. During deposition of the Yingcheng Formation, the climate was south Asian tropical. Vegetation consisted mainly of coniferous forest and herbal shrub. In addition, fresh and saline non-marine water dominated the lacustrine setting during deposition of these formations. Deposition of the Denglouku Formation, however, occurred under a hot and dry tropical climate. The vegetation was mostly coniferous forest and lake waters became saline. Palaeoclimate variation is correlated by the lake level change and the development of sedimentary facies. Palaeoclimate contribute to the formation of hydrocarbon source rocks and reservoir.

  14. Early Astronomy

    Thurston, Hugh

    The earliest investigations that can be called scientific are concerned with the sky: they are the beginnings of astronomy. Many early civilizations produced astronomical texts, and several cultures that left no written records left monuments and artifacts-ranging from rock paintings to Stonehenge-that show a clear interest in astronomy. Civilizations in China, Mesopotamia, India and Greece had highly developed astronomies, and the astronomy of the Mayas was by no means negligible. Greek astronomy, as developed by the medieval Arab philosophers, evolved into the astronomy of Copernicus. This displaced the earth from the central stationary position that almost all earlier astronomies had assumed. Soon thereafter, in the first decades of the seventeenth century, Kepler found the true shape of the planetary orbits and Galileo introduced the telescope for astronomical observations.

  15. 2.6 Ga Gabbro-tonalite-trondhjemite Complex and 2.5 Ga Potassic Granite in Quruqtagh. Geochronology, Geochemistry and Their Implications on the Early Precambrian Tectonic Evolution of the Tarim Block, NW China

    ZHANG Chuan-lin; LI Xian-hua; LI Zheng-xiang; YE Hai-min


    @@ Field observation, ages and geochemistry of the Neoarchaean intrusive complex in Quruqtagh in northern mar-gin of the Tarim Block, NW China, are reported to decipher the Neoarchaean tectonic evolution of the Tarim Block.

  16. Tracing Biosignature Preservation of Geothermally Silicified Microbial Textures into the Geological Record.

    Campbell, Kathleen A; Lynne, Bridget Y; Handley, Kim M; Jordan, Sacha; Farmer, Jack D; Guido, Diego M; Foucher, Frédéric; Turner, Susan; Perry, Randall S


    New Zealand and Argentine (Late Jurassic-Recent) siliceous hot-spring deposits (sinter) reveal preservation pathways of environmentally controlled, microbe-dominated sedimentary facies over geological time scales. Texturally distinctive, laminated to thinly layered, dense and vertically oriented, microtubular "palisade" fabric is common in low-temperature (geothermal deposits with mineralized microbial components are relevant analogs for Precambrian geobiology because early life is commonly preserved as microbial microfossils and biofilms in silica, some of it hydrothermal in origin. Yet the diagenetic "movie" has already been run. Hence, studying younger sinters of a range of ages provides an opportunity to "play it again" and follow the varied influences on biosignatures into the deep-time geological record.

  17. Late Precambrian Balkan-Carpathian ophiolite — a slice of the Pan-African ocean crust?: geochemical and tectonic insights from the Tcherni Vrah and Deli Jovan massifs, Bulgaria and Serbia

    Savov, Ivan; Ryan, Jeff; Haydoutov, Ivan; Schijf, Johan


    The Balkan-Carpathian ophiolite (BCO), which outcrops in Bulgaria, Serbia and Romania, is a Late Precambrian (563 Ma) mafic/ultramafic complex unique in that it has not been strongly deformed or metamorphosed, as have most other basement sequences in Alpine Europe. Samples collected for study from the Tcherni Vrah and Deli Jovan segments of BCO include cumulate dunites, troctolites, wehrlites and plagioclase wehrlites; olivine and amphibole-bearing gabbros; anorthosites; diabases and microgabbros; and basalts representing massive flows, dikes, and pillow lavas, as well as hyaloclastites and umbers (preserved sedimentary cover). Relict Ol, Cpx and Hbl in cumulate peridotites indicate original orthocumulate textures. Plagioclase in troctolites and anorthosites range from An 60 to An 70. Cumulate gabbro textures range from ophitic to poikilitic, with an inferred crystallization order of Ol-(Plag+Cpx)-Hbl. The extrusive rocks exhibit poikilitic, ophitic and intersertal textures, with Cpx and/or Plag (Oligoclase-Andesine) phenocrysts. The major opaques are Ti-Magnetite and Ilmenite. The metamorphic paragenesis in the mafic samples is Chl-Trem-Ep, whereas the ultramafic rocks show variable degrees of serpentinization, with lizardite and antigorite as dominant phases. Our samples are compositionally and geochemically similar to modern oceanic crust. Major element, trace element and rare earth element (REE) signatures in BCO basalts are comparable to those of MORB. In terms of basalt and dike composition, the BCO is a 'high-Ti' or 'oceanic' ophiolite, based on the classification scheme of Serri [Earth Planet. Sci. Lett. 52 (1981) 203]. Our petrologic and geochemical results, combined with the tectonic position of the BCO massifs (overlain by and in contact with Late Cambrian island arc and back-arc sequences), suggest that the BCO may have formed in a mid-ocean ridge setting. If the BCO records the existence of a Precambrian ocean basin, then there may be a relationship

  18. Poor understanding of the hydrogeological structure is a main cause of hand-dug wells failure in developing countries: A case study of a Precambrian basement aquifer in Bugesera region (Burundi)

    Bakundukize, Charles; Mtoni, Yohana; Martens, Kristine; Van Camp, Marc; Walraevens, Kristine


    This study investigates a Precambrian basement aquifer in Bugesera region, a typical African rural area in northeastern Burundi. Domestic water supply relies on groundwater which is tapped through hand-dug wells. Despite several attempts to increase the number of water points in the area, the water demand is still far from being met as a result of the high rate of well failure. This paper seeks to understand whether the hydrogeological structure and the spatial distribution of hydraulic parameters can explain the low productivity and the high failure rate of hand-dug wells. The hydrogeological structure inferred from the interpretation of a large number of vertical electrical soundings (VES) reveals a typical sequence of geoelectrical layers, which is characterized by an overall upwards fining from the fresh basement, over the fractured/weathered basement, to the overburden or saprolite with a clay-rich layer on top. Whereas the overall aquifer potential mainly depends on the thickness of the weathered overburden, the aquifer potential for shallow hand-dug wells is determined by the hydraulic conductivity of the upper few meters of the saturated zone. This upper zone was investigated in the pumping tests. The spatial distribution of the specific capacity reveals a wide variation of hydraulic parameters, depending on the well's position in the depth profile of the aquifer's hydraulic conductivity. The thickness of the potential aquifer is highest in the central part of the study area (pegmatitic and granitic intrusions) which has the highest overall aquifer potential compared to the surrounding metasedimentary formations. However, a thick weathered overburden will increase the groundwater potential of an aquifer for deep boreholes, whereas for hand-dug wells, the productivity can only be high if the thickness of the weathered overburden is small enough, or the water table is deep enough, to allow to tap the coarse part at the base of the overburden and/or part of

  19. High continental weathering rate during Early Cambrian: Evidence from Os isotopic composition of Early Cambrian Ocean

    Jiang, S.-Y.; Yang, J.-H.; Ling, H.-F.; Feng, H.-Z.; Chen, Y.-Q.; Chen, J.-H.


    The paleo-ocean environmental change during the Precambrian-Cambrian transition is a key issue related to the causes for an explosive radiation of different metazoan phyla during Early Cambrian. The chemical and isotopic compositions of marine sediments and chemical precipitates such as carbonates, phosphorites, siliceous rocks, and black shales record the changing composition and physical conditions of the seawater in which these rocks accumulated. Organic carbon-rich black shales from marine environments are commonly enriched in a number of trace elements such as Ni, Mo, V, Co, Cr, Au, U, As, Pb, Zn, Cu, Re, and platinum-group-elements (PGE). Recent researches have demonstrated that Re-Os isotopes and PGE contents in black shales are useful proxies for seawater chemistry. It is believed that Re and Os in orgainc-carbon rich black shales are mostly hydrogeneous in origin which were largely sequestered from seawater at the time of deposition. In South China, the Lower Cambrian black shale sequence of the Niutitang Formation (and lateral equivalents) exists broadly several thousands kilometers. The lowermost sequence of this formation contain a thin sulfide ore horizon with an apparently unique and extreme case of metal enrichments such as Mo, Ni, Se, Re, Os, As, Hg, Sb, Ag, Au, Pt, and Pd. In this study, we conducted a preliminary investigation of Re-Os isotopes and Plantium Group Element (PGE) distribution patterns of the balck shales and intercalated Ni-Mo polymetallic sulfide bed from Guizhou and Hunan Provinces. The high rOs(t) values of the black shales indicate that the Early Cambrian ocean in Yangtze Platform had a highly radiogenic Os, possibly as a result of high continental weathering rate at that time. The Ni-Mo polymetallic sulfide ores within the black shales have lower rOs(t) values than the black shales, and they show similar REE and PGE patterns as the hydrothermal siliceous rocks within the Lower Cambrian strata, which suggest that the Ni

  20. Investigating Sea Ice Regimes and Glacial Cycles of the Early Pleistocene in a Sediment Record from the Northwind Ridge, Western Arctic Ocean

    Dipre, G.; Polyak, L. V.; Ortiz, J. D.; Cook, A.; Oti, E.


    We are conducting a comprehensive study of a sediment record from the Arctic Ocean in order to improve our understanding of paleoceanographic conditions during the early Pleistocene, a potential paleo-analog for the current and future states of the Arctic. The study deals with a sediment core raised on the HOTRAX 2005 expedition from the Northwind Ridge, western Arctic Ocean. By comparison with an earlier reported stratigraphy (Polyak et al., 2013), the core dates back to estimated ca. 1.5 Ma. A suite of paleobiological, lithological, and geochemical proxies will be utilized to reconstruct paleoceanographic environments in the early Pleistocene part of the record. In contrast to most Arctic Ocean sediment cores, calcareous microfossils occur in abundance to ca. 1.2 Ma. This enables the use of microfaunal assemblages as proxies for sea-ice conditions, which control the seasonal organic production. Physical properties such as sediment density, grain size, and sediment fabric (based on XCT imagery) will be employed to determine the impact of glaciations on sedimentation. By reconstructing sea-ice history and glacial cycles, we will gain insights into poorly understood controls on the Arctic environments during the early Pleistocene and Mid-Pleistocene Transition.

  1. Precambrian ophiolites of Arabia; a summary of geologic settings, U-Pb geochronology, lead isotope characteristics, and implications for microplate accretion, Kingdom of Saudi Arabia

    Pallister, John S.; Stacey, J.S.; Fischer, L.B.; Premo, W.R.


    Disrupted ophiolites occur in linear belts as much as 900 km long between micro plates that collided during the late Proterozoic to form the Arabian Shield. The U-Pb zircon ages and lead-isotope data from these ophiolitic rocks help constrain the history of accretion of the Arabian Shield and thereby contribute to the definition of its microplates and terranes. Microplates of the central and western Arabian Shield are generally thought to represent intra-oceanic island arcs that range in age from about 900 Ma to 640 Ma; however, a region of the eastern Arabian Shield contains rocks of early Proterozoic age and may represent an exotic continental fragment entrained between the arc complexes.

  2. The origin of life near deep-sea hydrothermal systems during the Cambrian explosion: data from the Kyzyl Tashtyg sulphide deposit (Central Asia)

    Simonov, Vladimir; Terleev, Alexander; Safonova, Inna; Kotlyarov, Alexey; Stupakov, Sergey; Tokarev, Dmitry


    On Earth the solar radiation and the hydrothermal circulation both affect life evolution. Recent extensive studies of the World Ocean have shown that the biodiversity of Earth is linked with hydrothermal activity on the oceanic floor. These deep-sea ecosystems use chemical energy, not solar radiation. In the last quarter of the XX century, a new type of hydrothermal systems, so-called black smokers, was discovered in mid-oceanic ridges. As black smokers form sulfide ores and are surrounded by abundant bio-oases or symbioses, identification of their analogues in ancient orogenic belts is necessary for studying life origin and evolution. Of special importance are problems of life associated with deep-sea hydrothermal systems acted at the Precambrian-Cambrian boundary - the time of Cambrian explosion (Maruyama et al., 2013). During that explosion life significantly evolved and diversified due to dramatic changes of Earth's environment. Consequently, the early Cambrian - late Precambrian Kyzyl Tashtyg sulphide deposit of East Tuva in the Central Asian Orogenic Belt is of special interest. This deposit was formed on the bottom of ancient back-arc deep-sea basin as a result of black smoker hydrothermal activity and is hosted by volcanogenic-sedimentary rocks altered by the high temperature solutions. The altered Kyzyl Tashtyg basalts have an amygdules (filled by albite, epidote and carbonates), contain brown-green microfossils, often attached to their walls. The microfossils are thin tubes 5 to 25 microns in diameter and 500 microns long. This tubes are empty and have straight, curved or branching shape. Chemically, the tube material is close to epidote. In consideration of microscopic dimensions, simple morphology and similarity with modern tubular microorganisms, the studied tube-shaped microfossils can be related to cyanobacteria. Almost the same fossils, associated with oceanic basalt complexes, were described earlier (Furnes et al., 2007; Mcloughlin et al., 2007

  3. Latest Jurassic-early Cretaceous regressive facies, northeast Africa craton

    van Houten, F.B.


    Nonmarine to paralic detrital deposits accumulated in six large basins between Algeria and the Arabo-Nubian shield during major regression in latest Jurassic and Early Cretaceous time. The Ghadames Sirte (north-central Libya), and Northern (Egypt) basins lay along the cratonic margin of northeastern Africa. The Murzuk, Kufra, and Southern (Egypt) basins lay in the south within the craton. Data for reconstructing distribution, facies, and thickness of relevant sequences are adequate for the three northern basins only. High detrital influx near the end of Jurassic time and in mid-Cretaceous time produced regressive nubian facies composed largely of low-sinuosity stream and fahdelta deposits. In the west and southwest the Ghadames, Murzuk, and Kufra basins were filled with a few hundred meters of detritus after long-continued earlier Mesozoic aggradation. In northern Egypt the regressive sequence succeeded earlier Mesozoic marine sedimentation; in the Sirte and Southern basins correlative deposits accumulated on Precambrian and Variscan terranes after earlier Mesozoic uplift and erosion. Waning of detrital influx into southern Tunisia and adjacent Libya in the west and into Israel in the east initiated an Albian to early Cenomanian transgression of Tethys. By late Cenomanian time it had flooded the entire cratonic margin, and spread southward into the Murzuk and Southern basins, as well as onto the Arabo-Nubian shield. Latest Jurassic-earliest Cretaceous, mid-Cretaceous, and Late Cretaceous transgressions across northeastern Africa recorded in these sequences may reflect worldwide eustatic sea-level rises. In contrast, renewed large supply of detritus during each regression and a comparable subsidence history of intracratonic and marginal basins imply regional tectonic control. 6 figures.

  4. Arsenic-induced phosphate limitation under experimental Early Proterozoic oceanic conditions

    Chi Fru, Ernest; Hemmingsson, Christoffer; Holm, Mikaela; Chiu, Beverly; Iñiguez, Enrique


    Comparison of phosphorus concentrations associated with modern hydrothermal Fe(III)(oxyhydr)oxides and ancient Fe(III) oxide-rich iron formations, is used to estimate bioavailable Precambrian marine phosphorus (P) concentrations. This led to the proposition of a low dissolved P budget of ˜10-25% of present-day levels, before ˜1.9 billion years ago. Estimates incorporating ancient marine Si levels ≥ 0.67 mM instead suggested global dissolved P levels greater than today. Here we unite current experimental models that have considered NaCl solutions containing elevated dissolved Fe(II), Si, Ca2+ and Mg2+ ions in the incorporation of P in Precambrian marine Fe(III)(oxyhydr)oxides, in addition to arsenic as a hydrothermal proxy. We show that the coprecipitation of dissolved P and Fe(III)(oxyhydr)oxides from arsenic-rich marine waters produces an average P distribution coefficient of ˜0.072 (± 0.01) μM-1. This is comparable to the ˜ 0.07 μM-1 predicted for Fe(III)(oxyhydr)oxides in modern arsenic-rich, submarine hydrothermal settings, from which the lower Early Proterozoic dissolved marine P concentrations were predicted. As/P molar ratios below modern seawater ratios removed the negative feedback effect high Si impose on P scavenging by Fe(III)(oxyhydr)oxides. The binding of As(III) to Fe(III)(oxyhydr)oxides exhibits a lower competitive influence on P fixation. As(V) that likely became prominent in the surficially oxidized Early Proterozoic oceans induced dissolved P limitation because of preferential P sequestration at the expense of dissolved As(V) enrichment. The control of As on P scavenging by the precipitating Fe(III)(oxyhydr)oxides is strong regardless of common seawater cations (Mg2+ and Ca2+). The data suggest that the application of Si and Fe(III)(oxyhydr)oxides as an ancient seawater P proxy should consider chemical variability between depositional basins, taking into account the rather strong role hydrothermal arsenic has on the distribution of P in

  5. 中国鲁东造山带前寒武纪构造变形及其演化%Precambrian tectonic deformation and its evolution in Ludong orogenic belt China

    凌贤长; 杜绍安


    中国鲁东造山带前寒武纪构造变形可以划分出三个变形旋回与五个变形幕,即吕梁变形旋回第一变形幕,四堡变形旋回第二变形幕,以及晋宁变形旋回第三、四、五变形幕。前三幕表现为强塑性流动变形作用,而第四、五幕则分别属于较强塑性及中强塑性变形作用,这五个变形幕总的均以塑性变形作用为突出特征,说明它们的变形环境之间虽有变化,但不明显,只是变形机制和应力场型式有一定变化。第一变形幕导致麻粒岩相区域变质作用,并且产生区内最早的变形叶理,为尔后的构造变形奠定了基础。第二、三变形幕体现了碰撞带形成机制及过程,与超高压-高压变质杂岩、中酸性侵入杂岩及角闪岩相区域变质作用等关系密切,因此在区内前寒武纪地质演化中居于主导地位。第四、五变形幕反映碰撞带形成之后演化特征,控制了现今区域大地构造构格的形成。%Presents the Precambrian tectonic deformation in Chinaese Ludong orogenic belt divided into five episodes three cycles the first epoisode of Luliang cycle the second episode of Sipu cyclecoeval to the formation of eclogites the thirdcoeval to the formation of intermediate acidic intrusive complexes the fourth and fifth episodes of Jinning cycle. Intensive ductile flow deformation the first three episodes. Rather strong and medium strong ductile deformation happened in the last two episodes and concludes the deformation environment of the five episodes changed in some degree but not radically in other words the change only occurred as a certain degree of variation of deformation style and the attitude of stress field Granulite facies regional metamorphism happened in the first deformation episode to the formation of the earliest foliation providing the basis for further deformations in the studying area Deformation in the second and third episodes

  6. Timing of Precambrian melt depletion and Phanerozoic refertilization events in the lithospheric mantle of the Wyoming Craton and adjacent Central Plains Orogen

    Carlson, R.W.; Irving, A.J.; Schulze, D.J.; Hearn, B.C.


    Garnet peridotite xenoliths from the Sloan kimberlite (Colorado) are variably depleted in their major magmaphile (Ca, Al) element compositions with whole rock Re-depletion model ages generally consistent with this depletion occurring in the mid-Proterozoic. Unlike many lithospheric peridotites, the Sloan samples are also depleted in incompatible trace elements, as shown by the composition of separated garnet and clinopyroxene. Most of the Sloan peridotites have intermineral Sm-Nd and Lu-Hf isotope systematics consistent with this depletion occurring in the mid-Proterozoic, though the precise age of this event is poorly defined. Thus, when sampled by the Devonian Sloan kimberlite, the compositional characteristics of the lithospheric mantle in this area primarily reflected the initial melt extraction event that presumably is associated with crust formation in the Proterozoic-a relatively simple history that may also explain the cold geotherm measured for the Sloan xenoliths. The Williams and Homestead kimberlites erupted through the Wyoming Craton in the Eocene, near the end of the Laramide Orogeny, the major tectonomagmatic event responsible for the formation of the Rocky Mountains in the late Cretaceous-early Tertiary. Rhenium-depletion model ages for the Homestead peridotites are mostly Archean, consistent with their origin in the Archean lithospheric mantle of the Wyoming Craton. Both the Williams and Homestead peridotites, however, clearly show the consequences of metasomatism by incompatible-element-rich melts. Intermineral isotope systematics in both the Homestead and Williams peridotites are highly disturbed with the Sr and Nd isotopic compositions of the minerals being dominated by the metasomatic component. Some Homestead samples preserve an incompatible element depleted signature in their radiogenic Hf isotopic compositions. Sm-Nd tie lines for garnet and clinopyroxene separates from most Homestead samples provide Mesozoic or younger "ages" suggesting

  7. Petrology and diagenetic history of the upper shale member of the Late Devonian–Early Mississippian Bakken Formation, Williston Basin, North Dakota

    Neil S. Fishman,; Sven O. Egenhoff,; Boehlke, Adam; Lowers, Heather


    The organic-rich upper shale member of the upper Devonian–lower Mississippian Bakken Formation (Williston Basin, North Dakota, USA) has undergone significant diagenetic alteration, irrespective of catagenesis related to hydrocarbon generation. Alteration includes precipitation of numerous cements, replacement of both detrital and authigenic minerals, multiple episodes of fracturing, and compaction. Quartz authigenesis occurred throughout much of the member, and is represented by multiple generations of microcrystalline quartz. Chalcedonic quartz fills radiolarian microfossils and is present in the matrix. Sulfide minerals include pyrite and sphalerite. Carbonate diagenesis is volumetrically minor and includes thin dolomite overgrowths and calcite cement. At least two generations of fractures are observed. Based on the authigenic minerals and their relative timing of formation, the evolution of pore waters can be postulated. Dolomite and calcite resulted from early postdepositional aerobic oxidation of some of the abundant organic material in the formation. Following aerobic oxidation, conditions became anoxic and sulfide minerals precipitated. Transformation of the originally opaline tests of radiolaria resulted in precipitation of quartz, and quartz authigenesis is most common in more distal parts of the depositional basin where radiolaria were abundant. Because quartz authigenesis is related to the distribution of radiolaria, there is a link between diagenesis and depositional environment. Furthermore, much of the diagenesis in the upper shale member preceded hydrocarbon generation, so early postdepositional processes were responsible for occlusion of significant original porosity in the member. Thus, diagenetic mineral precipitation was at least partly responsible for the limited ability of these mudstones to provide porosity for storage of hydrocarbons.

  8. Petrology and diagenetic history of the upper shale member of the Late Devonian-Early Mississippian Bakken Formation, Williston Basin, North Dakota

    Neil S. Fishman,; Sven O. Egenhoff,; Boehlke, Adam; Lowers, Heather A.


    The organic-rich upper shale member of the upper Devonian–lower Mississippian Bakken Formation (Williston Basin, North Dakota, USA) has undergone significant diagenetic alteration, irrespective of catagenesis related to hydrocarbon generation. Alteration includes precipitation of numerous cements, replacement of both detrital and authigenic minerals, multiple episodes of fracturing, and compaction. Quartz authigenesis occurred throughout much of the member, and is represented by multiple generations of microcrystalline quartz. Chalcedonic quartz fills radiolarian microfossils and is present in the matrix. Sulfide minerals include pyrite and sphalerite. Carbonate diagenesis is volumetrically minor and includes thin dolomite overgrowths and calcite cement. At least two generations of fractures are observed. Based on the authigenic minerals and their relative timing of formation, the evolution of pore waters can be postulated. Dolomite and calcite resulted from early postdepositional aerobic oxidation of some of the abundant organic material in the formation. Following aerobic oxidation, conditions became anoxic and sulfide minerals precipitated. Transformation of the originally opaline tests of radiolaria resulted in precipitation of quartz, and quartz authigenesis is most common in more distal parts of the depositional basin where radiolaria were abundant. Because quartz authigenesis is related to the distribution of radiolaria, there is a link between diagenesis and depositional environment. Furthermore, much of the diagenesis in the upper shale member preceded hydrocarbon generation, so early postdepositional processes were responsible for occlusion of significant original porosity in the member. Thus, diagenetic mineral precipitation was at least partly responsible for the limited ability of these mudstones to provide porosity for storage of hydrocarbons.

  9. Plate tectonics on the early Earth: Limitations imposed by strength and buoyancy of subducted lithosphere

    van Hunen, Jeroen; van den Berg, Arie P.


    The tectonic style and viability of modern plate tectonics in the early Earth is still debated. Field observations and theoretical arguments both in favor and against the uniformitarian view of plate tectonics back until the Archean continue to accumulate. Here, we present the first numerical modeling results that address for a hotter Earth the viability of subduction, one of the main requirements for plate tectonics. A hotter mantle has mainly two effects: 1) viscosity is lower, and 2) more melt is produced, which in a plate tectonic setting will lead to a thicker oceanic crust and harzburgite layer. Although compositional buoyancy resulting from these thick crust and harzburgite might be a serious limitation for subduction initiation, our modeling results show that eclogitization significantly relaxes this limitation for a developed, ongoing subduction process. Furthermore, the lower viscosity leads to more frequent slab breakoff, and sometimes to crustal separation from the mantle lithosphere. Unlike earlier propositions, not compositional buoyancy considerations, but this lithospheric weakness could be the principle limitation to the viability of plate tectonics in a hotter Earth. These results suggest a new explanation for the absence of ultrahigh-pressure metamorphism (UHPM) and blueschists in most of the Precambrian: early slabs were not too buoyant, but too weak to provide a mechanism for UHPM and exhumation.

  10. A horizontal gene transfer supported the evolution of an early metazoan biomineralization strategy

    Wörheide Gert


    Full Text Available Abstract Background The synchronous and widespread adoption of the ability to biomineralize was a defining event for metazoan evolution during the late Precambrian/early Cambrian 545 million years ago. However our understanding on the molecular level of how animals first evolved this capacity is poor. Because sponges are the earliest branching phylum of biomineralizing metazoans, we have been studying how biocalcification occurs in the coralline demosponge Astrosclera willeyana. Results We have isolated and characterized a novel protein directly from the calcified spherulites of A. willeyana. Using three independent lines of evidence (genomic architecture of the gene in A. willeyana, spatial expression of the gene product in A. willeyana and genomic architecture of the gene in the related demosponge Amphimedon queenslandica, we show that the gene that encodes this protein was horizontally acquired from a bacterium, and is now highly and exclusively expressed in spherulite forming cells. Conclusions Our findings highlight the ancient and close association that exists between sponges and bacteria, and provide support for the notion that horizontal gene transfer may have been an important mechanism that supported the evolution of this early metazoan biomineralisation strategy.

  11. Permian-Early Triassic tectonics and stratigraphy of the Karoo Supergroup in northwestern Mozambique

    Bicca, Marcos Müller; Philipp, Ruy Paulo; Jelinek, Andrea Ritter; Ketzer, João Marcelo Medina; dos Santos Scherer, Claiton Marlon; Jamal, Daúd Liace; dos Reis, Adriano Domingos


    The Gondwana continent was the base of great basin inception, sedimentation and magmatism throughout the Cambrian to Middle Jurassic periods. The northwestern Mozambique igneous and metamorphic basement assemblages host the NW-trending Moatize Minjova Basin, which has great economic potential for coal and gas mining. This rift basin was activated by an S-SW stress field during the Early Permian period, as constrained by regional and field scale structural data. Tectonically induced subsidence in the basin, from the reactivation of NW-SE and NNE-SSW regional structures is well recorded by faults, folds and synsedimentary fractures within the Early Late Permian Moatize Formation. NW-SE, N-S and NE-SW field structures consist of post-Karoo reactivation patterns related to a NNE-SSW extension produced by the Pangea breakup and early inception stages of the Great East African Rift System. The Early Late Permian sequences of the Moatize-Minjova Basin are composed of fluvial meandering, coal-bearing beds of the Moatize Formation, which comprises mostly floodplain, crevasse splay and fluvial channel lithofacies associations, deposited in a cyclic pattern. This sequence was overlapped by a multiple-story, braided fluvial plain sequence of the Matinde Formation (Late Permian - Early Triassic). Lithofacies associations in the Matinde Formation and its internal relationships suggest deposition of poorly channelized braided alluvial plain in which downstream and probably lateral accretion macroforms alternate with gravity flow deposits. NW paleoflow measurements suggest that Permian fluvial headwaters were located somewhere southeast of the study area, possibly between the African and Antarctic Precambrian highlands.

  12. The silicon isotope record of early silica diagenesis

    Tatzel, Michael; von Blanckenburg, Friedhelm; Oelze, Marcus; Schuessler, Jan A.; Bohrmann, Gerhard


    The heavy isotopes of silicon are strongly enriched in some of the youngest, early diagenetically formed porcellanite layers from the Southwest Indian Ridge (Pleistocene) and the Maud Rise (Pliocene). These porcellanite layers are composed of opal-CT and were formed by the conversion of amorphous silica (opal-A) from siliceous sediment via dissolution-reprecipitation. Their bulk δ30Si values range between 1.7 and 2.3‰. Detritus-poor siliceous sediment surrounding these layers is significantly lower at -0.3 to 1.5‰. Sequential chemical extractions of bulk siliceous sediment show (i) preferential dissolution of diatoms featuring higher δ30Si than radiolaria and Al-Si components. The detailed investigation of porcellanite layers by micro-scale Si isotope and Al/Si analyses using UV femtosecond laser ablation ICP mass spectrometry show that (ii) precipitation of authigenic aluminum silicates enriched in light Si isotopes drives pore waters to even higher δ30Si. We suggest that the same processes redistributed stable silicon isotopes in precursor siliceous sediments of ancient chert. We infer that past environmental conditions can be reconstructed with high fidelity from the stable Si isotope composition of chert when initial seawater Si concentrations were high (such as in the Precambrian). Exchange of Si between layers during phase transformation (from opal-A to opal-CT and from opal-CT to quartz) is impeded when variable amounts of detrital minerals are present, because they control rates of silica phase transformation and hence the timing of dissolution-reprecipitation during burial.

  13. Problematic microfossils in ancient (Paleozoic) rocks of the Urals

    Leonova, L. V.; Soroka, E. I.


    To determine age and genesis of rock series fossiles of macro- and microbiote have a great importance. In altered rocks organogenic remnants could be preserved as relics of initial substrate or pseudomorphic replaced by hemogenic substance fossils. It is necessity in difference of replaced remnants and mineralogical aggregates.

  14. Precambrian crustal evolution and Cretaceous–Palaeogene faulting in West Greenland: Structural analysis of the northern Nagssugtoqidian orogen, West Greenland: an example of complex tectonic patterns in reworked high-grade metamorphic terrains

    Mazur, Stanislaw


    Full Text Available Structural analysis of the deeply eroded northern flank of the Palaeoproterozoic Nagssugtoqidian orogen shows marked regional variations in both the orientation and type of fabrics, as is characteristic of Precambrian high-grade terrains subjected to polyphase deformation. Here we investigate the relationship between strain, metamorphic grade, and the resulting structural patterns. The study area south of Aasiaat in West Greenland consists of amphibolite- togranulite-gradeArchaean orthogneisses and relatively thin supracrustal units. The regional foliation displays a WSW–ENE to SW–NE strike associated with steep to moderate dips towards the WNW or SSE. Lineation trends are WSW–ENE and generally plunge gently towards the WSW. Mesoscopic fold hinges are usually colinear with the regional lineation. A systematic change in the plunge of lineations occurs across the south-western part of the study area. Towards the south, the lineation plunge progressively increases, despite the generally uniform strike of foliation. This southward increase of lineation pitch is typically associated with the transition from L > S or L = S shape fabrics in rocks characterised by a low pitch, to S > L or S fabrics in the zone of moderate to high pitch. The structural patterns point to subdivision of the study area into a southern domain mostly characterised by S or S > L shape fabrics and a moderate to high angle of lineation pitch, and a northern domain showing L > S or L = S fabrics and low angles of lineation pitch. This subdivision corresponds well with the map scale boundary between granulite facies rocks in the south and amphibolite facies rocks farther north. The observed structural pattern may be explained by two alternative tectonic models: (1 northward indentation of the previously cooled granulite block into the rheologically weaker amphibolite domain, and (2 strain partitioning within a mid-crustal transpression zone. In model 2 the northern domain

  15. Sulfur Isotope Systematics and the Link Between Fluctuating Sulfate Levels and P Recycling in a Low Sulfate, Permanently Anoxic Lake (Lake McCarrons, MN): Implications for the Precambrian Rise of Oxygen

    Gomes, M. L.; Hurtgen, M. T.


    Seawater sulfate concentrations have been used to track the rise of oxygen in the Precambrian ocean-atmosphere system because the primary mode of sulfate delivery to the ocean is the oxidative weathering of sulfides on land. Ancient seawater sulfate concentrations have been inferred from the extent of sulfur (S) isotope fractionation incurred during bacterial sulfate reduction (BSR) where organisms preferentially utilize 32S (over 34S) in the process of reducing of sulfate to sulfide. Within this context, increased variability in δ34Spyrite values in Proterozoic (~2.3 Ga) sediments—along with a corresponding increase in the isotopic difference between sulfate and pyrite (Δ34S)—has been attributed to an increase in seawater sulfate concentrations (from 1 mM) and inferentially Earth-surface oxygen levels. However, most S isotope studies have been calibrated using modern marine sediments that contain sulfate-reducing bacteria that are adapted to the high concentration of sulfate in the modern ocean (~28mM). In order to better understand S isotope systematics within a low sulfate system and to improve our interpretive construct for S isotope results generated from ancient strata, we explore the magnitude of S isotope fractionations associated with microbial activity in the water column and sediments of a low sulfate (isotope difference between surface water sulfate and bottom water sulfide is ~5‰ (Δ34S) while in situ S isotope fractionations associated with BSR at the sediment-water interface approach 35‰; (3) sulfate reduction rates in the upper 3 cm of organic carbon rich sediment are ~0.1 µM cm-3 d-1, an order of magnitude lower than those recorded under higher (modern marine) sulfate concentrations; and (4) sulfate concentrations influence the efficiency of P recycling (as determined via bag incubation experiments). Here, we suggest that an increase in sulfate levels at ~2.3 Ga, as indicated by larger Δ34S values recorded in strata of this age

  16. Autism: Why Act Early?

    ... What's this? Submit Button Past Emails CDC Features Autism: Why Act Early? Language: English Español (Spanish) Recommend ... helped the world make sense." Florida teenager with Autism Spectrum Disorder "Because my parents acted early, I ...

  17. Cancer treatment -- early menopause

    ... this page: // Cancer treatment - early menopause To use the sharing features on this page, please enable JavaScript. Certain types of cancer treatments can cause women to have early menopause. This ...

  18. Overview of Early Intervention

    ... infant or toddler for early intervention (e.g., Down syndrome, Fragile X syndrome). Determining eligibility | The results of the evaluation will be used to determine your child’s eligibility for early intervention services. You and a ...

  19. Early Retirement Programs.

    Everett, Peter W.


    Early retirement programs offer individuals an alternative to the work ethic while allowing them to maintain job security. Examples are given of several early, partial, and phased retirement programs currently being used in universities and public school systems. (DF)

  20. An Early Cenozoic Ichthyolith Record from Demerara Rise (ODP Site 1258: Equatorial Atlantic Ocean)

    Bryant, R. M.; Sibert, E. C.; Norris, R. D.


    Peak global warmth during the early Eocene is a partial analog to the future structure of marine ecosystems in a high pCO2 world. Early Eocene oceans are generally regarded as supporting warmer oceans with lower overall productivity than today owing to the low concentrations of preserved organic matter in pelagic sediments. It has also been proposed that Eocene oceans were about as productive as now, but higher respiration rates in a warmer-than-modern ocean more efficiently recycled organic matter and nutrients. We investigated Eocene export productivity and its link to taxonomic diversity using the pelagic ichthyolith record. Ichthyoliths are calcium phosphate microfossils including fish teeth and shark denticles and their fragments, and are a unique paleoceanographic proxy because they represent a fossil record for marine vertebrates, a charismatic and tangible part of the ecosystem that generally goes unrepresented in the fossil record. Analysis of the ichthyolith record in Ocean Drilling Program Site 1258 (NE South America) shows a remarkable increase in accumulation rate of ichthyoliths from the Paleocene into the Eocene, suggesting that onset of the Early Eocene Climatic Optimum in the equatorial Atlantic was favorable to fish production. Our results suggest that, if anything, the early Eocene maintained higher productivity than in the late Paleocene. These results compare favorably with a record of ichthyolith accumulation in the South Pacific (DSDP 596), which also indicates unusually high rates of fish productivity in the peak of Eocene warm climates. Low resolution data sets from the Pacific suggest an explosion of morphotypes during the warm period associated with an increase in ichthyolith mass accumulation rates. Peak global warmth, therefore, appears to be associated with both higher fish production and higher taxonomic diversity than suggested by previous reconstructions of Eocene primary production. Increasing the amount of continuous records of

  1. Microbial contributions to the Precambrian Earth

    Margulis, L.; Bermudes, D.; Obar, R.


    Life has existed on Earth for approximately 3.5 billion years. For most of this time, prokaryotic communities provided the major biological forces changing the Earth. Many changes in atmospheric gas composition occurred during the Archean and Proterozoic eons as a result of microbial activity. Extant microbial communities were used to help understand the dynamics which contributed to these atmospheric changes. The microbial mat communities were characterized according to the organismic constituents. Symbiosis in microbial communities is recognized as a major force in cell evolution. Among the evolutinary enigmas investigated is the problem of the origin of the undulipodia. Undulipodial microtubules are still deployed for major cellular processes such as mitosis and meiosis. Several prokaryotes were tested for the presence of the S1-type protein, so far only spirochetes were found to possess it. The S1-type protein is being sought in cyanobacteria reported to contain microtubules.

  2. Optimizing Early Retirement Decisions.


    the military. The U.S. Army’s early retirement program is a temporary one designed to allow some soldiers to leave the service prior to 20 years of...whether it makes financial sense for an officer to select early retirement . A spreadsheet formulation is developed and used to indicate if and officer should select early retirement . The program investigates the decision that various civilian salary levels and various assumed discount rates.

  3. Geochemistry and Nd-Sr Isotopic Signatures of the Pensamiento Granitoid Complex, Rondonian-San Ignacio Province, Eastern Precambrian Shield of Bolivia: Petrogenetic Constraints for a Mesoproterozoic Magmatic Arc Setting

    Ramiro Matos


    Full Text Available The Pensamiento Granitoid Complex (PGC, located in the northern part of the eastern Precambrian shield of Bolivia, istectonically assigned to the Rondonian-San Ignacio Province (1.55 - 1.30 Ga of the Amazonian Craton that is made up byArchean and Proterozoic provinces. The Proterozoic ones result from accretionary orogens that become successively youngersouthwestwards, such as the Rondonian/San Ignacio (1.37 - 1.32 Ga and the Sunsás orogenies (1.20 - 1.00 Ga. The PGCcrops out mainly on the “Paragua craton” bounded to the south by the Sunsás belt, and composed of granites and subvolcanicterms, and subordinately of syenites, granodiorites, tonalites, trondhjemites and diorites as orogenic representatives of theRondonian/San Ignacio Orogeny, intrusive into the Lomas Maneches (ca. 1.68 Ga and Chiquitania (ca. 1.7 Ga complexes.Thirteen whole rock chemical analyses for major, trace and REE elements were performed for the La Junta, San Martín, Diamantina,Porvernir, San Cristobal, Piso Firme plutons of the PGC. The negative trends of MgO, Al2O3 and CaO contents withincreasing SiO2 suggest that fractional crystallization played an important role in the petrogenesis of the investigated rocks.The data also indicate a mainly peraluminous, sub-alkaline to high-K calc-alkaline composition, and fractionated LREE/HREE patterns are consistent with a magmatic arc character for these plutons. SHRIMP U-Pb zircon ages of the La Junta andSan Martín syn- to late-kinematic plutons are 1347 ± 21 Ma and 1373 ± 20 Ma respectively, and the Sm-Nd TDM model agesare between 1.9 to 2.0 Ga, while εNd(1330 values range from +1.8 to -4.3, respectively. In addition, the late- to post-kinematicDiamantina pluton yields SHRIMP U-Pb zircon age of 1340 ± 20 Ma, and variable Sm-Nd TDM model ages (1.6 to 1.9 Ga andεNd(1330 values (+0.4 to -1.2 that are comparable with previous results found for other coeval plutons. The Porvenir, San Cristobaland Piso Firme plutons show ε

  4. 北苏鲁超高压变质带前寒武纪基底研究新进展%Main Progresses in the Study of Precambrian Basement of the North Sulu Ultra-high Pressure Metamorphic Belt, Eastern China

    徐扬; 杨坤光; 李日辉; 侯方辉; 秦亚超


    The north Sulu ultra-high pressure (UHP) metamorphic belt which is located at the eastern Muping-Jimo fault in eastern Shandong Peninsula is mainly characterized by Neoproterozoic bimodal igneous rocks. And its assemblages include a large number of granitic gneiss and a small amount of ultra basic/basic metamorphic rocks and metasedimentary rocks. The previous research of geochemical, zircon U-Pb, Lu-Hf isotope data revealed the geologic succession of the north Sulu UHP terrane. The Neoarchean-Paleoproterozoic ancient crust was remained and its initial crust evolution might start from Neoarchean or even earlier, then it undergone a series of magma-volcano-metamorphic events during 1.8-2.2 Ga. The bimodal magmatism, which caused by the rifting of the Rodinia Supercontinent at mid-Neoproterozoic (0. 7 -0. 8 Ga) reworked the ancient and juvenile crust. As the same to the Sulu-Dabie orogen terrane, some characteristics of the Precambrian basement of the north Sulu UHP terrane are corresponding to Yangtze Block, and its northwestern boundary to the North China Block may be located along the Wulian-Yantai fault.%北苏鲁超高压变质带位于胶东牟平—即墨断裂以东的地区,其前寒武纪基底以出露新元古代的双峰式火成岩为主要特征,其主要岩石组合包括大量花岗片麻岩以及少量变(超)基性岩(榴辉岩)、变沉积岩.对花岗片麻岩、变质(超)基性岩的岩石组合、地球化学、锆石U-Pb和Lu-Hf同位素的研究表明,北苏鲁存在新太古代—古元古代的残留地壳,经历了1.8~2.2 Ga期间的岩浆-火山-变质事件;新元古代中期(0.72 ~0.80 Ga)与Rodinia超大陆的裂解相关的岩浆活动促使地壳的生长和再造,形成了北苏鲁的前寒武纪基底的主体;北苏鲁和苏鲁—大别造山带一样,其前寒武纪基底是扬子板块北缘的一部分,苏鲁造山带的西北边界是五莲—烟台断裂带.

  5. Geochemical Evidence for Subduction in the Early Archaean from Quartz-Carbonate-Fuchsite Mineralization, Isua Supracrustal Belt, West Greenland

    Pope, E. C.; Rosing, M. T.; Bird, D. K.


    Quartz, carbonate and fuchsite (chromian muscovite) is a common metasomatic assemblage observed in orogenic gold systems, both in Phanerozoic convergent margin settings, and within supracrustal and greenstone belts of Precambrian rocks. Geologic and geochemical observations in younger orogenic systems suggest that ore-forming metasomatic fluids are derived from subduction-related devolitilization reactions, implying that orogenic Au-deposits in Archaean and Proterozoic supracrustal rock suites are related to subduction-style plate tectonics beginning early in Earth history. Justification of this metasomatic-tectonic relationship requires that 1) Phanerozoic orogenic Au-deposits form in subduction-zone environments, and 2) the geochemical similarity of Precambrian orogenic deposits to their younger counterparts is the result of having the same petro-genetic origin. Hydrogen and oxygen isotope compositions of fuchsite and quartz from auriferous mineralization in the ca. 3.8 Ga Isua Supracrustal Belt (ISB) in West Greenland, in conjunction with elevated concentrations of CO2, Cr, Al, K and silica relative to protolith assemblages, suggest that this mineralization shares a common petro-tectonic origin with Phanerozoic orogenic deposits and that this type of metasomatism is a unique result of subduction-related processes. Fuchsite from the ISB has a δ18O and δD of +7.7 to +17.9% and -115 to -61%, respectively. δ18O of quartz from the same rocks is between +10.3 and +18.6%. Muscovite-quartz oxygen isotope thermometry indicates that the mineralization occurred at 560 ± 90oC, from fluids with a δD of -73 to -49% and δ18O of +8.8 to +17.2%. Calculation of isotopic fractionation during fluid-rock reactions along hypothetical fluid pathways demonstrates that these values, as well as those in younger orogenic deposits, are the result of seawater-derived fluids liberated from subducting lithosphere interacting with ultramafic rocks in the mantle wedge and lower crust

  6. Early College High Schools

    Dessoff, Alan


    For at-risk students who stand little chance of going to college, or even finishing high school, a growing number of districts have found a solution: Give them an early start in college while they still are in high school. The early college high school (ECHS) movement that began with funding from the Bill and Melinda Gates Foundation 10 years ago…

  7. Early Retirement Payoff

    Fitzpatrick, Maria D.; Lovenheim, Michael F.


    As public budgets have grown tighter over the past decade, states and school districts have sought ways to control the growth of spending. One increasingly common strategy employed to rein in costs is to offer experienced teachers with high salaries financial incentives to retire early. Although early retirement incentive (ERI) programs have been…

  8. Early Option Exercise

    Heje Pedersen, Lasse; Jensen, Mads Vestergaard

    A classic result by Merton (1973) is that, except just before expiration or dividend payments, one should never exercise a call option and never convert a convertible bond. We show theoretically that this result is overturned when investors face frictions. Early option exercise can be optimal when...... it reduces short-sale costs, transaction costs, or funding costs. We provide consistent empirical evidence, documenting billions of dollars of early exercise for options and convertible bonds using unique data on actual exercise decisions and frictions. Our model can explain as much as 98% of early exercises...

  9. Early Option Exercise

    Jensen, Mads Vestergaard; Heje Pedersen, Lasse


    A classic result by Merton (1973) is that, except just before expiration or dividend payments, one should never exercise a call option and never convert a convertible bond. We show theoretically that this result is overturned when investors face frictions. Early option exercise can be optimal when...... it reduces short-sale costs, transaction costs, or funding costs. We provide consistent empirical evidence, documenting billions of dollars of early exercise for options and convertible bonds using unique data on actual exercise decisions and frictions. Our model can explain as much as 98% of early exercises...

  10. Early Head Start Evaluation

    U.S. Department of Health & Human Services — Longitudinal information from an evaluation where children were randomly assigned to Early Head Start or community services as usual;direct assessments and...

  11. Earth's early biosphere

    Des Marais, D. J.


    Understanding our own early biosphere is essential to our search for life elsewhere, because life arose on Earth very early and rocky planets shared similar early histories. The biosphere arose before 3.8 Ga ago, was exclusively unicellular and was dominated by hyperthermophiles that utilized chemical sources of energy and employed a range of metabolic pathways for CO2 assimilation. Photosynthesis also arose very early. Oxygenic photosynthesis arose later but still prior to 2.7 Ga. The transition toward the modern global environment was paced by a decline in volcanic and hydrothermal activity. These developments allowed atmospheric O2 levels to increase. The O2 increase created new niches for aerobic life, most notably the more advanced Eukarya that eventually spawned the megascopic fauna and flora of our modern biosphere.

  12. (Reconceptualizing Early Childhood Education)?


    Second, I must stress the immensely precious and ..... 'useless' subjects such as emotions, sensitivity, .... a range of different sociological fields including early childhood, gender, .... The origins of intelligence in children (M. Cook, Trans.).

  13. Biogeochemistry: Early phosphorus redigested

    Poulton, Simon W.


    Atmospheric oxygen was maintained at low levels throughout huge swathes of Earth's early history. Estimates of phosphorus availability through time suggest that scavenging from anoxic, iron-rich oceans stabilized this low-oxygen world.

  14. Embracing early literacy indicators

    Broström, Stig; Hansen, Ole Henrik; Jensen, Anders Skriver


    Abstract til paper om early literacy indikatorer. Det paper abstractet er knyttet til var en del af et inviteret, selvorganiseret symposium som afrapporterede EASE-projektet ( på OMEP's 26. verdenskongres....

  15. The evolution of Phanerozoic seawater - Isotope paleothermometry finds consensus on Early Paleozoic warmth and constant seawater δ18O

    Grossman, E. L.; Henkes, G. A.; Passey, B. H.; Shenton, B.; Yancey, T. E.; Perez-Huerta, A.


    Evolution of metazoan life is closely linked to the Phanerozoic evolution of ocean temperatures and chemistry. Oxygen isotopic evidence for early Phanerozoic paleotemperatures has been equivocal, with decreasing δ18O values with age being interpreted as warmer early oceans, decreasing seawater δ18O with age, or increasing diagenetic alteration in older samples. Here we compare an updated compilation of oxygen isotope data for carbonate and phosphate fossils and microfossils (Grossman, 2012, Geol. Time Scale, Elsevier, 195-220) with a compilation of new and existing clumped isotope data. Importantly, these data are curated based on sample preservation with special consideration given to screening techniques, and tectonic and burial history. Burial history is critical in the preservation of carbonate clumped isotope temperatures in particular, which can undergo reordering in the solid state. We use a model derived for reordering kinetics (Henkes et al., 2014, Geochim. Cosmochim. Acta 139:362-382) to screen clumped isotope data for the effects of solid-state burial alteration. With minor but significant exceptions (Late Cretaceous, Early Triassic), average δ18O values (4 m.y. window, 2 m.y. steps) for post-Devonian brachiopods, belemnites, and foraminifera, representing tropical-subtropical surface ocean conditions, yield average isotopic temperatures below 30°C (assuming a seawater δ18O value [ -1‰ VSMOW] of an "ice-free" world). In contrast, Ordovician to Devonian data show sustained temperatures of 35-40°C. Likewise, isotopic paleotemperatures from conodont apatite, known to be resistant to isotopic exchange, follow the same pattern. Clumped isotope data derived from Paleozoic brachiopod shells that experienced minimal burial (< 100 °C) and <1% reordering according to the taxon-specific clumped isotope reordering model yield typical temperatures of 25-30°C for the Carboniferous, and 35-40°C for the Ordovician-Silurian. Inserting clumped temperatures and

  16. Early Prediction of Preeclampsia

    Leona C. Poon


    Full Text Available Effective screening for the development of early onset preeclampsia (PE can be provided in the first-trimester of pregnancy. Screening by a combination of maternal risk factors, uterine artery Doppler, mean arterial pressure, maternal serum pregnancy-associated plasma protein-A, and placental growth factor can identify about 95% of cases of early onset PE for a false-positive rate of 10%.

  17. Early Mover Advantages

    Bijwaard, Govert; Janssen, Maarten; Maasland, Emiel


    This paper analyzes empirically whether and if so to what extent later entrants in the European mobile telephony industry have a disadvantage vis-à-vis incumbents and early mover entrants. To analyze this question a dynamic model of market share development and a series of static models are considered. There is clear evidence of early mover advantage, mainly caused by the influence of the penetration rate: it pays to enter when still few people have acquired a mobile telephone. Another import...

  18. Early childhood aggression

    Alink, Lenneke Rosalie Agnes


    In this thesis the development, stability, and correlates of early childhood aggression were investigated. The normative development was examined in a general population sample using questionnaires completed by the parents of 12-, 24-, and 36-month-old children and again one year later. Results showed an early childhood aggression curve, with increasing rates of aggression in the second year of life and decreasing rates in the fourth year. One-year stabilities were moderate for 12-month-olds ...

  19. How early is early dark energy?

    Pettorino, Valeria; Wetterich, Christof


    We investigate constraints on early dark energy (EDE) from the Cosmic Microwave Background (CMB) anisotropy, taking into account data from WMAP9 combined with latest small scale measurements from the South Pole Telescope (SPT). For a constant EDE fraction we propose a new parametrization with one less parameter but still enough to provide similar results to the ones previously studied in literature. The main emphasis of our analysis, however, compares a new set of different EDE parametrizations that reveal how CMB constraints depend on the redshift epoch at which Dark Energy was non negligible. We find that bounds on EDE get substantially weaker if dark energy starts to be non-negligible later, with early dark energy fraction Omega_e free to go up to about 5% at 2 sigma if the onset of EDE happens at z < 100. Tight bounds around 1-2% are obtained whenever dark energy is present at last scattering, even if its effects switch off afterwards. We show that the CMB mainly constrains the presence of Dark Energy ...

  20. Massive and permanent decline of symbiont bearing morozovellids and δ13C perturbations across the Early Eocene Climatic Optimum at the Possagno section (Southern Alps of northeastern Italy

    V. Luciani


    Full Text Available The Early Eocene Climatic Optimum (EECO records the highest prolonged global temperatures over the past 70 Ma. Understanding the causes and timing of Eocene climate change remains a major challenge in Cenozoic paleoceanography, which includes the biotic response to climate variability and the changes among planktic foraminiferal assemblages across the EECO. The symbiont bearing and shallow dwelling genera Morozovella and Acarinina were important calcifiers in the tropical-subtropical early Paleogene oceans but almost completely disappeared at about 38 Ma, near the Bartonian/Priabonian boundary. We show here that morozovellids record a first critical step across the EECO through a major permanent decline in relative abundance from the Tethyan Possagno section and ODP Site 1051 in the western subtropical North Atlantic. Possible causes may include increased eutrophication, weak water column stratification, changes in ocean chemistry, loss of symbiosis and possible complex interaction with other microfossil groups. Relative abundances of planktic foraminiferal taxa at Possagno parallel negative shifts in both δ13C and δ18O of bulk sediment from Chron C24r to basal Chron C20r. The post-EECO stable isotopic excursions towards lighter values are of modest intensity. Significant though ephemeral modifications in the planktic foraminiferal communities occur during these minor isotopic excursions. These modifications are marked by pronounced increases in relative abundance of acarininids, in a manner similar to their behaviour during pre-EECO hyperthermals in the Tethyan settings, which suggest a pronounced biotic sensitivity to climate change of planktic foraminifera even during the post-EECO interval.

  1. Nature, origin and evolution of the granitoid-hosted early Proterozoic copper-molybdenum mineralization at Malanjkhand, Central India

    Sarkar, S. C.; Kabiraj, S.; Bhattacharya, S.; Pal, A. B.


    At Malanjkhand, Central India, lode-type copper (-molybdenum) mineralization occurs within calcalkaline tonalite-granodiorite plutonic rocks of early Proterozoic age. The bulk of the mineralization occurs in sheeted quartz-sulfide veins, and K-silicate alteration assemblages, defined by alkali feldspar (K-feldspar≫albite)+dusty hematite in feldspar±biotite±muscovite, are prominent within the ore zone and the adjacent host rock. Weak propylitic alteration, defined by albite+biotite+epidote/zoisite, surrounds the K-silicate alteration zone. The mineralized zone is approximately 2 km in strike length, has a maximum thickness of 200 m and dips 65° 75°, along which low-grade mineralization has been traced up to a depth of about 1 km. The ore reserve has been conservatively estimated to be 92 million tonnes with an average Cu-content of 1.30%. Supergene oxidation, accompanied by limited copper enrichment, is observed down to a depth of 100 m or more from the surface. Primary ores consist essentially of chalcopyrite and pyrite with minor magnetite and molybdenite. δ34S (‰) values in pyrite and chalcopyrite (-0.38 to +2.90) fall within the range characteristic of granitoid-hosted copper deposits. δ18O (‰) values for vein quartz (+6.99 to +8.80) suggest exclusive involvement of juvenile water. Annealed fabrics are common in the ore. The sequence of events that led to the present state of hypogene mineralization is suggested to be as follows: fracturing of the host rock, emplacement of barren vein quartz, pronounced wall-rock alteration accompanied by disseminated mineralization and the ultimate stage of intense silicification accompanied by copper mineralization. Fragments of vein quartz and altered wall rocks and striae in the ore suggest post-mineralization deformation. The recrystallization fabric, particularly in chalcopyrite and sphalerite, is a product of dynamic recrystallization associated with the post-mineralization shearing. The petrology of the host

  2. Early bile duct cancer

    Jae Myung Cha; Myung-Hwan Kim; Se Jin Jang


    Bile duct cancers are frequently diagnosed as advanced diseases. Over half of patients with advanced bile duct cancer present with unresectable malignancies and their prognosis has been very poor even after curative resections. Although there has been a need to diagnose bile duct cancer at its early stage, it has been a difficult goal to achieve due to our lack of knowledge regarding this disease entity. Early bile duct cancer may be defined as a carcinoma whose invasion is confined within the fibromuscular layer of the extrahepatic bile duct or intrahepatic large bile duct without distant metastasis irrespective of lymph node involvement. Approximately 3%-10% of resected bile duct cancers have been reported to be early cancers in the literature. The clinicopathological features of patients with early bile duct cancer differ from those of patients with advanced bile duct cancer, with more frequent asymptomatic presentation, characteristic histopathological findings,and excellent prognosis. This manuscript is organized to emphasize the need for convening an international consensus to develop the concept of early bile duct cancer.

  3. Early diagnosis of early stage lung cancer

    Andrej Debeljak


    Full Text Available Background: For the detection of premalignant changes of bronchial mucosa and early stages of lung cancer frequent chest X-ray, spiral low dose computed tomography, fluorescence bronchoscopy, sputum cytology (also with automated systems with genetic and molecular changes in the sputum cells and bronchial mucosa were used. These screening methods of the high-risk groups for lung cancer achieved: earlier diagnosis of lung cancer in lower stage, higher operability, longer 5-year survival, but without mortality reduction.Conclusions: In the clinical practice we can examine higher risk groups for lung cancer in randomised control trials with multimodality approach: frequent chest low-dose fast spiral computed tomography, sputum cytology with genetic and molecular examinations and fluorescence bronchoscopy. Smoking cessation remains the best means to achieve mortality reduction from lung cancer.

  4. Early Reionization in Cosmology

    Durrer, R


    The cosmic microwave background (CMB) anisotropies have turned out to represent one of the most stringent 'bottle necks' for scenarios of large scale structure formation. As a possibility to relax this constraint, it has been proposed that early reionization can damp CMB fluctuations on small scales due to photon diffusion in the ionized plasma. As an example, I investigate the recently proposed scenario with cold dark matter (CDM) and texture seeds. There, an analysis of CMB anisotropies shows that early reionization is a crucial ingredient for this scenario. Without damping, the small scale anisotropies would dominate and exceed observed limits. In this paper I present analytical and numerical results for the amount of damping due to early reionization for CMB perturbations induced by a collapsing texture. Furthermore, the spectral distortion of the CMB due to Compton scattering of the hotter plasma electrons is calculated. Next I discuss the physical processes which lead to a system of coupled ordinary dif...

  5. Early detection of psychosis

    Larsen, T. K.; Melle, I.; Auestad, B.


    Background During the last decades we have seen a new focus on early treatment of psychosis. Several reviews have shown that duration of untreated psychosis (DUP) is correlated to better outcome. However, it is still unknown whether early treatment will lead to a better long-term outcome....... This study reports the effects of reducing DUP on 5-year course and outcome.Method During 1997â€"2000 a total of 281 consecutive patients aged >17 years with first episode non-affective psychosis were recruited, of which 192 participated in the 5-year follow-up. A comprehensive early detection (ED) programme...... with public information campaigns and low-threshold psychosis detection teams was established in one healthcare area (ED-area), but not in a comparable area (no-ED area). Both areas ran equivalent treatment programmes during the first 2 years and need-adapted treatment thereafter.Results At the start...

  6. Early Islamic Syria

    Walmsley, Alan

    After more than a century of neglect, a profound revolution is occurring in the way archaeology addresses and interprets developments in the social history of early Islamic Syria-Palestine. This concise book offers an innovative assessment of social and economic developments in Syria...... for considerable cultural and economic continuity rather than devastation and unrelenting decline. Much new, and increasingly non-elite, architectural evidence and an ever-growing corpus of material culture indicate that Syria-Palestine entered a new age of social richness in the early Islamic period, even...

  7. Early life vaccination

    Nazerai, Loulieta; Bassi, Maria Rosaria; Uddbäck, Ida Elin Maria


    the first period of life and provide a pertinent alternative in infant vaccinology. To address this, infant mice were vaccinated with three different adenoviral vectors and the CD8+ T-cell response after early life vaccination was explored. We assessed the frequency, polyfunctionality and in vivo...... cytotoxicity of the elicited memory CD8+ T cells, as well as the potential of these cells to respond to secondary infections and confer protection. We further tested the impact of maternal immunity against our replication-deficient adenoviral vector during early life vaccination. Overall, our results indicate...

  8. The Earth's early evolution.

    Bowring, S A; Housh, T


    The Archean crust contains direct geochemical information of the Earth's early planetary differentiation. A major outstanding question in the Earth sciences is whether the volume of continental crust today represents nearly all that formed over Earth's history or whether its rates of creation and destruction have been approximately balanced since the Archean. Analysis of neodymium isotopic data from the oldest remnants of Archean crust suggests that crustal recycling is important and that preserved continental crust comprises fragments of crust that escaped recycling. Furthermore, the data suggest that the isotopic evolution of Earth's mantle reflects progressive eradication of primordial heterogeneities related to early differentiation.

  9. Early Cosmology Constrained

    Verde, Licia; Pigozzo, Cassio; Heavens, Alan F; Jimenez, Raul


    We investigate our knowledge of early universe cosmology by exploring how much additional energy density can be placed in different components beyond those in the $\\Lambda$CDM model. To do this we use a method to separate early- and late-universe information enclosed in observational data, thus markedly reducing the model-dependency of the conclusions. We find that the 95\\% credibility regions for extra energy components of the early universe at recombination are: non-accelerating additional fluid density parameter $\\Omega_{\\rm MR} < 0.006$ and extra radiation parameterised as extra effective neutrino species $2.3 < N_{\\rm eff} < 3.2$ when imposing flatness. Our constraints thus show that even when analyzing the data in this largely model-independent way, the possibility of hiding extra energy components beyond $\\Lambda$CDM in the early universe is seriously constrained by current observations. We also find that the standard ruler, the sound horizon at radiation drag, can be well determined in a way ...

  10. Early Learning in CRESPAR.

    Wasik, Barbara A.; Karweit, Nancy; Bond, Mary Alice; Woodruff, Lannette Burns; Jaeger, Gary; Adee, Sarah


    Summarizes research conducted by the Early Learning Program during the first 5 years of operation of the Center for Research on the Education of Children Placed At Risk (CRESPAR). Describes two integrated areas of research: practices that promote the development of language and literacy skills and systemic issues of school policy and teacher…

  11. Introduction to "Early psychosis

    McGorry, Patrick; Nordentoft, Merete; Simonsen, Erik


    warrants careful analysis. The Third International Early Psychosis Conference proved to be a watershed and was the largest and most vibrant meeting to that point. This preface aims to set the scene for a selection of contributions, derived from the array of new evidence reported in Copenhagen, and recently...

  12. Early childhood aggression

    Alink, Lenneke Rosalie Agnes


    In this thesis the development, stability, and correlates of early childhood aggression were investigated. The normative development was examined in a general population sample using questionnaires completed by the parents of 12-, 24-, and 36-month-old children and again one year later. Results show

  13. Early Mover Advantages

    G.E. Bijwaard (Govert); M.C.W. Janssen (Maarten); E. Maasland (Emiel)


    textabstractIn this paper we analyze empirically whether and if so to what extent later entrants in the European mobile telephony industry have a disadvantage vis-à-vis incumbents and early mover entrants. To analyze this question we consider a series of static models and a dynamic model of market s

  14. Teaching polymorphism early


    Is it possible to teach dynamic polymorphism early? What techniques could facilitate teaching it in Java. This panel will bring together people who have considered this question and attempted to implement it in various ways, some more completely than others. It will also give participants an oppo...

  15. Early Adolescent Ego Development.

    James, Michael A.


    Presented are the theoretical characteristics of social identity in early adolescence (ages 10 to 15). It is suggested that no longer is identity thought to begin with adolescence, but may have its beginnings in the preteen years. The article draws heavily on Eriksonian concepts. (Editor/KC)

  16. Early Childhood Trauma

    National Child Traumatic Stress Network, 2010


    Early childhood trauma generally refers to the traumatic experiences that occur to children aged 0-6. Because infants' and young children's reactions may be different from older children's, and because they may not be able to verbalize their reactions to threatening or dangerous events, many people assume that young age protects children from the…

  17. Early malignant syphilis*

    Ortigosa, Yara Martins; Bendazzoli, Paulo Salomão; Barbosa, Angela Marques; Ortigosa, Luciena Cegatto Martins


    Early malignant syphilis is a rare and severe variant of secondary syphilis. It is clinically characterized by lesions, which can suppurate and be accompanied by systemic symptoms such as high fever, asthenia, myalgia, and torpor state. We report a diabetic patient with characteristic features of the disease showing favorable evolution of the lesions after appropriate treatment. PMID:28300925

  18. Early Developments, 2002.

    Winton, Pam, Ed.; Buysse, Virginia, Ed.


    This document consists of the three 2002 issues of a journal reporting new research in early child development conducted by the Frank Porter Graham Child Development Center (FPG) at the University of North Carolina at Chapel Hill. Articles in the Winter 2002 issue highlight some current work at FPG on factors that enhance or inhibit social and…

  19. Creativity: The Early Years

    Shade, Rick; Shade, Patti Garrett


    There is a myth that some people are creative and others are not. However, all children are born creative. They love to explore, ask questions, and are incredibly imaginative. Parents are key in nurturing their child's creativity in the early years. This article offers resources and strategies parents can use at different ages and stages (newborn,…

  20. Music in Early Childhood.

    Feierabend, John


    Argues that music activities in early childhood education foster a variety of developmental skills. Analyzes Howard Gardner's theory of multiple intelligences, contending that music intelligence is a separate intelligence. Provides ways to identify and promote musical intelligence. Suggests methods for encouraging musical development. Using songs…

  1. Teaching polymorphism early


    Is it possible to teach dynamic polymorphism early? What techniques could facilitate teaching it in Java. This panel will bring together people who have considered this question and attempted to implement it in various ways, some more completely than others. It will also give participants...

  2. Bacterial Paleontology and Studies of Carbonaceous Chondrites

    Gerasimenko, L. M.; Hoover, Richard B.; Rozanov, Alexei Y.; Zhegallo, E. A.; Zhmur, S. I.


    The study of the fossilization processes of modern cyanobacteria provides insights needed to recognize bacterial microfossils. The fossilization of cyanobacteria is discussed and images of recent and fossil bacteria and cyanobacteria from the Early Proterozoic to Neogene carbonaceous rocks (kerites, shungites, and black shales) and phosphorites are provided. These are compared with biomorphic microstructures and possible microfossils encountered in-situ in carbonaceous meteorites.

  3. Quantitative evaluation of microplankton palaeobiogeography in the Ordovician-Early Silurian of the northern Trans European Suture Zone: implications for the timing of the Avalonia-Baltica collision.

    Vecoli, M; Samuelsson, J


    Quantitative analysis of assemblage similarity among chitinozoan and acritarch associations recovered from various sedimentary sequences across the Trans European Suture Zone (TESZ; southern Baltic Sea and northern Germany region), permits evaluation of changes in microplankton palaeobiogeography during the Ordovician in the study area. The present data confirm strong palaeobiogeographic differences between the lower Ordovician of the Rügen area, and the coeval domains of the East European Platform (EEP), corroborating the idea that the subsurface of Rügen should be considered palaeogeographically as the eastern extension of Avalonia.Cluster analysis of chitinozoan assemblages from numerous wells in the Rügen area, and one well from the southern margin of the EEP indicates that chitinozoan bioprovincialism reached its maximum during the Llanvirn; during this period, the Rügen microplankton communities were clearly Gondwanan in character. Calculations using the coefficient of similarity support the conclusion of a high similarity between Llanvirn acritarch assemblages from the Rügen subsurface and from coeval Perigondwana localities (e.g. Tunisia). Since the early Caradoc, this Gondwanan affinity of the Rügen microfossils starts to lessen, and becomes negligible during the late Caradoc. During latest Caradoc-early Ashgill through Llandovery times the chitinozoan assemblages from either side of the TESZ are undistinguishable. If palaeobiogeographical differentiation is primarily related to palaeolatitudinal distance, then the present data support closure of the Tornquist Ocean during late Caradoc-Ashgill times. The presence of reworked Llanvirn acritarchs of Perigondwanan affinity in middle Ashgill sedimentary sequences at the southern margin of the EEP, clearly shows that by this time erosion of an uplifted area was taking place. Accordingly, the closure of the Tornquist Ocean, and consequent Avalonia-Baltica collision must have taken place during the time

  4. Ordovician ocean plate stratigraphy and thrust duplexes of the Ballantrae Complex, SW Scotland: Implications for the pelagic deposition rate and forearc accretion in the closing Iapetus Ocean

    Fujisaki, Wataru; Asanuma, Hisashi; Suzuki, Kazue; Sawaki, Yusuke; Sakata, Shuhei; Hirata, Takafumi; Maruyama, Shigenori; Windley, Brian F.


    The Ballantrae Complex (at Bennane Lea in SW Scotland) contains important ocean plate stratigraphy (basalt, chert, mudstone, sandstone) in an accretionary prism that is associated with a classic Ordovician ophiolite. We used the ocean plate stratigraphy to sub-divide the prism into 11 tectonic units. To determine the depositional age of bedded cherts, zircons were separated from 9 tuff beds from 6 different units. All the tuffs have early to middle Ordovician ages, even though their present positions are mutually distant. These ages are consistent with microfossil records of radiolaria and graptolites. The stratigraphic-structural relationships demonstrate that the ocean plate stratigraphy has been repeated by bedding-parallel thrusts; this is typical of a modern accretionary duplex. We calculated the sedimentation rate of Early to Middle Ordovician bedded cherts at Bennane Lea on the basis of U-Pb zircon ages obtained from several tuff beds; the data indicate that the depositional rate (0.6-3 m/myr) was as slow as that of Mesozoic-Cenozoic equivalents defined by radiolaria. The age spectra of detrital zircons from Ballantrae sandstones show prominent single peaks at ca. 467 and 478 Ma, and a lack of Precambrian zircons. Integration of our new zircon ages with published isotopic data and palaeo-geographic maps indicates that the sandstones were deposited near an intra-oceanic arc and far from any continent containing Precambrian rocks. The pelagic-to-clastic sediments at Bennane Lea were deposited in the closing Iapetus Ocean from ca. 477 Ma to ca. 464 Ma, when they were accreted with the intra-oceanic arc of Ballantrae.

  5. Early Childhood Caries

    Yumiko Kawashita


    Full Text Available Dental caries is one of the most common childhood diseases, and people continue to be susceptible to it throughout their lives. Although dental caries can be arrested and potentially even reversed in its early stages, it is often not self-limiting and progresses without proper care until the tooth is destroyed. Early childhood caries (ECC is often complicated by inappropriate feeding practices and heavy infection with mutans streptococci. Such children should be targeted with a professional preventive program that includes oral hygiene instructions for mothers or caregivers, along with fluoride and diet counseling. However, these strategies alone are not sufficient to prevent dental caries in high-risk children; prevention of ECC also requires addressing the socioeconomic factors that face many families in which ECC is endemic. The aim of this paper is to systematically review information about ECC and to describe why many children are suffering from dental caries.

  6. The Early Sarmatian Knight

    Yablonsky Leonid T.


    Full Text Available During the study of the Early Sarmatian burials in the burial mounds near Filippovka village (Ilek district, Orenburg oblast, a large quantity of weapons and accessories were found, which make it possible to reconstruct the military costume. All the armament items from the burial can be divided into two major groups: offensive and defensive. The former includes bows and arrows, slingshots, spears, stilettos and war hammers (“bec de corbin” type; the latter is represented by a helmet and two varieties of scaly armor, made of iron and bone or horn. The accessories of the military costume found include sword-belt buckles with zoomorphic images, as well as a torque and a bracelet, which apparently served as insignia. The reconstructed image of an elite Early Sarmatian warrior is somewhat similar to the appearance of a Western European knight, but the Sarmatian knight was about 2000 years older.

  7. Early life vaccination

    Nazerai, Loulieta; Bassi, Maria Rosaria; Uddbäck, Ida Elin Maria;


    Intracellular pathogens represent a serious threat during early life. Importantly, even though the immune system of newborns may be characterized as developmentally immature, with a propensity to develop Th2 immunity, significant CD8+ T-cell responses may still be elicited in the context of optimal...... priming. Replication deficient adenoviral vectors have been demonstrated to induce potent CD8+ T-cell response in mice, primates and humans. The aim of the present study was therefore to assess whether replication-deficient adenovectors could overcome the risk of overwhelming antigen stimulation during...... the first period of life and provide a pertinent alternative in infant vaccinology. To address this, infant mice were vaccinated with three different adenoviral vectors and the CD8+ T-cell response after early life vaccination was explored. We assessed the frequency, polyfunctionality and in vivo...

  8. Samuel Goudsmit - Early Influences

    Goudsmit, Esther


    Samuel Goudsmit, born in 1902 in The Hague, Netherlands, earned his Ph.D. at the University of Leiden in 1926 with Paul Ehrenfest. The present talk will describe some aspects of his background and early formative years in order to provide context for the broad range of his professional life. Sam belonged to a large tribe of paternal and maternal uncles, aunts and first cousins; including his parents, grandparents and sister Ro, they numbered forty. Sam was the first of the tribe to be educated beyond high school. Early interests as a child and later as a university student in the Netherlands prefigured his significant and diverse contributions in several realms including not only physics but also teaching, Egyptology and scientific Intelligence. Bibliographic sources will include: The American Institute of Physics' Oral History Transcripts and photographs from the Emilio Segre visual archives, memoirs and conversations of those who knew Sam and also letters to his daughter, Esther.

  9. Early Permian bipedal reptile.

    Berman, D S; Reisz, R R; Scott, D; Henrici, A C; Sumida, S S; Martens, T


    A 290-million-year-old reptilian skeleton from the Lower Permian (Asselian) of Germany provides evidence of abilities for cursorial bipedal locomotion, employing a parasagittal digitigrade posture. The skeleton is of a small bolosaurid, Eudibamus cursoris, gen. et sp. nov. and confirms the widespread distribution of Bolosauridae across Laurasia during this early stage of amniote evolution. E. cursoris is the oldest known representative of Parareptilia, a major clade of reptiles.

  10. Hands of early primates.

    Boyer, Doug M; Yapuncich, Gabriel S; Chester, Stephen G B; Bloch, Jonathan I; Godinot, Marc


    Questions surrounding the origin and early evolution of primates continue to be the subject of debate. Though anatomy of the skull and inferred dietary shifts are often the focus, detailed studies of postcrania and inferred locomotor capabilities can also provide crucial data that advance understanding of transitions in early primate evolution. In particular, the hand skeleton includes characteristics thought to reflect foraging, locomotion, and posture. Here we review what is known about the early evolution of primate hands from a comparative perspective that incorporates data from the fossil record. Additionally, we provide new comparative data and documentation of skeletal morphology for Paleogene plesiadapiforms, notharctines, cercamoniines, adapines, and omomyiforms. Finally, we discuss implications of these data for understanding locomotor transitions during the origin and early evolutionary history of primates. Known plesiadapiform species cannot be differentiated from extant primates based on either intrinsic hand proportions or hand-to-body size proportions. Nonetheless, the presence of claws and a different metacarpophalangeal [corrected] joint form in plesiadapiforms indicate different grasping mechanics. Notharctines and cercamoniines have intrinsic hand proportions with extremely elongated proximal phalanges and digit rays relative to metacarpals, resembling tarsiers and galagos. But their hand-to-body size proportions are typical of many extant primates (unlike those of tarsiers, and possibly Teilhardina, which have extremely large hands). Non-adapine adapiforms and omomyids exhibit additional carpal features suggesting more limited dorsiflexion, greater ulnar deviation, and a more habitually divergent pollex than observed plesiadapiforms. Together, features differentiating adapiforms and omomyiforms from plesiadapiforms indicate increased reliance on vertical prehensile-clinging and grasp-leaping, possibly in combination with predatory behaviors in

  11. Early bioenergetic evolution

    Sousa, Filipa L.; Thiergart, Thorsten; Landan, Giddy; Nelson-Sathi, Shijulal; Pereira, Inês A. C.; Allen, John F.; Lane, Nick; Martin, William F.


    Life is the harnessing of chemical energy in such a way that the energy-harnessing device makes a copy of itself. This paper outlines an energetically feasible path from a particular inorganic setting for the origin of life to the first free-living cells. The sources of energy available to early organic synthesis, early evolving systems and early cells stand in the foreground, as do the possible mechanisms of their conversion into harnessable chemical energy for synthetic reactions. With regard to the possible temporal sequence of events, we focus on: (i) alkaline hydrothermal vents as the far-from-equilibrium setting, (ii) the Wood–Ljungdahl (acetyl-CoA) pathway as the route that could have underpinned carbon assimilation for these processes, (iii) biochemical divergence, within the naturally formed inorganic compartments at a hydrothermal mound, of geochemically confined replicating entities with a complexity below that of free-living prokaryotes, and (iv) acetogenesis and methanogenesis as the ancestral forms of carbon and energy metabolism in the first free-living ancestors of the eubacteria and archaebacteria, respectively. In terms of the main evolutionary transitions in early bioenergetic evolution, we focus on: (i) thioester-dependent substrate-level phosphorylations, (ii) harnessing of naturally existing proton gradients at the vent–ocean interface via the ATP synthase, (iii) harnessing of Na+ gradients generated by H+/Na+ antiporters, (iv) flavin-based bifurcation-dependent gradient generation, and finally (v) quinone-based (and Q-cycle-dependent) proton gradient generation. Of those five transitions, the first four are posited to have taken place at the vent. Ultimately, all of these bioenergetic processes depend, even today, upon CO2 reduction with low-potential ferredoxin (Fd), generated either chemosynthetically or photosynthetically, suggesting a reaction of the type ‘reduced iron → reduced carbon’ at the beginning of bioenergetic evolution

  12. Early modern sport

    Huggins, Mike


    The "early modern" has always suffered problems of periodization. Its beginnings overlap with the Late Middle Ages when sport and athletic exercise were moving away from military training. It encompasses the Renaissance, Reformation, and Counter-Reformation and the scientific shifts of the Age of Enlightenment, movements that were diverse chronologically, geographically, culturally and intellectually. Some historians link its beginnings to block-printing, the beginning of the Tudor period, or...

  13. Early Detection Of Cancer

    V B Bhatnagar


    Full Text Available Farly detection of cancer is based upon three fundamental assumptions, firstly that the trea'ment of benign and precancerous lesions reduces the incidence of cancer, secondly, that the treatment of in situ cancers is conducive to total cure and thirdly that early diagnosis and management of invasive cancer ensures be.ter survival. When patient seeks medical advice for vague symptoms, which could however be due to a possible malignant tumour at a particular site, the alert clinician should investigate the patient immediately to exclude cancer. At this stage cancer is usually not significantly advanced.Currently the U. I. C. C. (International Union for Cancer Control} is studying the epidemiology of cancers in various countries The importance of this is two folds : Firstly by focussing attention on a section of population vulnerable to a particular cancer an early detection is facilitated Secondly by changing the causative factors responsible to a particular cancer, the incidence of that cancer can be reduced e. g. reduction in lung cancer following campaigns against ciguette smoking and reductioi in breast cancer after campaigns for advocating breast feeding of infants, lowering fat consumption and encouraging self palpation of breast regularly.Indeed early diagnosis of cancer implies diagnosis of cancer in almost a symptomatic stage It involves motiva’ion of the population towards acquisitio : of knowledge, attitude and practice.. Epidemiologies and clinicians should be able to recognise high risk cases exposed to particular neoplasia and knowledge of alarming symptoms should be pro- pogated for wide publicity through common available media and means. Probable cases should have regular clhrcal examination periodically and relevant investigations including radiological, imaging techniques and Bio-Chemical examination should be undertaken as and when desired Suspicious lesions should be investigated by specific tests including smear cytology

  14. Precambrian crustal evolution and Cretaceous–Palaeogene faulting in West Greenland: Pre-Nagssugtoqidian crustal evolution in West Greenland: geology, geochemistry and deformation of supracrustal and granitic rocks north-east of Kangaatsiaq

    Watt, Gordon R.


    Full Text Available The area north-east of Kangaatsiaq features polyphase grey orthogneisses, supracrustal rocks and Kangaatsiaq granite exposed within a WSW–ENE-trending synform. The supracrustal rocks are comprised of garnet-bearing metapelites, layered amphibolites and layered, likewise grey biotite paragneisses. Their association and geochemical compositions are consistent with a metamorphosed volcano-sedimentary basin (containing both tholeiitic and calc-alkali lavas and is similar to other Archaean greenstone belts. The Kangaatsiaq granite forms a 15 × 3 km flat, subconcordant body of deformed,pink, porphyritic granite occupying the core of the supracrustal synform, and is demonstrably intrusive into the amphibolites. The granite displays a pronounced linear fabric (L or L > S. Thepost-granite deformation developed under lower amphibolite facies conditions (400 ± 50°C, and is characterised by a regular, NE–SW-trending subhorizontal lineation and an associated irregular foliation, whose poles define a great circle; together they are indicative of highly constrictional strain. The existence of a pre-granite event is attested by early isoclinal folds and a foliation within the amphibolites that is not present in the granite, and by the fact that the granite cuts earlier structures in the supracrustal rocks. This early event, preserved only in quartz-free lithologies, resulted in high-temperature fabrics being developed under upper amphibolite to granulite facies conditions.

  15. Vertebrate assemblages from the early Late Cretaceous of southeastern Morocco: An overview

    Cavin, L.; Tong, H.; Boudad, L.; Meister, C.; Piuz, A.; Tabouelle, J.; Aarab, M.; Amiot, R.; Buffetaut, E.; Dyke, G.; Hua, S.; Le Loeuff, J.


    OT1 assemblage, possibly corresponds to a specific, localised ecosystem within the Kem Kem beds compound assemblage. Microfossils and facies from the Aoufous Formation, corresponding to the top of the compound assemblage, provide evidence of extremely abiotic conditions (hypersalinity), and thus of great environmental instability. At the base of the Akrabou Formation the first ammonite bioevent, Neolobites, corresponds to the onset of the marine transgression in the early Late Cenomanian while the Agoult assemblage (Late Cenomanian?) contains a variety of small fish species that have Central Tethyan affinities. Finally, the youngest Mammites bioevent in the late Early Turonian corresponds to a deepening of the marine environment: this sequence is isochronous with the Goulmima assemblage, a diverse collection of fish and other marine taxa, and shows affinities with taxa from the South Atlantic, the Central Tethys and the Western Interior seaway of North America, and further highlights the biogeographical importance of these North African Late Cretaceous assemblages.

  16. History of early atomic clocks

    Ramsey, N.F. [Harvard Univ., Cambridge, MA (United States). Lyman Lab. of Physics


    This review of the history of early atomic clocks includes early atomic beam magnetic resonance, methods of separated and successive oscillatory fields, microwave absorption, optical pumping and atomic masers. (author)

  17. Early Life Exposures and Cancer

    Early-life events and exposures have important consequences for cancer development later in life, however, epidemiological studies of early-life factors and cancer development later in life have had significant methodological challenges.

  18. The late Neoproterozoic to early Cambrian sulphur cycle: an isotopic investigation of sedimentary rocks from the Yangtze platform

    Goldberg, T.; Strauss, H.


    The sulphur cycle responds to changes in seawater chemistry, biological evolution and tectonic activity. We follow an isotopic approach in order to constrain the state of the ocean/atmosphere system during the late Neoproterozoic and early Cambrian. For this purpose, sedimentary successions from the Yangtze platform, South China, were analysed for their sulphur isotopic composition in different S-bearing phases. The general stratigraphy comprises in ascending order the Doushantuo, Dengying and Niutitang formations. Main lithologies include carbonates, phosphorites, black shales and cherts. The sulphur isotopic composition of the late Neoproterozoic to early Cambrian seawater sulphate ranges from +30 to +35 ‰ as evident from calcium sulphates and trace sulphate in unaltered carbonates and phosphorites (Shields et al., 1999). Sulphur isotopes in chromium reducible and organically bound sulphur are displaced by about +40 ‰ from the seawater sulphate signal, indicating bacterial sulphate reduction. Isotope values range between -16 and +25 ‰ reflecting different environmental conditions, varying from open to closed/limiting conditions in respect to sulphate availability. Pyrite morphology is studied in order to characterize the diagenetic environment. Consistent with a biological origin for the sedimentary pyrite in the Neoproterozoic as well as in the Cambrian (Strauss, 2002) is the positive correlation between sulphide sulphur and organic carbon abundances. The availability of reactive iron is evaluated by means of the degree of pyritization (Raiswell et al., 1988). Raiswell, R. Buckley, F., Berner, R. &Anderson, T. (1988) Degree of pyritization of iron as a paleoenvironmental indicator of bottom-water oxygenation. Journal of Sedimentary Petrology, 58, No.5, 812-819 Shields, G., Strauss, H., Howe, S. &Siegmund, H. (1999) Sulphur isotope composition of sedimentary phosphorites from the basal Cambrian of China: implications for Neoproterozoic-Cambrian biochemical

  19. Early prevention of obesity

    Claudio Maffeis


    Full Text Available Childhood obesity is the metabolic disorder with the highest prevalence in both children and adults. Urgency to treat and prevent childhood obesity is based on the clear evidence that obesity tends to track from childhood to adulthood, is associated to morbidity also in childhood and to long-term mortality. Early life, i.e., intrauterine life and the first two years, is a sensitive window for prevention. Anatomical and functional maturation of the hypothalamic structures devoted to regulating energy intake and expenditure and body size mainly occurs in the first 1,000 days of life. Therefore, factors affecting the foetal exposition to maternal metabolic environment and early postnatal nutrition are crucial in modulating the definition of the metabolic programming processes in the brain. Maternal diseases, mainly malnutrition for defect or excess, obesity and diabetes, placental disorders and dysfunctions, maternal use of alcohol and drugs, smoking, affect long term metabolic programming of the foetus with lifelong consequences. Similarly, early nutrition contributes to complete the long-term metabolic regulating framework initiated in the uterus. Breastfeeding, adequate weaning, attention to portion size and diet composition are potential tools for reducing the obesity risk later in childhood. Longitudinal randomized controlled studies are needed for exploring the efficacy of obesity prevention strategies initiated after conception.Proceedings of the 10th International Workshop on Neonatology · Cagliari (Italy · October 22nd-25th, 2014 · The last ten years, the next ten years in Neonatology Guest Editors: Vassilios Fanos, Michele Mussap, Gavino Faa, Apostolos Papageorgiou

  20. Early Onset Werner Syndrome

    Berna İmge Aydoğan


    Full Text Available Werner syndrome (WS is a rare autosomal recessive adult-onset progeroid disorder characterized by the early onset of aged-appearance and age-related metabolic disorders. Symptoms of premature aging usually first develop in the second-third decades of life. We report a 27-year-old female who was admitted to our clinic at the age of eighteen with hyperglycemia. She was diagnosed with diabetes and type 4 dyslipidemia at the age of seven. In her family history, her parents were first cousins and she had three healthy brothers. On her first physical examination; she had bird-like face appearance, global hair loss, beaked nose, short stature and she was overweight. She had global hair loss with gray and thin hair. Hoarseness of voice and hyperkeratosis of skin were observed. She had bilateral cataracts and moderate sensorineural hearing loss. On psychiatric examination, borderline mental retardation was detected. She had severe insulin resistance and hypertriglyceridemia despite levothyroxine, gemfibrozil, omega-3 and intensive insulin treatment. Routine lipid apheresis was performed to lower the triglyceride levels reaching 5256 mg/dL. She also had focal segmental glomerulosclerosis, hepatosteatosis, osteoporosis and epilepsy. Disease was accompanied by several congenital deformities, such as Rathke’s cleft cyst, angiomyolipoma and femoral neck hypoplasia. WS is a rare genetic disorder characterized by multiple endocrine manifestations as well as soft tissue changes. We present a case of early disturbances that were diagnosed before typical clinical signs and symptoms. We propose that WS should be kept in mind when type 2 diabetes and hyperlipidemia are diagnosed early in childhood. Turk Jem 2015; 19: 99-104

  1. The Brahmaputra tale of tectonics and erosion: Early Miocene river capture in the Eastern Himalaya

    Bracciali, Laura; Najman, Yani; Parrish, Randall R.; Akhter, Syed H.; Millar, Ian


    The Himalayan orogen provides a type example on which a number of models of the causes and consequences of crustal deformation are based and it has been suggested that it is the site of a variety of feedbacks between tectonics and erosion. Within the broader orogen, fluvial drainages partly reflect surface uplift, different climatic zones and a response to crustal deformation. In the eastern Himalaya, the unusual drainage configuration of the Yarlung Tsangpo-Brahmaputra River has been interpreted either as antecedent drainage distorted by the India-Asia collision (and as such applied as a passive strain marker of lateral extrusion), latest Neogene tectonically-induced river capture, or glacial damming-induced river diversion events. Here we apply a multi-technique approach to the Neogene paleo-Brahmaputra deposits of the Surma Basin (Bengal Basin, Bangladesh) to test the long-debated occurrence and timing of river capture of the Yarlung Tsangpo by the Brahmaputra River. We provide U-Pb detrital zircon and rutile, isotopic (Sr-Nd and Hf) and petrographic evidence consistent with river capture of the Yarlung Tsangpo by the Brahmaputra River in the Early Miocene. We document influx of Cretaceous-Paleogene zircons in Early Miocene sediments of the paleo-Brahmaputra River that we interpret as first influx of material from the Asian plate (Transhimalayan arc) indicative of Yarlung Tsangpo contribution. Prior to capture, the predominantly Precambrian-Paleozoic zircons indicate that only the Indian plate was drained. Contemporaneous with Transhimalayan influx reflecting the river capture, we record arrival of detrital material affected by Cenozoic metamorphism, as indicated by rutiles and zircons with Cenozoic U-Pb ages and an increase in metamorphic grade of detritus as recorded by petrography. We interpret this as due to a progressively increasing contribution from the erosion of the metamorphosed core of the orogen. Whole rock Sr-Nd isotopic data from the same samples

  2. In search of early life: Carbonate veins in Archean metamorphic rocks as potential hosts of biomarkers

    Peters, Carl A.; Piazolo, Sandra; Webb, Gregory E.; Dutkiewicz, Adriana; George, Simon C.


    The detection of early life signatures using hydrocarbon biomarkers in Precambrian rocks struggles with contamination issues, unspecific biomarkers and the lack of suitable sedimentary rocks due to extensive thermal overprints. Importantly, host rocks must not have been exposed to temperatures above 250 °C as at these temperatures biomarkers are destroyed. Here we show that Archean sedimentary rocks from the Jeerinah Formation (2.63 billion yrs) and Carawine Dolomite (2.55 billion yrs) of the Pilbara Craton (Western Australia) drilled by the Agouron Institute in 2012, which previously were suggested to be suitable for biomarker studies, were metamorphosed to the greenschist facies. This is higher than previously reported. Both the mineral assemblages (carbonate, quartz, Fe-chlorite, muscovite, microcline, rutile, and pyrite with absence of illite) and chlorite geothermometry suggest that the rocks were exposed to temperatures higher than 300 °C and probably ∼400 °C, consistent with greenschist-facies metamorphism. This facies leads to the destruction of any biomarkers and explains why the extraction of hydrocarbon biomarkers from pristine drill cores has not been successful. However, we show that the rocks are cut by younger formation-specific carbonate veins containing primary oil-bearing fluid inclusions and solid bitumens. Type 1 veins in the Carawine Dolomite consist of dolomite, quartz and solid bitumen, whereas type 2 veins in the Jeerinah Formation consist of calcite. Within the veins fluid inclusion homogenisation temperatures and calcite twinning geothermometry indicate maximum temperatures of ∼200 °C for type 1 veins and ∼180 °C for type 2 veins. Type 1 veins have typical isotopic values for reprecipitated Archean sea-water carbonates, with δ13CVPDB ranging from - 3 ‰ to 0‰ and δ18OVPDB ranging from - 13 ‰ to - 7 ‰, while type 2 veins have isotopic values that are similar to hydrothermal carbonates, with δ13CVPDB ranging from - 18

  3. Final results on the Jurassic-Cretaceous boundary in the Gresten Klippenbelt (Austria): Macro-, micro-, nannofossils, isotopes, geochemistry, susceptibility, gamma-log and palaeomagnetic data as environmental proxies of the early Penninic Ocean history

    Lukeneder, A.; Halásová, E.; Kroh, A.; Mayrhofer, S.; Pruner, P.; Reháková, D.; Schnabl, P.; Sprovieri, M.


    Jurassic to Lower Cretaceous pelagic sediments are well known to form a major element of the northernmost tectonic units of the Gresten Klippenbelt (Lower Austria). The Penninic Ocean was a side tract of the Central Atlantic Oceanic System intercalated between the European and the Austroalpine plates. Its opening started during the Mid Jurrasic, as rifting of the of the oceanic crust between the European and the Austroalpine plates. The turnover of the deposition on the European shelf (Helvetic Zone) from deep-water siliciclastics into pelagic carbonates is correlated with the deepening of this newly arising ocean. Within the Gresten Klippenbelt Unit, this transition is reflected by the lithostratigraphic boundary between the Tithonian marl-limestone succession and the Berriasian limestones of the Blassenstein Formation. This boundary is well exposed in a newly discovered site at Nutzhof, in the heart of Lower Austria (Kroh and Lukeneder 2009, Lukeneder 2009, Pruner, Schnabl, and Lukeneder 2009, Reháková, Halásová and Lukeneder 2009). Biostratigraphy. According to microfossil (calcareous dinoflagellates, calpionellids) and palaeomagnetic data, the association indicates that the cephalopod-bearing beds of the Nutzhof section belong to the Carpistomiosphaera tithonica-Zone of the Early Tithonian up to the Calpionella Zone of the Middle Berriasian. This interval corresponds to the ammonoid zones from the Early Tithonian Hybonoticeras hybonotum-Zone up to the Middle Berriasian Subthurmannia occitanica-Zone. Ammonoids. Late Jurassic to Early Cretaceous ammonoids were collected at the Nutzhof locality in the eastern part of the Gresten Klippenbelt in Lower Austria. The cephalopod fauna from the Blassenstein Formation, correlated with micro- and nannofossil data from the marly unit and the limestone unit, indicates Early Tithonian to Middle Berriasian age (Hybonoticeras hybonotum Zone up to the Subthurmannia occitanica Zone). According to the correlation of the fossil

  4. Early Childhood Special Music Education

    Darrow, Alice-Ann


    The process of early intervention is a critical component of Early Childhood Special Music Education. Early intervention is the process of providing services, education, and support to young children who have disabilities or to children who are at-risk of developing needs that may affect their physical, cognitive, or emotional development. The…

  5. Expenditures for Early Intervention Services

    Hebbeler, Kathleen; Levin, Jesse; Perez, Maria; Lam, Irene; Chambers, Jay G.


    What does it cost to provide early intervention services? Data collected as part of the National Early Intervention Longitudinal Study were used to determine expenditures for infants, toddlers, and their families receiving services through Part C programs. The study found that the national average total expenditure for early intervention services…

  6. Early solar physics

    Meadows, A J


    Early Solar Physics reviews developments in solar physics, particularly the advent of solar spectroscopy and the discovery of relationships between the various layers of the solar atmosphere and between the different forms of solar activity. Topics covered include solar observations during 1843; chemical analysis of the solar atmosphere; the spectrum of a solar prominence; and the solar eclipse of December 12, 1871. Spectroscopic observations of the sun are also presented. This book is comprised of 30 chapters and begins with an overview of ideas about the sun in the mid-nineteenth century, fo

  7. Sonority and early words

    Kjærbæk, Laila; Boeg Thomsen, Ditte; Lambertsen, Claus


    Syllables play an important role in children’s early language acquisition, and children appear to rely on clear syllabic structures as a key to word acquisition (Vihman 1996; Oller 2000). However, not all languages present children with equally clear cues to syllabic structure, and since the spec......Syllables play an important role in children’s early language acquisition, and children appear to rely on clear syllabic structures as a key to word acquisition (Vihman 1996; Oller 2000). However, not all languages present children with equally clear cues to syllabic structure, and since...... acquisition therefore presents us with the opportunity to examine how children respond to the task of word learning when the input language offers less clear cues to syllabic structure than usually seen. To investigate the sound structure in Danish children’s lexical development, we need a model of syllable......-29 months. For the two children, the phonetic structure of the first ten words to occur is compared with that of the last ten words to occur before 30 months of age, and with that of ten words in between. Measures related to the sonority envelope, viz. sonority types and in particular sonority rises...

  8. Supermodels for early LHC

    Bauer, Christian W. [Theoretical Physics Group, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Berkeley Center for Theoretical Physics, University of California, Berkeley, CA 94720 (United States); Ligeti, Zoltan, E-mail: zligeti@lbl.go [Theoretical Physics Group, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Berkeley Center for Theoretical Physics, University of California, Berkeley, CA 94720 (United States); Schmaltz, Martin [Theoretical Physics Group, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Berkeley Center for Theoretical Physics, University of California, Berkeley, CA 94720 (United States); Physics Department, Boston University, Boston, MA 02215 (United States); Thaler, Jesse [Theoretical Physics Group, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Berkeley Center for Theoretical Physics, University of California, Berkeley, CA 94720 (United States); Walker, Devin G.E. [Theoretical Physics Group, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Berkeley Center for Theoretical Physics, University of California, Berkeley, CA 94720 (United States); Center for the Fundamental Laws of Nature, Jefferson Physical Laboratory, Harvard University, Cambridge, MA 02138 (United States)


    We investigate which new physics signatures could be discovered in the first year of the LHC, beyond the expected sensitivity of the Tevatron data by the end of 2010. We construct 'supermodels', for which the LHC sensitivity even with only 10 pb{sup -1} useful luminosity is greater than that of the Tevatron with 10 fb{sup -1}. The simplest supermodels involve s-channel resonances in the quark-antiquark and especially in the quark-quark channels. We concentrate on easily visible final states with small standard model backgrounds, and find that there are simple searches, besides those for Z{sup '} states, which could discover new physics in early LHC data. Many of these are well-suited to test searches for 'more conventional' models, often discussed for multi-fb{sup -1} data sets.

  9. Early times in tunneling

    García-Calderón, G; Garcia-Calderon, Gaston; Villavicencio, Jorge


    Exact analytical solutions of the time-dependent Schr\\"odinger equation with the initial condition of an incident cutoff wave are used to investigate the traversal time for tunneling. The probability density starts from a vanishing value along the tunneling and transmitted regions of the potential. At the barrier width it exhibits, at early times, a distribution of traversal times that typically has a peak $\\tau_p$ and a width $\\Delta \\tau$. Numerical results for other tunneling times, as the phase-delay time, fall within $\\Delta \\tau$. The B\\"uttiker traversal time is the closest to $\\tau_p$. Our results resemble calculations based on Feynman paths if its noisy behaviour is ignored.

  10. [Early cardiotoxicity of Hydroxychloroquine].

    Zerbib, Y; Guillaumont, M P; Touati, G; Duhaut, P; Schmidt, J


    Hydroxychloroquine (HCQ) is most frequently used in the treatment of systemic inflammatory diseases. Cardiac complications of anti-malarial drugs are uncommon, and most of the time are the result of a long-term exposition. In this case, cardiotoxicity is the consequence of the lysosomal dysfunction and the result of intracytoplasmic granular material inclusions. We report a 77-year-old woman who presented a very early and reversible cardiotoxicity, probably related to the quinidine like effect of the HCQ, 10 days after initiation of therapy for Whipple endocarditis. We discuss the different mechanisms of cardiotoxicity of anti-malarial drugs and their clinical manifestations. Copyright © 2015 Société nationale française de médecine interne (SNFMI). Published by Elsevier SAS. All rights reserved.

  11. Artritis Temprana Early Arthritis


    Full Text Available Hasta la década de los años ochenta se consideraba a la artritis reumatoide (AR como una enfermedad poco frecuente, de gravedad leve a moderada, que tenía una evolución lentamente, progresiva hacia el daño articular y la incapacidad. El aborde terapéutico convencional hasta ese momento, era el tratamiento clásico de la pirámide.Until the early the eighties was considered rheumatoid arthritis to (RA as a rare disease of mild to moderate severity, which had a slowly evolution towards joint damage and disability. The conventional therapeutic option until then, was the classic treatment of the pyramid.

  12. Sonority and early words

    Kjærbæk, Laila; Boeg Thomsen, Ditte; Lambertsen, Claus


    acquisition therefore presents us with the opportunity to examine how children respond to the task of word learning when the input language offers less clear cues to syllabic structure than usually seen. To investigate the sound structure in Danish children’s lexical development, we need a model of syllable...... structure; and as the theoretical basis for our analyses related to sonority we present Basbøll’s Sonority Syllable Model for phonotactics, which is based upon a non-circular version of a sonority hierarchy. We investigate spontaneous child language output in a longitudinal corpus with two children aged 9......Syllables play an important role in children’s early language acquisition, and children appear to rely on clear syllabic structures as a key to word acquisition (Vihman 1996; Oller 2000). However, not all languages present children with equally clear cues to syllabic structure, and since...

  13. Early-Onset Dementia

    Konijnenberg, Elles; Fereshtehnejad, Seyed-Mohammad; Kate, Mara Ten;


    BACKGROUND: Early-onset dementia (EOD) is a rare condition, with an often atypical clinical presentation, and it may therefore be challenging to diagnose. Specialized memory clinics vary in the type of patients seen, diagnostic procedures applied, and the pharmacological treatment given. The aim...... of this study was to investigate quality-of-care indicators in subjects with EOD from 3 tertiary memory clinics in 3 European countries. METHODS: We included 1325 newly diagnosed EOD patients, ages 65 years or younger, between January 1, 2007 and December 31, 2013, from the Danish Dementia Registry...... (Rigshospitalet, Copenhagen), the Swedish Dementia Registry ("SveDem", Karolinska University Hospital, Stockholm), and the Amsterdam Dementia Cohort (VU University Medical Center). RESULTS: The frequency of EOD among all dementia patients was significantly lower in Copenhagen (410, 20%) and Stockholm (284, 21...

  14. Polychronous (Early Cretaceous to Palaeogene) emplacement of the Mundwara alkaline complex, Rajasthan, India: 40Ar/39Ar geochronology, petrochemistry and geodynamics

    Pande, Kanchan; Cucciniello, Ciro; Sheth, Hetu; Vijayan, Anjali; Sharma, Kamal Kant; Purohit, Ritesh; Jagadeesan, K. C.; Shinde, Sapna


    The Mundwara alkaline plutonic complex (Rajasthan, north-western India) is considered a part of the Late Cretaceous-Palaeogene Deccan Traps flood basalt province, based on geochronological data (mainly 40Ar/39Ar, on whole rocks, biotite and hornblende). We have studied the petrology and mineral chemistry of some Mundwara mafic rocks containing mica and amphibole. Geothermobarometry indicates emplacement of the complex at middle to upper crustal levels. We have obtained new 40Ar/39Ar ages of 80-84 Ma on biotite separates from mafic rocks and 102-110 Ma on whole-rock nepheline syenites. There is no evidence for excess 40Ar. The combined results show that some of the constituent intrusions of the Mundwara complex are of Deccan age, but others are older and unrelated to the Deccan Traps. The Mundwara alkaline complex is thus polychronous and similar to many alkaline complexes around the world that show recurrent magmatism, sometimes over hundreds of millions of years. The primary biotite and amphibole in Mundwara mafic rocks indicate hydrous parental magmas, derived from hydrated mantle peridotite at relatively low temperatures, thus ruling out a mantle plume. This hydration and metasomatism of the Rajasthan lithospheric mantle may have occurred during Jurassic subduction under Gondwanaland, or Precambrian subduction events. Low-degree decompression melting of this old, enriched lithospheric mantle, due to periodic diffuse lithospheric extension, gradually built the Mundwara complex from the Early Cretaceous to Palaeogene time.

  15. Early Phanerozoic trace fossils from the Sierra Albarrana quartzites (Ossa-Morena Zone, Southwest Spain)

    Marcos, A.; Azor, A.; González, F.; Simancas, F.


    Three ichnogenera are described from a 50 to 500 m thick shallow-water sandstone-shale sequence (Sierra Albarrana Quartzites). The ichnofauna consists of the burrows of worm-like animals (Arenicolites, Monocraterion, and Skolithos). The age of this formation, previously considered to be Precambrian

  16. Silicon isotopes and trace elements in chert record early Archean basin evolution

    Geilert, Sonja; Vroon, Pieter Z.; van Bergen, Manfred J.


    Silicon isotopes of chemical sediments have received growing attention, given their applicability in the search for properties of ancient seawater. An important target is the reconstruction of secular changes in surface temperature of the Precambrian Earth, but interpretations are problematic since

  17. Early Phanerozoic trace fossils from the Sierra Albarrana quartzites (Ossa-Morena Zone, Southwest Spain)

    Marcos, A.; Azor, A.; González, F.; Simancas, F.


    Three ichnogenera are described from a 50 to 500 m thick shallow-water sandstone-shale sequence (Sierra Albarrana Quartzites). The ichnofauna consists of the burrows of worm-like animals (Arenicolites, Monocraterion, and Skolithos). The age of this formation, previously considered to be Precambrian

  18. Sedimentary Characteristics of Buried Sand Layers Deposited in a Coastal Swamp in West Aceh, Indonesia, in the Early 15th Century

    Morgan, T.; Monecke, K.; Meilianda, E.; Pilarczyk, J.; Rusydy, I.; Moena, A.; Muzhaffat, H.; Rais, A.; Yolanda, I. P.


    Sediment cores from the coastal region of West Aceh, Indonesia, an area largely affected by the December 2004 Sumatra Andaman earthquake and resulting Indian Ocean tsunami, preserve evidence of two buried sand layers of possible tsunamigenic origin deposited in the early 15th century. The study site is dominated by beach ridge morphology with an alternation of beach ridges and swales characteristic of long-term coastal progradation. We targeted a low-lying area landward of a prominent beach ridge that is thought to have formed in the aftermath of the last predecessor of the 2004 event, and marks the position of the coastline in the late 14th and early 15th century. Using a hand auger and plastic tubes, 80 core samples up to 2.5 m in depth were recovered. Sand samples were analyzed using a laser diffraction particle size analyzer and prepared for microfossil analysis. The swale deposits are mostly composed of peat and overlie shallow marine sands forming the base of the beach ridge plain. Within the uppermost centimeters, a number of cores show a <1 cm thick sand layer possibly deposited during tsunami inundation in 2004. Intercalated within the peat deposits we found two buried sand layers at a depth of 70-100 cm below the surface. The lower sand layer is 1-6 cm thick and could only be traced in a handful of cores; the upper layer is more widespread and consistently thicker, measuring 11-17 cm, with 5-14 cm of peat in between the two sand sheets. The sand layers consist of massive to normally graded fine to medium sand and show sharp upper and lower boundaries indicating abrupt depositional events. Grain size distributions of the 2004 tsunami sand as well as of buried sand layers match shoreface sediment samples retrieved in 10 m water depth, suggesting a predominantly offshore source. Based on initial radiocarbon ages and estimates of sedimentation rates, the two buried sand layers were deposited in the early 15th century and are separated by only a few decades.

  19. Peer Bullying During Early Childhood

    Uysal, Hatice; DİNÇER, Çağlayan


    Peer bullying during early childhood is discussed along with the literature reviewed in this article with the purpose of drawing attention to peer bullying during early childhood and its significance, and contributing to studies which are few in number in Turkey. Peer bullying during early childhood was considered with its definition and types, people who play key roles in peer bullying, factors (gender, age, parents, and friendship) that relate to peer bullying, and what should be done befor...

  20. Icebergs on early Mars

    Uceda, E.; Fairen, A.; Woodworth-Lynas, C.; Palmero Rodriguez, A.


    The smooth topography of the Martian northern lowlands has been classically equated to an ancient ocean basin. The High-Resolution Imaging Science Experiment (HiRISE) onboard the Mars Reconnaissance Orbiter (MRO) is providing unprecedented images of the Martian surface at scales of 25 to 32 cm per pixel. The analysis of this high-resolution imaging reveals the presence of three differentiated geomorphologies throughout the northern lowlands of Mars and the Hellas basin, which are informative of the presence of icebergs floating in ancient oceans and/or seas. These morphologies are: (i) scattered scour marks, including curvilinear furrows several km long and some meters deep; (ii) boulders ranging in size from 0.5 m to ~2 m in diameter, distributed forming clusters with sizes from several hundred meters to 1-2 km; and (iii) flat-topped and conical circular fractured mounds. The association of plough marks, clusters of boulders and mounds on the northern plains of Mars can be related to the dual processes of ice keel scouring and ice rafting of both glacial and non-glacial detritus by a floating ice canopy and icebergs. These processes are well documented on Earth and result in distinct morphologies on the ocean floor, which are analogous to features observed in the Martian basins. Importantly, the features are located in elevated areas of the northern plains and Hellas, near the dichotomy boundary and on local topographic highs. Such distribution is expected, as these relatively shoal areas are where the iceberg-related features should occur on Mars: these areas had shallow water depths, less than the iceberg's keel depth, and therefore keels reached through the full depth of the water column to impinge on the sediments below. The presence of icebergs floating in cold oceans early in Mars' history imply the occurrence of continental glaciers forming in the highlands and streaming northward towards the lowlands, and towards the Hellas and Argyre Basins. Glacier

  1. Geologic and Geochronologic Studies of the Early Proterozoic Kanektok Metamorphic Complex of Southwestern Alaska

    Turner, Donald L.; Forbes, Robert B.; Aleinikoff, John N.; McDougall, Ian; Hedge, Carl E.; Wilson, Frederic H.; Layer, Paul W.; Hults, Chad P.


    The Kanektok complex of southwestern Alaska appears to be a rootless terrane of early Proterozoic sedimentary, volcanic, and intrusive rocks which were metamorphosed to amphibolite and granulite facies and later underwent a pervasive late Mesozoic thermal event accompanied by granitic plutonism and greenschist facies metamorphism of overlying sediments. The terrane is structurally complex and exhibits characteristics generally attributed to mantled gneiss domes. U-Th-Pb analyses of zircon and sphene from a core zone granitic orthogneiss indicate that the orthogneiss protolith crystallized about 2.05 b.y. ago and that the protolithic sedimentary, volcanic and granitic intrusive rocks of the core zone were metamorphosed to granulite and amphibolite facies about 1.77 b.y. ago. A Rb-Sr study of 13 whole-rock samples also suggests metamorphism of an early Proterozoic [Paleoproterozoic] protolith at 1.77 Ga, although the data are scattered and difficult to interpret. Seventy-seven conventional 40K/40Ar mineral ages were determined for 58 rocks distributed throughout the outcrop area of the complex. Analysis of the K-Ar data indicate that nearly all of these ages have been totally or partially reset by a pervasive late Mesozoic thermal event accompanied by granitic plutonism and greenschist facies metamorphism. Several biotites gave apparent K-Ar ages over 2 Ga. These ages appear to be controlled by excess radiogenic 40Ar produced by the degassing protolith during the 1.77 Ga metamorphism and incorporated by the biotites when they were at temperatures at which Ar could diffuse through the lattice. Five amphibolites yielded apparent Precambrian 40K/40Ar hornblende ages. There is no evidence that these hornblende ages have been increased by excess argon. The oldest 40K/40Ar hornblende age of 1.77 Ga is identical to the sphene 207Pb/206Pb orthogneiss age and to the Rb-Sr 'isochron' age for six of the 13 whole-rock samples. The younger hornblende ages are interpreted as

  2. Early Solar System Bombardment: Exploring the Echos of Planetary Migration and Lost Ice Giants

    Bottke, William


    Heavily cratered surfaces on the Moon, Mars, Mercury show the terrestrial planets were battered by an intense bombardment during their first billion years or more, but the timing, sources, and dynamical implications of these impacts are controversial. The Late Heavy Bombardment refers to impact events that occurred after stabilization of planetary lithospheres such that they could be preserved as craters. Lunar melt rocks and meteorite shock ages point toward a discrete episode of elevated impact flux between ~3.5 to ~4.2 Ga and a relative quiescence between ~4.0-4.2 to ~4.4 Ga. Evidence from Precambrian impact spherule layers suggest a long-lived tail of terrestrial impactors lasted to ~2.0-2.5 Ga.Dynamical models that include populations residual from primary accretion and destabilized by giant planet migration can potentially account for observations, although all have pros and cons. The most parsimonious solution to match constraints is a hybrid model with discrete early, post-accretion and later, planetary instability-driven impactor populations.For the latter, giant planet instability models can successfully reproduce the orbits of the giant planets, the origin/properties of Jupiter/Neptune Trojans, irregular satellites, the structure of the main asteroid and Kuiper belts, and the presence of comet-like bodies in the main belt, Hilda, and Trojan asteroid populations. The best solutions, however, postulate there were once five giant planets: Jupiter, Saturn, and three ice giants, one that was eventually ejected out of the Solar System by a Jupiter encounter. Intriguing evidence for this “lost” ice giant planet can be found in the orbital properties of bodies captured in the main asteroid belt.The applicability of giant planet instabilities to exoplanet systems seems likely, with the initial configuration of giant planet orbits a byproduct of their early migration and subsequent capture into mutual mean motion resonances. The question is how long can a

  3. Subsidence and conversion of the Dead Sea basin to an inland erosion base level in the early middle Miocene as inferred from geomorphological analysis of its ancient western fluvial outlet

    Bar, Oded; Zilberman, Ezra


    The first major subsidence of the Dead Sea pull-apart basin (DSB) is evidenced by the thick Hufeira Member of the terrestrial Hazeva Formation. The age of the Hufeira Member and the conversion of the DSB to an inland erosion base level are not well constrained. For this purpose we studied the effect of the evolving basin on its ancient fluvial outlet to the Arad-Be'er Sheva Valley (ABSV), which served as a Miocene corridor between the embryonic DSB region in the east and the Mediterranean Sea in the west. We mapped and analyzed the morphostratigraphy of four series of rock-cut erosion surfaces (from top to bottom: the Barir, Kuseifa, Ar'ara, and Shemen surfaces). They are manifested in the east as fluvial erosion surfaces, capped by conglomerates, passing laterally westward to marine wave-cut surfaces, capped by a shallow marine limestone of the early middle Miocene Ziqlag Formation. The age of these surfaces is constrained to the early middle Miocene (Langhian) based on morphostratigraphy correlation with the Ziqlag Formation. Paleogeographic reconstruction of the two higher and older surfaces reveals transverse valleys, which drained the DSB region and crossed the present route of the regional water divide. These transverse valleys were presumably the western outlets to the Mediterranean Sea of the newly subsiding basin. Precambrian components in the assemblage of the clasts that cover the Kuseifa surface were not found in the Hufeira Member and thus reflect an ongoing post-Hufeira exumation of the DSB drainage basin. Hence, this early middle Miocene surface postdates the Hufeira Member, assigning an age of late early Miocene to the first major subsidence of the DSB. The two lower and younger surfaces represent local drainage systems confined to the ABSV. This transition from regional to local drainage system marks the establishment of the present regional water divide and the conversion of the DSB to an inland erosion base level during the early middle Miocene.

  4. Early Attachment Relationships and the Early Childhood Curriculum

    Cortazar, Alejandra; Herreros, Francisca


    This article explores the relationship between attachment theory and the early childhood curriculum. During the first years of life children develop early attachment relationships with their primary caregivers. These attachment relationships, either secure or insecure, will shape children's socio-emotional development. In the USA, the predominant…

  5. Critical Questions about Early Intervention and Early Childhood Special Education

    Winer, Abby; Hebbeler, Kathy; Nelson, Robin; Gundler, Darla; Cate, Debbie; Hudson, Laura; Taylor, Cornelia; Peters, Mary Louise


    What is a high-quality statewide data system? One characteristic is that it provides the information needed to address important questions about early intervention and early childhood special education. But what are those questions? What questions should data users, such as program directors, advocates, and policymakers, be asking? The Center for…

  6. Early reionization by miniquasars

    Madau, P; Oh, S P; Rees, Martin J; Volonteri, M; Madau, Piero; Rees, Martin J.; Volonteri, Marta; Haardt, Francesco


    Motivated by the recent detection by WMAP of a large optical depth to Thomson scattering -- implying a very early reionization epoch -- we assess a scenario where the universe was reionized by `miniquasars' powered by intermediate-mass black holes (IMBHs), the remnants of the first generation of massive stars. Pregalactic IMBHs form within minihalos above the cosmological Jeans mass collapsing at z=24, get incorporated through mergers into larger and larger systems, sink to the center owing to dynamical friction, and accrete cold material. The merger history of dark halos and associated IMBHs is followed by Monte Carlo realizations of the merger hierarchy in a LCDM cosmology. While seed IMBHs that are as rare as the 3.5-sigma peaks of the primordial density field evolve largely in isolation, a significant number of black hole binary systems will form if IMBHs populate the more numerous 3-sigma peaks instead. In the case of rapid binary coalescence a fraction of IMBHs will be displaced from galaxy centers and ...

  7. Early Repolarization Syndrome

    Frederic Sacher


    Full Text Available The electrocardiographic pattern of early repolarization (ER is common, with a particularly high prevalence reported amongst athletes and adolescents. It has long been associated with benign outcome [1-3]. Recently, an association between inferolateral ER pattern and sudden cardiac death (SCD has been established by different groups [4-7]. Population-based studies have also reported an increased mortality rate among patients with inferolateral ER pattern compared to controls [7-9]. To bring back together these differences, it is important to focus on the definition of ER pattern used in these different studies as well as the population included. The definition of ER pattern associated with sudden cardiac death was the presence of J point elevation more than or equal to 0.1mV in at least 2 contiguous inferior and/or lateral leads of a standard 12-lead ECG and not ST elevation as it was often the case in the studies with benign outcome. Any study dealing with ER should clearly indicate the definition used. Otherwise it cannot be interpreted. Talking about definition, ER syndrome is an ER pattern (as defined above associated with symptoms (syncope or aborted SCD and/or familial history of SCD as mentioned in the last HRS/EHRA/APHRS Expert Consensus Statement on the Diagnosis and Management of Patients with Inherited Primary Arrhythmia Syndromes [10]. It is important to recognise that having only an ER pattern is not a disease.


    John S. Abughazaleh; Mushtaq Ahmed; Ashok Anand; John H. Anderson; Charles Benham; Fred D. Brent; Thomas E. Chance; William K. Davis; Raymond F. Drnevich; Larry Hall; Ming He; Stephen A. Lang; David Mintner; Wendy Moore; Jimmy O. Ong; George Potoczniak; Adela G. Sanchez; Charles H. Schrader; Lalit S. Shah; Kalapi D. Sheth; Phil J. Shires; Rae Song


    The overall objective of this project is the three-phase development of an Early Entrance Coproduction Plant (EECP) that produces at least one product from at least two of the following three categories: Electric power (or heat); Fuels; and Chemicals. The objective is to have these products produced by technologies capable of using synthesis gas derived from coal and/or some other carbonaceous feedstock, such as petroleum coke. The objective of Phase I was to determine the feasibility and define the concept for the EECP located at a specific site and to develop a Research, Development, and Testing (RD and T) Plan for implementation in Phase II. This objective has now been accomplished. A specific site, Motiva Refinery in Port Arthur, Texas, has been selected as the location best suited for the EECP. The accomplishments of Phase I are discussed in detail in this Phase I Concept Report. A RD and T Plan and a preliminary project financing plan have been developed and are submitted separately from this report.


    Mushtaq Ahmed; John H. Anderson; Charles Benham; Earl R. Berry; Fred Brent; Belma Demirel; Ming He; Troy Raybold; Manuel E. Quintana; Lalit S. Shah; Kenneth A. Yackly


    The overall objective of this project is the three phase development of an Early Entrance Coproduction Plant (EECP) which produces at least one product from at least two of the following three categories: (1) electric power (or heat), (2) fuels, and (3) chemicals. The objective is to have these products produced by technologies capable of using synthesis gas derived from coal and/or other carbonaceous feedstocks. The objectives of Phase I were to determine the feasibility and define the concept for the EECP located at a specific site; develop a Research, Development, and Testing (RD&T) Plan for implementation in Phase II; and prepare a Preliminary Project Financing Plan. The objective of Phase II is to implement the work as outlined in the Phase I RD&T Plan to enhance the development and commercial acceptance of coproduction technology that produces high-value products, particularly those that are critical to our domestic fuel and power requirements. The project will resolve critical knowledge and technology gaps on the integration of gasification and downstream processing to coproduce some combination of power, fuels, and chemicals from coal and/or other carbonaceous feedstocks. The objective of Phase III is to develop an engineering design package and a financing and testing plan for an EECP located at a specific site. The project's intended result is to provide the necessary technical, economic, and environmental information needed by industry to move the EECP forward to detailed design, construction, and operation.

  10. Freud's early clinical work.

    Vogel, L Z


    Freud became a medical practitioner because it was impossible for him to pursue the desired career of a microscopic researcher. His education and training had not prepared him for the task of being a practicing physician. In his private practice he began treating some very intelligent, chaotic, demanding, volatile and disturbed patients. Anna von Lieben was one of these patients whom Freud treated very intensively for a long period of time. Elise Gomperz was another talented and severely pained early patient of Freud. Over a number of years, Freud was her psychiatrist and provided her with attentive care using a variety of treatment methods that were available to him at that time. Emmy von N.'s condition was also fluctuating and very demanding. The dramatic sense and chronic clinical course of these patients is compatible with the contemporary diagnostic category of Borderline Personality Disorder. Freud provided these patients with long-term supportive care while he attempted to cure them. At the same time, Freud committed himself to the theory of radical cure and downplayed the supportive, draining and difficult clinical work that he was doing.


    John S. Abughazaleh; Mushtaq Ahmed; Ashok Anand; John H. Anderson; Charles Benham; Fred D. Brent; Thomas E. Chance; William K. Davis; Raymond F. Drnevich; Larry Hall; Ming He; Stephen A. Lang; Jimmy O. Ong; Sarah J. Patel; George Potoczniak; Adela G. Sanchez; Charles H. Schrader; Lalit S. Shah; Phil J. Shires; Rae Song


    The overall objective of this project is the three phase development of an Early Entrance Coproduction Plant (EECP) which produces at least one product from at least two of the following three categories: (1) electric power (or heat), (2) fuels, and (3) chemicals. The objective is to have these products produced by technologies capable of using synthesis gas derived from coal and/or other carbonaceous feedstock. The objective of Phase I is to determine the feasibility and define the concept for the EECP located at a specific site and to develop a Research, Development, and Testing Plan (RD and T) for implementation in Phase II. The objective of Phase II is to implement the RD and T as outlined in the Phase I RD and T Plan to enhance the development and commercial acceptance of coproduction technology that produces high-value products, particularly those that are critical to our domestic fuel and power requirements. The project will resolve critical knowledge and technology gaps on the integration of gasification and downstream processing to coproduce some combination of power, fuels, and chemicals from coal and other feedstocks. The objective of Phase III is to develop an engineering design package and a financing plan for an EECP located at a specific site. The project's intended result is to provide the necessary technical, economic, and environmental information that will be needed to move the EECP forward to detailed design, construction, and operation by industry.

  12. Is credit for early action credible early action?

    Rolfe, C. [West Coast Environmental Law Research Foundation, Vancouver, BC (Canada); Michaelowa, A.; Dutschke, M. [Hamburg Institute for Economic Research, Hamburg, (Germany)


    Credit for early action as a tool for greenhouse gas emissions reduction is compared with various market instruments as a means of narrowing the gap between projected emssions and those of the Kyoto Protocol. Market instruments work by creating a market price for emissions and use the market to encourage reductions at the lowest price, which is done by placing limits on greenhouse gas emissions and allowing the market to decide where reductions occur, or by imposing a carbon tax or emissions charge. While they can be applied within a sector, they are usually used to encourage reductions throughout the economy or across large sectors. Credit for early action also creates an incentive for emissions reductions throughout the economy or at least across many sectors. Credit for early action tools do not work by either imposing a carbon tax or emissions charge or placing limits on emissions, rather they promise that entities that take action against greenhouse gases prior to the imposition of a carbon tax or emissions limits will receive a credit against future taxes or limits. An overview is provided of the Kyoto Protocol and the rationale for taking early action, and a review is included of the theory and specific proposals for market instruments and credit for early action. A comparative analysis is provided of these approaches by examining their relative efficiency, environmental effectiveness, and impacts on the redistribution of wealth. Credit for early action is viewed as problematic on a number of counts and is seen as an interim strategy for imposition while political support for market instruments develop. The environmental effectiveness of credit for early action is very difficult to predict, and credit for early action programs do not yield the lowest cost emissions reductions. Credit for early action programs will not achieve compliance with the Kyoto Protocol at the lowest cost, and credits for early action will increase the compliance costs for those who

  13. Formation of Precambrian Strata in Shandong Province——Isotopic Dating Evidences%山东省前寒武纪地层形成时代——同位素地质测年的证据

    王世进; 万渝生; 宋志勇; 杨恩秀; 董春艳; 王伟


    As showed by precise isotopic dating results,Yishui group was formed in the 2760~2700Ma,while Yanlingguan formation in Taishan group,Xiayazu formation and Mengjiatun formation in Liuhang group were formed in 2750~2700Ma.They all belong to early period of Neoarchean.Shangya formation and Shancaoyu formation of Liuhang formation in Taishan group were formed in 2600~2540Ma(intruded by quartz diorite rock units in Yishan rock group and monzogranite in Aolaishan rock group),while zircons ages of Jining group was(2561±24)Ma.They all belong to the late Archean.The formation period of Jingshan group and Fenzishan group is late Paleoproterozoic.Detrital zircon U-Pb age of Zhifu group was(1658±32) Ma and(1792±43)Ma.They were formed in the Mesoproterozoic.Detrital zircon U-Pb age of Huaguoshan group is 800~740Ma,and was formed in the Neoproterozoic.%精确同位素地质测年结果表明,沂水岩群形成时代为2 760~2 700Ma,泰山岩群雁翎关岩组、柳杭岩组下亚组和孟家屯岩组形成时代为2 750~2 700Ma,均属新太古代早期;泰山岩群柳杭岩组上亚组、山草峪岩组形成时代为2 600~2 540Ma(被峄山岩套石英闪长岩和傲徕山岩套二长花岗岩侵入),济宁岩群岩浆锆石年龄(2 561±24)Ma,均属新太古代晚期。荆山群和粉子山群的形成时代为古元古代晚期。芝罘群碎屑锆石U-Pb年龄(1 658±32)Ma、(1 792±43)Ma,形成时代为中元古代。云台岩群花果山组碎屑锆石U-Pb年龄800~740Ma,形成时代为新元古代。

  14. The Sm-Nd isotopic ages of the Early Precambrian mafic-ultramafic volcanic rocks in Yiyang, Hunan%湖南益阳早前寒武纪镁铁质-超镁铁质火山岩的Sm-Nd同位素年龄

    郭乐群; 唐晓珊; 彭和求


    益阳地区出露的似层状-层状镁铁质-超镁铁质火山岩的时代归属有不同的观点.研究认为其主要岩石类型为玄武质科马提岩和拉斑玄武岩.岩石地球化学和同位素年龄显示:玄武质科马提岩Sm-Nd全岩等时线年龄为(3 028±47)Ma,属中、新太古代洋中脊-岛弧火山岩;拉斑玄武岩年龄为(2 216±38)Ma,属古元古代.这一结果揭示了早前寒武纪在古扬子微板块(川中微板块)东南有多岛弧洋盆,湖南深部地壳有绿岩基底.

  15. Early-middle Eocene transition in calcareous nannofossil assemblages at IODP Site U1410 (Southeast Newfoundland Ridge, NW Atlantic)

    Cappelli, Carlotta; Agnini, Claudia; Yamamoto, Yuhji


    nannofossils, making this Site suitable for a comprehensive taxonomic revision of Nannotetrina and Chiasmolithus. Biohorizons related to species belonging to these two genera are used to mark middle Eocene biozone boundary, a better characterization of their taxonomy would thus improve their reliability as biostratigraphic tools. Furthermore, during the early middle Eocene a new evolutionary lineage, which includes S. kempii - S. perpendicularis- S. furcatholitoides morph. A - S. cuniculus - S. furcatholitoides morph. B occurred among sphenoliths. This plexus is characterized by progressive morphological changes which, if correctly identify, will allow for a very detailed subdivision of this interval. Even more interestingly, we would assess if there is any relationship between this evolutionary trend and the surrounding abiotic conditions. Agnini, C., Fornaciari, E., Raffi, I., Catanzariti, R., Pälike, H., Backman, J., and Rio, D., Newslett. Stratigr., 47, 131-181 (2014). Martini E., in: Farinacci, A. (Ed.), Proceedings 2nd International Conference Planktonic Microfossils Roma: Rome (Ed. Tecnosci.) 2, 739-785 (1971). Norris R.D., Wilson P.A., Blum P. and the IODP Expedition 342 Scientists, Proceedings of the Integrated Ocean Drilling Program, 342, 1-148 (2012). Zachos J., Pagani M., Sloan L., Thomas E., Billups K., Science, 292, 686-693 (2001).

  16. Early onset sebaceous carcinoma

    Kaltreider Sara A


    Full Text Available Abstract Background Ocular sebaceous carcinoma can masquerade as benign lesions resulting in delay of diagnosis. Early recognition is even more difficult in young patients where the disease rarely occurs. Here, we provide a clinicopathological correlation of ocular sebaceous carcinoma in a young individual lacking history of hereditary cancer or immunosuppression. Findings A detailed histopathological study including p53 DNA sequencing was performed on an aggressive sebaceous carcinoma presenting in a healthy 32 year-old Caucasian woman. She had no history of retinoblastoma, evidence for a hereditary cancer syndrome, or radiation therapy. However, she potentially was at risk for excessive UV light exposure. A detailed review of the literature is also provided. A moderately well differentiated sebaceous carcinoma was established histopathologically arising from the meibomian gland of the upper eyelid. In most areas, the cytoplasm contained small but distinct Oil-red-O positive vacuoles. Direct sequencing of p53 identified a G:C→A:T mutation at a dipyrimidine site. The mutation results in substitution of arginine for the highly conserved glycine at residue 199 located at the p53 dimer-dimer interface. Energy minimization structural modeling predicts that G199R will neutralize negative charges contributed by nearby inter- and intramonomeric glutamate residues. Discussion This study points to the importance of recognizing that sebaceous carcinoma can occur in young patients with no evidence for hereditary cancer risk or radiation therapy. The G199R substitution is anticipated to alter the stability of the p53 tetrameric complex. The role of UV light in the etiology of sebaceous carcinoma deserves further study. Our findings, taken together with those of others, suggest that different environmental factors could lead to the development of sebaceous carcinoma in different patients.

  17. Expertise of Early Childhood Educators

    Happo, Iiris; Määttä, Kaarina


    Every preschool age child in Finland has the right to day care and the expertise of educators is multidimensional. The aim of this article is to clarify the expertise of those early childhood educators, who have the competence of kindergarten teachers (n = 80). The data consisted of the early educators' stories of their growth towards expertise.…

  18. Early intervention services in psychosis

    Csillag, Claudio; Nordentoft, Merete; Mizuno, Masafumi


    AIM: Early intervention (EI) in psychosis is a comprehensive and evidence-based approach aimed at detection and treatment of psychotic symptoms in their early stages. This paper presents core features and noteworthy aspects of the evidence basis and limitations of EI, the importance of programme...

  19. Early Identification of Reading Difficulties

    Poulsen, Mads; Nielsen, Anne-Mette Veber; Juul, Holger


    Early screening for reading difficulties before the onset of instruction is desirable because it allows intervention that is targeted at prevention rather than remediation of reading difficulties. However, early screening may be too inaccurate to effectively allocate resources to those who need...

  20. Teachers in Early Childhood Policy

    Kilderry, Anna


    This paper examines teacher accountability and authority in early childhood policy. It reports on data from a study that investigated the influences affecting early childhood teacher decision-making at the preschool level in Victoria, Australia. Using a question raised by Ball "Where are the teachers in all this [policy]?" provided a…

  1. Missouri: Early Head Start Initiative

    Center for Law and Social Policy, Inc. (CLASP), 2012


    Missouri's Early Head Start/Child Care Partnership Project expands access to Early Head Start (EHS) services for children birth to age 3 by developing partnerships between federal Head Start, EHS contractors, and child care providers. Head Start and EHS contractors that participate in the initiative provide services through community child care…

  2. Early Childhood Inclusion in Spain

    Giné, Climent; Balcells-Balcells, Anna; Cañadas, Margarita; Paniagua, Gema


    This article describes early childhood inclusion in educational settings in Spain. First, we address the legislative framework of preschool education in Spain and offer a brief analysis of some relevant issues, including the current situation of early childhood education and inclusion at this stage. Second, current policies and practices relating…

  3. Voluntary Incentive Early Retirement Programs.

    Research Dialogues, 1988


    Arrangements in educational institutions for voluntary early retirement programs are discussed. Retirement at any age can be a profound and stressful lifetime change; and it can also represent a welcome transition into newly satisfying and rewarding opportunities. The focus is on: mandatory retirement (exceptions and the new meaning of "early");…

  4. Data Systems in Early Intervention.

    Hebbeler, Kathleen

    This study compiled descriptive information about what states are doing or planning to do with early intervention data systems, a component of early intervention systems as specified in Part H of the Individuals with Disabilities Education Act. The study examined the uses of data systems in eight states: Colorado, Maine, Maryland, Massachusetts,…

  5. Early sound distribution in auditorium

    JIANG Guorong; WANG Jiqing


    The importance of early sound, i.e., the direct sound and the first reflections, has long been recognized in auditorium design, but the distributions of early sound in auditorium received less investigation in the past. As we know, the early sound level in the audience area varies not only with the source/receiver distance and room constant, but also related with the room geometry, the absorption arrangement and the location of the source and receiver. The early reflections are of discrete components, so it can not be predicted by the diffused field theory. This paper presents the results of measurement in four halls showing the attenuation rates of early sound level with the source/receiver distance are often much larger than the theoretical predictions. Therefore, they may give overestimated results in acoustical design.

  6. Multiple sulfur-isotope signatures in Archean sulfates and their implications for the chemistry and dynamics of the early atmosphere

    Muller, Élodie; Philippot, Pascal; Rollion-Bard, Claire; Cartigny, Pierre


    Sulfur isotopic anomalies (∆33S and ∆36S) have been used to trace the redox evolution of the Precambrian atmosphere and to document the photochemistry and transport properties of the modern atmosphere. Recently, it was shown that modern sulfate aerosols formed in an oxidizing atmosphere can display important isotopic anomalies, thus questioning the significance of Archean sulfate deposits. Here, we performed in situ 4S-isotope measurements of 3.2- and 3.5-billion-year (Ga)-old sulfates. This in situ approach allows us to investigate the diversity of Archean sulfate texture and mineralogy with unprecedented resolution and from then on to deconvolute the ocean and atmosphere Archean sulfur cycle. A striking feature of our data is a bimodal distribution of δ34S values at ˜+5‰ and +9‰, which is matched by modern sulfate aerosols. The peak at +5‰ represents barite of different ages and host-rock lithology showing a wide range of ∆33S between -1.77‰ and +0.24‰. These barites are interpreted as primary volcanic emissions formed by SO2 photochemical processes with variable contribution of carbonyl sulfide (OCS) shielding in an evolving volcanic plume. The δ34S peak at +9‰ is associated with non-33S-anomalous barites displaying negative ∆36S values, which are best interpreted as volcanic sulfate aerosols formed from OCS photolysis. Our findings confirm the occurrence of a volcanic photochemical pathway specific to the early reduced atmosphere but identify variability within the Archean sulfate isotope record that suggests persistence throughout Earth history of photochemical reactions characteristic of the present-day stratosphere.

  7. Origin and hydrology of a large, intact Early Cambrian paleocave system and its role in overlying fluidisation structures, Arctic Canada

    Mathieu, Jordan; Turner, Elizabeth C.; Rainbird, Robert H.


    Paleokarst is most commonly expressed as subtle stratigraphic surfaces rather than large void systems penetrating deeply into the paleo-subsurface. In contrast, a regional Precambrian-Cambrian unconformity on Victoria Island (NWT, Canada), is associated with exceptional exposure of large, intact Cambrian paleocaverns (100 m diameter; tens of m high). The paleocaves are distributed along a paleo-horizontal plane, and an associated gryke network is present in the 30-60 m of Neoproterozoic dolostone between cave rooves and the base of overlying Cambrian sandstone; both are filled by Cambrian sandstone. The formation and preservation of such karst features require aggressive dissolution along a stable paleo-water-table shortly before transgression and deposition of shallow-marine sand over the dolostone. During the transgression, the karst network acted as a conduit for flowing groundwater that was discharged through overlying, unconsolidated Cambrian shallow-marine sand, producing water-escape structures (sand volcanoes and their conduits). The conduits are preserved as cylindrical remnants of the sand volcanoes' feeder pipes. Sediment fluidisation was probably caused by variations in the hydraulic-head gradient in a meteoric lens near the Cambrian coastline under a tropical climate with abundant, probably seasonally variable rainfall that caused pulses in subsurface fluid flow. Spatial distribution of the paleocaves and sand volcanoes suggests their formation on the southeast side of a recently faulted horst of Proterozoic carbonate bedrock that formed a nearshore island during early Cambrian sea-level rise. Fluidisation structures such as those reported here have generally been difficult to interpret owing to a lack of data on the fluid hydraulics of the underlying aquifer. This is the first report linking the hydraulics of a well-characterised paleokarst to development of fluid-escape structures. Such structures are widely known from sandstones overlying the sub

  8. Early diagnosis and early intervention in cerebral palsy

    Mijna eHadders-Algra


    Full Text Available This paper reviews the opportunities and challenges for early diagnosis and early intervention in cerebral palsy (CP. CP describes a group of disorders of the development of movement and posture, causing activity limitation, that are attributed to disturbances that occurred in the fetal or infant brain. Therefore the paper starts with a summary of relevant information from developmental neuroscience. Most lesions underlying CP occur in the second half of gestation, when developmental activity in the brain reaches its summit. Variations in timing of the damage not only result in different lesions, but also in different neuroplastic reactions and different associated neuropathologies. This turns CP into a heterogeneous en