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Sample records for embryo-bearing lowermost cambrian

  1. Arthropod pattern theory and Cambrian trilobites

    NARCIS (Netherlands)

    Sundberg, Frederick A.

    1995-01-01

    An analysis of duplomere (= segment) distribution within the cephalon, thorax, and pygidium of Cambrian trilobites was undertaken to determine if the Arthropod Pattern Theory (APT) proposed by Schram & Emerson (1991) applies to Cambrian trilobites. The boundary of the cephalon/thorax occurs within

  2. The Ecology of the Cambrian Radiation

    Science.gov (United States)

    Briggs, Derek E. G.

    The Cambrian radiation is one of the most exciting and controversial events in the fossil record. It was marked by a sudden abundance of shells, the first steep rise in plots of diversity through time, and the appearance of the fabulous soft-bodied fossils of the Burgess Shale in British Columbia and elsewhere in the world. The Cambrian radiation was also the subject of Steve Gould's Wonderful Life and Simon Conway Morris's Crucible of Creation.. The Ecology of the Cambrian Radiation is a long-awaited compilation that tackles one of the more impenetrable parts of the story. Interpretations of ecology are, after all, characteristically equivocal in rocks of this age.

  3. Upper Cambrian (Furongian) biostratigraphy in Scandinavia revisited

    DEFF Research Database (Denmark)

    Nielsen, Arne Thorshøj; Weidner, Thomas; Terfelt, Fredrik

    2014-01-01

    The traditional Furongian trilobite biozones of Scandinavia, recently proposed abandoned due to inconsistent boundary definitions [Terfelt, F., Eriksson, M.E., Ahlberg, P. & Babcock, L.E., 2008: Furongian Series (Cambrian) biostratigraphy of Scandinavia – a revision. Norwegian Journal of Geology88...... the Protopeltura and Peltura superzones, respectively. Accordingly, all Furongian superzones have a uniform naming style referring to a characteristic genus. The six Furongian superzones currently comprise 27 trilobite zones. The Paradoxides forchhammeri Superzone (Cambrian Series 3) is extended upwards...

  4. Cambrian trilobites with Siberian affinities, southwestern Alaska

    Energy Technology Data Exchange (ETDEWEB)

    Palmer, A.R.; Egbert, R.M.; Sullivan, R.; Knoth, J.S.

    1985-02-01

    Cambrian trilobites occur in two levels (about 7 m apart) in the core of a large, complex anticlinal structure in the area between the Taylor Mountains and the Hoholitna River in southwestern Alaska. The lower collection contains Erbia, Macannaia (a species close to Soviet forms described as Pagetia ferox Lermontova), two species of Kootenia (including one perhaps cospecific with forms from the central Brooks range), and several species of ptychoparioid trilobites. It is clear that biogeographic affinities are with the transitional facies of the eastern Siberian platform and the south Siberian foldbelt. In Soviet terms, the age of the collection falls in a disputed interval called latest Early Cambrian (Tojonian) by some authors, and earliest Middle Cambrian (Amgan) by others. In North American terms, Macannaia is known only from early Middle Cambrian beds. The younger collection contains abundant agnostids, a variety of conocoryphids, Paradoxides, and several species of ptychoparioid trilobites. This is an assemblage of undoubted late Middle Cambrian age, comparable to faunas described from the Maya State of the Siberian platform and the Paradoxides paradoxissimus Stage of the Baltic region. Both faunas are from ocean-facing or outer shelf environments. None of the key non-agnostid or non-pagetiid elements have been seen previously in deposits of Cambrian North America.

  5. Upper lower Cambrian (provisional Cambrian Series 2 trilobites from northwestern Gansu Province, China

    Directory of Open Access Journals (Sweden)

    Jan Bergström†

    2014-08-01

    Full Text Available Upper lower Cambrian (provisional Cambrian Series 2 trilobites are described from three sections through the Shuangyingshan Formation in the Beishan area, northwestern Gansu Province, China. The trilobite fauna is dominated by eodiscoid and corynexochid trilobites, together representing at least ten genera: Serrodiscus, Tannudiscus, Calodiscus, Pagetides, Kootenia, Edelsteinaspis, Ptarmiganoides?, Politinella, Dinesus and Subeia. Eleven species are described, of which seven are identified with previously described taxa and four described under open nomenclature. The composition of the fauna suggests biogeographic affinity with Siberian rather than Gondwanan trilobite faunas, and the Cambrian Series 2 faunas described herein and from elsewhere in northwestern China seem to be indicative of the marginal areas of the Siberian palaeocontinent. This suggests that the Middle Tianshan–Beishan Terrane may have been located fairly close to Siberia during middle–late Cambrian Epoch 2.

  6. A mysterious giant ichthyosaur from the lowermost Jurassic of Wales

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    Jeremy E. Martin

    2015-12-01

    Full Text Available Ichthyosaurs rapidly diversified and colonised a wide range of ecological niches during the Early and Middle Triassic period, but experienced a major decline in diversity near the end of the Triassic. Timing and causes of this demise and the subsequent rapid radiation of the diverse, but less disparate, parvipelvian ichthyosaurs are still unknown, notably because of inadequate sampling in strata of latest Triassic age. Here, we describe an exceptionally large radius from Lower Jurassic deposits at Penarth near Cardiff, south Wales (UK the morphology of which places it within the giant Triassic shastasaurids. A tentative total body size estimate, based on a regression analysis of various complete ichthyosaur skeletons, yields a value of 12–15 m. The specimen is substantially younger than any previously reported last known occurrences of shastasaurids and implies a Lazarus range in the lowermost Jurassic for this ichthyosaur morphotype.

  7. Early Cambrian sipunculan worms from southwest China.

    Science.gov (United States)

    Huang, Di-Ying; Chen, Jun-Yuan; Vannier, Jean; Saiz Salinas, J I

    2004-08-22

    We report the discovery of sipunculan worms from the Lower Cambrian Maotianshan Shale, near Kunming (southwest China). Their sipunculan identity is evidenced by the general morphology of the animals (sausage-shaped body with a slender retractable introvert and a wider trunk) and by other features, both external (e.g. perioral crown of tentacles, and hooks, papillae and wrinkle rings on the body surface) and internal (U-shaped gut, and the anus opening near the introvert-trunk junction). The three fossil forms (Archaeogolfingia caudata gen. et sp. nov., Cambrosipunculus tentaculatus gen. et sp. nov. and Cambrosipunculus sp.) have striking similarities to modern sipunculans, especially the Golfingiidae to which their evolutionary relationships are discussed. This study suggests that most typical features of extant sipunculans have undergone only limited changes since the Early Cambrian, thus indicating a possible evolutionary stasis over the past 520 Myr.

  8. The Cambrian to Devonian odyssey of the Brabant Massif within Avalonia: A review with new zircon ages, geochemistry, Sm-Nd isotopes, stratigraphy and palaeogeography

    Science.gov (United States)

    Linnemann, Ulf; Herbosch, Alain; Liégeois, Jean-Paul; Pin, Christian; Gärtner, Andreas; Hofmann, Mandy

    2012-05-01

    This study provides an up-to-date and comprehensive review of the Early Palaeozoic evolution of the Brabant Massif belonging to the Anglo-Brabant Deformation Belt. Situated at the southeastern side of Avalonia microplate, it is the only well-known part of the northern passive margin of the Rheic Ocean. The Cambrian-Silurian sedimentary pile is > 13 km thick, with > 9 km for the Cambrian only. The unraveling of this continuous registration reflects the successive rifting and drifting of Avalonia from the Gondwana mainland, followed by soft-collisional processes with Baltica and finally the formation of Laurussia. Based on recently established detailed stratigraphy, sedimentology and basin development, on U-Pb LA-ICP-MS analyses of igneous and detrital zircon grains along with geochemical data including Sm-Nd isotopes, a new geodynamic and palaeogeographic evolution is proposed. Brabant Megasequence 1 (lower Cambrian to lowermost Ordovician, > 9 km thick) represents an embayment of the peri-Gondwanan rift from which the Rheic Ocean has evolved. Detrital zircon ages demonstrate that the Brabant is a typical peri-Gondwanan terrane with a major Pan-African (Neoproterozoic age) and a mixed West African and Amazonian source (Palaeoproterozoic, Archaean and some Mesoproterozoic age). The transition towards the Avalonia drifting is marked by an unconformity and a short volcanic episode. The northward drift of Avalonia towards Baltica is recorded by the Megasequence 2 (Middle to Upper Ordovician, 1.3 km thick). The source for Mesoproterozoic zircons vanished, as the result of the Rheic Ocean opening and the isolation from Amazonian sources. The transition to Megasequence 3 is marked by a drastic change in palaeobathymetry and an important (sub)volcanic episode during a tectonic instability period (460-430 Ma), reflecting the Avalonia-Baltica soft docking as also shown by the reappearance of Mesoproterozoic detrital zircons, typical of Baltica. Unradiogenic Nd isotope

  9. Transdimensional Bayesian tomography of the lowermost mantle from shear waves

    Science.gov (United States)

    Richardson, C.; Mousavi, S. S.; Tkalcic, H.; Masters, G.

    2017-12-01

    The lowermost layer of the mantle, known as D'', is a complex region that contains significant heterogeneities on different spatial scales and a wide range of physical and chemical features such as partial melting, seismic anisotropy, and variations in thermal and chemical composition. The most powerful tools we have to probe this region are seismic waves and corresponding imaging techniques such as tomography. Recently, we developed compressional velocity tomograms of D'' using a transdimensional Bayesian inversion, where the model parameterization is not explicit and regularization is not required. This has produced a far more nuanced P-wave velocity model of D'' than that from traditional S-wave tomography. We also note that P-wave models of D'' vary much more significantly among various research groups than the corresponding S-wave models. This study therefore seeks to develop a new S-wave velocity model of D'' underneath Australia by using predominantly ScS-S differential travel times measured through waveform correlation and Bayesian transdimensional inversion to further understand and characterize heterogeneities in D''. We used events at epicentral distances between 45 and 75 degrees from stations in Australia at depths of over 200 km and with magnitudes between 6.0 and 6.7. Because of globally incomplete coverage of station and earthquake locations, a major limitation of deep earth tomography has been the explicit parameterization of the region of interest. Explicit parameterization has been foundational in most studies, but faces inherent problems of either over-smoothing the data, or allowing for too much noise. To avoid this, we use spherical Voronoi polygons, which allow for a high level of flexibility as the polygons can grow, shrink, or be altogether deleted throughout a sequence of iterations. Our technique also yields highly desired model parameter uncertainties. While there is little doubt that D'' is heterogeneous, there is still much that is

  10. Ichnology of the Early Cambrian Tal Group, Mussoorie Syncline ...

    Indian Academy of Sciences (India)

    Wadia Institute of Himalayan Geology, 33, General Mahadeo Singh Road, Dehradun 248 001, India. ∗ ... Mussoorie Syncline, being one of the five synclines, exposes the Cambrian ... Belt of Lesser Himalaya is represented by the Tal. Group.

  11. The oldest brachiopods from the lower cambrian of South Australia

    DEFF Research Database (Denmark)

    Topper, Timothy Paul; Holmer, Lars E.; Skovsted, Christian B.

    2013-01-01

    The morphology and organophosphatic shell structure of the paterinate brachiopod Askepasma is documented using new and previously collected specimens from the lower Cambrian of South Australia. Lack of adequately preserved material has seen the majority of paterinate specimens previously reported...... from South Australia referred to the genus Askepasma and treated under open nomenclature. Large collections of paterinates from the lower Cambrian Wilkawillina, Ajax, and Wirrapowie limestones in the Arrowie Basin, South Australia have prompted redescription of the type species Askepasma toddense...... and the erection of a new species, Askepasma saproconcha sp. nov. Askepasma saproconcha sp. nov. currently represents the oldest known brachiopod from the lower Cambrian successions in South Australia with a FAD in pre-trilobitic (Terreneuvian, Cambrian Stage 2, lower Atdabanian) strata in the basal part...

  12. Cause of Cambrian Explosion - Terrestrial or Cosmic?

    Science.gov (United States)

    Steele, Edward J; Al-Mufti, Shirwan; Augustyn, Kenneth A; Chandrajith, Rohana; Coghlan, John P; Coulson, S G; Ghosh, Sudipto; Gillman, Mark; Gorczynski, Reginald M; Klyce, Brig; Louis, Godfrey; Mahanama, Kithsiri; Oliver, Keith R; Padron, Julio; Qu, Jiangwen; Schuster, John A; Smith, W E; Snyder, Duane P; Steele, Julian A; Stewart, Brent J; Temple, Robert; Tokoro, Gensuke; Tout, Christopher A; Unzicker, Alexander; Wainwright, Milton; Wallis, Jamie; Wallis, Daryl H; Wallis, Max K; Wetherall, John; Wickramasinghe, D T; Wickramasinghe, J T; Wickramasinghe, N Chandra; Liu, Yongsheng

    2018-08-01

    We review the salient evidence consistent with or predicted by the Hoyle-Wickramasinghe (H-W) thesis of Cometary (Cosmic) Biology. Much of this physical and biological evidence is multifactorial. One particular focus are the recent studies which date the emergence of the complex retroviruses of vertebrate lines at or just before the Cambrian Explosion of ∼500 Ma. Such viruses are known to be plausibly associated with major evolutionary genomic processes. We believe this coincidence is not fortuitous but is consistent with a key prediction of H-W theory whereby major extinction-diversification evolutionary boundaries coincide with virus-bearing cometary-bolide bombardment events. A second focus is the remarkable evolution of intelligent complexity (Cephalopods) culminating in the emergence of the Octopus. A third focus concerns the micro-organism fossil evidence contained within meteorites as well as the detection in the upper atmosphere of apparent incoming life-bearing particles from space. In our view the totality of the multifactorial data and critical analyses assembled by Fred Hoyle, Chandra Wickramasinghe and their many colleagues since the 1960s leads to a very plausible conclusion - life may have been seeded here on Earth by life-bearing comets as soon as conditions on Earth allowed it to flourish (about or just before 4.1 Billion years ago); and living organisms such as space-resistant and space-hardy bacteria, viruses, more complex eukaryotic cells, fertilised ova and seeds have been continuously delivered ever since to Earth so being one important driver of further terrestrial evolution which has resulted in considerable genetic diversity and which has led to the emergence of mankind. Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.

  13. Proterozoic and early Cambrian protists: evidence for accelerating evolutionary tempo

    Science.gov (United States)

    Knoll, A. H.

    1994-01-01

    In rocks of late Paleoproterozoic and Mesoproterozoic age (ca. 1700-1000 million years ago), probable eukaryotic microfossils are widespread and well preserved, but assemblage and global diversities are low and turnover is slow. Near the Mesoproterozoic-Neoproterozoic boundary (1000 million years ago), red, green, and chromophytic algae diversified; molecular phylogenies suggest that this was part of a broader radiation of "higher" eukaryotic phyla. Observed diversity levels for protistan microfossils increased significantly at this time, as did turnover rates. Coincident with the Cambrian radiation of marine invertebrates, protistan microfossils again doubled in diversity and rates of turnover increased by an order of magnitude. Evidently, the Cambrian diversification of animals strongly influenced evolutionary rates, within clades already present in marine communities, implying an important role for ecology in fueling a Cambrian explosion that extends across kingdoms.

  14. Early Cambrian oxygen minimum zone-like conditions at Chengjiang

    DEFF Research Database (Denmark)

    Hammarlund, Emma U.; Gaines, Robert R.; Prokopenko, Maria G.

    2017-01-01

    in early Cambrian marine settings and the relationship of those conditions to early metazoan ecosystems is still emerging. Here, we report multi-proxy geochemical data from two drill cores through the early Cambrian (Series 2) Yu’anshan Formation of Yunnan, China. Results reveal dynamic water...... oxygen-minimum zones. The oxygenated benthic environments in which the Chengjiang biota thrived were proximal to, but sharply separated from, the open ocean by a persistent anoxic water mass that occupied a portion of the outer shelf. Oxygen depletion in the lower water column developed dynamically...

  15. Provenance of zircon of the lowermost sedimentary cover, Estonia, East-European Craton

    Directory of Open Access Journals (Sweden)

    Konsa, M.

    1999-12-01

    Full Text Available Bulk and accessory mineral composition of fresh and weathered crystalline rocks, and sedimentary deposits overlying the crystalline-sedimentary unconformity have been examined in core samples from 28 drill holes in Estonia. Before the Late Vendian to Early Cambrian regional subsidence and sedimentation, the region represented a flat plateau within the Svecofennian Domain. Palaeo-and Mesoproterozoic crystalline rocks, regardless their different initial mineral composition, subcrop under the Upper Vendian/Lower Cambrian sedimentary cover as usually intensely weathered rocks (saprolites composed of residual quartz, altered micas and prevailing clay minerals mainly of the kaolinite group. Thus, the bulk mineral composition of any basement crystalline rocks imparts no specific inherited rock-forming minerals into the covering sedimentary rocks. From the variety of accessory and opaque minerals of crystalline rocks, only zircon populations survived in saprolites. Crystalline rocks of different origin yield different zircons. Relationships between the zircon typology of the basement rocks having specific areas of distribution and the sedimentary rocks immediately overlying those crystalline rocks were the main subject of this study. The result is that siliciclastic sedimentary rocks covering weathered crystalline rocks only in places inherited zircons with typological features characteristic of specific basement areas. In northeastern Estonia, local lenses of the Oru Member (the earliest Upper Vendian sedimentary rocks in Estonia resembling the debris of weathered crystalline rocks yield accessory zircon which in a 1-2 m thick layer above the basement surface is similar to the zircons of the underlying weathering mantle of certain crystalline rocks. In the next unit, the Moldova Member, up to 43 m above the basement surface, a mixture of zircons resembling those of various local basement rocks has been found. Further upwards, in the Vendian and Lower

  16. Cambrian trace fossil Zoophycos from the Czech Republic

    Czech Academy of Sciences Publication Activity Database

    Doucek, J.; Mikuláš, Radek

    2014-01-01

    Roč. 65, č. 6 (2014), s. 403-409 ISSN 1335-0552 R&D Projects: GA ČR GA205/09/1521 Institutional support: RVO:67985831 Keywords : Cambrian * Bohemian Massif * Železné hory * ichnology * marine settings * Zoophycos Subject RIV: DB - Geology ; Mineralogy Impact factor: 0.761, year: 2014

  17. Compilation and network analyses of cambrian food webs.

    Directory of Open Access Journals (Sweden)

    Jennifer A Dunne

    2008-04-01

    Full Text Available A rich body of empirically grounded theory has developed about food webs--the networks of feeding relationships among species within habitats. However, detailed food-web data and analyses are lacking for ancient ecosystems, largely because of the low resolution of taxa coupled with uncertain and incomplete information about feeding interactions. These impediments appear insurmountable for most fossil assemblages; however, a few assemblages with excellent soft-body preservation across trophic levels are candidates for food-web data compilation and topological analysis. Here we present plausible, detailed food webs for the Chengjiang and Burgess Shale assemblages from the Cambrian Period. Analyses of degree distributions and other structural network properties, including sensitivity analyses of the effects of uncertainty associated with Cambrian diet designations, suggest that these early Paleozoic communities share remarkably similar topology with modern food webs. Observed regularities reflect a systematic dependence of structure on the numbers of taxa and links in a web. Most aspects of Cambrian food-web structure are well-characterized by a simple "niche model," which was developed for modern food webs and takes into account this scale dependence. However, a few aspects of topology differ between the ancient and recent webs: longer path lengths between species and more species in feeding loops in the earlier Chengjiang web, and higher variability in the number of links per species for both Cambrian webs. Our results are relatively insensitive to the exclusion of low-certainty or random links. The many similarities between Cambrian and recent food webs point toward surprisingly strong and enduring constraints on the organization of complex feeding interactions among metazoan species. The few differences could reflect a transition to more strongly integrated and constrained trophic organization within ecosystems following the rapid

  18. Compilation and network analyses of cambrian food webs.

    Science.gov (United States)

    Dunne, Jennifer A; Williams, Richard J; Martinez, Neo D; Wood, Rachel A; Erwin, Douglas H

    2008-04-29

    A rich body of empirically grounded theory has developed about food webs--the networks of feeding relationships among species within habitats. However, detailed food-web data and analyses are lacking for ancient ecosystems, largely because of the low resolution of taxa coupled with uncertain and incomplete information about feeding interactions. These impediments appear insurmountable for most fossil assemblages; however, a few assemblages with excellent soft-body preservation across trophic levels are candidates for food-web data compilation and topological analysis. Here we present plausible, detailed food webs for the Chengjiang and Burgess Shale assemblages from the Cambrian Period. Analyses of degree distributions and other structural network properties, including sensitivity analyses of the effects of uncertainty associated with Cambrian diet designations, suggest that these early Paleozoic communities share remarkably similar topology with modern food webs. Observed regularities reflect a systematic dependence of structure on the numbers of taxa and links in a web. Most aspects of Cambrian food-web structure are well-characterized by a simple "niche model," which was developed for modern food webs and takes into account this scale dependence. However, a few aspects of topology differ between the ancient and recent webs: longer path lengths between species and more species in feeding loops in the earlier Chengjiang web, and higher variability in the number of links per species for both Cambrian webs. Our results are relatively insensitive to the exclusion of low-certainty or random links. The many similarities between Cambrian and recent food webs point toward surprisingly strong and enduring constraints on the organization of complex feeding interactions among metazoan species. The few differences could reflect a transition to more strongly integrated and constrained trophic organization within ecosystems following the rapid diversification of species, body

  19. Tropical shoreline ice in the late Cambrian: Implications for earth's climate between the Cambrian Explosion and the Great Ordovician Biodiversification Event

    Science.gov (United States)

    Runkel, Anthony C.; MacKey, T.J.; Cowan, Clinton A.; Fox, David L.

    2010-01-01

    Middle to late Cambrian time (ca. 513 to 488 Ma) is characterized by an unstable plateau in biodiversity, when depauperate shelf faunas suffered repeated extinctions. This poorly understood interval separates the Cambrian Explosion from the Great Ordovician Biodiversification Event and is generally regarded as a time of sustained greenhouse conditions. We present evidence that suggests a drastically different climate during this enigmatic interval: Features indicative of meteoric ice are well preserved in late Cambrian equatorial beach deposits that correspond to one of the shelf extinction events. Thus, the middle to late Cambrian Earth was at least episodically cold and might best be considered a muted analogue to the environmental extremes that characterized the Proterozoic, even though cooling in the two periods may have occurred in response to different triggers. Such later Cambrian conditions may have significantly impacted evolution preceding the Ordovician radiation.

  20. Sediment Trapping by Emerged Channel Bars in the Lowermost Mississippi River during a Major Flood

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    Bo Wang

    2015-11-01

    Full Text Available The formation of channel bars has been recognized as the most significant sediment response to the highly trained Mississippi River (MR. However, no quantitative study exists on the dynamics of emerged channel bars and associated sediment accumulation in the last 500-kilometer reach of the MR from the Gulf of Mexico outlet, also known as the lowermost Mississippi River. Such knowledge is especially critical for riverine sediment management to impede coastal land loss in the Mississippi River Delta. In this study, we utilized a series of satellite images taken from August 2010 to January 2012 to assess the changes in surface area and volume of three large emerged channel bars in the lowermost MR following an unprecedented spring flood in 2011. River stage data were collected to develop a rating curve of surface areas detected by satellite images with flow conditions for each of the three bars. A uniform geometry associated with the areal change was assumed to estimate the bar volume changes. Our study reveals that the 2011 spring flood increased the surface area of the bars by 3.5% to 11.1%, resulting in a total surface increase of 7.3%, or 424,000 m2. Based on the surface area change, we estimated a total bar volume increase of 4.4%, or 1,219,900 m3. This volume increase would be equivalent to a sediment trapping of approximately 1.0 million metric tons, assuming a sediment bulk density of 1.2 metric tons per cubic meter. This large quantity of sediment is likely an underestimation because of the neglect of subaqueous bar area change and the assumption of a uniform geometry in volume estimation. Nonetheless, the results imply that channel bars in the lowermost MR are capable of capturing a substantial amount of sediment during floods, and that a thorough assessment of their long-term change can provide important insights into sediment trapping in the lowermost MR as well as the feasibility of proposed river sediment diversions.

  1. Oxygen, ecology, and the Cambrian radiation of animals

    Science.gov (United States)

    Sperling, Erik A.; Frieder, Christina A.; Raman, Akkur V.; Girguis, Peter R.; Levin, Lisa A.; Knoll, Andrew H.

    2013-08-01

    The Proterozoic-Cambrian transition records the appearance of essentially all animal body plans (phyla), yet to date no single hypothesis adequately explains both the timing of the event and the evident increase in diversity and disparity. Ecological triggers focused on escalatory predator-prey "arms races" can explain the evolutionary pattern but not its timing, whereas environmental triggers, particularly ocean/atmosphere oxygenation, do the reverse. Using modern oxygen minimum zones as an analog for Proterozoic oceans, we explore the effect of low oxygen levels on the feeding ecology of polychaetes, the dominant macrofaunal animals in deep-sea sediments. Here we show that low oxygen is clearly linked to low proportions of carnivores in a community and low diversity of carnivorous taxa, whereas higher oxygen levels support more complex food webs. The recognition of a physiological control on carnivory therefore links environmental triggers and ecological drivers, providing an integrated explanation for both the pattern and timing of Cambrian animal radiation.

  2. Early Cambrian pentamerous cubozoan embryos from South China.

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    Jian Han

    Full Text Available BACKGROUND: Extant cubozoans are voracious predators characterized by their square shape, four evenly spaced outstretched tentacles and well-developed eyes. A few cubozoan fossils are known from the Middle Cambrian Marjum Formation of Utah and the well-known Carboniferous Mazon Creek Formation of Illinois. Undisputed cubozoan fossils were previously unknown from the early Cambrian; by that time probably all representatives of the living marine phyla, especially those of basal animals, should have evolved. METHODS: Microscopic fossils were recovered from a phosphatic limestone in the Lower Cambrian Kuanchuanpu Formation of South China using traditional acetic-acid maceration. Seven of the pre-hatched pentamerous cubozoan embryos, each of which bears five pairs of subumbrellar tentacle buds, were analyzed in detail through computed microtomography (Micro-CT and scanning electron microscopy (SEM without coating. RESULTS: The figured microscopic fossils are unequivocal pre-hatching embryos based on their spherical fertilization envelope and the enclosed soft-tissue that has preserved key anatomical features arranged in perfect pentaradial symmetry, allowing detailed comparison with modern cnidarians, especially medusozoans. A combination of features, such as the claustrum, gonad-lamella, suspensorium and velarium suspended by the frenula, occur exclusively in the gastrovascular system of extant cubozoans, indicating a cubozoan affinity for these fossils. Additionally, the interior anatomy of these embryonic cubozoan fossils unprecedentedly exhibits the development of many new septum-derived lamellae and well-partitioned gastric pockets unknown in living cubozoans, implying that ancestral cubozoans had already evolved highly specialized structures displaying unexpected complexity at the dawn of the Cambrian. The well-developed endodermic lamellae and gastric pockets developed in the late embryonic stages of these cubozoan fossils are comparable with

  3. Genesis of early Cambrian phosphorite of Krol Belt, Lesser Himalaya

    Digital Repository Service at National Institute of Oceanography (India)

    Mazumdar, A.; Banerjee, D.M.

    depositional en- vironment. Similar shallow marine character for Late Vendian and Early Cambrian phosphorites have been recorded from Yangtze Basin (South China), Khub- shugul Basin (Mongolia), Karatau Basin (Kazakh- stan), Soltaniah Basin (Iran), Tal Basin.... This characteris- tic of microbial mats may enable them to bind the franco- lite microcrysts on their surfaces, giving rise to microbial laminations. The capacity of microbiota, viz. bacteria, fungi and cyanobacterial mat-forming microphytes to trap and bind...

  4. Cambrian and ordovician systems around the pacific basin (part 3)

    Energy Technology Data Exchange (ETDEWEB)

    Kobayashi, Teiichi

    1987-10-25

    This report describes the history of the studies made about old rocks and Cambrian and Ordovician Systems in North America. In last century, development of the Pre-Canbrian stratigraphy and mineral resources was started in Canada, while the New York System was instituted in the middle and east areas of North America, and it was later correlated to the European sequence. Walcott who published many reports including the vental anatomy of trilobites made invaluable contribution on the study of Cambrian geology. The Cambro-Ordovician faunas which distributed in the Appalachian mountains and further westerly beyond the lower Mississipy river were related to the European ones. The systems in the Cordilleran geosyncline was also described. Stratigraphy in the western sites is followed on the Alaskan faunas in the north which were allied to the Siberian faunas and later to the Eastern Asiatic ones. Lastly, Circum-Pacific Cambro-Ordovician belt was taken up. The eastern side of the Circum-Pacific Cambrian belt belonged to Olenellian province, and the other side constituted the Redlichia province. (2 figs, 5 tabs, 101 refs)

  5. Lower Cambrian biogeography and the prehistory of early animals

    Energy Technology Data Exchange (ETDEWEB)

    Signor, P.W. (Univ. of California, Davis (United States))

    1991-02-01

    Biogeographic distributions of animals reflect the complex interplay of biological and physical processes acting over geological time. In particular, plate tectonics and the evolution of lineages within clades play fundamental roles in determining faunal distributions. Ranges expand through vicariant events or dispersal and contract through local and regional extinctions. Vicariance promotes the evolutionary divergence of closely related lineages. Viewed as historical phenomena, biogeographic distributions can be employed to infer prior tectonic and evolutionary events. For example, the existence of modern marine faunal provinces reflects the interaction of evolution and plate tectonics. The Proterozoic history of skeletogenous organisms (and their ancestors) is a contentious subject, with many authors arguing that skeletogenous clades have no significant prehistory before their appearance in the fossil record. The existence of trilobite provinces dominated by different suborders, for example, suggests the trilobites evolved and dispersed, or were separated by plate movement, and then evolved independently for an extended period prior to their appearance in the fossil record. Similar arguments can be applied to other groups. The paleobiogeographic distribution of organisms also provides useful insights into late Proterozoic and Early Cambrian paleogeography. The provincial distribution of Early Cambrian taxa suggests that the putative Proterozoic supercontinent, if it existed, began to separate well before the Early Cambrian. Separate provinces would not have evolved had the various plates remained united. Therefore, the dawn of the Phanerozoic could not have coincided with the breakup of the Proterozoic supercontinent.

  6. Armored kinorhynch-like scalidophoran animals from the early Cambrian.

    Science.gov (United States)

    Zhang, Huaqiao; Xiao, Shuhai; Liu, Yunhuan; Yuan, Xunlai; Wan, Bin; Muscente, A D; Shao, Tiequan; Gong, Hao; Cao, Guohua

    2015-11-26

    Morphology-based phylogenetic analyses support the monophyly of the Scalidophora (Kinorhyncha, Loricifera, Priapulida) and Nematoida (Nematoda, Nematomorpha), together constituting the monophyletic Cycloneuralia that is the sister group of the Panarthropoda. Kinorhynchs are unique among living cycloneuralians in having a segmented body with repeated cuticular plates, longitudinal muscles, dorsoventral muscles, and ganglia. Molecular clock estimates suggest that kinorhynchs may have diverged in the Ediacaran Period. Remarkably, no kinorhynch fossils have been discovered, in sharp contrast to priapulids and loriciferans that are represented by numerous Cambrian fossils. Here we describe several early Cambrian (~535 million years old) kinorhynch-like fossils, including the new species Eokinorhynchus rarus and two unnamed but related forms. E. rarus has characteristic scalidophoran features, including an introvert with pentaradially arranged hollow scalids. Its trunk bears at least 20 annuli each consisting of numerous small rectangular plates, and is armored with five pairs of large and bilaterally placed sclerites. Its trunk annuli are reminiscent of the epidermis segments of kinorhynchs. A phylogenetic analysis resolves E. rarus as a stem-group kinorhynch. Thus, the fossil record confirms that all three scalidophoran phyla diverged no later than the Cambrian Period.

  7. Antarctica, supercontinents and the palaeogeography of the Cambrian 'explosion'

    Science.gov (United States)

    Dalziel, Ian

    2014-05-01

    Laurentia is bordered by latest Precambrian-Cambrian rifted margins and must therefore have been located within a Precambrian supercontinent. Geochronologic and geochemical evidence indicates that it was attached to parts of the East Antarctic craton within the Rodinian supercontinent in the late Mesoproterozoic. The Mawson craton of Antarctica rifted from the proto-Pacific margin of Laurentia during the Neooproterozoic, colliding with the present 'southern cone' of Laurentia at ~600 Ma along the Shackleton Range suture zone as Gondwana and Laurentia amalgamated to form the ephemeral Pannotia supercontinental assembly at the end of the Precambrian. The abrupt appearance of almost all animal phyla in the fossil record is often colloquially referred to as the Cambrian 'explosion' of life on Earth. It is also named 'Darwin's dilemma,' as he appreciated that this seemingly mysterious event posed a major problem for his theory of evolution by natural selection. It coincided with a time of major marine transgression over all the continents. Although the metazoan 'explosion' is now seen as more protracted than formerly recognized, it is still regarded one of the most critical events in the history of the biosphere. One of the most striking aspects of the earliest Cambrian fossils is geographic differentiation. In particular, the first benthic trilobite faunas on Laurentia, ancestral North America, and the newly amalgamated southern supercontinent of Gondwana are distinctly different. This has led to the suggestion of an unknown vicariant event intervening between an ancestral trilobite clade and higher members that are represented in the fossil record, possibly one related to the breakup of a supercontinent. Igneous rocks along the Panthalassic margin of Gondwana, including South America, southernmost Africa and the Ellsworth-Whitmore crustal block of Antarctica, and along the proto-Appalachian margin of Laurentia indicate that final separation of Laurentia from

  8. Relationship between the Neoproterozoic snowball Earth and Cambrian explosion

    Science.gov (United States)

    Maruyama, S.; Yoshihara, A.; Isozaki, Y.

    2007-12-01

    Origin of snowball Earth has been debated in terms of greenhouse gas (e.g., Hoffman and Schrag), obliqueness of Earth's rotation axis (Williams, 1975), true polar wander (Evans, 2003), Galactic cosmic ray radiation (Shaviv and Veizer, 2003; Svensmark, 2006), or weakened geomagnetism (Maruyama and Yoshihara, 2003). A major difficulty for the greenhouse gas hypothesis is the on-off switch causing decrease and increase of appropriate amounts of CO2 by plume- and plate tectonics, and also in available amount of CO2 in atmosphere to be consistent with the observations. In contrast, the cosmic ray radiation models due to the star burst peaked at 2.5- 2.1 Ga and 1.4-0.8 Ga can explain on-off switch more easily than the greenhouse gas model. Cosmic ray radiations, however, must be modified by the geomagnetic intensity, fluctuating 150"% to cause the snowball Earth. Time difference between the Neoproterozoic snowball Earth and Cambrian explosion is as large as 250 millions years, and this refuses their direct close-relationship. Role of frequent mass extinctions, i.e., 8 times during 100 m.y. from 585 Ma to 488 Ma, during the Ediacaran and Cambrian, has been proposed (Zhu et al., 2007). This frequency is one order of magnitude higher compared to that in the post-Ordovician time. Yet, the Cambrian explosion cannot be explained by mass extinction which replaced the vacant niches shortly after the mass extinction and never created a new animal with a new body plan. A new model proposed herein is derived from weakened geomagnetism and resultant extensive cosmic radiation to alter gene and genome for a long period over advancement of low magnetic intensity and cosmic radiations (Svensmark, 2006) from 1.2-0.8Ga. As to the new body plans of animals, it took an appreciably long time to prepare all 34 genometypes before the apparent Cambrian explosion. Geochemically extreme conditions and widened shallow marine environment on continental shelf by the return-flow of sweater into

  9. Linking lowermost mantle structure, core-mantle boundary heat flux and mantle plume formation

    Science.gov (United States)

    Li, Mingming; Zhong, Shijie; Olson, Peter

    2018-04-01

    The dynamics of Earth's lowermost mantle exert significant control on the formation of mantle plumes and the core-mantle boundary (CMB) heat flux. However, it is not clear if and how the variation of CMB heat flux and mantle plume activity are related. Here, we perform geodynamic model experiments that show how temporal variations in CMB heat flux and pulses of mantle plumes are related to morphologic changes of the thermochemical piles of large-scale compositional heterogeneities in Earth's lowermost mantle, represented by the large low shear velocity provinces (LLSVPs). We find good correlation between the morphologic changes of the thermochemical piles and the time variation of CMB heat flux. The morphology of the thermochemical piles is significantly altered during the initiation and ascent of strong mantle plumes, and the changes in pile morphology cause variations in the local and the total CMB heat flux. Our modeling results indicate that plume-induced episodic variations of CMB heat flux link geomagnetic superchrons to pulses of surface volcanism, although the relative timing of these two phenomena remains problematic. We also find that the density distribution in thermochemical piles is heterogeneous, and that the piles are denser on average than the surrounding mantle when both thermal and chemical effects are included.

  10. PARVULARUGOGLOBIGERINA EUGUBINA TYPE-SAMPLE AT CCESELLI (ITALY: PLANKTIC FORAMINIFERAL ASSEMBLAGE AND LOWERMOST DANIAN BIOSTRATIGRAPHIC IMPLICATIONS

    Directory of Open Access Journals (Sweden)

    IGNACIO ARENILLAS

    2000-11-01

    Full Text Available The Parvularugoglobigerina eugubina Biozone (lowermost Danian was defined at Gubbio (Italy to precisely define the Cretaceous/Paleogene (K/P boundary. It was defined by the total range of Pv. eugubina, but this small morphospecies presents some taxonomic problems. The Pv. eugubina holotype and the planktic foraminiferal assemblage of the Pv. eugubina type-sample at Ceselli (Ceselli 3 were revised to precise the biostratigraphic position of this biozone. Of the 21 morphospecies identified in Ceselli 3, 14 are early Paleocene species and 7 are possible Cretaceous survivors of the K/P boundary extinction event. To clarify the lowermost Danian bizonation, it was necessary to taxonomically revise Pv. eugubina and Pv. longiapertura, which have both been identified in this sample. Following the definition of Pv. eugubina and the original definition of the nominal biozone, the base of Pv. eugubina Biozone should be placed at the first appearance datum of the eponymous species and not at the first appearance datum of Pv. longiapertura. 

  11. Constraints on small-scale heterogeneity in the lowermost mantle from observations of near podal PcP precursors

    Science.gov (United States)

    Zhang, Baolong; Ni, Sidao; Sun, Daoyuan; Shen, Zhichao; Jackson, Jennifer M.; Wu, Wenbo

    2018-05-01

    Volumetric heterogeneities on large (∼>1000 km) and intermediate scales (∼>100 km) in the lowermost mantle have been established with seismological approaches. However, there are controversies regarding the level of heterogeneity in the lowermost mantle at small scales (a few kilometers to tens of kilometers), with lower bound estimates ranging from 0.1% to a few percent. We take advantage of the small amplitude PcP waves at near podal distances (0-12°) to constrain the level of small-scale heterogeneity within 250 km above the CMB. First, we compute short period synthetic seismograms with a finite difference code for a series of volumetric heterogeneity models in the lowermost mantle, and find that PcP is not identifiable if the small-scale heterogeneity in the lowermost mantle is above 2.5%. We then use a functional form appropriate for coda decay to suppress P coda contamination. By comparing the corrected envelope of PcP and its precursors with synthetic seismograms, we find that perturbations of small-scale (∼8 km) heterogeneity in the lowermost mantle is ∼0.2-0.5% beneath regions of the China-Myanmar border area, Okhotsk Sea and South America. Whereas strong perturbations (∼1.0%) are found beneath Central America. In the regions studied, we find that this particular type of small-scale heterogeneity in the lowermost mantle is weak, yet there are some regions requiring heterogeneity up to 1.0%. Where scattering is stronger, such as under Central America, more chemically complex mineral assemblages may be present at the core-mantle boundary.

  12. Lowermost mantle anisotropy near the eastern edge of the Pacific LLSVP: constraints from SKS-SKKS splitting intensity measurements

    Science.gov (United States)

    Deng, Jie; Long, Maureen D.; Creasy, Neala; Wagner, Lara; Beck, Susan; Zandt, George; Tavera, Hernando; Minaya, Estela

    2017-08-01

    Seismic anisotropy has been documented in many portions of the lowermost mantle, with particularly strong anisotropy thought to be present along the edges of large low shear velocity provinces (LLSVPs). The region surrounding the Pacific LLSVP, however, has not yet been studied extensively in terms of its anisotropic structure. In this study, we use seismic data from southern Peru, northern Bolivia and Easter Island to probe lowermost mantle anisotropy beneath the eastern Pacific Ocean, mostly relying on data from the Peru Lithosphere and Slab Experiment and Central Andean Uplift and Geodynamics of High Topography experiments. Differential shear wave splitting measurements from phases that have similar ray paths in the upper mantle but different ray paths in the lowermost mantle, such as SKS and SKKS, are used to constrain anisotropy in D″. We measured splitting for 215 same station-event SKS-SKKS pairs that sample the eastern Pacific LLSVP at the base of the mantle. We used measurements of splitting intensity(SI), a measure of the amount of energy on the transverse component, to objectively and quantitatively analyse any discrepancies between SKS and SKKS phases. While the overall splitting signal is dominated by the upper-mantle anisotropy, a minority of SKS-SKKS pairs (∼10 per cent) exhibit strongly discrepant splitting between the phases (i.e. the waveforms require a difference in SI of at least 0.4), indicating a likely contribution from lowermost mantle anisotropy. In order to enhance lower mantle signals, we also stacked waveforms within individual subregions and applied a waveform differencing technique to isolate the signal from the lowermost mantle. Our stacking procedure yields evidence for substantial splitting due to lowermost mantle anisotropy only for a specific region that likely straddles the edge of Pacific LLSVP. Our observations are consistent with the localization of deformation and anisotropy near the eastern boundary of the Pacific LLSVP

  13. Disparity, decimation and the Cambrian "explosion": comparison of early Cambrian and Present faunal communities with emphasis on velvet worms (Onychophora

    Directory of Open Access Journals (Sweden)

    Julián Monge-Nájera

    2000-06-01

    Full Text Available The controversy about a Cambrian "explosion" of morphological disparity (followed by decimation, cladogenesis and fossilization is of central importance for the history of life. This paper revisits the controversy (with emphasis in onychophorans, which include emblematic organisms such as Hallucigenia, presents new data about the Chengjiang (Cambrian of China faunal community and compares it and the Burgess Shale (Cambrian of Canada with an ecologically similar but modern tropical marine site where onychophorans are absent, and with a modern neotropical terrestrial onychophoran community. Biovolume was estimated from material collected in Costa Rica and morphometric measurements were made on enlarged images of fossils. Cambrian tropical mudflats were characterized by the adaptive radiation of two contrasting groups: the vagile arthropods and the sessile poriferans. Arthropods were later replaced as the dominant benthic taxon by polychaetes. Vagility and the exoskeleton may explain the success of arthropods from the Cambrian to the modern marine and terrestrial communities, both in population and biovolume. Food ecological displacement was apparent in the B. Shale, but not in Chengjiang or the terrestrial community. When only hard parts were preserved, marine and terrestrial fossil deposits of tropical origin are even less representative than deposits produced by temperate taxa, Chengjiang being an exception. Nutrient limitations might explain why deposit feeding is less important in terrestrial onychophoran communities, where carnivory, scavenging and omnivory (associated with high motility and life over the substrate became more important. Fossil morphometry supports the interpretation of "lobopod animals" as onychophorans, whose abundance in Chengjiang was equal to their abundance in modern communities. The extinction of marine onychophorans may reflect domination of the infaunal habitat by polychaetes. We conclude that (1 a mature ecological

  14. Moulting in the lobopodian Onychodictyon from the lower Cambrian of Greenland

    DEFF Research Database (Denmark)

    Topper, Timothy Paul; Skovsted, Christian B.; Peel, John S.

    2013-01-01

    A number of lobopodian taxa from the Cambrian display pairs of sclerotized plates symmetrically positioned along the dorsum of the animal, predominantly above the walking appendages. Most genera were described from complete body fossils exquisitely preserved in the famous Cambrian Lagerstatten, b...

  15. Syn-rift unconformities punctuating the lower-middle Cambrian transition in the Atlas Rift, Morocco

    Science.gov (United States)

    Álvaro, J. Javier; Ezzouhairi, Hassan; Clausen, Sébastien; Ribeiro, M. Luisa; Solá, Rita

    2015-04-01

    The Cambrian Tamdroust and Bab n'Ali Volcanic Complexes represent two magmatic episodes developed in the latest Ediacaran-Cambrian Atlas Rift of Morocco. Their rifting pulses were accompanied by accumulation of volcanosedimentary edifices (dominated by effusive lava flows in the former and explosive acidic aprons in the latter) associated with active tilting and uplift. Sealing of their peneplaned horst-and-graben palaeotopographies led to the onset of distinct onlapping geometries and angular discordances capping eroded basements ranging from the Ediacaran Ouarzazate Supergroup to the Cambrian Asrir Formation. Previous interpretations of these discordances as pull-apart or compressive events are revised here and reinterpreted in an extensional (rifting) context associated with active volcanism. The record of erosive unconformities, stratigraphic gaps, condensed beds and onlapping patterns across the traditional "lower-middle Cambrian" (or Cambrian Series 2-3) transition of the Atlas Rift must be taken into consideration for global chronostratigraphic correlation based on their trilobite content.

  16. Vegetation and plant food reconstruction of lowermost Bed II, Olduvai Gorge, using modern analogs.

    Science.gov (United States)

    Copeland, Sandi R

    2007-08-01

    Vegetation and plant foods for hominins of lowermost Bed II, Olduvai Gorge were modeled by examining vegetation in modern habitats in northern Tanzania (Lake Manyara, Ngorongoro, Serengeti) that are analogous to the paleolandscape in terms of climate, land forms, and soil types, as indicated by previous paleoenvironmental studies of Olduvai. Plant species in the modern habitats were identified in a series of sample plots, and those known to be eaten by modern humans, chimpanzees, or baboons were considered potentially edible for early hominins. Within the 50-80 kyr deposition of lowermost Bed II, periods of drier climate were characterized by low lake stands and a broad eastern lacustrine plain containing a mosaic of springs, marsh, woodland, and edaphic grassland. Based on results of this study, plant food diversity in each of those habitats was relatively low, but the mosaic nature of the area meant that hominins could reach several different habitat types within short distances, with access to potential plant foods including marsh plants, grass grains, roots, shrub fruits, edible parts from palms, leafy herbaceous plants, and Acacia pods, flowers, and gum. Based on Manyara analogs, a greater variety of plant foods, such as tree fruits (e.g., Ficus, Trichilia) and the roots and fruits of shrubs (e.g., Cordia, Salvadora) would be expected further east along the rivers in the lacustrine terrace and alluvial fans. Interfluves of the alluvial fans were probably less wooded and offered relatively fewer varieties of plant foods, but there is sparse paleoenvironmental evidence for the character of Olduvai's alluvial fans, making the choice of appropriate modern analogs difficult. In the western side of the basin, based on modern analogs in the Serengeti, riverine habitats provided the greatest variety of edible plant food species (e.g., Acacia, Grewia, Justicia). If the interfluves were grassland, then a large variety of potentially edible grasses and forbs were present

  17. In-situ observation of Asian pollution transported into the Arctic lowermost stratosphere

    Directory of Open Access Journals (Sweden)

    A. Roiger

    2011-11-01

    Full Text Available On a research flight on 10 July 2008, the German research aircraft Falcon sampled an air mass with unusually high carbon monoxide (CO, peroxyacetyl nitrate (PAN and water vapour (H2O mixing ratios in the Arctic lowermost stratosphere. The air mass was encountered twice at an altitude of 11.3 km, ~800 m above the dynamical tropopause. In-situ measurements of ozone, NO, and NOy indicate that this layer was a mixed air mass containing both air from the troposphere and stratosphere. Backward trajectory and Lagrangian particle dispersion model analysis suggest that the Falcon sampled the top of a polluted air mass originating from the coastal regions of East Asia. The anthropogenic pollution plume experienced strong up-lift in a warm conveyor belt (WCB located over the Russian east-coast. Subsequently the Asian air mass was transported across the North Pole into the sampling area, elevating the local tropopause by up to ~3 km. Mixing with surrounding Arctic stratospheric air most likely took place during the horizontal transport when the tropospheric streamer was stretched into long and narrow filaments. The mechanism illustrated in this study possibly presents an important pathway to transport pollution into the polar tropopause region.

  18. The bivalve Anopaea (Inoceramidae) from the Upper Jurassic-lowermost Cretaceous of Mexico

    Science.gov (United States)

    Zell, Patrick; Crame, J. Alistair; Stinnesbeck, Wolfgang; Beckmann, Seija

    2015-07-01

    In Mexico, the Upper Jurassic to lowermost Cretaceous La Casita and coeval La Caja and La Pimienta formations are well-known for their abundant and well-preserved marine vertebrates and invertebrates. The latter include conspicuous inoceramid bivalves of the genus Anopaea not formally described previously from Mexico. Anopaea bassei (Lecolle de Cantú, 1967), Anopaea cf. stoliczkai (Holdhaus, 1913), Anopaea cf. callistoensis Crame and Kelly, 1995 and Anopaea sp. are rare constituents in distinctive Tithonian-lower Berriasian levels of the La Caja Formation and one Tithonian horizon of the La Pimienta Formation. Anopaea bassei was previously documented from the Tithonian of central Mexico and Cuba, while most other members of Anopaea described here are only known from southern high latitudes. The Mexican assemblage also includes taxa which closely resemble Anopaea stoliczkai from the Tithonian of India, Indonesia and the Antarctic Peninsula, and Anopaea callistoensis from the late Tithonian to ?early Berriasian of the Antarctic Peninsula. Our new data expand the palaeogeographical distribution of the high latitude Anopaea to the Gulf of Mexico region and substantiate faunal exchange, in the Late Jurassic-earliest Cretaceous, between Mexico and the Antarctic Realm.

  19. Apparent splitting of S waves propagating through an isotropic lowermost mantle

    KAUST Repository

    Parisi, Laura

    2018-03-24

    Observations of shear‐wave anisotropy are key for understanding the mineralogical structure and flow in the mantle. Several researchers have reported the presence of seismic anisotropy in the lowermost 150–250 km of the mantle (i.e., D” layer), based on differences in the arrival times of vertically (SV) and horizontally (SH) polarized shear waves. By computing waveforms at period > 6 s for a wide range of 1‐D and 3‐D Earth structures we illustrate that a time shift (i.e., apparent splitting) between SV and SH may appear in purely isotropic simulations. This may be misinterpreted as shear wave anisotropy. For near‐surface earthquakes, apparent shear wave splitting can result from the interference of S with the surface reflection sS. For deep earthquakes, apparent splitting can be due to the S‐wave triplication in D”, reflections off discontinuities in the upper mantle and 3‐D heterogeneity. The wave effects due to anomalous isotropic structure may not be easily distinguished from purely anisotropic effects if the analysis does not involve full waveform simulations.

  20. Apparent splitting of S waves propagating through an isotropic lowermost mantle

    KAUST Repository

    Parisi, Laura; Ferreira, Ana M. G.; Ritsema, Jeroen

    2018-01-01

    Observations of shear‐wave anisotropy are key for understanding the mineralogical structure and flow in the mantle. Several researchers have reported the presence of seismic anisotropy in the lowermost 150–250 km of the mantle (i.e., D” layer), based on differences in the arrival times of vertically (SV) and horizontally (SH) polarized shear waves. By computing waveforms at period > 6 s for a wide range of 1‐D and 3‐D Earth structures we illustrate that a time shift (i.e., apparent splitting) between SV and SH may appear in purely isotropic simulations. This may be misinterpreted as shear wave anisotropy. For near‐surface earthquakes, apparent shear wave splitting can result from the interference of S with the surface reflection sS. For deep earthquakes, apparent splitting can be due to the S‐wave triplication in D”, reflections off discontinuities in the upper mantle and 3‐D heterogeneity. The wave effects due to anomalous isotropic structure may not be easily distinguished from purely anisotropic effects if the analysis does not involve full waveform simulations.

  1. A review of the Late Cambrian (Furongian) palaeogeography in the western Mediterranean region, NW Gondwana

    Science.gov (United States)

    Álvaro, J. Javier; Ferretti, Annalisa; González-Gómez, Cristina; Serpagli, Enrico; Tortello, M. Franco; Vecoli, Marco; Vizcaïno, Daniel

    2007-11-01

    The Cambrian-Ordovician transition of the western Mediterranean region (NW Gondwana) is characterized by the record of major erosive unconformities with gaps that range from a chronostratigraphic stage to a series. The hiatii are diachronous and involved progressively younger strata along the Gondwanan margin, from SW (Morocco) to NE (Montagne Noire). They can be related to development of a multi-stage rifting (further North), currently connected to the opening of the Rheic Ocean, and concomitant erosion on southern rift shoulders. The platforms of this margin of Gondwana occupied temperate-water, mid latitudes and were dominated by siliciclastic sedimentation, while carbonate factories were only episodically active in the Montagne-Noire platform. The Upper Cambrian is devoid of significant gaps in the southern Montagne Noire and the Iberian Chains. There, the sedimentation took place in a transgressive-dominated depositional system, with common offshore deposits and clayey substrates, and was bracketed by two major regressive trends. The Late Cambrian is also associated with the record of volcanic activity ( e.g., in the Cantabrian and Ossa-Morena zones, and the northern Montagne Noire), and widespread development of a tectonic instability that led to the episodic establishment of palaeotopographies and record of slope-related facies associations. Several immigration events are recognized throughout the latest Middle Cambrian, Late Cambrian and Tremadocian. The trilobites show a stepwise replacement of Acado-Baltic-type families ( e.g., the conocoryphid-paradoxidid-solenopleurid assemblage) characterized by: (i) a late Languedocian (latest Middle Cambrian) co-occurrence of Middle Cambrian trilobite families with the first anomocarid, dorypygid and proasaphiscid invaders; (ii) a Late Cambrian immigration replacing previous faunas, composed of trilobites (aphelaspidids, catillicephalids, ceratopygids, damesellids, eulomids, idahoiids, linchakephalids, lisariids

  2. Syn-rift unconformities punctuating the lower-middle Cambrian transition in the Atlas Rift, Morocco

    OpenAIRE

    Álvaro, J. Javier; Ezzouhairi, Hassan; Clausen, Sébastien; Ribeiro, Maria Luísa; Solá, Ana Rita

    2015-01-01

    The Cambrian Tamdroust and Bab n’Ali Volcanic Complexes represent two magmatic episodes developed in the latest Ediacaran–Cambrian Atlas Rift of Morocco. Their rifting pulses were accompanied by accumulation of volcanosedimentary edifices (dominated by effusive lava flows in the former and explosive acidic aprons in the latter) associated with active tilting and uplift. Sealing of their peneplaned horst-and-graben palaeotopographies led to the onset of distinct onlapping geometrie...

  3. The sedimentological characteristics of microbialites of the Cambrian in the vicinity of Beijing, China

    Directory of Open Access Journals (Sweden)

    Yin-Ye Wu

    2017-04-01

    Full Text Available With oil and gas exploration transferring to deeper and more ancient marine strata, more researches have been conducted about the Meso–Neoproterozoic and Cambrian microbial carbonate rocks by petroleum geologists. The Cambrian deposits experienced the first transgression of the Paleozoic, with shallow marine facies depositing in most areas, which are favorable for different kinds of biological reproduction. The Lower Cambrian in Beijing area is lithologically dominated by purple red shales interbedded with limestones, the Middle Cambrian is mainly composed of thick oolitic limestones, and the Upper Cambrian consists of thin limestones and flat-pebble conglomerates. Two beds of microbial carbonate rocks were discovered in the Cambrian outcrops in the vicinity of Beijing. One is from the Zhangxia Formation of Middle Cambrian, and the other is from the Gushan Formation of Upper Cambrian. The microbialites are characterized by combination of multiple stromatolites forming different bioherms. The bioherms are mostly in oval shape and with different sizes, which are 3–4 m long, and 1–3 m high. The surrounding strata beneath the bioherms are oolitic limestones. A central core of flat-pebble conglomerates occurred within each bioherm. Wavy or columnar stromatolites grow on the basis of flat-pebble conglomerates, with dentate erosional surfaces. The bioherm carbonate rocks are interpreted as products from a deep ramp sedimentary environment where potential oil and gas reservoirs can be found. The analysis of sedimentological characteristics of bioherm carbonate rocks and its lithofacies palaeogeography has significant implication for petroleum exploration. Research on geological record of microbialites is beneficial to investigating the Earth evolution, biodiversity, palaeoenvironment and palaeoclimate change, as well as biological extinction event during geological transitions. It also gives warning to human beings of modern biological crisis.

  4. Numerical model of the lowermost Mississippi River as an alluvial-bedrock reach: preliminary results

    Science.gov (United States)

    Viparelli, E.; Nittrouer, J. A.; Mohrig, D. C.; Parker, G.

    2012-12-01

    Recent field studies reveal that the river bed of the Lower Mississippi River is characterized by a transition from alluvium (upstream) to bedrock (downstream). In particular, in the downstream 250 km of the river, fields of actively migrating bedforms alternate with deep zones where a consolidated substratum is exposed. Here we present a first version of a one-dimensional numerical model able to capture the alluvial-bedrock transition in the lowermost Mississippi River, defined herein as the 500-km reach between the Old River Control Structure and the Gulf of Mexico. The flow is assumed to be steady, and the cross-section is divided in two regions, the river channel and the floodplain. The streamwise variation of channel and floodplain geometry is described with synthetic relations derived from field observations. Flow resistance in the river channel is computed with the formulation for low-slope, large sand bed rivers due to Wright and Parker, while a Chezy-type formulation is implemented on the floodplain. Sediment is modeled in terms of bed material and wash load. Suspended load is computed with the Wright-Parker formulation. This treatment allows either uniform sediment or a mixture of different grain sizes, and accounts for stratification effects. Bedload transport rates are estimated with the relation for sediment mixtures of Ashida and Michiue. Previous work documents reasonable agreement between these load relations and field measurements. Washload is routed through the system solving the equation of mass conservation of sediment in suspension in the water column. The gradual transition from the alluvial reach to the bedrock reach is modeled in terms of a "mushy" layer of specified thickness overlying the non-erodible substrate. In the case of a fully alluvial reach, the channel bed elevation is above this mushy layer, while in the case of partial alluvial cover of the substratum, the channel bed elevation is within the mushy layer. Variations in base

  5. Sedimentation and diagenesis at a Late Cambrian biomere extinction horizon

    Energy Technology Data Exchange (ETDEWEB)

    Grimm, K.A.; Miller, J.F.; Taylor, J.F.

    1985-01-01

    The base of the Eurekia apopsis Subzone of the Saukia Zone, slightly below the present Cambrian-Ordovician boundary, has been interpreted as a biomere extinction crisis for trilobites and conodonts. This boundary can be recognized to within two centimeters in platform carbonates in Utah, Nevada, Texas, and Oklahoma. Regional stratigraphy in West Utah reveals that this extinction horizon occurs within a shoaling upward sequence in which sedimentation was predominantly episodic. Shallow subtidal sedimentation, producing bioturbated mixed-skeletal wackestones and graded intraclastic grainsupportstones (tempestites), shifted to peritidal sedimentation through the boundary interval and for the duration of the E. apopsis Subzone. Associated lithofacies include sponge-dominated thrombolite mounds with tidal channels, sublittoral stromatolite reefs, and a restricted marine lagoon. The base of the E. apopsis Subzone in West Utah is a sharp contact but is interpreted as neither a disconformity nor a surface of subaerial exposure. In Texas, this boundary is a planar disconformity between biosparites. The bed underlying this surface displays features that reflect wholesale aragonite dissolution followed by two stages of inferred meteroic phreatic cementation. The surface is well washed and provided a clean substrate for epitaxial cementation across the boundary. The overlying basal strata of the E. apopsis Subzone are cemented with marine phreatic non-ferroan calcite and contain faunas that are strikingly dissimilar to those below.

  6. Particulate sulfur in the upper troposphere and lowermost stratosphere – sources and climate forcing

    Directory of Open Access Journals (Sweden)

    B. G. Martinsson

    2017-09-01

    Full Text Available This study is based on fine-mode aerosol samples collected in the upper troposphere (UT and the lowermost stratosphere (LMS of the Northern Hemisphere extratropics during monthly intercontinental flights at 8.8–12 km altitude of the IAGOS-CARIBIC platform in the time period 1999–2014. The samples were analyzed for a large number of chemical elements using the accelerator-based methods PIXE (particle-induced X-ray emission and PESA (particle elastic scattering analysis. Here the particulate sulfur concentrations, obtained by PIXE analysis, are investigated. In addition, the satellite-borne lidar aboard CALIPSO is used to study the stratospheric aerosol load. A steep gradient in particulate sulfur concentration extends several kilometers into the LMS, as a result of increasing dilution towards the tropopause of stratospheric, particulate sulfur-rich air. The stratospheric air is diluted with tropospheric air, forming the extratropical transition layer (ExTL. Observed concentrations are related to the distance to the dynamical tropopause. A linear regression methodology handled seasonal variation and impact from volcanism. This was used to convert each data point into stand-alone estimates of a concentration profile and column concentration of particulate sulfur in a 3 km altitude band above the tropopause. We find distinct responses to volcanic eruptions, and that this layer in the LMS has a significant contribution to the stratospheric aerosol optical depth and thus to its radiative forcing. Further, the origin of UT particulate sulfur shows strong seasonal variation. We find that tropospheric sources dominate during the fall as a result of downward transport of the Asian tropopause aerosol layer (ATAL formed in the Asian monsoon, whereas transport down from the Junge layer is the main source of UT particulate sulfur in the first half of the year. In this latter part of the year, the stratosphere is the clearly dominating source of

  7. Constraining lowermost mantle structure with PcP/P amplitude ratios from large aperture arrays

    Science.gov (United States)

    Ventosa, S.; Romanowicz, B. A.

    2015-12-01

    Observations of weak short-period teleseismic body waves help to resolve lowermost mantle structure at short wavelengths, which is essential for understanding mantle dynamics and the interactions between the mantle and core. Their limited amount and uneven distribution are however major obstacles to solve for volumetric structure of the D" region, topography of the core-mantle boundary (CMB) and D" discontinuity, and the trade-offs among them. While PcP-P differential travel times provide important information, there are trade-offs between velocity structure and core-mantle boundary topography, which PcP/P amplitude ratios can help resolve, as long as lateral variations in attenuation and biases due to focusing are small or can be corrected for. Dense broadband seismic networks help to improve signal-to-noise ratio (SNR) of the target phases and signal-to-interference ratio (SIR) of other mantle phases when the slowness difference is large enough. To improve SIR and SNR of teleseismic PcP data, we have introduced the slant-stacklet transform to define coherent-guided filters able to separate and enhance signals according to their slowness, time of arrival and frequency content. We thus obtain optimal PcP/P amplitude ratios in the least-square sense using two short sliding windows to match the P signal with a candidate PcP signal. This method allows us to dramatically increase the amount of high-quality observations of short-period PcP/P amplitude ratios by allowing for smaller events and wider epicentral distance and depth ranges.We present the results of measurement of PcP/P amplitude ratios, sampling regions around the Pacific using dense arrays in North America and Japan. We observe that short-period P waves traveling through slabs are strongly affected by focusing, in agreement with the bias we have observed and corrected for due to mantle heterogeneities on PcP-P travel time differences. In Central America, this bias is by far the stronger anomaly we observe

  8. Neoproterozoic–Cambrian stratigraphic framework of the Anti-Atlas and Ouzellagh promontory (High Atlas), Morocco

    Science.gov (United States)

    Alvaro, Jose Javier; Benziane, Fouad; Thomas, Robert; Walsh, Gregory J.; Yazidi, Abdelaziz

    2014-01-01

    In the last two decades, great progress has been made in the geochronological, chrono- and chemostratigraphic control of the Neoproterozoic and Cambrian from the Anti-Atlas Ranges and the Ouzellagh promontory (High Atlas). As a result, the Neoproterozoic is lithostratigraphically subdivided into: (i) the Lkest-Taghdout Group (broadly interpreted at c. 800–690 Ma) representative of rift-to-passive margin conditions on the northern West African craton; (ii) the Iriri (c. 760–740 Ma), Bou Azzer (c. 762–697 Ma) and Saghro (c. 760?–610 Ma) groups, the overlying Anezi, Bou Salda, Dadès and Tiddiline formations localized in fault-grabens, and the Ouarzazate Supergroup (c. 615–548 Ma), which form a succession of volcanosedimentary complexes recording the onset of the Pan-African orogeny and its aftermath; and (iii) the Taroudant (the Ediacaran–Cambrian boundary lying in the Tifnout Member of the Adoudou Formation), Tata, Feijas Internes and Tabanite groups that have recorded development of the late Ediacaran–Cambrian Atlas Rift. Recent discussions of Moroccan strata to select new global GSSPs by the International Subcommissions on Ediacaran and Cambrian Stratigraphy have raised the stratigraphic interest in this region. A revised and updated stratigraphic framework is proposed here to assist the tasks of both subcommissions and to fuel future discussions focused on different geological aspects of the Neoproterozoic–Cambrian time span.

  9. The onset of the 'Ordovician Plankton Revolution' in the late Cambrian

    DEFF Research Database (Denmark)

    Servais, Thomas; Perrier, Vincent; Danelian, Taniel

    2016-01-01

    Positive Carbon Isotope Excursion δ13Ccarb (SPICE) event in the late Cambrian (Paibian Stage, Furongian Series) has been related to a major increase in atmospheric O2 (from 10-18% to some 20 - 29%) and to increased oceanic nutrient availability. Here we analyze the diversification of the planktonic groups...... during the late Cambrian and Early Ordovician, in particular in relation to the SPICE event. Our analyses include the changing diversities of the phytoplankton (acritarchs), diverse groups of zooplankton (e.g., radiolarians, graptolites, chitinozoans) and the switch to a planktonic mode of life of fossil...... of the different planktonic organisms can be related directly to the SPICE event. However, a long term (10-20millionyears) oxygenation pulse related to the SPICE event might have fuelled the explosion of phytoplankton diversity observed in the latest Cambrian-Early Ordovician that led to completely modified...

  10. Arroyo del Soldado group: paleontology, dating and Vendian to Lower Cambrian, Uruguay

    International Nuclear Information System (INIS)

    Gaucher, C.; Sprechmann, P.

    1998-01-01

    The fossil content of the Vendian to Lower Cambrian Arroyo del Soldado Group of the Nico Perez Terrane of Uruguay is analysed.Organic walled microfossils represented by acritarchs, eukariotic algae (sensu lato) and iron bacteria are recognized. An updated list of these microfossils is presented, which were are now reported in the Yerbal and Barriga Negra formations.Events of weutrphic conditions were reconstructed. The occurrence of Cloudina riemkeae, the earliest known metazoanwith a mineralized skeleton is communicated for the first time in Uruguay. The organic walled microfossils as well as Cloudina riemkeae are indicative of a Vendian age, whereas the trace fossils of the uppermost unit(Cerro Victoria) suggest the Early Cambrian. This would imply that the Group contains the Precambrian-Cambrian boundary. The Arroyo del Soldado Group is correlated with the Jacadiga and Corunba Groups (Brasil) and the Nama Group (Namibia). (author)

  11. Carbonate rocks of Cambrian and Ordovician age in the Lancaster quadrangle, Pennsylvania

    Science.gov (United States)

    Meisler, Harold; Becher, Albert E.

    1968-01-01

    Detailed mapping has shown that the carbonate rocks of Cambrian and Ordovician age in the Lancaster quadrangle, Pennsylvania, can be divided into 14 rock-stratigraphic units. These units are defined primarily by their relative proportions of limestone and dolomite. The oldest units, the Vintage, Kinzers, and Ledger Formations of Cambrian age, and the Conestoga Limestone of Ordovician age are retained in this report. The Zooks Corner Formation, of Cambrian age, a dolomite unit overlying the Ledger Dolomite, is named here for exposures along Conestoga Creek near the village of Zooks Corner. The Conococheague (Cambrian) and Beekmantown (Ordovician) Limestones, as mapped by earlier workers, have been elevated to group rank and subdivided into formations that are correlated with and named for geologic units in Lebanon and Berks Counties, Pa. These formations, from oldest to youngest, are the Buffalo Springs, Snitz Creek, Millbach, and Richland Formations of the Conococheague Group, and the Stonehenge, Bpler, and Ontelaunee Formations of the Beekmantown Group. The Annville and Myerstown Limestones, which are named for lithologically similar units in Dauphin and Lebanon Counties, Pa., overlie the Beekmantown Group in one small area in the quadrangle.

  12. Biofacies evidence for Late Cambrian low-paleolatitude oceans, western United State and central Asia

    Energy Technology Data Exchange (ETDEWEB)

    Taylor, M.E. (Geological Survey, Denver, CO (United States)); Cook, H.E. (Geological Survey, Menlo Park, CA (United States)); Melnikova, L. (Palaeontological Inst., Moscow (Russian Federation))

    1991-02-01

    Biofacies that formed on carbonate platform-margin slopes adjacent to an early Paleozoic, low-paleolatitude paleoocean are contained in the Upper Cambrian Swarbrick Formation, Tyby Shale, and Upper Cambrian-lowest Ordovician Hales Limestone of the Hot Creek Range, Nevada, and the Upper Cambrian-lowest Ordovician part of the Shabakty Suite of the Malyi Karatau, southern Kazakhstan. These in-situ limestones formed in platform-margin slope and basin-plain environments. Shoal-water faunal assemblages occur in carbonate-turbidite and debris-flow deposits interbedded with in-situ deeper water assemblages of the submarine-fan facies. Abundant sponge spicules, geographically widespread benthic trilobites, and rare ostracodes occur in some of the in-situ beds. In contrast, the shoal-water platform environments were well oxygenated and contain mainly endemic trilobite assemblages. These biofacies characteristics support an interpretation that Late Cambrian oceans were poorly oxygenated, but not anoxic, below the surface mixing layer and that benthic trilobite faunas were widely distributed in response to the more-or-less continuous deep water, low-oxygen habitats. Elements of the Late Cambrian low-oxygen biofacies are widespread in the Tien Shan structural belt of China and the Soviet Union, in central and eastern China, and along the western margin of early Paleozoic North America. This facies distribution pattern defines the transition from low-paleolatitude, shoal-water carbonate platforms to open oceans which have since been destroyed by pre-Late Ordovician and pre-middle Paleozoic Paleotectonic activity.

  13. The Cambrian-Ordovician rocks of Sonora, Mexico, and southern Arizona, southwestern margin of North America (Laurentia): chapter 35

    Science.gov (United States)

    Page, William R.; Harris, Alta C.; Repetski, John E.; Derby, James R.; Fritz, R.D.; Longacre, S.A.; Morgan, W.A.; Sternbach, C.A.

    2013-01-01

    Cambrian and Ordovician shelf, platform, and basin rocks are present in Sonora, Mexico, and southern Arizona and were deposited on the southwestern continental margin of North America (Laurentia). Cambrian and Ordovician rocks in Sonora, Mexico, are mostly exposed in scattered outcrops in the northern half of the state. Their discontinuous nature results from extensive Quaternary and Tertiary surficial cover, from Tertiary and Mesozoic granitic batholiths in western Sonora, and from widespread Tertiary volcanic deposits in the Sierra Madre Occidental in eastern Sonora. Cambrian and Ordovician shelf rocks were deposited as part of the the southern miogeocline on the southwestern continental margin of North America.

  14. An unusual taphocoenosis of a sea urchin and a rectally inserted turriform gastropod from the lowermost Paleocene of Stevs klint, Denmark

    DEFF Research Database (Denmark)

    Milan, Jesper; Rasmussen, Bo Wilhelm; Vallon, Lothar H.

    2015-01-01

    A specimen of the common irregular echinoid Echinocorys sulcata (Goldfuss, 1826), recovered from the lowermost Paleocene Stevns Klint Formation, at Stevns Klint, Denmark, is of note in revealing a perfect external mold of the turriform gastropod Cerithiella fenestrata (Ravn, 1902) in the anal ope...

  15. Observing lowermost tropospheric ozone pollution with a new multispectral synergic approach of IASI infrared and GOME-2 ultraviolet satellite measurements

    Science.gov (United States)

    Cuesta, Juan; Foret, Gilles; Dufour, Gaëlle; Eremenko, Maxim; Coman, Adriana; Gaubert, Benjamin; Beekmann, Matthias; Liu, Xiong; Cai, Zhaonan; Von Clarmann, Thomas; Spurr, Robert; Flaud, Jean-Marie

    2014-05-01

    Tropospheric ozone is currently one of the air pollutants posing greatest threats to human health and ecosystems. Monitoring ozone pollution at the regional, continental and global scale is a crucial societal issue. Only spaceborne remote sensing is capable of observing tropospheric ozone at such scales. The spatio-temporal coverage of new satellite-based instruments, such as IASI or GOME-2, offer a great potential for monitoring air quality by synergism with regional chemistry-transport models, for both inter-validation and full data assimilation. However, current spaceborne observations using single-band either UV or IR measurements show limited sensitivity to ozone in the atmospheric boundary layer, which is the major concern for air quality. Very recently, we have developed an innovative multispectral approach, so-called IASI+GOME-2, which combines IASI and GOME-2 observations, respectively in the IR and UV. This unique multispectral approach has allowed the observation of ozone plumes in the lowermost troposphere (LMT, below 3 km of altitude) over Europe, for the first time from space. Our first analyses are focused on typical ozone pollution events during the summer of 2009 over Europe. During these events, LMT ozone plumes at different regions are produced photo-chemically in the boundary layer, transported upwards to the free troposphere and also downwards from the stratosphere. We have analysed them using IASI+GOME-2 observations, in comparison with single-band methods (IASI, GOME-2 and OMI). Only IASI+GOME-2 depicts ozone plumes located below 3 km of altitude (both over land and ocean). Indeed, the multispectral sensitivity in the LMT is greater by 40% and it peaks at 2 to 2.5 km of altitude over land, thus at least 0.8 to 1 km below that for all single-band methods. Over Europe during the summer of 2009, IASI+GOME-2 shows 1% mean bias and 21% precision for direct comparisons with ozonesondes and also good agreement with CHIMERE model simulations

  16. Stratigraphic significance of Cruziana: New data concerning the Cambrian-Ordovician ichnostratigraphic paradigm

    Energy Technology Data Exchange (ETDEWEB)

    Magwood, J.P.A.; Pemberton, S.G. (Univ. of Alberta, Edmonton (Canada))

    1990-08-01

    The classic Cambrian-Ordovician ichnostratigraphic paradigm originally developed in Europe is based on the assumption that Cruziana - ichnofossils presumably produced by trilobites - can be used in much the same way as trilobite body fossils have been used in chronostratigraphy. That these ichnofossils can be found in many otherwise unfossiliferous, shallow-marine siliciclastic deposits has made them extremely valuable as correlation tools. The paradigm has been used to date lower Paleozoic units in eastern Canada and Europe. It has also been used as supporting evidence to show close affinities between (1) eastern North America, Wales, and Spain and (2) Spain, northern Africa, and southern Asia. Ichnospecies indicative of the Lower Ordovician (Tremadocian and Arenigian), according to the paradigm, have been recovered from the Lower Cambrian (Atdabanian) Gog Group, near Lake Louise, Alberta, Canada. This discovery indicates that these ichnospecies cannot be used as global Lower Ordovician index fossils.

  17. Modern optics in exceptionally preserved eyes of Early Cambrian arthropods from Australia

    Science.gov (United States)

    Lee, Michael S. Y.; Jago, James B.; García-Bellido, Diego C.; Edgecombe, Gregory D.; Gehling, James G.; Paterson, John R.

    2011-06-01

    Despite the status of the eye as an ``organ of extreme perfection'', theory suggests that complex eyes can evolve very rapidly. The fossil record has, until now, been inadequate in providing insight into the early evolution of eyes during the initial radiation of many animal groups known as the Cambrian explosion. This is surprising because Cambrian Burgess-Shale-type deposits are replete with exquisitely preserved animals, especially arthropods, that possess eyes. However, with the exception of biomineralized trilobite eyes, virtually nothing is known about the details of their optical design. Here we report exceptionally preserved fossil eyes from the Early Cambrian (~515 million years ago) Emu Bay Shale of South Australia, revealing that some of the earliest arthropods possessed highly advanced compound eyes, each with over 3,000 large ommatidial lenses and a specialized `bright zone'. These are the oldest non-biomineralized eyes known in such detail, with preservation quality exceeding that found in the Burgess Shale and Chengjiang deposits. Non-biomineralized eyes of similar complexity are otherwise unknown until about 85 million years later. The arrangement and size of the lenses indicate that these eyes belonged to an active predator that was capable of seeing in low light. The eyes are more complex than those known from contemporaneous trilobites and are as advanced as those of many living forms. They provide further evidence that the Cambrian explosion involved rapid innovation in fine-scale anatomy as well as gross morphology, and are consistent with the concept that the development of advanced vision helped to drive this great evolutionary event.

  18. Cambrian and Ordovician Fossil-Lagerstätten in the Barrandian area

    Czech Academy of Sciences Publication Activity Database

    Fatka, O.; Budil, P.; Kraft, P.; Mergl, M.; Mikuláš, Radek; Valent, M.; Lajblová, K.; Rak, Š.; Steinová, M.; Szabad, M.; Micka, V.; Aubrechtová, M.; Lajbl, L.; Nohejlová, M.; Vodička, J.

    2012-01-01

    Roč. 18, č. 1 (2012), s. 22-25 ISSN 1212-6209. [Congress of CGS and SGS. Moninec, 2011.09.22-2011.09.25] R&D Projects: GA ČR GA205/06/0395; GA ČR GA205/09/1521 Institutional research plan: CEZ:AV0Z30130516 Keywords : Cambrian * Ordovician * Fossil-Lagerstätten Subject RIV: DB - Geology ; Mineralogy http://www.sci.muni.cz/gap/casop/

  19. Self-regulation of trilobite diversity in Murero (middle Cambrian, Spain) due to compensatory extinction

    Energy Technology Data Exchange (ETDEWEB)

    Lopez-Villalta, J.S.

    2016-07-01

    As species accumulate in a community, competition for available ecospace is expected to prevent the addition of new species and to facilitate species extinction, thus producing a dynamic equilibrium of diversity. This mechanism remains under debate since its empirical support comes mainly from indirect or partial evidence, with very few direct tests at the species level. Here a new method is described to detect the presence of selfregulation feedbacks between species richness and turnover rates. It consists of Monte Carlo simulations which randomize the distribution of species ranges among stratigraphic intervals, providing predictions which allow the detection of genuine self-regulation feedbacks in the real data. Since the simulations include any potential bias due to preservation, sampling, or change in depositional environment, and these biases would also affect the real dataset, they are thus ruled out as explanations for any difference found. This method is applied to one of the best known fossiliferous sequences worldwide, the Rambla de Valdemiedes in Murero (RV1 section, middle Cambrian, Spain), a classic locality that has been studied for more than 150 years and which stands out due to its excellent sampling density, continuous deposition, and homogeneous fossil preservation. The results show that trilobite species richness was self-regulated due to positive feedback with extinction rate, which implies that compensatory extinction regulated this fauna in spite of the on-going Cambrian radiation. The lack of evidence of any origination feedback suggests ecological opportunities were not limiting for new species to colonize this Cambrian community. (Author)

  20. Life cycle and morphology of a cambrian stem-lineage loriciferan.

    Science.gov (United States)

    Peel, John S; Stein, Martin; Kristensen, Reinhardt Møbjerg

    2013-01-01

    Cycloneuralians form a rich and diverse element within Cambrian assemblages of exceptionally preserved fossils. Most resemble priapulid worms whereas other Cycloneuralia (Nematoda, Nematomorpha, Kinorhyncha, Loricifera), well known at the present day, have little or no fossil record. First reports of Sirilorica Peel, 2010 from the lower Cambrian Sirius Passet fauna of North Greenland described a tubular lorica covering the abdomen and part of a well developed introvert with a circlet of 6 grasping denticles near the lorica. The introvert is now known to terminate in a narrow mouth tube, while a conical anal field is also developed. Broad muscular bands between the plates in the lorica indicate that it was capable of movement by rhythmic expansion and contraction of the lorica. Sirilorica is regarded as a macrobenthic member of the stem-lineage of the miniaturised, interstitial, present day Loricifera. Like loriciferans, Sirilorica is now known to have grown by moulting. Evidence of the life cycle of Sirilorica is described, including a large post-larval stage and probably an initial larva similar to that of the middle Cambrian fossil Orstenoloricusshergoldii.

  1. Life cycle and morphology of a cambrian stem-lineage loriciferan.

    Directory of Open Access Journals (Sweden)

    John S Peel

    Full Text Available Cycloneuralians form a rich and diverse element within Cambrian assemblages of exceptionally preserved fossils. Most resemble priapulid worms whereas other Cycloneuralia (Nematoda, Nematomorpha, Kinorhyncha, Loricifera, well known at the present day, have little or no fossil record. First reports of Sirilorica Peel, 2010 from the lower Cambrian Sirius Passet fauna of North Greenland described a tubular lorica covering the abdomen and part of a well developed introvert with a circlet of 6 grasping denticles near the lorica. The introvert is now known to terminate in a narrow mouth tube, while a conical anal field is also developed. Broad muscular bands between the plates in the lorica indicate that it was capable of movement by rhythmic expansion and contraction of the lorica. Sirilorica is regarded as a macrobenthic member of the stem-lineage of the miniaturised, interstitial, present day Loricifera. Like loriciferans, Sirilorica is now known to have grown by moulting. Evidence of the life cycle of Sirilorica is described, including a large post-larval stage and probably an initial larva similar to that of the middle Cambrian fossil Orstenoloricusshergoldii.

  2. Sources of increase in lowermost stratospheric sulphurous and carbonaceous aerosol background concentrations during 1999–2008 derived from CARIBIC flights

    Directory of Open Access Journals (Sweden)

    Johan Friberg

    2014-03-01

    Full Text Available This study focuses on sulphurous and carbonaceous aerosol, the major constituents of particulate matter in the lowermost stratosphere (LMS, based on in situ measurements from 1999 to 2008. Aerosol particles in the size range of 0.08–2 µm were collected monthly during intercontinental flights with the CARIBIC passenger aircraft, presenting the first long-term study on carbonaceous aerosol in the LMS. Elemental concentrations were derived via subsequent laboratory-based ion beam analysis. The stoichiometry indicates that the sulphurous fraction is sulphate, while an O/C ratio of 0.2 indicates that the carbonaceous aerosol is organic. The concentration of the carbonaceous component corresponded on average to approximately 25% of that of the sulphurous, and could not be explained by forest fires or biomass burning, since the average mass ratio of Fe to K was 16 times higher than typical ratios in effluents from biomass burning. The data reveal increasing concentrations of particulate sulphur and carbon with a doubling of particulate sulphur from 1999 to 2008 in the northern hemisphere LMS. Periods of elevated concentrations of particulate sulphur in the LMS are linked to downward transport of aerosol from higher altitudes, using ozone as a tracer for stratospheric air. Tropical volcanic eruptions penetrating the tropical tropopause are identified as the likely cause of the particulate sulphur and carbon increase in the LMS, where entrainment of lower tropospheric air into volcanic jets and plumes could be the cause of the carbon increase.

  3. 40Ar/39Ar dating of exceptional concentration of metals by weathering of Precambrian rocks at the Precambrian–Cambrian boundary

    DEFF Research Database (Denmark)

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

    2014-01-01

    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...... with mobilization on land of redox sensitive metals by oxidative terrestrial weathering. This unprecedented flushing of metals from the weathered Precambrian surface would have contributed to the chemistry of the earliest Cambrian ocean at a time of marked faunal evolution....

  4. Cambrian-lower Middle Ordovician passive carbonate margin, southern Appalachians: Chapter 14

    Science.gov (United States)

    Read, J. Fred; Repetski, John E.

    2012-01-01

    The southern Appalachian part of the Cambrian–Ordovician passive margin succession of the great American carbonate bank extends from the Lower Cambrian to the lower Middle Ordovician, is as much as 3.5 km (2.2 mi) thick, and has long-term subsidence rates exceeding 5 cm (2 in.)/k.y. Subsiding depocenters separated by arches controlled sediment thickness. The succession consists of five supersequences, each of which contains several third-order sequences, and numerous meter-scale parasequences. Siliciclastic-prone supersequence 1 (Lower Cambrian Chilhowee Group fluvial rift clastics grading up into shelf siliciclastics) underlies the passive margin carbonates. Supersequence 2 consists of the Lower Cambrian Shady Dolomite–Rome-Waynesboro Formations. This is a shallowing-upward ramp succession of thinly bedded to nodular lime mudstones up into carbonate mud-mound facies, overlain by lowstand quartzose carbonates, and then a rimmed shelf succession capped by highly cyclic regressive carbonates and red beds (Rome-Waynesboro Formations). Foreslope facies include megabreccias, grainstone, and thin-bedded carbonate turbidites and deep-water rhythmites. Supersequence 3 rests on a major unconformity and consists of a Middle Cambrian differentiated rimmed shelf carbonate with highly cyclic facies (Elbrook Formation) extending in from the rim and passing via an oolitic ramp into a large structurally controlled intrashelf basin (Conasauga Shale). Filling of the intrashelf basin caused widespread deposition of thin quartz sandstones at the base of supersequence 4, overlain by widespread cyclic carbonates (Upper Cambrian lower Knox Group Copper Ridge Dolomite in the south; Conococheague Formation in the north). Supersequence 5 (Lower Ordovician upper Knox in the south; Lower to Middle Ordovician Beekmantown Group in the north) has a basal quartz sandstone-prone unit, overlain by cyclic ramp carbonates, that grade downdip into thrombolite grainstone and then storm

  5. Complex Seismic Anisotropy at the Edges of a Very-low Velocity Province in the Lowermost Mantle

    Science.gov (United States)

    Wang, Y.; Wen, L.

    2005-12-01

    A prominent very-low velocity province (VLVP) in the lowermost mantle is revealed, and has been extensively mapped out in recent seismic studies (e.g., Wang and Wen, 2004). Seismic evidence unambiguously indicates that the VLVP is compositionally distinct, and its seismic structure can be best explained by partial melting driven by a compositional change produced in the early Earth's history (Wen, 2001; Wen et. al, 2001; Wang and Wen, 2004). In this presentation, we study the seismic anisotropic behavior inside the VLVP and its surrounding area using SKS and SKKS waveform data. We collect 272 deep earthquakes recorded by more than 80 stations in the Kaapvaal seismic array in southern Africa from 1997 to 1999. Based on the data quality, we choose SKS and SKKS waveform data for 16 earthquakes to measure the anisotropic parameters: the fast polarization direction and the splitting time, using the method of Silver and Chan (1991). A total of 162 high-quality measurements are obtained based on the statistics analysis of shear wave splitting results. The obtained anisotropy exhibits different patterns for the SKS and SKKS phases sampling inside the VLVP and at the edges of the VLVP. When the SKS and SKKS phases sample inside the VLVP, their fast polarization directions exhibit a pattern that strongly correlates with stations, gradually changing from 11°N~to 80°N~across the seismic array from south to north and rotating back to the North direction over short distances for several northernmost stations. The anisotropy pattern obtained from the analysis of the SKKS phases is the same as that from the SKS phases. However, when the SKS and SKKS phases sample at the edges of the VLVP, the measured anisotropy exhibits a very complex pattern. The obtained fast polarization directions change rapidly over a small distance, and they no longer correlate with stations; the measurements obtained from the SKS analysis also differ with those from the SKKS analysis. As the SKS and SKKS

  6. Evolution of oceanic molybdenum and uranium reservoir size around the Ediacaran-Cambrian transition: Evidence from western Zhejiang, South China

    Science.gov (United States)

    Xiang, Lei; Schoepfer, Shane D.; Shen, Shu-zhong; Cao, Chang-qun; Zhang, Hua

    2017-04-01

    The "Cambrian explosion" is one of the most fascinating episodes of diversification in the history of life; however, its relationship to the oxygenation of the oceans and atmosphere around the Ediacaran-Cambrian transition is not fully understood. Marine inventories of redox-sensitive trace elements reflect the relative balance of oxidative weathering on land and deposition in anoxic water masses, and can be used to explore the evolution of oceanic and atmospheric redox conditions. For this study, we conducted a series of geochemical analyses on the upper Lantian, Piyuancun, and Hetang formations in the Chunye-1 well, part of the lower Yangtze Block in western Zhejiang. Iron speciation results indicate that the entire studied interval was deposited under anoxic conditions, with three intervals of persistent euxinia occurring in the uppermost Lantian Fm., the lower Hetang Formation (Fm.), and the upper Hetang Fm. Molybdenum (Mo) and uranium (U) contents and Mo/TOC and U/TOC ratios from the anoxic/euxinic intervals of the Chunye-1 well, combined with published data from the sections in the middle and upper Yangtze Block, suggest that the oceanic Mo reservoir declined consistently from the Ediacaran to Cambrian Stage 3, while the size of the oceanic U reservoir remained relatively constant. Both metals were depleted in the ocean in lower Cambrian Stage 4, before increasing markedly at the end of Stage 4. The lack of an apparent increase in the size of the marine Mo and U reservoir from the upper Ediacaran to Cambrian Stage 3 suggests that oxic water masses did not expand until Cambrian Stage 4. The increase in marine Mo and U availability in the upper Hetang Fm. may have been due to the expansion of oxic water masses in the oceans, associated with oxygenation of the atmosphere during Cambrian Stage 4. This expansion of oxic waters in the global ocean postdates the main phase of Cambrian diversification, suggesting that pervasive oxygenation of the ocean on a large

  7. Review of the Cambrian volcanic activity in Morocco: geochemical fingerprints and geotectonic implications for the rifting of West Gondwana

    Science.gov (United States)

    Pouclet, André; El Hadi, Hassan; Álvaro, J. Javier; Bardintzeff, Jacques-Marie; Benharref, Mohammed; Fekkak, Abdelilah

    2018-03-01

    Volcanic activities related to the opening of a Cambrian rift in Morocco were widespread from the Fortunian to the Cambrian Epoch 3. Numerous data are available from northwestern volcanic sites, particularly in the western High Atlas, but they are scarce from the southeastern sites. New data are documented here from the volcanic formations exposed in the Jbel Tazoult n'Ouzina of the Tafilalt Province, eastern Anti-Atlas and dated to Cambrian Epoch 2-3. The Cambrian volcanic activities recorded in the High Atlas, Anti-Atlas, and Coastal Meseta are synthesized to refine their stratigraphic setting and to characterize their magmatic affinities and fingerprints. Six volcanic pulses are determined as tholeiitic, transitional, and alkaline suites. The tholeiitic and transitional magmas originated from primitive mantle and E-MORB-type sources with a spinel- and garnet-bearing lherzolite composition. Some of them were modified by assimilation-fractional crystallisation processes during crust-mantle interactions. The alkaline magmas fit with an OIB-type and a garnet-bearing lherzolite source. The palaeogeographic distribution of the magmatic suites was controlled by the lithospheric thinning of the Cambrian Atlas Rift and lithospheric constraints of the Pan-African metacraton and West African craton.

  8. Paleomagnetism of Early Cambrian Itabaiana mafic dikes (NE Brazil) and the final assembly of Gondwana

    Science.gov (United States)

    Trindade, Ricardo I. F.; D'Agrella-Filho, Manoel S.; Epof, Igor; Brito Neves, Benjamim B.

    2006-04-01

    Paleomagnetic analysis on 15 early Cambrian mafic dikes from Itabaiana (Paraíba State) yielded a southern (northwestern) direction with steep upward (downward) inclination ( Dm = 167.5°, Im = - 63.7°, α95 = 7.3°). AF and Thermal demagnetization, thermomagnetic curves, and hysteresis results suggest that this component is dominantly carried by fine-grained SD magnetite. The high stability of this component and positive baked contact tests on three dikes indicate it represents a primary thermoremanent magnetization. Ar-Ar analysis on whole-rock samples from two sites provides a strong constraint on the age of the Itabaiana paleomagnetic pole (134.6° E, 34.9° S; A95 = 7.3, K = 28) defined by plateau ages of 525 ± 5 and 526 ± 4 Ma. This pole completely satisfies six out of the seven quality criteria proposed by Van der Voo [R. Van der Voo, The reliability of paleomagnetic data, Tectonophysics 184 (1990) 1-9.] and permits a tight constraint on the Early Cambrian sector of the Gondwana apparent polar wander path. Paleogeographic reconstructions consistent with the available paleomagnetic and geological record show that Gondwana was sutured along three major orogenies, the Mozambique (Brasilano/Pan-African) Orogeny (800-650 Ma), the Kuunga Orogeny (570-530 Ma) and the Pampean-Araguaia Orogeny (540-520 Ma). We suggest that after rifting away from Laurentia at the end of the Neoproterozoic, opening the Iapetus ocean, the Amazonian craton and minor adjoining blocks, such as Rio Apa and Pampia, collided with the proto-Gondwana by Cambrian times at ca. 530-520 Ma. Unless for small adjustments, Gondwana was completely formed by 525 Ma whose paleogeography is defined by the Itabaiana pole.

  9. The Lower Cambrian of Scandinavia: Depositional environment, sequence stratigraphy and palaeogeography

    Science.gov (United States)

    Nielsen, Arne Thorshøj; Schovsbo, Niels Hemmingsen

    2011-08-01

    Lower Cambrian successions described from Scandinavia are reviewed and subjected to sequence stratigraphical analysis; comparisons are also made with successions described from northeast Poland, Estonia, Latvia and Lithuania. The treated stratigraphic interval is bounded upwards by a regional unconformity ascribed to the Hawke Bay Event. The East European regional stage classification, comprising the Rovnian, Lontovan, Dominopolian, Ljubomlian, Vergalian, Rausvian and Kibartian, is adopted for the Lower Cambrian of Scandinavia. These units are approximately equivalent to the Terreneuvian and Cambrian provisional series 2. The Rovnian and Lontovan stages are pre-trilobitic. The Dominopolian and 'Ljubomlian' stages encompass the ' Rusophycus' and Schmidtiellus mickwitzi zones; whether the former zone is of pre-trilobitic age is uncertain but possible. The 'Ljubomlian' is treated informally because the definition adopted in this paper does not correspond to the original concept of the stage. The Vergalian and Rausvian are for the time being classified as one combined stage. The lower main part of the Vergalian-Rausvian corresponds to the new informal Holmia kjerulfi- 'Ornamentaspis' linnarssoni zone, whereas the upper part is separated as the new informal Comluella?-Ellipsocephalus lunatus zone. This zone also includes the Kibartian Stage. Volborthella and poorly known olenellid trilobites range into the Kibartian and the stage is considered of Early Cambrian age. The Holmia inusitata Zone is abandoned; it is contemporaneous with the traditional ' O.' linnarssoni Zone. The autochthonous strata underlying the Hawke Bay unconformity in the Laisvall sector, Swedish Lapland, are assigned to the Laisberg and Grammajukku formations and it is proposed to abandon the Laisvall and Såvvare formations. The Laisberg Fm can locally be divided into the Ackerselet, Saivatj, Maiva, Kautsky Ore, Tjalek, Nadok Ore and Assjatj members. The Vakkejokk Breccia near Luopakte is likely

  10. Nd-Sr isotopic and geochemical systematics in Cambrian boninites and tholeiites from Victoria, Australia

    Science.gov (United States)

    Nelson, D. R.; Crawford, A. J.; McCulloch, M. T.

    1984-11-01

    Rocks with boninitic affinities have been recognised in a number of “ophiolites”, including the Cambrian Heathcote and Mt Wellington Greenstone Belts of Victoria. Boninites and high-Mg andesites from the Heathcote Greenstone Belt show a restricted range of initial ɛ Nd values of between +3.3 to +5.8. Extremely refractory boninites from the Mt Wellington Greenstone Belt have ɛ Nd ranging from +1.3 to -9. Ti/Zr is positively correlated with Sm/Nd with the Heathcote lavas generally possessing greater depletion of Ti and enrichment of Zr relative to the middle and heavy REE with increasing LREE/HREE. These data are consistent with the generation of boninites by partial melting of refractory peridotite following invasion by LREE- and Zr-enriched, low ɛ Nd fluids. Tholeiites overlying the boninites in both greenstone belts have flat REE patterns and ɛ Nd˜+5, lower than that anticipated for lavas derived from depleted MORB source reservoirs in the Cambrian, suggesting that their source was also contaminated by a LREE-enriched, low ɛ Nd component similar to that involved in the generation of the Howqua boninites. The added components have characteristics compatible with their derivation from subducted altered oceanic crust and/or from wet subducted sediments. The identification of boninites and other low-Ti lavas in the Victorian greenstone belts is strong evidence for island arc development in southeastern Australia during the Lower Cambrian and provides further support for a subduction-related origin for many ophiolites.

  11. Cambrian rivers and floodplains: the significance of microbial cementation, groundwater and aeolian sediment transport

    Science.gov (United States)

    Reesink, A. J. H.; Best, J.; Freiburg, J. T.; Nathan, W.

    2016-12-01

    Rivers that existed before land plants colonized the Earth are commonly considered to be unaffected by microbial activity on their floodplains, because the limited cementation produced by microbial activity is insufficient to stabilize the river banks. Although this assumption is likely correct, such emphasis on channel dynamics ignores the potential role of floodplain dynamics as an integral component of the river system. Detailed analysis of cores from the Cambrian Mount Simon Sandstone, Illinois, suggests that a significant proportion of the terrestrial sequence is composed of flat-bedded `crinkly' structures that provide evidence of cementation by soil crusts and microbial biofilms, and that promoted the adhesion of sediment to sticky surfaces. Wind ripples and local desert pavements were abundant. These findings highlight that sediment deposition on Cambrian floodplains was often dominated by wind in locations where the ground water table reached the surface, and was thus likely independent of sediment transport within the river channel. Erosion by wind would thus have been hindered by surface cementation and the formation of desert pavements. Such ground water control on deposition, and resistance to erosion by floodplain surface hardening, appear to have been the primary controls on Cambrian floodplain topography. Because floodplain topography poses a key control on channel and floodplain flow, these processes may have affected patterns of erosion and deposition, as well as reach-scale dynamics such as channel avulsions. The autonomous operation of wind-and-groundwater controlled floodplains makes pre-vegetated river systems more sensitive to climatic conditions such as precipitation and evaporation, and strikingly different from those that occurred after the development of land plants.

  12. Controls on gut phosphatisation: the trilobites from the Weeks Formation Lagerstätte (Cambrian; Utah.

    Directory of Open Access Journals (Sweden)

    Rudy Lerosey-Aubril

    Full Text Available Despite being internal organs, digestive structures are frequently preserved in Cambrian Lagerstätten. However, the reasons for their fossilisation and their biological implications remain to be thoroughly explored. This is particularly true with arthropods--typically the most diverse fossilised organisms in Cambrian ecosystems--where digestive structures represent an as-yet underexploited alternative to appendage morphology for inferences on their biology. Here we describe the phosphatised digestive structures of three trilobite species from the Cambrian Weeks Formation Lagerstätte (Utah. Their exquisite, three-dimensional preservation reveals unique details on trilobite internal anatomy, such as the position of the mouth and the absence of a differentiated crop. In addition, the presence of paired pygidial organs of an unknown function is reported for the first time. This exceptional material enables exploration of the relationships between gut phosphatisation and the biology of organisms. Indeed, soft-tissue preservation is unusual in these fossils as it is restricted to the digestive structures, which indicates that the gut played a central role in its own phosphatisation. We hypothesize that the gut provided a microenvironment where special conditions could develop and harboured a source of phosphorus. The fact that gut phosphatization has almost exclusively been observed in arthropods could be explained by their uncommon ability to store ions (including phosphorous in their digestive tissues. However, in some specimens from the Weeks Formation, the phosphatisation extends to the entire digestive system, suggesting that trilobites might have had some biological particularities not observed in modern arthropods. We speculate that one of them might have been an increased capacity for ion storage in the gut tissues, related to the moulting of their heavily-mineralised carapace.

  13. Controls on Gut Phosphatisation: The Trilobites from the Weeks Formation Lagerstätte (Cambrian; Utah)

    Science.gov (United States)

    Lerosey-Aubril, Rudy; Hegna, Thomas A.; Kier, Carlo; Bonino, Enrico; Habersetzer, Jörg; Carré, Matthieu

    2012-01-01

    Despite being internal organs, digestive structures are frequently preserved in Cambrian Lagerstätten. However, the reasons for their fossilisation and their biological implications remain to be thoroughly explored. This is particularly true with arthropods – typically the most diverse fossilised organisms in Cambrian ecosystems – where digestive structures represent an as-yet underexploited alternative to appendage morphology for inferences on their biology. Here we describe the phosphatised digestive structures of three trilobite species from the Cambrian Weeks Formation Lagerstätte (Utah). Their exquisite, three-dimensional preservation reveals unique details on trilobite internal anatomy, such as the position of the mouth and the absence of a differentiated crop. In addition, the presence of paired pygidial organs of an unknown function is reported for the first time. This exceptional material enables exploration of the relationships between gut phosphatisation and the biology of organisms. Indeed, soft-tissue preservation is unusual in these fossils as it is restricted to the digestive structures, which indicates that the gut played a central role in its own phosphatisation. We hypothesize that the gut provided a microenvironment where special conditions could develop and harboured a source of phosphorus. The fact that gut phosphatization has almost exclusively been observed in arthropods could be explained by their uncommon ability to store ions (including phosphorous) in their digestive tissues. However, in some specimens from the Weeks Formation, the phosphatisation extends to the entire digestive system, suggesting that trilobites might have had some biological particularities not observed in modern arthropods. We speculate that one of them might have been an increased capacity for ion storage in the gut tissues, related to the moulting of their heavily-mineralised carapace. PMID:22431989

  14. Ferroan dolomite cement in Cambrian sandstones: burial history and hydrocarbon generation of the Baltic sedimentary basin

    DEFF Research Database (Denmark)

    Sliaupa, S.; Cyziene, J.; Molenaar, Nicolaas

    2008-01-01

    The conditions and timing of carbonate cementation in Cambrian sandstones of the Baltic sedimentary basin were determined by oxygen and carbon stable isotope and chemical data in combination with optical and cathodoluminescence petrographic studies. Studied samples represent a range in present...... burial depth from 340 to 2150 m. The carbonate cement is dominantly ferroan dolomite that occurs as dispersed patches of poikilotopic crystals. Temperatures of dolomite precipitation, based on delta O-18 values, range from 27 degrees C in the shallow buried to 95 degrees C in the deep buried sandstones...

  15. THE FIRST RECORD OF CAMBRIAN CONODONTS FROM THE HUQF-HAUSHI OUTCROPS, OMAN, ARABIAN PENINSULA

    Directory of Open Access Journals (Sweden)

    GABRIELLA BAGNOLI

    2016-05-01

    Full Text Available Outcrops of Cambrian sediments of the uppermost Miqrat Formation, the Al Bashair Formation and the basal Barik Formation were sampled for conodont and palynomorph studies. The units are part of the Palaeozoic Haima Supergroup, exposed in the Huqf-Haushi area in central eastern Oman, Arabian Peninsula. Palynomorphs were absent but conodont samples yielded a small conodont fauna. The presence of Muellerodus? erectus allows the recognition of the Muellerodus? erectus Zone established for North China (late Paibian – early Jiangshanian, in accordance with previous reports on the trilobite fauna from the same interval.

  16. New data on the Lower Cambrian trilobites of Cortijos de Malagon (Spain

    Directory of Open Access Journals (Sweden)

    Jago, J. B.

    1989-04-01

    Full Text Available A Small trilobite fauna from the late Lower Cambrian Sanstones from Los Cortijos de Malagon of Southem Spain is described herein. This fauna ineludes the following taxa: Realaspis (? sp.; Kingaspis (? sp.; cf. Latoucheia sp. and Lusatiops afI. ribotanusd, Richter and Richter, 1948.En este trabajo se describe la fauna de trilobites del Cámbrico inferior de las areniscas de los Cortijos de Malagón en el SE español. Comprende Realaspis (? sp., Kingaspis (? sp.; cf. Latoucheia sp. y Lusatiops afI. ribotanus. Richter y Richter, 1948.

  17. Arthropod eyes: The early Cambrian fossil record and divergent evolution of visual systems.

    Science.gov (United States)

    Strausfeld, Nicholas J; Ma, Xiaoya; Edgecombe, Gregory D; Fortey, Richard A; Land, Michael F; Liu, Yu; Cong, Peiyun; Hou, Xianguang

    2016-03-01

    Four types of eyes serve the visual neuropils of extant arthropods: compound retinas composed of adjacent facets; a visual surface populated by spaced eyelets; a smooth transparent cuticle providing inwardly directed lens cylinders; and single-lens eyes. The first type is a characteristic of pancrustaceans, the eyes of which comprise lenses arranged as hexagonal or rectilinear arrays, each lens crowning 8-9 photoreceptor neurons. Except for Scutigeromorpha, the second type typifies Myriapoda whose relatively large eyelets surmount numerous photoreceptive rhabdoms stacked together as tiers. Scutigeromorph eyes are facetted, each lens crowning some dozen photoreceptor neurons of a modified apposition-type eye. Extant chelicerate eyes are single-lensed except in xiphosurans, whose lateral eyes comprise a cuticle with a smooth outer surface and an inner one providing regular arrays of lens cylinders. This account discusses whether these disparate eye types speak for or against divergence from one ancestral eye type. Previous considerations of eye evolution, focusing on the eyes of trilobites and on facet proliferation in xiphosurans and myriapods, have proposed that the mode of development of eyes in those taxa is distinct from that of pancrustaceans and is the plesiomorphic condition from which facetted eyes have evolved. But the recent discovery of enormous regularly facetted compound eyes belonging to early Cambrian radiodontans suggests that high-resolution facetted eyes with superior optics may be the ground pattern organization for arthropods, predating the evolution of arthrodization and jointed post-protocerebral appendages. Here we provide evidence that compound eye organization in stem-group euarthropods of the Cambrian can be understood in terms of eye morphologies diverging from this ancestral radiodontan-type ground pattern. We show that in certain Cambrian groups apposition eyes relate to fixed or mobile eyestalks, whereas other groups reveal concomitant

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

    DEFF Research Database (Denmark)

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

    2016-01-01

    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...... alga Acetabularia (Chlorophyta), which possesses an intrinsic lid-forming apparatus used during the organism's reproductive stage. Based on the observations on the fossil material and studies on the Acetabularia lid formation, we propose a model of operculum formation in the galeate plexus micro-organisms...

  19. Late Cambrian - Early Ordovician turbidites of Gorny Altai (Russia): Compositions, sources, deposition settings, and tectonic implications

    Science.gov (United States)

    Kruk, Nikolai N.; Kuibida, Yana V.; Shokalsky, Sergey P.; Kiselev, Vladimir I.; Gusev, Nikolay I.

    2018-06-01

    The Cambrian-Ordovician transition was the time of several key events in the history of Central Asia. They were the accretion of Mariana-type island arc systems to the Siberian continent, the related large-scale orogeny and intrusions of basaltic and granitic magma and the formation of a huge turbidite basin commensurate with the Bengal Gulf basin in the western part of the Central Asian orogenic belt (CAOB). The structure of the basin, as well as the sources and environments of deposition remain open to discussion. This paper presents new major- and trace-element data on Late-Cambrian-Early Ordovician turbidites from different parts of the Russian Altai and a synthesis of Nd isotope composition and ages of detrital zircons. The turbidites share chemical similarity with material shed from weathered continental arcs. Broad variations of CIA (39-73) and ICV (0.63-1.66) signatures in sandstones suggest origin from diverse sources and absence of significant sorting. Trace elements vary considerably and have generally similar patterns in rocks from different terranes. On the other hand, there are at least two provinces according to Nd isotope composition and age of detrital zircons. Samples from eastern Russian Altai contain only Phanerozoic zircons and have Nd isotope ratios similar to those in Early Cambrian island arcs (εNdt + 4.4… + 5.4; TNd(DM)-2-st = 0.8-0.9 Ga). Samples from central, western, and southern parts of Russian Altai contain Precambrian zircons (some as old as Late Archean) and have a less radiogenic Nd composition (εNdt up to -3.6; TNd(DM)-2-st up to 1.5 Ga). The chemical signatures of Late Cambrian to Early Ordovician turbidites indicate a provenance chemically more mature than the island arc rocks, and the presence of zircons with 510-490 Ma ages disproves their genetic relation with island arcs. The turbidite basin formed simultaneously with peaks of granitic and alkali-basaltic magmatism in the western Central Asian orogen and resulted from

  20. Specific activity and hazards of Archeozoic-Cambrian rock samples collected from the Weibei area of Shaanxi (China))

    International Nuclear Information System (INIS)

    Xinwei, L.; Lingqing, W.; Xiaodan, J.; Leipeng, Y.; Gelian, D.

    2006-01-01

    The present work deals with the radioactivity of the Archeozoic-Cambrian rocks of the Weibei area, Shaanxi (China)). A total of 45 rock samples of Archeozoic-Cambrian strata were investigated. The radionuclides of the samples, in Bq kg -1 , have been measured using Na(I)Tl gamma-ray spectrometer. The concentration of 226 Ra, 232 Th and 40 K in the Archeozoic-Cambrian rock samples range from 12.3 to 55.4, from 2.4 to 98.7 and from 58.6 to 1613.3 Bq kg -1 , respectively. The measured activity concentrations for these radionuclides were compared with the typical world average values. To assess the radiological hazard of the natural radioactivity in the samples, the radium equivalent activity, the external hazard index, internal hazard index and the annual gonadal dose equivalent associated with the radionuclides were calculated and compared with the international recommended values. (authors)

  1. Paleomagnetism of a well-dated marine succession in South China: A possible Late Cambrian true polar wander (TPW)

    Science.gov (United States)

    Jiao, Wen-Jun; Li, Yong-Xiang; Yang, Zhen-Yu

    2018-04-01

    The Cambrian true polar wander (TPW) hypothesis remains controversial largely because of the uncertainties in the quality and/or fidelity of the paleomagnetic data as well as their chronological control. Testing the TPW hypothesis requires high-quality paleomagnetic data of sufficient spatial and temporal resolutions. Here, we present paleomagnetic results of a continuous Cambrian shallow marine succession from South China where available detailed biostratigraphy provides exceptional chronological constraints. Forty-three sites of paleomagnetic samples were collected from this limestone-dominated succession. Stepwise thermal demagnetization generally reveals three-component magnetizations. Low- and intermediate-temperature components can be cleaned by ∼330 °C, and the high-temperature component (HTC) was isolated typically from ∼350 to ∼450 °C. A positive fold test and the presence of reversed polarity in the strata, together with rock magnetic data as well as the scanning electron microscopic (SEM) and transmission electron microscopic (TEM) results, collectively suggest that the HTCs are likely primary. A directional shift of the HTCs occurs between the lower-middle Cambrian and the upper Cambrian strata in the succession and is tentatively interpreted to indicate a ∼57° polar wander from ∼500.5 to 494 Ma. Because the rate of polar wander is too fast to be a tectonic origin, this polar wander is interpreted to represent a Late Cambrian TPW. This TPW appears coeval with the Steptoean positive carbon isotope excursion (SPICE) and the major trilobite mass extinctions, suggesting a potential link between the TPW and the Late Cambrian biotic and climatic changes. Because the proposed TPW event is exceptionally well-dated, it should be testable through examination of other worldwide sections.

  2. Cambrian Evolutionary Radiation: Context, correlation, and chronostratigraphy—Overcoming deficiencies of the first appearance datum (FAD) concept

    Science.gov (United States)

    Landing, Ed; Geyer, Gerd; Brasier, Martin D.; Bowring, Samuel A.

    2013-08-01

    Use of the first appearance datum (FAD) of a fossil to define a global chronostratigraphic unit's base can lead to intractable correlation and stability problems. FADs are diachronous—they reflect species' evolutionary history, dispersal, biofacies, preservation, collection, and taxonomy. The Cambrian Evolutionary Radiation is characterised by diachronous FADs, biofacies controls, and provincialism of taxa and ecological communities that confound a stable Lower Cambrian chronostratigraphy. Cambrian series and stage definitions require greater attention to assemblage zone successions and non-biostratigraphic, particularly carbon isotope, correlation techniques such as those that define the Ediacaran System base. A redefined, basal Cambrian Trichophycus pedum Assemblage Zone lies above the highest Ediacaran-type biotas (vendobionts, putative metazoans, and calcareous problematica such as Cloudina) and the basal Asteridium tornatum-Comasphaeridium velvetum Zone (acritarchs). This definition and the likely close correspondence of evolutionary origin and local FAD of T. pedum preserves the Fortune Head, Newfoundland, GSSP of the Cambrian base and allows the presence of sub-Cambrian, branched ichnofossils. The sub-Tommotian-equivalent base of Stage 2 (a suggested "Laolinian Stage") should be defined by the I'/L4/ZHUCE δ13C positive peak, bracketed by the lower ranges of Watsonella crosbyi and Aldanella attleborensis (molluscs) and the Skiagia ornata-Fimbrioglomerella membranacea Zone (acritarchs). The W. crosbyi and A. attleborensis FADs cannot define a Stage 2 base as they are diachronous even in the Newfoundland "type" W. crosbyi Zone. The Series 2 base cannot be based on a species' FAD owing to the provincialism of skeletalised metazoans in the Terreneuvian-Series 2 boundary interval and global heterochrony of the oldest trilobites. A Series 2 and Stage 3 (a suggested "Lenaldanian Series" and "Zhurinskyan Stage," new) GSSP base is proposed at the Siberian lower

  3. Arachnostega Bertling, 1992 in the Drumian (Cambrian) sediments of the Teplá-Barrandian region (Czech Republic)

    Czech Academy of Sciences Publication Activity Database

    Fatka, O.; Mikuláš, Radek; Szabad, M.; Micka, V.; Valent, M.

    2011-01-01

    Roč. 61, č. 4 (2011), s. 367-381 ISSN 0001-5709 R&D Projects: GA ČR GA205/06/0395; GA ČR GA205/09/1521 Institutional research plan: CEZ:AV0Z30130516 Keywords : Cambrian * Teplá-Barrandian region * ichnofossils * Jince Formation * Buchava Formation * Arachnostega * Cambrian (Czech Republic) Subject RIV: DB - Geology ; Mineralogy Impact factor: 0.565, year: 2011 https://geojournals.pgi.gov.pl/agp/article/view/9705

  4. Microbial involvement in the formation of Cambrian sea-floor silica-iron oxide deposits, Australia

    Science.gov (United States)

    Duhig, Nathan C.; Davidson, Garry J.; Stolz, Joe

    1992-06-01

    The Cambrian-Ordovician Mount Windsor volcanic belt in northern Australia is host to stratiform lenses of massive ferruginous chert that are spatially associated with volcanogenic massive sulfide occurrences, in particular the Thalanga zinc-lead-copper-silver deposit. The rocks are composed principally of Fe2O3 and SiO2, with very low concentrations of alkalic elements, and lithogenous elements such as Al, Zr, and Ti; they are interpreted as nearly pure chemical sediments. Textural evidence is documented of the integral role of filamentous bacteria (and/or fungi) in depositing iron from hydrothermal fluids, and of the inorganic precipitation of silica-iron-oxyhydroxide gels that subsequently matured to subcrystalline and crystalline silica forms. At least three distinct iron-accumulating microbial forms are distinguished: networks of septate filaments, nonseptate filament networks, and extremely coarse branching filaments that do not reconnect. Values for δ34S in disseminated pyrite are up to 50‰ lighter than those of contemporaneous Cambrian seawater, suggesting postdepositional colonization of some ironstones by sulfur-reducing bacteria. The site not only preserves the textural interplay of biological and inorganic depositional processes in exhalites, but also extends the oldest known instance of microbial mediation in vent-proximal hydrothermal iron precipitation to at least 500 Ma.

  5. Fossil embryos from the Middle and Late Cambrian period of Hunan, south China.

    Science.gov (United States)

    Dong, Xi-Ping; Donoghue, Philip C J; Cheng, Hong; Liu, Jian-Bo

    2004-01-15

    Comparative embryology is integral to uncovering the pattern and process of metazoan phylogeny, but it relies on the assumption that life histories of living taxa are representative of their antecedents. Fossil embryos provide a crucial test of this assumption and, potentially, insight into the evolution of development, but because discoveries so far lack phylogenetic constraint, their significance is moot. Here we describe a collection of embryos from the Middle and Late Cambrian period (500 million years ago) of Hunan, south China, that preserves stages of development from cleavage to the pre-hatching embryo of a direct-developing animal comparable to living Scalidophora (phyla Priapulida, Kinorhyncha, Loricifera). The latest-stage embryos show affinity to the Lower Cambrian embryo Markuelia, whose life-history strategy contrasts both with the primitive condition inferred for metazoan phyla and with many proposed hypotheses of affinity, all of which prescribe indirect development. Phylogenetic tests based on these embryological data suggest a stem Scalidophora affinity. These discoveries corroborate, rather than contradict, the predictions of comparative embryology, providing direct historical support for the view that the life-history strategies of living taxa are representative of their stem lineages.

  6. Kodymirus and the case for convergence of raptorial appendages in Cambrian arthropods.

    Science.gov (United States)

    Lamsdell, James C; Stein, Martin; Selden, Paul A

    2013-09-01

    Kodymirus vagans Chlupáč and Havlíček in Sb Geol Ved Paleontol 6:7-20, 1965 is redescribed as an aglaspidid-like arthropod bearing a single pair of enlarged raptorial appendages, which are shown to be the second cephalic appendage. A number of early Palaeozoic arthropods, recognized from predominantly Cambrian Konservat-Lagerstätten, are known to have borne single pairs of large raptorial appendages. They are well established for the iconic yet problematic anomalocarids, the common megacheirans, and the ubiquitous bivalved Isoxys. Further taxa, such as fuxianhuiids and Branchiocaris, have been reported to have single pairs of specialized cephalic appendages, i.e., appendages differentiated from a largely homonomous limbs series, members of which act in metachronal motion. The homology of these raptorial appendages across these Cambrian arthropods has often been assumed, despite differences in morphology. Thus, anomalocaridids, for instance, have long multiarticulate "frontal appendages" consisting of many articles bearing an armature of paired serial spines, while megacheirans and Isoxys have short "great appendages" consisting of few articles with well-developed endites or elongate fingers. Homology of these appendages would require them to belong to the same cephalic segment. We argue based on morphological evidence that, to the contrary, the raptorial appendages of some of these taxa can be shown to belong to different cephalic segments and are the result of convergence in life habits. K. vagans is yet another important example for this, representing an instance for this morphology from a marginal marine environment.

  7. Discharge controls on the sediment and dissolved nutrient transport flux of the lowermost Mississippi River: Implications for export to the ocean and for delta restoration

    Science.gov (United States)

    Allison, Mead A.; Pratt, Thad C.

    2017-12-01

    Lagrangian longitudinal surveys and fixed station data are utilized from the lowermost Mississippi River reach in Louisiana at high and low discharge in 2012-2013 to examine the changing stream power, sediment transport capacity, and nitrate conveyance in this backwater reach of the river. Nitrate appears to remain conservative through the backwater reach at higher discharges (>15,000 m3/s), thus, nitrate levels supplied from the catchment are those exported to the Gulf of Mexico, fueling coastal hypoxia. At lower discharges, interaction with fine sediments and organic matter stored on the bed due to estuarine and tidal processes, likely elevates nitrate levels prior to entering the Gulf: a further 1-2 week long spike in nitrate concentrations is associated with the remobilization of this sediments during the rising discharge phase of the Mississippi. Backwater characteristics are clearly observed in the study reach starting at river kilometer 703 (Vicksburg) in both longitudinal study periods. Stream power at the lowermost station is only 16% of that at Vicksburg in the high discharge survey, and 0.6% at low flow. The high-to-low discharge study differential in unit stream power at a station increases between Vicksburg and the lowermost station from a factor of 3 to 47-50 times. At high discharge, ∼30% of this energy loss can be ascribed to the removal of water to the Atchafalaya at Old River Control. Suspended sediment flux decreases downstream in the studied reach in both studies: the lowermost station has 75% of the flux at Vicksburg in the high discharge study, and 0.9% in the low discharge study. The high discharge values, given that this study was conducted during the highest rising hydrograph of the water year, are augmented by sediment resuspended from the bed that was deposited in the previous low discharge phase. Examination of this first detailed field observation studies of the backwater phenomenon in a major river, shows that observed suspended

  8. Estimation of porosity of Khewra sandstone of cambrian age by using helium porosimeter and its application in reservoir evaluation

    International Nuclear Information System (INIS)

    Khan, M.S.; Bhatti, A.A.; Gillani, S.T.A.; Raza, A.

    2012-01-01

    Estimation of petrophysical properties of the rock formations played decisive role in all the processes of petroleum exploration. The Cambrian sequence is well established as reservoir rocks in the various parts of the world from where petroleum is being tapped. The Cambrian sequence has been encountered in the Potwar area and limited petroleum is being produced from the Adhi Oil Field. The Khewra Sandstone of the Cambrian sequence is outcropped in the Khewra Gorge, Salt Range Pakistan below an unconformity qf the Tobra Formation. For the assessment of porosity and reservoir characterization Helium Porosimeter has been used, six samples Qf the upper horizon were collected from various locations of the Khewra Gorge and the Khewra Choha Sadden Shah road side section; cores were prepared from these samples according to the instrument standard. The results of this study revealed that the upper horizon Qf the Khewra Sandstone Formation has good porosity ranging from 18.76% to 21.07%, porosity varied in different parts of the formation. These results are in good agreement with the internationally reported values for petroleum reservoir of the Cambrian sandstone. (author)

  9. Lack of inhibiting effect of oil emplacement on quartz cementation: Evidence from Cambrian reservoir sandstones, Paleozoic Baltic Basin

    DEFF Research Database (Denmark)

    Molenaar, Nicolaas; Cyziene, Jolanta; Sliaupa, Saulius

    2008-01-01

    Currently, the question of whether or not the presence of oil in sandstone inhibits quartz cementation and preserves porosity is still debated. Data from a number of Cambrian sandstone oil fields and dry fields have been studied to determine the effects of oil emplacement on quartz cementation. T...

  10. Paleoecologic Implications of Ichnofossils Associated with Slightly Skeletonized Body Fossils, Middle Cambrian of the Barrandian Area, Czech Republic

    Czech Academy of Sciences Publication Activity Database

    Mikuláš, Radek; Fatka, O.; Szabad, M.

    2012-01-01

    Roč. 19, č. 4 (2012), s. 199-210 ISSN 1042-0940 R&D Projects: GA ČR GA205/09/1521 Institutional support: RVO:67985831 Keywords : Middle Cambrian * ichnofossils * slightly skeletonized fauna * Barrandian area Subject RIV: DB - Geology ; Mineralogy Impact factor: 0.727, year: 2012

  11. Decoupling of body-plan diversification and ecological structuring during the Ediacaran-Cambrian transition: evolutionary and geobiological feedbacks.

    Science.gov (United States)

    Mángano, M Gabriela; Buatois, Luis A

    2014-04-07

    The rapid appearance of bilaterian clades at the beginning of the Phanerozoic is one of the most intriguing topics in macroevolution. However, the complex feedbacks between diversification and ecological interactions are still poorly understood. Here, we show that a systematic and comprehensive analysis of the trace-fossil record of the Ediacaran-Cambrian transition indicates that body-plan diversification and ecological structuring were decoupled. The appearance of a wide repertoire of behavioural strategies and body plans occurred by the Fortunian. However, a major shift in benthic ecological structure, recording the establishment of a suspension-feeder infauna, increased complexity of the trophic web, and coupling of benthos and plankton took place during Cambrian Stage 2. Both phases were accompanied by different styles of ecosystem engineering, but only the second one resulted in the establishment of the Phanerozoic-style ecology. In turn, the suspension-feeding infauna may have been the ecological drivers of a further diversification of deposit-feeding strategies by Cambrian Stage 3, favouring an ecological spillover scenario. Trace-fossil information strongly supports the Cambrian explosion, but allows for a short time of phylogenetic fuse during the terminal Ediacaran-Fortunian.

  12. Cambrian nepheline syenite complex at Jabal Sawda, Midyan region, Kingdom of Saudi Arabia

    Science.gov (United States)

    Liddicoat, W.K.; Ramsay, C.R.; Hedge, C.E.

    1986-01-01

    The only nepheline syenite complex presently known in the Arabian Shield is at Jabal Sawda, about 30 km S of Haql in the extreme NW of Saudi Arabia. It is a post-tectonic, composite intrusion with a crudely concentric structure. A core of leuco-nepheline syenite, a partial ring of mela-nepheline syenite, and an almost complete outer ring of alkali-feldspar syenite are the main rock units. Several mega-inclusions of porphyritic nepheline syenite, nepheline monzosyenite, malignite and ijolite are present in the leuco-nepheline syenite. The chemical composition is notable for very high values of Al2O3, Na2O, Ba, La, Nb, Sr and Zr. U{single bond}Pb isotope dating indicates an emplacement age of 553 ?? 4 Ma, one of an increasing number of reliable Cambrian isotope dates in the northern Red Sea region. ?? 1986.

  13. The anatomy, taphonomy, taxonomy and systematic affinity of Markuelia: Early Cambrian to Early Ordovician scalidophorans

    Science.gov (United States)

    Dong, X.-P.; Bengtson, S.; Gostling, N.J.; Cunningham, J.A.; Harvey, T.H.P.; Kouchinsky, A.; Val'Kov, A.K.; Repetski, J.E.; Stampanoni, M.; Marone, F.; Donoghue, P.C.J.

    2010-01-01

    Markuelia is a vermiform, annulated introvertan animal known as embryonic fossils from the Lower Cambrian to Lower Ordovician. Analysis of an expanded and revised dataset for Introverta shows that the precise position of Markuelia within this clade is dependent on the taxa included. As a result, Markuelia is assigned to the scalidophoran total group to reflect uncertainty as to whether it is a stem-scalidophoran or a stem-priapulid. The taxonomy of the genus is revised to provide an improved taxonomic framework for material assigned to Markuelia. Five species are recognized: M. secunda Val'kov, M. hunanensis Dong and Donoghue, M. lauriei Haug et al., M. spinulifera sp. nov. and M. waloszeki sp. nov. Finally, the preservation of Markuelia is evaluated in the light of both the taphonomy of the fossil embryos themselves and the experimental taphonomy of the priapulid Priapulus caudatus, which has been proposed as both a close relative and an anatomical analogue of Markuelia. ?? The Palaeontological Association.

  14. Why did life develop on the surface of the Earth in the Cambrian?

    Directory of Open Access Journals (Sweden)

    Carlo Doglioni

    2016-11-01

    Full Text Available Life was limited for most of Earth's history, remaining at a primitive stage and mostly marine until about 0.55 Ga. In the Paleozoic, life eventually exploded and colonized the continental realm. Why had there been such a long period of delayed evolution of life? Early life was dominated by Archaea and Bacteria, which can survive ionizing radiation better than other organisms. The magnetic field preserves the atmosphere, which is the main shield of UV radiation. We explore the hypothesis that the Cambrian explosion of life could have been enabled by the increase of the magnetic field dipole intensity due to the solidification of the inner core, caused by the cooling of the Earth, and the concomitant decrease with time of the high-energy solar flux since the birth of the solar system. Therefore, the two phenomena could be responsible for the growth and thickening of the atmosphere and the development of land surface life.

  15. Uranium isotopes distinguish two geochemically distinct stages during the later Cambrian SPICE event

    DEFF Research Database (Denmark)

    Dahl, Tais Wittchen; Boyle, Richard A.; Canfield, Donald E.

    2014-01-01

    . Here we report high-precision uranium isotopic data in marine carbonates deposited during the Late Cambrian 'SPICE' event, at ca. 499 Ma, documenting a well-defined -0.18‰ negative δ238U excursion that occurs at the onset of the SPICE event's positive δ13C and δ34S excursions, but peaks (and tails off......) before them. Dynamic modelling shows that the different response of the U reservoir cannot be attributed solely to differences in residence times or reservoir sizes - suggesting that two chemically distinct ocean states occurred within the SPICE event. The first ocean stage involved a global expansion...... depletion in the oceans (Gill et al., 2011). We discuss scenarios for how an interval of elevated pyrite and organic carbon burial could have been sustained without widespread euxinia in the water column (both non-sulfidic anoxia and/or a more oxygenated ocean state are possibilities). Either way, the SPICE...

  16. Cambrian nepheline syenite complex at Jabal Sawda, Midyan region, Kingdom of Saudi Arabia

    Science.gov (United States)

    Liddicoat, W. K.; Ramsay, C. R.; Hedge, C. E.

    The only nepheline syenite complex presently known in the Arabian Shield is at Jabal Sawda, about 30 km S of Haql in the extreme NW of Saudi Arabia. It is a post-tectonic, composite intrusion with a crudely concentric structure. A core of leuco-nepheline syenite, a partial ring of mela-nepheline syenite, and an almost complete outer ring of alkali-feldspar syenite are the main rock units. Several mega-inclusions of porphyritic nepheline syenite, nepheline monzosyenite, malignite and ijolite are present in the leuco-nepheline syenite. The chemical composition is notable for very high values of Al 2O 3, Na 2O, Ba, La, Nb, Sr and Zr. U sbnd Pb isotope dating indicates an emplacement age of 553 ± 4 Ma, one of an increasing number of reliable Cambrian isotope dates in the northern Red Sea region.

  17. Trilobite-based biostratigraphy (arthropoda-trilobita) and related faunas of the Cambrian from Sonora, Mexico

    Science.gov (United States)

    Cuen-Romero, F. J.; Valdez-Holguín, J. E.; Buitrón-Sánchez, B. E.; Monreal, R.; Enríquez-Ocaña, L. F.; Aguirre-Hinojosa, E.; Ochoa-Granillo, J. A.; Palafox-Reyes, J. J.

    2018-04-01

    A biostratigraphic analysis based on trilobites of the main Cambrian outcrops from Sonora, Mexico is performed. The data are based on a combination of field work and published sources, including four previously studied locations from northern and eastern Sonora (Caborca, Cananea, Mazatán, and Arivechi) as well as a new location in the central part of the state of Sonora (San José de Gracia). Chronostratigraphic positions are assigned to the Cambrian outcrops according to Peng et al., 2012 and Cohen et al., 2017. In the Caborca area, the Puerto Blanco, Proveedora, Buelna, Cerro Prieto, Arrojos and El Tren formations comprise a wide range of biozones, which starts from the Fritzaspis Zone until the Glossopleura walcotti Zone (Begadean-Lincolnian Series, global Stage 3-Stage 5, Series 2-Series 3). The Bolsa Quartzite and the Abrigo Limestone exposed in Cananea area are assigned to the Cedaria/Cedarina dakotaensis Zone until the Crepicephalus Zone (Lincolnian Series-Marjuman Stage, global Series 3-Guzhangian). In the San José de Gracia area, The Proveedora, Buelna, Cerro Prieto and El Gavilán formations range from the ?Bristolia mohavensis or ?Bristolia insolens zones until the upper part of Mexicella mexicana Zone, Albertella highlandensis Subzone (Series 2-Series 3, Stage 4-Stage 5). In the Arivechi area, the La Sata, El Mogallón, La Huerta and the Milpillas formations range from Poliella denticulata Zone to the Elvinia Zone (Lincolnian-Millardan, Delamaran-Steptoean, global Series 3-Furongian, Stage 5-Paibian). Paleozoic marine fauna distribution in northwest Mexico and the southwest United States of America, suggest that during this time an extensive faunal province existed, containing a great variety of marine invertebrates with notorious intraspecific affinity. The biotic association includes poriferans, archaeocyathids, brachiopods, mollusks, arthropods and echinoderms as predominant elements.

  18. A new stalked filter-feeder from the middle Cambrian Burgess Shale, British Columbia, Canada.

    Directory of Open Access Journals (Sweden)

    Lorna J O'Brien

    Full Text Available Burgess Shale-type deposits provide invaluable insights into the early evolution of body plans and the ecological structure of Cambrian communities, but a number of species, continue to defy phylogenetic interpretations. Here we extend this list to include a new soft-bodied animal, Siphusauctum gregarium n. gen. and n. sp., from the Tulip Beds (Campsite Cliff Shale Member, Burgess Shale Formation of Mount Stephen (Yoho National Park, British Columbia. With 1,133 specimens collected, S. gregarium is clearly the most abundant animal from this locality.This stalked animal (reaching at least 20 cm in length, has a large ovoid calyx connected to a narrow bilayered stem and a small flattened or bulb-like holdfast. The calyx is enclosed by a flexible sheath with six small openings at the base, and a central terminal anus near the top encircled by indistinct openings. A prominent organ, represented by six radially symmetrical segments with comb-like elements, surrounds an internal body cavity with a large stomach, conical median gut and straight intestine. Siphusauctum gregarium was probably an active filter-feeder, with water passing through the calyx openings, capturing food particles with its comb-like elements. It often occurs in large assemblages on single bedding planes suggesting a gregarious lifestyle, with the animal living in high tier clusters. These were probably buried en masse more or less in-situ by rapid mud flow events.Siphusauctum gregarium resembles Dinomischus, another Cambrian enigmatic stalked animal. Principal points of comparison include a long stem with a calyx containing a visceral mass and bract-like elements, and a similar lifestyle albeit occupying different tiering levels. The presence in both animals of a digestive tract with a potential stomach and anus suggest a grade of organization within bilaterians, but relationships with extant phyla are not straightforward. Thus, the broader affinities of S. gregarium remain

  19. Phase transition and thermal equations of state of (Fe,Al)-bridgmanite and post-perovskite: Implication for the chemical heterogeneity at the lowermost mantle

    Science.gov (United States)

    Sun, Ningyu; Wei, Wei; Han, Shunjie; Song, Junhao; Li, Xinyang; Duan, Yunfei; Prakapenka, Vitali B.; Mao, Zhu

    2018-05-01

    In this study, we have determined the phase boundary between Mg0.735Fe0.21Al0.07Si0.965O3-Bm and PPv and the thermal equations of state of both phases up to 202 GPa and 2600 K using synchrotron X-ray diffraction in laser heated diamond anvil cells. Our experimental results have shown that the combined effect of Fe and Al produces a wide two-phase coexistence region with a thickness of 26 GPa (410 km) at 2200 K, and addition of Fe lowers the onset transition pressure to 98 GPa at 2000 K, consistent with previous experimental results. Furthermore, addition of Fe was noted to reduce the density (ρ) and bulk sound velocity (VΦ) contrasts across the Bm-PPv phase transition, which is in contrast to the effect of Al. Using the obtained phase diagram and thermal equations of state of Bm and PPv, we have also examined the effect of composition variations on the ρ and VΦ profiles of the lowermost mantle. Our modeling results have shown that the pyrolitic lowermost mantle should be highly heterogeneous in composition and temperature laterally to match the observed variations in the depth and seismic signatures of the D″ discontinuity. Normal mantle in a pyrolitic composition with ∼10% Fe and Al in Bm and PPv will lack clear seismic signature of the D″ discontinuity because the broad phase boundary could smooth the velocity contrast between Bm and PPv. On the other hand, Fe-enriched regions close to the cold slabs may show a seismic signature with a change in the velocity slope of the D″ discontinuity, consistent with recent seismic observations beneath the eastern Alaska. Only regions depleted in Fe and Al near the cold slabs would show a sharp change in velocity. Fe in such regions could be removed to the outer core by strong core-mantle interactions or partitions together with Al to the high-pressure phases in the subduction mid ocean ridge basalts. Our results thus have profound implication for the composition of the lowermost mantle.

  20. Selenium and hazardous elements distribution in plant-soil-water system and human health risk assessment of Lower Cambrian, Southern Shaanxi, China.

    Science.gov (United States)

    Du, Yajun; Luo, Kunli; Ni, Runxiang; Hussain, Rahib

    2018-03-01

    The natural selenium poisoning due to toxic Se levels in food chain had been observed in humans and animals in Lower Cambrian outcrop areas in Southern Shaanxi, China. To find out the distribution pattern of selenium and other hazardous elements in the plant, soil and water of Lower Cambrian in Southern Shaanxi, China, and their possible potential health risk, a total of 30 elements were analyzed and the health risk assessment of 18 elements was calculated. Results showed that the soil, plant and natural water of Lower Cambrian all had relatively high Se levels. In Lower Cambrian, the soil was enriched with Se, As, Ba, Cu, Mo, Ni, Zn, Ga, Cd and Cr (1.68 food intake was the major pathway. For minimizing potential health risk, the local inhabitants should use the mix-imported food with local growing foods.

  1. Le volcanisme cambrien du Maroc central : implications géodynamiquesThe Central Morocco Cambrian volcanism: geodynamic implications

    Science.gov (United States)

    Ouali, Houssa; Briand, Bernard; Bouchardon, Jean-Luc; Capiez, Paul

    2003-05-01

    In southeastern Central Morocco, the Bou-Acila volcanic complex is considered of Cambrian age. In spite of low-grade metamorphic effect, initial volcanic texture and mineralogy can be recognized and volcanic rocks are dominated by dolerites and porphyric dolerites. The initial mineralogy is composed of plagioclases, pyroxenes and dark minerals. A secondary mineral assemblage is composed of albite, epidote, chlorite and calcite. According to their immobile elements compositions, the southeastern central Morocco metavolcanites are of within-plate continental tholeiites. This volcanism and those recognized in many other areas in Morocco confirm a Cambrian extensive episode within the Gondwana supercontinent. To cite this article: H. Ouali et al., C. R. Geoscience 335 (2003).To cite this article: H. Ouali et al., C. R. Geoscience 335 (2003).

  2. Multiple sources of metals of mineralization in Lower Cambrian black shales of South China: Evidence from geochemical and petrographic study

    Czech Academy of Sciences Publication Activity Database

    Pašava, J.; Kříbek, B.; Vymazalová, A.; Sýkorová, Ivana; Žák, Karel; Orberger, B.

    2008-01-01

    Roč. 58, č. 1 (2008), s. 25-42 ISSN 1344-1698 R&D Projects: GA AV ČR IAA300460510 Institutional research plan: CEZ:AV0Z30460519; CEZ:AV0Z30130516 Keywords : multiple source * Cambrian Ni-Mo-polymetalic black shale * SEDEX barite deposit Subject RIV: DD - Geochemistry Impact factor: 0.377, year: 2008

  3. The Early Cambrian Mianyang-Changning Intracratonic Sag and Its Control on Petroleum Accumulation in the Sichuan Basin, China

    Directory of Open Access Journals (Sweden)

    Shugen Liu

    2017-01-01

    Full Text Available The older and deeper hydrocarbon accumulations receive increasing attention across the world, providing more technical and commercial challenges to hydrocarbon exploration. We present a study of an asymmetrical, N-S striking intracratonic sag which developed across the Sichuan basin, south China, from Late Ediacaran to Early Cambrian times. The Mianyang-Changning intracratonic sag is ~50 km wide, with its steepest part in the basin center. In particular the eastern margin shows its greatest steepness. Five episodes in the evolutions of the sag can be recognized. It begins in the Late Ediacaran with an uplift and erosion correlated to Tongwan movement. Initial extension occurred during the Early Cambrian Maidiping period, when more strata of the Maidiping Formation were deposited across the sag. Subsequently, maximum extension occurred during the Early Cambrian Qiongzhusi period that resulted in 450–1700 m thick Maidiping-Canglangpu Formations being deposited in the sag. Then, the sag disappeared at the Longwangmiao period, as it was infilled by the sediments. The intracratonic sag has significant influence on the development of high-quality reservoirs in the Dengying and Longwangmiao Formations and source-rock of the Niutitang Formation. It thus indicates that a high probability for oil/gas accumulation exists along the intracratonic sag, across the central Sichuan basin.

  4. Isotopic investigation of the late neoproterozoic and early cambrian carbon cycle on the northern Yangtze platform, south China

    International Nuclear Information System (INIS)

    Guo Qingjun; Liu Congqiang; Harald Strauss; Tatiana Goldberg

    2003-01-01

    The Precambrian-Cambrian transition is one of the critical time intervals in Earth history. Profound geotectonic, climatic and biological changes occur during the late Neoproterozoic and its transition into the early Cambrian. This study has researched on paired carbonate and organic carbon isotope determinations from Nanjiang, Sichuan Province of the Yangtze Platform, and provided a preliminary geochemical explanation for environmental variations and bio-events observed on the northern Yangtze Platform during the Precambrian-Cambrian transitional interval and their causal relationship. Organic carbon isotopic compositions on sediments vary from -35.8 to -30.1‰ at Nanjiang section; carbonate carbon isotopic compositions change between -3.5 and +0.5‰. Various carbon and sulphur isotopic compositions, different pyrite and organic matter content reflect changing environment and burial of organic matter in the Dengying Fm., the lower and upper part of Niutitang Fm. Anoxic conditions result in widespread preservation of organic rich sediments and pyrites in the black shales on the Yangtze Platform. (authors)

  5. Ichnologic evidence of a Cambrian age in the southern Amazon Craton: Implications for the onset of the Western Gondwana history

    Science.gov (United States)

    Santos, Hudson P.; Mángano, M. Gabriela; Soares, Joelson L.; Nogueira, Afonso C. R.; Bandeira, José; Rudnitzki, Isaac D.

    2017-07-01

    Colonization of the infaunal ecospace by burrowing bilaterians is one of the most important behavioral innovations during the Ediacaran-Cambrian transition. The establishment of vertical burrows by suspension feeders in high-energy nearshore settings during Cambrian Age 2 is reflected by the appearance of the Skolithos Ichnofacies. For the first time, unquestionable vertical burrows typical of the Skolithos Ichnofacies, such as Skolithos linearis, Diplocraterion parallelum and Arenicolites isp., are recorded from nearshore siliciclastic deposits of the Raizama Formation, southeastern Amazon Craton, Brazil. Integration of ichnologic and sedimentologic datasets suggests that these trace fossils record colonization of high-energy and well-oxygenated nearshore sandy environments. Chronostratigraphically, the presence of these vertical burrows indicates an age not older than early Cambrian for the Raizama Formation, which traditionally has been regarded as Ediacaran. Therefore, the Raizama ichnofauna illustrates the advent of modern Phanerozoic ecology marked by the Agronomic Revolution. The discovery of the Skolithos Ichnofacies in these shallow-marine strata suggests possible connections between some central Western Gondwana basins.

  6. Pan African Collisional Tectonics Along the Moroccan West African Craton Continued to Ediacaran-Cambrian Boundary

    Science.gov (United States)

    Hefferan, K. P.; Samson, S. D.; Rice, K.; Soulaimani, A.

    2016-12-01

    Precision geochronologic dating and field mapping in the Anti-Atlas Mountains of Morocco document a Neoproterozoic Pan African orogenic cycle consisting of three distinct orogenic events: Iriri-Tichibanine orogeny (760-700 Ma), Bou Azzer orogeny (680-640 Ma) and the WACadomian orogeny (620 Ma to either 555 or 544 Ma). The Iriri-Tichibanine and Bou Azzer orogenies involved northward directed subduction beneath island arc volcanic terranes. These orogenic events generated calc-alkaline magmatism and supra-subduction zone ophiolites exposed in the Bou Azzer and Siroua erosional inliers. The WACadomian orogeny involved subduction and collision of the Cadomia arc complex with the West African Craton and generation of clastic sedimentary basins. The termination of the WACadomian orogeny has been the subject of debate as calc-alkaline to high K magmatism and folding continued to 544 Ma: Was 620-544 Ma calc-alkaline to high K magmatism and clastic basin development due to a) continental rift basin tectonics or b) southward directed subduction and collisional tectonics with associated back arc basin tectonism? We present field and geochemical data supporting the continuation of subduction-collisional tectonics to the Ediacaran-Cambrian boundary 544 Ma. Field mapping in the Central Anti-Atlas (Agadir Melloul) clearly documents an angular unconformity between Ouarzazate Group and Adoudounian limestones (N 30°31'28.91", W07°48'29.12"). Volcaniclastic rocks of Ouarzazate Group (615-545 Ma) are clearly folded and unconformably overlain by Adoudou Formation (541-529 Ma) limestones to the north. Geochemical discrimination diagrams on Latest Neoproterozoic calc-alkaline to high K igneous rocks throughout the Anti-Atlas plot in subduction and collisional arc magma domains. Back arc basin tectonism is likely responsible for localized extensional basins but continental rift tectonics and passive margin sedimentation did not begin in the Anti-Atlas Mountains until Early

  7. Sedimentary mode and reservoir distribution of the Cambrian carbonate & evaporate paragenesis system in the Sichuan Basin

    Directory of Open Access Journals (Sweden)

    Anna Xu

    2016-11-01

    Full Text Available The Cambrian carbonate & evaporite paragenesis system in the Sichuan Basin is made up of the Longwangmiao, Gaotai and Xixiangchi Fms. So far, great breakthrough has been made only in the Longwangmiao Fm instead of the latter two, and the Anyue Gasfield was discovered in the center of this basin. In this paper, therefore, the Cambrian carbonate & evaporite paragenesis system in the Sichuan Basin was analyzed in terms of its structural–sedimentary setting, sequence stratigraphic framework, sedimentary facies and the distribution of evaporites by using various geologic, logging and seismic data. Then, the geological model of sedimentary facies was established and the distribution range of favorable reservoirs was predicted. Based on these studies, the following results are obtained. Firstly, the palaeotectonic framework is characterized by the style of “one depression between two uplifts” in the setting of a large SE dipping slope, and the stratigraphic filling is in the structure of “onlapping at the bottom and truncation at the top” which is thin in the west and thick in the east. Secondly, three third-order sequence cycles which, on the whole, become shallow upward are developed from bottom to top, and gypsum-salt rocks are mainly located at the high system tract (HST of third-order sequences and concentrated in the Wanzhou–Yibin sag. Thirdly, the geological model of sedimentary facies is composed of three major sedimentary structural layers from bottom to top, namely the evaporative carbonate ramp, the evaporative diamictic restricted platform and the evaporative restricted platform. The sedimentary environment changes from the open to the closed and the penesaline for a long time, and then back to the open. The distribution of shoals changes from the pattern of “dual banks” in a large area to more scattered shoals and banded shoals, while the evaporative lagoon and tidal flat shrink. Fourthly, the reservoir distribution is

  8. Experimental taphonomy and the anatomy and diversity of the earliest fossil vertebrates (Chengjiang Biota, Cambrian, China)

    Science.gov (United States)

    Purnell, Mark; Gabbott, Sarah; Murdock, Duncan; Cong, Peiyun

    2016-04-01

    The oldest fossil vertebrates are from the Lower Cambrian Chengjiang biota of China, which contains four genera of fish-like, primitive vertebrates: Haikouichthys, Myllokunmingia, Zhongjianichthys and Zhongxiniscus. These fossils play key roles in calibrating molecular clocks and informing our view of the anatomy of animals close to the origin of vertebrates, potentially including transitional forms between vertebrates and their nearest relatives. Despite the evident importance of these fossils, the degree to which taphonomic processes have affected their anatomical completeness has not been investigated. For example, some or all might have been affected by stemward slippage - the pattern observed in experimental decay of non-biomineralised chordates in which preferential decay of synapomorphies and retention of plesiomorphic characters would cause fossil taxa to erroneously occupy more basal positions than they should. This hypothesis is based on experimental data derived from decay of non-biomineralised chordates under laboratory conditions. We have expanded this analysis to include a broader range of potentially significant environmental variables; we have also compared and combined the results of experiments from several taxa to identify general patterns of chordate decay. Examination of the Chengjiang vertebrates in the light of these results demonstrates that, contrary to some assertions, experimentally derived models of phylogenetic bias are applicable to fossils. Anatomical and phylogenetic interpretations of early vertebrates that do not take taphonomic biases into account risk overestimating diversity and the evolutionary significance of differences between fossil specimens.

  9. Preservation and phylogeny of Cambrian ecdysozoans tested by experimental decay of Priapulus

    Science.gov (United States)

    Sansom, Robert S.

    2016-09-01

    The exceptionally preserved Cambrian fossil record provides unique insight into the early evolutionary history of animals. Understanding of the mechanisms of exceptional soft tissue preservation frames all interpretations of the fauna and its evolutionary significance. This is especially true for recent interpretations of preserved nervous tissues in fossil ecdysozoans. However, models of soft tissue preservation lack empirical support from actualistic studies. Here experimental decay of the priapulid Priapulus reveal consistent bias towards rapid loss of internal non-cuticular anatomy compared with recalcitrant cuticular anatomy. This is consistent with models of Burgess Shale-type preservation and indicates that internal tissues are unlikely to be preserved with fidelity if organically preserved. This pattern, along with extreme body margin distortion, is consistent with onychophoran decay, and is therefore resolved as general for early ecdysozoans. Application of these patterns to phylogenetic data finds scalidophoran taxa to be very sensitive to taphonomically informed character coding, but not panarthropodan taxa. Priapulid decay also have unexpected relevance for interpretation of myomeres in fossil chordates. The decay data presented serve not only as a test of models of preservation but also a framework with which to interpret ecdysozoan fossil anatomies, and the subsequent evolutionary inferences drawn from them.

  10. Replacement of benthic communities in two Neoproterozoic-Cambrian subtropical-to-temperate rift basins, High Atlas and Anti-Atlas, Morocco

    Science.gov (United States)

    Clausen, Sébastien; Álvaro, J. Javier; Zamora, Samuel

    2014-10-01

    The ‘Cambrian explosion’ is often introduced as a major shift in benthic marine communities with a coeval decline of microbial consortia related to the diversification of metazoans and development of bioturbation (‘Agronomic Revolution’). Successive community replacements have been reported along with ecosystem diversification and increase in guild complexity from Neoproterozoic to Cambrian times. This process is recorded worldwide but with regional diachroneities, some of them directly controlled by the geodynamic conditions of sedimentary basins. The southern High Atlas and Anti-Atlas of Morocco record development of two rifts, Tonian (?) - early Cryogenian and latest Ediacarian-Cambrian in age, separated by the onset of the Pan-African Orogeny. This tectonically controlled, regional geodynamic change played a primary control on pattern and timing of benthic ecosystem replacements. Benthic communities include microbial consortia, archaeocyathan-thromboid reefal complexes, chancelloriid-echinoderm-sponge meadows, and deeper offshore echinoderm-dominated communities. Microbial consortia appeared in deeper parts of the Tonian (?) - early Cryogenian fluvio-deltaic progradational rift sequences, lacustrine environments of the Ediacaran Volcanic Atlasic Chain (Ouarzazate Supergroup) and the Ediacaran-Cambrian boundary interval, characterized by the peritidal-dominated Tifnout Member (Adoudou Formation). They persisted and were largely significant until Cambrian Age 3, as previous restricted marine conditions precluded the immigration of shelly metazoans in the relatively shallow epeiric parts of the Cambrian Atlas Rift. Successive Cambrian benthic communities were replaced as a result of distinct hydrodynamic and substrate conditions, which allow identification of biotic (e.g., antagonistic relationships between microbial consortia and echinoderms, and taphonomic feedback patterns in chancelloriid-echinoderm-sponge meadows) and abiotic (e.g., rifting

  11. Stable isotope (δ13Cker, δ13Ccarb, δ18Ocarb distribution along a Cambrian outcrop section in the eastern Tarim Basin, NW China and its geochemical significance

    Directory of Open Access Journals (Sweden)

    Hu Liu

    2017-01-01

    Full Text Available This study investigated the geochemical features of the lower Paleozoic strata of Yaerdang Mountain outcrop along with the core samples from well TD2∈ in the eastern Tarim Basin, NW China. The total organic carbon abundance, hydrocarbon-generating precursor biospecies, and stable isotope ratios of organics and carbonate (δ13Cker, δ13Ccarb and δ18Ocarb were comprehensively studied for their possible correlative constraints during sedimentary evolution. The results revealed that the δ13Cker (VPDB of Cambrian kerogens along the outcrop section varied from −34.6‰ to −28.4‰, indicating an increasing tendency from the lower Cambrian to the upper Cambrian. This was on the whole accompanied by the variation in the δ13Ccarb and δ18Ocarb along the profile, which might be associated with the changes in the sea level and also in the compositional variation of benthic and planktonic biomass. The large variation in the stable carbon isotope ratios up to 6‰ along the outcrop section reflected the heterogeneity of the Cambrian source rocks from the eastern Tarim Basin. Hence, the 13C-enriched crude oils from well TD2∈ might have been derived from a localized stratum of Cambrian source rocks. The results from this study showed the possibility of multiple source kitchens in the Cambrian–lower Ordovician portion of Tarim Basin.

  12. The age, nature and likely genesis of the Cambrian Khantaishir arc, Lake Zone, Mongolia

    Science.gov (United States)

    Janoušek, Vojtěch; Jiang, Yingde; Schulmann, Karel; Buriánek, David; Hanžl, Pavel; Lexa, Ondrej; Ganchuluun, Turbat; Battushig, Altanbaatar

    2014-05-01

    Recent discovery of the huge Cambrian arc in the Khantaishir Mountain Range (SE Mongolian Altai) suggests that the principal Neoproterozoic and Devonian-Carboniferous episodes of crustal growth in the Central Asian Orogenic Belt (CAOB) (Sengör et al. 1993) have to be revised. This probably the largest arc system known in the Mongolian tract of the CAOB is seemingly intrusive into the Neoproterozoic accretionary wedge (the Lake Zone) in the N and underthrust southwards below the Palaeozoic volcanosedimentary prism (Gobi Altai Zone). The arc shows a section from deep, ultramafic cumulates to shallower crustal levels of the magmatic system and thus provides an excellent opportunity to study this important period of crustal growth in the Mongolian CAOB. The magmatic rocks are intermediate to ultrabasic (SiO2 = 39.2-61.8 wt. %), rather primitive (mg# = 45-60) Amp-Bt tonalites to coarse-grained Amp gabbros and hornblendites. They are Na-rich (Na2O/K2O = 1.3-9.7 by wt.), exclusively metaluminous and mostly subalkaline, except for the ultrabasic types that enter the alkaline domain due to accumulation of Amp crystals. The P-T conditions calculated using the Amp thermobarometer of Ridolfi et al. (2010) show that the gabbro crystallized at 930-950 ° C and 0.36-0.43 GPa. The (normal-) calc-alkaline chemistry and characteristic trace-element enrichment in hydrous-fluid mobile large-ion lithophile elements (LILE: Rb, Ba, Th, U, K and Pb) over high-field strength elements (HFSE: Nb and Ta) confirm an origin within an igneous arc. The newly obtained LA ICP-MS zircon ages for three tonalites-diorites range between 516 ± 2 Ma and 494 ± 3 Ma. While zircons in two of them give high initial ɛHf values (+8 to +14), implying a derivation by (near) closed-system fractionation from little modified, depleted-mantle derived magmas, the third contains significantly different component (ɛHf = +3 to +6). The latter component may have come from a distinct, less depleted

  13. Population Structure, Life Strategies and Systematics of Phosphatocope Ostracods from the Middle Cambrian of Bornholm

    Directory of Open Access Journals (Sweden)

    I. Hinz-Schallreuter

    1998-01-01

    Full Text Available She Middle Cambrian Borregård Member of Bornholm which is the stratigraphical equivalent to the Baltoscandian Exsulans Limestone yielded a rich and comparatively diverse ostracod fauna in its upper part. It comprises eight species out of four genera. They belong to three known subfamilies that are redefined on the basis of special characters of the contact margin. An ontogenetic character unknown from typical ostracods is documented in several species: during early ontogeny the gestalt (l:h ratio develops constantly in becoming increasingly longer until the so-called ontogenetical turning point (OTP from which the direction of growth focusses on carapace height. This phenomenon may be explained by changes in body morphology. The Borregård association represents an ecologic community type differing from other yet recorded Middle Cambrian communities in the Baltoscandic region. Apart from Vestrogothia longispinosa which is a common faunal element in Baltoscandian ostracod faunas, the yet recorded species of Bidimorpha are unknown from other Baltoscandian occurrences. Vice versa, the known species of Bidimorpha described from Swedish occurrences have not been recognized in the rich Borregård community. Similarly, Falites insula and Hesslandona abdominalis may be of local significance, too, but the respective records from contemporaneous Swedish localities are insufficient in this respect, yet. Due to specific morphological adaptations, the four genera are assumed to represent different benthic life strategies. New taxa are: Bidimorpha arator n. sp., Bidimorpha labiator n. sp., Bidimorpha sexspinosa n. sp., Falites insula n. sp., Hesslandona abdominalis n. sp., Vestrogothia herrigi n. sp. and Vestrogothia minilaterospinata n. sp. Aus dem mittelkambrischen Borregård Member von Bornholm, einem zeitlichen Äquivalent des baltoskandischen Exsulanskalkes, wurde eine reiche und vergleichsweise diverse Ostrakodenfauna gewonnen. Sie umfaßt 8 Arten aus

  14. Depositional Architecture of Late Cambrian-Early Ordovician Siliciclastic Barik Formation; Al Huqf Area, Oman

    Science.gov (United States)

    Abbasi, Iftikhar Ahmed

    2017-04-01

    Early Paleozoic siliciclastics sediments of the Haima Supergroup are subdivided into a number of formations and members based on lithological characteristics of various rock sequences. One of the distinct sandstone sequence, the Barik Formation (Late Cambrian-Early Ordovician) of the Andam Group is a major deep gas reservoir in central Oman. The sandstone bodies are prospective reservoir rocks while thick shale and clay interbeds act as effective seal. Part of the Barik Formation (lower and middle part) is exposed in isolated outcrops in Al Huqf area as interbedded multistoried sandstone, and green and red shale. The sandstone bodies are up to 2 meters thick and can be traced laterally for 300 m to over 1 km. Most of sandstone bodies show both lateral and vertical stacking. Two types of sandstone lithofacies are identified on the basis of field characteristics; a plane-bedded sandstone lithofacies capping thick red and green color shale beds, and a cross-bedded sandstone lithofacies overlying the plane-bedded sandstone defining coarsening upward sequences. The plane-bedded sandstone at places contains Cruziana ichnofacies and bivalve fragments indicating deposition by shoreface processes. Thick cross-bedded sandstone is interpreted to be deposited by the fluvial dominated deltaic processes. Load-casts, climbing ripples and flaser-bedding in siltstone and red shale indicate influence of tidal processes at times during the deposition of the formation. This paper summarizes results of a study carried out in Al Huqf area outcrops to analyze the characteristics of the sandstone-body geometry, internal architecture, provenance and diagenetic changes in the lower and middle part of the formation. The study shows build-up of a delta complex and its progradation over a broad, low-angle shelf where fluvial processes operate beside shoreface processes in a vegetation free setting. Keywords: Andam Group, Barik Formation, Ordovician sandstone, Al Huqf, Central Oman,

  15. Paleoarchean and Cambrian observations of the geodynamo in light of new estimates of core thermal conductivity

    Science.gov (United States)

    Tarduno, John; Bono, Richard; Cottrell, Rory

    2015-04-01

    Recent estimates of core thermal conductivity are larger than prior values by a factor of approximately three. These new estimates suggest that the inner core is a relatively young feature, perhaps as young as 500 million years old, and that the core-mantle heat flux required to drive the early dynamo was greater than previously assumed (Nimmo, 2015). Here, we focus on paleomagnetic studies of two key time intervals important for understanding core evolution in light of the revisions of core conductivity values. 1. Hadean to Paleoarchean (4.4-3.4 Ga). Single silicate crystal paleointensity analyses suggest a relatively strong magnetic field at 3.4-3.45 Ga (Tarduno et al., 2010). Paleointenity data from zircons of the Jack Hills (Western Australia) further suggest the presence of a geodynamo between 3.5 and 3.6 Ga (Tarduno and Cottrell, 2014). We will discuss our efforts to test for the absence/presence of the geodynamo in older Eoarchean and Hadean times. 2. Ediacaran to Early Cambrian (~635-530 Ma). Disparate directions seen in some paleomagnetic studies from this time interval have been interpreted as recording inertial interchange true polar wander (IITPW). Recent single silicate paleomagnetic analyses fail to find evidence for IITPW; instead a reversing field overprinted by secondary magnetizations is defined (Bono and Tarduno, 2015). Preliminary analyses suggest the field may have been unusually weak. We will discuss our on-going tests of the hypothesis that this interval represents the time of onset of inner core growth. References: Bono, R.K. & Tarduno, J.A., Geology, in press (2015); Nimmo, F., Treatise Geophys., in press (2015); Tarduno, J.A., et al., Science (2010); Tarduno, J.A. & Cottrell, R.D., AGU Fall Meeting (2014).

  16. Depositional and diagenetic variability within the Cambrian Mount Simon Sandstone: Implications for carbon dioxide sequestration

    Science.gov (United States)

    Bowen, B.B.; Ochoa, R.I.; Wilkens, N.D.; Brophy, J.; Lovell, T.R.; Fischietto, N.; Medina, C.R.; Rupp, J.A.

    2011-01-01

    The Cambrian Mount Simon Sandstone is the major target reservoir for ongoing geologic carbon dioxide (CO2) sequestration demonstrations throughout the midwest United States. The potential CO2 reservoir capacity, reactivity, and ultimate fate of injected CO2 depend on textural and compositional properties determined by depositional and diagenetic histories that vary vertically and laterally across the formation. Effective and efficient prediction and use of the available pore space requires detailed knowledge of the depositional and diagenetic textures and mineralogy, how these variables control the petrophysical character of the reservoir, and how they vary spatially. Here, we summarize the reservoir characteristics of the Mount Simon Sandstone based on examination of geophysical logs, cores, cuttings, and analysis of more than 150 thin sections. These samples represent different parts of the formation and depth ranges of more than 9000 ft (>2743 m) across the Illinois Basin and surrounding areas. This work demonstrates that overall reservoir quality and, specifically, porosity do not exhibit a simple relationship with depth, but vary both laterally and with depth because of changes in the primary depositional facies, framework composition (i.e., feldspar concentration), and diverse diagenetic modifications. Diagenetic processes that have been significant in modifying the reservoir include formation of iron oxide grain coatings, chemical compaction, feldspar precipitation and dissolution, multiple generations of quartz overgrowth cementation, clay mineral precipitation, and iron oxide cementation. These variables provide important inputs for calculating CO2 capacity potential, modeling reactivity, and are also an important baseline for comparisons after CO2 injection. Copyright ??2011. The American Association of Petroleum Geologists/Division of Environmental Geosciences. All rights reserved.

  17. Three Cambrian fossils assembled into an extinct body plan of cnidarian affinity.

    Science.gov (United States)

    Ou, Qiang; Han, Jian; Zhang, Zhifei; Shu, Degan; Sun, Ge; Mayer, Georg

    2017-08-15

    The early Cambrian problematica Xianguangia sinica , Chengjiangopenna wangii , and Galeaplumosus abilus from the Chengjiang biota (Yunnan, China) have caused much controversy in the past and their phylogenetic placements remain unresolved. Here we show, based on exceptionally preserved material (85 new specimens plus type material), that specimens previously assigned to these three species are in fact parts of the same organism and propose that C. wangii and G. abilus are junior synonyms of X. sinica Our reconstruction of the complete animal reveals an extinct body plan that combines the characteristics of the three described species and is distinct from all known fossil and living taxa. This animal resembled a cnidarian polyp in overall morphology and having a gastric cavity partitioned by septum-like structures. However, it possessed an additional body cavity within its holdfast, an anchoring pit on the basal disk, and feather-like tentacles with densely ciliated pinnules arranged in an alternating pattern, indicating that it was a suspension feeder rather than a predatory actiniarian. Phylogenetic analyses using Bayesian inference and maximum parsimony suggest that X. sinica is a stem-group cnidarian. This relationship implies that the last common ancestor of X. sinica and crown cnidarians was probably a benthic, polypoid animal with a partitioned gastric cavity and a single mouth/anus opening. This extinct body plan suggests that feeding strategies of stem cnidarians may have been drastically different from that of their crown relatives, which are almost exclusively predators, and reveals that the morphological disparity of total-group Cnidaria is greater than previously assumed.

  18. Metamorphosis Is Ancestral for Crown Euarthropods, and Evolved in the Cambrian or Earlier.

    Science.gov (United States)

    Wolfe, Joanna M

    2017-09-01

    Macroevolutionary developmental biology employs fossilized ontogenetic data and phylogenetic comparative methods to probe the evolution of development at ancient nodes. Despite the prevalence of ecologically differentiated larval forms in marine invertebrates, it has been frequently presumed that the ancestors of arthropods were direct developers, and that metamorphosis may not have evolved until the Ordovician or later. Using fossils and new dated phylogenies, I infer that metamorphosis was likely ancestral for crown arthropods, contradicting this assumption. Based on a published morphological dataset encompassing 217 exceptionally preserved fossil and 96 extant taxa, fossils were directly incorporated into both the topology and age estimates, as in "tip dating" analyses. Using data from post-embryonic fossils representing 25 species throughout stem and crown arthropod lineages (as well as most of the 96 extant taxa), characters for metamorphosis were assigned based on inferred ecological changes in development (e.g., changes in habitat and adaptive landscape). Under all phylogenetic hypotheses, metamorphosis was supported as most likely ancestral to both ecdysozoans and euarthropods. Care must be taken to account for potential drastic post-embryonic morphological changes in evolutionary analyses. Many stem group euarthrpods may have had ecologically differentiated larval stages that did not preserve in the fossil record. Moreover, a complex life cycle and planktonic ecology may have evolved in the Ediacaran or earlier, and may have typified the pre-Cambrian explosion "wormworld" prior to the origin of crown group euarthropods. © The Author 2017. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology. All rights reserved. For permissions please email: journals.permissions@oup.com.

  19. Proterozoic structure, cambrian rifting, and younger faulting as revealed by a regional seismic reflection network in the Southern Illinois Basin

    Science.gov (United States)

    Potter, C.J.; Drahovzal, James A.; Sargent, M.L.; McBride, J.H.

    1997-01-01

    Four high-quality seismic reflection profiles through the southern Illinois Basin, totaling 245 km in length, provide an excellent regional subsurface stratigraphic and structural framework for evaluation of seismic risk, hydrocarbon occurrence, and other regional geologic studies. These data provide extensive subsurface information on the geometry of the intersection of the Cambrian Reelfoot and Rough Creek rifts, on extensive Proterozoic reflection sequences, and on structures (including the Fluorspar Area Fault Complex and Hicks Dome) that underlie a transitional area between the well-defined New Madrid seismic zone (to the southwest) and a more diffuse area of seismicity in the southern Illinois Basin. Our principal interpretations from these data are listed here in order of geologic age, from oldest to youngest: 1. Prominent Proterozoic layering, possibly equivalent to Proterozoic (???1 Ga) Middle Run Formation clastic strata and underlying (1.3-1.5 Ga) volcanic rocks of the East Continent rift basin, has been strongly deformed, probably as part of the Grenville foreland fold and thrust belt. 2. A well-defined angular unconformity is seen in many places between Proterozoic and Cambrian strata; a post-Grenville Proterozoic sequence is also apparent locally, directly beneath the base of the Cambrian. 3. We infer a major reversal in Cambrian rift polarity (accommodation zone) in the Rough Creek Graben in western Kentucky. 4. Seismic facies analysis suggests the presence of basin-floor fan complexes at and near the base of the Cambrian interval and within parts of a Proterozoic post-Grenville sequence in several parts of the Rough Creek Graben. 5. There is an abrupt pinchout of the Mount Simon Sandstone against crystalline basement beneath the Dale Dome (near the Texaco no. 1 Cuppy well, Hamilton County) in southeastern Illinois, and a more gradual Mount Simon pinchout to the southeast. 6. Where crossed by the seismic reflection line in southeast Illinois, some

  20. Paleomagnetic and magnetostratigraphic investigations of the whitehorse group/quartermaster (Dewey Lake) formation (upper permian-lowermost triassic) in the Palo Duro basin, northwest Texas, USA

    Science.gov (United States)

    Collins, Dylan R.

    In northwest Texas, upper Permian to lowermost Triassic hematite-cemented detrital sedimentary rocks, which include a small number of regionally extensive ash beds, were deposited during the time interval of the greatest mass extinction event sequences in Earth history. The magnetic polarity stratigraphy, as well as key rock magnetic properties, of the upper Whitehorse Group (WH) and Quartermaster formations (QM) at selected sections in the Palo Duro Basin, have been determined using thermal, and chemical demagnetization approaches and anisotropy of magnetic susceptibility, acquisition of isothermal remanent magnetization (IRM) and backfield demagnetization, and thermal demagnetization of three component IRM methods. Demagnetization results show that the WH/QM contains a primary/near-primary characteristic remanent magnetization at each level sampled and thus the magnetic polarity stratigraphy for each section can be compared with existing polarity time scales across the Permian-Triassic boundary. Estimated site mean directions yield a paleomagnetic pole for the latest Permian for North America of 57.8°N, 130.6°E from 38 sampled sites.

  1. Trace fossils accompanying possible "Ediacaran organisms" in the Middle Cambrian sediments of the St. Petersburg Region, Russia

    Czech Academy of Sciences Publication Activity Database

    Natalin, N. M.; Mikuláš, Radek; Dronov, A. V.

    2010-01-01

    Roč. 60, č. 1 (2010), s. 71-75+[2] ISSN 0001-5709 R&D Projects: GA ČR GA205/04/0151; GA ČR GA205/09/1521 Institutional research plan: CEZ:AV0Z30130516 Keywords : Skolithos ichnofacies * Edicarian-like organism * Middle Cambrian * shallow-marine * Baltic Shied * ichnology (Russia) Subject RIV: DB - Geology ; Mineralogy Impact factor: 0.779, year: 2010 https://geojournals.pgi.gov.pl/agp/article/view/9821/8355

  2. Hydrogeology of the Cambrian-Ordovician aquifer system in the northern Midwest: B in Regional aquifer-system analysis

    Science.gov (United States)

    Young, H.L.; Siegel, D.I.

    1992-01-01

    The Cambrian-Ordovician aquifer system contains the most extensive and continuous aquifers in the northern Midwest of the United States. It is the source of water for many municipalities, industries, and rural water users. Since the beginning of ground-water development from the aquifer system in the late 1800's, hydraulic heads have declined hundreds of feet in the heavily pumped Chicago-Milwaukee area and somewhat less in other metropolitan areas. The U.S. Geological Survey has completed a regional assessment of this aquifer system within a 161,000-square-mile area encompassing northern Illinois, northwestern Indiana, Iowa, southeastern Minnesota, northern Missouri, and Wisconsin.

  3. Detrital zircon U-Pb geochronology of Cambrian to Triassic miogeoclinal and eugeoclinal strata of Sonora, Mexico

    Science.gov (United States)

    Gehrels, G.E.; Stewart, John H.

    1998-01-01

    One hundred and eighty two individual detrital zircon grains from Cambrian through Permian miogeoclinal strata, Ordovician eugeoclinal rocks, and Triassic post-orogenic sediments in northwestern Sonora have been analyzed. During Cambrian, Devonian, Permian, and Triassic time, most zircons accumulating along this part of the Cordilleran margin were shed from 1.40-1.45 and 1.62-1.78 Ga igneous rocks that are widespread in the southwestern United States and northwestern Mexico. Zircons with ages of approximately 1.11 Ga are common in Cambrian strata and were apparently shed from granite bodies near the sample site. The sources of 225-280 Ma zircons in our Triassic sample are more problematic, as few igneous rocks of these ages are recognized in northwestern Mexico. Such sources may be present but unrecognized, or the grains could have been derived from igneous rocks of the appropriate ages to the northwest in the Mojave Desert region, to the east in Chihuahua and Coahuila, or to the south in accreted(?) arc-type terranes. Because the zircon grains in our Cambrian and Devonian to Triassic samples could have accumulated in proximity to basement rocks near their present position or in the Death Valley region of southern California, our data do not support or refute the existence of the Mojave-Sonora megashear. Ordovician strata of both miogeoclinal and eugeoclinal affinity are dominated by >1.77 Ga detrital zircons, which are considerably older than most basement rocks in the region. Zircon grains in the miogeoclinal sample were apparently derived from the Peace River arch area of northwestern Canada and transported southward by longshore currents. The eugeoclinal grains may also have come from the Peace River arch region, with southward transport by either sedimentary or tectonic processes, or they may have been shed from off-shelf slivers of continents (perhaps Antarctica?) removed from the Cordilleran margin during Neoproterozoic rifting. It is also possible that the

  4. High-Precision U-Pb Geochronology and Correlation: An example Using the Neoproterozic-Cambrian Transition

    Science.gov (United States)

    Bowring, S. A.; Grotzinger, J. P.; Amthor, J.; Martin, M. E.

    2001-05-01

    The precise, global correlation of Precambrian and Paleozoic sedimentary rocks can be achieved using temporally calibrated chemostratigraphic records. This approach is essential for determining rates and causes of environmental and faunal change, including mass extinctions. For example, The Neoproterozoic is marked by major environmental change, including periods of global glaciation, large fluctuations in the sequestration of carbon and major tectonic reorganization followed by the explosive diversification of animals in the earliest Cambrian. The extreme climatic change associated with these glaciations have been implicated as a possible trigger for the Cambrian explosion. The recognition of thin zircon-bearing air-fall ash in Neoproterozoic and Cambrian rocks has allowed the establishment of a high-precision temporal framework for animal evolution and is helping to untangle the history of glaciations. In some cases analytical uncertainties translate to age uncertainties of less than 1 Ma and when integrated with chemostratigraphy, the potential for global correlations at even higher resolution. Progress in the global correlation of Neoproterozoic strata has been achieved through the use of C and Sr isotope chemostratigraphy although it has been hampered by a lack of precise geochronological and faunal control. For example, the period from ca 800-580 Ma is characterized by at least two and perhaps as many as four glacial events that are interpreted by many to be global glaciations on a "Snowball Earth". A lack of precise chronological constraints on the number and duration of glaciations, multiple large excursions in the carbon isotopic record, and an absence of detailed biostratigraphy have complicated global correlation and hindered our understanding of this important period of Earth history. However, the ongoing integration of chemostratigraphic and geochronological data are improving temporal resolution and detailed correlations. These data are critical for

  5. Diachronism in the late Neoproterozoic-Cambrian arc-rift transition of North Gondwana: A comparison of Morocco and the Iberian Ossa-Morena Zone

    Science.gov (United States)

    Álvaro, J. Javier; Bellido, Félix; Gasquet, Dominique; Pereira, M. Francisco; Quesada, Cecilio; Sánchez-García, Teresa

    2014-10-01

    In the northwestern border of the West African craton (North Gondwana), a transition from late Neoproterozoic subduction/collision to Cambrian rift processes was recorded in the Anti-Atlas (Morocco) and in the Ossa-Morena Zone (Iberia). Cambrian rifting affected both Pan-African and Cadomian basements in a stepwise and diachronous way. Subsequently, both areas evolved into a syn-rift margin episodically punctuated by uplift and tilting that precluded Furongian sedimentation. A comparison of sedimentary, volcanic and geodynamic evolution is made in the late Neoproterozoic (Pan-African and Cadomian) belts and Cambrian rifts trying to solve the apparent diachronous (SW-NE-trending) propagation of an early Palaeozoic rifting regime that finally led to the opening of the Rheic Ocean.

  6. The strata and palaeo-geomorphology framework at the end of neoproterozoic and development mode of source rocks at the beginning of Cambrian in Tarim Basin, China

    Directory of Open Access Journals (Sweden)

    Xin Yang

    2017-12-01

    Full Text Available Referred to the new recognition from petroleum exploration of the Sinian to Cambrian in South China, it could be considered that the distribution of the early Cambrian source rocks was controlled by the palaeo-geomorphology at the end of Neoproterozoic in the Tarim Basin. Based on the zircon U-Pb dating of pyroclastic rock samples from the clastic rock stratum under the bottom of Cambrian carbonate rocks, the stratigraphic correlation of the Sinian to Cambrian was conducted to build the palaeo-geomorphology framework at the end of Neoproterozoic in Tarim Basin. Lastly, according to the development mode of source rocks at the beginning of Cambrian, the distribution of source rocks was predicted initially through the division of seismic facies. The youngest zircon concordia age of pyroclastic rocks from the bottom of well Tong 1 is 707±8Ma. It was revealed by the strata framework of the Sinian to Cambrian, the palaeo-geomorphology at the end of Neoproterozoic in Tarim Basin was characterized by an uplift highland in Bachu-Tazhong area, the south north high-low, and the west is higher than the east. The distribution of source rocks in the bottom of the Cambrian on the palaeo-platform and slopes was coincident with the Upper Sinian dolomite basically. But the contemporaneous sediment happened to be absent or changed in sedimentary facies on the uplift and its edges. From the seismic facies of the strata under the bottom of Cambrian, it could be concluded that source rocks in the type of the Xishanbraque Group (∈1xs was limited in the Manjiaer Depression, while the source rocks in the type of the Yuertusi Group (∈1y are widely distributed in south of Tabei Uplift, east Awat Depression, and even the Maigt Slope. However, among the west Awat Depression and western Tanguzibasi Depression, and the middle area of the Bachu-Tazhong Uplifts, the contemporaneous source rocks may have changed into sedimentary facies of tidal flat and lagoon, instead of

  7. A comparative assessment of the role of anoxia during the Cambrian SPICE event

    Science.gov (United States)

    LeRoy, M.; Gill, B. C.; Sperling, E. A.

    2017-12-01

    The Cambrian SPICE (Steptoean Positive Carbon Isotope Excursion) is recognized as a major oceanographic event recorded in globally-distributed stratigraphic sections as positive isotopic excursions in marine carbonates (δ13Ccarb), organic matter (δ13Corg), sulfate (δ34SCAS) and pyrite (δ34Spy). A proposed mechanism for these observed isotopic trends is that a transient increase in the areal extent of anoxic conditions within the oceans fostered enhanced burial of organic carbon and pyrite. However, direct sedimentary (e.g., abundant black shale) and geochemical (e.g., redox proxy) evidence for such a shift is scant. While the antiquity of this event is likely responsible for loss of much of this evidence, through destruction by tectonic processes, a number of stratigraphic successions suitable for investigating this hypothesis exist. Here we explore the relationship between anoxia and the SPICE using previously published and novel data generated from core material from three sedimentary basins distributed along the margins of the Iapetus Ocean. The units studied are: the Nolichucky Formation of eastern Laurentia, the Alum Shale of Baltica, and the Outwoods Shale of Avalonia. Our iron speciation data indicate consistently oxic conditions prior to the SPICE along Laurentia, while Avalonia was oxic with intervals of anoxia, and Baltica was persistently anoxic. With the initiation of the SPICE, anoxic conditions intensified in Laurentia and Avalonia and continued to persist in Baltica. This redox shift was coupled with a sharp rise in δ34Spy at all three locations. Average total organic carbon (TOC) showed little change in relation to the SPICE at the Laurentia location ( 0.15 wt%), but showed an increase in conjunction with the excursion in both the Avalonia ( 1 to 1.5 wt%) and Baltica ( 8 to 12 wt%) sections. Large differences in nutrient availability and sedimentation rates are likely responsible for the between-site disparity in TOC, while overall, anoxia

  8. X-ray tomographic microscopy tightens affinity of the early Cambrian Oymurania to the brachiopod stem group

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    Artem Kouchinsky

    2017-03-01

    Full Text Available The geologically rapid biotic evolution in the early Cambrian is marked by the first appearance of major groups of animals in the fossil record (e.g., Budd and Jensen 2000; Kouchinsky et al. 2012. Along with the earliest crown-group representatives of the phylum Brachiopoda, more basal branches of the phylogenetic tree belonging to the stem-group Brachiopoda, such as tannuolinids and mikwitziids, diversified and became widespread during the early Cambrian (e.g., Williams and Holmer 2002; Balthasar et al. 2009; Skovsted et al. 2014. Synchrotron-radiation X-ray tomographic microscopy (SRXTM of Oymurania gravestocki reveals the microstructure of its calcium-phosphatic shell differentiated into two layers and intersecting systems of canals. The outer layer shows the acrotretoid columnar microstructure and the inner layer consists of continuous prismatic columns. Phosphatized setae preserved within tangential canals, as well as perpendicular canals of Micrina–Setatella type demonstrate homology with the tannuolinid Micrina and the mickwitziid Setatella. A unique and novel combination of microstructural features in Oymurania confirms its evolutionary position within the brachiopod stem group.

  9. Disc-shaped fossils resembling porpitids or eldonids from the early Cambrian (Series 2: Stage 4 of western USA

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    Bruce S. Lieberman

    2017-06-01

    Full Text Available The morphology and affinities of newly discovered disc-shaped, soft-bodied fossils from the early Cambrian (Series 2: Stage 4, Dyeran Carrara Formation are discussed. These specimens show some similarity to the Ordovician Discophyllum Hall, 1847; traditionally this taxon had been treated as a fossil porpitid. However, recently it has instead been referred to as another clade, the eldonids, which includes the enigmatic Eldonia Walcott, 1911 that was originally described from the Cambrian Burgess Shale. The status of various Proterozoic and Phanerozoic taxa previously referred to porpitids and eldonids is also briefly considered. To help ascertain that the specimens were not dubio- or pseudofossils, elemental mapping using energy dispersive X-ray spectroscopy (EDS was conducted. This, in conjunction with the morphology of the specimens, indicated that the fossils were not hematite, iron sulfide, pyrolusite, or other abiologic mineral precipitates. Instead, their status as biologic structures and thus actual fossils is supported. Enrichment in the element carbon, and also possibly to some extent the elements magnesium and iron, seems to be playing some role in the preservation process.

  10. Redox history of the Three Gorges region during the Ediacaran and Early Cambrian as indicated by the Fe isotope

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    Yusuke Sawaki

    2018-01-01

    To circumvent this deficiency, we drilled a fossiliferous Ediacaran to Early Cambrian sedimentary succession in the Three Gorges region, South China. We analyzed the iron isotope ratios (δ56/54Fe of pyrite grains in the drill cores using laser ablation multi collector inductively coupled plasma mass spectrometry. The results demonstrate large variations in δ56/54Fe, from −1.6 to 1.6‰, and positive iron isotope ratios are observed in many successions. The presence of positive δ56/54Fe in pyrite indicates that the ferrous iron in the seawater was partially oxidized, suggesting that seawater at Three Gorges was ferruginous during the Ediacaran and Early Cambrian periods. However, aggregated pyrite grains in organic carbon-rich black shales at Member 4 of the Doushantuo Formation and the base of the Shuijingtuo Formation yield near-zero δ56/54Fe values; this suggests that the ocean was transiently dominated by sulfidic conditions during these periods. Notably negative δ56/54Fe values, lower than −1‰, can be interpreted as a signature of DIR. The DIR also might contribute in part to the re-mineralization of organic matter during the largest negative carbon isotope anomaly in the Ediacaran.

  11. Oxygen-isotope trends and seawater temperature changes across the Late Cambrian Steptoean positive carbon-isotope excursion (SPICE event)

    Science.gov (United States)

    Elrick, M.; Rieboldt, S.; Saltzman, M.; McKay, R.M.

    2011-01-01

    The globally recognized Late Cambrian Steptoean positive C-isotope excursion (SPICE) is characterized by a 3???-5??? positive ??13C shift spanning SPICE represents a widespread ocean anoxic event leading to enhanced burial/preservation of organic matter (Corg) and pyrite. We analyzed ??18O values of apatitic inarticulate brachiopods from three Upper Cambrian successions across Laurentia to evaluate paleotemperatures during the SPICE. ??18O values range from ~12.5??? to 16.5???. Estimated seawater temperatures associated with the SPICE are unreasonably warm, suggesting that the brachiopod ??18O values were altered during early diagenesis. Despite this, all three localities show similar trends with respect to the SPICE ??13C curve, suggesting that the brachiopod apatite preserves a record of relative ??18O and temperature changes. The trends include relatively high ??18O values at the onset of the SPICE, decreasing and lowest values during the main event, and an increase in values at the end of the event. The higher ??18O values during the global extinction at the onset of the SPICE suggests seawater cooling and supports earlier hypotheses of upwelling of cool waters onto the shallow shelf. Decreasing and low ??18O values coincident with the rising limb of the SPICE support the hypothesis that seawater warming and associated reduced thermohaline circulation rates contributed to decreased dissolved O2 concentrations, which enhanced the preservation/burial of Corg causing the positive ??13C shift. ?? 2011 Geological Society of America.

  12. Three-dimensionally preserved minute larva of a great-appendage arthropod from the early Cambrian Chengjiang biota

    Science.gov (United States)

    Liu, Yu; Melzer, Roland R.; Haug, Joachim T.; Haug, Carolin; Briggs, Derek E. G.; Hörnig, Marie K.; He, Yu-yang; Hou, Xian-guang

    2016-05-01

    A three-dimensionally preserved 2-mm-long larva of the arthropod Leanchoilia illecebrosa from the 520-million-year-old early Cambrian Chengjiang biota of China represents the first evidence, to our knowledge, of such an early developmental stage in a short-great-appendage (SGA) arthropod. The larva possesses a pair of three-fingered great appendages, a hypostome, and four pairs of well-developed biramous appendages. More posteriorly, a series of rudimentary limb Anlagen revealed by X-ray microcomputed tomography shows a gradient of decreasing differentiation toward the rear. This, and postembryonic segment addition at the putative growth zone, are features of late-stage metanauplii of eucrustaceans. L. illecebrosa and other SGA arthropods, however, are considered representative of early chelicerates or part of the stem lineage of all euarthropods. The larva of an early Cambrian SGA arthropod with a small number of anterior segments and their respective appendages suggests that posthatching segment addition occurred in the ancestor of Euarthropoda.

  13. In situ ∼2.0 Ma trees discovered as fossil rooted stumps, lowermost Bed I, Olduvai Gorge, Tanzania.

    Science.gov (United States)

    Habermann, Jörg M; Stanistreet, Ian G; Stollhofen, Harald; Albert, Rosa M; Bamford, Marion K; Pante, Michael C; Njau, Jackson K; Masao, Fidelis T

    2016-01-01

    The discovery of fossil rooted tree stumps in lowermost Lower Bed I from the western Olduvai Basin, Tanzania, age-bracketed by the Naabi Ignimbrite (2.038 ± 0.005 Ma) and Tuff IA (1.88 ± 0.05 Ma), provides the first direct, in situ, and to date oldest evidence of living trees at Olduvai Gorge. The tree relicts occur in an interval dominated by low-viscosity mass flow and braided fluvial sediments, deposited at the toe of a largely Ngorongoro Volcano-sourced volcaniclastic fan apron that comprised a widely spaced network of ephemeral braided streams draining northward into the Olduvai Basin. Preservation of the trees occurred through their engulfment by mass flows, post-mortem mold formation resulting from differential decay of woody tissues, and subsequent fluvially-related sediment infill, calcite precipitation, and cast formation. Rhizolith preservation was triggered by the interaction of root-induced organic and inorganic processes to form rhizocretionary calcareous root casts. Phytolith analyses were carried out to complete the paleoenvironmental reconstruction. They imply a pronounced seasonality and indicate a wooded landscape with grasses, shrubs, and sedges growing nearby, comparable to the low, open riverine woodland (unit 4c) along the Garusi River and tributaries in the Laetoli area. Among the tree stump cluster were found outsized lithic clasts and those consisting of quartzite were identified as Oldowan stone tool artifacts. In the context of hominin activity, the identification of wooded grassland in association with nearby freshwater drainages and Oldowan artifacts significantly extends our paleoenvironmental purview on the basal parts of Lower Bed I, and highlights the hitherto underrated role of the yet poorly explored western Olduvai Gorge area as a potential ecologically attractive setting and habitat for early hominins. Copyright © 2015 Elsevier Ltd. All rights reserved.

  14. Sedimentary evolution of the Mesozoic continental redbeds using geochemical and mineralogical tools: the case of Upper Triassic to Lowermost Jurassic Monte di Gioiosa mudrocks (Sicily, southern Italy)

    Science.gov (United States)

    Perri, Francesco; Critelli, Salvatore; Mongelli, Giovanni; Cullers, Robert L.

    2011-10-01

    The continental redbeds from the Internal Domains of the central-western Mediterranean Chains have an important role in the palaeogeographic and palaeotectonic reconstructions of the Alpine circum-Mediterranean orogen evolution since these redbeds mark the Triassic-Jurassic rift-valley stage of Tethyan rifting. The composition and the sedimentary evolution of the Middle Triassic to Lowermost Jurassic continental redbeds of the San Marco d'Alunzio Unit (Peloritani Mountains, Southern Italy), based on mineralogical and chemical analyses, suggests that the studied mudrock sediments share common features with continental redbeds that constitute the Internal Domains of the Alpine Mediterranean Chains. Phyllosilicates are the main components in the mudrocks. The 10 Å-minerals (illite and micas), the I-S mixed layers, and kaolinite are the most abundant phyllosilicates. The amount of illitic layers in I-S mixed layers coupled with the illite crystallinity values (IC) are typical of high degree of diagenesis, corresponding to a lithostatic/tectonic loading of about 4-5 km. The mineralogical assemblage coupled with the A-CN-K plot suggest post-depositional K-enrichments. Palaeoweathering proxies (PIA and CIW) record intense weathering at the source area. Further, the studied sediments are affected by reworking and recycling processes and, as consequence, it is likely these proxies monitor cumulative effect of weathering. The climate in the early Jurassic favoured recycling and weathering occurred under hot, episodically humid climate with a prolonged dry season. The source-area is the low-grade Paleozoic metasedimentary basement. Mafic supply is minor but not negligible as suggested by provenance proxies.

  15. The Sirius Passet Lagerstätte: silica death masking opens the window on the earliest mat ground community of the Cambrian Explosion

    NARCIS (Netherlands)

    Strang, Katie M; Armstrong, Howard; Harper, David A. T.; Trabucho-Alexandre, João

    2016-01-01

    The Sirius Passet Lagerstätte (SP), Peary Land, North Greenland, occurs in black slates deposited at or just below storm wave base. It represents the earliest Cambrian microbial mat community with exceptional preservation, predating the Burgess Shale by 10 million years. Trilobites from the SP are

  16. Composition and origin of Early Cambrian Tiantaishan phosphorite-Mn carbonate ores, Shaanxi Province, China

    Science.gov (United States)

    Hein, J.R.; Fan, D.; Ye, J.; Liu, T.; Yeh, H.-W.

    1999-01-01

    The Tiantaishan phosphorite-Mn carbonate ores occur in the Early Cambrian Tananpo Formation in complexly folded and faulted rocks located in southern Shaanxi Province. About 65 x 106 tonnes of 17% P2O5 ore reserves exist and Mn-ore reserves are about 8.3 x 106 tonnes of +18% Mn. The stratigraphic sequence in ascending order consists of black phyllite, black to gray phosphorite ore, black phyllite, rhodochrostone ore, Mn mixed-carbonates, and dolostone. Data are presented from microprobe mineral chemistry, whole-rock chemistry, stable isotopes of carbonates, X-ray mineralogy, petrographic and SEM observations, and statistical analysis of chemical data. The dominant ore-forming minerals are hydroxy- and carbonate fluorapatite and Ca rhodochrosite, with Mg kutnahorite and dolomite comprising the Mn mixed-carbonate section. Pyrite occurs in all rock types and alabandite (MnS) occurs throughout the rhodochrostone section. The mean P2O5 content of phosphorite is 31% and argillaceous phosphorite is 16%, while the mean MnO content of rhodochrostone ore is 37%. Phosphorite ores are massive, spheroidal, laminated, and banded, while rhodochrostone ores have oolitic, spheroidal, and granular fabrics. The most distinguishing characteristics of the ores are high total organic carbon (TOC) contents (mean 8.4%) in the phosphorite and high P2O5 contents (mean 2.7%) in the rhodochrostone ore. The atypically high TOC contents in the Tiantaishan phosphorite probably result from very strong productivity leading to high sedimentation rates accompanied by weak reworking of sediments; poor utilization of the organic matter by bacteria; and/or partial replacement of bacterial or algal mats by the apatite. The depositional setting of the ores was the margin of an epicontinental seaway created as a direct consequence of global processes that included break-up of a supercontinent, formation of narrow seaways, creation of extensive continental shelves, overturn of stagnant, metal-rich deep

  17. Assessment of Suspended Sand Availability under Different Flow Conditions of the Lowermost Mississippi River at Tarbert Landing during 1973–2013

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    Sanjeev Joshi

    2015-12-01

    Full Text Available Rapid land loss in the Mississippi River Delta Plain has led to intensive efforts by state and federal agencies for finding solutions in coastal land restoration in the past decade. One of the proposed solutions includes diversion of the Mississippi River water into drowning wetland areas. Although a few recent studies have investigated flow-sediment relationships in the Lowermost Mississippi River (LmMR, defined as the 500 km reach from the Old River Control Structure to the river’s Gulf outlet, it is unclear how individual sediment fractions behave under varying flow conditions of the river. The information can be especially pertinent because the quantity of coarse sands plays a critical role for the Mississippi-Atchafalaya River deltaic development. In this study, we utilized long-term (1973–2013 records on discharge and sediments at Tarbert Landing of the LmMR to assess sand behavior and availability under different river flow regimes, and extreme sand transport events and their recurrence. We found an average annual sand load (SL of 27.2 megatonnes (MT during 1973 and 2013, varying largely from 3.37 to 52.30 MT. For the entire 41-year study period, a total of approximately 1115 MT sand were discharged at Tarbert Landing, half of which occurred during the peak 20% flow events. A combination of intermediate, high and peak flow stages (i.e., river discharge was ≥18,000 cubic meter per second produced about 71% of the total annual SL within approximately 120 days of a year. Based on the long-term sediment assessment, we predict that the LmMR has a high likelihood to transport 4 to 446 thousand tonnes of sand every day over the next 40 years, during which annual sand loads could reach a maximum of 51.68 MT. Currently, no effective plan is in place to utilize this considerably high sand quantity and we suggest that river engineering and sediment management in the LmMR consider practices of hydrograph-based approach for maximally capturing

  18. Properties of inertia-gravity waves in the lowermost stratosphere as observed by the PANSY radar over Syowa Station in the Antarctic

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    M. Mihalikova

    2016-05-01

    Full Text Available Inertia-gravity waves (IGWs are an important component for the dynamics of the middle atmosphere. However, observational studies needed to constrain their forcing are still insufficient especially in the remote areas of the Antarctic region. One year of observational data (January to December 2013 by the PANSY radar of the wind components (vertical resolution of 150 m and temporal resolution of 30 min are used to derive statistical analysis of the properties of IGWs with short vertical wavelengths ( ≤ 4 km and ground-based periods longer than 4 h in the lowermost stratosphere (height range 10 to 12 km with the help of the hodograph method. The annual change of the IGWs parameters are inspected but no pronounced year cycle is found. The year is divided into two seasons (summer and winter based on the most prominent difference in the ratio of Coriolis parameter (f to intrinsic frequency (ω^ distribution. Average of f∕ω^  for the winter season is 0.40 and for the summer season 0.45 and the average horizontal wavelengths are 140 and 160 km respectively. Vertical wavelengths have an average of 1.85 km through the year. For both seasons the properties of IGWs with upward and downward propagation of the energy are also derived and compared. The percentage of downward propagating waves is 10.7 and 18.4 % in the summer and winter season respectively. This seasonal change is more than the one previously reported in the studies from mid-latitudes and model-based studies. It is in agreement with the findings of past radiosonde data-based studies from the Antarctic region. In addition, using the so-called dual-beam technique, vertical momentum flux and the variance of the horizontal perturbation velocities of IGWs are examined. Tropospheric disturbances of synoptic-scale are suggested as a source of episodes of IGWs with large variance of horizontal perturbation velocities, and this is shown in a number of cases.

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

    DEFF Research Database (Denmark)

    Zhou, Lingli; Friis, Henrik; Yang, Tian

    2017-01-01

    show a depletion of major elements in the following order: Na N Ca N Mg N 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...... but lost most of the plagioclase. The LSF has a comparable weathering history (CIA = 63–73), but the plagioclase is better preserved (PIA = 65–78). The significant variation of weathering rates of plagioclase and K-feldspar in the basement granite and the provenance of sandstone from the Borggård borehole...... are likely due to the different permeability developed within the internal crystal structures, a Ca- rich plagioclase original composition of the plagioclase, and the occurrence of weathering in a very humid climate. K metasomatism occurred in the basement granite and sandstone in both the Borggård and the G...

  20. Extensional tectonics and sedimentary response of the Early–Middle Cambrian passive continental margin, Tarim Basin, Northwest China

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    Zhiqian Gao

    2012-09-01

    Full Text Available The fact that several half-grabens and normal faults developed in the Lower–Middle Cambrian of Tazhong (central Tarim Basin and Bachu areas in Tarim Basin, northwest China, indicates that Tarim Basin was under extensional tectonic setting at this time. The half-grabens occur within a linear zone and the normal faults are arranged in en echelon patterns with gradually increasing displacement eastward. Extensional tectonics resulted in the formation of a passive continental margin in the southwest and a cratonic margin depression in the east, and most importantly, influenced the development of a three-pronged rift in the northeast margin of the Tarim Basin. The fault system controlled the development of platform – slope – bathyal facies sedimentation of mainly limestone-dolomite-gypsum rock-saline rock-red beds in the half-grabens. The NW-SE trending half-grabens reflect the distribution of buried basement faults.

  1. Late Ediacaran-Cambrian structures and their reactivation during the Variscan and Alpine cycles in the Anti-Atlas (Morocco)

    Science.gov (United States)

    Soulaimani, A.; Michard, A.; Ouanaimi, H.; Baidder, L.; Raddi, Y.; Saddiqi, O.; Rjimati, E. C.

    2014-10-01

    The post-Pan-African evolution of the northern border of the West African Craton is largely controlled by the remobilisation of Late Neoproterozoic basement faults. The Upper Ediacaran volcanic and volcano-sedimentary sequences of the Ouarzazate Group show dramatic and rapid thickness changes, consistent with active extensional faulting associated with post-orogenic collapse and incipient continental rifting. The geometry and kinematics of these faults differ from west to east in the Anti-Atlas. N- to NE-trending faults dominate in western Anti-Atlas in response to E-W to NW-SE pure extension, while a transtensive opening regime characterize the central (Bou Azzer) and eastern (Saghro-Ougnate) Anti-Atlas. The marine incursion in the west-central Anti-Atlas during the late Ediacaran-Early Cambrian occurred without major geodynamical break between the continental Ouarzazate Group and marine sediments of the Adoudou Fm. Extensional tectonics went on during the Early Cambrian, being concentrated in the western and central parts of the belt. From Middle Cambrian to Lower Devonian and mainly due to thermal subsidence, the Anti-Atlas basement was buried under marine sediments with dominant south-derived detrital input. Basement faults control the distribution of subsiding versus shallow areas. During the Middle-Late Devonian, the dislocation of the Saharan platform occurred, mainly in the eastern Anti-Atlas where Precambrian faults were also remobilized during the Early Carboniferous. During the Variscan orogeny, the Paleozoic series of the Anti-Atlas basin were involved in folding tectonics, concomitant with the uplift of Proterozoic basement blocks bounded by inherited basement faults. The pre-existing rift-related faults were variably inverted across the Anti-Atlas. In the westernmost part of the belt, Variscan shortening induced positive inversions along the remobilized basement faults, but in some cases, some faults preserved an apparently normal throw. Some hidden

  2. Lower Cambrian-Ediacaran Paleogeography and True Polar Wander with New Paleomagnetic Constraints from West African Craton

    Science.gov (United States)

    Robert, B.; Besse, J.; Blein, O.; Greff-Lefftz, M.; Baudin, T.; Fernando, L.; Meslouh, S.; Belbadaoui, M.

    2014-12-01

    Paleomagnetic data from Laurentia and Baltica continents suggest fast large oscillations of the virtual geomagnetic poles (VGP) from high to low latitudes during the Ediacaran (635-542 Ma). These data are interpreted in the literature either as oscillations of the Earth magnetic dipole between polar and equatorial positions, or as True Polar Wander (TPW), implying a very fast tumbling of continents and perhaps, of whole Earth. In this study, we try to test these hypotheses by bringing new paleomagnetic data on volcanic series from another continent, the West African Craton (WAC). We have sampled well dated pyroclastic and lava flows from the Ouarzazate and Taroudant groups in the Anti-Atlas, (Morocco). 480 samples from 105 sites were thermally demagnetized in our laboratory. Our preliminary results highlight two major groups of directions, mainly carried by hematite, magnetite also contributing sometimes to the magnetization. The first group consists of a dual polarity high inclination direction that may represent the original magnetization. The observed paleolatitude is compatible with that predicted by the lower Cambrian-Ediacaran apparent polar wander path (APWP) of Gondwana, assuming that the WAC was already accreted to Gondwana at this age. Nevertheless, a complete agreement between our pole and the APWP needs a local rotation of around 80° on a vertical axis. The second group displays a single polarity direction, with a shallow inclination and a south-east declination. This direction is close to the expected direction derived from the Permo-Carboniferous segment of the Gondwana APWP, and may represent a remagnetization acquired during the Kiaman reversed polarity superchron. Our preliminary paleomagnetic results thus display large changes in the VGP position, as also evidenced by others on Baltica and Laurentia. However, their interpretation does not favor TPW episodes or equatorial Earth magnetic dipole during the lower Cambrian-Ediacaran periods, but

  3. The sedimentary facies characteristics and lithofacies palaeogeography during Middle-Late Cambrian, Sichuan Basin and adjacent area

    Directory of Open Access Journals (Sweden)

    Feifan Lu

    2017-06-01

    Full Text Available Combined with the regional strata filling characteristics of Middle-Upper Cambrian, the present paper conducts a systematic research on sedimentary facies in the basin and its peripheral area by utilizing 164 field outcrops and drilling and coring data. Further, the method of “multi-factor comprehensive synthesis based on single-factor analysis” was employed to investigate the sedimentary facies and palaeogeography of the study area and establish the sedimentary facies model. Stratigraphic reveals that the study area represents the pattern of thin-northwest and thick-southeast by stretching northeast-southwest. Within the present basin, the pattern of “one thin and two thick” predominates, while outside the basin “four thin and three thick” filling feature was found. Sedimentary facies shows that the study area was featured by rimmed carbonate platform. Specifically, carbonate platform, slope and northeastern corner Qinling paleooceanic Basin and southeastern corner Jiangnan Bain was identified from the west to the east. The carbonate platform contains restricted platform, evaporation-restricted platform, semi-restricted platform and the platform margin. Single factor analysis and lithofacies palaeogeographic characteristics manifests that during Middle-Late Cambrian, the western Old land evolved into peneplain stage, and that the eastern and southwestern sub-sags remained connected to the open-sea to some extent. At the time, the shllow seawater circulation was relatively restricted, while the ancient seabed tended to be flat and evaporation characteristics significantly diminished. Secondary sea-level fluctuation intensively influenced the development of scaled grain beach. It is suggested that tide marginal beach, intraplatform shoal subfacies zone, along with Shiqian-SangZhi in southeast and Zhenba-Xinshan in northeast platform-margin beach subfacies zone to be preferable targets for the favorable reservoir facies zone and

  4. Morphology and ultrastructure of epilithic versus cryptic, microbial growth in lower Cambrian phosphorites from the Montagne Noire, France.

    Science.gov (United States)

    Alvaro, J J; Clausen, S

    2010-03-01

    The lower Cambrian grainy phosphorites of the northern Montagne Noire occur interbedded with grey to black, laminated to massive shales and limestones deposited along the edge of a continental shelf, associated with slope-related facies and unstable substrates. The concentration of phosphate took place by repeated alternations of low sedimentation rates and condensation (hardgrounds), in situ early-diagenetic precipitation of fluorapatite, winnowing and polyphase reworking of previously phosphatized skeletons and hardground-derived clasts. The succession of repeated cycles of sedimentation, phosphate concentration, and reworking led to multi-event phosphate deposits rich in allochthonous particles. Phosphogenesis was primarily mediated by microbial activity, which is evidenced by the abundance of phosphatized putative microbial remains. These occur as smooth and segmented filaments, sheaths, and ovoid-shaped coccoids. These simple morphologies commonly form composite frameworks as a result of their aggregation and entanglement, leading to the record of biofilms, microbial mats, and complex networks. These infested the calcitic skeletonized microfossils that littered the substrate. Microbial activity evidences epilithic (anisotropic coatings on skeletons), euendolithic (perforating skeletal walls), and cryptoendolithic (lining inter- and intraparticulate pores) strategies, the latter dominated by bundles of filaments and globular clusters that grew along the cavities of helcionellids and hyoliths. According to their epilithic versus cryptic strategies, microbial populations that penetrated and dwelled inside hard skeletal substrates show different network and colonial morphologies. These early Cambrian shell concentrations were the loci of a stepwise colonization made by saprophytic to mutualistic, cyanobacterial-fungal consortia. Their euendolithic and cryptoendolithic ecological niches provided microbial refugia to manage the grazing impact mainly led by metazoans.

  5. Summer to Winter Diurnal Variabilities of Temperature and Water Vapour in the Lowermost Troposphere as Observed by HAMSTRAD over Dome C, Antarctica

    Science.gov (United States)

    Ricaud, P.; Genthon, C.; Durand, P.; Attié, J.-L.; Carminati, F.; Canut, G.; Vanacker, J.-F.; Moggio, L.; Courcoux, Y.; Pellegrini, A.; Rose, T.

    2012-04-01

    The HAMSTRAD (H2O Antarctica Microwave Stratospheric and Tropospheric Radiometers) microwave radiometer operating at 60 GHz (oxygen line, thus temperature) and 183 GHz (water vapour line) has been permanently deployed at the Dome C station, Concordia, Antarctica [75°06'S, 123°21'E, 3,233 m above mean sea level] in January 2010 to study long-term trends in tropospheric absolute humidity and temperature. The great sensitivity of the instrument in the lowermost troposphere helped to characterize the diurnal cycle of temperature and H2O from the austral summer (January 2010) to the winter (June 2010) seasons from heights of 10 to 200 m in the planetary boundary layer (PBL). The study has characterized the vertical resolution of the HAMSTRAD measurements: 10-20 m for temperature and 25-50 m for H2O. A strong diurnal cycle in temperature and H2O (although noisier) has been measured in summertime at 10 m, decreasing in amplitude with height, and phase-shifted by about 4 h above 50 m with a strong H2O-temperature correlation (>0.8) throughout the entire PBL. In autumn, whilst the diurnal cycle in temperature and H2O is less intense, a 12-h phase shift is observed above 30 m. In wintertime, a weak diurnal signal measured between 10 to 200 m is attributed to the methodology employed, which consists of monthly averaged data, and that combines air masses from different origins (sampling effect) and not to the imprint of the null solar irradiation. In situ sensors scanning the entire 24-h period, radiosondes launched at 2000 local solar time (LST) and European Centre for Medium-Range Weather Forecasts (ECMWF) analyses at 0200, 0800, 1400 and 2000 LST agree very well with the HAMSTRAD diurnal cycles for temperature and relatively well for absolute humidity. For temperature, HAMSTRAD tends to be consistent with all the other datasets but shows a smoother vertical profile from 10 to 100 m compared to radiosondes and in-situ data, with ECMWF profiles even smoother than HAMSTRAD

  6. Precambrian-Cambrian boundary in the Tal formation of Garhwal Lesser Himalaya : Rb-Sr age evidence from black shales underlying phosphorites

    International Nuclear Information System (INIS)

    Sharma, K.K.; Rameshwar Rao, D.; Azmi, R.J.; Gopalan, K.; Pantulu, G.V.C.

    1991-01-01

    The recently reported faunal evidence for placing the Precambrian-Cambrian boundary within the main phosphorite unit of the Chert-Phosphorite Member of the Tal Formation, Garhwal Lesser Himalaya, is supported by the present report of 626 ± 13 myr for the whole-rock Rb-Sr isochron age of the black shales directly underlying the phosphorite band. (author). 15 refs., 2 figs., 1 tab

  7. Water-quality assessment of the Cambrian-Ordovician aquifer system in the northern Midwest, United States

    Science.gov (United States)

    Wilson, John T.

    2012-01-01

    This report provides a regional assessment of groundwater quality of the Cambrian-Ordovician aquifer system, based primarily on raw water samples collected by the NAWQA Program during 1995 through 2007. The NAWQA Program has published findings in local study-unit reports encompassing parts of the Cambrian-Ordovician aquifer system. Data collected from the aquifer system were used in national synthesis reports on selected topics such as specific water-quality constituent classes, well type, or aquifer material; however, a synthesis of groundwater quality at the principal aquifer scale has not been completed and is therefore the major purpose of this report. Water samples collected by the NAWQA Program were analyzed for various classes of characteristics including physical properties, major ions, trace elements, nutrients and dissolved organic carbon, radionuclides (tritium, radon, and radium), pesticides, and volatile organic compounds. Subsequent sections of this report provide discussions on these classes of characteristics. The assessment objectives of this report are to (1) summarize constituent concentrations and compare them to human-health benchmarks and non-health guidelines; (2) determine the geographic distribution of constituent concentrations and relate them to various factors such as confining conditions, well type, land use, and groundwater age; and (3) evaluate near-decadal-scale changes in nitrate concentrations and pesticide detections. The most recent sample collected from each well by the NAWQA Program was used for most analyses. Near-decadal-scale changes in nitrate concentrations and pesticide detections were evaluated for selected well networks by using the most recent sample from each well and comparing it to the results from a sample collected 7 or 11 years earlier. Because some of the NAWQA well networks provide a limited areal coverage of the aquifer system, data for raw water samples from other USGS sources and state agencies were included

  8. Morphology and function in the Cambrian Burgess Shale megacheiran arthropod Leanchoilia superlata and the application of a descriptive matrix

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    Haug Joachim T

    2012-08-01

    Full Text Available Abstract Background Leanchoilia superlata is one of the best known arthropods from the middle Cambrian Burgess Shale of British Columbia. Here we re-describe the morphology of L. superlata and discuss its possible autecology. The re-description follows a standardized scheme, the descriptive matrix approach, designed to provide a template for descriptions of other megacheiran species. Results Our findings differ in several respects from previous interpretations. Examples include a more slender body; a possible hypostome; a small specialised second appendage, bringing the number of pairs of head appendages to four; a further sub-division of the great appendage, making it more similar to that of other megacheirans; and a complex joint of the exopod reflecting the arthropod’s swimming capabilities. Conclusions Different aspects of the morphology, for example, the morphology of the great appendage and the presence of a basipod with strong median armature on the biramous appendages indicate that L. superlata was an active and agile necto-benthic predator (not a scavenger or deposit feeder as previously interpreted.

  9. Late Cambrian magmatic arc activity in peri-Gondwana: geochemical evidence from the Basal Allochthonous Units of NW Iberia

    Energy Technology Data Exchange (ETDEWEB)

    Andonaegui, P.; Abati, J.; Díez-Fernández, R.

    2017-07-01

    The North African section of the Gondwana margin was the site of voluminous, arc-related magmatism during the Late Neoproterozoic (Avalonian–Cadomian orogen). The lower (and older) metasedimentary sequence that constitutes the Basal Units of the Allochthonous Complexes of NW Iberia was deposited in that setting. In these units, sedimentation was followed by the intrusion of tonalites and granodiorites in the late Cambrian (ca. 493–489Ma). In the Late Paleozoic, the collision of Gondwana and Laurussia (Variscan orogeny) deformed and metamorphosed the whole ensemble. New whole rock geochemical analysis performed in seven samples of metatonalites and fourteen samples of metagranodiorites are characterized by: i) slight enrichment in incompatible elements (Rb, Ba, Th, U), ii) negative anomalies in Nb, Ta, P, and Ti, and iii) negative anomalies in Eu. These chemical features are in agreement with a subduction-related setting for the genesis of both types of magma, which is also supported by chemical discrimination using tectonic setting diagrams. Positive anomalies of Pb suggest a crustal component. The new geochemical data reveal that the convergent orogen that ruled the paleogeography of the Gondwana periphery during the Neoproterozoic (Cadomian orogen) remained active bey.

  10. 226Ra and 228Ra in ground water of the Cambrian-Ordovician Aquifer System in northern Illinois

    International Nuclear Information System (INIS)

    Gilkeson, R.H.; Holtzman, R.B.

    1982-01-01

    Over a large region of Illinois, ground water of the Cambrian-Ordovician Aquifer System exceeds the US EPA drinking water standard of 5 pCi/L for the combined concentration of 226 Ra and 228 Ra. 226 Ra concentrations range from 226 Ra is the geochemistry of uranium in the ground-water flow system, while the 228 Ra activity in ground water which ranges from 232 Th-bearing minerals in the aquifer strata. The comparison of recent analyses to historical data gathered over the last 20 years indicates that, with few exceptions, 226 Ra and 228 Ra activities in ground water have remained constant. The combined concentrations of the two nuclides in ground water of the aquifer system ranged from 226 Ra concentrations were high (greater than or equal to 10 pCi/L), those of 228 Ra were low (less than or equal to 2 pCi/L), but, with few exceptions, in regions where 228 Ra concentrations were high, those of 226 Ra were also high. The range of values raises questions concerning the validity of the US EPA regulation which requires analysis for 228 Ra only when the concentration of 226 Ra exceeds 3.0 pCi/L

  11. Exceptionally preserved Cambrian trilobite digestive system revealed in 3D by synchrotron-radiation X-ray tomographic microscopy.

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    Mats E Eriksson

    Full Text Available The Cambrian 'Orsten' fauna comprises exceptionally preserved and phosphatised microscopic arthropods. The external morphology of these fossils is well known, but their internal soft-tissue anatomy has remained virtually unknown. Here, we report the first non-biomineralised tissues from a juvenile polymerid trilobite, represented by digestive structures, glands, and connective strands harboured in a hypostome from the Swedish 'Orsten' fauna. Synchrotron-radiation X-ray tomographic microscopy enabled three-dimensional internal recordings at sub-micrometre resolution. The specimen provides the first unambiguous evidence for a J-shaped anterior gut and the presence of a crop with a constricted alimentary tract in the Trilobita. Moreover, the gut is Y-shaped in cross section, probably due to a collapsed lumen of that shape, another feature which has not previously been observed in trilobites. The combination of anatomical features suggests that the trilobite hypostome is functionally analogous to the labrum of euarthropods and that it was a sophisticated element closely integrated with the digestive system. This study also briefly addresses the preservational bias of the 'Orsten' fauna, particularly the near-absence of polymerid trilobites, and the taphonomy of the soft-tissue-harbouring hypostome.

  12. Formation conditions, accumulation models and exploration direction of large-scale gas fields in Sinian-Cambrian, Sichuan Basin, China

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    Guoqi Wei

    2016-02-01

    Full Text Available According to comprehensive research on forming conditions including sedimentary facies, reservoirs, source rocks, and palaeo-uplift evolution of Sinian-Cambrian in Sichuan Basin, it is concluded that: (1 large-scale inherited palaeo-uplifts, large-scale intracratonic rifts, three widely-distributed high-quality source rocks, four widely-distributed karst reservoirs, and oil pyrolysis gas were all favorable conditions for large-scale and high-abundance accumulation; (2 diverse accumulation models were developed in different areas of the palaeo-uplift. In the core area of the inherited palaeo-uplift, “in-situ” pyrolysis accumulation model of paleo-reservoir was developed. On the other hand, in the slope area, pyrolysis accumulation model of dispersed liquid hydrocarbon was developed in the late stage structural trap; (3 there were different exploration directions in various areas of the palaeo-uplift. Within the core area of the palaeo-uplift, we mainly searched for the inherited paleo-structural trap which was also the foundation of lithological-strigraphic gas reservoirs. In the slope areas, we mainly searched for the giant structural trap formed in the Himalayan Period.

  13. Cambrian archaeocyathan metazoans: revision of morphological characters and standardization of genus descriptions to establish an online identification tool

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    Adeline Kerner

    2011-11-01

    Full Text Available Archaeocyatha represent the oldest calcified sponges and the first metazoans to build bioconstructions in association with calcimicrobes. They are a key group in biology, evolutionary studies, biostratigraphy, paleoecology and paleogeography of the early Cambrian times. The establishing of a new standardized terminology for archaeocyathans description has permitted the creation of the first knowledge base in English including descriptions of all archaeocyathan genera. This base, using the XPER² software package, is an integral part of the -Archaeocyatha- a knowledge base website, freely available at url http://www.infosyslab.fr/archaeocyatha. The website is composed of common information about Archaeocyatha, general remarks about the knowledge base, the description of the 307 genera recognized with images of type-specimens of type-species for each genus, as well as additional morphological data, an interactive free access key and its user guide.The automatic analysis and comparison of the digitized descriptions have identified some genera with highly similar morphology. These results are a great help for future taxonomic revisions and suggest a number of possible synonymies that require further study.

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

    Science.gov (United States)

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

    2017-08-01

    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. New Au-U deposit type in the weathering crust in tectonicmetasomatite zones of Pre-Cambrian shields

    International Nuclear Information System (INIS)

    Tarkhanov, A.

    2014-01-01

    Au-U mineralization is widely distributed in the tectonic-metasomatite zones of Pre-Cambrian shields (Aldan Shield, Ukraine Shield and others). The industrial ores are located only in several areas at depths of more than 150-300 m. Uranium mineralization is represented by uranotitnates and the gold mineralization by auriferous pyrite. The zone of weathering is present to the depth of 100-150 m. The feldspars are replaced by the clay minerals, carbonates are dissovled, sulfides are oxidized and the secondary minerals of uranium replace uranotitanates.The golden mineralization in the envelope of weathering is represented by the fine-grained native gold. The particle size is 40-50 nm. Uranium mineralization is in the form of relict brannerite, tuyamunite, torbernite, carnotite. The gold content is 1-2 g/t, and uranium content 0.01- 0.05% U. Ore bodies of gold and uranium are located inside the tectonic-metasomatite zones. The zones of maximum concentration of these metals may not coincide. The gold ore bodies have the length of hundreds meters and a thickness of 1-5 m. The vertical extent of the secondary Au-U mineralization is 100-150 m. 20 laboratory samples of ore from the weathered zone were tested by the method of heap leaching. The first stage is the uranium leach by diluted sulfuric acid. The second stage is the cyanation of gold and silver. The experimental data indicates leach rate of uranium 75%, gold 80-97%, silver 50-60%. Gold resources in the continous zone is estimated to be 80 t. Gold resources of the several other zones inside the area of 100 km 2 are estimated as 220 t. The heap leach process can be used for profitable development of the low-grade deposits. This method helps to increase the resources of gold and uranium. (author)

  16. The origin of increased salinity in the Cambrian-Vendian aquifer system on the Kopli Peninsula, northern Estonia

    Science.gov (United States)

    Karro, Enn; Marandi, Andres; Vaikmäe, Rein

    Monitoring of the confined Cambrian-Vendian aquifer system utilised for industrial water supply at Kopli Peninsula in Tallinn over 24 years reveals remarkable changes in chemical composition of groundwater. A relatively fast 1.5 to 3.0-fold increase in TDS and in concentrations of major ions in ed groundwater is the consequence of heavy pumping. The main sources of dissolved load in Cambrian-Vendian groundwater are the leaching of host rock and the other geochemical processes that occur in the saturated zone. Underlying crystalline basement, which comprises saline groundwater in its upper weathered and fissured portion, and which is hydraulically connected with the overlying Cambrian-Vendian aquifer system, is the second important source of ions. The fractured basement and its clayey weathering crust host the Ca-Cl type groundwater, which is characterised by high TDS values (2-20 g/L). Intensive water ion accelerates the exchange of groundwaters and increases the area of influence of pumping. Chemical and isotopic studies of groundwater indicate an increasing contribution of old brackish water from the crystalline basement and rule out the potential implication of an intrusion of seawater into aquifer. L'origine de la salinité croissante dans le système aquifère du Cambrien-Vendien dans la péninsule de Kopli, nord de l'Estonie Le suivi à long terme du système aquifère captif du Cambrien-Vendien utilisé pour l'approvisionnement d'eaux industrielles dans la Péninsule de Kopli, nord de l'Estonie, révèle de remarquables changements dans la composition chimique des eaux souterraines. Une augmentation de facteur 1.5 à 3 de la TDS et des concentrations en ions majeurs dans l'eau souterraine est la conséquence de pompages intensifs. Les sources principales des charges dissoutes dans les eaux de l'aquifère du Cambrien-Vendien sont le lessivage des roches et d'autres phénomènes géochimiques ayant lieu dans la zone saturée. Le soubassement rocheux cristallin

  17. Characterization of the Lower Cambrian sandstone aquifer in the Swedish Baltic Sea area - assessment regarding its potential suitability for storage of CO2

    Science.gov (United States)

    Erlström, M.; Sivhed, U.

    2012-04-01

    In the Baltic region the Cambrian sandstone is considered to have great economic value concerning its aquifer and reservoir properties. Its potential as petroleum reservoir is well known, especially from the Polish, Lithuanian and Russian sectors of the Baltic Sea where oil and gas has been found in anticline traps in the sandstone sequence. Offshore exploration in the Swedish sector has so far not encountered any significant findings of oil and gas. However, the extensive exploration has generated data, which is now being used for assessing the overall properties regarding suitability for storage of CO2. The Swedish primary industry has a great interest in finding potential sites for storage of CO2. A suitable site in the Baltic Sea would be a most favourable alternative in comparison to more remote alternatives such as deep saline aquifers in the North Sea. The Lower Cambrian is in the Swedish sector of the Baltic Sea composed of three main sandstone units varying in thickness between 5 and 50 m occurring within an up to 250 m thick Cambrian sequence dominated by fine-grained terriclastic sediments. The limit of Lower Palaeozoic sequence in the Baltic area is today defined by erosional truncation because of the gently dipping Lower Palaeozoic sequence. To the north and northwest, the limit is found in the Pre-Quaternary, whereas the erosional limit is deeply buried beneath Permian and Mesozoic sediments to the south. Here the Lower Palaeozoic limit is buried to depths reaching more than 2 km. The Cambrian sequence in the distal parts of the Swedish sector occurs at depths of c. 1300 m while it constitutes the bedrock surface in a narrow zone trending from Öland to the north of of Gotland. Sandstone beds constitute 40-60% of the total Cambrian sequence. The main sandstone units have a regional distribution of several thousands of square kilometres. The up to 50 m thick Faludden sandstone member exhibits the best reservoir properties including porosities in the

  18. Basalts and picrites from a plume-type ophiolite in the South Qilian Accretionary Belt, Qilian Orogen: Accretion of a Cambrian Oceanic Plateau?

    Science.gov (United States)

    Zhang, Yuqi; Song, Shuguang; Yang, Liming; Su, Li; Niu, Yaoling; Allen, Mark B.; Xu, Xin

    2017-05-01

    Oceanic plateaus with high-Mg rocks in the present-day oceanic crust have attracted much attention for their proposed mantle-plume origins and abnormally high mantle potential temperatures (Tp). However, equivalent rocks in ancient oceanic environments are usually poorly preserved because of deformation and metamorphism. Here we present petrological, geochronological and geochemical data for pillow lavas from Cambrian ophiolites in the Lajishan and Yongjing regions of the South Qilian Accretionary Belt (SQAB), from the southern part of the Qilian Orogen, northern China. Three rock groups can be identified geochemically: (1) sub-alkaline basalts with enriched mid- ocean ridge basalt (E-MORB) affinity; (2) alkaline basalts with oceanic island basalt (OIB) features, probably derived from partial melting of an enriched mantle source; and (3) picrites with MgO (18-22 wt%). Cr-numbers [Cr# = Cr/(Cr + Al)] of spinels from the picrites suggest 18-21% degree of partial melting at the estimated mantle potential temperature (Tp) of 1489-1600 °C, equivalent to values of Cenozoic Hawaiian picrites (1500-1600 °C). Zircons from one gabbro sample yielded a U-Pb Concordia age of 525 ± 3 Ma, suggesting the oceanic crust formed in the Cambrian. Available evidence suggests that Cambrian mantle plume activity is preserved in the South Qilian Accretionary Belt, and influenced the regional tectonics: "jamming" of the trench by thick oceanic crust explains the emplacement and preservation of the oceanic plateau, and gave rise to the generation of concomitant Ordovician inner-oceanic island arc basalts via re-organisation of the subduction zones in the region.

  19. The oldest known digestive system consisting of both paired digestive glands and a crop from exceptionally preserved trilobites of the Guanshan Biota (Early Cambrian, China.

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    Melanie J Hopkins

    Full Text Available The early Cambrian Guanshan biota of eastern Yunnan, China, contains exceptionally preserved animals and algae. Most diverse and abundant are the arthropods, of which there are at least 11 species of trilobites represented by numerous specimens. Many trilobite specimens show soft-body preservation via iron oxide pseudomorphs of pyrite replacement. Here we describe digestive structures from two species of trilobite, Palaeolenus lantenoisi and Redlichia mansuyi. Multiple specimens of both species contain the preserved remains of an expanded stomach region (a "crop" under the glabella, a structure which has not been observed in trilobites this old, despite numerous examples of trilobite gut traces from other Cambrian Lagerstätten. In addition, at least one specimen of Palaeolenus lantenoisi shows the preservation of an unusual combination of digestive structures: a crop and paired digestive glands along the alimentary tract. This combination of digestive structures has also never been observed in trilobites this old, and is rare in general, with prior evidence of it from one juvenile trilobite specimen from the late Cambrian Orsten fauna of Sweden and possibly one adult trilobite specimen from the Early Ordovician Fezouata Lagerstätte. The variation in the fidelity of preservation of digestive structures within and across different Lagerstätten may be due to variation in the type, quality, and point of digestion of food among specimens in addition to differences in mode of preservation. The presence and combination of these digestive features in the Guanshan trilobites contradicts current models of how the trilobite digestive system was structured and evolved over time. Most notably, the crop is not a derived structure as previously proposed, although it is possible that the relative size of the crop increased over the evolutionary history of the clade.

  20. The oldest known digestive system consisting of both paired digestive glands and a crop from exceptionally preserved trilobites of the Guanshan Biota (Early Cambrian, China).

    Science.gov (United States)

    Hopkins, Melanie J; Chen, Feiyang; Hu, Shixue; Zhang, Zhifei

    2017-01-01

    The early Cambrian Guanshan biota of eastern Yunnan, China, contains exceptionally preserved animals and algae. Most diverse and abundant are the arthropods, of which there are at least 11 species of trilobites represented by numerous specimens. Many trilobite specimens show soft-body preservation via iron oxide pseudomorphs of pyrite replacement. Here we describe digestive structures from two species of trilobite, Palaeolenus lantenoisi and Redlichia mansuyi. Multiple specimens of both species contain the preserved remains of an expanded stomach region (a "crop") under the glabella, a structure which has not been observed in trilobites this old, despite numerous examples of trilobite gut traces from other Cambrian Lagerstätten. In addition, at least one specimen of Palaeolenus lantenoisi shows the preservation of an unusual combination of digestive structures: a crop and paired digestive glands along the alimentary tract. This combination of digestive structures has also never been observed in trilobites this old, and is rare in general, with prior evidence of it from one juvenile trilobite specimen from the late Cambrian Orsten fauna of Sweden and possibly one adult trilobite specimen from the Early Ordovician Fezouata Lagerstätte. The variation in the fidelity of preservation of digestive structures within and across different Lagerstätten may be due to variation in the type, quality, and point of digestion of food among specimens in addition to differences in mode of preservation. The presence and combination of these digestive features in the Guanshan trilobites contradicts current models of how the trilobite digestive system was structured and evolved over time. Most notably, the crop is not a derived structure as previously proposed, although it is possible that the relative size of the crop increased over the evolutionary history of the clade.

  1. Accumulation conditions and enrichment patterns of natural gas in the Lower Cambrian Longwangmiao Fm reservoirs of the Leshan-Longnǚsi Palaeohigh, Sichuan Basin

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    Xu Chunchun

    2014-10-01

    Full Text Available As several major new gas discoveries have been made recently in the Lower Cambrian Longwangmiao Fm reservoirs in the Leshan-Longnǚsi Palaeohigh of the Sichuan Basin, a super-huge gas reservoir group with multiple gas pay zones vertically and cluster reservoirs laterally is unfolding in the east segment of the palaeohigh. Study shows that the large-scale enrichment and accumulation of natural gas benefits from the good reservoir-forming conditions, including: (1 multiple sets of source rocks vertically, among which, the high-quality Lower Paleozoic source rocks are widespread, and have a hydrocarbon kitchen at the structural high of the Palaeohigh, providing favorable conditions for gas accumulation near the source; (2 three sets of good-quality reservoirs, namely, the porous-vuggy dolomite reservoirs of mound-shoal facies in the 2nd and 4th members of the Sinian Dengying Fm as well as the porous dolomite reservoirs of arene-shoal facies in the Lower Cambrian Longwangmiao Fm, are thick and wide in distribution; (3 structural, lithological and compound traps developed in the setting of large nose-like uplift provide favorable space for hydrocarbon accumulation. It is concluded that the inheritance development of the Palaeohigh and its favorable timing configuration with source rock evolution are critical factors for the extensive enrichment of gas in the Lower Cambrian Longwangmiao Fm reservoirs. The structural high of the Palaeohigh is the favorable area for gas accumulation. The inherited structural, stratigraphic and lithological traps are the favorable sites for gas enrichment. The areas where present structures and ancient structures overlap are the sweet-spots of gas accumulation.

  2. Zn-Pb Ores of Mississippi Valley Type in the Lycksele-Storuman District, Northern Sweden: A Possible Rift-Related Cambrian Mineralisation Event

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    Kjell Billström

    2012-06-01

    Full Text Available The epigenetic Zn-Pb deposits in the Lycksele-Storuman ore district, northern Sweden, are hosted by Paleoproterozoic basement near the margin of the Caledonian mountains. A paleogeographic reconstruction suggests that platform sediments, including Cambrian shales, overlaid the mineralised basement. The mineralisation type, containing sphalerite, galena, calcite and fluorite, is confined to veins and breccias and interpreted to be of Mississippi Valley Type (MVT style. There is no appreciable wall rock alteration. Fluid inclusion work reveals coexisting aqueous and hydrocarbon fluids. Ore deposition is interpreted to have occurred during mixing of two fluids; a cool (

  3. Les microbialites de l'Anti-Atlas occidental (Maroc) : marqueurs stratigraphiques et témoins des changements environnementaux au Cambrien inférieur Stratigraphic and environmental significance of the Lower-Cambrian western Anti-Atlasic microbialites (Morocco)

    Science.gov (United States)

    Benssaou, Mohammed; Hamoumi, Naima

    2004-02-01

    Three microbialite forms are recognized in the Lower-Cambrian succession of Irherm area in the western Anti-Atlas (Morocco). Stromatolites, which correspond to non-calcified shallow marine laminated microbialites, are well developed in the basal Lower-Cambrian succession. Occurrence of calcified microbial thrombolites, in the middle part of this succession, reflects an increasing sea level from the peritidal zone to the subtidal environment. In the upper part of this succession, a second increasing water depth event and the development of branching archaeocyathan reefal framework lead to dendritic microbialite emergence. To cite this article: M. Benssaou, N. Hamoumi, C. R. Geoscience 336 (2004).

  4. Evidence for gill slits and a pharynx in Cambrian vetulicolians: implications for the early evolution of deuterostomes

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    Ou Qiang

    2012-10-01

    Full Text Available Abstract Background Vetulicolians are a group of Cambrian metazoans whose distinctive bodyplan continues to present a major phylogenetic challenge. Thus, we see vetulicolians assigned to groups as disparate as deuterostomes and ecdysozoans. This divergence of opinions revolves around a strikingly arthropod-like body, but one that also bears complex lateral structures on its anterior section interpreted as pharyngeal openings. Establishing the homology of these structures is central to resolving where vetulicolians sit in metazoan phylogeny. Results New material from the Chengjiang Lagerstätte helps to resolve this issue. Here, we demonstrate that these controversial structures comprise grooves with a series of openings. The latter are oval in shape and associated with a complex anatomy consistent with control of their opening and closure. Remains of what we interpret to be a musculature, combined with the capacity for the grooves to contract, indicate vetulicolians possessed a pumping mechanism that could process considerable volumes of seawater. Our observations suggest that food captured in the anterior cavity was transported to dorsal and ventral gutters, which then channeled material to the intestine. This arrangement appears to find no counterpart in any known fossil or extant arthropod (or any other ecdysozoan. Anterior lateral perforations, however, are diagnostic of deuterostomes. Conclusions If the evidence is against vetulicolians belonging to one or other group of ecdysozoan, then two phylogenetic options seem to remain. The first is that such features as vetulicolians possess are indicative of either a position among the bilaterians or deuterostomes but apart from the observation that they themselves form a distinctive and recognizable clade current evidence can permit no greater precision as to their phylogenetic placement. We argue that this is too pessimistic a view, and conclude that evidence points towards vetulicolians being

  5. Sedimentology of SPICE (Steptoean positive carbon isotope excursion): A high-resolution trace fossil and microfabric analysis of the middle to late Cambrian Alum Shale Formation, southern Sweden

    Science.gov (United States)

    Egenhoff, Sven; Fishman, Neil; Ahlberg, Per; Maletz, Jorg; Jackson, Allison; Kolte, Ketki; Lowers, Heather; Mackie, James; Newby, Warren; Petrowsky, Matthew

    2015-01-01

    The Cambrian Alum Shale Formation in the Andrarum-3 core from Scania, southern Sweden, consists of black siliciclastic mudstone with minor carbonate intercalations. Four facies comprise three siliciclastic mudstones and one fine-grained carbonate. The facies reflect deposition along a transect from deep ramp to basin on a Cambrian shelf. The three mudstone facies contain abundant clay clasts and laterally variable siltstone laminae. Bed-load transport processes seem to have dominated deposition on this deep shelf. These sedimentary rocks record mainly event deposition, and only relatively few, thin laminae probably resulted from suspension settling. The Alum Shale Formation deep shelf did not show a bioturbation gradient, but fecal strings are common and Planolites burrows are rare in all mudstone facies. Evidence for biotic colonization indicates that this mudstone environment was not persistently anoxic, but rather was most likely intermittently dysoxic. The Alum Shale Formation in the Andrarum-3 core shows an overall decrease of grain size, preserved energy indicators, and carbonate content upsection interpreted to reflect a deepening upward. The succession can also be divided into four small-scale fining-upward cycles that represent deepening, and four overlying coarsening-upward cycles that represent upward shallowing.

  6. Stratigraphic framework of Cambrian and Ordovician rocks in the central Appalachian Basin from Medina County, Ohio, through southwestern and south-central Pennsylvania to Hampshire County, West Virginia

    Science.gov (United States)

    Ryder, Robert T.; Harris, Anita G.; Repetski, John E.; revised and digitized by Crangle, Robert D.

    2003-01-01

    A 275-mi-long restored stratigraphic cross section from Medina County, Ohio, through southwestern and south-central Pennsylvania to Hampshire County, W. Va., provides new details on Cambrian and Ordovician stratigraphy in the central Appalachian basin and the structure of underlying Precambrian basement rocks. From west to east, the major structural elements of the block-faulted basement in this section are (1) the relatively stable, slightly extended craton, which includes the Wooster arch, (2) the fault-controlled Ohio-West Virginia hinge zone, which separates the craton from the adjoining Rome trough, (3) the Rome trough, which consists of an east-facing asymmetric graben and an overlying sag basin, and (4) a positive fault block, named here the South-central Pennsylvania arch, which borders the eastern margin of the graben part of the Rome trough. Pre-Middle Ordovician structural relief on Precambrian basement rocks across the down-to-the-west normal fault that separates the Rome trough and the adjoining South-central Pennsylvania arch amounted to between 6,000 and 7,000 ft. The restored cross section shows eastward thickening of the Cambrian and Ordovician sequence from about 3,000 ft near the crest of the Wooster arch at the western end of the section to about 5,150 ft at the Ohio-West Virginia hinge zone adjoining the western margin of the Rome trough to about 19,800 ft near the depositional axis of the Rome trough. East of the Rome trough, at the adjoining western edge of the South-central Pennsylvania arch, the Cambrian and Ordovician sequence thins abruptly to about 13,500 ft and then thins gradually eastward across the arch to about 12,700 ft near the Allegheny structural front and to about 10,150 ft at the eastern end of the restored section. In general, the Cambrian and Ordovician sequence along this section consists of four major lithofacies that are predominantly shallow marine to peritidal in origin. In ascending stratigraphic order, the lithofacies

  7. Proposed stratotype for the base of the highest Cambrian stage at the first appearance datum of Cordylodus andresi, Lawson Cove section, Utah, USA

    Science.gov (United States)

    Miller, J.F.; Ethington, Raymond L.; Evans, K.R.; Holmer, L.E.; Loch, James D.; Popov, L.E.; Repetski, J.E.; Ripperdan, R.L.; Taylor, John F.

    2006-01-01

    We propose a candidate for the Global Standard Stratotype-section and Point (GSSP) for the base of the highest stage of the Furongian Series of the Cambrian System. The section is at Lawson Cove in the Ibex area of Millard County, Utah, USA. The marker horizon is the first appearance datum (FAD) of the conodont Cordylodus andresi Viira et Sergeyeva in Kaljo et al. [Kaljo, D., Borovko, N., Heinsalu, H., Khazanovich, K., Mens, K., Popov, L., Sergeyeva, S., Sobolevskaya, R., Viira, V., 1986. The Cambrian-Ordovician boundary in the Baltic-Ladoga clint area (North Estonia and Leningrad Region, USSR). Eesti NSV Teaduste Akadeemia Toimetised. Geologia 35, 97-108]. At this section and elsewhere this horizon also is the FAD of the trilobite Eurekia apopsis (Winston et Nicholls, 1967). This conodont characterizes the base of the Cordylodus proavus Zone, which has been recognized in many parts of the world. This trilobite characterizes the base of the Eurekia apopsis Zone, which has been recognized in many parts of North America. The proposed boundary is 46.7 m above the base of the Lava Dam Member of the Notch Peak Formation at the Lawson Cove section. Brachiopods, sequence stratigraphy, and carbon-isotope geochemistry are other tools that characterize this horizon and allow it to be recognized in other areas. ?? 2006 Nanjing Institute of Geology and Palaeontology, CAS.

  8. Reconstruction of the Paleoenvironment of the Early Cambrian Yurtus Black Shale in the Tarim Basin, Northwestern China, and Its Control on Organic Matter Accumulation

    Science.gov (United States)

    Li, J.; Ding, W.; Dong, L.

    2017-12-01

    The black shale in the early Cambrian Yurtus Formation (>521 Ma) in the Tarim basin, northwestern China, is characterized by its high TOC value (up to 16%) andgreat lateral continuity. It has been proven to be high-quality hydrocarbon source rocks. Abundant phytoplanktons and small shelly fossils have been reported from the lower Yurtus chert. However, recent biomarker discovery of aryl isoprenoid hydrocarbons suggests the existence of green sulfur bacteria, which indicates that the water column was stratified and the photic zone was prevailingly euxinic. These seemingly contradictory observations hamper our further understanding of the paleoenvironment in which the Yurtus shale was deposited and its control on the accumulation of organic matter. In this study, we systematically collected samples from the Yurtus Formation at the Kungaikuotan Section, and measured the organic carbon and nitrogen isotopic compositions and the content of trace element Barium (Ba). The strong negative excursions of nitrogen isotope ( -13‰) in the lower and upper parts of the Yurtus Formation are likely attributed to the biological activity of green and purple sulfur bacteria, which is consistent with our organic carbon isotope data as well as previous biomarker discovery. As green sulfur bacteria can only live in euxinic photic zone, it may indicate that the water column above this euxinic zone contains prolific organic matters which consume all the dissolved oxidants in surface ocean. It is well accepted that Ba flux can be used as an indicator for surface ocean primary productivity. Significant increase of barium content (from matter in the early Cambrian surface ocean mainly result from extremely high primary productivity. The abundant phytoplankton fossil record from this time period also supports this interpretation. In summary, high TOC in the Yurtus shale may derive from the extremely high primary productivity of phytoplanktons. Organic matter consumes all the dissolved

  9. Discovery and basic characteristics of high-quality source rocks found in the Yuertusi Formation of the Cambrian in Tarim Basin, China

    Directory of Open Access Journals (Sweden)

    Guangyou Zhu

    2016-02-01

    Full Text Available The Upper Paleozoic strata of the Tarim Basin have abundant resources of marine oil and gas. In the Tahe area, Halahatang area, and Tazhong area of the basin, many large-scale oilfields have been found. These oilfields have a confirmed oil and gas reserves worth more than 2.5 billion tons and have completed the annual output of more than 14 million tons of marine oil and gas equivalent. The belief that the only main hydrocarbon source rocks are of the Cambrian or Ordovician is still controversial. Chemists have made significant progress and have effectively lead the oil and gas exploration in Tarim Basin. Due to the complexity of the basin and the limitation of samples, the research work, and fine contrast is restricted. In this article, we investigated the Cambrian strata outcrop of Tarim Basin in detail. By analyzing a lot of outcrops, high-quality hydrocarbon source rocks of Yuertusi Formation have been found in more than 10 outcrop points in Aksu region. The source rocks' lithology is black shale with total organic carbon (TOC content that ranges between 2% and 16%. Total organic carbon (TOC of the black shale layer could be as much as 4%–16%, especially in the outcrops of the Yutixi and Shiairike. This by far is the best marine hydrocarbon source rock that was found in China. The source rocks were distributed consistently in the Aksu region, the thickness of which is about 10–15 m. It was formed in a sedimentary environment of a middle gentle slope to a low gentle slope. Organic matter enrichment is controlled by the upwelling currents. The thick strata of dolostone that developed in the Xiaoerblak Formation are considered to be good reservoirs of the beach and microbial reef in the upper strata of Yuertusi Formation. No hydrocarbon source rocks have been found in the outcrop of Xiaoerblak Formation. The thick strata of gyprock and mudstone development are a set of satisfactory cap layer in the Lower Cambrian. This hydrocarbon

  10. The Late Cambrian SPICE (δ13C) event and the Sauk II-Sauk III regression: new evidence from Laurentian basins in Utah, Iowa, and Newfoundland

    Science.gov (United States)

    Saltzman, Matthew R.; Cowan, Clinton A.; Runkel, Anthony C.; Runnegar, Bruce; Stewart, Michael C.; Palmer, Allison R.

    2004-01-01

    Carbon isotope data from Upper Cambrian sections in three Laurentian basins in northern Utah, central Iowa, and western Newfoundland record a large positive ??13C excursion (SPICE event) of up to + 5???. Peak ??13C ratios are well dated by trilobite collections to the middle of the Steptoean Stage (Dunderbergia Zone) and occur during maximum regression associated with formation of the Sauk II-Sauk III subsequence boundary on the North American craton. Maximum regression was marked by an influx of quartz sand into carbonate-platform settings in all three widely separated basins. In northern Utah, this quartz sand formed a thick sequence known as the Worm Creek Quartzite, which marks a conspicuous interruption of carbonate deposition during the Middle to Late Cambrian in the region. In western Newfoundland, the thickness of the quartz sand unit is much reduced but still marks a brief shutdown of the carbonate factory that is unique to the Cambrian shelf succession of the area. In the central Iowa area of the cratonic interior, an upward-shallowing carbonate succession culminates in cross-stratified trilobite grainstones at the peak of the SPICE in Dunderbergia Zone time, and the lowest point on the relative-sea-level curve is associated with the occurrence of coarse quartz sand derived from the encroaching shoreface. Although it is difficult to determine precisely the departure from baseline ??13C that marks the beginning of the SPICE excursion in the stratigraphic successions analyzed, our results are consistent with a rise and subsequent fall in ??13C tracking a major regressive-transgressive event recorded across northern Laurentia. The correlation of a major ??13C excursion with regression is similar to that described for the Late Ordovician, for which the pattern has been attributed to either increased carbonate relative to terrigenous weathering rates as ice sheets covered up organic-matter-containing silicates at high latitudes or high productivity and organic

  11. Ages, geochemistry and tectonic implications of the Cambrian igneous rocks in the northern Great Xing'an Range, NE China

    Science.gov (United States)

    Feng, Zhiqiang; Liu, Yongjiang; Li, Yanrong; Li, Weimin; Wen, Quanbo; Liu, Binqiang; Zhou, Jianping; Zhao, Yingli

    2017-08-01

    The Xinlin-Xiguitu suture zone, located in the Great Xing'an Range, NE China, in the eastern segment of the Central Asian Orogenic Belt (CAOB), represents the boundary between the Erguna and Xing'an micro-continental blocks. The exact location of the Xinlin-Xiguitu suture zone has been debated, especially, the location of the northern extension of the suture zone. In this study, based on a detailed field, geochemical, geochronological and Sr-Nd-Hf isotope study, we focus our work on the Cambrian igneous rocks in the Erguna-Xing'an block. The Xinglong granitoids, mainly include ∼520 Ma diorite, ∼470 Ma monzogranite and ∼480 Ma pyroxene diorite. The granitoids show medium to high-K calc-alkaline series characteristics with post-collision granite affinity. The circa 500 Ma granitoids have low εHf (t) values (-16.6 to +2.2) and ancient two-stage model (TDM2) ages between 1317 Ma and 2528 Ma. These results indicate the primary magmas of the Xinglong granitoids were probably derived from the partial melting of a dominantly Paleo-Mesoproterozoic ;old; crustal source with possible different degrees of addition of juvenile materials, and formed in a post-collision tectonic setting after the amalgamation of the Erguna and Xing'an blocks. Compared with the Xinglong granitoids, the Duobaoshan igneous rocks are consisted of the approximately coeval rhyolitic tuffs (491 ± 5 Ma) and ultramafic intrusions (497 ± 5 Ma) within the Duobaoshan Formation. They are generally enriched in large ion lithophile elements (LILEs) and depleted in high field strength elements (HFSEs; e.g., Nb, Ta, and Ti), consistent with the geochemistry of igneous rocks from island arcs or active continental margins. The ultramafic rocks have high positive εHf (t) values (+1.3 to +15) and εNd (t) (+1.86 to +2.28), and relatively young two-stage model (TDM2) ages and low initial 87Sr/86Sr ratios (0.70628-0.70853), indicating the partial melting of a depleted mantle source from a subducted slab in

  12. Facies and porosity origin of reservoirs: Case studies from the Cambrian Longwangmiao Formation of Sichuan Basin, China, and their implications on reservoir prediction

    Directory of Open Access Journals (Sweden)

    Anjiang Shen

    2018-02-01

    Full Text Available The dolostone of the Cambrian Longwangmiao Formation has been a significant gas exploration area in Sichuan Basin. In Gaoshiti-Moxi regions, a giant gas pool with thousands of billion cubic meters' reserve has been discovered. However, the origin of the reservoir and the distribution patterns are still disputed, eventually constraining the dolostone exploration of the Longwangmiao Formation. This paper focuses on the characteristics, origin, and distribution patterns of the dolostone reservoir in the Longwangmiao Formation based on: the outcrop geological survey, cores, thin-sections observation, reservoir geochemical characteristics study, and reservoir simulation experiments. As a result, two realizations were acquired: (1 The Cambrian Longwangmiao Formation could be divided into upper and lower part in Sichuan Basin. Based on the two parts of the Longwangmiao Formation, two lithofacies paleogeographic maps were generated. In addition, the carbonate slope sedimentary models were established. The grainstone shoals are mainly distributed in the shallow slope of the upper part in the Longwangmiao Formation. (2 The grainstone shoals are the developing basis of the dolostone reservoir in the Longwangmiao Formation. Moreover, the contemporaneous dissolution was a critical factor of grainstone shoal reservoir development in the Longwangmiao Formation. Controlled by the exposure surface, the dissolution vugs are not only extensively distributed, but also successively developed along the contemporaneous pore zones. Hence, the distribution patterns could be predicted. The geological understandings of the origin of dolostone reservoir in the Longwangmiao Formation show that the reservoir distributed in the areas of karstification in the Gaoshiti-Moxi regions, as well as the widespread grainstone shoals in the whole basin, are the potential exploration targets. Keywords: Sichuan Basin, Longwangmiao Formation, Carbonate slope, Dolograinstone shoal

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

    Science.gov (United States)

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

    2005-01-01

    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.

  14. The evolution of the passive continental margin of Norway and its adjacent mainland - using the sub-Cambrian peneplain as a reference surface.

    Science.gov (United States)

    Gabrielsen, R. H.; Faleide, J. I.; Jarsve, E. M.

    2012-04-01

    The structuring, uplift and subsidence of the passive margin and shelf of Norway and its adjacent mainland were affected by several profound geological processes, including inherited basement structural grain related to the Proterozoic and Caledonian orogens and also including the extensional collapse of the Caledonides (Gabrielsen et al. 2000). This has been followed by several stages of late Palaoezoic - Cenozoic rifting and associated thermotectonic activity, Cenozoic accelerated uplift of uncertain origin of the hinterland, creating an irregular pattern of upheaval and, finally Pleistocene - Holocene glacial loading and unloading (Gabrielsen et al. 2010). These processes have strongly influenced the topography of the hinterland, thus causing and acting in concert with climate fluctuations (Nielsen et al. 2009). The correlation of erosional surfaces of regional significance on the shelf and on the mainland is a key to the evaluating the total topography of the margin. Because of the lack of datable surfaces on the mainland, this is problematic. The so-called Paleic surface has been used in this context, but its age and nature is not well constrained and the absence of post-Caledonian rocks in the western and central mainland of southern Norway adds to this complexity. In contrast, the sub-Cambrian peneplain, which is found in larger parts of Scandinavia, is well established when it comes to dating and development (e.g. Strøm 1948). It is generally accepted that this surface had only a minor topography, if any, throughout Scandinavia at the earliest Cambrian. Hence, its present relief is the result of the accumulated vertical displacements from the Caledonian to the Present. Still, even though it was well established through regional mapping already in the late 19th century, much remains in the detailed documentation of this important surface. To improve the topographic accuracy in its characterization, fieldwork has been initiated to establish a detailed WNW

  15. Precambrian-Cambrian provenance of Matinde Formation, Karoo Supergroup, northwestern Mozambique, constrained from detrital zircon U-Pb age and Lu-Hf isotope data

    Science.gov (United States)

    Bicca, Marcos Müller; Jelinek, Andrea Ritter; Philipp, Ruy Paulo; de Carvalho Lana, Cristiano; Alkmim, Ana Ramalho

    2018-02-01

    The Permian-Triassic time interval was a period of high sedimentation rates in the intracontinental Karoo rift basin of northwestern Mozambique, reflecting high exhumation rates in the surrounding high ground Precambrian-Cambrian basement and juxtaposed nappes. U-Pb LA-MC-ICPMS dating and Lu-Hf isotopic analysis of detrital zircons from the Late Permian-Early Triassic Matinde Formation of the Karoo Supergroup is used as a reliable proxy to map denudation patterns of source regions. Data allow discrimination of U-Pb age populations of ca. 1250-900 Ma, a secondary population between ca. 900-700 and a major contribution of ages around ca. 700-490 Ma. Zircon grains of the Mesoproterozoic age population present Mesoproterozoic (1000-1500 Ma) to Paleoproterozoic (1800-2300 Ma) Hf TDM ages, with positive (0 to +11) and negative εHf values (-3 to -15), respectively. The younger U-Pb age population also presents two different groups of zircon grains according to Lu-Hf isotopes. The first group comprise Paleoproterozoic (1800-2300 Ma) ages, with highly negative εHf values, between -10 and -22, and the second group exhibits Mesoproterozoic ages (1200-1500 Ma), with increased juvenile εHf values (ca. 0 to -5). These Hf isotopes reinforce the presence of unexposed ancient crust in this region. The oldest U-Pb age population resembles the late stages of Grenville Orogeny and the Rodinia Supercontinent geotectonic activity mostly represented by magmatic rocks, which are widely present in the basement of northern Mozambique. The juvenile Hf-isotope signature with an older age component is associated to rocks generated from subduction processes with crust assimilation by continental arcs, which we correlate to rocks of the Nampula Complex, south and east of the Moatize-Minjova Basin. The U-Pb ages between 900 and 700 Ma were correlated to the calc-alkaline magmatism registered in the Guro Suite, related to the breakup phase of Rodinia, and mark the western limit of the Moatize

  16. Cambrian origin of the CYP27C1-mediated vitamin A1-to-A2 switch, a key mechanism of vertebrate sensory plasticity

    Science.gov (United States)

    Morshedian, Ala; Toomery, Matthew B.; Pollock, Gabriel E.; Frederiksen, Rikard; Enright, Jennifer; McCormick, Stephen; Cornwall, M. Carter; Fain, Gordon L.; Corbo, Joseph C.

    2017-01-01

    The spectral composition of ambient light varies across both space and time. Many species of jawed vertebrates adapt to this variation by tuning the sensitivity of their photoreceptors via the expression of CYP27C1, an enzyme that converts vitamin A1 into vitamin A2, thereby shifting the ratio of vitamin A1-based rhodopsin to red-shifted vitamin A2-based porphyropsin in the eye. Here, we show that the sea lamprey (Petromyzon marinus), a jawless vertebrate that diverged from jawed vertebrates during the Cambrian period (approx. 500 Ma), dynamically shifts its photoreceptor spectral sensitivity via vitamin A1-to-A2 chromophore exchange as it transitions between photically divergent aquatic habitats. We further show that this shift correlates with high-level expression of the lamprey orthologue of CYP27C1, specifically in the retinal pigment epithelium as in jawed vertebrates. Our results suggest that the CYP27C1-mediated vitamin A1-to-A2 switch is an evolutionarily ancient mechanism of sensory plasticity that appeared not long after the origin of vertebrates.

  17. Sequence stratigraphy of the Upper Cambrian (Furongian; Jiangshanian and Sunwaptan) Tunnel City Group, Upper Mississippi Valley: Transgressing assumptions of cratonic flooding

    Science.gov (United States)

    Eoff, Jennifer D.

    2014-01-01

    New data from detailed measured sections permit comprehensive analysis of the sequence framework of the Furongian (Upper Cambrian; Jiangshanian and Sunwaptan stages) Tunnel City Group (Lone Rock Formation and Mazomanie Formation) of Wisconsin and Minnesota. The sequence-stratigraphic architecture of the lower part of the Sunwaptan Stage at the base of the Tunnel City Group, at the contact between the Wonewoc Formation and Lone Rock Formation, records the first part of complex polyphase flooding (Sauk III) of the Laurentian craton, at a scale smaller than most events recorded by global sea-level curves. Flat-pebble conglomerate and glauconite document transgressive ravinement and development of a condensed section when creation of accommodation exceeded its consumption by sedimentation. Thinly-bedded, fossiliferous sandstone represents the most distal setting during earliest highstand. Subsequent deposition of sandstone characterized by hummocky or trough cross-stratification records progradational pulses of shallower, storm- and wave-dominated environments across the craton before final flooding of Sauk III commenced with carbonate deposition during the middle part of the Sunwaptan Stage. Comparison of early Sunwaptan flooding of the inner Laurentian craton to published interpretations from other parts of North America suggests that Sauk III was not a single, long-term accommodation event as previously proposed.

  18. Use of cycle stacking patterns to define third-order depositional sequences: Middle to Late Cambrian Bonanza King Formation, southern Great basin

    Energy Technology Data Exchange (ETDEWEB)

    Montanez, I.P.; Droser, M.L. (Univ. of California, Riverside (United States))

    1991-03-01

    The Middle to Late Cambrian Bonanza King Formation (CA, NV) is characterized by superimposed scales of cyclicity. Small-scale cycles (0.5 to 10m) occur as shallowing-upward peritidal and subtidal cycles that repeat at high frequencies (10{sup 4} to 10{sup 5}). Systematic changes in stacking patterns of meter-scale cycles define several large-scale (50-250 m) third-order depositional sequences in the Bonanza King Formation. Third-order depositional sequences can be traced within ranges and correlated regionally across the platform. Peritidal cycles in the Bonanza King Formation are both subtidal- and tidal flat-dominated. Tidal flat-dominated cycles consist of muddy bases grading upward into thrombolites or columnar stromatolites all capped by planar stromatolites. Subtidal cycles in the Bonanza King Formation consist of grainstone bases that commonly fine upward and contain stacked hardgrounds. These are overlain by digitate-algal bioherms with grainstone channel fills and/or bioturbated ribbon carbonates with grainstone lenses. Transgressive depositional facies of third-order depositional sequences consist primarily of stacks of subtidal-dominated pertidial cycles and subtidal cycles, whereas regressive depositional facies are dominated by stacks of tidal flat-dominated peritidal cycles and regoliths developed over laminite cycle caps. The use of high frequency cycles in the Bonanza King Formation to delineate regionally developed third-order depositional sequences thus provides a link between cycle stratigraphy and sequence stratigraphy.

  19. Sedimentary facies of the upper Cambrian (Furongian; Jiangshanian and Sunwaptan) Tunnel City Group, Upper Mississippi Valley: new insight on the old stormy debate

    Science.gov (United States)

    Eoff, Jennifer D.

    2014-01-01

    New data from detailed measured sections permit a comprehensive revision of the sedimentary facies of the Furongian (upper Cambrian; Jiangshanian and Sunwaptan stages) Tunnel City Group (Lone Rock Formation and Mazomanie Formation) of Wisconsin and Minnesota. Heterogeneous sandstones, comprising seven lithofacies along a depositional transect from shoreface to transitional-offshore environments, record sedimentation in a storm-dominated, shallow-marine epicontinental sea. The origin of glauconite in the Birkmose Member and Reno Member of the Lone Rock Formation was unclear, but its formation and preserved distribution are linked to inferred depositional energy rather than just net sedimentation rate. Flat-pebble conglomerate, abundant in lower Paleozoic strata, was associated with the formation of a condensed section during cratonic flooding. Hummocky cross-stratification was a valuable tool used to infer depositional settings and relative paleobathymetry, and the model describing formation of this bedform is expanded to address flow types dominant during its genesis, in particular the importance of an early unidirectional component of combined flow. The depositional model developed here for the Lone Rock Formation and Mazomanie Formation is broadly applicable to other strata common to the early Paleozoic that document sedimentation along flooded cratonic interiors or shallow shelves.

  20. A normalised seawater strontium isotope curve. Possible implications for Neoproterozoic-Cambrian weathering rates and the further oxygenation of the Earth

    International Nuclear Information System (INIS)

    Shields, G.A.

    2007-01-01

    The strontium isotope composition of seawater is strongly influenced on geological time scales by changes in the rates of continental weathering relative to ocean crust alteration. However, the potential of the seawater 87 Sr/ 86 Sr curve to trace globally integrated chemical weathering rates has not been fully realised because ocean 87 Sr/ 86 Sr is also influenced by the isotopic evolution of Sr sources to the ocean. A preliminary attempt is made here to normalise the seawater 87 Sr/ 86 Sr curve to plausible trends in the 87 Sr/ 86 Sr ratios of the three major Sr sources: carbonate dissolution, silicate weathering and submarine hydrothermal exchange. The normalised curve highlights the Neoproterozoic-Phanerozoic transition as a period of exceptionally high continental influence, indicating that this interval was characterised by a transient increase in global weathering rates and/or by the weathering of unusually radiogenic crustal rocks. Close correlation between the normalised 87 Sr/ 86 Sr curve, a published seawater δ 34 S curve and atmospheric pCO 2 models is used here to argue that elevated chemical weathering rates were a major contributing factor to the steep rise in seawater 87 Sr/ 86 Sr from 650 Ma to 500 Ma. Elevated weathering rates during the Neoproterozoic-Cambrian interval led to increased nutrient availability, organic burial and to the further oxygenation of Earth's surface environment. Use of normalised seawater 87 Sr/ 86 Sr curves will, it is hoped, help to improve future geochemical models of Earth System dynamics. (orig.)

  1. Palaeoenvironmental and geochemical approach of Archaeocyath-rich facies from Lower Cambrian of Western Gondwana margin at Central Iberian Zone (Urda, Toledo Mountains, Spain)

    Science.gov (United States)

    Menéndez, Silvia; Rodríguez-Martínez, Marta; Moreno-Eris, Elena; Perejón, Antonio; Reitner, Joachim

    2010-05-01

    Archaeocyath-rich facies are located in a quarry close to Urda village, at Toledo Mountains, Spain. The outcrops belong to the Caliza de los Navalucillos Formation and they record a considerably high diverse archaeocyath assemblage in the Lower Cambrian successions from the Central Iberian Zone (Julivert et al. 1972 [1974]). In fact, it is first time recorded the presence of Agyrekocyathus, Dokidocyathus, and Plicocyathus in the Central Iberian Zone. Therefore Plicocyathus is no longer exclusive to biozone VI in Spain. The presence of Anthomorpha is characteristic for the early Botomian, presently early Stage 4 (ICS, 2009), and the assemblage corresponds to the biozone VII (late Ovetian, following the biozonation of Perejón & Moreno-Eiris, 2006). The fossiliferous part of the succession is formed by seven lithofacies, all of them tectonically folded and with a low grade metamorphic overprint. They are comprised by two main groups of facies: (a) mound-shaped to massive lithofacies (A1, A2, A3, A4) and (b) massive to bedded and nodular lithofacies (B1, B2, B3). Archaeocyaths occur in several facies: (A1) mound-shaped white marble with irregular to stromatactoid cavities; (A2) massive mottled white to grey limestone; (A3) massive grey limestone with slumps levels; (A4) massive archaeocyath-rich orange limestone; as well as in carbonate nodules embedded in siltstones and cherts (B1, B2 and B3). The best preserved assemblage comes from the nodule record, where fossils are partially pyritized. This type of preservation is exceptional and has never been described before. XRD and wavelength-dispersive electron microprobe analyses reveal the presence of pyrite and pyrrotine partially altered to iron oxides and hydroxides (hematite and goethite) surrounding the archaeocyath cups. In Central Iberian Zone, the development of mounds and nodular facies like those described here is unusual, although the Botomian marks the peak for Early Cambrian archaeocyathan-microbial mounds

  2. Deep mantle roots and continental hypsometry: implications for whole-Earth elemental cycling, long-term climate, and the Cambrian explosion

    Science.gov (United States)

    Lee, C. T.

    2016-12-01

    Cambrian explosion, the largest biological diversification event in Earth's history.

  3. Logging identification for the Lower Cambrian Niutitang shale reservoir in the Upper Yangtze region, China: A case study of the Cengong block, Guizhou Province

    Directory of Open Access Journals (Sweden)

    Ruyue Wang

    2016-06-01

    Full Text Available Currently, China has achieved a breakthrough in the Lower Silurian Longmaxi shale in Sichuan Basin and its surrounding areas. Compared to the Longmaxi shale, the Lower Cambrian Niutitang shale, which has a greater deposition thickness and wider distribution area, is another significant stratum for China's shale gas. Geophysical well logging is one of the most significant methods used for identification and evaluation of shale gas reservoirs throughout the process of shale gas exploration and development. In this paper, the logging response of the Niutitang shale is summarized to “four high and four low”, this was determined through a comparative analysis of three shale gas wells in the Cen'gong block. The Geochemical logging (GEM data shows that as the depth goes deeper the content of Si (quartz increases and the content of Al, Fe, K (Potassium, and Clay minerals decreases. In addition, the Niutitang shale mainly has the feature of a single peak or two continuous peaks in T2 spectrum on the nuclear magnetic resonance (NMR logging response. This has a longer T2 time and greater amplitude than normal shales. The logging response of various lithology and preservation is summarized by overlapping and a cross-plot analysis with the spectral gamma-ray, resistivity, density, acoustic, and compensated neutron logging data, which are sensitive to organic-rich shales. Moreover, the resistivity and acoustic logging data are sensitive to gas content, fluid properties, and preservation conditions, which can be used as indicators of shale gas content and preservation.

  4. Ediacaran to Cambrian magmatic suites in the Rio Grande do Norte domain, extreme Northeastern Borborema Province (NE of Brazil): Current knowledge

    Science.gov (United States)

    do Nascimento, Marcos Antonio Leite; Galindo, Antonio Carlos; de Medeiros, Vladimir Cruz

    2015-03-01

    The Ediacaran-Cambrian plutonic activity is one of the most important geological features of the Rio Grande do Norte Domain (Borborema Province, NE Brazil). It is represented by several batholiths, stocks and dykes. Based on the petrographic, geochemical and geochronological characteristic of different rocks, this plutonic activity can be grouped in six separate suites: shoshonitic (Shos), porphyritic high-K calc-alkaline (PHKCalcAlk), equigranular high K calc-alkaline (EHKCalcAlk), calc-alkaline (CalcAlk), alkaline (Alk) and charnockitic alkaline (ChAlk). Geochemically, the Shos, CalcAlk and Alk suites are differentiated from the others, while ChAlc can be distinguished from the others in some diagrams. The greatest difficulty lies in distinguishing between the chemically similar PHKCalcAlk and EHKCalcAlk. To this end, existing geochronological data as well as related petrographic and textural field aspects may be used to distinguish the two mentioned suites (PHKCalcAlk and EHKCalcAlk). Petrographically, the Shos suite has composition between gabbro/diorite and quartz monzonite. Monzogranites (with subordinate granodiorites and quartz monzonites) predominate in both PHKCalcAlk and EHKCalcAlk. Calc is composed of granodiorites to tonalites. Alc is formed by alkali feldspar granites (with subordinate alkali feldspar quartz syenites and syenogranites), whereas ChAlc has quartz mangerites and charnockites. The suites were emplaced between the Ediacaran (635-541 Ma) and Cambrian (541-485 Ma), predominantly in the Ediacaran, based on 34 U-Pb datings (zircon, titanite, monazite and columbite-tantalite), 17 Rb-Sr (whole rock) and 1 Sm-Nd (total rock and mineral) internal isochrons. The Shos suite has U-Pb ages varying from 599 ± 16 (Poço Verde pluton) to 579 ± 7 (Acari and São João do Sabugi plutons), slightly older than those of the PHKCalcAlk suite, which ranges between 591 ± 4 Ma (Totoró pluton) and 544 ± 7 Ma (São José de Espinharas pluton). The Calc

  5. Paleo-environmental conditions of the Early Cambrian Niutitang Formation in the Fenggang area, the southwestern margin of the Yangtze Platform, southern China: Evidence from major elements, trace elements and other proxies

    Science.gov (United States)

    Li, Jin; Tang, Shuheng; Zhang, Songhang; Xi, Zhaodong; Yang, Ning; Yang, Guoqiao; Li, Lei; Li, Yanpeng

    2018-06-01

    The Precambrian/Cambrian transition was a key time in Earth history, especially for marine biological evolution and oceanic chemistry. The redox-stratification with oxic shallow water and anoxic (even euxinic) deeper water in the Early Cambrian Yangtze Sea, which gradually became completely oxygenated, has been suggested as a possible trigger for the "Cambrian explosion" of biological diversity. However, for some areas in northern Guizhou where the exploration and research are lacking, identifying this pattern of redox-stratification by paleo-environmental analysis from borehole data is still in need. Here, we report a remarkable variation range in trace elements (Mo, V, U, Ni, Th, Co, Sc, Zn and Cu), molar Corg:P ratios and pyrite morphology from 27 core samples from one new drill hole (XY1, located in the Fenggang area, northern Guizhou) on the Yangtze Platform, South China. High levels of Ba (from 3242 ppm to 33,800 ppm) and total organic carbon (TOC; from 4% to 9.36%) in 15 core samples in the Lower Member (LM) of the Niutitang Formation indicated elevated primary productivity in the study area. Redox change was recorded based on enrichment factors (EFs) for RSTEs (Mo, U, and V), redox proxies (V/(V + Ni), Ni/Co, V/Sc and Th/U), Corg:P ratios and particle size of framboidal pyrite. These signatures demonstrate that the LM was deposited under anoxic conditions with sulfidic episodes, whereas the Upper Member (UM) of the Niutitang Formation was deposited under suboxic/oxic conditions with intermittently anoxic episodes. Mo/TOC ratios (from 3.72 to 39.86, mean 18.76) suggest weak-moderate water mass restriction. Mo-U covariation patterns (strong but variable enrichment of Mo and U; MoEF ranging from 31.45 to 257.97; UEF ranging from 4.68 to 39.07) in the LM show alternation of particulate shuttling and redox conditions occurred in the Early Cambrian Yangtze Sea, whereas Mo-U covariation patterns (moderate Mo enrichment but depletion or non-enrichment of U; mean Mo

  6. A Cambrian mixed carbonate-siliciclastic platform in SW Gondwana: evidence from the Western Sierras Pampeanas (Argentina) and implications for the early Paleozoic paleogeography of the proto-Andean margin

    Science.gov (United States)

    Ramacciotti, Carlos D.; Casquet, César; Baldo, Edgardo G.; Galindo, Carmen; Pankhurst, Robert J.; Verdecchia, Sebastián O.; Rapela, Carlos W.; Fanning, Mark

    2018-05-01

    The Western Sierras Pampeanas (WSP) of Argentina record a protracted geological history from the Mesoproterozoic assembly of the Rodinia supercontinent to the early Paleozoic tectonic evolution of SW Gondwana. Two well-known orogenies took place at the proto-Andean margin of Gondwana in the Cambrian and the Ordovician, i.e., the Pampean (545-520 Ma) and Famatinian (490-440 Ma) orogenies, respectively. Between them, an extensive continental platform was developed, where mixed carbonate-siliciclastic sedimentation occurred. This platform was later involved in the Famatinian orogeny when it underwent penetrative deformation and metamorphism. The platform apparently extended from Patagonia to northwestern Argentina and the Eastern Sierras Pampeanas, and has probable equivalents in SW Africa, Peru, and Bolivia. The WSP record the outer (deepest) part of the platform, where carbonates were deposited in addition to siliciclastic sediments. Detrital zircon U-Pb SHRIMP ages from clastic metasedimentary successions and Sr-isotope compositions of marbles from the WSP suggest depositional ages between ca. 525 and 490 Ma. The detrital zircon age patterns further suggest that clastic sedimentation took place in two stages. The first was sourced mainly from re-working of the underlying Neoproterozoic metasedimentary rocks and the uplifted core of the early Cambrian Pampean orogen, without input from the Paleoproterozoic Río de la Plata craton. Sediments of the second stage resulted from the erosion of the still emerged Pampean belt and the Neoproterozoic Brasiliano orogen in the NE with some contribution from the Río de la Plata craton. An important conclusion is that the WSP basement was already part of SW Gondwana in the early Cambrian, and not part of the exotic Precordillera/Cuyania terrane, as was previously thought.

  7. The Sanrafaelic remagnetization revisited: Magnetic properties and magnetofabrics of Cambrian-Ordovician carbonates of the Eastern Precordillera of San Juan, Argentina

    Science.gov (United States)

    Fazzito, Sabrina Y.; Rapalini, Augusto E.; Poiré, Daniel G.

    2017-11-01

    Systematic rock-magnetic and magnetofabric studies were carried out on samples from twenty-three palaeomagnetic sites distributed on the La Laja, Zonda, La Flecha, La Silla and San Juan Formations, which constitute a thick middle Cambrian to early Ordovician carbonate sequence exposed in the Eastern Precordillera of Argentina. Previous palaeomagnetic studies on these rocks showed that this succession is characterized by a recent full overprint in the lower levels and a post-tectonic Permian remagnetization associated to the widespread Sanrafaelic event in the upper part. Our investigation revealed that the fluctuations of the magnetic properties are stratigraphically (lithologically) controlled. Anisotropy of magnetic and anhysteretic susceptibility measurements defined consistent fabrics along the entire section that switch progressively from "inverse", at the bottom, to "normal", at the top, with "intermediate" fabrics occurring mainly at medium levels. Degree of dolomitization significantly affects many rock-magnetic parameters, but appears unrelated to the presence of the Permian remagnetization, which is determined to reside in magnetite despite the complex magnetic mineralogy shown by the studied carbonates. Hysteresis cycles of rocks affected by the Sanrafaelic remagnetization are governed by ferromagnetic fractions showing a clear difference respect to those not affected and characterized by the dominance of paramagnetic or diamagnetic signals. The magnetic fabrics and mineralogical characterization rule out a thermoviscous origin and suggest a chemical remagnetization originated in the authigenic formation of magnetite for the Sanrafaelic overprint. X-ray diffraction analyses indicate that clay minerals are virtually absent in the whole succession with no traces of illite in any sample, discarding burial diagenesis of clay minerals for the origin of the remagnetization. Lack of late Palaeozoic magmatic rocks near the study area difficults correlation of

  8. Sedimentary mode and reservoir genesis of dual grain banks at the Lower Cambrian Longwangmiao Fm carbonate ramp in the Sichuan Basin

    Directory of Open Access Journals (Sweden)

    Jinhu Du

    2016-11-01

    Full Text Available The gas reservoir of the Lower Cambrian Longwangmiao Fm in the Sichuan Basin is a supergiant integral marine carbonate gas reservoir whose single scale is currently the largest in China. In order to figure out its sedimentary model and reservoir genesis, its geological structures and sedimentary settings and facies were analyzed comprehensively and the lithofacies paleographic map was plotted. It is revealed that the following sedimentary facies are successively developed in the Longwangmiao Fm from West Sichuan to Southeast Chongqing: diamictic tidal flat at the back ramp, grain bank (the upper bank at the inner/shallow ramp – interbank sea (depression, deeper open bay at the platform depression of inner ramp → evaporative lagoon → evaporative tidal flat, tempestite at the middle ramp – barrier beach – mud mound beach (the lower bank, and outer ramp – basin. Accordingly, the specific sedimentary model of dual grain banks in the Longwangmiao Fm carbonate ramp was established as follows. Firstly, in this model, dual grain banks are symmetrically developed with Wanzhou–Yibin platform depression as the axis, on whose dual sides the paleohighs have shallow water bodies with strong energy. Compared with the classical model, the new one has a new upper bank which is developed around the paleohighs covering an area of about 8 × 104 km2. Secondly, the upper bank is large for its paleogeomorphology being located at the highest position with the strongest water energy during deposition. Therefore, it is prone to dolomitization and meteoric dissolution respectively during contemporaneous–penecontemporaneous hot-dry and hot-humid periods, and especially the Caledonian–Early Hercynian denudation wedge out tends to undergo post-supergene multiphase karstification. Therefore, quality reservoirs are more developed on scale. Thirdly, the intergranular pores and vermes moldic pores were dissolved and enlarged due to the multiphase

  9. Climatic-oceanic forcing on the organic accumulation across the shelf during the Early Cambrian (Age 2 through 3) in the mid-upper Yangtze Block, NE Guizhou, South China

    Science.gov (United States)

    Yeasmin, Rumana; Chen, Daizhao; Fu, Yong; Wang, Jianguo; Guo, Zenghui; Guo, Chuan

    2017-02-01

    The organic-rich sediments were widely deposited over the entire Yangtze Block during the Early Cambrian (late Nemakit-Daldynian to Botomian). In the mid-upper Yangtze region, northeastern Guizhou, South China, they comprise, in ascending order, the Niutitang, Jiumenchong and lower Bianmachong formations which are dominated by black shales except the middle one characterized by interbedded shales-limestones. Three third-order depositional sequences are identified in the two studied sections located on the upper slope to basin of the open shelf. The organic-rich sediments were mostly deposited notably during transgressions on the shallower upper slope-margin (TOC up to 25 wt.%) where they are characterized by co-increases in C, P, Fe, and Ba concentrations, indicating the highest organic productivity and coupled C, P and Fe cycling there. In contrast, in the shelf basin, the concomitant organic-rich sediments yield lower organic (TOC Block within the north mid-low-latitude trade-wind zone during deposition (the Early Cambrian). As such, enhanced offshore currents driven by the trade winds could have further induced the upwelling of nutrient-rich deep waters along the shelf during the transgressions, although tended to wane onwards, leading to the tempo-spatial heterogeneities in organic production and redox state across the shelf sea.

  10. Geology and lithogeochemistry of hydrothermal mudstones from the upper block near the Duck Pond volcanogenic massive sulfide (VMS) deposit, Newfoundland, Canada: evidence for low-temperature venting into oxygenated mid-Cambrian seawater

    Science.gov (United States)

    Piercey, Stephen J.; Squires, Gerry; Brace, Terry

    2018-02-01

    Pyrite- and pyrrhotite-rich mudstones are spatially associated with Cambrian ( 512-509 Ma) volcanogenic massive sulfide (VMS) deposits throughout the Tally Pond group, central Newfoundland, Canada. At the Duck Pond mine, sulfide-rich mudstones are hosted within a weakly mineralized upper block that structurally overlies the deposit but is older ( 513 versus 509 Ma). The mudstones are laminated, 10-30-cm thick, and pyrite- and pyrrhotite-rich and occur along pillow lava selvages, or in between pillow lavas, rhyolite flows, and volcaniclastic rocks. The mudstones are laterally extensive and proximal to the mudstone host rocks are hydrothermally altered to epidote-quartz-chlorite (basalt host) and sericite-quartz (rhyolite host). Lithogeochemical data for the sulfide-rich mudstones reflect the varying contributions of elements from sedimentary detritus, hydrothermal discharge, and hydrogenous scavenging from middle Cambrian seawater. The mudstones have minor detrital element abundances and significant hydrothermal element enrichments (i.e., elevated Fe2O3, S, Pb, Zn, Cu, and Ba concentrations, high Fe/Al ratios). The hydrothermal mudstones are also enriched in oxyanions (i.e., P2O5, U, V, Cr, Ni, Co, and Hg), interpreted to have been enriched via oxidative scavenging from seawater by Fe-oxide/oxyhydroxide particles. The mudstones also have REE-Y signatures similar to modern oxygenated seawater with high Y/Ho and negative Ce anomalies (Ce/Ce* = 0.40-0.86; average = 0.58), which correlate with adsorbed oxyanion concentrations. The low Eu/Eu* (1.02-1.86; average = 1.22) in the mudstones suggest that they were deposited from low-temperature (residence time to scavenge oxyanions from seawater and inherit a middle Cambrian seawater signature. The predominant seawater REE-Y-oxyanion signature in the Duck Pond upper block sulfide-rich mudstones suggests that they are distal hydrothermal sedimentary rocks that could have formed up to 10 km from their original vent sources

  11. Radium mobility and the age of groundwater in public-drinking-water supplies from the Cambrian-Ordovician aquifer system, north-central USA

    Science.gov (United States)

    Stackelberg, Paul E.; Szabo, Zoltan; Jurgens, Bryant C.

    2018-01-01

    High radium (Ra) concentrations in potable portions of the Cambrian-Ordovician (C-O) aquifer system were investigated using water-quality data and environmental tracers (3H, 3Hetrit, SF6, 14C and 4Herad) of groundwater age from 80 public-supply wells (PSWs). Groundwater ages were estimated by calibration of tracers to lumped parameter models and ranged from modern (1 Myr) in the most downgradient, confined portions of the potable system. More than 80 and 40 percent of mean groundwater ages were older than 1000 and 50,000 yr, respectively. Anoxic, Fe-reducing conditions and increased mineralization develop with time in the aquifer system and mobilize Ra into solution resulting in the frequent occurrence of combined Ra (Rac = 226Ra + 228Ra) at concentrations exceeding the USEPA MCL of 185 mBq/L (5 pCi/L). The distribution of the three Ra isotopes comprising total Ra (Rat = 224Ra + 226Ra + 228Ra) differed across the aquifer system. The concentrations of 224Ra and 228Ra were strongly correlated and comprised a larger proportion of the Rat concentration in samples from the regionally unconfined area, where arkosic sandstones provide an enhanced source for progeny from the 232Th decay series. 226Ra comprised a larger proportion of the Ratconcentration in samples from downgradient confined regions. Concentrations of Rat were significantly greater in samples from the regionally confined area of the aquifer system because of the increase in 226Ra concentrations there as compared to the regionally unconfined area. 226Ra distribution coefficients decreased substantially with anoxic conditions and increasing ionic strength of groundwater (mineralization), indicating that Ra is mobilized to solution from solid phases of the aquifer as adsorption capacity is diminished. The amount of 226Ra released from solid phases by alpha-recoil mechanisms and retained in solution increases relative to the amount of Ra sequestered by adsorption processes or co

  12. Le graben de l'Anti-Atlas occidental (Maroc) : contrôle tectonique de la paléogéographie et des séquences au Cambrien inférieurThe Lower-Cambrian western Anti-Atlasic graben: tectonic control of palaeogeography and sequential organisation

    Science.gov (United States)

    Benssaou, Mohammed; Hamoumi, Naı̈ma

    2003-03-01

    In the Moroccan western Anti-Atlas, the combined extensive tectonic events with a long-term sea-level rise is the main factor on building vertical stacking transgressive-regressive sequences. In the Ait Abdallah-Boussafene axis, the subsidence processes, relayed by a brutal platform tilting generated an elongated NE-SW graben. This is an evidence of the persistence of the Anti-Atlasic rifting process during the last part of the Lower-Cambrian succession.

  13. Precambrian tholeiitic-dacitic rock-suites and Cambrian ultramafic rocks in the Pennine nappe system of the Alps: Evidence from Sm-Nd isotopes and rare earth elements

    Science.gov (United States)

    Stille, P.; Tatsumoto, M.

    1985-04-01

    Major element, trace element and Sm-Nd isotope analyses were made of polymetamorphic hornblendefelses, plagioclase amphibolites and banded amphibolites from the Berisal complex in the Simplon area (Italy, Switzerland) to determine their age, origin and genetic relationships. In light of major and rare earth element data, the hornblendefelses are inferred to have originally been pyroxene-rich cumulates, the plagioclase amphibolites and the dark layers of the banded amphibolites to have been tholeiitic basalts and the light layers dacites. The Sm-Nd isotope data yield isochron ages of 475±81 Ma for the hornblendefelses, 1,018±59 Ma for the plagioclase amphibolites and 1,071±43 Ma for the banded amphibolites. The 1 Ga magmatic event is the oldest one ever found in the crystalline basement of the Pennine nappes. The Sm -Nd isotope data support the consanguinity of the tholeiitic dark layers and the dacitic light layers of the banded amphibolites with the tholeiitic plagioclase amphibolites and the ultramafic hornblendefelses. The initial ɛ Nd values indicate that all three rock types originated from sources depleted in light rare earth elements. We suggest that plagioclase and banded amphibolites were a Proterozoic tholeiite-dacite sequence that was strongly deformed and flattened during subsequent folding. The hornblendefelses are thought to be Cambrian intrusions of pyroxene-rich material.

  14. Chlorine activation and ozone destruction in the northern lowermost stratosphere

    NARCIS (Netherlands)

    Lelieveld, J; Bregman, A; Scheeren, HA; Strom, J; Carslaw, KS; Fischer, H; Siegmund, PC; Arnold, F

    1999-01-01

    We report aircraft measurements from the Stratosphere-Troposphere Experiments by Aircraft Measurements (STREAM) II campaign, performed during February 1995 from Kiruna, northern Sweden, near 67 degrees N latitude. We have measured trace species, e.g., O-3, nitrogen compounds, HCl, hydrocarbons, CO,

  15. Structure in the lowermost mantle from seismic anisotropy

    Science.gov (United States)

    Walpole, J.; Wookey, J. M.; Nowacki, A.; Walker, A.; Kendall, J. M.; Masters, G.; Forte, A. M.

    2017-12-01

    Anisotropy is well established in D'' and places important constraints on the nature and dynamics of this elusive region. We present the results of a recent study probing anisotropy in D'', over a large area, using shear wave splitting on core-reflected ScS phases. Our dataset contains laterally continuous coverage beneath a large swath of east Asia - extending about 3000 km along the CMB - from south-east Asia to the north-east Pacific. The centre of this area represents a large down-welling core for subduction that has occurred over several super-continent cycles. In the centre of this region we observe a clear VSV}>V{SH fabric, in direct conflict with the prevailing view that fast, `cold', regions are associated with VSH}>V{SV fabric. Furthermore, systematic rotation of the fast axis traces out an apparent dome-like feature extending over thousands of km, albeit complicated by some short-scale variability. The dataset also samples regions where slab material may be actively impinging on the CMB; and a region corresponding to the edge of the Pacific LLSVP. We interpret our results in light of a combined computational geodynamic-petrofabric-seismic study designed to test the possibility that anisotropy is caused by the lattice preferred orientation of post-perovskite. We take into account the important finite-frequency effects of wave propagation in our synthetics by using the SPECFEM3D_GLOBE code; this can lead to drastically different results when compared to the less accurate ray theory.

  16. Eutectic melting temperature of the lowermost Earth's mantle

    Science.gov (United States)

    Andrault, D.; Lo Nigro, G.; Bolfan-Casanova, N.; Bouhifd, M.; Garbarino, G.; Mezouar, M.

    2009-12-01

    Partial melting of the Earth's deep mantle probably occurred at different stages of its formation as a consequence of meteoritic impacts and seismology suggests that it even continues today at the core-mantle boundary. Melts are important because they dominate the chemical evolution of the different Earth's reservoirs and more generally the dynamics of the whole planet. Unfortunately, the most critical parameter, that is the temperature profile inside the deep Earth, remains poorly constrained accross the planet history. Experimental investigations of the melting properties of materials representative of the deep Earth at relevant P-T conditions can provide anchor points to refine past and present temperature profiles and consequently determine the degree of melting at the different geological periods. Previous works report melting relations in the uppermost lower mantle region, using the multi-anvil press [1,2]. On the other hand, the pyrolite solidus was determined up to 65 GPa using optical observations in the laser-heated diamond anvil cell (LH-DAC) [3]. Finally, the melting temperature of (Mg,Fe)2SiO4 olivine is documented at core-mantle boundary (CMB) conditions by shock wave experiments [4]. Solely based on these reports, experimental data remain too sparse to draw a definite melting curve for the lower mantle in the relevant 25-135 GPa pressure range. We reinvestigated melting properties of lower mantle materials by means of in-situ angle dispersive X-ray diffraction measurements in the LH-DAC at the ESRF [5]. Experiments were performed in an extended P-T range for two starting materials: forsterite and a glass with chondrite composition. In both cases, the aim was to determine the onset of melting, and thus the eutectic melting temperatures as a function of pressure. Melting was evidenced from drastic changes of diffraction peak shape on the image plate, major changes in diffraction intensities in the integrated pattern, disappearance of diffraction rings, and changes in the relation between sample-temperature and laser-power. In this work, we show that temperatures higher than 4000 K are necessary for melting mean mantle at the 135 GPa pressure found at the core mantle boundary (CMB). Such temperature is much higher than that from estimated actual geotherms. Therefore, melting at the CMB can only occur if (i) pyrolitic mantle resides for a very long time in contact with the outer core, (ii) the mantle composition is severely affected by additional elements depressing the solidus such as water or (iii) the temperature gradient in the D" region is amazingly steep. Other implications for the temperature state and the lower mantle properties will be presented. References (1) Ito et al., Phys. Earth Planet. Int., 143-144, 397-406, 2004 (2) Ohtani et al., Phys. Earth Planet. Int., 100, 97-114, 1997 (3) Zerr et al., Science, 281, 243-246, 1998 (4) Holland and Ahrens, Science, 275, 1623-1625, 1997 (5) Schultz et al., High Press. Res., 25, 1, 71-83, 2005.

  17. Trace- and rare-earth element geochemistry and Pb-Pb dating of black shales and intercalated Ni-Mo-PGE-Au sulfide ores in Lower Cambrian strata, Yangtze Platform, South China

    Science.gov (United States)

    Jiang, Shao-Yong; Chen, Yong-Quan; Ling, Hong-Fei; Yang, Jing-Hong; Feng, Hong-Zhen; Ni, Pei

    2006-08-01

    The Lower Cambrian black shale sequence of the Niutitang Formation in the Yangtze Platform, South China, hosts an extreme metal-enriched sulfide ore bed that shows >10,000 times enrichment in Mo, Ni, Se, Re, Os, As, Hg, and Sb and >1,000 times enrichment in Ag, Au, Pt, and Pd, when compared to average upper continental crust. We report in this paper trace- and rare-earth-element concentrations and Pb-Pb isotope dating for the Ni-Mo-PGE-Au sulfide ores and their host black shales. Both the sulfide ores and their host black shales show similar trace-element distribution patterns with pronounced depletion in Th, Nb, Hf, Zr, and Ti, and extreme enrichment in U, Ni, Mo, and V compared to average upper crust. The high-field-strength elements, such as Zr, Hf, Nb, Ta, Sc, Th, rare-earth elements, Rb, and Ga, show significant inter-element correlations and may have been derived mainly from terrigenous sources. The redox sensitive elements, such as V, Ni, Mo, U, and Mn; base metals, such as Cu, Zn, and Pb; and Sr and Ba may have been derived from mixing of seawater and venting hydrothermal sources. The chondrite-normalized REE patterns, positive Eu and Y anomalies, and high Y/Ho ratios for the Ni-Mo-PGE-Au sulfide ores are also suggestive for their submarine hydrothermal-exhalative origin. A stepwise acid-leaching Pb-Pb isotope analytical technique has been employed for the Niutitang black shales and the Ni-Mo-PGE-Au sulfide ores, and two Pb-Pb isochron ages have been obtained for the black shales (531±24 Ma) and for the Ni-Mo-PGE-Au sulfide ores (521±54 Ma), respectively, which are identical and overlap within uncertainty, and are in good agreement with previously obtained ages for presumed age-equivalent strata.

  18. Electric property evidences of carbonification of organic matters in marine shales and its geologic significance: A case study of the Lower Cambrian Qiongzhusi shale in the southern Sichuan Basin

    Directory of Open Access Journals (Sweden)

    Yuman Wang

    2014-12-01

    Full Text Available Searching for some reliable evidences that can verify the carbonification of organic matters in marine shales is a major scientific issue in selecting shale gas fairways in old strata. To this end, based on core, logging and testing data, the electric property of two organic-rich shale layers in the Lower Cambrian Qiongzhusi Fm. and the Lower Silurian Longmaxi Fm. in the southern Sichuan Basin was compared to examine the carbonification signs of organic matters in the Qiongzhusi shale and its influence on gas occurrence in the shales. The following conclusions were reached: (1 the electric property experiment shows that the Qiongzhusi shale in the study area has had carbonification of organic matters. The low resistivity of dry samples from this highly mature organic-rich shale and ultra-low resistivity on downhole logs can be used to directly judge the degree of organic matter carbonification and the quality of source rocks; (2 in the Changning area, the Qiongzhusi shale shows low resistivity of dry samples and low to ultra-low resistivity on logs, indicating that organic matters are seriously carbonized, while in the Weiyuan area, the Qiongzhusi shale shows a basically normal resistivity on log curves, indicating its degree of graphitization between the Longmaxi Fm. and Qiongzhusi Fm. in the Changning area; (3 shale with medium-to-high resistivity is remarkably better than that with ultra-low resistivity in terms of gas generation potential, matrix porosity and gas adsorption capacity; (4 industrial gas flow has been tested in the organic shales with medium-to-high resistivity in the Jianwei–Weiyuan–Tongnan area in the north, where the Qiongzhusi shale is a favorable shale gas exploration target.

  19. 3D geomechanical modeling and numerical simulation of in-situ stress fields in shale reservoirs: A case study of the lower Cambrian Niutitang formation in the Cen'gong block, South China

    Science.gov (United States)

    Liu, Jingshou; Ding, Wenlong; Yang, Haimeng; Wang, Ruyue; Yin, Shuai; Li, Ang; Fu, Fuquan

    2017-08-01

    An analysis of the in-situ state of stress in a shale reservoir was performed based on comprehensive information about the subsurface properties from wellbores established during the development of an oil and gas field. Industrial-level shale gas production has occurred in the Niutitang formation of the lower Cambrian Cen'gong block, South China. In this study, data obtained from hydraulic fracturing, drilling-induced fractures, borehole breakout, global positioning system (GPS), and well deviation statistics have been used to determine the orientation of the maximum horizontal principal stress. Additionally, hydraulic fracturing and multi-pole array acoustic logging (XMAC) were used to determine the vertical variations in the in-situ stress magnitude. Based on logging interpretation and mechanical experiments, the spatial distributions of mechanical parameters were obtained by seismic inversion, and a 3D heterogeneous geomechanical model was established using a finite element stress analysis approach to simulate the in-situ stress fields. The effects of depth, faults, rock mechanics, and layer variations on the principal stresses, horizontal stress difference (Δσ), horizontal stress difference coefficient (Kh), and stress type coefficient (Sp) were determined. The results show that the direction of the maximum principal stress is ESE 120°. Additionally, the development zones of natural fractures appear to correlate with regions with high principal stress differences. At depths shallower than 375 m, the stress type is mainly a thrust faulting stress regime. At depths ranging from 375 to 950 m, the stress type is mainly a strike-slip faulting stress regime. When the depth is > 950 m, the stress type is mainly a normal faulting stress regime. Depth, fault orientation, and rock mechanics all affect the type of stress. The knowledge regarding the Cen'gong block is reliable and can improve borehole stability, casing set point determination, well deployment

  20. Evidence of syn tectonic tephrites with nepheline in the Sidi Said Maachou Cambrian basin (coastal Meseta, Morocco); geo dynamic implications; Mise en evidence de tephrites a nepheline syntectoniques dans le bassin cambrien de Sidi Said Maachou (Meseta cotiere, Maroc); signification geodynamique

    Energy Technology Data Exchange (ETDEWEB)

    Remmal, T.; Mohsine, A.; El Hatimi, N.

    2009-07-01

    Based on a combined structural, petrographic, and geochemical analysis, a new interpretation of the basic magmatism of Sidi Said Maachou (coastal Meseta) in two stages of emplacement is proposed. The first stage is characterized by transitional pyroclastic flows that have accompanied the opening of the West-Mesetian basin, during the Cambrian; the second stage is made of dykes of basalts, dolerites, and tephrites bearing nepheline. The emplacement of this undersaturated alkaline magma is associated to a sinistral sub meridian shear zone which has been activated at the end of the Caledonian orogenesis, by a mantellic advection. (Author) 32 refs.

  1. Enrolment in Conocoryphe heberti Munier-Chalmas and Bergeron, 1889 (Middle Cambrian, Iberian Chain, NE Spain) and coaptive structures within family Conocoryphidae; Enrollamiento en Conocoryphe heberti Munier-Chalmas and Bergeron, 1889 (Cambrico Medio, Cadena Iberica, NE de Espana) y estructuras coaptativas en la familia

    Energy Technology Data Exchange (ETDEWEB)

    Esteve, J.

    2009-07-01

    Enrolled Conocoryphe heberti is described with detail and compared with the conocoryphid Occatharia sdzuyi, both very abundant in the middle Cambrian from the Mediterranean subprovince. Both show different morphological novelties very useful to enrol and interlock the trilobite body. The morphological study allows us to recognize coaptative devices that show the possibility of a tight encapsulation enrolment. The coaptative devices are analyzed in cephalons, pigidia and almost completed outstretched trilobites of Bailiella levyi, Bailiaspis souchoni and Parabailiella languedocensis belonging to the same family. The coaptative structures analyzed show enough variability in cephalons and pigidia that allow suggesting several enrolment types within conocoryphids. (Author) 54 refs.

  2. Journal of Earth System Science | Indian Academy of Sciences

    Indian Academy of Sciences (India)

    The Early Permian succession of the Salt Range has been classified into four formations, which together indicates a changing climatic regime during the Early Permian in the Salt Range region. The lower-most, Tobra Formation unconformably overlies a Cambrian sequence and is composed of tillite, diamictite and fresh ...

  3. Early Cambrian wave-formed shoreline deposits

    DEFF Research Database (Denmark)

    Clemmensen, Lars B; Glad, Aslaug Clemmensen; Pedersen, Gunver Krarup

    2017-01-01

    -preserved subaqueous dunes and wave ripples indicates deposition in a wave-dominated upper shoreface (littoral zone) environment, and the presence of interference ripples indicates that the littoral zone environment experienced water level fluctuations due to tides and/or changing meteorological conditions. Discoidal....... During this period, wave-formed shoreline sediments (the Vik Member, Hardeberga Formation) were deposited on Bornholm and are presently exposed at Strøby quarry. The sediments consist of fine- and medium-grained quartz-cemented arenites in association with a few silt-rich mudstones. The presence of well...

  4. Palynological study (spores, Acritarchs and Chitinozoans) in the paleozoic (Cambrian to Dinantian) of western and meridional Morocco (biostratigraphy, paleo-bio-geography and characterisation of organic matter); Etude palynologique (spores, Chitinozoaires, Acritarches) dans le Paleozoique: Cambrien a Dinantien du Maroc occidental et meridional (biostratigraphie, paleobiogeographie et caracterisation de la matiere organique)

    Energy Technology Data Exchange (ETDEWEB)

    Rahmani, K.

    1995-01-27

    The palynological study of paleozoic levels in ten wells and two cross sections in western and meridional Morocco has permit to establish the inventory of organic micro-fossils. Some of these are spores and Acritarchs which constitute much rich and more conserved than to Chitinozoans. The different associations yield from the middle Cambrian to the lower Carboniferous have allowed the setting of a bio-zonation. This latter, consists of 7 biozones based on Carboniferous and Acritarchs in the lower Paleozoic, and 12 biozones in the Devonian and lower Carboniferous based essentially on the spores. This bio-zonation however, does not provide full information. This is due to the degradation of the micro-fossils, their absence of an unsuitable facies, a shortage of samples, erosion or lack of sedimentation. Most of these short comings were dated and their importance was considered in relation to the different epeirogeny known in Morocco. The biozones distinguished were based on index taxa of spores, Chitinozoans or Acritarchs which coexist with biostratigraphic micro-fossils in Morocco or in others regions referred to. This biozones allowed: the indication of the precision of many subdivisions within the Paleozoic of the studied areas the setting of local, regional and intercontinental correlations, subsequently: Anti-Atlas, Moroccan Meseta, Algeria, Libya, North, America, Canada and Europe. The paleo-bio-geographic evolution traced from the middle Cambrian to the lower Carboniferous has demonstrated that the position of Morocco between north Gondwana and Avalonia zone at the lower Paleozoic and between Africa and Europe during the upper Paleozoic, has associated this area to different geological phenomena. Morocco also constituted a paleo-bio-geographic bridge which has allowed diverse exchanges, especially floristic one, between the Gondvanian and the Laurasian domains. This privileged position of Morocco in the geographic and geologic line has certainly influenced the

  5. SHRIMP chronology of the Magallanes Basin basement, Tierra del Fuego: Cambrian plutonism and Permian high-grade metamorphism Geocronología SHRIMP del basamento de la Cuenca de Magallanes, Tierra del Fuego: plutonismo Cámbrico y metamorfismo Pérmico de alto grado

    Directory of Open Access Journals (Sweden)

    Francisco Hervé

    2010-07-01

    Full Text Available Five new SHRTMP U-Pb zircon ages are reported for gneisses and foliated plutonic rocks belonging to the Tierra del Fuego igneous and metamorphic basement complex (TFIMC, obtained from the bottom of borehole cores through the Magallanes Basin. Three of the samples yielded weighted mean 206Pb/238U ages (523±7 Ma, 522±6 Ma and 538±6 Ma, interpreted as indicating Early Cambrian igneous crystallization of the host rocks. A migmatitic gneiss shows peaks at ca. 950-1,100 Ma and 560-650 Ma from inherited zircon grains in addition to two grains with ages of ca. 525 Ma, suggesting involvement of Grenvillian and Brasiliano material in the protolith of a Cambrian migmatite. A cordierite-sillimanite-garnet gneiss contains igneous zircons of Cambrian age and a population of U-rich metamorphic Permian zircons, indicating that a Permian high-grade metamorphic and anatectic (P=2-3 kbar, T=730-770°C event affected the Cambrian igneous rocks or sedimentary rocks derived from them. Cambrian/Ediacaran plutonic rocks are known from the basement of NW Argentina, the Sierra de la Ventana, the Cape Fold Belt in South Africa, and the Ross Orogen in Antarctica. The Permian metamorphic event is coeval with the deformation and low-grade metamorphism of the sedimentary successions that overlie the basement in many of these areas. In Tierra del Fuego at least 8 to 12 km of cover rocks were removed following the high-grade Permian metamorphic episode and the unconformable deposition of the Tobífera Formation volcanic rocks in the Middle to Late Jurassic. This eroded cover could nave been an important source of detritus for the conglomeratic Permian and Triassic? Successions of neighboring regions in South America, Africa and Antarctica.Cinco nuevas edades radiométricas logradas mediante análisis U-Pb en circón utilizando el SHRIMP, fueron determinadas en gneises y rocas plutónicas foliadas obtenidas desde el fondo de pozos de sondajes en la Cuenca de Magallanes y

  6. Palynology of uppermost Jurassic and lowermost Cretaceous strata in the Eastern Netherlands

    NARCIS (Netherlands)

    Burger, D.

    1965-01-01

    The present investigation is a systematical treatment of the sporomorphs from strata at the Jurassic-Cretaceous boundary in the eastern Netherlands Twente area, and an attempt to apply palynology to detailed stratigraphical study, by making use of quantitative pollen analyses. The rock samples used

  7. Pre-cambrian geochronology in Rio Grande do Norte, Brazil

    International Nuclear Information System (INIS)

    Galindo, A.C.

    1981-08-01

    The Precambrian region polyciclic caracter, in the Rio Grande do Norte State has make difficulties to its geochronological and geological studies. Four importants tectonometamorphic occurences identified dissimulate the original isotopic composition of the rocks. Is much defined the presence of three geochronological events wich left vestiges in the differents Serido litological units. The first event is related with Jequie cicle (2,7 b.y) and related with the Caico Group rocks. The second important event define the Transamazonic cicle (2.1 b.y). The third is correlated with Brazilian Cicle, when occurred the granitoids and pegmatites bodies formation. This third event was the last in this region and affect the other units too. (C.D.G.) [pt

  8. Nonbiomineralized carapaces in Cambrian seafloor landscapes (Sirius Passet, Greenland)

    DEFF Research Database (Denmark)

    Mangano, M. Gabriela; Bromley, Richard Granville; Harper, David A. T.

    2012-01-01

    a significant role. Although some trace fossils (e.g., annulated structures) may be related to scavenging and/or deposit feeding, morphologic evidence suggests that this is not always the case. Interconnected burrow systems provide evidence for re-use of structures, suggesting grazing on or farming of bacteria...

  9. The Cambrian cavalcades in the Cuchilla Dionisio sub ground. Uruguay

    International Nuclear Information System (INIS)

    Bossi, J.

    2010-01-01

    Most tratadistes consider that Sierra Ballena shear zone (SBSZ) is the western limit of an all octon block after the paper of Boss i and Gauche r (2004) showing a detailed geological map. The same method was applied to sporulation block in the Ne of Treinta y Tres city. It was obtained a 1/100.000 geological map with photo geology and 140 field data in an area of 3500 k m2. This document allowed to discover two kinds of mega - faults put in action at the same time (about 525 Ma): a mega shear zone N30E80E with proto - to ultramylonites similar to SBSZ and a regional thrust fault with vergence to NNW. The thrust fault has different features according to the affected type of rocks. At La Micaela, the mica schists are thrust ed by gneisses and migmatites. To the N W the gneisses became firstly sharply laminated and then, horizontal ultramylonites. Both kind of faulting produced at the same time may not be explained by an orthogonal collision and instead of it, is a naturalist proof of tangential collision and alcoholisation nature of the crustal block. In order to easily understand the new proposal it is necessary to change Paso del Dragón fm by Micaela fm, Cuchilla Dionisio Terrane by Treinta y Tres; Punta del Este Terrane by Punta del Este sub - terrane

  10. An Ediacaran–Cambrian thermal imprint in Rajasthan, western India ...

    Indian Academy of Sciences (India)

    The basalt flows sometimes show pillow structures and spilitization .... moisture. About 0.2 g of each sample was packed in alu- minium capsules. The Minnesota ...... building processes; In: Magmatism in India through Time. (eds) Sheth H C ...

  11. Cambrian horses in the field Dionisio Blade (Uruguay)

    International Nuclear Information System (INIS)

    Bossi, J.; Gaucher, C.

    2010-01-01

    The shear zone of Sierra Ballena (ZCSB) , is considered the western boundary of an allochthonous block by most writers from the definition of Land Blade Dionisio. The same method to the northern block NE of the city of Thirty- Three was applied. The geological map at 1:100,000 and 1:40,000 photogeology supported by field observations 140 covers an area of ​​3500 km2, allowed 525 Ma to discover that simultaneously produce sinistral megashear N30E, 80E and a mount (horse Amarillo ) with convergence towards the NNW . The megashear consists proto and ultramylonites petrológicamente being identical to ZCSB and age < 532 Ma The horse varies by rock type . On Micaela mica schist are ridden by gneisses and migmatites . In the center, the gneisses are rolled every few inches in W are ultramylonites sub - horizontal . The simultaneity of both phenomena is unexplained by head-on collision of cratons and explained by tangential collision from the SSE with tectonic transport to the north , representing a naturalistic aloctonía test

  12. Basinal analysis of the Ecca and Lowermost Beaufort Beds and associated coal, uranium and heavy mineral beach sand occurrences

    International Nuclear Information System (INIS)

    Ryan, P.J.; Whitfield, G.G.

    1979-01-01

    The regional sediment transport directions, major provenance areas and the controlling palaeotectonic and palaeogeographic frameworks of sedimentation have been reconstructed for the Great Karoo Basin during the Permian. Analyses of this magnitude can be useful in regional exploration programmes for coal, uranium and fossil heavy mineral beach sand deposits. The strong palaeogeographic control on coal deposition is demonstrated by the fact that some of the most important deposits accumulated in topographically low lying areas on the pre-Karoo surface. Such areas formed sheltered environments ideal for the growth and accumulation of organic material. Elsewhere relatively slow rates of subsidence of a broad, protected, low lying delta plain controlled the deposition of coal. North of the main Karoo Basin many of the coal deposits are confined to structurally controlled linear basins. Hundreds of sedimentary uranium occurrences of varying grade and size occur within a broad, discontinuous belt in the Lower Beaufort of the southwestern portion of the Karoo Basin. The uranium mineralization occurs in a variety of fluvial deposits usually rich in carbonaceous material. Minute tuffaceous fragments, reflecting contemporaneous vulcanism, form a minor but significant constituent in some of the uraniferous sandstones. The uranium occurrences are confined largely to the Southern and Western Facies of the Lower Beaufort, and occur mainly within the confines of the Karoo Trough. Consolidated heavy mineral beach deposits have been found in the predominantly fluvio-deltaic Middle Ecca Group of the Northern Facies at a number of widely separated locations. These deposits were formed by shore line processes, such as the reworking of delta-front sands, during periods of temporary marine regression

  13. Lithofacies palaeogeography and biostratigraphy of the lowermost horizons of the Middle Triassic Hallstatt Limestones (Argolis Peninsula, Greece

    Directory of Open Access Journals (Sweden)

    Fotini A. Pomoni

    2013-07-01

    Taking into consideration the present location of the Hallstatt Formation, in the context of the Hellenides, an area suitable for the deposition of the Hallstatt Limestones, should be located between the sub-Pelagonian (western part of the Pelagonian zone and Pindos geotectonic zones, which during the Triassic corresponded to a platform slope and a deep ocean, respectively. The widespread Middle Triassic Han Bulog Limestones (ammonoid-bearing pelagic limestones from Triassic successions of the Eastern Alps (Dinarides, Hellenides may have formed partly in similar slope environments.

  14. Tomography of core-mantle boundary and lowermost mantle coupled by geodynamics: joint models of shear and compressional velocity

    Directory of Open Access Journals (Sweden)

    Gaia Soldati

    2015-03-01

    Full Text Available We conduct joint tomographic inversions of P and S travel time observations to obtain models of delta v_P  and delta v_S in the entire mantle. We adopt a recently published method which takes into account the geodynamic coupling between mantle heterogeneity and core-mantle boundary (CMB topography by viscous flow, where sensitivity of the seismic travel times to the CMB is accounted for implicitly in the inversion (i.e. the CMB topography is not explicitly inverted for. The seismic maps of the Earth's mantle and CMB topography that we derive can explain the inverted seismic data while being physically consistent with each other. The approach involved scaling P-wave velocity (more sensitive to the CMB to density anomalies, in the assumption that mantle heterogeneity has a purely thermal origin, so that velocity and density heterogeneity are proportional to one another. On the other hand, it has sometimes been suggested that S-wave velocity might be more directly sensitive to temperature, while P heterogeneity is more strongly influenced by chemical composition. In the present study, we use only S-, and not P-velocity, to estimate density heterogeneity through linear scaling, and hence the sensitivity of core-reflected P phases to mantle structure. Regardless of whether density is more closely related to P- or S-velocity, we think it is worthwhile to explore both scaling approaches in our efforts to explain seismic data. The similarity of the results presented in this study to those obtained by scaling P-velocity to density suggests that compositional anomaly has a limited impact on viscous flow in the deep mantle.

  15. Biostratigraphy of the Furongian (upper Cambrian) Alum Shale Formation at Degerhamn, Öland, Sweden

    DEFF Research Database (Denmark)

    Rasmussen, Bo Wilhelm; Rasmussen, Jan A.; Nielsen, Arne Thorshøj

    2017-01-01

    ) similis Chronozone; S. modestus has not previously been reported from Öland. The uppermost parts of the O. gibbosus, O. truncatus, P. spinulosa and C. tumida zones are reworked. Peltura minor may range into the basal C. linnarssoni Zone; alternatively it is also reworked. Ctenopyge (Ctenopyge) directa...

  16. Thermochronological constraints on the Cambrian to recent geological evolution of the Argentina passive continental margin

    Science.gov (United States)

    Kollenz, Sebastian; Glasmacher, Ulrich A.; Rossello, Eduardo A.; Stockli, Daniel F.; Schad, Sabrina; Pereyra, Ricardo E.

    2017-10-01

    Passive continental margins are geo-archives that store information from the interplay of endogenous and exogenous forces related to continental rifting, post-breakup history, and climate changes. The recent South Atlantic passive continental margins (SAPCMs) in Brazil, Namibia, and South Africa are partly high-elevated margins ( 2000 m a.s.l.), and the recent N-S-trending SAPCM in Argentina and Uruguay is of low elevation. In Argentina, an exception in elevation is arising from the higher topography (> 1000 m a.s.l.) of the two NW-SE-trending mountain ranges Sierras Septentrionales and Sierras Australes. Precambrian metamorphic and intrusive rocks, and siliciclastic rocks of Ordovician to Permian age represent the geological evolution of both areas. The Sierras Australes have been deformed and metamorphosed (incipient - greenschist) during the Gondwanides Orogeny. The low-temperature thermochronological (LTT) data (history of the Gondwanides and the Mesozoic and Cenozoic South Atlantic geological evolution. Upper Carboniferous zircon (U-Th/He)-ages (ZHe) indicate the earliest cooling below 180 °C/1 Ma. Most of the ZHe-ages are of Upper Triassic to Jurassic age. The apatite fission-track ages (AFT) of Sierras Septentrionales and the eastern part of Sierras Australes indicate the South Atlantic rifting and, thereafter. AFT-ages of Middle to Upper Triassic on the western side of the Sierras Australes are in contrast, indicating a Triassic exhumation caused by the eastward thrusting along the Sauce Grande wrench. The corresponding t-T models report a complex subsidence and exhumation history with variable rates since the Ordovician. Based on the LTT-data and the numerical modelling we assume that the NW-SE-trending mountain ranges received their geographic NW-SE orientation during the syn- to post-orogenic history of the Gondwanides.

  17. The Precambrian/Lower Cambrian pluton from Vila Nova (Central Portugal)

    Energy Technology Data Exchange (ETDEWEB)

    Reis, A. I. M.; Silva, M. M. V. G.; Antunes, I. M. H. R.

    2010-07-01

    The Vila Nova pluton is a small, Pre-Variscan granitic body that intruded rocks of the Central Iberian Zone near the contact with the Ossa Morena Zone and is affected by several shear zones and faults. Its contact metamorphic aureole is constituted by micaschist with porphyroblasts in the outer zone and hornfels in the inner zone. Small mainstreamed xenoliths are dispersed all over the body. The pluton has a great mineralogical heterogeneity with pronounced variations in muscovite/biotite and plagioclase/ microcline contents and is classified as granite, granodiorite or tonalite. It is a leuco granite, highly peraluminous (A/CN K = 1.31 - 1.64), magnesian and calc-alkaline to alkaline-calcic. The variation diagrams show curvilinear trends with silica. Eu/Eu* = 0.47 - 0.77 and there is a slight enrichment in LREE relative to HREE. The normalized diagrams indicated dominantly crustal granite, related to subduction. U-Pb isotopic data of zircon and monazite gives 540-542 Ma age. (Author) 19 refs.

  18. The Precambrian/Lower Cambrian pluton from Vila Nova (Central Portugal

    Directory of Open Access Journals (Sweden)

    Reis, A. I.M.

    2010-06-01

    Full Text Available The Vila Nova pluton is a small, Pre-Variscan granitic body that intruded rocks of the Central Iberian Zone near the contact with the Ossa Morena Zone and is affected by several shear zones and faults. Its contact metamorphic aureole is constituted by micaschist with porphyroblasts in the outer zone and hornfels in the inner zone. Small metasedimentar xenoliths are dispersed all over the body. The pluton has a great mineralogical heterogeneity with pronounced variations in muscovite/biotite and plagioclase/microcline contents and is classified as granite, granodiorite or tonalite. It is a leucogranite, highly peraluminous (A/CNK = 1.31 – 1.64, magnesian and calc-alkaline to alkaline-calcic. The variation diagrams show curvilinear trends with silica. Eu/Eu* = 0.47 – 0.77 and there is a slight enrichment in LREE relative to HREE. The normalized diagrams indicated dominantly crustal granite, related to subduction. U-Pb isotopic data of zircon and monazite gives 540-542 Ma age.

    El plutón de Vila Nova es un pequeño cuerpo granítico pre-varisco, que intruyó en las rocas de la Zona Centro Ibérica, cerca del contacto con la Zona de Ossa Morena, siendo afectado por varias fallas y zonas de cizalla. Su aureola de metamorfismo de contacto consiste en esquistos con porfiroblastos y corneanas. Pequeños xenolitos metasedimentarios aparecen dispersos por todo el cuerpo granítico. Presenta una gran diversidad mineralógica, con amplias variaciones en las relaciones biotita/moscovita y microclina/plagioclasa, siendo clasificado como tonalita-granodiorita-granito. Se trata de un leucogranito fuertemente peralumínico (A/CNK = 1.31 – 1.64, magnesiano y calco-alcalino a alcalino-cálcico. Los diagramas muestran variaciones curvilíneas con la variación de sílice. Eu/Eu* = 0.47 – 0.77 y hay un ligero enriquecimiento de LREE en relación con HREE. Los diagramas indican que la norma es un granito dominante de la corteza, relacionados con la subducción. El isótopo U-Pb circón y monacita indican una edad de 540-542 Ma.

  19. Petrographic and geochemical composition of kerogen in the Furongian (U. Cambrian) Alum Shale, central Sweden

    DEFF Research Database (Denmark)

    Sanei, H.; Petersen, H. I.; Schovsbo, N. H.

    2014-01-01

    that organic-rich Alum Shale (TOC: 8.9-28.0. wt.%) contains mainly immature, predominantly algal-derived kerogen with unusually reduced hydrocarbon generation potential as suggested by relatively low Hydrogen Index (HI) values (HI: 251-471. mg HC/g TOC) and high degree of aromaticity. In the absence of thermal...

  20. Biogenic gas in the Cambrian-Ordovcian Alum Shale (Denmark and Sweden)

    Energy Technology Data Exchange (ETDEWEB)

    Schulz, H.M.; Wirth, R.; Biermann, S.; Arning, E.T. [Helmholtz-Zentrum Potsdam - Deutsches GeoForschungsZentrum GFZ, Potsdam (Germany); Krueger, M.; Straaten, N. [BGR Hannover (Germany); Bechtel, A. [Montanuniv. Leoben (Austria); Berk, W. van [Technical Univ. of Clausthal (Germany); Schovsbo, N.H. [Geological Survey of Denmark and Greenland - GEUS, Copenhagen (Denmark); Crabtree, Stephen [Gripen Gas (Sweden)

    2013-08-01

    Shale gas is mainly produced from thermally mature black shales. However, biogenic methane also represents a resource which is often underestimated. Today biogenic methane is being produced from the Upper Devonian Antrim Shale in the Michigan Basin which was the most successfully exploited shale gas system during the 1990-2000 decade in the U.S.A. before significant gas production from the Barnett Shale started (Curtis et al., 2008). The Cambro-Ordovician Alum Shale in northern Europe has thermal maturities ranging from overmature in southern areas (Denmark and southern Sweden) to immature conditions (central Sweden). Biogenic methane is recorded during drilling in central Sweden. The immature Alum Shale in central Sweden has total organic carbon (TOC) contents up to 20 wt%. The hydrogen index HI ranges from 380 to 560 mgHC/gTOC at very low oxygen index (OI) values of around 4 mg CO{sub 2}/gTOC, Tmax ranges between 420 - 430 C. The organic matter is highly porous. In general, the Alum Shale is a dense shale with intercalated sandy beds which may be dense due to carbonate cementation. Secondary porosity is created in some sandy beds due to feldspar dissolution and these beds serve as gas conduits. Methane production rates with shale as substrate in the laboratory are dependent on the kind of hydrocarbon-degrading microbial enrichment cultures used in the incubation experiments, ranging from 10-620 nmol/(g*d). In these experiments, the CO{sub 2} production rate was always higher than for methane. Like the northern part of North America, also Northern European has been covered by glaciers during the Pleistocene and similar geological processes may have developed leading to biogenic shale gas formation. For the Antrim Shale one hypothesis suggests that fresh waters, recharged from Pleistocene glaciation and modern precipitation, suppressed basinal brine salinity along the northern margins of the Michigan Basin to greater depths and thereby enhancing methanogenesis. This local geological phenomenon leads to the fact that microbes with the potential to form biogenic methane flourish in such aqueous realms with low contents of total dissolved solids. Similar systems may have developed during the Quaternary in the Alum Shale. In contrast, the overmature Alum Shale which was recovered during drilling in the framework of the GASH project on Bornholm island (Denmark, Baltic Sea), showed no methane production potential in incubation experiments. However, ancient biogenic methane production can be retraced from the occurrence of layered, repeating barite precipitations.

  1. High-resolution stable isotope stratigraphy of the upper Cambrian and Ordovician in the Argentine Precordillera

    DEFF Research Database (Denmark)

    Sial, A.N.; Peralta, S.; Gaucher, C.

    2013-01-01

    We report the occurrence of important carbon isotope excursions in early Paleozoic formations of the Eastern and Central Argentine Precordillera. The Steptoean positive isotope carbon excursion (SPICE) is known from North America, Kazakhstan, South China, Australia and South America, and the nega......We report the occurrence of important carbon isotope excursions in early Paleozoic formations of the Eastern and Central Argentine Precordillera. The Steptoean positive isotope carbon excursion (SPICE) is known from North America, Kazakhstan, South China, Australia and South America......, and the negative isotope carbon excursion (SNICE) has been described for the first time in South America. We report here the record of the SPICE and SNICE in a single section in the Eastern Precordillera. In the Central Precordillera, a minor middle Darriwilian positive carbon isotope excursion (MDICE) and a late...

  2. Faunal succession in the upper Cambrian (Furongian) Leptoplastus Superzone at Slemmestad, southern Norway

    DEFF Research Database (Denmark)

    Rasmussen, Bo Wilhelm; Nielsen, Arne Thorshøj; Schovsbo, Niels H.

    2015-01-01

    The ‘Middle’ Cambrian–Tremadocian Alum Shale Formation is generally strongly tectonised in the Oslo area (southern Norway) and, as such, no complete succession through the Furongian exists in the area. The present paper presents a restored part of the Furongian interval through the Leptoplastus S...

  3. Biozonation of the furongian (upper Cambrian) alum shale formation at Hunneberg, Sweden

    DEFF Research Database (Denmark)

    Rasmussen, Bo Wilhelm; Rasmussen, Jan Audun Liljeroth; Nielsen, Arne Thorshøj

    2016-01-01

    The Furongian Alum Shale at Nygård, Hunneberg, Sweden, has been sampled for trilobites. The section is ≥12.20 m thick and comprises a relatively thick Olenus superzone, overlain by more condensed Parabolina, Leptoplastus, Protopeltura and Peltura superzones. The section is truncated low in the Pe......The Furongian Alum Shale at Nygård, Hunneberg, Sweden, has been sampled for trilobites. The section is ≥12.20 m thick and comprises a relatively thick Olenus superzone, overlain by more condensed Parabolina, Leptoplastus, Protopeltura and Peltura superzones. The section is truncated low...

  4. Cephalic and appendage morphology of the Cambrian arthropod Sidneyia inexpectans Walcott, 1911

    DEFF Research Database (Denmark)

    Stein, Martin

    2013-01-01

    on taphonomically deformed specimens, where the head was either partly folded, or entirely flipped under the thorax, resulting in the dorsal shield being mistaken for an extensive doublure. Rather than an extensive doublure, there is a broad hypostome, and the head comprises ocular, antennular, and at least two...... postantennular appendage bearing segments. The appendage morphology is shown to be consistent with artiopodan affinities. The exopod is of the bilobate flap-like type with lamellae inserting on the proximal portion, earlier proposed as a potential autapomorphy of Artiopoda. Reinforcement of artiopodan affinities...

  5. Stratigraphy and Structure of the Subsurface Cambrian and Ordovician Carbonates of New York.

    Science.gov (United States)

    Rickard, Lawrence V.

    This publication presents a description of 137 wells in New York State and adjacent parts of Pennsylvania. Correlations with surface exposures are established. Maps and cross sections display the thickness, structure, and stratigraphic relationships of the carbonates described. A paleogeologic map of New York State at the end of the Early…

  6. Students Explore Fossil Creatures of the Cambrian Period Burgess Shale through Model-Making

    Science.gov (United States)

    Anderson, Andrea E.; Zhbanova, Ksenia; Gray, Phyllis; Teske, Jolene K.; Rule, Audrey C.

    2016-01-01

    This practical article features an arts-integrated science unit on fossils of the Burgess Shale for fourteen elementary/middle school students at a weeklong summer day camp. The day camp had a theme of recycling, reduction and reuse; all of the fossil models had substantial recycled components to support this theme. Next Generation Science…

  7. Geochemistry of the Cambrian Sirius Passet Lagerstätte, Northern Greenland

    DEFF Research Database (Denmark)

    Le Boudec, Ange; Ineson, Jon; Rosing, Minik Thorleif

    2014-01-01

    to be broken down into variable proportions of two inputs, a dry felsic component and a hydrous mafic component (smectite or chlorite). Zircons U-Pb ages indicate multiple sources, the local Proterozoic basement of Northern Greenland (1250–2400 Ma) and Pan-African felsic magmas (620–650 Ma) from across...

  8. The late Cambrian (Furongian) Acerocarina Superzone (new name) on Kinnekulle, Vastergotland, Sweden

    DEFF Research Database (Denmark)

    Weidner, Thomas; Nielsen, Arne Thorshøj

    2013-01-01

    , Vastergotland, yielded Parabolina heres heres, P. transiens, Peltura costata, Peltura scarabaeoides westergaardi and Sphaerophthalmus alatus. In addition, A. granulata, Pelturina punctifera and Leptoplastides? sp. were collected from loose boulders deriving from the same interval. This is the first unambiguous...

  9. External morphology of Lightiella monniotae (Crustacea, Cephalocarida) in the light of Cambrian 'Orsten' crustaceans

    DEFF Research Database (Denmark)

    Olesen, Jørgen; Haug, Joachim T.; Maas, Andreas

    2011-01-01

    The species-poor meiofaunal Cephalocarida have played an important role in discussions of the phylogeny and evolution of Crustacea since their discovery in 1955. One reason may be that the morphology of cephalocarids includes some aspects of putatively ancient appearance, such as the simple roof-...... has again proved to be especially appropriate because of the small size of these animals, and because it permits direct comparisons with other similarly small crustaceans and the ‘Orsten’ crustaceans and their larvae....

  10. Spatiotemporal Distribution and Assemblages of Fishes below the Lowermost Dam in Protected Reach in the Yangtze River Main Stream: Implications for River Management

    Science.gov (United States)

    Li, Junyi; Zhang, Hui; Lin, Danqing; Wu, Jinming; Wang, Chengyou; Xie, Xuan

    2016-01-01

    Now more and more ecologists concern about the impacts of dam construction on fish. However, studies of fishes downstream Gezhouba Dam were rarely reported except Chinese sturgeon (Acipenser sinensis Gray). In this study, catch investigations and five hydroacoustic detections were completed from 2015 to 2016 to understand the distribution, size, and categories of fishes and their relationship with the environmental factors below Gezhouba Dam in protected reach in the Yangtze River main stream. Results showed significant differences in fish distribution and TS (target strength) between wet and flood seasons. Mean TS in five hydroacoustic detections were −59.98 dB, −54.70 dB, −56.16 dB, −57.90 dB, and −59.17 dB, respectively, and dominant fish species are Coreius guichenoti (Bleeker), Siniperca chuatsi (Basilewsky), and Pelteobagrus vachelli (Richardson). In the longitudinal direction, fish preferred to stay in some specific sections like reaches 2, 4, 7, 8, 11, and 16. Since hydrology factors change greatly in different seasons, environmental characteristics vary along the reaches, and human activities play an important role in the fish behavior, it is concluded that great cross-season changes in hydrology lead to the differences in TS and fish assemblages and that geography characteristics, especially channel geography, together with human activities influence fish longitudinal distribution. This finding provides basic knowledge of spatiotemporal distribution and assemblages of fishes in the extended reaches downstream Gezhouba Dam. In addition, it offers implications for river management. It could also serve as reference of future research on fish habitat. PMID:27843943

  11. Soft-sediment deformation structures interpreted as seismites in the uppermost Aptian to lowermost Albian transgressive deposits of the Chihuahua basin (Mexico)

    Science.gov (United States)

    Blanc, E.J.-P.; Blanc-Aletru, M. -C.; Mojon, P.-O.

    1998-01-01

    Several levels of soft-sediment deformation structures (s.-s.d.s.) cut by synsedimentary normal faults have been observed in the transition beds between the "Las Vigas" and "La Virgen" formations (Cretaceous) in the northeastern part of the Chihuahua basin in Mexico. These structures consisted of four kinds of motifs (floating breccias, flame-like structures, large pillow structures, and wavy structures). They are restricted to five "stratigraphie" levels (Z1-Z5) and surrounded by undeformed beds in fluvio-lacustrine and tidal deposits and can be traced over a distance of several hundred meters. This deformation is interpreted to have resulted from the combined effects of liquidization and shear stress in soft-sediments due to local earthquakes in the area which could have been generated during the rifting stage of the Chihuahua basin. New constraints placed on the age of the "Las Vigas" Formation (bracketed by Late Aptian charophytes at the bottom and colomiellids of late Aptian to earliest Albian age at the top) suggest that this synrift tectonism lasted at least until the end of the Aptian. ?? Springer-Verlag 1998.

  12. Stratigraphy and facies of the Nocedo, Fueyo and Ermita formations (Upper Devonian to lowermost Carboniferous) in León, N Spain

    NARCIS (Netherlands)

    Loevezijn, van G.B.S.

    1986-01-01

    The Asturo-Leonese Basin is one of the three large palaeogeographical units of the Cantabrian Zone. In the north the basin is bounded by the Asturian Geanticline and the Palencian Basin. In the south the Palaeozoic succession is covered by Mesozoic and Tertiairy deposits. The Upper Devonian to

  13. Stratigraphy, tectonic and ore potential of pre-cambrian unities from Serro region-MG (Mato Grosso quadrangle)

    International Nuclear Information System (INIS)

    Assis, L.C. de.

    1982-01-01

    Geological and stratigraphic elements of the Proterozoic units of the Serro region, Mato Grosso Quadrangle, show the absence of the faciological transition between the Espinhaco Group and the Minas Supergroup. Occurs in this region is a lithostratigraphical sequence of four distinct units: the Crystalline Basement; the Volcano-Sedimentary Sequence of Serro; the Minas Supergroup. The ore potential of the region includes: quartz veins, within the Galho do Miguel Formation; diamond, within the Sopa conglomerates; gold, in alluvial deposits and remobilized in quartz veins of the Sopa-Brumadinho Formation; bauxite, in the metabasics; uranium in the metaconglomerates of Moeda Formation; iron, in Caue Formation; chromium, gold and base metals in the Volcano-Sedimentary Sequence of Serro. Emphasis is given to the characterization of the Volcano-Sedimentary Sequence of Serro and its mineralization that is characterized as a stratiform massif with important volcano-sedimentary contribution, possible, a greenstone belt, with high gold-bearing potential. (author)

  14. The Strontium Isotope Record of Zavkhan Terrane Carbonates: Strontium Isotope Stability Through the Ediacaran-Cambrian Transition

    OpenAIRE

    Petach, Tanya N.

    2015-01-01

    First order trends in the strontium isotopic (87Sr/86Sr) composition of seawater are controlled by radiogenic inputs from the continent and non-radiogenic inputs from exchange at mid-ocean ridges. Carbonates precipitated in seawater preserve trace amounts of strontium that record this isotope ratio and therefore record the relative importance of mid-ocean ridge and weathering chemical inputs to sea water composition. It has been proposed that environmental changes during the Ediacaran-Cambria...

  15. Chronology of neoproterozoic-cambrian granitic magmatism in the Aracuai Belt, Eastern Brazil, based on single zircon evaporating dating

    International Nuclear Information System (INIS)

    Noce, Carlos Mauricio; Soares, Antonio Carlos Pedrosa; Macambira, Moacir Jose Buenano

    2000-01-01

    Granitic magmatism related to the orogenic stages of the Aracuai Belt took place at 595-575 Ma, and are represented by two distinct suites. One is composed of I-type granitoids and includes the following plutons: Brasilandia (595±3 Ma), Sao Vitor (576±4 Ma) and Guarataia (574± 2 Ma). The other suite comprises S-type granites like the Ataleia (591±5 Ma) and Wolf (582±5 Ma) plutons. After a long period of magnetic quiescence, a batholith composed of the Caladao granite and Padre Paraiso charnockite intruded at 519±2 Ma. This magmatic episode is probably associated to the collapse of the orogen. (author)

  16. Provenance signature of pre-cambrian and mesozoic rocks in the nearshore placers of Konkan, central west coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Gujar, A.R.; Angusamy, N.; Rajamanickam, G.V.

    region shows a characteristic suite of 17 types of heavy minerals. Their abundance shows hardly any drastic variation in the four bays studied. Overwhelming presence of minerals like garnet and kyanite in the studied four bays points to the source...

  17. Glauconitic deposits at Julegård on the south coast of Bornholm, Denmark dated to the Cambrian

    DEFF Research Database (Denmark)

    Clemmensen, Lars B.; Bromley, Richard Granville; Holm, Paul Martin

    2011-01-01

    Bioturbated, glauconitic siltstones and sandstones are overlain by presumed Upper Triassic deposits at coastal exposures at Julegård on the south coast of Bornholm. These glauconitic deposits have not previously been dated. A 40Ar-39Ar dating of the glaucony gives an age of 493 ± 2 Ma suggesting ...... of Rusophycus Hall, 1852, probably trilobite trace fossils, are also represented....

  18. A bradoriid and brachiopod dominated shelly fauna from the furongian (Cambrian) of Västergötland, Sweden

    DEFF Research Database (Denmark)

    Topper, Timothy Paul; Skovsted, Christian B.; Harper, David Alexander Taylor

    2013-01-01

    A small assemblage of shelly fossils, dominated by the brachiopod Treptotreta jucunda and the bradoriid arthropod Mongolitubulus aspermachaera new species is described from a Furongian limestone of Västergötland, south-central Sweden. Mongolitubulus aspermachaera is represented in the assemblage ...... include typical Baltic Furongian representatives, such as the trilobite Parabolina, the agnostoid Agnostus and the phosphatocopids Hesslandona and Vestrogothia....

  19. Results of high-temperature processing of high-carbon materials from the lower cambrian period of the Earth's history

    International Nuclear Information System (INIS)

    Maslov, O.D.

    2016-01-01

    The paper reports on the observation of spontaneous fission of nuclides, concentrated in fly ash during the combustion of high-carbon (graphite) material, chemogenic siliceous-carbonaceous rocks and carbonaceous shale in the mixture with brown coal. In the samples obtained, the spontaneous fission was measured by track method. The zones of precipitation of spontaneous fission of nuclides and their lighter homologues on thermochromatographic column were determined. A nuclide with a half-life of 62 d was detected in the alkaline trap. The chemical treatment procedure included co-precipitation with iron hydroxide, dissolution in NH 4 OH + H 2 O 2 solution and distillation by heating up to 100°C followed by AgI co-precipitation. Based on the chemical behavior it can be concluded that the detected radionuclide belongs to the halides. The content of the parent nuclide in high-carbon (graphite) material and chemogenic siliceous-carbonaceous rock corresponds to 10 -14 g/g. [ru

  20. Insights from stable S and O isotopes into biogeochemical processes and genesis of Lower Cambrian barite–pyrite concretions of South China

    Digital Repository Service at National Institute of Oceanography (India)

    Goldberg, T.; Mazumdar, A.; Strauss, H.; Shields, G.

    water trace metal chemistry of laminated sediments from the Gulf of California, Mexico. Marine Chemistry 14, 89-106. Canfield, D.E., 2001. Biogeochemistry of sulphur isotopes. In: Valley, J.W. & Cole, D.R. (Eds.), Stable Isotope Geochemistry. Reviews.... Age curves of sulphur and oxygen isotopes in marine sulphate and their mutual interpretation. Chemical Geology 28, 199-206. Coleman, M.L. & Raiswell, R., 1981. Carbon, oxygen and sulphur isotope variations in concretions from the Upper Lias of N...

  1. A highly diverse trilobite fauna with Avalonian affinities from the Middle Cambrian Acidusus atavus Zone (Drumian Stage) of Bornholm, Denmark

    DEFF Research Database (Denmark)

    Weidner, Thomas; Nielsen, Arne Thorshøj

    2014-01-01

    ? applanata, Acadagnostus aff. bulkurensis and Phalagnostus ovalis. A few faunal elements originally described from Bohemia and Australia are also present, viz. Hydrocephalus aff. carens, Phalagnostus nudus, Skryjagnostus pompeckji, Hypagnostus aff. clipeus, Euagnostus aff. interstrictus and Euagnostus? aff...

  2. Magmatic evolution and REE mineralization in the early Cambrian Jbel Boho igneous complex in the Bou Azzer inlier (Anti-Atlas/Morocco)

    OpenAIRE

    Benaouda, Rachid

    2015-01-01

    The igneous rocks of Jbel Boho emerged in three phases: an initial phase with alkaline volcanism followed by the intrusion of a syenitic pluton and later the emplacement of a dyke swarm. The Jbel Boho alkaline complex shows some interesting aspects of hydrothermal REE mineralization in the late differentiation stage. REE mineralization is found in a rhyolitic dyke and some late hydrothermal veins. Synchysite-(Ce), which was identified by EPMA analysis, is the main REE mineral.

  3. Colour origin of red sandstone beds within the Hüdai Formation (Early Cambrian), Aydıncık (Mersin), southern Turkey

    OpenAIRE

    KADİR, Muhsin EREN Selahattin

    2013-01-01

    A randomized complete block design field study with split plot arrangements was conducted during 2006-2007 and 2007-2008 at the Agronomic Research Station in Khanewal, Pakistan, to evaluate if seed priming could improve grain yield and water use efficiency of late-sown wheat under limited water supply conditions. Seeds of cultivar Inqlab-91 received one of the following treatments: they were soaked in aerated distilled water for 12 or 24 h (hydropriming), layered between moist gunny bags for ...

  4. Organic chemistry and petrology of barven and Mo-Ni-PGE mineralized marine black Thales of the Lower Cambrian Niutitang Formation (South China)

    Czech Academy of Sciences Publication Activity Database

    Kříbek, B.; Sýkorová, Ivana; Pašava, J.; Machovič, Vladimír

    2007-01-01

    Roč. 72, 3-4 (2007), s. 240-256 ISSN 0166-5162 R&D Projects: GA AV ČR IAA300460510 Institutional research plan: CEZ:AV0Z30460519 Keywords : organic particles * reflectance * micro-Raman spectra Subject RIV: DD - Geochemistry Impact factor: 1.625, year: 2007

  5. Provencance of the late Proterozoic to early Cambrian metaclastic sediments ot the Sierra de San Luis (Eastern Sierras Pampeanas) and Cordillera Oriental, Argentina

    DEFF Research Database (Denmark)

    Drobe, M.; López de Luchi, M.; Steenken, A.

    2009-01-01

    Provenance studies have been performed utilising major and trace elements, Nd systematics, whole rock Pb-Pb isotopes and zircon U/Pb SHRIMP data on metasedimentary rocks of the Sierra de San Luis (Nogolí Metamorphic Complex, Pringles Metamorphic Complex, Conlara Metamorphic Complex and San Luis...... is depicted for all the complexes using major and trace elements. The Pringles Metamorphic Complex shows indications for crustal recycling, pointing to a bimodal provenance. Major volcanic input has to be rejected due to Th/Sc, Y/Ni and Cr/V ratios for all units. The eNd(540 Ma) data is lower for the San Luis...... Formation and higher for the Conlara Metamorphic Complex, as compared to the other units, in which a good consistency is given. This is similar to the TDM ages, where the metapsammitic samples of the San Luis Formation are slightly older. The spread of data is largest for the Pringles Metamorphic Complex...

  6. Unraveling the tectonic evolution of a Neoproterozoic-Cambrian active margin in the Ribeira Orogen (Se Brazil): U-Pb and Lu-Hf provenance data

    Energy Technology Data Exchange (ETDEWEB)

    Fernandes, Gabriel Lamounier de F. [Servico Geologico do Estado do Rio de Janeiro (DRM-RJ), Niteroi, RJ (Brazil); Schmitt, Renata; Bongiolo, Everton M.; Mendes, Julio [Universidade Federal do Rio de Janeiro (UFRJ), RJ (Brazil); Basei, Miguel S. [Universidade de Sao Paulo (USP), SP (Brazil)

    2015-07-01

    Full text: The Neoproterozoic-Ordovician Central Ribeira Orogen, in SE Brazil, presents two contrasting tectonic domains in its southern portion: (a) The Arc Domain constituted of Neoproterozoic to Paleozoic magmatic rocks and low P-high T metamorphic para (Sao Fidelis Group) - and ortho- derived units (in Oriental Terrane); and (b) The Basement Domain, constituted of a Paleoproterozoic and Neoproterozoic medium P-high T metamorphic para (Palmital-Buzios Succession)- and ortho-derived units (in Cabo Frio Tectonic Domain). Our work focuses on paraderived rocks sequences from both domains. The provenance analysis using U-Pb and Lu-Hf in zircon grains is presented here as an effective tool to unravel the paleogeography and nature of the pre-collisional sedimentary basins. We performed 505 analyses (U-Pb) on detrital zircon grains and some metamorphic overgrowths from six paragneiss samples. Besides, 141 analyses (Lu-Hf) in six samples only on the detrital zircon grains domains. All samples present a main peak from Neoproterozoic sources (750-570 Ma) and the other minor peak in the Stenian/Tonian periods (1200-850Ma), this indicate an orogenic contribution for this basin. Scarce register from the Mesoproterozoic and two peaks in the Archean/Paleoproterozoic (2.6 and 1.9 Ga) are recognized as a contribution from an ancient continent. The Lu-Hf data reveals a juvenile source for the detrital zircon grains from Buzios Succession while Palmital and Sao Fidelis Group units show a main crustal signature for their detrital zircon population. Based on the U-Pb and Lu-Hf data presented here, plus petrological data, geological correlations, and compilation of data from literature, we propose a tectonic model for the origin of para-derived rocks from the eastern part of the Ribeira Orogen. Starting with an extensional environment of ca. 600 Ma in a back-arc basin (Buzios succession deposition) and continuing as an active margin between 570 and 550 Ma in the fore-arc and prism basin (Sao Fidelis Group and Palmital succession). (author)

  7. Detrital zircons from samples of five Neo proterozoic sandstone units deposited on Uruguay and Argentina: about evolution of paleographic Rio de la Plata craton

    International Nuclear Information System (INIS)

    Gaucher, C.; Poire, D.G.; Pamoukaghlian, K.; Gomez Peral, L.; Finney, S.; Valencia, V.; Blanco, G.

    2007-01-01

    We report U-Pb ages of detrital zircons from samples of five Neoproterozoic sandstone units deposited on the Rio de la Plata Craton (RPC) in Uruguay and Argentina. Quartz-arenites of the Piedras de Afilar Formation show typical Transamazonian ages, with peaks at 2.00-2.07, 1.87 and 1.78 Ga. However, the most important zircon population is Mesoproterozoic, showing maxima at 1.49, 1.35, 1.25 and 1.0 Ga. Zircons recovered from two sandstone levels in the Arroyo del Soldado Group (Yerbal and Cerros San Francisco formations) are mostly Archean in age, with maxima at 3.2 and 2.7 Ga. Palaeoproterozoic zircons are also prominent in this unit, with peaks at 2.45 and 2.18, with the latter a typical Transamazonian age. Two samples from the Sierras Bayas Group in Tandilia (Argentina) show different age spectra. Sandstones of the Villa Monica Formation show a unimodal zircon population of Transamazonian age (peak at 2.13 Ga). Sandstones of the Cerro Largo Formation are characterized by a dominant Transamazonian zircon population (peaks at 2.15, 2.0 and 1.79), but also important Archean-lowermost Palaeoproterozoic (3.33, 2.99, 2.7, 2.47 Ga) and Mesoproterozoic peaks (1.55, 1.23 and 1.06). The abundance of Mesoproterozoic detrital zircons is surprising. A proto-Andean, Mesoproterozoic belt is suggested as the source of the Mesoproterozoic detritus. Archean rocks of the RPC crop out only in the Nico Perez Terrane in Uruguay, suggesting that the Nico Perez Terrane was much closer to Tandilia than it is today. The sinistral reactivation of the Sarandi del Yi Shear Zone in the Cambrian, as a result of tangential collision of the Cuchilla Dionisio-Pelotas Terrane, may explain this observations. The absence of Neoproterozoic zircons shows that the studied units were deposited in a stable continental margin opening to the East and South. These Neoproterozoic basins had obviously no contribution whatsoever from Brasiliano-Pan African belts, supporting the idea of Cambrian terrane

  8. Why are small scale demonstration projects important for the future of CCS?

    Science.gov (United States)

    Leetaru, H. E.; Bauer, R. A.; McBride, J. H.; Freiburg, J. T.; Greenberg, S. E.

    2017-12-01

    Carbon Capture and Storage (CCS) is moving toward large-scale commercial projects and the U.S. Department of Energy is supporting a new CarbonSAFE initiative to assist in the development of a 50 million tonnes geologic storage project. This type of large commercial CCS project will rely on lessons learned from smaller DOE CCS projects such as the Illinois Basin-Decatur Project (IBDP) and the Illinois Industrial Carbon Capture and Storage (IL-ICCS) Project located one mile north of IBDP. Over a three year period ending 2014 IBDP injected almost one million tonnes of CO2 into the Mt. Simon Sandstone, and the IL-ICCS project which commenced injection in 2017 will inject another four million tonnes over a four year period. The IBDP has recorded microseismic events within the study area through continuous downhole seismic monitoring before, during, and after injection. Monitoring shows that microseismicity increased during injection and originate not only in the Cambrian Mt. Simon Sandstone (the target reservoir), but also in the underlying Argenta clastics and deeper Precambrian igneous rocks as SW-NE elongate clusters aligned in strike to the maximum in situ stress direction. An interpretation of site 3D seismic reflection data suggests that much of the microseismicity is proximal to interpreted faults that extend from the basement up into the lowermost Mt. Simon strata. The faults proximally associated with microseismic activity are oriented parallel with respect to the maximum stress direction. The seismic monitoring of the IBDP indicate that the assessment of induced seismic potential associated with commercial-scale CCS requires not only identification of a suitable reservoir and its petrophysical characteristics, but also the extent and orientation of existing faults and their relation to regional stress orientation. Assessment of regional fault orientation using 3D seismic reflection data can be extremely useful to understanding the risks of induced seismicity

  9. Inheritance, Variscan tectonometamorphic evolution and Permian to Mesozoic rejuvenations in the metamorphic basement complexes of the Romanian Carpathians revealed by monazite microprobe geochronology

    Science.gov (United States)

    Săbău, Gavril; Negulescu, Elena

    2014-05-01

    Monazite U-Th-Pb chemical dating reaches an acceptable compromise between precision and accuracy on one side, and spatial resolution and textural constraints on the other side. Thus it has a powerful potential in testing the coherence of individual metamorphic basement units, and enabling correlations among them. Yet, sensitivity and specificity issues in monazite response to thermotectonic events, especially in the case of superposed effects, remain still unclear. Monazite dating at informative to detailed scale in the main metamorphic basement units of the Carpathians resulted in complex age spectra. In the main, the spectra are dominated by the most pervasive thermal and structural overprint, as checked against independent geochronological data. Post-peak age resetting is mostly present, but statistically subordinate. Resetting in case of superposed events is correlated with the degree of textural and paragenetic overprinting, inheritances being always indicated by more or less well-defined age clusters. The lack of relict ages correlating with prograde structural and porphyroblast zonation patterns is indicative for juvenile formations. Age data distribution in the Carpathians allowed distinction of pre-Variscan events, syn-metamorphic Variscan tectonic stacking of juvenile and reworked basement, post-Variscan differential tectonic uplift, as well as prograde metamorphic units ranging down to Upper Cretaceous ages. In the South Carpathians, the Alpine Danubian domain consists of several Variscan and Alpine thrust sheets containing a metamorphic complex dominated by Upper Proterozoic to Lower Cambrian metamorphic and magmatic ages (Lainici-Păiuş), and several complexes with metamorphic overprints ranging from Carboniferous to Lower Permian. Any correlation among these units, as well as geotectonic models placing a Lower Paleozoic oceanic domain between pre-existing Lainici-Păiuş and Drăgşan terranes are precluded by the age data. Other basement of the

  10. Electrical structure of the lithosphere across the Western Paraná suture zone: the role of a Neoproterozoic-Cambrian subduction in generating the Paraná Magmatic Province

    Science.gov (United States)

    Dragone, G. N.; Bologna, M.; Gimenez, M. E.; Alvarez, O.; Lince Klinger, F. G.; Correa-Otto, S.; Ussami, N.

    2017-12-01

    The Paraná Magmatic Province (PMP) together with the Etendeka Province (EP) in Africa is one of the Earth's largest igneous provinces originated prior to the Western Gondwanaland break-up and the inception of the South Atlantic Ocean in the Lower Cretaceous. Geochemical data of PMP-EP basalts collected since late 1980's indicate the origin of PMP-EP by melting of a heterogeneous and enriched subcontinental lithospheric mantle with fast rate of eruption (borders of the PMP, the Western Paraná suture zone (WPS in Fig. 1). We discuss the electrical properties of the lithosphere along three MT profiles across the WPS. MT-A profile (Padilha et al., 2015, JGR) extends from Rio Apa craton towards the center of PMP (high-TiO2 basalts). Profile MT-B extends from Tebicuary craton towards the center of PMP (low-TiO2) and profile MT-C extends from Rio de la Plata craton towards the southern PMP (low- and high-TiO2). All profiles show a resistive ( 104 ohm m) and thick (> 150 km) lithosphere in the cratonic areas whereas the electrical lithosphere is thinner (<100 km) with alternating high and low resistivities within PMP. Vertically elongated and high electrical conductivity anomalies ( 10 ohm m) centered at 40 km depth occur along the -30 mGal contour line in the three profiles, and are interpreted as the location of the suture and former subduction zone. We will discuss the correlation between geochemical and petrological characteristics of basalts and the electrical properties of the lithospheric mantle underneath.

  11. Sulfur and strontium isotopic compositions of carbonate and evaporite rocks from the late Neoproterozoic–early Cambrian Bilara Group (Nagaur-Ganganagar Basin, India): Constraints on intrabasinal correlation and global sulfur cycle

    Digital Repository Service at National Institute of Oceanography (India)

    Mazumdar, A.; Strauss, H.

    (e.g., Kampschulte et al., 2001; Kampschulte and Strauss, 2004). The latter process delivers substantial amounts of nutrients to the ocean, triggering an increase in primary productivity. Subsequent delivery of organic matter to the sediment in turn... be consistent with a scenario in which the enhanced delivery of nutrients from continental weathering resulted in increasing primary production and greater subsequent remineralization of sedimentary organic matter, causing sulfate limitation and a Rayleigh...

  12. Primary Data on U/Pb-Isotope Ages and Lu/Hf-Isotope Geochemical Systematization of Detrital Zircons from the Lopatinskii Formation (Vendian-Cambrian Transition Levels) and the Tectonic Nature of Teya-Chapa Depression (Northeastern Yenisei Ridge)

    Science.gov (United States)

    Kuznetsov, N. B.; Priyatkina, N. S.; Rud'ko, S. V.; Shatsillo, A. V.; Collins, W. J.; Romanyuk, T. V.

    2018-03-01

    The main results are presented on U/Pb-isotope dating of 100 detrital zircons and, selectively, on the Lu/Hf-isotope system of 43 grains from sandstones of the Lopatinskii formation (the lower stratigraphic level of the Chingasan group). Ages from 896 ± 51 to 2925 ± 38 Ma were obtained with a pronounced maximum of 1890 Ma in the curve of probability density, along with ɛHf estimates from +8.4 to-15.1, which allow one to throw doubt upon the molasse nature of the Lopatinskii formation.

  13. Preliminary Assessment McGhee - Tyson ANGB, McGhee - Tyson Municipal Airport, Knoxville, Tennessee

    Science.gov (United States)

    1988-06-01

    shales and siltstones are 700.2000 .0 brown, brownish gray, medium to dark gray. lossililerous. calcareous: limestones are argillaceous to pure , gray...shale. PUMPKIN Shale and siltstone, reddish-brown to qsoyish-red. gteenish~gtary and 100-750 VALLEY SHALE oliv*egray: with thin sandstones. limestones...Rogersville shale Wrt..............Cambrian Rutledge limestone Ipv ..............Cambrian Pumpkin Valley ................... Cambrian Rome Figure 111.2

  14. Reflectance measurements of zooclasts and solid bitumen in Lower Paleozoic shales, southern Scandinavia

    DEFF Research Database (Denmark)

    Petersen, Henrik I.; Schovsbo, Niels H.; Nielsen, Arne Thorshøj

    2013-01-01

    -like particles and graptolite fragments. The Middle Cambrian to Furongian (upper Cambrian) shales may contain sparse fragments of vase-shaped microfossils (VSM) that seem to follow the maturation trend of chitinozoans. In the present sample set, the reflectance of chitinozoans and VSM is comparable...

  15. Some problematic shallow-marine structures

    NARCIS (Netherlands)

    Manten, A.A.

    The lowermost Devonian beds in Gotland (Sweden) were deposited in a very shallow marine environment, close to the coast. In these beds three structures were observed, whose mode of formation cannot be explained by the author.

  16. Les marqueurs structuraux et magmatiques de l'extension crustale au Protérozoïque terminal-Cambrien basal autour du massif de Kerdous (Anti-Atlas occidental, Maroc)

    Science.gov (United States)

    Soulaimani, Abderrahmane; Essaifi, Abderrahim; Youbi, Nassrddine; Hafid, Ahmid

    2004-12-01

    During the Late Precambrian-Early Cambrian times, the borders of the Kerdous inlier were affected by normal faults where thick conglomerates (Ouarzazate Group: PIII), grading progressively upwards into Cambrian marine sediments, were accumulated along their hanging walls. This tectonic activity persisted during the Early Cambrian and was accompanied by a magmatic activity resulting mainly in the emplacement of continental tholeiitic basalts. These tectono-sedimentary and magmatic events are related to the crustal extensional episode that affected the northwestern Gondwana margin during the opening of the Iapetus Ocean during Late Proterozoic times. To cite this article: A. Soulaimani et al., C. R. Geoscience 336 (2004).

  17. Tectono-thermal evolution of the India-Asia collision zone based on ...

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    on India-Eurasia collision in the Arabian sea region taken from the Indus group, ... cambrian basement reactivation: products of continental collision; J. Geol. ... Dubey A K 2004 Structural evolution of Himalaya: field studies, experimental ...

  18. The long-term impact of magnesium in seawater on foraminiferal mineralogy: Mechanism and consequences

    NARCIS (Netherlands)

    van Dijk, I.; de Nooijer, L.J.; Hart, M.B.; Reichart, G.-J.

    2016-01-01

    Foraminifera are unicellular protists, primarily known for their calcium carbonate shells thatprovide an extensive fossil record. This record, ranging from Cambrian to present shows both major shiftsand gradual changes in the relative occurrence of taxa producing different polymorphs of carbonate.

  19. Uranium project GEO 2 attachment: cronostratigraphy aplied to Uranium research; Proyecto Uranio anexo GEO 2: cronoestratigrafia aplicada a la investigacion de Uranio

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1983-07-01

    In the article, different sources of information about Uranium stratigraphy from Uruguay have been reviewed. Some results have been presented in Upper Cambrian period and Precambrian era, specially Devonian, Carboniferous and Silurian period.

  20. Uranium project GEO 2 attachment: cronostratigraphy aplied to Uranium research

    International Nuclear Information System (INIS)

    1983-01-01

    In the article, different sources of information about Uranium stratigraphy from Uruguay have been reviewed. Some results have been presented in Upper Cambrian period and Precambrian era, specially Devonian, Carboniferous and Silurian period

  1. Isotopic and sedimentological clues to productivity change in Late ...

    Indian Academy of Sciences (India)

    R.Narasimhan(krishtel emaging) 1461 1996 Oct 15 13:05:22

    markers and to study changes in carbon reser- ..... Chakraborty P P 1996 Facies and sequence development in some late ... Cambrian transition: Death valley, United States; Geol- ... tral Brazil: Bambui and Paranoa groups; Precambrian.

  2. 1 Observations on the ichnospecies Monomorphichnus multilineatus ...

    Indian Academy of Sciences (India)

    24

    The Ediacaran-Cambrian Marwar Supergroup exposed in the western Rajasthan ... Small Shelly Fauna (SSF) represented by ichnofossils and body fossils ... global distribution of genus Monomorphichnus, mode of preservation, size ...... Ediacaran Jodhpur Sandstone, Marwar Supergroup, western Rajasthan; J. Asian Earth.

  3. Zoophycos macroevolution since 541 Ma

    OpenAIRE

    Li-Jun Zhang; Ruo-Ying Fan; Yi-Ming Gong

    2015-01-01

    Zoophycos is one of the most complex and enigmatic trace fossils recorded in marine strata from Cambrian to Quaternary worldwide, which is invaluable for the study of Phanerozoic development of organism–environment interactions. Here we address and demonstrate the macroevolution of Phanerozoic Zoophycos by assembling 448 points in constructing the Phanerozoic Zoophycos database based on 291 papers from 1821 to 2015 and 180 specimens from Cambrian to Palaeogene. The comprehensive dataset revea...

  4. Embryogenic calli induced in interspecific (Elaeis guineensis x E. oleifera hybrid zygotic embryos

    Directory of Open Access Journals (Sweden)

    Paula Cristina da Silva Angelo

    2009-01-01

    Full Text Available The hybridization between oil palm (Elaeis guineensis and caiaué (E. oleifera plants is directed to obtainprogenies presenting high yields like oil palm but with reduced shoot height and resistance to lethal yellowing like caiaué.Cloning F1, BC1 and BC2 progenies can make the replication of selection trials easier. The objective of this work was to inducesomatic embryogenesis in interspecific zygotic embryos collected 100 days after pollination. Three progenies were cultivatedin an induction medium developed for Tenera (E. guineensis tp. dura x pisifera embryos. The number of embryos bearing calliand germinating was recorded and submitted to the Z test. Calli were weighted and submitted to histological analysis.Progenies differed in the number of embryos presenting plumules and calli simultaneously. By the ninth month, the apices ofincompletely developed somatic embryos were observed protruding from the surfaces of nodular calli. Highly embryogenicand friable secondary calli producing globular somatic embryos were not observed.

  5. Types and characteristics of carbonate reservoirs and their implication on hydrocarbon exploration: A case study from the eastern Tarim Basin, NW China

    Directory of Open Access Journals (Sweden)

    Shiwei Huang

    2017-02-01

    Full Text Available Carbonate rocks are deposited in the Ordovician, Cambrian, and Sinian of eastern Tarim Basin with a cumulative maximum thickness exceeding 2000 m. They are the main carriers of oil and gas, and a great deal of natural gas has been found there in the past five years. Based on lithofacies and reservoir differences, natural gas exploration domains of eastern Tarim Basin can be classified into five types: Ordovician platform limestone; Ordovician platform dolomite; Cambrian platform margin mound shoal; Cambrian slope gravity flow deposits, and; Sinian dolomite. Carbonate reservoir characteristics of all the types were synthetically analyzed through observation on drilling core and thin sections, porosity and permeability measurement, and logging data of over 10 drilling wells. We find distribution of part of good fracture and cave reservoir in carbonate platform limestone of Ordovician. In the Ordovician, platform facies dolomite is better than limestone, and in the Cambrian, platform margin mound shoal dolomite has large stacking thickness. Good quality and significantly thick carbonate gravity deposit flow can be found in the Cambrian slope, and effective reservoir has also been found in Sinian dolomite. Commercial gas has been found in the limestone and dolomite of Ordovician in Shunnan and Gucheng areas. Exploration experiences from these two areas are instructive, enabling a deeper understanding of this scene.

  6. Comparison of Magnetic and Moessbauer Results Obtained for Palaeozoic Rocks of Hornsund, Southern Spitsbergen, Arctic

    International Nuclear Information System (INIS)

    Szlachta, K.; Galazka-Friedman, J.; Michalski, K.; Brzozka, K.; Gorka, B.

    2008-01-01

    This analysis was performed as a part of the palaeomagnetic project focused on the reconstruction of the palaeogeographic position of the Svalbard Archipelago and adjacent crustal units (European Arctic) in the Palaeozoic and Mesozoic. Three rock formations | Cambrian, Devonian and Carboniferous were sampled in the area of Hornsund, southern Spitsbergen. The main aim of the presented study is to identify ferromagnetic minerals (sensu lato) - the carriers of the natural remanent magnetisation in the investigated rocks. A wide range of magnetic methods were used: the Lowrie tests, unblocking temperatures determinations and the measurement of coercivity spectra as well as the Moessbauer studies. In Devonian and Carboniferous samples all applied methods indicate the domination of the hematite natural remanent magnetisation carrier. In Cambrian rocks magnetic measurements reveal a mixture of ferromagnetic (sensu lato) minerals with varying coercivities and unblocking temperatures. The Moessbauer data improve the identification, suggesting that in Cambrian rocks the carrier of the dominating natural remanent magnetisation component is maghemite. (authors)

  7. Sequential development of platform to off-platform facies of the great American carbonate bank in the central Appalachians: chapter 15

    Science.gov (United States)

    Brezinski, David K.; Taylor, John F.; Repetski, John E.

    2012-01-01

    In the central Appalachians, carbonate deposition of the great American carbonate bank began during the Early Cambrian with the creation of initial ramp facies of the Vintage Formation and lower members of the Tomstown Formation. Vertical stacking of bioturbated subtidal ramp deposits (Bolivar Heights Member) and dolomitized microbial boundtsone (Fort Duncan Member) preceded the initiation of platform sedimentation and creation of sand shoal facies (Benevola Member) that was followed by the development of peritidal cyclicity (Daragan Member). Initiation of peritidal deposition coincided with the development of a rimmed platform that would persist throughout much of the Cambrian and Early Odrovician. At the end of deposition of the Waynesboro Formation, the platform became subaerially exposed because of the Hawke Bay regression, bringing the Sauk I supersequence to and end. In the Conestoga Valley of eastern Pennsylvania, Early Cambrian ramp deposition was succeeded by deposition of platform-margin and periplatfrom facies of the Kinzers Formation.

  8. Sophisticated digestive systems in early arthropods.

    Science.gov (United States)

    Vannier, Jean; Liu, Jianni; Lerosey-Aubril, Rudy; Vinther, Jakob; Daley, Allison C

    2014-05-02

    Understanding the way in which animals diversified and radiated during their early evolutionary history remains one of the most captivating of scientific challenges. Integral to this is the 'Cambrian explosion', which records the rapid emergence of most animal phyla, and for which the triggering and accelerating factors, whether environmental or biological, are still unclear. Here we describe exceptionally well-preserved complex digestive organs in early arthropods from the early Cambrian of China and Greenland with functional similarities to certain modern crustaceans and trace these structures through the early evolutionary lineage of fossil arthropods. These digestive structures are assumed to have allowed for more efficient digestion and metabolism, promoting carnivory and macrophagy in early arthropods via predation or scavenging. This key innovation may have been of critical importance in the radiation and ecological success of Arthropoda, which has been the most diverse and abundant invertebrate phylum since the Cambrian.

  9. Sedimentological aspects of four Lower-Paleozoic formations in the northern part of the province of León (Spain)

    NARCIS (Netherlands)

    Oele, E.

    1964-01-01

    This paper deals with the sedimentary structures and sedimentary petrography of the four lowermost formations of the Paleozoic as developed in the Northern part of the Province of León (Cantabrian Mountains, Spain). Three of the four formations have a detrital character, and one consists of

  10. Journal of Earth System Science | Indian Academy of Sciences

    Indian Academy of Sciences (India)

    The common growth of `late' muscovite over sillimanite in migmatite may be the result of this process, and in ux of exogenous H2O may not be necessary. However, in general, metasomatism in the evolution of the crust remains a contentious issue. Processes in the lower-most crust may be inferred from studies of xenolith ...

  11. carryover of soil-applied herbicides on flue-cured tobacco

    African Journals Online (AJOL)

    An outbreak of a tobacco leaf disorder characterized by interveinal chlorosis of lowermost leaves was recorded for the first time in fields on the Beau Champ Sugar Estate in October 2003. Given that tobacco is grown on sugar cane rotational lands, herbicide simulation trials were conducted from 2005 to 2007 at Réduit, ...

  12. Sadhana | Indian Academy of Sciences

    Indian Academy of Sciences (India)

    The method uses the boundary growing approach to extract the lowermost and uppermost coordinates of pixels of characters of text lines present in the document, which can be subjected to linear regression analysis (LRA) to determine the skew angle of a skewed document. Further, the proposed technique works fine for ...

  13. Interrogation of distributional data for the End Ordovician crisis interval

    DEFF Research Database (Denmark)

    Mac Ørum Rasmussen, Christian; Harper, David Alexander Taylor

    2011-01-01

    The uppermost Ordovician–lowermost Silurian (Upper Katian–Rhuddanian) is surveyed with respect to the a- and ß-diversity of rhynchonelliformean brachiopods. The survey is based on new collections as well as existing literature, compiled in a large, georeferenced database. The brachiopod faunas ar...

  14. The structure of the window of Bobbio : (northern Apennines, Italy)

    NARCIS (Netherlands)

    den Haan, J.A.

    1979-01-01

    Field work in the tectonic window of Bobbio has demonstrated the following tectonic units: Tuscan unit, the lowermost unit in the window. It is composed of a turbiditic sequence of Oligocene or Early Miocene age, folded into a large recumbent syncline with a gently NE-dipping NE limb and a steeply

  15. The structure of the window of Bobbio : (northern Apennines, Italy)

    NARCIS (Netherlands)

    Haan, J.A. den

    1979-01-01

    Field work in the tectonic window of Bobbio has demonstrated the following tectonic units: Tuscan unit, the lowermost unit in the window. It is composed of a turbiditic sequence of Oligocene or Early Miocene age, folded into a large recumbent syncline with a gently NE-dipping NE limb and a

  16. Thermally stimulating mechanically-lifted well production

    Energy Technology Data Exchange (ETDEWEB)

    Richardson, E.A.; Hinson, R.A.

    1984-06-19

    A well which is producing slowly by artificial lift can be economically heated by first inflowing a nitrogen-generating solution, to form a pool of reacting liquid near the uppermost opening into the reservoir, then inflowing more solution while artificially-lifting liquid from near the lowermost opening into the reservoir at a rate substantially equalling the inflow rate.

  17. Un exemple de volcanisme calco-alcalin de type orogénique mis en place en contexte de rifting (Cambrien de l'oued Rhebar, Meseta occidentale, Maroc)

    Science.gov (United States)

    El Hadi, Hassan; Tahiri, Abdelfatah; Simancas Cabrera, Fernando; González Lodeiro, Francisco; Azor Pérez, Antonio; Jesús Martínez Poyatos, David

    2006-03-01

    The Middle Cambrian calc-alkaline Oued Rhebar volcanic complex (western Meseta, Morocco) compares with rocks originated in orogenic contexts. The La/Nb ratios are relatively high (5.2), suggesting a lithospheric mantle origin. The La/Ta ratios, higher than 26, and the negative Nb anomaly indicate a lithospheric source contaminated by the continental crust. These rocks were generated in the Mesetian Mid-Cambrian rift and would have inherited their orogenic signature from the partial melting of a previously metasomatized mantle. To cite this article: H. El Hadi et al., C. R. Geoscience 338 (2006).

  18. Imaging paleoslabs in the D″ layer beneath Central America and the Caribbean using seismic waveform inversion.

    Science.gov (United States)

    Borgeaud, Anselme F E; Kawai, Kenji; Konishi, Kensuke; Geller, Robert J

    2017-11-01

    D″ (Dee double prime), the lowermost layer of the Earth's mantle, is the thermal boundary layer (TBL) of mantle convection immediately above the Earth's liquid outer core. As the origin of upwelling of hot material and the destination of paleoslabs (downwelling cold slab remnants), D″ plays a major role in the Earth's evolution. D″ beneath Central America and the Caribbean is of particular geodynamical interest, because the paleo- and present Pacific plates have been subducting beneath the western margin of Pangaea since ~250 million years ago, which implies that paleoslabs could have reached the lowermost mantle. We conduct waveform inversion using a data set of ~7700 transverse component records to infer the detailed three-dimensional S-velocity structure in the lowermost 400 km of the mantle in the study region so that we can investigate how cold paleoslabs interact with the hot TBL above the core-mantle boundary (CMB). We can obtain high-resolution images because the lowermost mantle here is densely sampled by seismic waves due to the full deployment of the USArray broadband seismic stations during 2004-2015. We find two distinct strong high-velocity anomalies, which we interpret as paleoslabs, just above the CMB beneath Central America and Venezuela, respectively, surrounded by low-velocity regions. Strong low-velocity anomalies concentrated in the lowermost 100 km of the mantle suggest the existence of chemically distinct denser material connected to low-velocity anomalies in the lower mantle inferred by previous studies, suggesting that plate tectonics on the Earth's surface might control the modality of convection in the lower mantle.

  19. Geochemistry and hydrogeochemical process of groundwater in the ...

    African Journals Online (AJOL)

    user

    This valley, presenting a synclinal structure, is filled by thick. Meso-cenozoic sedimentary formations, often discordant, essen- tially composed of detrital, carbonate or evaporates deposits and based on a pre-Cambrian folded basement. Also, the greater part of these sedimentary formations is covered with sand dunes and.

  20. Late Quaternary stratigraphic development in the lower Luni, Mahi ...

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    in the Thar desert as compared to that at the desert margin; this makes purely lithostratigraphic correlations ... Significant accumulation of continental sedimen- .... cambrian granites near Dharoi, in the foothill zone. ...... Oil. Nat. Gas Comm., Dehradun. 6(2) 37–50. DeCelles P G, Gehrels G E, Quade J and Ojha T P 1998.

  1. Devonian sand injections and volcanism in the Murzuq Basin (south-west Libya)

    DEFF Research Database (Denmark)

    Moreau, Julien; Ghienne, Jean-Francois

    system is original by its interaction with volcanism and its situation in an epicontinental intracratonic basin. The sand injections form a seal-bypass system between the Ordovician-Cambrian reservoirs and the Lower Devonian sandstones, breaching through the Silurian shale seal (and source rock...

  2. Epistemic values in the Burgess Shale debate

    DEFF Research Database (Denmark)

    Baron, Christian

    2009-01-01

    Focusing primarily on papers and books discussing the evolutionary and systematic interpretation of the Cambrian animal fossils from the Burgess Shale fauna, this paper explores the role of epistemic values in the context of a discipline (paleontology) striving to establish scientific authority w...

  3. Ore levels in Paleozoic of Semipalatinsk test site

    International Nuclear Information System (INIS)

    Ergaliev, G.Kh.; Myasnikov, A.K.; Fomichev, V.I.

    1999-01-01

    The regularity of the deposition of main mineralization of industrial types within Semipalatinsk test site proves and here and there defines more exactly location of the ore levels in Eastern Kazakhstan. Two mega levels, namely: Cambrian-Ordovician (siliceous-basalt, island-arc) and Carboniferous (especially carbonaceous-tarragons) ones are the most perspective for localizing the leading gold mineralization in the region

  4. Planetary biology and microbial ecology. Biochemistry of carbon and early life

    Science.gov (United States)

    Margulis, L. (Editor); Nealson, K. H. (Editor); Taylor, I. (Editor)

    1983-01-01

    Experiments made with cyanobacteria, phototrophic bacteria, and methanogenic bacteria are detailed. Significant carbon isotope fractionation data is included. Taken from well documented extant microbial communities, this data provides a basis of comparison for isotope fractionation values measured in Archean and Proterozoic (preCambrian) rocks. Media, methods, and techniques used to acquire data are also described.

  5. The evolution of shell form in tropical terrestrial microsnails

    NARCIS (Netherlands)

    Liew, Thor Seng

    2014-01-01

    Mollusca form an important animal phylum that first appeared in the Cambrian, and today is,after Arthropoda, the second largest animal phylum, with more than 100,000 extant species(Bieler, 1992, Brusca and Brusca, 2003), with the class Gastropoda accounting for 80% of the extant species in the

  6. Origin of brackish groundwater in a sandstone aquifer on Bornholm, Denmark

    DEFF Research Database (Denmark)

    Jørgensen, Niels Oluf; Heinemeier, Jan

    2008-01-01

    A multi-isotope approach in combination with hydrochemical data and borehole logging is applied to identify the source of brackish groundwater in a borehole in the well field of Neksø Municipal Waterworks in Bornholm, Denmark. The aquifer lithology consists of fractured Lower Cambrian sandstones...

  7. Cambrian–early Ordovician volcanism across the South Armorican and Occitan domains of the Variscan Belt in France: Continental break-up and rifting of the northern Gondwana margin

    Directory of Open Access Journals (Sweden)

    André Pouclet

    2017-01-01

    Full Text Available The Cambrian–lower Ordovician volcanic units of the South Armorican and Occitan domains are analysed in a tectonostratigraphic survey of the French Variscan Belt. The South Armorican lavas consist of continental tholeiites in middle Cambrian–Furongian sequences related to continental break-up. A significant volcanic activity occurred in the Tremadocian, dominated by crustal melted rhyolitic lavas and initial rifting tholeiites. The Occitan lavas are distributed into five volcanic phases: (1 basal Cambrian rhyolites, (2 upper lower Cambrian Mg-rich tholeiites close to N-MORBs but crustal contaminated, (3 upper lower–middle Cambrian continental tholeiites, (4 Tremadocian rhyolites, and (5 upper lower Ordovician initial rift tholeiites. A rifting event linked to asthenosphere upwelling took place in the late early Cambrian but did not evolve. It renewed in the Tremadocian with abundant crustal melting due to underplating of mixed asthenospheric and lithospheric magmas. This main tectono-magmatic continental rift is termed the “Tremadocian Tectonic Belt” underlined by a chain of rhyolitic volcanoes from Occitan and South Armorican domains to Central Iberia. It evolved with the setting of syn-rift coarse siliciclastic deposits overlain by post-rift deep water shales in a suite of sedimentary basins that forecasted the South Armorican–Medio-European Ocean as a part of the Palaeotethys Ocean.

  8. Uruguay report

    International Nuclear Information System (INIS)

    Quintanilla, R.

    1988-01-01

    The best ancients rocks in Uruguay are composed by the crystalline shield. In this shield are recognised two big units. The Rio de la Plata insular shelf and the Atlantic zone insular shelf. The geological post-cambrian environment is determined by the deposit basins and the basaltic plateau.

  9. Origen de la escapolita en metapelitas y rocas anfibolicas de series del Cambrico Inferior del Occidente de Asturias (NW de España)

    NARCIS (Netherlands)

    Suárez, O.; Arias, E.

    1981-01-01

    Levels of layered green rocks, characterized by the presence of a fibrous green tremolitic-actinolitic amphibole and/or scapolite, cropping out in the core of the San Martin anticline in the base of Vegadeo limestone (Lower Cambrian) are studied. The origin of the scapolite, under the point of view

  10. Cranberry magnetite deposits Avery County, N.C., and Carter County, Tenn.

    Science.gov (United States)

    Kline, M.H.; Ballard, T.J.

    1948-01-01

    The Cranberry magnetite deposits occur in pre-Cambrian granite-gneiss in a belt extending from 3 miles southeast of Cranberry, N.C., to about 6 miles southwest of Magnetic City, Tenn. The belt forms a curve, elongated to the north, approximately 26 miles in length.

  11. Zircon provenance of SW Caledonian phyllites reveals a distant Timanian sediment source

    Czech Academy of Sciences Publication Activity Database

    Sláma, Jiří; Pedersen, R. B.

    2015-01-01

    Roč. 172, č. 4 (2015), s. 465-478 ISSN 0016-7649 Institutional support: RVO:67985831 Keywords : East-European-Craton * LA-ICP-MS * Norwegian Caledonides * detrial zircon * U-PB * Scandinavian Caledonides * LU-HF * Cambrian papaeogeography * South Norwey * Oslo region Subject RIV: DB - Geology ; Mineralogy Impact factor: 2.473, year: 2015

  12. Groundwater recharge in the Kolokani-Nara region in Mali

    International Nuclear Information System (INIS)

    Dincer, T.; Dray, M.; Zuppi, G.M.; Guerre, A.; Tazioli, G.S.; Traore, S.

    1984-01-01

    The area studied is part of the Nara, Kolokani, Banamba and Koulikoro regions and lies between the Mauritanian frontier and Bamako. It is a Sahel zone devoid of active surface hydrography, the annual rainfall varying between 1000 mm in the south and 400 mm in the north. The altitude decreases from 600 m to 250 m from the Mandingues Plateaux to the Nara plain. The Nara area consists of a basin filled with Cambrian schists containing seams of dolomitic limestones and sandstones cemented by limestone. The thickness of the series is thought to be about 300-500 m. The area of the Mandingues Plateaux is composed of Lower Cambrian sandstone-schist formations with a thickness of several hundred metres, covered with a crust of weathering. The two formations have aquifers of the same type - they are discontinuous with predominantly fissure-type permeability. The permeable zones in the Cambrian schist aquifers are more discontinuous than those in the Cambrian sandstones and are less developed in depth. The recharge conditions, on the other hand, are quite good on account of the sand cover which allows rapid infiltration of rain water. The Lower Cambrian aquifer is highly heterogeneous but much less discontinuous. The transfer of groundwater takes place at the level of small local sub-basins over short distances. The hydrogeological and hydrogeochemical data point to the existence of recent recharge and mixing with older water. The groundwater renewal rate indicates, in many cases, limited water reserves. Infiltration is associated, in some cases, with storms of greater intensity and, in other cases, also with small sudden showers. Under natural conditions, the infiltrated water is generally used up by evapotranspiration. Under conditions of exploitation, a fraction of this recharge is recovered either almost directly or indirectly by replacement of the water taken from the fissured zones of the substratum. (author)

  13. Gravity enhanced acoustic levitation method and apparatus

    Science.gov (United States)

    Barmatz, M. B.; Allen, J. L.; Granett, D. (Inventor)

    1985-01-01

    An acoustic levitation system is provided for acoustically levitating an object by applying a single frequency from a transducer into a resonant chamber surrounding the object. The chamber includes a stabilizer location along its height, where the side walls of the chamber are angled so they converge in an upward direction. When an acoustic standing wave pattern is applied between the top and bottom of the chamber, a levitation surface within the stabilizer does not lie on a horizontal plane, but instead is curved with a lowermost portion near the vertical axis of the chamber. As a result, an acoustically levitated object is urged by gravity towards the lowermost location on the levitation surface, so the object is kept away from the side walls of the chamber.

  14. In situ trace gas and particle measurements in the summer lower stratosphere during STREAM II. Implications for O{sub 3} production

    Energy Technology Data Exchange (ETDEWEB)

    Bregman, A; Lelieveld, J; Scheeren, H A [Institute for Marine and Atmospheric Sciences, Utrecht (Netherlands); Arnold, F; Buerger, V; Schneider, J [Max-Planck-Inst. for Nuclear Physics, Heidelberg (Germany); Fischer, H; Waibel, A [Max-Planck-Inst. fuer Chemie, Mainz (Germany); Siegmund, P C; Wauben, W M.F. [Koninklijk Nederlands Meteorologisch Inst., De Bilt (Netherlands); Stroem, J [Stockholm Univ. (Sweden). Dept. of Meteorology

    1998-12-31

    In situ aircraft measurements of O{sub 3}, CO, HNO{sub 3}, and aerosol particles are presented, performed over the North Sea region in the summer lower stratosphere during the STREAM-II campaign (Stratosphere Troposphere Experiments by Aircraft Measurements). Elevated CO mixing ratios are attributed to mixing of polluted tropospheric air into the lowermost extra-tropical stratosphere. Model calculations illustrate that the O{sub 3} production efficiency of NO{sub x} is smaller than previously assumed, under conditions with relatively high HNO{sub 3} mixing ratios, as observed during STREAM-II. The model simulations further suggest a relatively high O{sub 3} production efficiency from CO oxidation, as a result of the relatively high ambient HNO{sub 3} and NO{sub x} concentrations, implying that upward transport of CO rich air enhances O{sub 3} production in the lowermost stratosphere. (author) 13 refs.

  15. Method of charging instruments into liquid metal coolant

    International Nuclear Information System (INIS)

    Yamazaki, Hiroshi

    1980-01-01

    Purpose: To alleviate the thermal shock of a reactor charging machine when charging the machine into liquid metal coolant after the machine is preheated in cover gas. Method: When a reactor fueling machine reaches at the lowermost portion the position immediately above liquid metal coolant surface level, the machine is stopped moving down. The reactor fueling machine is heated at the lowermost portion by thermal radiation from the surface of the liquid metal coolant. After the machine is thus preheated in cover gas, it is again steadily moved down by a winch and charged into the liquid metal coolant. Therefore, the thermal shock of the machine becomes low when charging the machine into the liquid metal coolant to eliminate the damage and deformation at the machine. (Yoshihara, H.)

  16. The Upper Miocene of the Rostov Dome (Eastern Paratethys: Implication of the chronostratigraphy and bivalvia-based biostratigraphy

    Directory of Open Access Journals (Sweden)

    Ruban Dmitry A.

    2005-01-01

    Full Text Available The Rostov Dome is located in the south of the Russian Platform. In the Late Miocene this area was embraced by the Eastern Paratethys. The implications of a recently developed Neogene chronostratigraphy to the studied area are discussed. The Sarmatian regional stage corresponds to the upper part of the Langhian, the entire Serravalian and the lower part of the Tortonian global stages; the Maeotian regional stage corresponds to the upper part of the Tortonian and the lowermost horizons of the Messinian global stages; the Pontian regional stage corresponds to most of the Messinian and the lowermost Zanclean global stages. A first Bivalvia-based bio-stratigraphic framework is proposed for the territory of the Rostov Dome. Five biozones were established within the Serravalian-Messinian: Tapes vitalianus, Cerastoderma fittoni-Cerastoderma subfittoni, Congeria panticapaea, Congeria amygdaloides navicula and Monodacna pseudocatillus-Prosodacna schirvanica.

  17. In situ trace gas and particle measurements in the summer lower stratosphere during STREAM II. Implications for O{sub 3} production

    Energy Technology Data Exchange (ETDEWEB)

    Bregman, A.; Lelieveld, J.; Scheeren, H.A. [Institute for Marine and Atmospheric Sciences, Utrecht (Netherlands); Arnold, F.; Buerger, V.; Schneider, J. [Max-Planck-Inst. for Nuclear Physics, Heidelberg (Germany); Fischer, H.; Waibel, A. [Max-Planck-Inst. fuer Chemie, Mainz (Germany); Siegmund, P.C.; Wauben, W.M.F. [Koninklijk Nederlands Meteorologisch Inst., De Bilt (Netherlands); Stroem, J. [Stockholm Univ. (Sweden). Dept. of Meteorology

    1997-12-31

    In situ aircraft measurements of O{sub 3}, CO, HNO{sub 3}, and aerosol particles are presented, performed over the North Sea region in the summer lower stratosphere during the STREAM-II campaign (Stratosphere Troposphere Experiments by Aircraft Measurements). Elevated CO mixing ratios are attributed to mixing of polluted tropospheric air into the lowermost extra-tropical stratosphere. Model calculations illustrate that the O{sub 3} production efficiency of NO{sub x} is smaller than previously assumed, under conditions with relatively high HNO{sub 3} mixing ratios, as observed during STREAM-II. The model simulations further suggest a relatively high O{sub 3} production efficiency from CO oxidation, as a result of the relatively high ambient HNO{sub 3} and NO{sub x} concentrations, implying that upward transport of CO rich air enhances O{sub 3} production in the lowermost stratosphere. (author) 13 refs.

  18. Archeological and Palynological Analysis of Specimens and Materials Recovered in Two Historic Period Privies and a Well in Saint Alice Revetment, Saint James Parish, Louisiana.

    Science.gov (United States)

    1982-01-01

    remains. The lowermost of these samples (#49) contained no economic re- mains but #47 and #48 each contained a squash or pumpkin seed (Cucurbita). The...and grape seeds in Zone K and the presence of watermelon seeds, and squash (or pumpkin ) seeds, and a trace of corn pollen in Zone J also support these...about 20. For absolute ach- romatic colors, ( pure grays, white and black), which have zero chroma and no hue, the letter N (neutral) takes the place

  19. Centrifugal pump assembly for use in nuclear reactor plants or the like

    International Nuclear Information System (INIS)

    Honold, E.; Ruepp, M.

    1975-01-01

    A description is given of a vertical centrifugal pump assembly for use as a primary recirculating pump in a nuclear reactor plant which has an uppermost shaft which is driven by a motor, a lowermost shaft which drives the impeller of the pump, and an intermediate shaft which is movable axially between the uppermost and lowermost shafts and carries a housing for radial and/or thrust bearings. A rigid coupling between the lowermost shaft and the intermediate shaft is disengaged when the intermediate shaft is lifted to thereby afford access to certain parts of the lowermost shaft. The uppermost shaft can drive the intermediate shaft through the medium of a flexible coupling having coupling elements mounted on the lower end of the uppermost shaft and the upper end of the intermediate shaft, and a distancing sleeve whose internal threads are in permanent mesh with external threads of the two coupling elements. A shroud which surrounds the flexible coupling has a maximum-diameter tubular section rigid with the housing for the bearings, a minimum-diameter tubular section rigid with but detachable from the casing of the motor, and a median tubular section which penetrates into the maximum-diameter section when the intermediate shaft is lifted. When the minimum-diameter section is detached from the casing of the motor, it can be slid, together with the intermediate section, into the maximum-diameter section to thereby afford access to the flexible coupling. The rigid coupling has two coaxial coupling elements which are mounted at the upper end of the pump shaft and the lower end of the intermediate shaft and may have teeth which mate when the intermediate shaft assumes its lower end position in which it can drive the pump

  20. The occurrence of a shallow-water Ammobaculoides assemblage in the Middle Jurassic (Bajocian) Dhruma Formation of Central Saudi Arabia

    Science.gov (United States)

    Kaminski, Michael A.; Hammad Malik, Muhammad; Setoyama, Eiichi

    2018-01-01

    We report the occurrence of an Ammobaculoides-dominated assemblage in the lowermost member of the Middle Jurassic Dhruma Formation exposed west of Riyadh, Saudi Arabia. The new species Ammobaculoides dhrumaensis n.sp. is described from the green shale of the D1 unit (also known as the Balum Member) of the Dhruma Formation, which has been assigned an early Bajocian age based on ammonites. Our new finding constitutes the oldest reported worldwide occurrence of the agglutinated foraminiferal genus Ammobaculoides Plummer, 1932.

  1. Chemical trends in ocean islands explained by plume–slab interaction

    Science.gov (United States)

    Dannberg, Juliane; Gassmöller, Rene

    2018-04-01

    Earth's surface shows many features, of which the genesis can be understood only through their connection with processes in Earth's deep interior. Recent studies indicate that spatial geochemical patterns at oceanic islands correspond to structures in the lowermost mantle inferred from seismic tomographic models. This suggests that hot, buoyant upwellings can carry chemical heterogeneities from the deep lower mantle toward the surface, providing a window to the composition of the lowermost mantle. The exact nature of this link between surface and deep Earth remains debated and poorly understood. Using computational models, we show that subducted slabs interacting with dense thermochemical piles can trigger the ascent of hot plumes that inherit chemical gradients present in the lowermost mantle. We identify two key factors controlling this process: (i) If slabs induce strong lower-mantle flow toward the edges of these piles where plumes rise, the pile-facing side of the plume preferentially samples material originating from the pile, and bilaterally asymmetric chemical zoning develops. (ii) The composition of the melt produced reflects this bilateral zoning if the overlying plate moves roughly perpendicular to the chemical gradient in the plume conduit. Our results explain some of the observed geochemical trends of oceanic islands and provide insights into how these trends may originate.

  2. New Zircon U-Pb Age Constrain of the Origin of Devil's River Uplift (SW Texas) and Insights into the Late Proterozoic and Paleozoic Evolution of the Southern Margin of Laurentia

    Science.gov (United States)

    Rodriguez, E.; Dickerson, P. W.; Stockli, D. F.

    2017-12-01

    The Devils River Uplift (DRU) in SW Texas records the evolution of the southern Laurentian margin from Grenvillian orogenesis and assembly of Rodinia, to its fragmentation by rifting, and to the amalgamation of Pangaea. It was cored by a well (Shell No. 1 Stewart), penetrating Precambrian gneisses and Cambrian metasediments and sandstones. New zircon LA-ICP-MS data from a total of 10 samples elucidate the crystallization and depositional ages, as well as the detrital provenance, of Precambrian and Cambrian rocks from the DRU. Zircons from five Precambrian crystalline basement samples (6000-9693') yield uniform U-Pb crystallization ages of 1230 Ma that are similar to ages for young gneisses of the Valley Spring Domain (Llano uplift) in central Texas, where they mark the cessation of arc magmatism within the Grenville orogenic belt. The 1230 Ma igneous basement is overlain by L.-M. Cambrian metasedimentary rocks ( 4000-6000') with maximum depositional ages of 533-545 Ma. Detrital zircons from Cambrian strata are dominated by a 1070-1080 Ma population, likely derived from basement units exposed in Texas (Llano uplift, Franklin Mts.), with minor contributions from local 1230 Ma Precambrian basement and the 1380-1500 Ma Granite Rhyolite Province. The L.-M. Cambrian interval is dominated (>80%) by Neoproterozoic detrital magmatic zircons with two major distinct age clusters at 570-700 Ma and 780-820 Ma, supporting a two-stage Rodinia rift model and providing strong evidence for major Cryogenian-Eocambrian intraplate magmatism along the southern margin of Rodinia. Moreover, detrital zircon signatures for L.-M. and U. Cambrian strata strongly correlate with those from the Cuyania terrane of W. Argentina - notably the W. Sierras Pampeanas (Sa. Pie de Palo, Sa. de Maz): 1230 Ma from metasandstones (PdP); 1081-1038 Ma from metasiliciclastics (PdP, SdM); Cryogenian-Eocambrian [774 & 570 Ma] plutons (SdM, PdP). In summary, these new zircon U-Pb data from DRU in SW Texas show

  3. Oxygen as a driver of early arthropod micro-benthos evolution.

    Directory of Open Access Journals (Sweden)

    Mark Williams

    Full Text Available BACKGROUND: We examine the physiological and lifestyle adaptations which facilitated the emergence of ostracods as the numerically dominant Phanerozoic bivalve arthropod micro-benthos. METHODOLOGY/PRINCIPAL FINDINGS: The PO(2 of modern normoxic seawater is 21 kPa (air-equilibrated water, a level that would cause cellular damage if found in the tissues of ostracods and much other marine fauna. The PO(2 of most aquatic breathers at the cellular level is much lower, between 1 and 3 kPa. Ostracods avoid oxygen toxicity by migrating to waters which are hypoxic, or by developing metabolisms which generate high consumption of O(2. Interrogation of the Cambrian record of bivalve arthropod micro-benthos suggests a strong control on ecosystem evolution exerted by changing seawater O(2 levels. The PO(2 of air-equilibrated Cambrian-seawater is predicted to have varied between 10 and 30 kPa. Three groups of marine shelf-dwelling bivalve arthropods adopted different responses to Cambrian seawater O(2. Bradoriida evolved cardiovascular systems that favoured colonization of oxygenated marine waters. Their biodiversity declined during intervals associated with black shale deposition and marine shelf anoxia and their diversity may also have been curtailed by elevated late Cambrian (Furongian oxygen-levels that increased the PO(2 gradient between seawater and bradoriid tissues. Phosphatocopida responded to Cambrian anoxia differently, reaching their peak during widespread seabed dysoxia of the SPICE event. They lacked a cardiovascular system and appear to have been adapted to seawater hypoxia. As latest Cambrian marine shelf waters became well oxygenated, phosphatocopids went extinct. Changing seawater oxygen-levels and the demise of much of the seabed bradoriid micro-benthos favoured a third group of arthropod micro-benthos, the ostracods. These animals adopted lifestyles that made them tolerant of changes in seawater O(2. Ostracods became the numerically

  4. Functional Redundancy of ERK1 and ERK2 MAP Kinases during Development

    Directory of Open Access Journals (Sweden)

    Christophe Frémin

    2015-08-01

    Full Text Available ERK1 and ERK2 are the effector kinases of the ERK1/2 MAP-kinase signaling pathway, which plays a central role in transducing signals controlling cell proliferation, differentiation, and survival. Deregulated activity of the ERK1/2 pathway is linked to a group of developmental syndromes and contributes to the pathogenesis of various human diseases. One fundamental question that remains unaddressed is whether ERK1 and ERK2 have evolved unique physiological functions or whether they are used redundantly to reach a threshold of global ERK activity. Here, we show that the extent of development of the mouse placenta and embryo bearing different combinations of Erk1 and Erk2 alleles is strictly correlated with total ERK1/2 activity. We further demonstrate that transgenic expression of ERK1 fully rescues the embryonic and placental developmental defects associated with the loss of ERK2. We conclude that ERK1 and ERK2 exert redundant functions in mouse development.

  5. Development of a chromosomally integrated metabolite-inducible Leu3p-alpha-IPM "off-on" gene switch.

    Directory of Open Access Journals (Sweden)

    Maria Poulou

    2010-08-01

    Full Text Available Present technology uses mostly chimeric proteins as regulators and hormones or antibiotics as signals to induce spatial and temporal gene expression.Here, we show that a chromosomally integrated yeast 'Leu3p-alpha-IotaRhoMu' system constitutes a ligand-inducible regulatory "off-on" genetic switch with an extensively dynamic action area. We find that Leu3p acts as an active transcriptional repressor in the absence and as an activator in the presence of alpha-isopropylmalate (alpha-IotaRhoMu in primary fibroblasts isolated from double transgenic mouse embryos bearing ubiquitously expressing Leu3p and a Leu3p regulated GFP reporter. In the absence of the branched amino acid biosynthetic pathway in animals, metabolically stable alpha-IPM presents an EC(50 equal to 0.8837 mM and fast "OFF-ON" kinetics (t(50ON = 43 min, t(50OFF = 2.18 h, it enters the cells via passive diffusion, while it is non-toxic to mammalian cells and to fertilized mouse eggs cultured ex vivo.Our results demonstrate that the 'Leu3p-alpha-IotaRhoMu' constitutes a simpler and safer system for inducible gene expression in biomedical applications.

  6. Ubiquitous overexpression of a transgene encoding the extracellular portion of the Drosophila roughest-irregular chiasm C protein induces early embryonic lethality.

    Science.gov (United States)

    Moda, L; Machado, R C; Ramos, R G

    2000-09-01

    The cell adhesion molecule Rst-irreC is a transmembrane glycoprotein of the immunoglobulin superfamily involved in several important developmental processes in Drosophila, including axonal pathfinding in the optic lobe and programmed cell death and pigment cell differentiation in the pupal retina. As an initial step towards the "in vivo" functional analysis of this protein we have generated transgenic fly stocks carrying a truncated cDNA construct encoding only the extracellular domain of Rst-IrreC under the transcriptional control of the heat shock inducible promoter hsp70. We show that heat-shocking embryos bearing the transgene during the first 8hs of development lead to a 3-4 fold reduction in their viability compared to wild type controls. The embryonic lethality can already be produced by applying the heat pulse in the first 3hs of embryonic development, does not seem to be suppressed in the absence of wildtype product and is progressively reduced as the heat treatment is applied later in embryogenesis. These results are compatible with the hypothesis of the lethal phenotype being primarily due to heterophilic interactions between Rst-IrreC extracellular domain and an yet unknown ligand.

  7. Evolution of mineralizing brines in the east Tennessee Mississippi Valley-type ore field

    Energy Technology Data Exchange (ETDEWEB)

    Kesler, S.E.; Gesink, J.A.; Haynes, F.M. (Univ. of Michingan, Ann Arbor (USA))

    1989-05-01

    The east Tennessee Mississippi Valley-type (MVT) ore field contains barite-fluorite and sphalterite deposits in a continuous paleoaquifer consisting of breccia zones in the Upper Cambrian-Lower Ordovician Knox Group. Paragenetic observations and fluid inclusion compositions in these deposits indicate that the Knox paleoaquifer was invaded first by Ca-rich brines (Ca:Na about 1) that deposited fluorite and barite, and later by Na-Ca brines (Ca:Na = 0.1 to 0.5) that deposited sphalerite. Geologic relation sindicate that these brines were derived from the southeast, in the area of the Middle Ordovician Servier foreland shale basin, and that imposed by fluorite solubility indicate further that all original connate water in the Sevier basin was required to deposit the estimated flourite reserves of the ore field.Thus, the later, sphalerite-depositing brines represent recycled meteoric water from the Sevier basin or connate brines from underlying (Cambrian) shales.

  8. Return to Black Mountain palaeomagnetic reassessment of the Chatsworth and Ninmaroo formations, western Queensland, Australia

    CERN Document Server

    Anderson, K L; Lackie, M A; Schmidt, P W; 10.1111/j.1365-246X.2003.02164.x

    2004-01-01

    Palaeomagnetic results from late Middle Cambrian-Early Ordovician carbonate sequences sampled at Black Mountain (Mt Unbunmaroo), Mt Datson and near Chatsworth Station (southeastern Georgina Basin) are presented. A palaeomagnetic reassessment of these carbonates was designed in an effort to constrain regional magnetization ages as results from an earlier study, conducted at Mt Unbunmaroo, play a pivotal role in a proposed Cambrian inertial interchange true polar wander (IITPW) event. Remanent magnetizations within these carbonates were found to be variably developed with most specimens displaying two of the five isolated components. Component PF, for which goethite is the identified remanence carrier, is thought to reflect a chemical remanent magnetization of recent origin. Component TR, held by haematite, has a palaeomagnetic pole consistent with the Tertiary segment of Australia's apparent polar wander path (APWP) and most probably was acquired as a consequence of prolonged weathering during this period. The...

  9. Examination of the Reelfoot Rift Petroleum System, south-central United States, and the elements that remain for potential exploration and development

    Science.gov (United States)

    Coleman, James; Pratt, Thomas L.

    2016-01-01

    The Reelfoot rift is one segment of a late Proterozoic(?) to early Paleozoic intracontinental rift complex in the south-central United States. The rift complex is situated beneath Mesozoic to Cenozoic strata of the Mississippi embayment of southeastern Missouri, northeastern Arkansas, and western Tennessee and Kentucky. The rift portion of the stratigraphic section consists primarily of synrift Cambrian and Ordovician strata, capped by a postrift sag succession of Late Ordovician to Cenozoic age. Potential synrift source rocks have been identified in the Cambrian Elvins Shale. Thermal maturity of Paleozoic strata within the rift ranges from the oil window to the dry gas window. Petroleum generation in Elvins source rocks likely occurred during the middle to late Paleozoic. Upper Cretaceous sedimentary rocks unconformably overlie various Paleozoic units and define the likely upper boundary of the petroleum system.

  10. New K-Ar constraints on the onset of subsidence in the Canning Basin, Western Australia

    International Nuclear Information System (INIS)

    Shaw, R.D.; Tyler, I.M.; Griffin, T.J.; Webb, A.

    1992-01-01

    Structural mapping and reconnaissance K-Ar studies have helped to delineate and date the latest deformational stages (D4 and D5) in the King Leopold Orogen, to the north of the Canning Basin. The dates have been determined for schists selected from both contractional shear zones and from rocks metamorphosed to the lower greenschist facies during the final phase of basement deformation. These dates imply that the basement-deforming event started in the latest Precambrian to earliest Cambrian (ca 560 Ma), and that tectonism recurred in the latest Cambrian to earliest Ordovician (ca 500 Ma). The final contractional deformation is slightly older than the oldest-known sedimentary rocks in the basin (latest Tremadoc), and helps to define the time that basin subsidence started. 23 refs., 3 tabs., 2 figs

  11. Geomorphology of the north flank of the Uinta Mountains

    Science.gov (United States)

    Bradley, W.H.

    1936-01-01

    The Uinta Mountains, whose northern margin is almost coincident with the southern boundary of Wyoming, extend from the Wasatch Range eastward across the northern part of Utah into northwestern Colorado. They were carved out of a large, simple anticlinal fold of sedimentary rocks arched up into essentially their present attitude at the end of the Cretaceous period. The Uinta Mountain group (Uinta quartzite of previous reports) a series of brick-red to purplish-red quartzite and sandstone beds of pre-Cambrian age, aggregating more than 12,000 feet in thickness, makes up the central mass of the range. Flanking the quartzite core and sharing its anticlinal structure are beds of limestone, sandstone, and shale ranging in age from Upper or Middle Cambrian to Upper Cretaceous. These rocks, which have a total thickness of about 15,000 feet, have been eroded from the higher part of the range, so the upturned edges of the harder

  12. The transnational regime complex for climate change

    OpenAIRE

    Kenneth W Abbott

    2012-01-01

    In climate change, as in other areas, recent years have produced a ‘Cambrian explosion’ of transnational institutions, standards, financing arrangements, and programs. As a result, climate governance has become complex, fragmented, and decentralized, operating without central coordination. Most studies of climate governance focus on inter­state institutions. In contrast, I map a different realm of climate change governance: the diverse array of transnational schemes. I analyze this emerging s...

  13. International Uranium Resources Evaluation Project (IUREP) national favourability studies: Sweden

    International Nuclear Information System (INIS)

    1977-11-01

    Sweden, covers an area of approx. 450 000 square kilometers. It has a population of 8 millions. With few exceptions in the northern part the access can be regarded as good. A dense network of motorroads and railroad exists. The results obtained by the exploration works combined with other available geo-information permit a separation of two principal uranium provinces in Sweden. The first one is confined to sediments of Upper Cambrian and Lower Ordovician which appears in Southern Sweden and along the border of the Caledonian mountain range in Central Sweden. The uranium occurrence are stratiform, of blackshale type which occurs in the Peltura zone of Upper Cambrian or they are associated to a phosphatite-bearing unit of Lower Ordovician overlying the Cambrian shale formation. The distribution of uranium in Upper Cambrian rocks is in general dependant on their lithology which itself is related to the paleography. This conditions explain relatively higher uranium content of the shale from Billigen.The potential resources of the province are estimated at about 1 million tonnes uranium. The second uranium province, called Arjeplog-Arvidsjaur, situated immediately south of the Arctic circle, comprises one deposit - Pleutajokk - and a group of more than twenty occurrences of similar characteristics and age (1 700 - 1 800 my.). The results of the past exploration have shown that uranium is present in different types of rocks. Because of the presence of uranium in many of the pegmatites the possibility of the formation of large low grade deposits should be tested. Favourable areas are those regions where the geological conditions are similar to the geology of the Grenville province in Canada or the Damara belt of SW-Africa. Special studies are recommended on this subject

  14. Terreneuvian stratigraphy and faunas from the Anabar Uplift, Siberia

    Directory of Open Access Journals (Sweden)

    Artem Kouchinsky

    2017-06-01

    Full Text Available Assemblages of mineralized skeletal fossils are described from limestone rocks of the lower Cambrian Nemakit-Daldyn, Medvezhya, Kugda-Yuryakh, Manykay, and lower Emyaksin formations exposed on the western and eastern flanks of the Anabar Uplift of the northern Siberian Platform. The skeletal fossil assemblages consist mainly of anabaritids, molluscs, and hyoliths, and also contain other taxa such as Blastulospongia, Chancelloria, Fomitchella, Hyolithellus, Platysolenites, Protohertzina, and Tianzhushanella. The first tianzhushanellids from Siberia, including Tianzhushanella tolli sp. nov., are described. The morphological variation of Protohertzina anabarica and Anabarites trisulcatus from their type locality is documented. Prominent longitudinal keels in the anabaritid Selindeochrea tripartita are demonstrated. Among the earliest molluscs from the Nemakit-Daldyn Formation, Purella and Yunnanopleura are interpreted as shelly parts of the same species. Fibrous microstructure of the outer layer and a wrinkled inner layer of mineralised cuticle in the organophosphatic sclerites of Fomitchella are reported. A siliceous composition of the globular fossil Blastulospongia is reported herein and a possible protistan affinity similar to Platysolenites is discussed. New carbon isotope data facilitate correlation both across the Anabar Uplift and with the Terreneuvian Series of the IUGS chronostratigraphical scheme for the Cambrian System. The base of Cambrian Stage 2 is provisionally placed herein within the Fortunian‒Cambrian Stage 2 transitional interval bracketed by the lowest appearance of Watsonella crosbyi and by a slightly higher horizon at the peak of carbon isotope excursion Iʹ from western flank of the Anabar Uplift. Correlation across the Siberian Platform of the fossiliferous Medvezhya and lower Emyaksin formations showing δ13Ccarb excursion Iʹ with the upper Sukharikha Formation containing excursion 5p and upper Ust’-Yudoma Formation

  15. Early paleozoic granitoids in the southern Vanoise basement: U-Pb geochronology of the Arpont meta-granite (Savoy, French Alps); Granitoides d`age paleozoique inferieur dans le socle de Vanoise meridionale: geochronologie U-Pb du metagranite de l`Arpont (Alpes de Savoir, France)

    Energy Technology Data Exchange (ETDEWEB)

    Bertrand, J.M. [Laboratoire de geodynamique des chaines alpines, LGCA-CISM, 73 - Le Bourget-du-Lac (France); Leterrier, J. [Centre de recherches petrographiques et geochimique, 54 - Vandoeuvre-les-Nancy (France)

    1997-12-01

    The U-Pb age of a meta-granite from southern Vanoise (Brianconnais` domain) at 479{+-} 4 Ma confirms hat the micaschists which dominate this pre-alpine basement are, at least, of Early Paleozoic age. The rare magmatic rocks occurring in Vanoise and showing alkaline affinities, may be compared to the orthogneisses belonging to the Cambrian-Ordovician extensional event well known in other parts of the Varican belt. (authors) 27 refs.

  16. Late Proterozoic to Early Palaeozoic platform deposits of Southern Moravia (Czech Republic)

    Czech Academy of Sciences Publication Activity Database

    Mikuláš, Radek; Gilíková, H.; Vavrdová, Milada

    2008-01-01

    Roč. 52, č. 4 (2008), s. 335-348 ISSN 1641-7291 R&D Projects: GA ČR GA205/04/0151; GA ČR GA205/06/0395 Institutional research plan: CEZ:AV0Z30130516 Keywords : Brunovistulicum * Cambrian * facies analysis * ichnology * acritarcha Subject RIV: DB - Geology ; Mineralogy Impact factor: 0.892, year: 2008 http://www.pgi.gov.pl/images/stories/G_Q/52_4/mikulas.pdf

  17. Not armour, but biomechanics, ecological opportunity and increased fecundity as keys to the origin and expansion of the mineralized benthic metazoan fauna

    OpenAIRE

    Cohen, B.L.

    2005-01-01

    This paper offers a new biotic interaction hypothesis for the Cambrian 'explosion' of mineralized, benthic, metazoan diversity. It proposes that organic-mineral composite structures (e.g. shells and muscle lever-arms) originated in Proterozoic lineages of primary larva-like, but reproductively competent, pelagic bilaterians because mineralization was both mechanically and energetically favourable, not because it provided armour against predation. Increased strength and rigidity of composite s...

  18. Migrated hydrocarbons in outcrop samples: revised petroleum exploration directions in the Tarim Basin

    Energy Technology Data Exchange (ETDEWEB)

    Li, Maowen; Snowdon, Lloyd [Geological Survey of Canada, Calgary, AB (Canada); Xiao, Zhongyao [CNPC Tarim Petroleum Exploration Bureau, Kuerle, Xinjiang (China); Lin, Renzi [Petroleum Univ., Changping, Beijing (China); Wang, Peirong; Hou, Dujie [Jianghan Petroleum Univ., Hubei (China); Zhang, Linye [SINOPEC Shengli Petroleum Bureau, Dongying, Shandong (China); Zhang, Shuichang; Liang, Digang [Research Inst. of Petroleum Exploration and Development, Beijing (China)

    2000-07-01

    The application of age-specific biomarker distributions established from mature exploration areas of the Tarim Basin, northwestern China, indicates that most Carboniferous-Permian outcrop samples in the eastern segment of the Southwest Depression, previously believed to have significant petroleum source potential, in fact contain migrated hydrocarbons derived from Cambrian-Lower Ordovician strata. New geochemical results have led to a major revision of petroleum exploration directions in this area. (Author)

  19. HapticScreenを用いたメディアインスタレーション : ANOMALOCARIS(<特集>インタラクティブアート)

    OpenAIRE

    岩田, 洋夫; 矢野, 博明; 中泉, 文孝

    2000-01-01

    "ANOMALOCARIS" is an interactive work, which represents virtual creature through visual and haptic sensation. Anomalocaris is a name of an animal that supposed to live during the Cambrian Era. Virtual anomalocaris is displayed on the HapticScreen. HapticScreen is a new configuration of a force feedback device. HapticScreen has an innovative mechanism that creates sense of touch on whole palm. The device deforms itself to present shapes of virtual object. Typical force feedback device uses a g...

  20. Whole-rock U-Pb dating of the Shuijingtuo formation sedimentary rocks in the Yangtze Gorge

    International Nuclear Information System (INIS)

    Zheng, Y.F.; Huang, B.

    1990-01-01

    Black shale and enclosed limestone lenticule from Lower Cambrian Shuijingtuo Formation in the Yangtze Gorge is successfully dated by whole-rock U-Pb method. The results yield a concordant age of about 573±14 Ma, in excellent agreement with both stratigraphic and palaeontologic evidence. The whole-rock U-Pb method can provide a reliable approach for age determination of sedimentary stratum. (orig.) [de

  1. Caracterización geoquímica y estudio comparativo de plagiogranitos de las Zonas Surportuguesa y Ossa-Morena (SO del Macizo Ibérico, España)

    OpenAIRE

    Bellido, F.; Díez-Montes, A.; Sánchez-García, T.

    2010-01-01

    Plagiogranites and albitic rocks belonging to contrasted magmatic associations of different ages and geodynamic environments outcrop in Ossa-Morena (OMZ) and Surportuguese (SPZ) Zones. OMZ plagiogranites are related with Cambrian-Ordovician rifting and represent a part of the felsic members of a bimodal magmatic suite and show oceanic plagiogranites affinities. SPZ plagiogranites are related with a Carboniferous volcano-plutonic calc-alkaline suite related with Variscan Orogeny. Both plagiogr...

  2. Dating of retrograde metamorphism in Western Carpathians by K-Ar analysis of muscovites

    International Nuclear Information System (INIS)

    Cambel, B.; Korikovskij, S.P.; Krasivskaya, I.S.; Arakelyants, M.M.

    1986-01-01

    Using the K-Ar isotope dating method of muscovites it was found that many retrogradely metamorphosed rocks are the results of Variscan retrograde metamorphism and are not pre-Cambrian or Alpine metamorphites (diaphthorites). Samples for dating were taken from the Western Carpathian crystalline formation. The content of radiogenic argon was determined by mass spectrometry using the method of isotope dilution. (M.D.)

  3. A molecular palaeobiological exploration of arthropod terrestrialization

    DEFF Research Database (Denmark)

    Lozano-Fernandez, Jesus; Carton, Robert; Tanner, Alastair R.

    2016-01-01

    to the colonization of land is the most likely scenario.Molecular clock analyses confirmed an origin for the three terrestrial lineages bracketed between the Cambrian and the Silurian. While molecular divergence times for Arachnida are consistent with the fossil record,Myriapoda are inferred to have colonized land......, consistent with morphological arguments for convergence in tracheal systems. This article is part of the themed issue ‘Dating species divergences using rocks and clocks’....

  4. On the origin of optics

    Science.gov (United States)

    Parker, Andrew R.

    2011-03-01

    The first optical devices in animals evolved in the Cambrian period. The first reflector known dates from around 508 million years ago (Ma); the first eyes with lenses evolved at around 521 Ma. Consideration of the introduction of vision leads to a hypothesis for the cause of evolution's Big Bang—the Cambrian explosion. Suddenly, and for no obvious reason, the range and variety of life-forms erupted somewhere between 520 and 515 Ma (as limited by of our dating techniques). At no other time in Earth's history there has been such a profusion, such an exuberance, and such an overwhelming diversity in so short time, within one million years. Prior to this Cambrian explosion event, all animals were soft-bodied and mainly worm-like, as they had been for millions of years before that. But during the Cambrian explosion many of the major animal groups on Earth today independently evolved their hard body parts for the first time. Following the appearance of the first trilobites, some animals evolved shells and spines, some with bright colours, to visually warn of their new armour. Others evolved streamlined appearances and swimming oars to advise trilobites that they could not be caught. The Light Switch Theory provides an explanation for what triggered this event—that it was the development of vision (in trilobites); the introduction of optics. Once visual capability arose, it allowed predators to identify prey, triggering an arms race. From here on, vision became a dominant force of evolution and resulted in the eyes and reflecting optics that we have in nature today. This paper provides a summary of the first optical devices to evolve in animals, along with the implications of these in their relevance to the Big Bang of evolution, written for the physical sciences.

  5. The Baltic Basin: structure, properties of reservoir rocks, and capacity for geological storage of CO2

    Directory of Open Access Journals (Sweden)

    Vaher, Rein

    2009-12-01

    Full Text Available Baltic countries are located in the limits of the Baltic sedimentary basin, a 700 km long and 500 km wide synclinal structure. The axis of the syneclise plunges to the southwest. In Poland the Precambrian basement occurs at a depth of 5 km. The Baltic Basin includes the Neoproterozoic Ediacaran (Vendian at the base and all Phanerozoic systems. Two aquifers, the lower Devonian and Cambrian reservoirs, meet the basic requirements for CO2 storage. The porosity and permeability of sandstone decrease with depth. The average porosity of Cambrian sandstone at depths of 80–800, 800–1800, and 1800–2300 m is 18.6, 14.2, and 5.5%, respectively. The average permeability is, respectively, 311, 251, and 12 mD. Devonian sandstone has an average porosity of 26% and permeability in the range of 0.5–2 D. Prospective Cambrian structural traps occur only in Latvia. The 16 largest ones have CO2 storage capacity in the range of 2–74 Mt, with total capacity exceeding 400 Mt. The structural trapping is not an option for Lithuania as the uplifts there are too small. Another option is utilization of CO2 for enhanced oil recovery (EOR. The estimated total EOR net volume of CO2 (part of CO2 remaining in the formation in Lithuania is 5.6 Mt. Solubility and mineral trapping are a long-term option. The calculated total solubility trapping capacity of the Cambrian reservoir is as high as 11 Gt of CO2 within the area of the supercritical state of carbon dioxide.

  6. Geological map of Uruguay Esc 1,100,000. Fuente del Puma Sheet G-27

    International Nuclear Information System (INIS)

    Preciozzi, F.; Pena, S.

    1990-01-01

    This work is about the geological map of Uruguay Esc.1.100.000 (Fuente del Puma) and the explanatory memoranda which describes the geological , lithological and sedimentological characteristics soils. The area corresponding to Fuente del Puma is located in the SW of Lavalleja and NW of Maldonado town and its stratigraphy belong to the Cretaceous and Cenozoic formations as well as the Cambrian and upper Precambrian

  7. Stratigraphic model deposit Ofi Inf SDZ-2X A1, Jun in block in Orinoco Oil belt

    International Nuclear Information System (INIS)

    Martinez, E.; Sandoval, D.

    2010-01-01

    This work is about the Stratigraphic model deposit O fi I nf SDZ-2X A1, Junin block in Orinoco Oil belt.This model was based on a chrono stratigraphic interpretation and was defined the correlation between the main and secondary surfaces. The wells of the study area pass through the Cambrian, Cretaceous and Miocene sediments. The last is more interesting for the study because of the stratigraphic and sand body surface presence

  8. The oldest known priapulid-like scalidophoran animal and its implications for the early evolution of cycloneuralians and ecdysozoans.

    Science.gov (United States)

    Liu, Yunhuan; Xiao, Shuhai; Shao, Tiequan; Broce, Jesse; Zhang, Huaqiao

    2014-05-01

    Morphological phylogenetic analyses suggest that scalidophorans (priapulids, loriciferans, and kinorhynchs) and nematoids (nematodes and nematomorphs) form the ecdysozoan clade Cycloneuralia, which is a sister group to panarthropods. It has been proposed that extant priapulids and Cambrian priapulid-like scalidophorans, because of their conserved evolution, have the potential to illuminate the ancestral morphology, ecology, and developmental biology of highly derived ecdysozoans such as nematods and arthropods. As such, Cambrian fossils, particularly Markuelia and possibly olivooids, can inform the early evolution of scalidophorans, cycloneuralians, and ecdysozoans. However, the scalidophoran Markuelia is known exclusively as embryo fossils, and the olivooids have been alternatively interpreted as cnidarians or cycloneuralians. Here, we describe a post-embryonic scalidophoran fossil Eopriapulites sphinx new genus and species, which represents the oldest known scalidophoran, from the early Cambrian Period (∼535 Ma) in South China. E. sphinx is similar to modern scalidophorans in having an introvert armed with hollow scalids, a collar with coronal scalids, and a pharynx with pharyngeal teeth, but its scalids and pharyngeal teeth are arranged in a hexaradial pattern. Phylogenetically resolved as a stem-group scalidophoran, E. sphinx shares a hexaradial pattern with the hexaradial arrangement of certain anatomical structures in kinorhynchs, loriciferans, nematoids, and Cambrian fossils such as Eolympia pediculata, which could also be a scalidophoran. Thus, the bodyplan of ancestral cycloneuralians may have had a component of hexaradial symmetry (i.e., some but not necessarily all anatomical parts are hexaradially arranged). If panarthropods are nested within paraphyletic cycloneuralians, as several molecular phylogenetic analyses suggest, the ancestral ecdysozoans may have been a legless worm possibly with a component of hexaradial symmetry. © 2014 Wiley

  9. Paleozoic unconformities favorable for uranium concentration in northern Appalachian basin

    International Nuclear Information System (INIS)

    Dennison, J.M.

    1986-01-01

    Unconformities can redistribute uranium from protore rock as ground water moves through poorly consolidated strata beneath the erosion surface, or later moves along the unconformity. Groundwater could migrate farther than in present-day lithified Paleozoic strata in the Appalachian basin, now locally deformed by the Taconic and Allegheny orogenies. Several paleoaquifer systems could have developed uranium geochemical cells. Sandstone mineralogy, occurrences of fluvial strata, and reduzate facies are important factors. Other possibilities include silcrete developed during desert exposure, and uranium concentrated in paleokarst. Thirteen unconformities are evaluated to determine favorable areas for uranium concentration. Cambrian Potsdam sandstone (New York) contains arkoses and possible silcretes just above crystalline basement. Unconformities involving beveled sandstones and possible fluvial strata include Cambrian Hardyston sandstone (New Jersey), Cambrian Potsdam Sandstone (New York), Ordovician Oswego and Juniata formations (Pennsylvania and New York), Silurian Medina Group (New York), and Silurian Vernon, High Falls, and Longwood formations (New York and New Jersey). Devonian Catskill Formation is beveled by Pennsylvanian strata (New York and Pennsylvania). The pre-Pennsylvanian unconformity also bevels Lower Mississippian Pocono, Knapp, and Waverly strata (Pennsylvania, New York, and Ohio), truncates Upper Mississippian Mauch Chunk Formation (Pennsylvania), and forms paleokarst on Mississippian Loyalhanna Limestone (Pennsylvania) and Maxville Limestone (Ohio). Strata associated with these unconformities contain several reports of uranium. Unconformities unfavorable for uranium concentration occur beneath the Middle Ordovician (New York), Middle Devonian (Ohio and New York), and Upper Devonian (Ohio and New York); these involve marine strata overlying marine strata and probably much submarine erosion

  10. New paleomagnetic data from Siberia: Non-uniformitarian geomagnetic field around the Proterozoic-Phanerozoic boundary?

    Science.gov (United States)

    Pavlov, V.; Shatsillo, A.; Kouznetsov, N.; Gazieva, E.

    2017-12-01

    There is a range of evidence, mainly from sedimentary and volcanic rocks of the Laurentia and Baltica cratons, that argue for the anomalous character of the Ediacaran-Early Cambrian paleomagnetic record. This feature could be linked either to some peculiarities of the paleomagnetic record itself or to some unusual geophysical event that would have taken place around the Proterozoic-Phanerozoic boundary (e.g., true polar wander or nonuniformitarian geomagnetic field behavior). In the latter case, the traces of this event should be observed in Ediacaran-Early Cambrian rocks anywhere there is a possibility to observe a primary paleomagnetic signal. In previous work, we reported results that suggested an anomalous paleomagnetic record in Siberian Ediacaran-Lower Cambrian rocks. Here we present new Siberian data that indicate a very high geomagnetic reversal frequency during this period and the coexistence of two very different paleomagnetic directions. We speculate that these features could be due either to a near-equatorial geomagnetic dipole during the polarity transitions or to alternation between axial and near equatorial dipoles not directly linked with polarity reversals.

  11. Multi proxy approach to evaluate and delineate the potential of hot springs in the Kotli District (Kashmir, Pakistan)

    Energy Technology Data Exchange (ETDEWEB)

    Anees, M.; Shah, M.; Qureshi, A.; Manzoor, S.

    2017-11-01

    Tattapani hot springs are located near the Kotli District of Azad Kashmir, Pakistan. This study evaluates these hot springs based on surface geological information, radon emission measurements, hydro-geochemical and isotopic signatures and potential source mechanisms. Field observations reveal that the hot springs are located at the crest of the Tattapani anticline along the faulted contact of Cambrian carbonates with Paleocene siliciclastics. In addition, remnants of igneous intrusions in the Cambrian carbonates are commonly observed. Spatial distribution of radon emissions (ranging between 2.1 and 29.5KBq m-3) indicates an anomalous zone located over the Cambrian-Paleocene faulted contact. Hydro-geochemical data show sodium-bicarbonate affinity of hot springs. The highest surface temperature of these springs is recorded at 60.8ºC. Average reservoir temperatures based on silica and cation geo-thermometers are 101ºC and 115ºC, respectively. Giggenbach ternary diagram (Na-K-Mg) suggests a non-equilibrium state between fluid and rock, whereas isotopic and chemical data indicate heat loss by conductive cooling and mixing with groundwater during the flow of thermal water up to the surface. Oxygen and deuterium isotopes indicate that thermal water is of meteoric origin, rain and/or snow in the north at higher altitudes providing the potential recharge. Furthermore, absence of tritium in the thermal water suggests a residence time of more than 50 years.

  12. REE geochemistry and genesis of Daxin uranium deposit

    International Nuclear Information System (INIS)

    Li Zhixing; Qi Fucheng; He Zhongbo; Zhang Zilong

    2011-01-01

    Through the analysis on typical REE parameters,chondrite-normalized REE patterns and hierarchical cluster analysis of rocks in the structural-geochemical zonation in Daxin uranium deposit, the paper discusses the uranium source and genesis. The study shows that the uranium source mainly came from Cambrian System. The Devonian System is maily as the favorable room for saving ores in addition to pre-concentrated room for uranium. Underground water resulted from early and late Yanshanian movement and the heating of volcanic rock was turned into geothermal water and it was moved upward by the force of tectonic movement. The geothermal water mainly extracted active uranium from the Cambrian rocks, then moved upward along main regional fault (F2) connecting the Cambrian rocks and the Devonian rocks until it arrived in structural fracture zone which was controlled by secondary faults (F13, F23, F33). At last, the uranium element in geothermal water was precipitated and concentrated into the uranium deposit in reducing environment of enriched organic material and pyrite. (authors)

  13. Biogenic magnetite as a primary remanence carrier in limestone deposits

    Science.gov (United States)

    Chang, Shih-Bin R.; Kirschvink, Joseph L.; Stolz, John F.

    1987-06-01

    Studies on the microbial communities and magnetic phases of samples collected from carbonate oozes at Sugarloaf Key, FL, U.S.A. and calcareous laminated sediments from Laguna Figueroa, Baja California, Mexico have revealed the existence of magnetotactic bacteria and ultrafine-grained single domain magnetite in both environments. Magnetotactic bacteria were identified by light and electron microscopy. The single domain magnetite was detected by coercivity spectra analysis with a SQUID magnetometer and examined under the transmission electron microscope. The similarity, in terms of size and shape, between the single domain magnetite found in these sediments and the magnetite observed in the bacterial magnetosome from enriched cultures indicates the ultrafine-grained magnetite in these two marine environments was biologically formed. These results, combined with the common occurrences of ultrafine-grained magnetite in limestone deposits detected rock magnetically, suggest biogenic magnetite may be present and contribute to the magnetic remanence in these rocks. Several Cambrian limestone samples, separately collected from Siberia, China, and Kazakhstan, were examined for the presence of bacterial magnetite. Samples from the Lower Cambrian Sinskian Formation at Siberia Platform were found to contain both a large amount of apparently bacterial magnetite particles and a very stable primary magnetic component. Post-Cambrian diagenesis does not seem to affect the microgranulometry of these apparently bacterial magnetite crystals or the magnetic remanence carried by them. Assessing the potential role of biogenic magnetite as a primary remanence carrier in other Phanerozoic limestone deposits ought to be further pursued.

  14. Paleogeographic significance of Clavohamulus hintzei Miller (Conodonta) and other Ibexian conodonts in an early Paleozoic carbonate platform facies of the Argentine Precordillera

    Science.gov (United States)

    Lehnert, O.; Miller, J.F.; Repetski, J.E.

    1997-01-01

    Pre-Tremadocian conodonts and trilobites and Tremadocian conodonts are reported from the Cambrian and Ordovician La Silla Formation in the Cerro La Silla section in east-southeast Ja??chal, San Juan Province, Argentina. A shallow marine conodont fauna contains elements of Clavohamulus hintzei Miller, a common species in North America, but reported for the first time from the early Paleozoic platform carbonates of the western Argentine Precordillera. The presence of this species suggests a correlation with the Clavohamulus hintzei conodont subbiozone of the Cordylodus intermedius conodont biozone in North America, considered Early Ordovician (Skullrockian Stage, Ibexian Series) in North America, but by South American and European standards, this biozone would be of latest Cambrian age. C. hintzei and associated conodonts of the La Silla Formation are typical of the tropical faunas of the North American Midcontinent Faunal Province; Late Cambrian trilobites from lower in the formation also are typical North American taxa. The presence of these faunas in the platform carbonates is consistent with plate reconstructions suggesting that the Precordillera was in a tropical or subtropical position close to Laurentia during the late Precambrian and early Paleozoic. These new paleontological data provide one more argument for recent models of the Precordillera as a displaced terrane derived from the Ouachita Embayment at the southern margin of Laurentia.

  15. Ozone control of biological activity during Earth's history, including the KT catastrophe

    Science.gov (United States)

    Sheldon, W. R.

    1994-01-01

    There have been brief periods since the beginning of the Cambrian some 600 m.y. ago when mass extinctions destroyed a significant fraction of living species. The most widely studied of these events is the catastrophe at the KT boundary that ended the long dominance of the dinosaurs. In addition to mass extinctions, there is another profound discontinuity in the history of Earth's biota, the explosion of life at the end of the Precambrian era which is an episode that is not explained well at all. For some 3 b.y. before the Cambrian, life had been present on Earth, but maintained a low level of activity which is an aspect of the biota that is puzzling, especially during the last two-thirds of that period. During the last 2 b.y. before the Cambrian, conditions at the Earth's surface were suitable for a burgeoning of the biota, according to most criteria: the oceans neither boiled nor were fozen solid during this time, and the atmosphere contained sufficient O for the development of animals. The purpose of this paper is to suggest that mass extinctions and the lackluster behavior of the Precambrian biota share a common cause: an inadequate amount of ozone in the atmosphere.

  16. Geologic studies to identify the source for high levels of radium and barium in illinois ground-water supplies: a preliminary report. Final report

    International Nuclear Information System (INIS)

    Cartwright, K.; Specht, S.A.; Gilkeson, R.H.; Griffin, R.A.; Larson, T.E.

    1978-08-01

    Analyses of water from municipal wells in Illinois by the Illinois Environmental Protection Agency showed that more than 300 wells exceeded the upper limit for gross alpha radiation in drinking water. More than 30 wells exceeded the upper limit for barium in drinking water. High levels of radiation in ground water were more extensive in areal distribution than the high levels of barium. All of the affected wells were finished in bedrock, primarily in rocks of the Cambrian and Ordovician Systems of northern Illinois. The geologic settings in which the high levels of radiation and barium were documented indicated that the problem was not restricted to Illinoise. The source of the radiation in ground water was thought to be the natural occurrence of the radioactive elements uranium-238 and thorium-232 in the aquifer rocks. Analyses of a limited number of rock samples indicated that uranium and thorium concentrations were highest in fine-grained sediments in the aquifer systems; the highest concentration was in shales that confine the aquifer. Chemical analyses of rock samples indicated that high concentrations of barium were widespread in rocks of the Cambrian and Ordovician Systems. The concentration of barium in ground water was controlled by solubility equilibria reactions with sulfate ion. A map showing sulfate ion concentration in the Cambrian-Ordovician Aquifer could be used to delimit regions where barium might occur at concentrations exceeding 1 milligram/liter

  17. Correlation of structural lineaments with oil discoveries in Potwar sub-basin, Pakistan

    International Nuclear Information System (INIS)

    Iqbal, M.; Ali, S.M.

    2001-01-01

    The Potwar sub-basin is located in the foothills of western Himalayas. It is developed as a result of continent collision between the Indian and Eurasian plates. This sub-basin is one of the major oil and gas producing-region of the country. Clastics of Cambrian, Permian, Jurassic, Paleocene, and carbonates of Permian, Paleocene, and Eocene are producing reservoir. Fractured and eocene carbonate reservoirs (Sakesar and Chorgali) are the main producing horizons in the region. Shale of infra-Cambrian-Cambrian and Paleocene are the main source rocks in the area. Interpretation of satellite data for lineament analysis coupled with stress models indicate that 63% of oil and gas fields fall along and 37% within 2-5 km radius of extensional lineaments and their corresponding open fractured zones developed due to various stress regimes. It is therefore suggested that exploration for hydrocarbon may be targeted in the strike extension of the mentioned lineaments in areas where optimum conditions for hydrocarbon generation exist. (author)

  18. Equinodermos del Cámbrico de España: situación actual de las investigaciones y perspectivas futuras

    Directory of Open Access Journals (Sweden)

    Zamora, S.

    2011-06-01

    Full Text Available This paper reviews all finds of Cambrian echinoderms from Spain since their first discovery in the XIX century. Recent research techniques used for the study of echinoderms are also described, providing a guide for procedure. Sampling in new fossiliferous localities from the Cambrian of North Spain and the review of classic ones has yielded more than 2,000 echinoderm fossils. These include species belonging to five major classes, Cincta, Eocrinoidea, Edrioasteroidea, Stylophora and Ctenocystoidea, which show the highest diversity reported from Gondwana. These results suggest that echinoderms underwent major diversification during the middle Cambrian, with many groups more widely distributed than previously thought. These arguments suggest that many classes originated in the lower Cambrian where only a few taxa have been described. Finally, I offer some suggestions about where research efforts need to be focussed for a better knowledge of Cambrian echinoderm faunas in Gondwana.

    En este trabajo se presenta una revisión histórica de todos los equinodermos cámbricos descubier tos en España, desde su primer hallazgo a finales del siglo XIX y las técnicas actuales que se utilizan para su estudio. El muestreo sistemático de nuevas localidades cámbricas del Norte de España y la revisión de otras ya conocidas, ha proporcionado más de 2.000 ejemplares de equinodermos. En total se han reconocido taxones pertenecientes a cinco clases: Cincta, Eocrinoidea, Edrioasteroidea, Stylophora y Ctenocystoidea, que muestran la mayor diversidad para este periodo en Gondwana. Estos hallazgos muestran que los equinodermos alcanzaron su primer pico de diversidad durante el Cámbrico medio. Esto, unido a la amplia distribución paleobiogeográfica de algunos clados, nos advierte de un origen para muchos grupos en el Cámbrico inferior, donde sólo unos pocos taxones han sido descritos a nivel mundial. Por último se dan algunas ideas de hacia d

  19. Origin and implications of a thrust-bound gypsiferous unit along the western edge of Jabal Sumeini, northern Oman Mountains

    Science.gov (United States)

    Cooper, David J. W.; Ali, Mohammed Y.; Searle, Michael P.

    2018-04-01

    The Oman Mountains comprise a series of thrust sheets of Neo-Tethyan oceanic rocks that were emplaced onto the Arabian continental margin during obduction of the Semail Ophiolite during the Late Cretaceous. Three separate groups of anomalous gypsiferous bodies intrude the allochthonous units along faults over a distance of about 150 km in the Hawasina Window, Jabal Qumayrah and Jabal Sumeini. The bodies at Jabal Sumeini form a band about 4 km long and up to 100 m wide along a late-stage thrust that restacks the allochthon over a post-emplacement Maastrichtian-Palaeogene sedimentary succession. The gypsum shows evidence of flow-folding and contains numerous clasts and rafts of a range of quartzose sandstones, but with only a minor component from carbonates from the Neo-Tethyan Sumeini Group in the hanging-wall. Palaeogene limestones from the footwall succession are essentially absent. Strontium isotope ratios are high and intersect with the open ocean-water reference curve for the Late Cambrian-Ordovician and Late Miocene-Pliocene. They are also noticeably higher than the ratios from the two other gypsiferous outcrop areas in the Oman Mountains and from outcrops of Ediacaran-Early Cambrian salt domes in central Oman. However, the regional stratigraphy points towards a source of the gypsum from either an Ediacaran-Early Cambrian Ara Group salt basin or from the Lower Fars Formation (Early-Middle Miocene), and derivation of the sandstone clasts and rafts from thick Lower Palaeozoic clastic sequences. The discrepancy with the ages inferred from the strontium isotope data can be attributed to deposition of the gypsum in restricted conditions not in equilibrium with the prevailing ocean water. Two models are presented, for an Ediacaran-Early Cambrian and an Early-Middle Miocene source. While the latter cannot be wholly discounted, the stratigraphic and structural context point more strongly towards an Ediacaran-Early Cambrian Ara Group source of the gypsum. This was

  20. Bedrock Geology and Asbestos Deposits of the Upper Missisquoi Valley and Vicinity, Vermont

    Science.gov (United States)

    Cady, Wallace Martin; Albee, Arden Leroy; Chidester, A.H.

    1963-01-01

    The upper Missisquoi Valley and vicinity as described in this report covers an area of about 250 square miles at the headwaters of the Missisquoi River in north-central Vermont. About 90 percent of the area is forested and the remainder is chiefly farm land. The topography reflects the geologic structure and varied resistance of the bedrock to erosion. Most of the area is on the east limb of the Green Mountain anticlinorium, which is the principal structural feature of Vermont. The bedrock is predominantly sedimentary and volcanic rock that has been regionally metamorphosed. It was intruded before metamorphism by mafic and ultramafic igneous rocks, and after metamorphism by felsic and mafic igneous rocks. The metamorphosed sedimentary and volcanic rocks range in age from Cambrian(?) to Middle Silurian, the intrusive igneous rocks from probably Late Ordovician to probably late Permian. Metamorphism and principal folding in the region occurred in Middle Devonian time. The metamorphosed sedimentary and volcanic rocks make up a section at least 25,000 feet thick and can be divided into nine formations. The Hazens Notch formation of Cambrian(?) and Early Cambrian age is characterized by carbonaceous schist. It is succeeded in western parts of the area by the Jay Peak formation of Early Cambrian age, which is chiefly a schist that is distinguished by the general absence of carbonaceous zones; in central parts of the area the Hazens Notch formation is followed by the Belvidere Mountain amphibolite, probably the youngest of the formations of Early Cambrian age. The Ottauquechee formation, composed of carbonaceous phyllite and quartzite, and phyllitic graywacke, is of Middle Cambrian age. The Stowe formation of Late Cambrian(?) and Early(?) Ordovician age overlies the Ottauquechee and is predominantly noncarbonaceous schist, though it also contains greenstone and carbonaceous schist and phyllite. The Umbrella Hill formation of Middle Ordovician age is characteristically a

  1. Simulating the Seismic Signal of Phase Transitions in the Deepest Mantle (Invited)

    Science.gov (United States)

    Walker, A.; Dobson, D. P.; Nowacki, A.; Wookey, J. M.; Forte, A. M.; Kendall, J. M.

    2013-12-01

    The discovery of the perovskite to post-perovskite phase transition in (Mg,Fe)SiO3 explains many of the seismic observations of the lowermost mantle including the presence of multiple seismic discontinuities and significant seismic anisotropy. However, the explanations of many detailed features remain elusive. The recent discovery of a topotactic relationship between the orientation of perovskite and post-perovskite crystals in a partially transformed analogue opens the possibility of texture inheritance through the phase transition [1]. This must be captured in simulations designed to explain the anisotropy of the lowermost mantle, especially those which link mantle dynamics with seismic observations. We have extended our previous work linking models of flow in the lowermost mantle with simulations of texture development and predictions of seismic anisotropy [2] to account for the topotaxy between perovskite and post-perovskite. In particular, we compare four cases: (1) As in [2], anisotropy is only generated in post-perovskite by dislocation mediated deformation dominated by one of a number of slip systems, phase transitions destroy texture and ferropericlase and perovskite dominated rocks are isotropic. (2) Although phase transitions destroy texture, ferropericlase and/or perovskite deform by dislocation motion permitting the generation of seismic anisotropy in warmer regions of the mantle where post-perovskite is unstable. We account for the possibility of the inversion of slip-system activities in ferropericlase at high pressure as suggested by models of dislocation motion based on atomic scale simulations [3]. (3) Allow texture development by dislocation motion in perovskite and post-perovskite and texture inheritance through phase transitions by the mechanism described in [1]. However, we assume that the bulk of the lower mantle deforms by a mechanism that does not lead to the development of texture and so begin the simulation from a random distribution of

  2. In situ measurements of the NO{sub x} distribution and variability over the eastern North Atlantic

    Energy Technology Data Exchange (ETDEWEB)

    Ziereis, H.; Schlager, H.; Schulte, P.; Koehler, I.; Marquardt, R.; Feigl, C.

    1998-11-01

    Between 1994 and 1996 the research aircraft Falcon of the ``Deutsches Zentrum fuer Luft- und Raumfahrt (DLR)`` was used to probe the upper troposphere and lowermost stratosphere over the eastern North Atlantic. In situ measurements of NO, NO{sub 2}, and O{sub 3} were performed during 32 flights. The measurements were carried out during five aircraft campaigns in summer and late autumn, respectively, based from Shannon/Ireland and Prestwick/Scotland. Most of the flights were conducted in the region of the North Atlantic flight corridor. Main objectives of these measurements included the study of the large scale distribution of NO and NO{sub x} and the development of a ``climatology`` of NO{sub x} in a region of the atmosphere that is strongly affected by aircraft emissions. Substantial variability of NO and NO{sub x} volume mixing ratios was observed in the upper troposphere and lowermost stratosphere. In spite of this variability a significant seasonal dependence was found. NO mean values (averages over all measurements made during one campaign) at altitudes between 10,500 and 11,500 m, where most of the data have been obtained, ranged between about 0.1 and 0.14 ppbv in summer and 0.03 and 0.10 ppbv in late autumn. NO and NO{sub x} did not show a significant gradient across the tropopause. The correlation between NO{sub x} and O{sub 3} in the upper troposphere and lowermost stratosphere was only very weak. The present measurements represent a suitable data set for comparison with predictions of the NO{sub x} distribution in the upper troposphere over the eastern North Atlantic by three dimensional models. A comparison with the NO{sub x} fields simulated with the climate model ECHAM 3 extended by a simplified NO{sub x} chemistry reveals good agreement for summer and autumn conditions. (orig.) 44 refs.

  3. Downstream lightening and upward heavying, sorting of sediments of uniform grain size but differing in density

    Science.gov (United States)

    Viparelli, E.; Solari, L.; Hill, K. M.

    2014-12-01

    Downstream fining, i.e. the tendency for a gradual decrease in grain size in the downstream direction, has been observed and studied in alluvial rivers and in laboratory flumes. Laboratory experiments and field observations show that the vertical sorting pattern over a small Gilbert delta front is characterized by an upward fining profile, with preferential deposition of coarse particles in the lowermost part of the deposit. The present work is an attempt to answer the following questions. Are there analogous sorting patterns in mixtures of sediment particles having the same grain size but differing density? To investigate this, we performed experiments at the Hydrosystems Laboratory at the University of Illinois at Urbana-Champaign. During the experiments a Gilbert delta formed and migrated downstream allowing for the study of transport and sorting processes on the surface and within the deposit. The experimental results show 1) preferential deposition of heavy particles in the upstream part of the deposit associated with a pattern of "downstream lightening"; and 2) a vertical sorting pattern over the delta front characterized by a pattern of "upward heavying" with preferential deposition of light particles in the lowermost part of the deposit. The observed downstream lightening is analogous of the downstream fining with preferential deposition of heavy (coarse) particles in the upstream part of the deposit. The observed upward heavying was unexpected because, considering the particle mass alone, the heavy (coarse) particles should have been preferentially deposited in the lowermost part of the deposit. Further, the application of classical fractional bedload transport relations suggests that in the case of mixtures of particles of uniform size and different densities equal mobility is not approached. We hypothesize that granular physics mechanisms traditionally associated with sheared granular flows may be responsible for the observed upward heavying and for the

  4. Core evidence of paleoseismic events in Paleogene deposits of the Shulu Sag in the Bohai Bay Basin, east China, and their petroleum geologic significance

    Science.gov (United States)

    Zheng, Lijing; Jiang, Zaixing; Liu, Hui; Kong, Xiangxin; Li, Haipeng; Jiang, Xiaolong

    2015-10-01

    The Shulu Sag, located in the southwestern corner of the Jizhong Depression, Bohai Bay Basin of east China, is a NE-SW trending, elongate Cenozoic half-graben basin. The lowermost part of the third member of the Shahejie Formation in this basin is characterized by continental rudstone and calcilutite to calcisiltite facies. Based on core observation and regional geologic analysis, seismites are recognized in these lacustrine deposits, which include soft-sediment deformation structures (sedimentary dikes, hydraulic shattering, diapir structures, convolute lamination, load-flame structures, ball-and-pillow structures, loop bedding, and subsidence structures), synsedimentary faults, and seismoturbidites. In addition, mixed-source rudstones, consisting of the Paleozoic carbonate clasts and in situ calcilutite clasts in the lowermost submember of Shahejie 3, appear in the seismites, suggesting an earthquake origin. A complete representative vertical sequence in the lowermost part of the third member found in well ST1H located in the central part of the Shulu Sag shows, from the base to the top: underlying undeformed layers, synsedimentary faults, liquefied carbonate rocks, allogenetic seismoturbidites, and overlying undeformed layers. Seismites are widely distributed around this well and there are multiple sets of stacked seismites separated by undeformed sediment. The nearby NW-trending Taijiazhuang fault whose fault growth index is from 1.1 to 1.8 and the NNE-trending Xinhe fault with a fault growth index of 1.3-1.9 may be the source of the instability to create the seismites. These deformed sedimentary layers are favorable for the accumulation of oil and gas; for example, sedimentary dikes can cut through many layers and serve as conduits for fluid migration. Sedimentary faults and fractures induced by earthquakes can act as oil and gas migration channels or store petroleum products as well. Seismoturbidites and mixed-source rudstones are excellent reservoirs due to

  5. From theory to practice

    International Nuclear Information System (INIS)

    Sinisalmi, T.; Oesch, P.

    1997-01-01

    Extensive research conducted at the Oulujoki River has led to practical measures aimed at alleviating the impact of short-term regulation. Amongst other things, the power plants on the river have begun to implement a fish management plan conceived for each individual reservoir and to create spawning areas for river-spawning fish. The raising of the reservoir level at Merikoski, the lowermost of the river plants, will be started in the autumn of 1997 and will considerably enhance recreational opportunities along the section of the river below the Montta plant, where the adverse effects of fluctuations in the river's water level have been the most severe

  6. The composition and evolution of an Oligocene regolith on top of the Sesia–Lanzo Zone (Western Alps)

    DEFF Research Database (Denmark)

    Kapferer, Notburga; Mercolli, Ivan; Berger, Alfons

    2011-01-01

    An Oligocene paleosurface (regolith) lies on top of the high-pressure metamorphic rocks of the Sesia–Lanzo Zone near Biella, NW Italy. Only the saprock, the lowermost part in a regolith profile, is preserved. No evidence for any paleosoil can be observed. Field observations indicate that the rego...... with this sequence of subaerial rocks being very close to the intrusion depth of the Valle del Cervo Pluton at the time of its emplacement (4–7 km; Zanoni et al., in Rend Online SGI Note Brevi 1: 199–202, 2008; Zanoni et al., in Int Geol Rev 52: 1244–1267, 2010 and references therein)....

  7. From theory to practice

    Energy Technology Data Exchange (ETDEWEB)

    Sinisalmi, T.; Oesch, P. [ed.

    1997-11-01

    Extensive research conducted at the Oulujoki River has led to practical measures aimed at alleviating the impact of short-term regulation. Amongst other things, the power plants on the river have begun to implement a fish management plan conceived for each individual reservoir and to create spawning areas for river-spawning fish. The raising of the reservoir level at Merikoski, the lowermost of the river plants, will be started in the autumn of 1997 and will considerably enhance recreational opportunities along the section of the river below the Montta plant, where the adverse effects of fluctuations in the river`s water level have been the most severe

  8. Matuyama-age lithic tools from the Sima del Elefante site, Atapuerca (northern Spain).

    Science.gov (United States)

    Parés, Josep M; Pérez-González, Alfredo; Rosas, Antonio; Benito, A; Bermúdez de Castro, J M; Carbonell, E; Huguet, R

    2006-02-01

    Paleomagnetic results obtained from the sedimentary fill at the Sima del Elefante site in Atapuerca, Spain, reveal a geomagnetic reversal, interpreted as the Matuyama-Brunhes boundary (0.78 Ma). The uppermost lithostratigraphic units (E17 through E19), which contain Mode II and III archaeological assemblages, display normal polarity magnetization, whereas the six lowermost units (E9 through E16) yield negative latitudinal virtual geomagnetic pole positions. Units E9 through E13, all of which display reverse magnetic polarity, contain Mode I (Oldowan) lithic tools, testifying to the presence of humans in the early Pleistocene (0.78-1.77 Ma).

  9. Crocodilian faunal renewal in the Upper Oligocene of Western Europe

    Science.gov (United States)

    Antunes, Miguel Telles; Cahuzac, Bruno

    1999-01-01

    The presence of Tomistomine Crocodilians ( Tomistoma sp.) is first recorded in the Upper Oligocene of Western Europe (Chattian, Saint-Geours-de-Maremne, Aquitaine basin). Immigration, probably of Asiatic origin, occurred ca. 26 Ma, prior to the previously earliest records for Lowermost Miocene. Tomistoma points to warm, at least subtropical environments, in agreement with data on invertebrates and fish fauna. Immigrations to Western Europe of Tomistoma (and of Gavialis, in Miocene times) during Upper Oligocene and Lower-Middle Miocene seem related to climatic warming and eustatic rise events. There was a renewal of the European Crocodilian fauna, much impoverished in Late Eocene and reduced to Diplocynodon.

  10. The Pindiro Group (Triassic to Early Jurassic Mandawa Basin, southern coastal Tanzania): Definition, palaeoenvironment, and stratigraphy

    Science.gov (United States)

    Hudson, W. E.; Nicholas, C. J.

    2014-04-01

    This paper defines the Pindiro Group of the Mandawa Basin, southern coastal Tanzania based on studies conducted between 2006 and 2009 with the objective of understanding the evolution of this basin. This work draws upon field data, hydrocarbon exploration data, unconventional literature, and the scant published materials available. The paper focuses on the evolution, depositional environments, and definition of the lowermost sedimentary package, which overlies unconformably the metamorphic basement of Precambrian age. The package is described here as the Pindiro Group and it forms the basal group of the Mandawa Basin stratigraphy.

  11. An anisotropic shear velocity model of the Earth's mantle using normal modes, body waves, surface waves and long-period waveforms

    Science.gov (United States)

    Moulik, P.; Ekström, G.

    2014-12-01

    We use normal-mode splitting functions in addition to surface wave phase anomalies, body wave traveltimes and long-period waveforms to construct a 3-D model of anisotropic shear wave velocity in the Earth's mantle. Our modelling approach inverts for mantle velocity and anisotropy as well as transition-zone discontinuity topographies, and incorporates new crustal corrections for the splitting functions that are consistent with the non-linear corrections we employ for the waveforms. Our preferred anisotropic model, S362ANI+M, is an update to the earlier model S362ANI, which did not include normal-mode splitting functions in its derivation. The new model has stronger isotropic velocity anomalies in the transition zone and slightly smaller anomalies in the lowermost mantle, as compared with S362ANI. The differences in the mid- to lowermost mantle are primarily restricted to features in the Southern Hemisphere. We compare the isotropic part of S362ANI+M with other recent global tomographic models and show that the level of agreement is higher now than in the earlier generation of models, especially in the transition zone and the lower mantle. The anisotropic part of S362ANI+M is restricted to the upper 300 km in the mantle and is similar to S362ANI. When radial anisotropy is allowed throughout the mantle, large-scale anisotropic patterns are observed in the lowermost mantle with vSV > vSH beneath Africa and South Pacific and vSH > vSV beneath several circum-Pacific regions. The transition zone exhibits localized anisotropic anomalies of ˜3 per cent vSH > vSV beneath North America and the Northwest Pacific and ˜2 per cent vSV > vSH beneath South America. However, small improvements in fits to the data on adding anisotropy at depth leave the question open on whether large-scale radial anisotropy is required in the transition zone and in the lower mantle. We demonstrate the potential of mode-splitting data in reducing the trade-offs between isotropic velocity and

  12. Vojnovskytesidae - a new family of Mississippian Rugosa (Anthozoa)

    Science.gov (United States)

    Fedorowski, Jerzy; Kullmann, Jürgen

    2013-12-01

    Fedorowski, J. and Kullmann, J. 2013. Vojnovskytesidae - a new family of Mississippian Rugosa (Anthozoa). Acta Geologica Polonica, 63(4), 657-679. Warszawa. Two new species of the genus Vojnovskytes Fedorowski, 2009, namely V. marcinowskii and V. arcuatus, and a new genus, Vojnimitor, based on the new species V. proiectus, all from Mississippian strata of northern Spain, are described. Vojnovskytes variabilis (Vojnovsky-Krieger, 1934), the type species for the genus from the lowermost Visean strata of southern Urals, also is discussed and illustrated. Characters displayed by the taxa mentioned permit introduction of a new family Vojnovskytesidae.

  13. Steroid receptor coactivators 1 and 2 mediate fetal-to-maternal signaling that initiates parturition.

    Science.gov (United States)

    Gao, Lu; Rabbitt, Elizabeth H; Condon, Jennifer C; Renthal, Nora E; Johnston, John M; Mitsche, Matthew A; Chambon, Pierre; Xu, Jianming; O'Malley, Bert W; Mendelson, Carole R

    2015-07-01

    The precise mechanisms that lead to parturition are incompletely defined. Surfactant protein-A (SP-A), which is secreted by fetal lungs into amniotic fluid (AF) near term, likely provides a signal for parturition; however, SP-A-deficient mice have only a relatively modest delay (~12 hours) in parturition, suggesting additional factors. Here, we evaluated the contribution of steroid receptor coactivators 1 and 2 (SRC-1 and SRC-2), which upregulate SP-A transcription, to the parturition process. As mice lacking both SRC-1 and SRC-2 die at birth due to respiratory distress, we crossed double-heterozygous males and females. Parturition was severely delayed (~38 hours) in heterozygous dams harboring SRC-1/-2-deficient embryos. These mothers exhibited decreased myometrial NF-κB activation, PGF2α, and expression of contraction-associated genes; impaired luteolysis; and elevated circulating progesterone. These manifestations also occurred in WT females bearing SRC-1/-2 double-deficient embryos, indicating that a fetal-specific defect delayed labor. SP-A, as well as the enzyme lysophosphatidylcholine acyltransferase-1 (LPCAT1), required for synthesis of surfactant dipalmitoylphosphatidylcholine, and the proinflammatory glycerophospholipid platelet-activating factor (PAF) were markedly reduced in SRC-1/-2-deficient fetal lungs near term. Injection of PAF or SP-A into AF at 17.5 days post coitum enhanced uterine NF-κB activation and contractile gene expression, promoted luteolysis, and rescued delayed parturition in SRC-1/-2-deficient embryo-bearing dams. These findings reveal that fetal lungs produce signals to initiate labor when mature and that SRC-1/-2-dependent production of SP-A and PAF is crucial for this process.

  14. Formation of phreatomagmatic pipes in the Tunguska Basin (Siberia, Russia) during the end-Permian

    Science.gov (United States)

    Polozov, Alexander; Svensen, Henrik; Planke, Sverre

    2010-05-01

    We recently proposed that numerous pipes piercing sedimentary rocks of Tunguska Basin triggered the Permian-Triassic mass extinction (Svensen et al., 2009). Large amounts of greenhouse and poisonous gases were released through the pipes and into P-Tr atmosphere, partly formed by heating of petroleum-bearing evaporites. The sub-volcanic part of the Siberian Traps was emplaced in the Tunguska Basin sedimentary sequences, which includes Pre-Cambrian source rocks, Early Cambrian evaporites, and Paleozoic terrigenous and coal-bearing rocks. Spectacular breccia pipes are numerous in the evaporate-parts of the basin, and are filled with volcaniclastic rocks and commercial magnetite mineralization. Although these pipes have been intensively studied in order to understand the iron ore formation, the origin and formation of the pipes is poorly understood. Many researchers emphasize that magma-sediments interaction as a key reason of pipe formation, whereas phreatomagmatic hypothesis are also proposed. In order to improve the understanding of pipe formation and ore-deposition, we have studied a basalt-rich breccia pipe piercing Cambrian evaporates at the Nepa locality in East Siberia. Textural features of the volcanic fragments in the breccias include lapilli, Pele's hear, glassy basalt and dolerite clasts, blocks of tuffs in addition to sedimentary rocks. Calcite and halite are the most common types of cement. We have studied minerals from the breccia cement and from reaction rims around clasts in order to understand the hydrothermal system that developed after the pipe formed. Calcite and dolomite are the dominating carbonates, and two types of anhydrite is present. Biotite, Cl-Fe-bearing amphibole (hastingsite), and Cl-F-apatite are amongst early hydrothermal minerals covering magmatic clast and lapillies. Our new data confirm (i) the phreatomagmatic nature of breccia filling in the Tunguska Basin pipes and (ii) the key role of sedimentary brine and petroleum involved in

  15. Differentiating pedogenesis from diagenesis in early terrestrial paleoweathering surfaces formed on granitic composition parent materials

    Science.gov (United States)

    Driese, S.G.; Medaris, L.G.; Ren, M.; Runkel, Anthony C.; Langford, R.P.

    2007-01-01

    Unconformable surfaces separating Precambrian crystalline basement and overlying Proterozoic to Cambrian sedimentary rocks provide an exceptional opportunity to examine the role of primitive soil ecosystems in weathering and resultant formation of saprolite (weathered rock retaining rock structure) and regolith (weathered rock without rock structure), but many appear to have been affected by burial diagenesis and hydrothermal fluid flow, leading some researchers to discount their suitability for such studies. We examine one modern weathering profile (Cecil series), four Cambrian paleoweathering profiles from the North American craton (Squaw Creek, Franklin Mountains, Core SQ-8, and Core 4), one Neoproterozoic profile (Sheigra), and one late Paleoproterozoic profile (Baraboo), to test the hypothesis that these paleoweathering profiles do provide evidence of primitive terrestrial weathering despite their diagenetic and hydrothermal overprinting, especially additions of potassium. We employ an integrated approach using (1) detailed thin-section investigations to identify characteristic pedogenic features associated with saprolitization and formation of well-drained regoliths, (2) electron microprobe analysis to identify specific weathered and new mineral phases, and (3) geochemical mass balance techniques to characterize volume changes during weathering and elemental gains and losses of major and minor elements relative to the inferred parent materials. There is strong pedogenic evidence of paleoweathering, such as clay illuviation, sepic-plasmic fabrics, redoximorphic features, and dissolution and alteration of feldspars and mafic minerals to kaolinite, gibbsite, and Fe oxides, as well as geochemical evidence, such as whole-rock losses of Na, Ca, Mg, Si, Sr, Fe, and Mn greater than in modern profiles. Evidence of diagenesis includes net additions of K, Ba, and Rb determined through geochemical mass balance, K-feldspar overgrowths in overlying sandstone sections, and

  16. Geology of the Nevada Test Site and nearby areas, southern Nevada

    International Nuclear Information System (INIS)

    Sinnock, S.

    1982-10-01

    The Department of Energy's Nevada Test Site (NTS) lies in the southern part of the Great Basin Section of the Basin and Range Physiographic Province. This report addresses the geological setting of the NTS in the context of the current waste isolation policy. The intent is to provide a synthesis of geological conditions at the NTS and nearby areas so that a general background of information is available for assessing the possible role of geology in providing protections for humans from buried radioactive wastes. The NTS is characterized by alluvium-filled, topgraphically closed valleys surrounded by ranges composed of Paleozoic sedimentary rocks and Tertiary volcanic tuffs and lavas. The Paleozoic rocks are a miogeosynclinal sequence of about 13,000 ft of pre-Cambrian to Cambrian clastic deposits (predominantly quartzites) overlain by about 14,000 ft of Cambrian through Devonian carbonates, 8000 ft of Mississippian argillites and quartzites, and 3000 ft of Pennsylvanian to Permian limestones. Tertiary volcanic rocks are predominatly silicic composition and were extruded from numerous eruptive centers during Miocene and Pliocene epochs. Within eruptive caldera depressions, volcanic deposits accumulated to perhaps 10,000 ft in total thickness, thinning to extinction outward from the calderas. Extrusion of minor amounts of basalts accompanied Pliocene and Pleistocene filling of structural basins with detritus from the ranges. Regional compressional and extensional structures as well as local volcanic structures occur in the NTS region. Normal extensional faulting coincided with the outbreak of volcanism during the Miocene and was superimposed on existing Mesozoic structures. Continued extensional deformation may be occurring at the present time

  17. Hydrogeologic and geochemical studies of selected natural radioisotopes and barium in groundwater in Illinois. Final report

    International Nuclear Information System (INIS)

    Gilkeson, R.H.; Cartwright, K.; Cowart, J.B.; Holtzman, R.B.

    1983-05-01

    Dissolved concentrations of the natural radioisotopes 222 Rn, 226 Ra, 228 Ra, 230 Th, 232 Th, 234 U and 238 U and the element Ba 2+ were investigated in a study of high concentrations of 226 Ra, 228 Ra, and Ba 2+ in groundwater from the Cambrian and Ordovician bedrock of northern Illinois. The high radium and barium concentrations are naturally present in the major aquifers - the sandstone bedrock; therefore, remedial well construction measures will not lower the concentrations. The combined concentrations of 226 Ra and 228 Ra range from 2.3 to 50.2 pCi/L; the majority of analyses exceed the limit in the drinking water regulations of 5.0 pCi/L. The 226 Ra/ 228 Ra activity ratio ranges from 0.2 to 41.0; a 226 Ra analysis has no validity for predicting the 228 Ra concentration. Important controls on dissolved 226 Ra concentrations are secondary U on the sandstone matrix and the ionic strength of groundwater. The distribution of accessory minerals that contain 232 Th is believed to be an important control on dissolved 228 Ra concentrations. Locally the dissolved 226 Ra and 228 Ra concentrations are affected by dissolution-precipitation of secondary barite. Dissolved concentrations of 222 Rn and U are less than proposed drinking water regulations. The extreme enrichment in 234 U that occurs widespread in groundwater from the Cambrian and Ordovician bedrock is unique and problematic. The enrichment may reflect recharge of uranium to the bedrock by glacial processes. Dissolved Ba 2+ concentrations range from 2+ concentrations occur in groundwater that is depleted in dissolved SO 4 2- by anaerobic microbial reactions. A map presents the distribution of Ba 2+ in groundwater from the Cambrian and Ordovician bedrock in northeastern Illinois. 60 references, 13 figures, 3 tables

  18. Trait-based diversification shifts reflect differential extinction among fossil taxa.

    Science.gov (United States)

    Wagner, Peter J; Estabrook, George F

    2014-11-18

    Evolution provides many cases of apparent shifts in diversification associated with particular anatomical traits. Three general models connect these patterns to anatomical evolution: (i) elevated net extinction of taxa bearing particular traits, (ii) elevated net speciation of taxa bearing particular traits, and (iii) elevated evolvability expanding the range of anatomies available to some species. Trait-based diversification shifts predict elevated hierarchical stratigraphic compatibility (i.e., primitive→derived→highly derived sequences) among pairs of anatomical characters. The three specific models further predict (i) early loss of diversity for taxa retaining primitive conditions (elevated net extinction), (ii) increased diversification among later members of a clade (elevated net speciation), and (iii) increased disparity among later members in a clade (elevated evolvability). Analyses of 319 anatomical and stratigraphic datasets for fossil species and genera show that hierarchical stratigraphic compatibility exceeds the expectations of trait-independent diversification in the vast majority of cases, which was expected if trait-dependent diversification shifts are common. Excess hierarchical stratigraphic compatibility correlates with early loss of diversity for groups retaining primitive conditions rather than delayed bursts of diversity or disparity across entire clades. Cambrian clades (predominantly trilobites) alone fit null expectations well. However, it is not clear whether evolution was unusual among Cambrian taxa or only early trilobites. At least among post-Cambrian taxa, these results implicate models, such as competition and extinction selectivity/resistance, as major drivers of trait-based diversification shifts at the species and genus levels while contradicting the predictions of elevated net speciation and elevated evolvability models.

  19. Paleozoic stratigraphy and tectonics in northernmost Nevada: Implications for the nature of the Antler orogeny

    Energy Technology Data Exchange (ETDEWEB)

    Ketner, K.B. (Geological Survey, Denver, CO (United States)); Ehman, K.D. (Exxon Production Research Co., Houston, TX (United States)); Repetski, J.E.; Stamm, R.G.; Wardlaw, B.R. (Geological Survey, Reston, VA (United States))

    1993-04-01

    Recent mapping and revised ages have clarified geologic relations in northern Nevada. In the Bull Run Mountains-Copper Mountains area, Proterozoic quartzite, phyllite, marble, and greenstone are overlain successively, depositionally, and nearly concordantly by the Cambrian Prospect Mountain Quartzite, Pioche Shale, and Eldorado Dolomite; the Cambrian to Ordovician Tennessee Mountain Formation composed of limestone, siltstone, and greenstone; the Ordovician Valmy Formation composed of a lower member of greenstone, limestone, mudstone, and chert, and an upper member of quartzite and argillite; and, disconformably by a Mississippian sequence of interbedded conglomerate, limestone, siltstone, and greenstone. The Prospect Mountain, Pioche, and Eldorado form a relatively shallow-water, shelf sequence containing trilobites and displaying cross-bedding, ooliths, oncolites, and fenestral fabric. The overlying Tennessee Mountain and Valmy are devoid of such features and contain many black, finely laminated, and graded strata, suggesting a deeper-water environment. This upper Proterozoic to Permian sequence is interpreted as indicating: (1) increased tectonic subsidence or sea-level rise in the latter part of the Cambrian; (2) elevation above sea level and erosion of Devonian, Silurian, and Upper Ordovician rocks in earliest Mississippian; (3) subsidence below sea level in later Early Mississippian; (4) elevation above sea level with sporadic, moderate deformation, and local, deep erosion in medial Pennsylvanian; (5) subsidence below sea level in medial Pennsylvanian or later; (6) intermittent eruption of basic volcanics peaking in Early Ordovician and again in Mississippian. The disconformable relation between the Valmy Formation and overlying Mississippian strata indicates that the Antler orogeny of earliest Mississippian age, here consisted primarily of uplift and deep erosion. Evidence of strong Early Mississippian folding and contractional faulting is not apparent.

  20. Giving the early fossil record of sponges a squeeze.

    Science.gov (United States)

    Antcliffe, Jonathan B; Callow, Richard H T; Brasier, Martin D

    2014-11-01

    Twenty candidate fossils with claim to be the oldest representative of the Phylum Porifera have been re-analysed. Three criteria are used to assess each candidate: (i) the diagnostic criteria needed to categorize sponges in the fossil record; (ii) the presence, or absence, of such diagnostic features in the putative poriferan fossils; and (iii) the age constraints for the candidate fossils. All three criteria are critical to the correct interpretation of any fossil and its placement within an evolutionary context. Our analysis shows that no Precambrian fossil candidate yet satisfies all three of these criteria to be a reliable sponge fossil. The oldest widely accepted candidate, Mongolian silica hexacts from c. 545 million years ago (Ma), are here shown to be cruciform arsenopyrite crystals. The oldest reliable sponge remains are siliceous spicules from the basal Cambrian (Protohertzina anabarica Zone) Soltanieh Formation, Iran, which are described and analysed here in detail for the first time. Extensive archaeocyathan sponge reefs emerge and radiate as late as the middle of the Fortunian Stage of the Cambrian and demonstrate a gradual assembly of their skeletal structure through this time coincident with the evolution of other metazoan groups. Since the Porifera are basal in the Metazoa, their presence within the late Proterozoic has been widely anticipated. Molecular clock calibration for the earliest Porifera and Metazoa should now be based on the Iranian hexactinellid material dated to c. 535 Ma. The earliest convincing fossil sponge remains appeared at around the time of the Precambrian-Cambrian boundary, associated with the great radiation events of that interval. © 2014 The Authors. Biological Reviews © 2014 Cambridge Philosophical Society.

  1. Neoproterozoic-Early Paleozoic Peri-Pacific Accretionary Evolution of the Mongolian Collage System: Insights From Geochemical and U-Pb Zircon Data From the Ordovician Sedimentary Wedge in the Mongolian Altai

    Science.gov (United States)

    Jiang, Y. D.; Schulmann, K.; Kröner, A.; Sun, M.; Lexa, O.; Janoušek, V.; Buriánek, D.; Yuan, C.; Hanžl, P.

    2017-11-01

    Neoproterozoic to early Paleozoic accretionary processes of the Central Asian Orogenic Belt have been evaluated so far mainly using the geology of ophiolites and/or magmatic arcs. Thus, the knowledge of the nature and evolution of associated sedimentary prisms remains fragmentary. We carried out an integrated geological, geochemical, and zircon U-Pb geochronological study on a giant Ordovician metasedimentary succession of the Mongolian Altai Mountains. This succession is characterized by dominant terrigenous components mixed with volcanogenic material. It is chemically immature, compositionally analogous to graywacke, and marked by significant input of felsic to intermediate arc components, pointing to an active continental margin depositional setting. Detrital zircon U-Pb ages suggest a source dominated by products of early Paleozoic magmatism prevailing during the Cambrian-Ordovician and culminating at circa 500 Ma. We propose that the Ordovician succession forms an "Altai sedimentary wedge," the evolution of which can be linked to the geodynamics of the margins of the Mongolian Precambrian Zavhan-Baydrag blocks. This involved subduction reversal from southward subduction of a passive continental margin (Early Cambrian) to the development of the "Ikh-Mongol Magmatic Arc System" and the giant Altai sedimentary wedge above a north dipping subduction zone (Late Cambrian-Ordovician). Such a dynamic process resembles the tectonic evolution of the peri-Pacific accretionary Terra Australis Orogen. A new model reconciling the Baikalian metamorphic belt along the southern Siberian Craton with peri-Pacific Altai accretionary systems fringing the Mongolian microcontinents is proposed to explain the Cambro-Ordovician geodynamic evolution of the Mongolian collage system.

  2. Uranium deposits in the Beaverlodge area, northern Saskatchewan: their relationship to the Martin Group (Proterozoic) and the underlying basement

    International Nuclear Information System (INIS)

    Mazimhaka, P.K.; Hendry, H.E.

    1989-01-01

    The rocks of the Martin Group crop out in an area 60 km by 50 km north of Lake Athabasca near Uranium City, northern Saskatchewan. This area has numerous uranium showings within a few kilometres of the unconformity below the Martin Group. Mineralization occurs in fault zones, in basement rocks and in sedimentary and volcanic rocks of the Martin Group. Martin Group sediments accumulated in alluvial fans, braided streams, and ephemeral lakes. The thickest sequence (8 km to 10 km) is preserved in the Beaverlodge area, near Uranium City. The style of sedimentation changed through time as the basin evolved from deposition of conglomeratic detritus along fault scarps to the accumulation of silt in ephemeral lakes. The uneven nature of the sub-Martin unconformity surface, the lithotype of the lowermost conglomerates and breccias (Beaverlodge Formation), and the shape of the basin fill indicate deposition in fault-controlled basins. The earliest economic uranium mineralization in the rocks of the Martin Group was epigenetic. The mineralization was coeval with that in basement rocks. Economic mineralization in basement rocks and in the lowermost formation of the Martin Group is close to the unconformity. Epigenetic uranium mineralization thus appears to have resulted from processes that were related, in time and space, to either the formation of the unconformity or the deposition of the Martin Group or both. (author). 29 refs, 5 figs

  3. Nuclear reactor control column

    International Nuclear Information System (INIS)

    Bachovchin, D.M.

    1982-01-01

    The nuclear reactor control column comprises a column disposed within the nuclear reactor core having a variable cross-section hollow channel and containing balls whose vertical location is determined by the flow of the reactor coolant through the column. The control column is divided into three basic sections wherein each of the sections has a different cross-sectional area. The uppermost section of the control column has the greatest crosssectional area, the intermediate section of the control column has the smallest cross-sectional area, and the lowermost section of the control column has the intermediate cross-sectional area. In this manner, the area of the uppermost section can be established such that when the reactor coolant is flowing under normal conditions therethrough, the absorber balls will be lifted and suspended in a fluidized bed manner in the upper section. However, when the reactor coolant flow falls below a predetermined value, the absorber balls will fall through the intermediate section and into the lowermost section, thereby reducing the reactivity of the reactor core and shutting down the reactor

  4. Sensitivity of Gravity Wave Fluxes to Interannual Variations in Tropical Convection and Zonal Wind.

    Science.gov (United States)

    Alexander, M Joan; Ortland, David A; Grimsdell, Alison W; Kim, Ji-Eun

    2017-09-01

    Using an idealized model framework with high-frequency tropical latent heating variability derived from global satellite observations of precipitation and clouds, the authors examine the properties and effects of gravity waves in the lower stratosphere, contrasting conditions in an El Niño year and a La Niña year. The model generates a broad spectrum of tropical waves including planetary-scale waves through mesoscale gravity waves. The authors compare modeled monthly mean regional variations in wind and temperature with reanalyses and validate the modeled gravity waves using satellite- and balloon-based estimates of gravity wave momentum flux. Some interesting changes in the gravity spectrum of momentum flux are found in the model, which are discussed in terms of the interannual variations in clouds, precipitation, and large-scale winds. While regional variations in clouds, precipitation, and winds are dramatic, the mean gravity wave zonal momentum fluxes entering the stratosphere differ by only 11%. The modeled intermittency in gravity wave momentum flux is shown to be very realistic compared to observations, and the largest-amplitude waves are related to significant gravity wave drag forces in the lowermost stratosphere. This strong intermittency is generally absent or weak in climate models because of deficiencies in parameterizations of gravity wave intermittency. These results suggest a way forward to improve model representations of the lowermost stratospheric quasi-biennial oscillation winds and teleconnections.

  5. Use of {sup 10}Be exposure ages and Schmidt hammer data for correlation of moraines in the Krkonose Mountains, Poland/Czech Republic

    Energy Technology Data Exchange (ETDEWEB)

    Engel, Zbynek; Krizek, Marek [Charles Univ., Prague (Czech Republic). Dept. of Physical Geography and Geoecology; Traczyk, Andrzej [Wroclaw Univ. (Poland). Dept. of Geomorphology; Braucher, Regis [CEREGE, Aix-en-Provence (France); Woronko, Barbara [Warsaw Univ. (Poland). Dept. of Geography and Regional Development

    2011-06-15

    Exposure ages and relative-age data are presented from eight sites in the Lomnica and Lomniczka valleys to provide essential information for reconstructing local glaciation chronology. A combination of {sup 10}Be exposure ages and Schmidt hammer data obtained for moraines indicate relatively short period of glacier accumulation lasting from 17.0{+-}0.4 ka to 13.6{+-}0.9 ka. Exposure age of 8.4{+-}0.3 ka measured on the lowermost section of the Lomnica cirque headwall further confirms the view of glacier preservation in favourable sites until the beginning of the Holocene. A comparison of the obtained chronological data with timing of mountain glaciation in the nearby Upa Valley is used to propose the first correlative model of Late Quaternary glaciation in the eastern part of the Krkonose Mountains. The correlation implies that the lowermost preserved moraines originated during the local maximum of the last glaciation whereas recessional moraines were deposited until the Lateglacial period. A subsequent melting of glaciers terminated at the beginning of the Holocene. The implications of the model are discussed and further investigations are suggested to extend its validity to the whole mountain area. (orig.)

  6. Summary of northern Atlantic coastal plain hydrology and its relation to disposal of high-level radioactive waste in buried crystalline rock; a preliminary appraisal

    Science.gov (United States)

    Lloyd, O.B.; Larson, J.D.; Davis, R.W.

    1985-01-01

    Interpretation of available hydrologic data suggests that some areas beneath the Coastal Plain in the States of Delaware, Maryland, New Jersey, North Carolina, and Virginia might have some potential for the disposal of nuclear waste in crystalline rock that is buried beneath the Coastal Plain sediments. The areas of major interest occur where the top of the basement rock lies between 1,000 and 4,000 feet below sea level, the aquifer(s) immediately above the basement rock are saturated with saline water, confining material overlies the saline water bearing aquifer(s), and groundwater flow in the saline water aquifer(s) can be established. Preliminary data on (1) the distribution and thickness of the lowermost aquifers and confining beds, (2) the distribution of hydraulic conductivity in the lowermost aquifers, (3) estimated hydraulic heads and inferred direction of lateral groundwater flow for 1980, and (4) the distribution of saline water and brine, indicate eastern parts of the study area relatively best meet most of the criteria proposed for sediments that would overlie any potential buried crystalline-rock disposal site.

  7. Diatom assemblages as guides to flow conditions during the 2004 Indian Ocean tsunami at Phra Thong Island, Thailand

    Science.gov (United States)

    Sawai, Y.; Jankaew, K.; Martin, M. E.; Choowong, M.; Charoentitirat, T.; Prendergast, A.

    2008-12-01

    Diatom assemblages in the 2004 tsunami deposits of Phra Thong Island, Thailand represent flow conditions during the tsunami. The tsunami deposit consists of single or multiple graded beds. Diatom assemblages in the lowermost part of the deposit predominantly comprise beach and subtidal species. In the middle part of the deposit, the assemblages are dominated by marine plankton with increasing finer fractions. A mixed assemblage of freshwater, brackish, and marine species occupies the uppermost part of the deposit. Changes in flow conditions during the tsunami can explain these diatom assemblage variations. During fast current velocities, medium sand is deposited; only beach and subtidal diatoms that live attached to the sand can be incorporated into the tsunami deposit under these flow conditions. It is difficult for diatoms in suspension to settle out under fast current velocities. With decreasing current velocities, marine plankton can settle out of the water column .Finally, during the suspension stage (calm currents) between tsunami waves, the entrained freshwater, brackish, and marine species settle out with mud and plant trash. Fewer broken valves in the lowermost part of the deposit is probably a results of rapid entrainment, whilst selective breakage of marine plankton (Thalassionema nitzschioides, and Thalassiosira and Coscinodiscus spp.) in the middle part of the deposit probably results from abrasion by turbulent current before their deposition.

  8. Measurement of magnetic susceptibility on tailings cores report on cores obtained from the Ontario Research Foundation lysimeter experiment

    International Nuclear Information System (INIS)

    1984-10-01

    Bulk susceptibility and induced magnetic remanence results are reported for 40 cores obtained from the uranium tailings lysimeter experiment at the Ontario Research Foundation. Both methods indicate a broad threefold subdivision of the tailings pile. An upper zone is characterized by an enhanced susceptibility level, which is related to enhanced concentration of both magnetite and hematite. Depletion zones, where present, are of limited areal extent and strongly developed. An intermediate zone is characterized by a mixture of large areas of reduced susceptibility that separate smaller regions of slightly enhanced susceptibility. The zones of susceptibility depletion appear to define a dendritic drainage pattern. Locally in this zone magnetite is enhanced and hematite depleted. In the lowermost zone susceptibility levels are reduced over most of the tailings bed. Only in the upper most right hand corner is there any vestige of a positive susceptibility concentration. Both magnetite and hematite are strongly depleted in this lower zone. Visually it is apparent that this lowermost depleted zone correlates to the zones of strongest 'yellowcake' development

  9. Morphodynamics of the Final 500 Kilometers of the Mississippi River

    Science.gov (United States)

    Wang, B.; Xu, Y. J.

    2017-12-01

    Channel dynamics of alluvial rivers in their lower reaches can strongly influence deltaic development. In this study, we analyzed over 6,000 single-beam cross-sectional measurements surveyed in 1992, 2004, and 2013 in the last 500-km reach of the highly engineered Mississippi River, a.k.a. the lowermost Mississippi River (LmMR), starting from the river's Gulf outlet to its avulsion into the Atchafalaya River. We applied Inverse Distance Weighted interpolation to downscale the survey records into 10 x 10 m Digital Elevation Models. We assessed riverbed deformation from bank to bank and quantified georeferenced changes in riverbed sediment volume and mass. We intended to test the hypothesis that the lower reach of a large alluvial river can function as a conduit for sediment transport under the current engineering focus of navigation safety and flood control. Our analysis shows that in the past two decades, nearly 70% of the riverine sand is trapped within the LmMR, and that continuous riverbed aggradation occurred below the Mississippi-Atchafalaya diversion, presenting favorable backwater conditions for avulsion. Backwater effects have mainly controlled riverbed deformation in the LmMR, while flow reduction may have also contributed to channel aggradation in the uppermost and lowermost reaches. The study reveals the considerable complexity of geomorphic responses of a large alluvial river to human interventions, strongly suggesting that future river engineering and management need also to focus on strategies that will improve sediment transport to the downstream river delta.

  10. An aircraft-borne chemical ionization – ion trap mass spectrometer (CI-ITMS for fast PAN and PPN measurements

    Directory of Open Access Journals (Sweden)

    H. Schlager

    2011-02-01

    Full Text Available An airborne chemical ionization ion trap mass spectrometer instrument (CI-ITMS has been developed for tropospheric and stratospheric fast in-situ measurements of PAN (peroxyacetyl nitrate and PPN (peroxypropionyl nitrate. The first scientific deployment of the FASTPEX instrument (FASTPEX = Fast Measurement of Peroxyacyl nitrates took place in the Arctic during 18 missions aboard the DLR research aircraft Falcon, within the framework of the POLARCAT-GRACE campaign in the summer of 2008. The FASTPEX instrument is described and characteristic properties of the employed ion trap mass spectrometer are discussed. Atmospheric data obtained at altitudes of up to ~12 km are presented, from the boundary layer to the lowermost stratosphere. Data were sampled with a time resolution of 2 s and a 2σ detection limit of 25 pmol mol−1. An isotopically labelled standard was used for a permanent on-line calibration. For this reason the accuracy of the PAN measurements is better than ±10% for mixing ratios greater than 200 pmol mol−1. PAN mixing ratios in the summer Arctic troposphere were in the order of a few hundred pmol mol−1 and generally correlated well with CO. In the Arctic boundary layer and lowermost stratosphere smaller PAN mixing ratios were observed due to a combination of missing local sources of PAN precursor gases and efficient removal processes (thermolysis/photolysis. PPN, the second most abundant PAN homologue, was measured simultaneously. Observed PPN/PAN ratios range between ~0.03 and 0.3.

  11. The sedimentary sequence from the Lake Ķūži outcrop, central Latvia: implications for late glacial stratigraphy

    Directory of Open Access Journals (Sweden)

    Tiiu Koff

    2011-06-01

    Full Text Available Sediment samples from an outcrop in the near-shore area of Lake Ķūži (Vidzeme Heights, Central Latvia were investigated using palaeobotanical (pollen and macrofossil analysis and lithological (grain-size analysis methods and accelerator mass spectrometry 14C dating. A dark, organic-rich sediment layer was found below 1.7 m of sandy layers approximately 30 cm above the present lake level. Radiocarbon dating of a wood sample from the lowermost layer (11 050 ± 60 14C BP, 13 107–12 721 cal BP shows that the layer is of late glacial age. The composition of the pollen spectra is characterized by Betula nana, Cyperaceae pollen and spores of Equisetum, confirming that the lowermost sediments were formed during the late glacial. Fossils of obligate aquatic organisms in the upper layer, which include oospores of Characeae and seeds of Potamogeton, indicate an open water environment. Pollen of Myriophyllum and Potamogeton and non-pollen palynomorphs, such as algal Botryococcus and Pediastrum cf. boryanum, confirm this conclusion. The pollen assemblage from the greyish loam layer following this lacustrine phase shows a pattern characteristic of the Younger Dryas vegetation before the start of the real expansion of birch forests at the beginning of the Holocene.

  12. Stratigraphic architecture of back-filled incised-valley systems: Pennsylvanian-Permian lower Cutler beds, Utah, USA

    Science.gov (United States)

    Wakefield, Oliver J. W.; Mountney, Nigel P.

    2013-12-01

    The Pennsylvanian to Permian lower Cutler beds collectively form the lowermost stratigraphic unit of the Cutler Group in the Paradox Basin, southeast Utah. The lower Cutler beds represent a tripartite succession comprising lithofacies assemblages of aeolian, fluvial and shallow-marine origin, in near equal proportion. The succession results from a series of transgressive-regressive cycles, driven by repeated episodes of climatic variation and linked changes in relative sea-level. Relative sea-level changes created a number of incised-valleys, each forming through fluvial incision during lowered base-level. Aeolian dominance during periods of relative sea-level lowstand aids incised-valley identification as the erosive bounding surface juxtaposes incised-valley infill against stacked aeolian faces. Relative sea-level rises resulted in back-flooding of the incised-valleys and their infill via shallow-marine and estuarine processes. Back-flooded valleys generated marine embayments within which additional local accommodation was exploited. Back-filling is characterised by a distinctive suite of lithofacies arranged into a lowermost, basal fill of fluvial channel and floodplain architectural elements, passing upwards into barform elements with indicators of tidal influence, including inclined heterolithic strata and reactivation surfaces. The incised-valley fills are capped by laterally extensive and continuous marine limestone elements that record the drowning of the valleys and, ultimately, flooding and accumulation across surrounding interfluves (transgressive surface). Limestone elements are characterised by an open-marine fauna and represent the preserved expression of maximum transgression.

  13. Carbohydrate Status of Tulip Bulbs during Cold-Induced Flower Stalk Elongation and Flowering.

    Science.gov (United States)

    Lambrechts, H.; Rook, F.; Kolloffel, C.

    1994-01-01

    The effect of a cold treatment on the carbohydrate status of the scales and flower stalk of Tulipa gesneriana L. cv Apeldoorn bulbs during growth after planting was studied and compared with bulbs not given cold treatment. Bulbs were stored dry for 12 weeks at 5[deg]C (precooled) or 17[deg]C (noncooled). Only the 5[deg]C treatment led to rapid flower stalk elongation and flowering following planting at higher temperatures. Precooling enhanced mobilization of starch, fructans, and sucrose in the scales. The cold-stimulated starch breakdown was initially accompanied by increased [alpha]-amylase activity per scale. In noncooled bulbs, [alpha]-amylase activity slightly decreased or remained more or less constant. Cold-induced flower stalk elongation was partially accompanied by a decrease in the sucrose content and an increase in the glucose content and invertase activity per g dry weight. The starch content in internodes initially decreased and subsequently increased; [alpha]-amylase activity per g dry weight of the lowermost internode showed a peak pattern during starch breakdown and increased thereafter. The internodes of noncooled bulbs, on the contrary, accumulated sucrose. Their glucose content and invertase activity per g dry weight remained low. Starch breakdown was not found and [alpha]-amylase activity per g dry weight of the lowermost internode remained at a low level. Precooling of tulip bulbs thus favors reserve mobilization in the scales and flower stalk and glucose accumulation in the elongating internodes. PMID:12232100

  14. Geology and Geochemistry of the Poco de Fora region-Curaca river valley-Bahia-Brazil

    International Nuclear Information System (INIS)

    Figueiredo, M.C.H. de.

    1976-01-01

    In the Poco de Fora region level rocks of light metamorphism, from Caraiba group, corresponding to: - a meta-sedimentar sequence from Lower Pre-cambrian (Archean) - maphic-ultramaphic bodies with Fe and Cu sulphides of volcanogenic origin, and - sienitic ortho-gneiss. Geological, petrographic, geochemistry and geochronological studies were done. The sienitic-intrusion, from the upper crust, occur during the Archean-beginning of the Proterozoic. All the region was re-mobilized, and the sienitic was metamorphosed during Transamazonic Orogeny (2.200 to 1.800 m.y.). (C.D.G.) [pt

  15. Oxygen isotope composition as late glacial palaeoclimate indicators of groundwater recharge in the Baltic Basin

    International Nuclear Information System (INIS)

    Mokrik, R.; Mazeika, J.

    2002-01-01

    Several hypotheses were established to explain low δ 18 O values of groundwater which have been found in the Estonian Homocline. Traces of depleted groundwater were found also in other parts of the Baltic Basin near the shoreline. From data collected in this and previous studies, the δ 18 O values of groundwater in most aquifers are known to range from -7.7 to -13.9 per mille. However, the groundwater in Estonia in the Cambrian-Vendian aquifer system has significantly lower δ 18 O values, which vary mainly from -18 to -22.5 per mille. The overlying Ordovician-Cambrian aquifer is also depleted in 18 O, but, as a rule, the degree of depletion is several per mille less than in case of the Cambrian- Vendian aquifer. The thickness of the depleted water in Estonia reaches 450 m. At similar depths beneath Gotland Island (Sweden Homocline), groundwater has significantly higher δ 18 O values (from -5.7 to -6.1 per mille). A hydrogeologic model, depicting conditions during the pre Late Glacial, and accounting for hydraulic connections between the lake and river systems through taliks in permafrost, was developed to explain the observed groundwater isotope data. According to the adopted model, penetration of isotopically depleted surface waters could have reached depths of up to 500 m, with subsequent mixing between subglacial meltwater and old groundwater of Huneborg-Denekamp time. Traces of this penetration were discovered only near the shoreline, where δ 18 O values vary from -12 to -13.9 per mille and 14 C is below 4%. In the territory of the Estonian Homocline, the hydraulically close connection via the Cambrian-Vendian aquifer between talik systems of the Gulf of Riga and the Gulf of Finland existed through permafrost before the Late Glacial. This was due to subglacial recharge during the recessional Pandivere (12 ka BP) and Palivere (11.2 ka BP) phases, which is also associated with recharge of isotopically depleted groundwater. (author)

  16. Time constraints on the tectonic evolution of the eastern Sierras Pampeanas (Central Argentina)

    DEFF Research Database (Denmark)

    Siegesmund, Siegfried; Steenken, A; Martino, R D

    2010-01-01

    The application of the SHRIMP U/Pb dating technique to zircon and monazite of different rock types of the Sierras de Córdoba provides an important insight into the metamorphic history of the basement domains. Additional constraints on the Pampean metamorphic episode were gained by Pb/Pb stepwise...... leaching (PbSL) experiments on two titanite and garnet separates. Results indicate that the metamorphic history recorded by Crd-free gneisses (M2) started in the latest Neoproterozoic/earliest Cambrian (553 and 543 Ma) followed by the M4 metamorphism at ~530 Ma that is documented in the diatexites. Zircon...

  17. Early Paleozoic U-Pb age of zircons from meta-granophyres f the Grand-Saint-Bernard nappe (zona interna, Aosta Valley, Italy); Age paleozoique inferieur (U-Pb sur zircon) de metagranophyres de la nappe du Grand-Saint-Bernard (zona interna, Vallee d'Aoste, Italie)

    Energy Technology Data Exchange (ETDEWEB)

    Bertrand, J.M. [Laboratoire de Geodynamique des Chaines Alpines, LGCA, Campus Scientifique, 73 - Le Bourget-du-Lac (France)

    2000-04-01

    The U-Pb age of a meta-granophyre from the Val de Rhemes (Brianconnais basement of the Aosta valley) of 511{+-}9 Ma suggests that the micaschists which dominate the pre-alpine basement of the Grand-Saint-Bernard Nappe are, in part, of Early Paleozoic age. The Brianconnais domain is characterized by a Cambrian to Ordovician alkalineto sub-alkaline (monzonitic) magmatism, similar in age to orthogneisses known in other parts of the Variscan belt and generally interpreted as related to an extensional event. (authors)

  18. Data-base system for northern Midwest regional aquifer-system analysis

    Science.gov (United States)

    Kontis, A.L.; Mandle, Richard J.

    1980-01-01

    The U.S. Geological Survey is conducting a study of the Cambrian and Ordovician aquifer system of the northern Midwest as part of a national series of Regional Aquifer-Systems Analysis (RASA). An integral part of this study will be a simulation of the ground-water flow regime using the Geological Survey's three-dimensional finite-difference model. The first step in the modeling effort is the design and development of a systematic set of processes to facilitate the collection, evaluation, manipulation, and use of large quantities of information. A computerized data-base system to accomplish these goals has been completed for the northern Midwest RASA.

  19. Fission-track dating of apatite from deep borehole ATK-1 at Atikokan, Ontario

    International Nuclear Information System (INIS)

    Naeser, C.W.; Crowley, K.D.

    1990-01-01

    Fission-track age and lengths have been determined on apatite separated from core recovered from the ATK-1 deep borehole at Atikokan, Ontario. The apatite ages decrease down the borehole, from 515 ± 72 Ma at the top to 376 ± 46 Ma at a depth of 993 m. The mean confined track length for fossil fission tracks in the apatite is 12.4 μm. Within the limits of the measurement the track lengths are the same for all the samples. The results of this study indicate that the rocks found currently at the surface have never been heated above ∼100C since Upper Cambrian time

  20. A new perspective on the significance of the Ranotsara shear zone in Madagascar

    DEFF Research Database (Denmark)

    Schreurs, Guido; Giese, Jörg; Berger, Alfons

    2010-01-01

    only a marked deflection along its central segment. The ductile deflection zone is interpreted as a result of E-W indentation of the Antananarivo Block into the less rigid, predominantly metasedimentary rocks of the Southwestern Madagascar Block during a late phase of the Neoproterozoic/Cambrian East...... the central segment of the Ranotsara Zone, confirmed by apatite-fission track results, may have led to the formation of a shallow Neogene basin underlying the Ranotsara plain. The present-day drainage pattern suggests on-going normal fault activity along the central segment. The Ranotsara Zone...

  1. GEOCHEMICAL CHARACTERISTICS OF TIANMENSHAN COMPOSITE PLUTON, SOUTH CHINA

    Directory of Open Access Journals (Sweden)

    Yanjiao Chen

    2017-01-01

    Full Text Available The southern Jiangxi province is located at east Nanling range, which is an important W-Sn metallogenic province of China. The Early Yanshanian Tianmenshan is composed of the main-phase porphyritic biotite granite and the highly differentiated fine-gained biotite granite, intruding in the Lower Cambrian Niujiaohe Formation. The main-phase granite and the late-stage highly differentiated granite emplaced at 152–158 Ma and 152–151 Ma, respectively. The later was in the center of the pluton as a ovalize shape, with a transitional contact with the main-phase granite.

  2. Age relationships from U-Th-Pb isotope studies of uranium mineralization in Wernecke breccias, Yukon Territory

    International Nuclear Information System (INIS)

    Archer, A.

    1986-01-01

    Pb-U ± Th isotope analyses for 17 specimens of uraniferous breccia from the northeastern Wernecke Mountains reveal several apparent ages for mineralization. The oldest date, 1194 Ma, reflects either initial emplacement of the breccias or their modification by effects of the Rackla of Rapitan (Windermere) thick clastic wedges and iron formation. The 510 Ma date reflects mid-Cambrian mineralization roughly coincident with regional uplift (and attendant karstification) and development of thick clastic wedges. This was also an important period for Pb-Zn mineralization. Younger dates resulted from continuing remobilization, and all isotopic ages for mineralized breccia reflect movements associated with the Richardson Fault array

  3. International Uranium Resources Evaluation Project (IUREP) national favourability studies: People's Republic of Mongolia

    International Nuclear Information System (INIS)

    1977-12-01

    Mongolia, a country of 1,525,000 square kilometers, and a population of almost the same number of people is land locked between China and USSR. Historically it's closest ties have been with China, but it is now more closely associated with USSR. Geologically it's complex - most exposed formations are younger than PreCambrian although old exist. Potential for uranium is considered fairly good because the fairly complex geology appears to be favourable both for continental sandstone type deposits and calcretes (less than 50%) and vein type, and other deposits (more than 50$). Considerable effort should be made to obtain additional information related to Mongolian geology. (author)

  4. Aerial gamma ray and magnetic survey, Jefferson City Quadrangle, Missouri. Final report

    International Nuclear Information System (INIS)

    1980-11-01

    The Jefferson City quadrangle covers approximately 7500 square miles at the Northwestern end of the Ozark uplift. Lithified material exposed, ranges in age from Cambrian through Pennsylvanian, but Pennsylvanian sediments dominate the surface as mapped. Some alluvium is mapped in river flood plain areas. A search of available literature revealed no known uranium deposits. A total of 95 uranium anomalies were detected and are discussed briefly in this report. All anomalies are related to cultural features, but those associated with coal mine tailings appear to have some significance. Magnetic data appear to relate to complexities in the underlying Precambrian rocks

  5. Revisión del enrollamiento en los trilobites del Cámbrico español y su implicación en la evolución de los trilobites

    Directory of Open Access Journals (Sweden)

    Esteve, Jorge

    2013-12-01

    Full Text Available The middle Cambrian trilobites found in the locality of Purujosa as well as other localities from the Iberian Chains such as Murero and Mesones (Zaragoza show a large number of new enrolment devices as well as high variability of enrolment types ever describe in Cambrian times, they show that enrolment was a very spread behavior in Cambrian times. In this paper I carried out a revision of the coaptative structures or interlocking devices, which are in the cephalon and in the pigidia, as well as a revision of the articulating devices through the thorax needed for enrolment. The different enrolment types are described and discussed with special emphasis in Cambrian trilobites. For first time enrolled specimens of Agraulos longicephalus and Ctenocephalus antiquus are figured. I describe the different enrolled trilobites found in the locality of Purujosa such as Solenopleuropsis, Pardailhania, Schopfaspis?, Agraulos, Ctenocephalus and Eccaparadoxides. Finally I discuss the importance of such behavior for trilobite evolution.Los trilobites del Cámbrico medio encontrados en Purujosa y otras localidades de las Cadenas Ibéricas como Murero y Mesones (Zaragoza poseen un gran número de nuevas estructuras de enrollamiento, así como tipos de enrollamiento que previamente no se habían descrito en el Cámbrico, mostrando que el enrollamiento era habitual también en este periodo. En este trabajo se han revisado las estructuras coaptativas o de cierre situadas tanto en el cefalón como en el pigidio de los trilobites, así como las distintas articulaciones presentes en el tórax necesarias para el enrollamiento. También se describen y discuten los distintos tipos de enrollamiento especialmente en los trilobites del Cámbrico medio español. Se muestran por primera vez ejemplares de Agraulos longicephalus y Ctenocephalus antiquus en posición enrollada, Por último se discute la influencia de este comportamiento en la evolución de los trilobites.

  6. Les minéralisations Cu_(Ni_Bi_U_Au_Ag) d'Ifri (district du Haut Seksaoua, Maroc) : apport de l'étude texturale au débat syngenèse versus épigenèseThe Cu_(Ni_Bi_U_Au_Ag) mineralization of Ifri ('Haut Seksaoua' district, Morocco): contribution of a textural study to the discussion syngenetic versus epigenetic

    Science.gov (United States)

    Barbanson, Luc; Chauvet, Alain; Gaouzi, Aziz; Badra, Lakhifi; Mechiche, Mohamed; Touray, Jean Claude; Oukarou, Saı̈d

    2003-11-01

    The Cu ore of Ifri is a chalcopyrite stockwork hosted by Cambrian formations and was until now interpreted as a syngenetic massive sulphide deposit. Textural studies highlight two generations of pyrite early (Py I) and late (Py II) with respect to the regional deformation. The chalcopyrite stockwork overprinted Py II, outlining the epigenetic nature of the Cu mineralization. Regarding the origin of Cu-depositing fluids, the presence in the stockwork paragenesis of an U, W, Sn association and preliminary Pb/Pb dating of a brannerite belonging to this association suggest a contribution of the Tichka granite. To cite this article: L. Barbanson et al., C. R. Geoscience 335 (2003).

  7. Branched alkanes from ancient and modern sediments: isomer discrimination by GC/MS with multiple reaction monitoring

    Energy Technology Data Exchange (ETDEWEB)

    Summons, R.E.

    1987-01-01

    Linked scanning of a tandem sector mass spectrometer has been used to identify abundant, first field free region (FFR1) unimolecular fragmentations in branched and isoprenoid hydrocarbons. The most intense, structure-specific reactions were selected to establish multiple reaction monitoring (MRM) parameters for GC/MS analysis. This methodology has been used to study the identify of co-eluting and closely eluting hydrocarbon biomarkers from modern and ancient sediments and from extant microorganisms. Some sediments of Cambrian and Proterozoic age have been found to contain suites of monomethylalkanes with all possible isomers present and with little apparent preference for the site of branching.

  8. Hydrogeology of the carbonate rocks of the Lebanon Valley, Pennsylvania

    Science.gov (United States)

    Meisler, Harold

    1963-01-01

    The Lebanon Valley, which is part of the Great Valley in southeastern Pennsylvania, is underlain by carbonate rocks in the southern part and by shale in the northern part. The carbonate rocks consist of alternating beds of limestone and dolomite of Cambrian and Ordovician age. Although the beds generally dip to the south, progressively younger beds crop out to the north, because the rocks are overturned. The stratigraphic units, from oldest to youngest, are: the Buffalo Springs Formation, Snitz Creek, Schaefferstown, Millbach, and Richland Formations of the Conococheague Group; the Stonehenge, Rickenbach, Epler, and Ontelaunee Formations of the Beekmantown Group; and the Annville, Myerstown, and Hershey Limestones.

  9. Sedimentary tectonic evolution and reservoir-forming conditions of the Dazhou–Kaijiang paleo-uplift, Sichuan Basin

    Directory of Open Access Journals (Sweden)

    Yueming Yang

    2016-12-01

    Full Text Available Great breakthrough recently achieved in the Sinian–Lower Paleozoic gas exploration in the Leshan–Longnüsi paleo-uplift, Sichuan Basin, has also made a common view reached, i.e., large-scale paleo-uplifts will be the most potential gas exploration target in the deep strata of this basin. Apart from the above-mentioned one, the other huge paleo-uplifts are all considered to be the ones formed in the post-Caledonian period, the impact of which, however, has rarely ever been discussed on the Sinian–Lower Paleozoic oil and gas reservoir formation. In view of this, based on outcrops, drilling and geophysical data, we analyzed the Sinian–Lower Paleozoic tectonic setting and sedimentary background in the East Sichuan Basin, studied the distribution rules of reservoirs and source rocks under the control of paleo-uplifts, and finally discussed, on the basis of structural evolution analysis, the conditions for the formation of Sinian–Lower Paleozoic gas reservoirs in this study area. The following findings were achieved. (1 The Dazhou–Kaijiang inherited uplift in NE Sichuan Basin which was developed before the Middle Cambrian controlled a large area of Sinian and Cambrian beach-facies development. (2 Beach-facies reservoirs were developed in the upper part of the paleo-uplift, while in the peripheral depression belts thick source rocks were developed like the Upper Sinian Doushantuo Fm and Lower Cambrian Qiongzhusi Fm, so there is a good source–reservoir assemblage. (3 Since the Permian epoch, the Dazhou–Kaijiang paleo-uplift had gradually become elevated from the slope zone, where the Permian oil generation peak occurred in the slope or lower and gentle uplift belts, while the Triassic gas generation peak occurred in the higher uplift belts, both with a favorable condition for hydrocarbon accumulation. (4 The lower structural layers, including the Lower Cambrian and its underlying strata, in the East Sichuan Basin, are now equipped with a

  10. Uranium prospecting in Cerro Partido Region-Encruzilhada do Sul Basin-RS, Brazil

    International Nuclear Information System (INIS)

    Fraenkel, M.O.

    1974-01-01

    The Cerro Partido residual basin is a shallow (85 meters) and small (25km 2 ) sedimentary basin, a remainder of the erosive cicle, enclosed in the pre-cambrian granitic rocks of the Rio Grande do Sul Shield. Grades of 0.2 + U 3 O 8 were found in its upper-paleozoic sandstones and shales drilles for uranium. The small size and thicknesses of these concentrations prevent their economic mining. However, the different levels of the shield exposed by tectonics, the intrusive granitic, riolitic and syenitic rocks, the anomalous uranium contents in sedimentary and crystalline rocks recommend further investigations on the shield area

  11. Uranium reduction by carbon oxide during ore formation

    International Nuclear Information System (INIS)

    Matyash, I.V.; Gavrusevich, I.B.; Pasal'skaya, L.F.; Shcherba, D.I.

    1981-01-01

    Using the method of gas chromatography the gas content in Pre-Cambrian granitoils of various types and in natrometasomatites associted with them is studied. It is established that granites associated with ore-bearing albitites have sharply elevated amounts of CO as compared with granites, which do not include mineralization. Simultaneously in ore samples the absence or sharply low amounts of CO as compared with ore-free samples is observed, that is reverse dependence of CO and ore components. Carbon oxide is the reducing agent of uranium mineralization and alongside with other reducing agents can be a geochemical barrier in the process of ore formation [ru

  12. Geologic map of the Bateman Spring Quadrangle, Lander County, Nevada

    Science.gov (United States)

    Ramelli, Alan R.; Wrucke, Chester T.; House, P. Kyle

    2017-01-01

    This 1:24,000-scale geologic map of the Bateman Spring 7.5-minute quadrangle in Lander County, Nevada contains descriptions of 24 geologic units and one cross section. Accompanying text includes full unit descriptions and references. This quadrangle includes lower Paleozoic siliciclastic sedimentary rocks of the Roberts Mountain allochthon, Miocene intrusive dikes, alluvial deposits of the northern Shoshone Range piedmont, and riverine deposits of the Reese and Humboldt rivers.Significant findings include: refined age estimates for the Ordovician-Cambrian Valmy Formation and Devonian Slaven Chert, based on new fossil information; and detailed mapping of late Quaternary fault traces along the Shoshone Range fault system.

  13. Digital data in support of studies and assessments of coal and petroleum resources in the Appalachian basin: Chapter I.1 in Coal and petroleum resources in the Appalachian basin: distribution, geologic framework, and geochemical character

    Science.gov (United States)

    Trippi, Michael H.; Kinney, Scott A.; Gunther, Gregory; Ryder, Robert T.; Ruppert, Leslie F.; Ruppert, Leslie F.; Ryder, Robert T.

    2014-01-01

    The Appalachian basin is a mature basin containing abundant oil, gas, and coal resources. Its fossil-fuel-bearing strata range in age from Cambrian to Permian and extend over the States of New York, Pennsylvania, Maryland, Ohio, West Virginia, Virginia, Kentucky, Tennessee, Georgia, and Alabama. The basin has provided abundant fossil fuels to support the Nation’s economic growth for at least 150 years and U.S. Geological Survey (USGS) assessments suggest that substantial untapped resources remain. A merger of new and old geologic data and ideas is required to locate and extract those remaining resources.

  14. Mechanism for Burgess Shale-type preservation

    DEFF Research Database (Denmark)

    Gaines, Robert R.; Hammarlund, Emma U.; Hou, Xianguang

    2012-01-01

    Exceptionally preserved fossil biotas of the Burgess Shale and a handful of other similar Cambrian deposits provide rare but critical insights into the early diversification of animals. The extraordinary preservation of labile tissues in these geographically widespread but temporally restricted......-oxygen bottom water conditions at the sites of deposition resulted in reduced oxidant availability. Subsequently, rapid entombment of fossils in fine-grained sediments and early sealing of sediments by pervasive carbonate cements at bed tops restricted oxidant flux into the sediments. A permeability barrier...

  15. Stromatolitic iron oxides: Evidence that sea-level changes can cause sedimentary iridium anomalies

    Science.gov (United States)

    Wallace, Malcolm W.; Keays, Reid R.; Gostin, Victor A.

    1991-06-01

    In an attempt to understand the origin of an Ir-rich unit near the Late Devonian Frasnian-Famennian (F/F) boundary in the Canning basin of Western Australia, we have examined two lithologically similar Early Cambrian and late Oligocene age horizons from southeastern Australia. Both consist of stromatolitic iron oxide and carbonate petrographically similar to the Ir-rich Frutexites microstromatolites near the F/F boundary. Significant siderophile and chalcophile element anomalies (Ir, Pt, and Ru up to 1.1, 14, and 1.2 ppb, respectively) at both horizons have a geochemistry similar to that of the F/F Frutexites anomaly. As with the F/F bed, the Cambrian and Oligocene stromatolitic beds are closely associated with synsedimentary hardgrounds that contain evidence of subaerial exposure. We suggest that all of these Ir-rich stromatolitic beds developed in response to relative sea-level change and represent periods of condensed marine sedimentation. It is probable that condensation was produced by rapid drowning following subaerial exposure.

  16. Zoophycos macroevolution since 541 Ma

    Science.gov (United States)

    Zhang, Li-Jun; Fan, Ruo-Ying; Gong, Yi-Ming

    2015-10-01

    Zoophycos is one of the most complex and enigmatic trace fossils recorded in marine strata from Cambrian to Quaternary worldwide, which is invaluable for the study of Phanerozoic development of organism-environment interactions. Here we address and demonstrate the macroevolution of Phanerozoic Zoophycos by assembling 448 points in constructing the Phanerozoic Zoophycos database based on 291 papers from 1821 to 2015 and 180 specimens from Cambrian to Palaeogene. The comprehensive dataset reveals, for the first time, five peaks and six depressions in Phanerozoic Zoophycos occurrence frequency. Secondly, the palaeogeographical distribution of Zoophycos is closely associated with the supercontinent Pangaea shifting, independent of the latitude. Our data also attest that the bathymetrical shift of Zoophycos from the littoral-neritic to bathyal environments is synchronized with the tiering shift from shallow to deep. By detailed comparison with body fossils, geochemical and palaeogeographical records, we conclude that the macroevolution of Phanerozoic Zoophycos is multi-affected by the global biodiversity expansion, benthic nutrient enhancement, and the biotic macroevolution of the Zoophycos-producers. The macroevolution of development evidenced by the morphological changes of Zoophycos and other trace fossils, may have great implications on the behavioural and physiological adaptation of ancient animals to the environments.

  17. C, Sr and Sr isotopic composition on probable vendian- tommotian carbonate sequences in Nw Argentina

    International Nuclear Information System (INIS)

    Sial, A. N.; Ferreira, V.P; Toselli, A.J.; Acenolaza, F.G; Pimentel, M.M; Parada, M.A; Alonso, R.N

    2001-01-01

    C-isotope stratigraphy is one of the most powerfool tools in Precambrian chronostratigraphy, especially when sediments lack recognizable animal fossils. The δ 13 C secular variation curves for marine carbonates in the Neoproterozoic-Cambrian interval show strong positive-negative excursions, several of them interpreted as the stratigraphic position of ancient ice ages (Hoffman et al. 1998). The Sr isotope composition of the seawater for this age interval is characterized by a continuous increase of 87 Sr/ 86 Sr that is interrupted, several times, by sharp rises, which represent important changes in the Earth history (Montanez et al. 2000). Only limited data on the behavior of C and Sr isotopes in carbonates are available in South America. We examine here carbonate sequences from the Argentine Precordillera, San Juan province, and from other carbonate sequences in NW Argentina that could be, potentially, proxies for the Precambrian-Cambrian transition. We have studied their δ 13 C and 87 Sr/ 86 Sr chemostratigraphy and compare it to global C and Sr isotope secular variation curves for this time span. This study aims to improve the relatively coarse stratigraphic resolution provided only by the study of the fossil record in some of the carbonate successions under consideration (au)

  18. Use of relational databases to evaluate regional petroleum accumulation, groundwater flow, and CO2 sequestration in Kansas

    Science.gov (United States)

    Carr, T.R.; Merriam, D.F.; Bartley, J.D.

    2005-01-01

    Large-scale relational databases and geographic information system tools are used to integrate temperature, pressure, and water geo-chemistry data from numerous wells to better understand regional-scale geothermal and hydrogeological regimes of the lower Paleozoic aquifer systems in the mid-continent and to evaluate their potential for geologic CO2 sequestration. The lower Paleozoic (Cambrian to Mississippian) aquifer systems in Kansas, Missouri, and Oklahoma comprise one of the largest regional-scale saline aquifer systems in North America. Understanding hydrologic conditions and processes of these regional-scale aquifer systems provides insight to the evolution of the various sedimentary basins, migration of hydrocarbons out of the Anadarko and Arkoma basins, and the distribution of Arbuckle petroleum reservoirs across Kansas and provides a basis to evaluate CO2 sequestration potential. The Cambrian and Ordovician stratigraphic units form a saline aquifer that is in hydrologic continuity with the freshwater recharge from the Ozark plateau and along the Nemaha anticline. The hydrologic continuity with areas of freshwater recharge provides an explanation for the apparent underpressure in the Arbuckle Group. Copyright ?? 2005. The American Association of Petroleum Geologists. All rights reserved.

  19. Penetrative trace fossils from the late Ediacaran of Mongolia: early onset of the agronomic revolution

    Science.gov (United States)

    Oji, Tatsuo; Dornbos, Stephen Q.; Yada, Keigo; Hasegawa, Hitoshi; Gonchigdorj, Sersmaa; Mochizuki, Takafumi; Takayanagi, Hideko; Iryu, Yasufumi

    2018-02-01

    The Cambrian radiation of complex animals includes a dramatic increase in the depth and intensity of bioturbation in seafloor sediment known as the `agronomic revolution'. This bioturbation transition was coupled with a shift in dominant trace fossil style from horizontal surficial traces in the late Precambrian to vertically penetrative trace fossils in the Cambrian. Here we show the existence of the first vertically penetrative trace fossils from the latest Ediacaran: dense occurrences of the U-shaped trace fossil Arenicolites from late Precambrian marine carbonates of Western Mongolia. Their Ediacaran age is established through stable carbon isotope chemostratigraphy and their occurrence stratigraphically below the first appearance of the trace fossil Treptichnus pedum. These Arenicolites are large in diameter, penetrate down to at least 4 cm into the sediment, and were presumably formed by the activity of bilaterian animals. They are preserved commonly as paired circular openings on bedding planes with maximum diameters ranging up to almost 1 cm, and as U- and J-shaped tubes in vertical sections of beds. Discovery of these complex penetrative trace fossils demonstrates that the agronomic revolution started earlier than previously considered.

  20. Detrital zircon ages in Buller and Takaka terranes, New Zealand : constraints on early Zealandia history

    International Nuclear Information System (INIS)

    Adams, C.J.; Mortimer, N.; Campbell, H.J.; Griffin, W.L.

    2015-01-01

    Detrital zircon ages are presented for 34 early Palaeozoic sandstones from Buller and Takaka terranes, New Zealand, and formerly adjacent parts of Australia-Antarctica. The Buller-Takaka datasets always have two major groups: Ordovician-late Neoproterozoic, 444-700 Ma (but mainly 540-700 Ma), termed 'Gondwana Assembly' (GA), and early Neoproterozoic-Mesoproterozoic, 700-1600 Ma (but mainly 900-1200 Ma), termed 'Rodinia Assembly' (RA). In both terranes, significant age components within these groups are strikingly similar and also have RA/GA ratios, 0.6-1.8. The Cambrian volcanic arc of the Takaka Terrane has contributed little to the zircon patterns. Proportions of Late Cambrian-Early Ordovician zircons, characteristic of granitoid sources in the Ross-Delamerian Orogen are low. The zircons are predominantly reworked with contemporary zircons only evident in a few Buller datasets. The zircon patterns suggest that two major sources (late Mesoproterozoic and late Neoproterozoic), enduring over 120 Ma, were widely distributed and it is postulated they form Precambrian basement beneath southern Zealandia. (author).

  1. Zoophycos macroevolution since 541 Ma.

    Science.gov (United States)

    Zhang, Li-Jun; Fan, Ruo-Ying; Gong, Yi-Ming

    2015-10-09

    Zoophycos is one of the most complex and enigmatic trace fossils recorded in marine strata from Cambrian to Quaternary worldwide, which is invaluable for the study of Phanerozoic development of organism-environment interactions. Here we address and demonstrate the macroevolution of Phanerozoic Zoophycos by assembling 448 points in constructing the Phanerozoic Zoophycos database based on 291 papers from 1821 to 2015 and 180 specimens from Cambrian to Palaeogene. The comprehensive dataset reveals, for the first time, five peaks and six depressions in Phanerozoic Zoophycos occurrence frequency. Secondly, the palaeogeographical distribution of Zoophycos is closely associated with the supercontinent Pangaea shifting, independent of the latitude. Our data also attest that the bathymetrical shift of Zoophycos from the littoral-neritic to bathyal environments is synchronized with the tiering shift from shallow to deep. By detailed comparison with body fossils, geochemical and palaeogeographical records, we conclude that the macroevolution of Phanerozoic Zoophycos is multi-affected by the global biodiversity expansion, benthic nutrient enhancement, and the biotic macroevolution of the Zoophycos-producers. The macroevolution of development evidenced by the morphological changes of Zoophycos and other trace fossils, may have great implications on the behavioural and physiological adaptation of ancient animals to the environments.

  2. Cambro-ordovician sea-level fluctuations and sequence boundaries: The missing record and the evolution of new taxa

    Science.gov (United States)

    Lehnert, O.; Miller, J.F.; Leslie, Stephen A.; Repetski, J.E.; Ethington, Raymond L.

    2005-01-01

    The evolution of early Palaeozoic conodont faunas shows a clear connection to sea-level changes. One way that this connection manifests itself is that thick successions of carbonates are missing beneath major sequence boundaries due to karstification and erosion. From this observation arises the question of how many taxa have been lost from different conodont lineages in these incomplete successions. Although many taxa suffered extinction due to the environmental stresses associated with falling sea-levels, some must have survived in these extreme conditions. The number of taxa missing in the early Palaeozoic tropics always will be unclear, but it will be even more difficult to evaluate the missing record in detrital successions of higher latitudes. A common pattern in the evolution of Cambrian-Ordovician conodont lineages is appearances of new species at sea-level rises and disappearances at sea-level drops. This simple picture can be complicated by intervals that consistently have no representatives of a particular lineage, even after extensive sampling of the most complete sections. Presumably the lineages survived in undocumented refugia. In this paper, we give examples of evolution in Cambrian-Ordovician shallowmarine conodont faunas and highlight problems of undiscovered or truly missing segments of lineages. ?? The Palaeontological Association.

  3. Mitogenomics and phylogenomics reveal priapulid worms as extant models of the ancestral Ecdysozoan.

    Science.gov (United States)

    Webster, Bonnie L; Copley, Richard R; Jenner, Ronald A; Mackenzie-Dodds, Jacqueline A; Bourlat, Sarah J; Rota-Stabelli, Omar; Littlewood, D T J; Telford, Maximilian J

    2006-01-01

    Research into arthropod evolution is hampered by the derived nature and rapid evolution of the best-studied out-group: the nematodes. We consider priapulids as an alternative out-group. Priapulids are a small phylum of bottom-dwelling marine worms; their tubular body with spiny proboscis or introvert has changed little over 520 million years and recognizable priapulids are common among exceptionally preserved Cambrian fossils. Using the complete mitochondrial genome and 42 nuclear genes from Priapulus caudatus, we show that priapulids are slowly evolving ecdysozoans; almost all these priapulid genes have evolved more slowly than nematode orthologs and the priapulid mitochondrial gene order may be unchanged since the Cambrian. Considering their primitive bodyplan and embryology and the great conservation of both nuclear and mitochondrial genomes, priapulids may deserve the popular epithet of "living fossil." Their study is likely to yield significant new insights into the early evolution of the Ecdysozoa and the origins of the arthropods and their kin as well as aiding inference of the morphology of ancestral Ecdysozoa and Bilateria and their genomes.

  4. A history of Proterozoic terranes in southern South America: From Rodinia to Gondwana

    Directory of Open Access Journals (Sweden)

    C. Casquet

    2012-03-01

    Full Text Available The role played by Paleoproterozoic cratons in southern South America from the Mesoproterozoic to the Early Cambrian is reconsidered here. This period involved protracted continental amalgamation that led to formation of the supercontinent Rodinia, followed by Neoproterozoic continental break-up, with the consequent opening of Clymene and Iapetus oceans, and finally continental re-assembly as Gondwana through complex oblique collisions in the Late Neoproterozoic to Early Cambrian. The evidence for this is based mainly on a combination of precise U-Pb SHRMP dating and radiogenic isotope data for igneous and metamorphic rocks from a large area extending from the Rio de la Plata craton in the east to the Argentine Precordillera in the west and as far north as Arequipa in Peru. Our interpretation of the paleogeographical and geodynamic evolution invokes a hypothetical Paleoproterozoic block (MARA embracing basement ultimately older than 1.7 Ga in the Western Sierras Pampeanas (Argentina, the Arequipa block (Peru, the Rio Apa block (Brazil, and probably also the Paraguaia block (Bolivia.

  5. Did CDM particles of mass 2.47 x 10(-3) eV interact with precursor biopolymers and nucleic acids to initiate and boost lifeforms on Earth?

    Science.gov (United States)

    Rosen, Gerald

    2011-06-01

    Recent observations and theoretical studies have shown that non-baryonic Cold Dark Matter (CDM), which constitutes about 84% of all matter in the Universe, may feature a complex-scalar-field that carries particles of mass ≅ 2.47 x 10(-3)eV with the associated Compton range m(-1) ≅8.02 x 10(-3) cm, a distance on the scale of extended bionucleic acids and living cells. Such a complex-scalar-field can enter a weak-isospin Lorentz-invariant interaction that generates the flow of right-handed electrons and induces a chirality-imbued quantum chemistry on the m (-1) scale. A phenomenological Volterra-type equation is proposed for the CDM-impacted time development of N, the number of base pairs in the most advanced organism at Earth-age t. The solution to this equation suggests that the boosts in N at t ≅ 1.1 Gyr (advent of the first living prokaryotic cells), at t ≅ 2.9 Gyr (advent of eukaryotic single-celled organisms) and finally at t ≅ 4.0 Gyr (the Cambrian explosion) may be associated with three multi-Myr-duration cosmic showers of the complex-scalar-field CDM particles. If so, the signature of the particles may be detectible in Cambrian rocks.

  6. Analysis on uranium mineralization-formation condition and prospecting potential in Xidamingshan metallogenic belt

    International Nuclear Information System (INIS)

    Li Zhixing; Qi Fucheng; He Zhongbo; Zhang Zilong

    2012-01-01

    There are many different opinions about the source of uranium and metallogenic mechanism in Xidamingshan metallogenic belt. therefore it blocked uranium resources potential evaluation and ore exploration. Through absorb in- formation and investigate Daxin deposit and systematic analysis on samples. It is believed that uranium source mainly came from Cambrian System, a little came from the deep. The Devonian System is favorable room for saving ores in addition to be pre-concentrated room for uranium. Also, there are new cognition about uranium metallogenic mechanism, establish ore-forming series of Xidamingshan metallogenic belt, It is proposed that uranium mineralization have experienced 4 stages; It is cleared that hydrothermal fluid superposition transform type uranium deposit is main genetic type, ancient karst accumulate type is secondary genetic type, the later is formed by leaching the former and then precipitate, enrichment in ancient karst congeries, which is formed nearby faults and with the movement of Xishan structural movement. It is proven that metallogenic potential of Xidamingshan metallogenic belt is good. Tectonic rock controlled by subsidiary fracture nearby regional main fault, which connected with the Cambrian System and the Devonian System, and the deep of the deposit is guideline of mineral prospecting next stage. (authors)

  7. Mid–Late Neoproterozoic rift-related volcanic rocks in China: Geological records of rifting and break-up of Rodinia

    Directory of Open Access Journals (Sweden)

    Linqi Xia

    2012-07-01

    Full Text Available Early Cambrian and Mid–Late Neoproterozoic volcanic rocks in China are widespread on several Precambrian continental blocks, which had aggregated to form part of the Rodinia supercontinent by ca. 900 Ma. On the basis of petrogeochemical data, the basic lavas can be classified into two major magma types: HT (Ti/Y > 500 and LT (Ti/Y  0.85 and HT2 (Nb/La ≤ 0.85, and LT1 (Nb/La > 0.85 and LT2 (Nb/La ≤ 0.85 subtypes, respectively. The geochemical variation of the HT2 and LT2 lavas can be accounted for by lithospheric contamination of asthenosphere- (or plume- derived magmas, whereas the parental magmas of the HT1 and LT1 lavas did not undergo, during their ascent, pronounced lithospheric contamination. These volcanics exhibit at least three characteristics: (1 most have a compositional bimodality; (2 they were formed in an intracontinental rift setting; and (3 they are genetically linked with mantle plumes or a mantle surperplume. This rift-related volcanism at end of the Mid–Neoproterozoic and Early Cambrian coincided temporally with the separation between Australia–East Antarctica, South China and Laurentia and between Australia and Tarim, respectively. The Mid–Late Neoproterozoic volcanism in China is the geologic record of the rifting and break-up of the supercontinent Rodinia.

  8. International Uranium Resources Evaluation Project (IUREP) national favourability studies: Jordan

    International Nuclear Information System (INIS)

    1977-08-01

    Jordanian geology is dominated by the Great Rift Valley System. Most of the country is covered by Cretaceous and Eocene sediments, largely sandstones and limestones. These include phosphorates and bituminous limestones in the Upper Cretaceous, South of the Dead Sea, Mesozoic and Paleozoic rocks overlie exposed granitic Pre Cambrian basement rocks carrying many minor intrusives . Phosphates provide the main mineral export of Jordan. The Natural Resources Authority (Geological Survey and Bureau of Mines) initiated a survey in 1972 of the distribution of uranium on the phosphorite horizon. In 1974 the Survey calculated that the uranium content of the phosphate areas surveyed up to that time was 5 million metric tonnes U 3 O 8 . The average U 3 O 8 content is approximately 0.02% U 3 O 8 . The exploitation of such resources would be as a byproduct of the phosphate industry and dependent on the rate of phosphate production and the capacity of triple super-phosphate plants, none of which exist at the present time. In the southern area in Paleozoic and Pre Cambrian areas there are some hopes of conventional type deposits being found but the potential appears to be small. (author)

  9. Geochronologic synthesis of the Piedra Alta Terrane, Uruguay

    International Nuclear Information System (INIS)

    Preciozzi, F.; Peel, E.

    2006-01-01

    In the Pre cordillera of Córdoba there are sixteen bands of ductile deformation, which allows tectonic significance assign them to four groups. One of them, which belongs to Deformation Gaza Tunnels, consists of post metamorphic strips uprooting of Orogen Pampeano Cambrian reverse nature, produced by convergent general shear (transpressional), related to collisional stages terrain Posthumous Pampa against Gondwana margin, and famatinian subduction. New radiometric data obtained by the K / Ar method amphiboles and micas allow better narrow activity tectonics of the strip, which would have nucleated after the M2 metamorphic peak (ca. 534 Ma), uprooted the Orogen Cambrian and Ordovician exhumándolo up early (onset of subduction Famatinian), when located the Charquina (474 ​​Ma) granodiorite. The period of tectonic activity FDLT (ca. 64 Ma), coincide with the approach of land Cuyania the Gondwana margin, prior to placement and final collision in the Middle to Late Ordovician. At the same time, in the field Pampeano they would be producing con tractional stages end collision with terrain Pampa the western margin of Gondwana. Subsequently, the FDLT would have cooled to the middle Silurian, when the Sierras de Cordoba and San Luis They continued their exhumation through isotherm muscovite. After cooling this generalized, deformation occurs and Devonian magmatism that penetrativamente affected the Pre cordillera eastern

  10. Causes and timing of future biosphere extinctions

    Directory of Open Access Journals (Sweden)

    S. Franck

    2006-01-01

    Full Text Available We present a minimal model for the global carbon cycle of the Earth containing the reservoirs mantle, ocean floor, continental crust, biosphere, and the kerogen, as well as the combined ocean and atmosphere reservoir. The model is specified by introducing three different types of biosphere: procaryotes, eucaryotes, and complex multicellular life. During the entire existence of the biosphere procaryotes are always present. 2 Gyr ago eucaryotic life first appears. The emergence of complex multicellular life is connected with an explosive increase in biomass and a strong decrease in Cambrian global surface temperature at about 0.54 Gyr ago. In the long-term future the three types of biosphere will die out in reverse sequence of their appearance. We show that there is no evidence for an implosion-like extinction in contrast to the Cambrian explosion. In dependence of their temperature tolerance complex multicellular life and eucaryotes become extinct in about 0.8–1.2 Gyr and 1.3–1.5 Gyr, respectively. The ultimate life span of the biosphere is defined by the extinction of procaryotes in about 1.6 Gyr.

  11. A cosmopolitan late Ediacaran biotic assemblage: new fossils from Nevada and Namibia support a global biostratigraphic link

    Science.gov (United States)

    Smith, E. F.; Nelson, L. L.; Tweedt, S. M.; Zeng, H.; Workman, Jeremiah B.

    2017-01-01

    Owing to the lack of temporally well-constrained Ediacaran fossil localities containing overlapping biotic assemblages, it has remained uncertain if the latest Ediacaran (ca 550–541 Ma) assemblages reflect systematic biological turnover or environmental, taphonomic or biogeographic biases. Here, we report new latest Ediacaran fossil discoveries from the lower member of the Wood Canyon Formation in Nye County, Nevada, including the first figured reports of erniettomorphs, Gaojiashania, Conotubus and other problematic fossils. The fossils are spectacularly preserved in three taphonomic windows and occur in greater than 11 stratigraphic horizons, all of which are below the first appearance of Treptichnus pedum and the nadir of a large negative δ13C excursion that is a chemostratigraphic marker of the Ediacaran–Cambrian boundary. The co-occurrence of morphologically diverse tubular fossils and erniettomorphs in Nevada provides a biostratigraphic link among latest Ediacaran fossil localities globally. Integrated with a new report of Gaojiashania from Namibia, previous fossil reports and existing age constraints, these finds demonstrate a distinctive late Ediacaran fossil assemblage comprising at least two groups of macroscopic organisms with dissimilar body plans that ecologically and temporally overlapped for at least 6 Myr at the close of the Ediacaran Period. This cosmopolitan biotic assemblage disappeared from the fossil record at the end of the Ediacaran Period, prior to the Cambrian radiation.

  12. Field trip guidebook for the post-meeting field trip: The Central Appalachians

    Science.gov (United States)

    Taylor, John F.; Loch, James D.; Ganis, G. Robert; Repetski, John E.; Mitchell, Charles E.; Blackmer, Gale C.; Brezinski, David K.; Goldman, Daniel; Orndorff, Randall C.; Sell, Bryan K.

    2015-01-01

    The lower Paleozoic rocks to be examined on this trip through the central Appalachians represent an extreme range of depositional environments. The lithofacies we will examine range from pelagic radiolarian chert and interbedded mudstone that originated on the deep floor of the Iapetus Ocean, through mud cracked supratidal dolomitic laminites that formed during episodes of emergence of the long-lived Laurentian carbonate platform, to meandering fluvial conglomerate and interstratified overbank mudstone packages deposited in the latest stages of infilling of the Taconic foredeep. In many ways this field trip is about contrasts. The Upper Cambrian (Furongian) and Lower Ordovician deposits of the Sauk megasequence record deposition controlled primarily by eustatic sea level sea level fluctuations that influenced deposition along the passive, southern (Appalachian) margin of the paleocontinent of Laurentia. The only tectonic influence apparent in these passive margin deposits is the expected thickening of the carbonate stack toward the platform margin as compared to the thinner (and typically shallower) facies that formed farther in toward the paleoshoreline. Carbonates overwhelmingly dominate the passive margin succession. Clastic influx was minimal and consisted largely of eastward transport of clean cratonic sands across the platform from the adjacent inner detrital belt to the west during higher order (2nd and 3rd order) regressions.In contrast, Middle and Upper Ordovician deposits of the Tippecanoe megasequence record the strong influence of tectonics, specifically Iapetus closure. The first signal of this tectonic transformation was the arrival of arc-related ash beds that abound in the active margin carbonates. Subsequent intensification of Taconic orogenesis resulted in the foundering of the carbonate platform under the onslaught of fine siliciclastics arriving from offshore tectonic sources to the east, creating a deep marine flysch basin where graptolitic

  13. Geology of Paleozoic Rocks in the Upper Colorado River Basin in Arizona, Colorado, New Mexico, Utah, and Wyoming, Excluding the San Juan Basin

    Science.gov (United States)

    Geldon, Arthur L.

    2003-01-01

    The geology of the Paleozoic rocks in the Upper Colorado River Basin in Arizona, Colorado, New Mexico, Utah, and Wyoming, was studied as part of the U.S. Geological Survey's Regional Aquifer-System Analysis Program to provide support for hydrogeological interpretations. The study area is segmented by numerous uplifts and basins caused by folding and faulting that have recurred repeatedly from Precambrian to Cenozoic time. Paleozoic rocks in the study area are 0-18,000 feet thick. They are underlain by Precambrian igneous, metamorphic, and sedimentary rocks and are overlain in most of the area by Triassic formations composed mostly of shale. The overlying Mesozoic and Tertiary rocks are 0-27,000 feet thick. All Paleozoic systems except the Silurian are represented in the region. The Paleozoic rocks are divisible into 11 hydrogeologic units. The basal hydrogeologic unit consisting of Paleozoic rocks, the Flathead aquifer, predominantly is composed of Lower to Upper Cambrian sandstone and quartzite. The aquifer is 0-800 feet thick and is overlain gradationally to unconformably by formations of Cambrian to Mississippian age. The Gros Ventre confining unit consists of Middle to Upper Cambrian shale with subordinate carbonate rocks and sandstone. The confining unit is 0-1,100 feet thick and is overlain gradationally to unconformably by formations of Cambrian to Mississippian age. The Bighom aquifer consists of Middle Cambrian to Upper Ordovician limestone and dolomite with subordinate shale and sandstone. The aquifer is 0-3,000 feet thick and is overlain unconformably by Devonian and Mississipplan rocks. The Elbert-Parting confining unit consists of Lower Devonian to Lower Mississippian limestone, dolomite, sandstone, quartzite, shale, and anhydrite. It is 0-700 feet thick and is overlain conformably to unconformably by Upper Devonian and Mississippian rocks. The Madison aquifer consists of two zones of distinctly different lithology. The lower (Redwall-Leadville) zone

  14. Biomass burning plumes and the aging of black carbon aerosols in the tropopause region observed with the CARIBIC single particle soot photometer

    Science.gov (United States)

    Ditas, J.; Ma, N.; Zhang, Y.; Assmann, D. N.; Neumaier, M.; Wang, S.; Wang, J.; Zahn, A.; Hermann, M.; Brenninkmeijer, C. A. M.; Poeschl, U.; Su, H.; Cheng, Y.

    2017-12-01

    Biomass burning (BB) events can release large amounts of refractory black carbon (rBC) into the upper troposphere and lowermost stratosphere (UT/LMS) (Dahlkötter et al., 2014). To explore this effect, a Single Particle Soot Photometer (SP2) was added to the scientific payload of the instrumented CARIBIC container that is installed monthly in the cargo bay of a passenger aircraft (the IAGOS-CARIBIC atmospheric observatory, www.iagos.org). Regular measurement flights with different destinations are performed, covering an area of about 120°W to 120°E and 75°N to 30°S. A wide range of in situ measurements (CO, O3, greenhouse gases, aerosol particles and volatile organic compounds) is combined with a collection of air and aerosol samples for laboratory analyses. Since August 2014, the SP2 measures BC number and mass concentration at altitudes between 8 and 12 km. More than 600 BC measurement hours show a strong impact of BB emissions on the lowermost stratosphere. The BB plumes are identified with the help of concurrent carbon monoxide and acetonitrile measurements showing substantially increased concentrations compared to their background level. Transported into the lowermost stratosphere, BB smoke can be transported over long distances and the BC particles can stay in the atmosphere up to one year. The monthly missions of four consecutive CARIBIC flights sometimes enable to revisit a certain air mass, as was the case during a measurement flight to San Francisco in August 2014, with a stopover time of 2h. The revisited biomass burning plume located over the Altlantic ocean near Greenland was traced back by backward and forward trajectories to open fires in Canada (upper Fig.). The transit time of the smoke plume was estimated to 16 - 19h which perfectly matches our flight time difference ( 18h). Based on the LEO-fit method (Leading Edge Only fit) from Gao et al. (2007), the mixing state of the BC particles within the BB plume was calculated. Our unique data set

  15. Geochemical and palynological records for the end-Triassic Mass-Extinction Event in the NE Paris Basin (Luxemburg)

    Science.gov (United States)

    Kuhlmann, Natascha; van de Schootbrugge, Bas; Thein, Jean; Fiebig, Jens; Franz, Sven-Oliver; Hanzo, Micheline; Colbach, Robert; Faber, Alain

    2016-04-01

    The End-Triassic mass-extinction event is one of the "big five" mass extinctions in Earth's history. Large scale flood basalt volcanism associated with the break-up of Pangaea, which resulted in the opening of the central Atlantic Ocean, is considered as the leading cause. In addition, an asteroid impact in Rochechouart (France; 201 ± 2 Ma) may have had a local influence on ecosystems and sedimentary settings. The Luxembourg Embayment, in the NE Paris Basin, offers a rare chance to study both effects in a range of settings from deltaic to lagoonal. A multidisciplinary study (sedimentology, geochemistry, palynology) has been carried out on a number of outcrops and cores that span from the Norian to lower Hettangian. Combined geochemical and palynological records from the Boust core drilled in the NE Paris Basin, provide evidence for paleoenvironmental changes associated with the end-Triassic mass-extinction event. The Triassic-Jurassic stratigraphy of the Boust core is well constrained by palynomorphs showing the disappaerance of typical Triassic pollen taxa (e.g. Ricciisporites tuberculates) and the occurrence of the marker species Polypodiisporites polymicroforatus within the uppermost Rhaetian, prior to the Hettangian dominance of Classopollis pollen. The organic carbon stable isotope record (δ13Corg) spanning the Norian to Hettangian, shows a series of prominent negative excursions within the middle Rhaetian, followed by a trend towards more positive values (approx -24 per mille) within the uppermost Rhaetian Argiles de Levallois Member. The lowermost Hettangian is characterized by a major negative excursion, reaching - 30 per mille that occurs in organic-rich sediments. This so-called "main negative excursion" is well-known from other locations, for example from Mariental in Northern Germany and from St Audrie's Bay in England, and Stenlille in Denmark. Based on redox-sensitive trace element records (V, Cr, Ni, Co, Th, U) the lowermost Hettangian in most of

  16. Multi-method chronological investigation of a Middle Paleolithic stratigraphic context in Eastern Transylvania, Romania

    Science.gov (United States)

    Veres, Daniel; Cosac, Marian; Muratoreanu, George; Niţǎ, Loredana; Schmidt, Christoph; Hambach, Ulrich; Hubay, Katalin; Alexandru, Radu; Cuculici, Roxana; Lucian Buzea, Dan; Dumitraşcu, Valentin

    2016-04-01

    The Middle to Upper Paleolithic transition is one of the crucial periods of change in the prehistory of Europe due to the full emergence, continent-wide, of modern human technologies, detrimental of Neanderthal survival. Knowledge about the transition is vast, however, the evidence for cultural and technological developments in the Carpathian - Lower Danube area is still rather sparse. Here we discuss latest results arising from an archaeological-chronological investigation of a Middle Paleolithic context within the Varghis karst, eastern Transylvania, Romania. Combining our results with these of previous excavations, we can distinguish several stages of habitation in the area comprising a rock shelter connected to a newly discovered filled-in cave entrance. Reanalysis of the deeper stratigraphy previously unexcavated shows that at least two main habitation levels have been preserved. In both levels, the bone assemblages (Bos/Bison, Capra, Canis lupus, Ursus spaeleus) directly associated with lithics point to human-accumulation of material. In order to augment the typological cultural considerations, we applied direct radiocarbon dating on bones from within the occupation layers and on scattered charcoal, for the latter following a two-step combustion protocol (1). Radiocarbon dating on bones suggests the lowermost occupation layer is >43.4 radiocarbon kyr BP old, whereas the preliminary infrared stimulated luminescence (IRSL) ages on the lowermost productive layer and above it indicate surprisingly old ages of ca. 120 kyr and respectively, ca. 70 kyr. Multiple-protocol dating of charcoal found within the two habitation layers produced ages >38 radiocarbon kyr BP, suggesting that the lowermost habitation layer unequivocally pertains to the Middle Paleolithic industries. For the upper productive layer, radiocarbon dating of charcoal found 20 cm above it produced a surprisingly young age of 17.4 radiocarbon kyr BP. However, as the carbon content of this sample was

  17. Early Bashkirian Rugosa (Anthozoa) from the Donets Basin (Ukraine). Part 6. The Family Aulophyllidae Dybowski, 1873

    Science.gov (United States)

    Fedorowski, Jerzy

    2017-12-01

    Seven genera (one new), belonging to four subfamilies, seven named species (six new), four species left in open nomenclature and two specimens included in this paper as unnamed Aulophyllidae are described from strata ranging from the lowermost Bashkirian Limestone D510 to the lower Bashkirian Limestone F1. A new genus: Voragoaxum and six new species: Dibunophyllum medium, Dibunophylloides columnatus, D. paulus, D. similis, Voragoaxum cavum and Rozkowskia lenta are introduced. Comparison of the ontogeny of the earliest Bashkirian species of Nina Fedorowski, 2017a and Dibunophylloides Fomichev, 1953 suggest the derivation by descent of the Family Bothrophyllidae from the Subfamily Dibunophyllinae. This means that true bothrophylla are absent in the Mississippian strata of the Western European Province and, perhaps, in the contemporaneous strata of other areas as well.

  18. Lateral temperature variations at the core-mantle boundary deduced from the magnetic field

    Science.gov (United States)

    Bloxham, Jeremy; Jackson, Andrew

    1990-01-01

    Recent studies of the secular variation of the earth's magnetic field over periods of a few centuries have suggested that the pattern of fluid motion near the surface of earth's outer core may be strongly influenced by lateral temperature variations in the lowermost mantle. This paper introduces a self-consistent method for finding the temperature variations near the core surface by assuming that the dynamical balance there is geostrophic and that lateral density variations there are thermal in origin. As expected, the lateral temperature variations are very small. Some agreement is found between this pattern and the pattern of topography of the core-mantle boundary, but this does not conclusively answer to what extent core surface motions are controlled by the mantle, rather than being determined by processes in the core.

  19. Fractionation of rare earths elements in weathering profiles on phonolites in area of Lages, Santa Catarina, Brazil

    International Nuclear Information System (INIS)

    Formoso, M.L.L.; Valeton, J.; Retzmann, R.

    1989-01-01

    Niobium and rare earth elements are associated with alkaline intrusions, especially in sequences containing carbonatites. During deep ferralitic weathering on the Lower Tertiary peneplanation plain REE are mobilized and depleted as well in the lower saprolite as in the upper ferralite, except Cerium which shows a positive anormaly. Triangular diagrams of Ce, Nd, La represent a relative enrichment of La, whereas comparing Ce, La and Nb, the increase of Niobium is strongest with rising weathering. After intersection of the landscape into inselbergs and lowering of the aquifers a later period of mobilization and migration of the REE together with manganese, aluminium and silica took place in descending direction. Their absolute enrichment by precipitation is concentrated in fissure fillings and porespaces in the lowermost part of the profiles. Main minerals are lithiophorite and halloysite. (author) [pt

  20. Biostratigraphy of the Cretaceous/Tertiary boundary in the Sirwan Valley (Sulaimani Region, Kurdistan, NE Iraq)

    Science.gov (United States)

    Sharbazheri, Khalid Mahmood; Ghafor, Imad Mahmood; Muhammed, Qahtan Ahmad

    2009-10-01

    The Cretaceous/Tertiary (K/T) boundary sequence, which crops out in the studied area is located within the High Folded Zone, in the Sirwan Valley, northeastern Iraq. These units mainly consist of flysch and flysch-type successions of thick clastic beds of Tanjero/Kolosh Formations. A detailed lithostratigraphic study is achieved on the outcropping uppermost part of the Upper Cretaceous successions (upper part of Tanjero Formation) and the lowermost part of the Kolosh Formation. On the basis of the identified planktonic foraminiferal assemblages, five biozones are recorded from the uppermost part of Tanjero Formation and four biozones from the lower part of the Kolosh Formation (Lower Paleocene) in the Sirwan section. The biostratigraphic correlations based on planktonic foraminiferal zonations showed a comparison between the biostratigraphic zones established in this study and other equivalents of the commonly used planktonic zonal scheme around the Cretaceous/Tertiary boundary in and outside Iraq.

  1. Biostratigraphy of the upper Bajocian-middle Callovian (Middle Jurassic), South America

    Science.gov (United States)

    Riccardi, A. C.; Westermann, G. E. G.; Elmi, S.

    The biostratigraphic division of the upper Bajocian-middle Callovian of South America is based on ammonites from different sections of the following provinces and regions: Neuquén, Mendoza, and San Juan in Argentina; Malleco, Linares, Talca, Atacama, Antofagasta, and Tarapacá in Chile. The complete upper Bajocian-middle Callovian succession includes the following biostratigraphic units: the Megasphaeroceras magnum assemblage zone, lowermost upper Bajocian; the Cadomites-Tulitidae mixed assemblages, (?lower) middle and upper Bathonian; the Steinmanni zone, index Lilloettia steinmanni (Spath), uppermost Bathonian, with two local horizons— Stenocephalites gerthi horizon (Argentina) and Choffatia jupiter horizon (northern Chile); the Vergarensis zone, index Eurycephalites vergarensis (Burck.), near the Bathonian-Callovian boundary; the Bodenbenderi zone, index Neuqueniceras (Frickites) bodenbenderi (Tornq.), lower Callovian; the Proximum zone, index Hecticoceras proximum Elmi, uppermost lower Callovian; and the Rehmannia (Loczyceras) patagoniensis horizon, middle Callovian.

  2. Non-spill control squared cascade

    International Nuclear Information System (INIS)

    Kai, Tsunetoshi; Inoue, Yoshiya; Oya, Akio; Suemori, Nobuo.

    1974-01-01

    Object: To reduce a mixed loss thus enhancing separating efficiency by the provision of a simple arrangement wherein a reflux portion in a conventional spill control squared cascade is replaced by a special stage including centrifugal separators. Structure: Steps in the form of a square cascade, in which a plurality of centrifugal separators are connected by pipe lines, are accumulated in multistage fashion to form a squared cascade. Between the adjoining steps is disposed a special stage including a centrifugal separator which receives both lean flow from the upper step and rich flow from the lower step. The centrifugal separator in the special stage has its rich side connected to the upper step and its lean side connected to the lower step. Special stages are each disposed at the upper side of the uppermost step and at the lower side of the lowermost step. (Kamimura, M.)

  3. Crestal unconformities on an exposed Jurassic tilted fault block, Wollaston Forland, East Greenland as an analogue for buried hydrocarbon traps

    DEFF Research Database (Denmark)

    Surlyk, Finn; Korstgård, J.

    2013-01-01

    The stratigraphy of successions exposed in footwall crests of tilted fault blocks is commonly highly complex. Crestal stratigraphy and structure are particularly difficult to unravel in the subsurface due to poor seismic resolution across fault zones, footwall collapse, and coalescing syn- and post......-rift unconformities. Crestal ridges are important elements in basin evolution, as they form drainage divides and sediment sources for aprons along footwall scarps and hangingwall deltas. A Middle Jurassic – lowermost Cretaceous footwall crest is exceptionally well exposed in the mountain Stratumbjerg in Wollaston...... Forland, East Greenland. Rifting and block tilting was initiated in the (?)Bajocian, intensified in the Oxfordian–Kimmeridgian, culminated in latest Jurassic, Volgian, time and faded out in the earliest Cretaceous. The main border faults of the westward tilted blocks trend roughly N–S. The first early syn...

  4. Nuclear fuel rod

    International Nuclear Information System (INIS)

    Kaneuji, Akira; Akitake, Jun-ichi; Kondo, Yoshiaki.

    1997-01-01

    A buckling member is inserted between a pellet at the lowermost portion and a lower end plug. The buckling member comprises a buckling pipe and an upper lid which engage coaxially with each other. The buckling pipe is a stainless hollow cylindrical pipe, and an expanding portion is formed at the intermediate portion. If pellets and a cladding tube are adhered by mechanical interaction during reactor operation, the thermal expansion of pellets at a portion upper than the adhered portion is absorbed by a coil spring. The thermal expansion of the pellets at a portion lower than the adhered portion is absorbed to the buckling member, and if the compression load is increased exceeding a predetermined value, the buckling pipe is bucked at an expandable portion and shrinks to absorb thermal expansion of pellets. (I.N.)

  5. Geological techniques utilized in trap Spring Field discovery, Railroad Valley, Nye County, Nevada

    Energy Technology Data Exchange (ETDEWEB)

    Dolly, E.D.

    1980-01-01

    The trap at Eagle Springs Field is a combination stratigraphic truncation-subcrop-fault trap. Production occurs from matrix and fracture porosity in reservoirs in the Sheep Pass Formation (Cretaceous and Eocene) and the Garrett Ranch volcanic group (Oligocene). Probably the most unique feature about the field is that the production occurs from the highest position on the lowermost fault block at the basin margin. On the adjacent higher fault blocks the reservoir beds were removed by erosion during the basin and range orogenic event. The position of the truncated edge of the lower Tertiary reservoir units is controlled by the fault pattern at the margin of the valley-basin Graben. Detailed geomorphic studies indicated that this fault pattern may be identified at the surface. Regional geomorphic mapping of fault patterns was conducted to localize areas with possible subcrop truncation patterns similar to Eagle Springs Field. 20 references.

  6. Short-term variability in bacterial abundance, cell properties, and incorporation of leucine and thymidine in subarctic sea ice

    DEFF Research Database (Denmark)

    Kaartokallio, H.; Sogaard, D. H.; Norman, L.

    2013-01-01

    Sea ice is a biome of immense size and provides a range of habitats for diverse microbial communities, many of which are adapted to living at low temperatures and high salinities in brines. We measured simultaneous incorporation of thymidine (TdR) and leucine (Leu), bacterial cell abundance...... and cell population properties (by flow cytometry) in subarctic sea ice in SW Greenland. Short-term temporal variability was moderate, and steep environmental gradients, typical for sea ice, were the main drivers of the variability in bacterial cell properties and activity. Low nucleic acid (LNA) bacteria...... and marine biofilm systems. Leu: TdR ratios were high (up to >300) in lowermost ice layers, and when compared to published respiration measurements, these results suggest non-specific Leu incorporation. There was evidence of polyhydroxyalkanoate (PHA)-containing bacteria in the sea ice, shown by brightly...

  7. Fracture diagnostics with tube wave reflection logs

    International Nuclear Information System (INIS)

    Medlin, W.L.

    1991-01-01

    This paper reports on the Tube Wave Reflection Log (TWRL) which is acoustic logging method which provides information about the height, location and conductivity of hydraulically induced fractures behind perforated casing. The TWRL tool consists of a transmitter and closely spaced receiver. The transmitter is driven with a short, low frequency tone burst to generate long wavelength tube waves which are little attenuated in unperforated casing. They are partially reflected when they pass perforated intervals communicating with a hydraulically induced fracture. The tool listens for such reflections for 0.1 seconds following each excitation burst. As the tool is moved uphole at logging speed, the transmitter is excited at each foot of depth. VDL displays of the TWRL records provide reflection traces whose projections define the uppermost and lower-most perforations communicating with the fracture. The strength of the reflections depends on the ease of fluid flow into the fracture and thus, is an indicator of fracture conductivity

  8. Integrated Outcrop and Subsurface Studies of the Interwell Environment of Carbonate Reservoirs: Clear Fork (Leonaradian Age) Reservoirs, West Texas and New Mexico

    International Nuclear Information System (INIS)

    Lucia, F.J.; Ruppel, S.C.

    2001-01-01

    Characterization of cycle and facies architecture on lower Clear Fork and lowermost upper Clear Fork equivalent outcrops in Apache Canyon of Sierra Diablo was complete. The focus of detailed study in Apache Canyon has been the upper Clear Fork section because this interval contains the productive interval in South Wasson field, the preliminary subsurface study area. Parts of three high-frequency sequences (HFS), each 60 to 100 ft thick, are present on the south wall of Apache Canyon. HFS's display an upper-deepening or backstepping pattern associated with longer-term sea level rise. Each HFS is composed of upward-shallowing cycles whose thickness, facies composition, and continuity vary within and between HFS's

  9. An early Brunhes (age for the Lower Paleolithic tool-bearing Kozarnika cave sediments, Bulgaria

    Science.gov (United States)

    Muttoni, Giovanni; Sirakov, Nikolas; Guadelli, Jean-Luc; Kent, Dennis V.; Scardia, Giancarlo; Monesi, Edoardo; Zerboni, Andrea; Ferrara, Enzo

    2017-12-01

    We present a new sedimentological profile and a magnetostratigraphy of the tool-bearing Kozarnika cave sediments from Bulgaria. Modal analysis of cave infilling sedimentary texture indicates that the tool-bearing layers contain a sizable fraction of sediment interpreted as loess. We also find evidence for a relatively thick and well defined normal magnetic polarity in the upper-middle part of the section interpreted as a record of the Brunhes Chron, followed down-section by reverse polarity directions interpreted as a record of the Matuyama Chron. The lowermost levels with Lower Paleolithic tools (Layers 13a-c) lie in the early Brunhes at a nominal maximum age of ∼0.75 Ma, while the Brunhes-Matuyama boundary (0.78 Ma) falls in Layer 13 Lower immediately below. This finding represents a conspicuous revision of previous age estimates for the same tool-bearing layers.

  10. La coupe d'Ouled Haddou (Rif externe oriental) : un affleurement continu de la transition Crétacé Paléogène au Maroc, révélé par les Foraminifères planctoniquesThe Ouled Haddou section (oriental external Rif): a continuous outcrop of the Cretaceous Palaeogene transition in Morocco, revealed by planktonic Foraminifera

    Science.gov (United States)

    Toufiq, Abdelkabir; Bellier, Jean-Pierre; Boutakiout, Mohamed; Feinberg, Hugues

    2002-10-01

    In the Ouled Haddou section, deposits of the Uppermost Maastrichtian correspond to the Abathomphalus mayaroensis Biozone. The index species is regularly present until the Cretaceous-Palaeogene boundary, which is marked by a mass extinction affecting 41 species (large and complex). Some Cretaceous small species persist in the Lowermost Danian. The first levels of the Danian are assigned to the Guembelitria cretacea Biozone, in which the species index persist without being affected, and the first species of the Tertiary appear. The upper part of the Lower Danian corresponds to the succession of Parvularugoglobigerina eugubina, Parasubbotina pseudobulloides, and Subbotina triloculinoides Biozones. From the P. eugubina Biozone, associations of Danian vary to undergo a complete renewal in the upper zones. The Ouled Haddou section, described for the first time, presents, according to planktonic Foraminifera, a complete record of the Cretaceous-Palaeogene transition. To cite this article: A. Toufiq et al., C. R. Geoscience 334 (2002) 995-1001.

  11. Sedimentation and lithostratigraphy of the Vuosaari multiple till sequence in Helsinki, southern Finland

    Directory of Open Access Journals (Sweden)

    Hirvas, H.

    1995-12-01

    Full Text Available A multiple till sequence interbedded with sorted sediments has been investigated at Vuosaari, Helsinki, Finland. The investigation was carried out using standard sedimentological procedures combined with microfossil analysis in order to determine the genesis of the exposed sediments. This evidence is used to correlate lithostratigraphically the sequence with adjacent multiple till sequences in other parts of southern Finland (south of the Salpausselkä zone. It is concluded that all three till beds at Vuosaari are of basal origin that were laid down by separate ice flow phases. In contrast two rhythmite beds between the tills are thought to have been deposited in open water. The sediments at Vuosaari may have been laid down during the Weichselian glaciation although it is also possible that the lowermost till bed represents Saalian till.

  12. Colonic cell proliferation in normal mucosa of patients with colon cancer

    International Nuclear Information System (INIS)

    Becciolini, A.; Balzi, M.; Faraoni, P.; Tisti, E.; Thyrion, G.Z.; Giache, V.; Bandettini, L.; Potten, C.S.

    1998-01-01

    Cell kinetics parameters have been analysed in colonic mucosa at different distances from a tumour in patients with colon carcinoma. Total cell number (TCN), 3 H thymidine labelling index (TLI), mitotic index (MI), Goblet cell index (GCI) and the distribution of labelled cells along the crypt column (cell position frequency plot) were determined in well-aligned crypts. Total cell number, GCI and the labelled cell position frequency plots were similar in different samples from the same individual. A negative linear correlation between TCN and TLI was observed. The analysis of the cell position plots showed two patterns (1) with a high concentration in the bottom fifth of the crypt and (2) with frequent labelled cells at high positions. Whereas a negative correlation between overall TLI and the percent contribution to the TLI of the lowermost fifth was seen, the correlation was positive for the next 3 fifths and labelling was absent in the last part of the crypt. (orig.)

  13. STS-74 view of ODS from Payload Changout Room

    Science.gov (United States)

    1995-01-01

    Workers at Launch Pad 39A are preparing to close the payload bay doors on the Space Shuttle Atlantis for its upcoming launch on Mission STS-74 and the second docking with the Russian Space Station Mir. Uppermost in the payload bay is the Orbiter Docking System (ODS), which also flew on the first docking flight between the Space Shuttle and MIR. Lowermost is the primary payload of STS-74, the Russian-built Docking Module. During the mission, the Docking Module will first be attached to ODS and then to Mir. It will be left attached to Mir to become a permanent extension that will afford adequate clearance between the orbiter and the station during future dockings. At left in the payload bay, looking like a very long pole, is the Canadian-built Remote Manipulator System arm that will be used by the crew to hoist the Docking Module and attach it to the ODS.

  14. Quantifying pollution transport from the Asian monsoon anticyclone into the lower stratosphere

    Directory of Open Access Journals (Sweden)

    F. Ploeger

    2017-06-01

    Full Text Available Pollution transport from the surface to the stratosphere within the Asian monsoon circulation may cause harmful effects on stratospheric chemistry and climate. Here, we investigate air mass transport from the monsoon anticyclone into the stratosphere using a Lagrangian chemistry transport model. We show how two main transport pathways from the anticyclone emerge: (i into the tropical stratosphere (tropical pipe, and (ii into the Northern Hemisphere (NH extratropical lower stratosphere. Maximum anticyclone air mass fractions reach around 5 % in the tropical pipe and 15 % in the extratropical lowermost stratosphere over the course of a year. The anticyclone air mass fraction correlates well with satellite hydrogen cyanide (HCN and carbon monoxide (CO observations, confirming that pollution is transported deep into the tropical stratosphere from the Asian monsoon anticyclone. Cross-tropopause transport occurs in a vertical chimney, but with the pollutants transported quasi-horizontally along isentropes above the tropopause into the tropics and NH.

  15. On the relative motions of long-lived Pacific mantle plumes.

    Science.gov (United States)

    Konrad, Kevin; Koppers, Anthony A P; Steinberger, Bernhard; Finlayson, Valerie A; Konter, Jasper G; Jackson, Matthew G

    2018-02-27

    Mantle plumes upwelling beneath moving tectonic plates generate age-progressive chains of volcanos (hotspot chains) used to reconstruct plate motion. However, these hotspots appear to move relative to each other, implying that plumes are not laterally fixed. The lack of age constraints on long-lived, coeval hotspot chains hinders attempts to reconstruct plate motion and quantify relative plume motions. Here we provide 40 Ar/ 39 Ar ages for a newly identified long-lived mantle plume, which formed the Rurutu hotspot chain. By comparing the inter-hotspot distances between three Pacific hotspots, we show that Hawaii is unique in its strong, rapid southward motion from 60 to 50 Myrs ago, consistent with paleomagnetic observations. Conversely, the Rurutu and Louisville chains show little motion. Current geodynamic plume motion models can reproduce the first-order motions for these plumes, but only when each plume is rooted in the lowermost mantle.

  16. Chlorophenol and alkylphenol concentrations in sediment and mussel tissues collected from selected locations in Kentucky Lake, USA

    Energy Technology Data Exchange (ETDEWEB)

    Loganathan, B.; Brown, B.; Owen, D. [Murray State Univ., Murray, KY (United States); Sajwan, K. [Savannah State Univ., Savannah, GA (United States)

    2004-09-15

    Kentucky (KY) Lake is one the major human-constructed lakes in the US. It serves as an ultimate repository of substances entering this watershed from portions of seven southeastern states, which include a sizeable fraction of the U.S. chemical processing, agricultural chemical products and electronics manufacturing industries. Although a few studies have examined the levels of chlorinated organics in the KY Lake and the lowermost Tennessee River, there have been no reports on the distribution on the levels of chlorophenols and alkylphenols in sediment and/or biological tissues from this region. In this study, sediment, and freshwater mussels were collected from selected locations in KY Lake and Lake Barkley and analyzed for CPs and APs. Furthermore, wood samples from abandoned docks, navigational towers and wood found in the lake bottom were also analyzed to examine the sources of CPs to the lakes.

  17. The Neogene lakes on the Balkan land

    Directory of Open Access Journals (Sweden)

    Krstić Nadežda

    2012-01-01

    Full Text Available Palaeogeographic maps of the lacustrine Miocene and Pliocene have been constructed according to all the known geological data. The Lakes of the Balkan Land, depending on the tectonics, migrated due to causes from the deep subsurface. There are several phases of the Miocene lakes: the lowermost Miocene transiting from marine Oligocene, Lower, Middle, Upper Miocene covering, in patches, the main part of the Land. The Pliocene lakes spread mostly to the north of the Balkan Land and covered only its marginal parts. Other lake-like sediments, in fact freshened parts of the Black Sea Kuialnician (Upper Pliocene, stretched along the middle and southern portions of the Balkan Peninsula (to the south of the Balkan Mt.. Subsequently, the Balkan Peninsula was formed.

  18. Early Holocene estuary development of the Hesselø Bay area, southern Kattegat, Denmark and its implication for Ancylus Lake drainage

    DEFF Research Database (Denmark)

    Bendixen, Carina; Boldreel, Lars Ole; Jensen, Jørn Bo

    2017-01-01

    environment and a description of coastal processes associated with a river outlet into the bay are presented. Weichselian glacial deposits form the lowermost interpreted unit, covered by late glacial (LG) and postglacial (PG, Holocene) sediments. A funnel-shaped estuary existed at the mouth of channels......High-resolution shallow seismic data, sediment core information, radiocarbon dating and sequence stratigraphy have been used to interpret the late glacial to early Holocene geological evolution of Hesselø Bay in the southern Kattegat, Denmark. A reconstruction of the early Holocene coastal...... in the period 10.3–9.2 cal. ka BP; the channels drained water from south to north. The early PG is characterised by estuarine and coastal deposits. The early Holocene bars that developed in the estuary are preserved as morphological features on the present-day seabed, possibly as a result of rapid relative sea...

  19. MJO-Related Tropical Convection Anomalies Lead to More Accurate Stratospheric Vortex Variability in Subseasonal Forecast Models.

    Science.gov (United States)

    Garfinkel, C I; Schwartz, C

    2017-10-16

    The effect of the Madden-Julian Oscillation (MJO) on the Northern Hemisphere wintertime stratospheric polar vortex in the period preceding stratospheric sudden warmings is evaluated in operational subseasonal forecasting models. Reforecasts which simulate stronger MJO-related convection in the Tropical West Pacific also simulate enhanced heat flux in the lowermost stratosphere and a more realistic vortex evolution. The time scale on which vortex predictability is enhanced lies between 2 and 4 weeks for nearly all cases. Those stratospheric sudden warmings that were preceded by a strong MJO event are more predictable at ∼20 day leads than stratospheric sudden warmings not preceded by a MJO event. Hence, knowledge of the MJO can contribute to enhanced predictability, at least in a probabilistic sense, of the Northern Hemisphere polar stratosphere.

  20. Oyster-bioimmured ammonites from the Upper Albian of Annopol, Poland: stratigraphic and palaeobiogeographic implications

    Science.gov (United States)

    Machalski, Marcin; Kennedy, William J.

    2013-12-01

    Machalski, M. and Kennedy, W.J. 2013. Oyster-bioimmured ammonites from the Upper Albian of Annopol, Poland: stratigraphic and palaeobiogeographic implications. Acta Geologica Polonica, 63 (4), 545-554. Warszawa. Ammonites Mortoniceras (Subschloenbachia) sp. are preserved as attachment scars on the oyster shells from the topmost portion of the Albian succession at Annopol, Poland. These oyster-bioimmured ammonites show a closest affinity to the representatives of Mortoniceras (Subschloenbachia) characteristic of the upper Upper Albian Mortoniceras perinflatum Zone. No ammonites indicative of the uppermost Albian-lowermost Cenomanian Praeschloenbachia briacensis Zone are recorded. Thus, the hiatus at the Albian-Cenomanian boundary at Annopol embraces the latter zone. The presence (and dominance) of Mortoniceras in the upper Upper Albian ammonite assemblage of Annopol suggests that the representatives of this Tethyan genus could migrate into the epicratonic areas of Poland directly from the Tethyan Realm, via the Lwow (Lviv) region.

  1. Iron-carbonate interaction at Earth's core-mantle boundary

    Science.gov (United States)

    Dorfman, S. M.; Badro, J.; Nabiei, F.; Prakapenka, V.; Gillet, P.

    2015-12-01

    Carbon storage and flux in the deep Earth are moderated by oxygen fugacity and interactions with iron-bearing phases. The amount of carbon stored in Earth's mantle versus the core depends on carbon-iron chemistry at the core-mantle boundary. Oxidized carbonates subducted from Earth's surface to the lowermost mantle may encounter reduced Fe0 metal from disproportionation of Fe2+ in lower mantle silicates or mixing with the core. To understand the fate of carbonates in the lowermost mantle, we have performed experiments on sandwiches of single-crystal (Ca0.6Mg0.4)CO3 dolomite and Fe foil in the laser-heated diamond anvil cell at lower mantle conditions of 49-110 GPa and 1800-2500 K. Syntheses were conducted with in situ synchrotron X-ray diffraction to identify phase assemblages. After quench to ambient conditions, samples were sectioned with a focused Ga+ ion beam for composition analysis with transmission electron microscopy. At the centers of the heated spots, iron melted and reacted completely with the carbonate to form magnesiowüstite, iron carbide, diamond, magnesium-rich carbonate and calcium carbonate. In samples heated at 49 and 64 GPa, the two carbonates exhibit a eutectoid texture. In the sample heated at 110 GPa, the carbonates form rounded ~150-nm-diameter grains with a higher modal proportion of interspersed diamonds. The presence of reduced iron in the deep lower mantle and core-mantle boundary region will promote the formation of diamonds in carbonate-bearing subducted slabs. The complete reaction of metallic iron to oxides and carbides in the presence of mantle carbonate supports the formation of these phases at the Earth's core-mantle boundary and in ultra-low velocity zones.

  2. Fluvial to Lacustrine Facies Transitions in Gale Crater, Mars

    Science.gov (United States)

    Sumner, Dawn Y.; Williams, Rebecca M. E.; Schieber, Juergen; Palucis, Marisa C.; Oehler, Dorothy Z.; Mangold, Nicolas; Kah, Linda C.; Gupta, Sanjeev; Grotzinger, John P.; Grant, John A., III; hide

    2015-01-01

    NASA's Curiosity rover has documented predominantly fluvial sedimentary rocks along its path from the landing site to the toe of the Peace Vallis alluvial fan (0.5 km to the east) and then along its 8 km traverse across Aeolis Palus to the base of Aeolis Mons (Mount Sharp). Lacustrine facies have been identified at the toe of the Peace Vallis fan and in the lowermost geological unit exposed on Aeolis Mons. These two depositional systems provide end members for martian fluvial/alluvial-lacustrine facies models. The Peace Vallis system consisted of an 80 square kilometers alluvial fan with decimeter-thick, laterally continuous fluvial sandstones with few sedimentary structures. The thin lacustrine unit associated with the fan is interpreted as deposited in a small lake associated with fan runoff. In contrast, fluvial facies exposed over most of Curiosity's traverse to Aeolis Mons consist of sandstones with common dune-scale cross stratification (including trough cross stratification), interbedded conglomerates, and rare paleochannels. Along the southwest portion of the traverse, sandstone facies include south-dipping meter-scale clinoforms that are interbedded with finer-grained mudstone facies, interpreted as lacustrine. Sedimentary structures in these deposits are consistent with deltaic deposits. Deltaic deposition is also suggested by the scale of fluvial to lacustrine facies transitions, which occur over greater than 100 m laterally and greater than 10 m vertically. The large scale of the transitions and the predicted thickness of lacustrine deposits based on orbital mapping require deposition in a substantial river-lake system over an extended interval of time. Thus, the lowermost, and oldest, sedimentary rocks in Gale Crater suggest the presence of substantial fluvial flow into a long-lived lake. In contrast, the Peace Vallis alluvial fan onlaps these older deposits and overlies a major unconformity. It is one of the youngest deposits in the crater, and

  3. Task 50 - deposition of lignites in the Fort Union Group and related strata of the northern Great Plains

    Energy Technology Data Exchange (ETDEWEB)

    Hartman, J.H.; Roth, B.; Kihm, A.J.

    1997-08-11

    Late Cretaceous, Paleocene, and early Eocene geologic and paleontologic studies were undertaken in western North Dakota, eastern and south-central Montana, and northwestern and northeastern Wyoming. These study areas comprise the Williston, Bighorn, and Powder River Basins, all of which contain significant lignite resources. Research was undertaken in these basins because they have the best geologic sections and fossil record for the development of a chronostratigraphic (time-rock) framework for the correlation of lignite beds and other economic resources. A thorough understanding of the precise geologic age of the deposition of sediments permits a powerful means of interpreting the record of geologic events across the northern Great Plains. Such an understanding allows for rigorous interpretation of paleoenviromnents and estimates of resource potential and quality in this area of economically significant deposits. This work is part of ongoing research to document change in the composition of molluscan fossil faunas to provide a paleoenvironmentally sensitive independent means of interpreting time intervals of brief duration during the Late Cretaceous, Paleocene, and Eocene. This study focuses on the record of mollusks and, to a lesser extent, mammals in the (1) Hell Creek-Tullock Formations, which include the Cretaceous-Paleocene boundary, in the western portion of the Williston Basin, Montana; (2) uppermost Cretaceous, Paleocene, and lowermost Eocene strata in western North Dakota, which -includes the last interior seaway in North Dakota; (3) upper Paleocene and lowermost Eocene of the northern portion of the Bighorn Basin of south-central Montana and northwestern Wyoming; and (4) Powder River Basin of northeastern Wyoming and southeastern Montana. The geologic record provides different physical and paleontological information to aid in interpreting the geologic record through the study interval.

  4. The Chicxulub impact is synchronous with the planktonic foraminifera mass extinction at the Cretaceous/Paleogene boundary: new evidence from the Moncada section, Cuba

    Energy Technology Data Exchange (ETDEWEB)

    Arenillas, I.; Arz, J.A.; Grajales-Nishimura, J.M.; Melendez, A.; Rojas-Consuegra, R.

    2016-07-01

    The Moncada section, western Cuba, is one of the few sections across the Cretaceous/Paleogene (K/Pg) boundary in the Gulf of Mexico and Caribbean where an Ir anomaly has been identified toward and above the top of a clastic unit, locally called the Moncada Formation (Fm.). The Moncada Fm. is enriched in ejecta (altered glass spherules, shocked quartz, melt rock fragments, etc.) and represents the local Complex Clastic Unit (CCU) linked to the Chicxulub impact event. This CCU is overlain by a 2-3cm thick bed of Ir-rich, dark, calcareous claystone which represents the “K/T Boundary Clay” at Moncada. All lowermost Danian Planktonic Foraminiferal zones and Acme-Stages (PFAS) were identified, suggesting stratigraphic continuity across the Danian and indicating that the Moncada Fm. is K/Pg boundary in age. High-resolution biostratigraphic data suggest that the mass extinction event of planktonic foraminifera at the K/Pg boundary was more severe than previously suggested. The absence of cosmopolitan, generalist Cretaceous species in the Danian deposits of Moncada supports the hypothesis that only Guembelitria survived the mass extinction triggered by the Chicxulub impact event. The high Ir-concentration and the ejecta-rich clay laminations identified in the lowermost Danian of Moncada (Ancón Fm.) are explained partly as the redeposition of ejecta material eroded and reworked from higher topographic levels, still contaminated by toxic trace elements (e.g., Cu and Ni) of meteoritic origin. These pollutants of meteoritic origin could have affected the ecological conditions of the pelagic environment for thousands of years after the K/Pg boundary, being particularly intense just after the Chicxulub impact. The ecological stress due to the pollutants partly explains the catastrophic mass extinction of planktonic foraminifera at the K/Pg boundary and their subsequent evolutionary radiation. (Author)

  5. Biorhythms, deciduous enamel thickness, and primary bone growth: a test of the Havers-Halberg Oscillation hypothesis.

    Science.gov (United States)

    Mahoney, Patrick; Miszkiewicz, Justyna J; Pitfield, Rosie; Schlecht, Stephen H; Deter, Chris; Guatelli-Steinberg, Debbie

    2016-06-01

    Across mammalian species, the periodicity with which enamel layers form (Retzius periodicity) in permanent teeth corresponds with average body mass and the pace of life history. According to the Havers-Halberg Oscillation hypothesis (HHO), Retzius periodicity (RP) is a manifestation of a biorhythm that is also expressed in lamellar bone. Potentially, these links provide a basis for investigating aspects of a species' biology from fossilized teeth. Here, we tested intra-specific predictions of this hypothesis on skeletal samples of human juveniles. We measured daily enamel growth increments to calculate RP in deciduous molars (n = 25). Correlations were sought between RP, molar average and relative enamel thickness (AET, RET), and the average amount of primary bone growth (n = 7) in humeri of age-matched juveniles. Results show a previously undescribed relationship between RP and enamel thickness. Reduced major axis regression reveals RP is significantly and positively correlated with AET and RET, and scales isometrically. The direction of the correlation was opposite to HHO predictions as currently understood for human adults. Juveniles with higher RPs and thicker enamel had increased primary bone formation, which suggests a coordinating biorhythm. However, the direction of the correspondence was, again, opposite to predictions. Next, we compared RP from deciduous molars with new data for permanent molars, and with previously published values. The lowermost RP of 4 and 5 days in deciduous enamel extends below the lowermost RP of 6 days in permanent enamel. A lowered range of RP values in deciduous enamel implies that the underlying biorhythm might change with age. Our results develop the intra-specific HHO hypothesis. © 2016 Anatomical Society.

  6. Enamel biorhythms of humans and great apes: the Havers-Halberg Oscillation hypothesis reconsidered.

    Science.gov (United States)

    Mahoney, Patrick; Miszkiewicz, Justyna J; Pitfield, Rosie; Deter, Chris; Guatelli-Steinberg, Debbie

    2017-02-01

    The Havers-Halberg Oscillation (HHO) hypothesis links evidence for the timing of a biorhythm retained in permanent tooth enamel (Retzius periodicity) to adult body mass and life history traits across mammals. Potentially, these links provide a way to access life history of fossil species from teeth. Recently we assessed intra-specific predictions of the HHO on human children. We reported Retzius periodicity (RP) corresponded with enamel thickness, and cusp formation time, when calculated from isolated deciduous teeth. We proposed the biorhythm might not remain constant within an individual. Here, we test our findings. RP is compared between deciduous second and permanent first molars within the maxillae of four human children. Following this, we report the first RPs for deciduous teeth from modern great apes (n = 4), and compare these with new data for permanent teeth (n = 18) from these species, as well as with previously published values. We also explore RP in teeth that retain hypoplastic defects. Results show RP changed within the maxilla of each child, from thinner to thicker enameled molars, and from one side of a hypoplastic defect to the other. When considered alongside correlations between RP and cusp formation time, these observations provide further evidence that RP is associated with enamel growth processes and does not always remain constant within an individual. RP of 5 days for great ape deciduous teeth lay below the lowermost range of those from permanent teeth of modern orangutan and gorilla, and within the lowermost range of RPs from chimpanzee permanent teeth. Our data suggest associations between RP and enamel growth processes of humans might extend to great apes. These findings provide a new framework from which to develop the HHO hypothesis, which can incorporate enamel growth along with other physiological systems. Applications of the HHO to fossil teeth should avoid transferring RP between deciduous and permanent enamel, or including

  7. Representation of tropical deep convection in atmospheric models – Part 2: Tracer transport

    Directory of Open Access Journals (Sweden)

    C. R. Hoyle

    2011-08-01

    Full Text Available The tropical transport processes of 14 different models or model versions were compared, within the framework of the SCOUT-O3 (Stratospheric-Climate Links with Emphasis on the Upper Troposphere and Lower Stratosphere project. The tested models range from the regional to the global scale, and include numerical weather prediction (NWP, chemical transport, and chemistry-climate models. Idealised tracers were used in order to prevent the model's chemistry schemes from influencing the results substantially, so that the effects of modelled transport could be isolated. We find large differences in the vertical transport of very short-lived tracers (with a lifetime of 6 h within the tropical troposphere. Peak convective outflow altitudes range from around 300 hPa to almost 100 hPa among the different models, and the upper tropospheric tracer mixing ratios differ by up to an order of magnitude. The timing of convective events is found to be different between the models, even among those which source their forcing data from the same NWP model (ECMWF. The differences are less pronounced for longer lived tracers, however they could have implications for modelling the halogen burden of the lowermost stratosphere through transport of species such as bromoform, or short-lived hydrocarbons into the lowermost stratosphere. The modelled tracer profiles are strongly influenced by the convective transport parameterisations, and different boundary layer mixing parameterisations also have a large impact on the modelled tracer profiles. Preferential locations for rapid transport from the surface into the upper troposphere are similar in all models, and are mostly concentrated over the western Pacific, the Maritime Continent and the Indian Ocean. In contrast, models do not indicate that upward transport is highest over western Africa.

  8. Flow in the Deep Mantle from Seisimc Anisotropy: Progress and Prospects

    Science.gov (United States)

    Long, M. D.

    2017-12-01

    Observations of seismic anisotropy, or the directional dependence of seismic wavespeeds, provide one some of the most direct constraints on the pattern of flow in the Earth's mantle. In particular, as our understanding of crystallographic preferred orientation (CPO) of olivine aggregates under a range of deformation conditions has improved, our ability to exploit observations of upper mantle anisotropy has led to fundamental discoveries about the patterns of flow in the upper mantle and the drivers of that flow. It has been a challenge, however, to develop a similar framework for understanding flow in the deep mantle (transition zone, uppermost lower mantle, and lowermost mantle), even though there is convincing observational evidence for seismic anisotropy at these depths. Recent progress on the observational front has allowed for an increasingly detailed view of mid-mantle anisotropy (transition zone and uppermost lower mantle), particularly in subduction systems, which may eventually lead to a better understanding of mid-mantle deformation and the dynamics of slab interaction with the surrounding mid-mantle. New approaches to the observation and modeling of lowermost mantle anisotropy, in combination with constraints from mineral physics, are progressing towards interpretive frameworks that allow for the discrimination of different mantle flow geometries in different regions of D". In particular, observational strategies that involve the use of multiple types of body wave phases sampled over a range of propagation azimuths enable detailed forward modeling approaches that can discriminate between different mechanisms for D" anisotropy (e.g., CPO of post-perovskite, bridgmanite, or ferropericlase, or shape preferred orientation of partial melt) and identify plausible anisotropic orientations. We have recently begun to move towards a full waveform modeling approach in this work, which allows for a more accurate simulation for seismic wave propagation. Ongoing

  9. Siberia, the wandering northern terrane, and its changing geography through the Palaeozoic

    Science.gov (United States)

    Cocks, L. Robin M.; Torsvik, Trond H.

    2007-05-01

    -Siberia, the North China Terrane, the Manchurides terranes (including the Khingan-Bureya Massif area), the Gurvanshayan Terrane, the Ala Shan Terrane, the Qaidam-Qilian Terrane, the Tarim Terrane, the Junggar Terrane, the Tien Shan terranes and the various Kazakh terranes, did not become part of the Siberian Terrane assemblage until they accreted to it in the Upper Palaeozoic or later during the formation of Pangea. The Farewell Terrane of Alaska includes typical Lower and Middle Palaeozoic Siberian endemic faunas, but its Palaeozoic position is unknown. Cambrian to Early Silurian palaeomagnetic poles from the southern and northern parts of the Siberian Craton differ, but can be matched with an Euler pole of 60°N, 120°E and a rotation angle of 13°. We link this observation with Devonian rifting in the Viljuy Basin near the centre of the craton and also postulate that this rifting rejuvenated an older Precambrian rift zone, since 1-1.1 Ga poles from southern and northern Siberia differ as much as 23° around the same Euler pole. A revised Palaeozoic apparent polar wander (APW) path is presented for the Siberian Craton in which pre-Devonian poles are corrected for Viljuy Basin rifting. There is also much Late Devonian tectonic activity in the Altai-Sayan area, which may be linked. The APW path implies that Siberia was located at low southerly latitudes at the dawn of the Palaeozoic and slowly drifted northward (different APW path alternatives that result in two very different convergence scenarios between Siberia and Baltica/Kazakh terranes. There are a newly-constructed succession of palaeogeographic maps of Siberia and its nearby areas at various times from the Cambrian to the Permian as, firstly, the peri-Siberian terranes and, secondly, the remainder of the Central Asian terranes accreted to it. Prior to the Early Ordovician, Siberia was in the southern hemisphere, but after that it drifted northwards and for most of the Phanerozoic it has been one of the few larger

  10. Portable audio magnetotellurics - experimental measurements and joint inversion with radiomagnetotelluric data from Gotland, Sweden

    Science.gov (United States)

    Shan, Chunling; Kalscheuer, Thomas; Pedersen, Laust B.; Erlström, Mikael; Persson, Lena

    2017-08-01

    Field setup of an audio magnetotelluric (AMT) station is a very time consuming and heavy work load. In contrast, radio magnetotelluric (RMT) equipment is more portable and faster to deploy but has shallower investigation depth owing to its higher signal frequencies. To increase the efficiency in the acquisition of AMT data from 10 to 300 Hz, we introduce a modification of the AMT method, called portable audio magnetotellurics (PAMT), that uses a lighter AMT field system and (owing to the disregard of signals at frequencies of less than 10 Hz) shortened data acquisition time. PAMT uses three magnetometers pre-mounted on a rigid frame to measure magnetic fields and steel electrodes to measure electric fields. Field tests proved that the system is stable enough to measure AMT fields in the given frequency range. A PAMT test measurement was carried out on Gotland, Sweden along a 3.5 km profile to study the ground conductivity and to map shallow Silurian marlstone and limestone formations, deeper Silurian, Ordovician and Cambrian sedimentary structures and crystalline basement. RMT data collected along a coincident profile and regional airborne very low frequency (VLF) data support the interpretation of our PAMT data. While only the RMT and VLF data constrain a shallow ( 20-50 m deep) transition between Silurian conductive ( 1000 Ωm resistivity) limestone, the single-method inversion models of both the PAMT and the RMT data show a transition into a conductive layer of 3 to 30 Ωm resistivity at 80 m depth suggesting the compatibility of the two data sets. This conductive layer is interpreted as saltwater saturated succession of Silurian, Ordovician and Cambrian sedimentary units. Towards the lower boundary of this succession (at 600 m depth according to boreholes), only the PAMT data constrain the structure. As supported by modelling tests and sensitivity analysis, the PAMT data only contain a vague indication of the underlying crystalline basement. A PAMT and RMT

  11. Geological and physicochemical controls of the spatial distribution of partition coefficients for radionuclides (Sr-90, Cs-137, Co-60, Pu-239,240 and Am-241) at a site of nuclear reactors and radioactive waste disposal (St. Petersburg region, Russian Federation).

    Science.gov (United States)

    Rumynin, Vyacheslav G; Nikulenkov, Anton M

    2016-10-01

    The paper presents a study of the sorption properties of sediments of different geological ages and lithological types, governing radionuclide retention in the subsurface (up to 160 m beneath the surface) within the area of potential influence of the Northwestern Center of Atomic Energy (NWCAE), St. Petersburg region, RF. The focus of this work is mostly on the sedimentary rocks of two types, i.e., weakly cemented sandstone and lithified clay formations of Cambrian and Vendian series. The first lithological unit is associated with a groundwater reservoir (Lomonosov aquifer), and the second one, with both a relative aquitard in the upper part of the Vendian formation (Kotlin clay) and a regional aquifer (Gdov aquifer) in the lower part of the formation. The main mechanisms responsible for the variability of the sorption distribution coefficient (Kd, defined as the ratio of the concentration of solute on solid phase to its concentration in solution at equilibrium) was identified for radionuclides such as Sr-90, Cs-137, Co-60, Pu-239,240, and Am-241. It was shown that the main factors contributing to the chemical heterogeneity of the Cambrian sandstone were related to the presence of secondary minerals (iron and magnesium oxides and hydroxides produced by the weathering process) in trace amounts, forming correlated layer structures. The statistical analysis of nonlinear isotherms confirmed this conclusion. For the Vendian formation, a determinate trend was established in the Kd change over depth as a result of temporal trends in the sedimentation process and pore-water chemistry. The geostatistical characteristics and the spatial correlation models for describing linear sorption of different radionuclides are not identical, and the exhibition of chemical heterogeneity of sedimentary rock of a particular lithological type depends on radionuclide chemistry. Moreover, variogram analysis for some Kd data sets (both in Cambrian and Vendian formations) demonstrates the

  12. Geochronological data on the Amsinassene-Tefedest Block (Central Hoggar, Algerian Sahara) and evidence for its polycyclic evolution

    International Nuclear Information System (INIS)

    Vialette, Y.; Vitel, G.

    1979-01-01

    The history of the Amsinassene-Tefedest Block, in the central Hoggar domain, is characterized by a polycyclic evolution. The unreliable 1970 Ma age obtained on the Arechchoum gneisses, known to be Suggarian-Eburnean, might represent the effect of the Eburnean orogeny. A Rb/Sr whole-rock age on the leucocratic fractions of gneisses point to a kibaran migmatization. This age confirms the existence of a Kibaran orogeny shown in the Aleksod area. The Pharusian-Pan African cycle, in this domain, is characterized by the emplacement of huge granitic bodies during two distinct magnetic phases: one of Late Proterozoic age (670 Ma) or Imezzarian phase, the other of Cambrian age as shown by the 546 and 515 Ma Rb/Sr whole-rock ages obtained on late kinematic granitic plutons, Iskelian phase. The younger mineral ages (470-430 Ma) indicate late vertical uplift of the central Hoggar. (Auth.)

  13. Large colonial organisms with coordinated growth in oxygenated environments 2.1 Gyr ago

    DEFF Research Database (Denmark)

    El Albani, Abderrazak; Bengtson, Stefan; Canfield, Donald Eugene

    2010-01-01

    of colonial organisms. The structures are up to 12 cm in size and have characteristic shapes, with a simple but distinct ground pattern of flexible sheets and, usually, a permeating radial fabric. Geochemical analyses suggest that the sediments were deposited under an oxygenated water column. Carbon...... and sulphur isotopic data indicate that the structures were distinct biogenic objects, fossilized by pyritization early in the formation of the rock. The growth patterns deduced from the fossil morphologies suggest that the organisms showed cell-to-cell signalling and coordinated responses, as is commonly...... associated with multicellular organization(9). The Gabon fossils, occurring after the 2.45-2.32-Gyr increase in atmospheric oxygen concentration(10), may be seen as ancient representatives of multicellular life, which expanded so rapidly 1.5 Gyr later, in the Cambrian explosion....

  14. The amphioxus genome and the evolution of the chordate karyotype

    Energy Technology Data Exchange (ETDEWEB)

    Putnam, Nicholas H.; Butts, Thomas; Ferrier, David E.K.; Furlong, Rebecca F.; Hellsten, Uffe; Kawashima, Takeshi; Robinson-Rechavi, Marc; Shoguchi, Eiichi; Terry, Astrid; Yu, Jr-Kai; Benito-Gutierrez, Elia; Dubchak, Inna; Garcia-Fernandez, Jordi; Gibson-Brown, Jeremy J.; Grigoriev, Igor V.; Horton, Amy C.; de Jong, Pieter J.; Jurka, Jerzy; Kapitonov, Vladimir; Kohara, Yuji; Kuroki, Yoko; Lindquist, Erika; Lucas, Susan; Osoegawa, Kazutoyo; Pennacchio, Len A.; Salamov, Asaf A.; Satou, Yutaka; Sauka-Spengler, Tatjana; Schmutz[, Jeremy; Shin-I, Tadasu; Toyoda, Atsushi; Bronner-Fraser, Marianne; Fujiyama, Asao; Holland, Linda Z.; Holland, Peter W. H.; Satoh, Nori; Rokhsar, Daniel S.

    2008-04-01

    Lancelets ('amphioxus') are the modern survivors of an ancient chordate lineage with a fossil record dating back to the Cambrian. We describe the structure and gene content of the highly polymorphic {approx}520 million base pair genome of the Florida lancelet Branchiostoma floridae, and analyze it in the context of chordate evolution. Whole genome comparisons illuminate the murky relationships among the three chordate groups (tunicates, lancelets, and vertebrates), and allow reconstruction of not only the gene complement of the last common chordate ancestor, but also a partial reconstruction of its genomic organization, as well as a description of two genome-wide duplications and subsequent reorganizations in the vertebrate lineage. These genome-scale events shaped the vertebrate genome and provided additional genetic variation for exploitation during vertebrate evolution.

  15. Multi-data integration of exploration criteria and selection of prospecting targets

    International Nuclear Information System (INIS)

    Dechang, L.; Jingke, Z.; Maorong, S.; Guojuan, W.

    1991-01-01

    In this paper based on the analysis of the exploration criteria for Shengyuan Basin-a uranium ore field, the multi-data integration and information extraction of exploration criteria are carried out on computer and image processing system so that the areas with best combinations of exploration criteria are directly displayed on the screen. Six prospecting targets are selected through the field examination. Shengyuan basin in Jiangxi province is a uranium-producing, Jurassic Cretaceous volcanic-sedimentary basin with an area of about 400 sq km. Its basement consists of Sinian-Cambrian rocks with Caledonian granites intruded. Several uranium deposits, occurrences and anomalies were discovered over the basin region which, therefore, becomes a very important uranium ore field in China

  16. Comparison among chemical, mineralogical and physical analysis from alluvial clays from counties of Southwest of Minas Gerais state (Brazil)

    International Nuclear Information System (INIS)

    Gaspar Junior, L.A.; Varajao, A.F.D.C.; Souza, M.H.O.; Moreno, M.M.T.

    2011-01-01

    The studied area is located in the southwestern portion of Minas Gerais State, encompassing the counties of Alfenas, Areado, Machado, Poco Fundo, Campestre, Serrania, Monte Belo, Bandeira do Sul, Botelhos and Cabo Verde. This region is dominated by strongly weathered pre-cambrian rocks in association with colluvial-alluvial sediments. The present work consisted in a comparison among the mineralogical (X-Ray Diffraction), textural (Laser Granulometry), chemical (X-Ray Fluorescence) and technological (mechanical resistance, water absorption, etc, made in specimen tests) properties of the clays collected on potteries located in these counties. The mineralogical and chemical analysis displayed the kaolinitic nature of the clays from this region, showing also small amount of interlayered clays and large amount of quartz. The best results of physical analysis were obtained for clays from the counties of Cabo Verde and Monte Belo due to the presence of lower values of SiO 2 (quartz) associated with a finer particle size distribution. (author)

  17. Petrology and geochronology of the Cacapava do Sul batholith, state of Rio Grande do Sul, Brazil

    International Nuclear Information System (INIS)

    Sartori, P.L.P.; Kawashita, K.

    1985-01-01

    The batholith of Cacapava do Sul, Brazil, is composed of granitic rocks represented by leucogranites, syenogranites, monzogranites and granodiorites, arranged in a complex way. These rocks represent a calcalkaline suite of compressional tectonic setting. The general characteristics described with respect to it's petrography, chemical composition and geological setting show similarities with mesozone plutons. The pluton intruded the metamorphic rocks of the Vacacai Formation and the type of emplacement mechanism was forceful. According to the Rb-Sr total rock isochron age determinations, its consolidation took place throughout the Cambrian period. This result agrees with previous K-Ar age determinations. The intrusion occurred at the end of the Brasiliano orogenic cycle, when the metamorphic and folding phenomena had already ceased and the morphogenesis was in progress, since the temperature for radiometric argon retention was reached rapidly. (D.J.M.) [pt

  18. An interpretation of the tectonostratigraphic framework of the Murray Basin region of southeastern Australia, based on an examination of airborne magnetic patterns

    Science.gov (United States)

    Brown, C. M.; Tucker, D. H.; Anfiloff, V.

    1988-11-01

    New pixel map representations of regional total magnetic intensity data reveal previously unknown characteristics of the basement concealed beneath thin Cainozoic sediments of the Murray Basin in southeastern Australia. Interpretations of magnetic patterns in terms of structural features allow a revised interpretation of the nature of the tectonostratigraphic framework underlying and flanking the basin. The magnetic data indicate that arcuate or curvilinear structural trends under the Murray Basin do not conform with those of the exposed Lachlan Fold Belt to the east and suggest that the basement concealed beneath the basin, together with that exposed in the Victorian Highlands to the south, forms a distinct composite tectonostratigraphic terrane. Beneath the southwestern Murray Basin ?Proterozoic-Lower Cambrian metasediments of the Padthaway Ridge of the Kanmantoo Fold Belt display a northwesterly trending structural grain and a previously unsuspected continuity of structural trend with Adelaidean-Cambrian rocks of the Mount Lofty Ranges to the west. In the south, Cambrian volcanics of the Black Range and Stavely greenstone belts have similar magnetic response and appear to be components of a single elongate and strongly magnetic domain which extends to the northwest for at least 400 km (Stavely Belt). To the north a similar but entirely concealed northeasterly trending magnetic domain can also be interpreted as volcanics (Lake Wintlow Belt). Together these two magnetic domains appear to form an arcuate zone of volcanics, with a concave-to-the-east configuration, located at a possible suture between the Lachlan and Kanmantoo Fold Belts beneath the western Murray Basin. In the south the magnetic imagery indicates that metasediments of the ?Cambro-Ordovician Stawell Belt produce magnetic patterns distinct from those produced by the metasediments of the adjacent Ordovician Bendigo Belt, which can itself be subdivided into a number of areas of distinct magnetic

  19. Proceedings of the bright futures in Canada conference : building talent for a powerful tomorrow : powerline technician symposium

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2009-07-01

    This powerline technician symposium was held as part of the Electricity Sector Council (ESC) project conducted to report on emerging practices related to the recruitment, retention, and training of powerline technicians. Participants at the symposium were provided with an in-depth discussion of the ESC's situational analysis of the powerline technical trade in Canada. Electric power industry professionals from across Canada discussed regional practices related to the training and recruitment of new powerline technicians. Training programs discussed at the symposium included Cambrian College's powertechmodel; New Brunswick Power's mobile learning program; Hydro Ottawa's apprentice program; and Bright Futures BC's apprentice program. Career materials and methods of promoted the skilled labour market in Canada were also presented. The symposium featured a panel discussion as well as 4 panel PowerPoint presentations. tabs., figs.

  20. Field examination of shale and argillite in northern Nye County, Nevada

    International Nuclear Information System (INIS)

    Connolly, J.R.; Woodward, L.A.; Emanuel, K.M.; Keil, K.

    1981-12-01

    Thirty-two locales underlain by clay-rich strata ranging from Cambrian Pioche Shale to Mississippian Chainman Shale and equivalents were examined in northern Nye County, Nevada. The text of the report summarizes data for each stratigraphic unit examined. Checklists for tabulating field data at each locale are included in an appendix. Working guidelines used to evaluate the locales include a minimum thickness of 150 m (500 ft) of relatively pure clay-rich bedrock, subsurface depth between 150 m (500 ft) and 900 m (3000 ft), low topographic relief, low seismic and tectonic activity, and avoidance of areas with mineral resource production or potential. Field studies indicate that only the Chainman Shale, specifically in the central and northern parts of the Pancake Range, appears to contain sites that meet these guidelines

  1. National uranium resource evaluation: Sheridan Quadrangle, Wyoming and Montana

    International Nuclear Information System (INIS)

    Damp, J.N.; Jennings, M.D.

    1982-04-01

    The Sheridan Quadrangle of north-central Wyoming was evaluated for uranium favorability according to specific criteria of the National Uranium Resource Evaluation program. Procedures consisted of geologic and radiometric surveys; rock, water, and sediment sampling; studying well logs; and reviewing the literature. Five favorable environments were identified. These include portions of Eocene Wasatch and Upper Cretaceous Lance sandstones of the Powder River Basin and Lower Cretaceous Pryor sandstones of the Bighorn Basin. Unfavorable environments include all Precambrian, Cambrian, Ordovician, Permian, Triassic, and Middle Jurassic rocks; the Cretaceous Thermopolis, Mowry, Cody, Meeteetse, and Bearpaw Formations; the Upper Jurassic Sundance and Morrison, the Cretaceous Frontier, Meseverde, Lance, and the Paleocene Fort Union and Eocene Willwood Formations of the Bighorn Basin; the Wasatch Formation of the Powder River Basin, excluding two favorable areas and all Oligocene and Miocene rocks. Remaining rocks are unevaluated

  2. Aquatic characterization for resources at risk in eastern Canada

    Energy Technology Data Exchange (ETDEWEB)

    Fraser, A S

    1986-12-01

    To ascertain quantitative estimates of resources at risk for eastern Canada, linkage must be made between geological terrain sensitivity to acid deposition and water chemistry. An evaluation has been made of watershed areas principally in the Province of Quebec to identify and characterize factors related to LRTAP effects. The watershed areas are geographically located within the bounds of the high sulphate deposition zone of the continental plume. To identify specific test watersheds for detailed analysis, alkalinity frequency distributions were computed. A selection of watersheds has been made that spans the Pre-Cambrian shield region of the Laurentian highlands, the St. Lawrence lowlands and the Gaspe Peninsula. There is evidence that areas in the far eastern areas of Quebec, removed from strong anthropogenic sources may be considered as approaching critical levels of alkalinity. Ionic composition for selected watersheds display similar chemical characteristics. These differences have been assessed in light of the common effects of sulphate deposition. 11 references.

  3. Subsurface-controlled geological maps for the Y-12 plant and adjacent areas of Bear Creek Valley

    International Nuclear Information System (INIS)

    King, H.L.; Haase, C.S.

    1987-04-01

    Bear Creek Valley in the vicinity of the US Department of Energy Y-12 Plant is underlain by Middle to Late Cambrian strata of the Conasauga Group. The group consists of interbedded limestones, shales, mudstones, and siltstones, and it can be divided into six discrete formations. Bear Creek Valley is bordered on the north by Pine Ridge, which is underlain by sandstones, siltstones, and shales of the Rome Formation, and on the south by Chestnut Ridge, which is underlain by dolostones of the Knox Group. Subsurface-controlled geological maps illustrating stratigraphic data and formational contacts for the formations within the Conasauga Group have been prepared for the Y-12 Plant vicinity and selected areas in Bear Creek Valley westward from the plant. The maps are consistent with all available surface and subsurface data for areas where sufficient data exist to make map construction feasible. 13 refs

  4. When a 520 million-year-old Chengjiang fossil meets a modern micro-CT--a case study.

    Science.gov (United States)

    Liu, Yu; Scholtz, Gerhard; Hou, Xianguang

    2015-08-04

    The 520 million-year-old Chengjiang biota of China (UNESCO World Heritage) presents the earliest known evidence of the so-called Cambrian Explosion. Studies, however, have mainly been limited to the information exposed on the surface of the slabs. Thus far, structures preserved inside the slabs were accessed by careful removal of the matrix, in many cases with the unfortunate sacrifice of some "less important" structures, which destroys elements of exceptionally preserved specimens. Here, we show for the first time that microtomography (micro-CT) can reveal structures situated inside a Chengjiang fossil slab without causing any damage. In the present study a trilobitomorph arthropod (Xandarella spectaculum) can be reliably identified only with the application of micro-CT. We propose that this technique is an important tool for studying three-dimensionally preserved Chengjiang fossils and, most likely, also those from other biota with a comparable type of preservation, specifically similar iron concentrations.

  5. When a 520 million-year-old Chengjiang fossil meets a modern micro-CT – a case study

    Science.gov (United States)

    Liu, Yu; Scholtz, Gerhard; Hou, Xianguang

    2015-01-01

    The 520 million-year-old Chengjiang biota of China (UNESCO World Heritage) presents the earliest known evidence of the so-called Cambrian Explosion. Studies, however, have mainly been limited to the information exposed on the surface of the slabs. Thus far, structures preserved inside the slabs were accessed by careful removal of the matrix, in many cases with the unfortunate sacrifice of some “less important” structures, which destroys elements of exceptionally preserved specimens. Here, we show for the first time that microtomography (micro-CT) can reveal structures situated inside a Chengjiang fossil slab without causing any damage. In the present study a trilobitomorph arthropod (Xandarella spectaculum) can be reliably identified only with the application of micro-CT. We propose that this technique is an important tool for studying three-dimensionally preserved Chengjiang fossils and, most likely, also those from other biota with a comparable type of preservation, specifically similar iron concentrations. PMID:26238773

  6. Study of the gas contents of rocks: An approach to the evolution of atmospheres on the earth and planets

    Science.gov (United States)

    Barker, C.

    1972-01-01

    A high vacuum system was built for extracting volatiles from rocks either by heating or crushing, and preliminary analyses of the volatiles were made for selected terrestrial basalts and granites. The apparatus and experimental procedures are described, and the major problems associated with water measurement and choice of argon to replace neon as the internal standard are discussed. Preliminary analyses of granites and basalts indicate the following: All analyses lie in the H2O-CO2-CO triangle on a C-H-O ternary diagram. The compositions of the volatiles plot in distinct, but overlapping, areas of the C-H-O diagram. Pre-Cambrian granites have a higher volatile content than younger granites. Continental basalts have a higher volatile content than oceanic basalts.

  7. Discussion of metallogenic substance source of Xiangshan uranium orefield

    International Nuclear Information System (INIS)

    Shao Fei; Tang Xiangsheng; Zou Maoqin; Hu Maomei; He Xiaomei; Chen Xiaoming; Xu Hengli

    2008-01-01

    Analysis of uranium source is a key problem for study on uranium deposit genesis. Based on analysis of general implication for determination of uranium source on distribution characteristics of regional uranium abundance, according to temporal and spatial evolution of regional metallogenic substances in process of geological history, and combining with indication for analysis of uranium source by Pb isotopic composition of ores and REE geochemistry of both rocks and ores in Xiangshan orefield, Lower Cambrian strata are determined as regional uranium source bed, Xiangshan volcanic basin is the accumulation area for regional metallogenic substances, magma and hydrothermal solution of post magmatism are media for uranium. Magmatism realizes uranium migration from 'source' to 'accumulation'. In process of magmatic evolution, uranium transformed into gas phase to provide substance base for uranium mineralization. Fluid-rock interaction of post magmatism also promoted some uranium from schist of the basement and rhyodacite into metallogenic solution. (authors)

  8. Marine diatom study and stratigraphy of cenozoic sediments in the coastal plain between Morro da Jureia and Barra do Una, State of Sao Paulo, Brazil

    International Nuclear Information System (INIS)

    Servant-Vildary, S.; Soguio, K.

    1992-01-01

    Samples of sediments obtained from cores of four wells drilled by Nuclebras, in the coastal plain of State of Sao Paulo, have been here studied from diatom flora viewpoint. The irregular surface of the crystalline pre-Cambrian basements rocks is locally covered by the Pliocene Pariquera-Acu Formation - like deposits, whose contact with the Quaternary sediments is flat, being situated about 40 m bellow the present sea-level. The contact between the Holocene Santos Formation and the probable Pleistocene Cananeia Formation is very difficult to be recognized. It has been tentatively established based on two radiocarbon ages. Dominantly clayey-silty intervals from the wells F-003 and F-004, probably related to the Cananeia Formation, have been selectively sampled and studied for definition of their diatom flora assemblage. (author)

  9. Utilization of geophysical nuclear methods on apatite mines from Gaviao and gold from Jacobina mountain - Bahia, Brazil

    International Nuclear Information System (INIS)

    Barreto, P.T.

    1974-01-01

    This thesis is part of the sub-project Analysis of Rocks and Minerals by Gamma-Spectrometry of the Program of Research and Postgraduation in Geophysics of the Federal University of Bahia. It presents: 1) the results of preliminary radio-geological surveying in Cenozoic, Mesozoic and Pre-Cambrian lands between the cities of Salvador and Miguel Calmon; detailed radiogeological works in two radioactive anomalous areas: Gaviao at Riachao de Jacuipe town, and Canavieiras mine and vicinities at Jacobina town, state of Bahia. The combined results of field gamma-ray survey, gamma-spectrometry accomplished at laboratory from samples, petrographical and mineralogical studies led to the correlation between apatita mineralization with thorium, and Gold with uranium in the Comglomerates of Serra do Corrego formation giving the possibilities in both cases of making the prospection and exploration by the cintilometry. (author)

  10. Ordovician of the Sauk megasequence in the Ozark region of northern Arkansas and parts of Missouri and adjacent states: Chapter 11

    Science.gov (United States)

    Ethington, Raymond L.; Repetski, John E.; Derby, James R.

    2012-01-01

    Exposures of Ordovician rocks of the Sauk megasequence in Missouri and northern Arkansas comprise Ibexian and lower Whiterockian carbonates with interspersed sandstones. Subjacent Cambrian strata are exposed in Missouri but confined to the subsurface in Arkansas. The Sauk-Tippecanoe boundary in this region is at the base of the St. Peter Sandstone. Ulrich and associates divided the Arkansas section into formations early in the 20th century, principally based on sparse collections of fossil invertebrates. In contrast, the distribution of invertebrate faunas and modern studies of conodonts will be emphasized throughout this chapter. Early workers considered many of the stratigraphic units to be separated by unconformities, but modern analysis calls into question the unconformable nature of some of their boundaries. The physical similarity of the several dolomites and sandstones, complex facies relations, and lack of continuous exposures make identification of individual formations difficult in isolated outcrops.

  11. Radiometric geochronology of the Himalaya

    International Nuclear Information System (INIS)

    Saini, H.S.

    1982-01-01

    The radiometric age data obtained by different dating methods have been interpreted in terms of possible orogenic activities prevailing in the Himalaya. In general, the age data confirm four main events, the Precambrian, the Late Precambrian-Cambrian Assyntian (Caledonian), the Late Palaeozoic-Hercynian and the Late Cretaceous-Tertiary Himalayan orogeny. The mineral dates are particularly significant in delineating different phases of the last i.e. the Himalayan orogeny which indicates main activity of the young Himalayan metamorphism around 70 to 50 Ma and followed by a momentous phase of major uplift during 25 to 10 Ma, which was responsible for the rise of the deeper part of the Himalaya into great folds and thrust slices and the formation of nappe structures. (author)

  12. A paired apatite and calcite clumped isotope thermometry approach to estimating Cambro-Ordovician seawater temperatures and isotopic composition

    Science.gov (United States)

    Bergmann, Kristin D.; Finnegan, Seth; Creel, Roger; Eiler, John M.; Hughes, Nigel C.; Popov, Leonid E.; Fischer, Woodward W.

    2018-03-01

    The secular increase in δ18O values of both calcitic and phosphatic marine fossils through early Phanerozoic time suggests either that (1) early Paleozoic surface temperatures were high, in excess of 40 °C (tropical MAT), (2) the δ18O value of seawater has increased by 7-8‰ VSMOW through Paleozoic time, or (3) diagenesis has altered secular trends in early Paleozoic samples. Carbonate clumped isotope analysis, in combination with petrographic and elemental analysis, can deconvolve fluid composition from temperature effects and therefore determine which of these hypotheses best explain the secular δ18O increase. Clumped isotope measurements of a suite of calcitic and phosphatic marine fossils from late Cambrian- to Middle-late Ordovician-aged strata-the first paired fossil study of its kind-document tropical sea surface temperatures near modern temperatures (26-38 °C) and seawater oxygen isotope ratios similar to today's ratios.

  13. Physicomechanical parameters of sedimentary rocks in eastern Sichuan, China

    International Nuclear Information System (INIS)

    Guo, Jian; Sun, Yan; Shu, Liangshu; Zhu, Wenbin; Wang, Feng; Li, Benliang; Liu, Deliang

    2009-01-01

    Rock samples were collected and selected from the sedimentary covering strata from Cambrian to Jurassic in eastern Sichuan, China, which belongs to the Upper Yangtze plate. Physicomechanical parameters were measured systematically. Based on parametric texture characteristics and observation data of geology, five regional layer-slip systems are derived. The five layer-slip systems correspond to five reservoir–cover systems, as the incompetent beds correspond to cover beds and the competent beds to reservoir beds. In comparison with the Middle and Lower Yangtze plates, the physicomechanical parameters, lithologic composition and structural characteristics are basically similar to the Upper Yangtze plate. This comparison offers some insight into the oil and gas reservoir–cover systems in the region

  14. Recent understanding of the Svalbard basement in the light of new radiometric age determinations

    International Nuclear Information System (INIS)

    Ohta, Y.

    1992-01-01

    Several tectonothermal events in the pre-Carboniferous basement of Svalbard during Caledonian and Proterozoic times have been dated recently by radiometric age determinations. Three or four stages have been recognized in the Caledonian period; a post-orogentic graben formation during the Devonian, a late Caledonian event in the Middle Silurian, an earely Caledonian event in the Middle Ordovician and possibly an earliest event in the Middle to Late Cambrian. The Grenvillian event, 950-1270 Ma, has been well established by both radiometric ages and unconformities in Nordaustlandet and southwestern Spitsbergen. Sveco-Karelian ages, 1670-1750 Ma, also have been obtained from Ny Friesland, northerneastern Spitsbergen. Two even older ages (zircon U-Pb) upper intercept ages), 2.1 and 3.2 Ga, may suggest the presence of still older crust in Svalbard and adjacent areas. 40 refs., 2 figs

  15. Rock Rb-Sr ages from Bananal region - Sao Paulo State, Brazil

    International Nuclear Information System (INIS)

    Dias Neto, C.M.; Tassinari, C.G.C.; Silva, M.E.

    1996-01-01

    New Rb-Sr whole rock isochron ages have been determined for the main lithological units that occur in Sao Paulo and Rio de Janeiro States. These rocks belong to Serra do Mar domain. The purpose of this work is to characterize the sequence of the geological events as well as the possible relationship between the different rocks. The geochronological data suggest that the paragneisses and the basement rocks, represented by ortho gneisses nuclei, were generated under amphibolite conditions around 700 Ma. At the same time the leucogranites were generated by partial melting processes and injected into both gneiss types. Tarditectonic granitic magmatic activities took place within ductile shear zones. One of the granites, the Getulandia granite, yielded an age of 514 Ma, falling in the range of the late Brasiliano Cycle which extended into the Middle Cambrian. (author). 9 figs., 1 tab

  16. Nutrient enhanced short rotation coppice for biomass in central Wales

    Energy Technology Data Exchange (ETDEWEB)

    Hodson, R.W.; Slater, F.M.; Lynn, S.F.; Randerson, P.F. [Univ. of Wales (United Kingdom)

    1993-12-31

    Two projects involving short rotation willow coppice are taking place on the eastern side of the Cambrian Mountains in central Wales. One project examines, as an alternative land use, the potential of short rotation willow coppice variously enhanced by combinations of lime, phosphorous and potassium fertilizers and also digested sewage sludge on an acidic upland site at an altitude of 260m. The first year results of this project are described in detail, showing the necessity for limestone additions and also demonstrating that of the four willow varieties established, Salix dasyclados is the only possible, profitable fuel crop. The other project involving willow in a filter bed system is outlined along with an additional project investigating the effect of sewage sludge additions on the Rubus fruticosus production in a birch dominated mixed deciduous woodland.

  17. Géochimie et cadre géodynamique du volcanisme néoprotérozoïque terminal (vendien) du Haut Atlas occidental, Maroc(Geochemical features and tectonic setting of late Neoproterozoic Vendian volcanism in the western High Atlas, Morocco)

    Science.gov (United States)

    Jouhari, A.; El-Archi, A.; Aarab, M.; El-Attari, A.; Ennih, N.; Laduron, D.

    2001-05-01

    Late Neoproterozoic Vendian volcanic and volcaniclastic rocks are widely distributed in the western High Atlas. They are located north of the Tizi n'Test Fault, separating the West African Craton from a northerly adjacent craton. These volcanic rocks overlie a semipelitic formation, which represents the equivalent of the Tidilline and Anzi Formations of the Anti-Atlas. The geochemical characteristics of these volcanic rocks suggest a calc-alkaline active margine environment associated with the post Pan-African tectonics. They differ from those of the Anti-Atlas by their lower content of K 2O. The later rock type was generated by a melting process of the crust subducted beneath the northern craton. A carbonate-shale unit, which contains examples of interstratified calc-alkaline dacite, overlies the volcanic succession, demonstrating that the volcanic activity continued sporadically until Early Cambrian times.

  18. Gravitational Wave Detection in the Introductory Lab

    Science.gov (United States)

    Burko, Lior M.

    2017-05-01

    A long time ago in a galaxy far, far away, two black holes, one of mass 36 solar masses and the other of mass 29 solar masses, were dancing their death waltz, leading to their coalescence and the emission of gravitational waves carrying away with them three solar masses of energy. More precisely, it happened 1.3 billion years ago at a distance of 410 Mpc. When the waves were emitted, the most complex life forms on Earth were eukaryotes. As the gravitational waves propagated toward Earth, it changed much. Five hundred million years after the waves were emitted, or 800 million years ago, the first multicellular life forms emerged on Earth. Earth saw the Cambrian explosion 500 million years ago. Sixty-six million years ago the Cretaceous-Paleogene extinction event caused the disappearance of the dinosaurs. The first modern humans appeared 250,000 years ago.

  19. Ecological interactions in Cloudina from the Ediacaran of Brazil: implications for the rise of animal biomineralization.

    Science.gov (United States)

    Becker-Kerber, Bruno; Pacheco, Mírian Liza Alves Forancelli; Rudnitzki, Isaac Daniel; Galante, Douglas; Rodrigues, Fabio; Leme, Juliana de Moraes

    2017-07-14

    At the Ediacaran/Cambrian boundary, ecosystems witnessed an unparalleled biological innovation: the appearance of shelled animals. Here, we report new paleoecological and paleobiological data on Cloudina, which was one of the most abundant shelled animals at the end of the Ediacaran. We report the close association of Cloudina tubes with microbial mat textures as well as organic-rich material, syndepositional calcite and goethite cement between their flanges, thus reinforcing the awareness of metazoan/microorganism interactions at the end of the Ediacaran. The preservation of in situ tubes suggests a great plasticity of substrate utilization, with evidence of different life modes and avoidance behavior. Geochemical analysis revealed walls composed of two secondary laminae and organic sheets. Some walls presented boreholes that are here described as predation marks. Taken together, these data add further information regarding the structuring of shelled animal communities in marine ecosystems.

  20. Toward understanding the evolution of vertebrate gene regulatory networks: comparative genomics and epigenomic approaches.

    Science.gov (United States)

    Martinez-Morales, Juan R

    2016-07-01

    Vertebrates, as most animal phyla, originated >500 million years ago during the Cambrian explosion, and progressively radiated into the extant classes. Inferring the evolutionary history of the group requires understanding the architecture of the developmental programs that constrain the vertebrate anatomy. Here, I review recent comparative genomic and epigenomic studies, based on ChIP-seq and chromatin accessibility, which focus on the identification of functionally equivalent cis-regulatory modules among species. This pioneer work, primarily centered in the mammalian lineage, has set the groundwork for further studies in representative vertebrate and chordate species. Mapping of active regulatory regions across lineages will shed new light on the evolutionary forces stabilizing ancestral developmental programs, as well as allowing their variation to sustain morphological adaptations on the inherited vertebrate body plan. © The Author 2015. Published by Oxford University Press. All rights reserved. For permissions, please email: journals.permissions@oup.com.

  1. Biologic History and the Cardinal Rule of Life

    Science.gov (United States)

    Schopf, J. W.

    2004-12-01

    ,000 Ma ago, they first evolved slowly -- following the Cardinal Rule of Life -- until ˜1,000 Ma ago when sexual reproduction took over. This development markedly speeded the development of new species that could compete, and eventually dominate, in habitats previously owned by their non-sexual prokaryotic ancestors, as evidenced both in the fossil record and by molecular biology-based rRNA phylogenetic trees. The third innovation was cellular differentiation and multicelluarity. Although the "Cambrian Explosion" -- the great radiation of animal life during the Cambrian Period beginning ˜550 Ma ago -- is commonly viewed as reflecting this event, it seems more a continuum than a step-function change. Evolution speeded in the half-billion years between 1,000 Ma ago and the beginning of the Cambrian: phytoplankton gave rise to multicellular seaweeds by ˜850 Ma; and primitive protozoans, present as early as ˜950 Ma, had by ˜600 Ma given rise to soft-bodied multicelled animals. Soon thereafter, animals developed shelly protective armor -- marking the beginning of the Cambrian Period, and thus of the Phanerozoic Eon. The Phanerozoic history of life is familiar to all, from spore-producing to seed-producing to flowering plants, from animals without backbones to fish, land-dwelling vertebrates, then birds and mammals. Plants ("eatees") and animals ("eaters") co-evolved in sequence. Again, life followed the Cardinal Rule, changing little, then evolving rapidly, as new ecologic opportunities became available.

  2. Lithostratigraphy, sedimentology and paleography from The Arroyo del Soldado group

    International Nuclear Information System (INIS)

    Gaucher, C.; Sprechmann, P.; Montana, J.; Martinez, S.

    1998-01-01

    The lithostratigraphy of the Vendian to Lower Cambrian Arroyo del Soldado Group of the Nico Perez Terrane is presented. The Yerbal Formation is defined and the Barriga Negra Formation is included in the Group. The Arroyo del Soldado Group represents a transgressive - regressive sequence developed on a passive continental margin, reaching a thickness of 5000m. The lithofacies succession is mainly explained by the combination of tectonic processes, global climatic - and sea level changes. Its geographic extension allows the determination of the eastern and southern boundaries of the Nico Perez Terrane. The known surface of this Terrane is therefore considerably increased. Several outcroups previously assigned to the Lavalleja Group are in this paper included in the Arroyo del Soldado Group, using sedimentalogical and paleontological criteria

  3. Volatile earliest Triassic sulfur cycle

    DEFF Research Database (Denmark)

    Schobben, Martin; Stebbins, Alan; Algeo, Thomas J.

    2017-01-01

    model experiment. Exposure of evaporite deposits having a high δ 34S may account for the source change, with a possible role for the Siberian Traps volcanism by magmatic remobilization of Cambrian rock salt. A high sulfur cycle turnover rate would have left the ocean system vulnerable to development......Marine biodiversity decreases and ecosystem destruction during the end-Permian mass extinction (EPME) have been linked to widespread marine euxinic conditions. Changes in the biogeochemical sulfur cycle, microbial sulfate reduction (MSR), and marine dissolved sulfate concentrations during...... fractionation and point to a more universal control, i.e., contemporaneous seawater sulfate concentration.The MSR-trend transfer function yielded estimates of seawater sulfate of 0.6-2.8mM for the latest Permian to earliest Triassic, suggesting a balanced oceanic S-cycle with equal S inputs and outputs...

  4. The influence of rock movement on the stress/strain situation in tunnels or bore holes with radioactive canisters embedded in a bentonite/quartz buffer mass

    International Nuclear Information System (INIS)

    Pusch, R.

    1977-08-01

    The report presents the author's main ideas concerning the possible recurence of large unexpected movements in Swedish pre-Cambrian rock and gives the theoretical basis for the calculation of stress and strain in the canisters and the buffer mass. A rough calculation shows that a sudden and large shear strain at actual depths will only occur along already existing continous weak zones in the bedrock. In situ rock investigations to find and locate weak zones are essential. Shear tests with a model shear apparatus were run with the canister embedded in 10 percent bentonite 90 percent quarz buffer mass. The least favourable theory (Meyerhof) gave high contact pressures which cause high bending momentum on the canister. The stresses can be reduced by changing the geometry of the canister. (L.B.)

  5. Stratigraphic and tectonic revision of Cerro Olivo Complex located of Southeastern of Uruguay

    International Nuclear Information System (INIS)

    Masquelin, E.

    2004-01-01

    This paper presents a stratigraphic and tectonic revision of Cerro Olivo Complex, located in the Southeastern part of the Uruguayan Predevonian Shield. This informal lithostratigraphic unit constitutes the country rock for the emplacement of late-orogenic granitoids, during Neoproterozoic to Cambrian times. This unit groups all the lithodemes affected by deformation and metamorphism. Recent studies indicate the presence of straight gneisses of quartzo-feldspathic composition in the coast of Maldonado Department. These rocks were interpreted as the result of intense deformation in high temperature. These tectonites base a new stratigraphic insight for the complex. They allow their lithotypes to be organized by petrotectonic features, being a function of PT conditions for every last strain process [es

  6. Characteristics of gravity and magnetic field and their relationship with uranium mineralization in northern Guangxi area

    International Nuclear Information System (INIS)

    Shu Xiaojing; Yin Zhongfan; Hao Yuhua; guan Nansheng; Li Xuexun

    1993-08-01

    The characteristics of gravity and magnetic field, deep-seated structures and their relationship with uranium mineralization in Northern Guangxi are investigated. Especially, based on geophysical investigation, the distinguishing features of uranium ore-forming are discussed, involved with the uranium source body, the heating force and mechanical force of granite magma acted on uranium mineralization, the deep-seated geological process, the hydrothermal activity, the formation environments of granite-type uranium deposit, the source of pyrite and its influence on uranium mineralization, the uranium ore-forming of Sinian-Cambrian periods and devonian period formations, and the simple model of uranium ore-forming. On the basis of the relationship of uranium mineralization with geophysical field, as well as the ore-forming geological environments inferred by gravity and magnetic field investigation, the physical-geological model is established in order to predicate uranium prospect

  7. Biomineralization and the carbon isotope record

    International Nuclear Information System (INIS)

    Degens, E.T.; Ittekkot, V.; Kazmierczak, J.

    1986-01-01

    The advent of biomineralization at the turn of the Precambrian/Cambrian boundary has been a major event in the Earth's evolutionary history. With this there has been a major shift from abiotic to biotic formation of minerals such as phosphates and carbonates and, subsequently, silica. The dominant factor which effected this shift is a change in ocean's chemistry with respect to its Ca 2+ and mineral nutrient contents. Mechanism controlling the biotic mineral formation is different from that controlling the abiotic one in that the former is enzymically controlled. It is suggested that this difference is also manifested in the stable carbon isotope fractionation between the two processes and has implication for the interpretation of stable carbon isotope record. (Author)

  8. Stabilization of the coupled oxygen and phosphorus cycles by the evolution of bioturbation

    DEFF Research Database (Denmark)

    Boyle, Richard; Dahl, Tais Wittchen; Dale, A. W.

    2014-01-01

    Animal burrowing and sediment-mixing (bioturbation) began during the run up to the Ediacaran/Cambrian boundary(1-3), initiating a transition(4,5) between the stratified Precambrian(6) and more well-mixed Phanerozoic(7) sedimentary records, against the backdrop of a variable(8,9) global oxygen...... reservoir probably smaller in size than present(10,11). Phosphorus is the long-term(12) limiting nutrient for oxygen production via burial of organic carbon(13), and its retention (relative to carbon) within organic matter in marine sediments is enhanced by bioturbation(14-18). Here we explore...... the biogeochemical implications of a bioturbation-induced organic phosphorus sink in a simple model. We show that increased bioturbation robustly triggers a net decrease in the size of the global oxygen reservoir-the magnitude of which is contingent upon the prescribed difference in carbon to phosphorus ratios...

  9. Notes on the geology and meteorology of sites infected with white-nose syndrome before July 2010 in Southeastern United States

    Science.gov (United States)

    Swezey, Christopher S.; Garrity, Christopher P.

    2011-01-01

    Since 2006, numerous bat colonies in North America have experienced unusually high incidences of mortality. In these colonies, bats are infected by a white fungus named Geomyces destructans, which has been observed on bat muzzles, noses, ears, and (or) wings. Although it is not exactly certain how and why these bats are dying, this condition has been named white-nose syndrome (WNS). WNS appears to have spread from an initial infection site at a cave in New York, and was first identified south of Pennsylvania during January 2009. By the end of June 2010, 41 infected sites had identified in the states of West Virginia, Maryland, Delaware, Virginia, and Tennessee. Most of these sites are natural caves in limestone of either Cambrian-Ordovician age or Silurian-Devonian age. Published air temperature values in these WNS-infected caves range from -3.3 to 15.6 °C, and humidity measurements range from 68 to 100 %.

  10. Solar rotation and activity in the past and their possible influence upon the evolution of life

    International Nuclear Information System (INIS)

    Geyer, E.H.

    1981-01-01

    It is proposed that the rotational angular momentum of the lower Main Sequence stars determines the intensity of their magnetic spot activity. As a consequence of this feedback coupling, the stellar rotation and the activity decay exponentially by magnetic braking of the induced stellar flare- and wind-activity. Therefore, the Sun should have rotated much faster and must have shown a very enhanced activity in its early history. This strong solar activity in the past could have influenced the evolution of terrestrial life, and may explain the stagnation of maritime life for about 2 x 10 9 yr, the diversification of species during the Cambrian formation, and the land conquest by life in the upper Silurian system. (Auth.)

  11. Solar rotation and activity in the past and their possible influence upon the evolution of life

    Energy Technology Data Exchange (ETDEWEB)

    Geyer, E H [Bonn Univ. (Germany, F.R.). Sternwarte

    1981-06-01

    It is proposed that the rotational angular momentum of the lower Main Sequence stars determines the intensity of their magnetic spot activity. As a consequence of this feedback coupling, the stellar rotation and the activity decay exponentially by magnetic braking of the induced stellar flare- and wind-activity. Therefore, the Sun should have rotated much faster and must have shown a very enhanced activity in its early history. This strong solar activity in the past could have influenced the evolution of terrestrial life, and may explain the stagnation of maritime life for about 2 x 10/sup 9/ yr, the diversification of species during the Cambrian formation, and the land conquest by life in the upper Silurian system.

  12. Characterization of a branch of the phylogenetic tree

    International Nuclear Information System (INIS)

    Samuel, Stuart A.; Weng, Gezhi

    2003-04-01

    We use a combination of analytic models and computer simulations to gain insight into the dynamics of evolution. Our results suggest that certain interesting phenomena should eventually emerge from the fossil record. For example, there should be a 'tortoise and hare effect': Those genera with the smallest species death rate are likely to survive much longer than genera with large species birth and death rates. A complete characterization of the behavior of a branch of the phylogenetic tree corresponding to a genus and accurate mathematical representations of the various stages are obtained. We apply our results to address certain controversial issues that have arisen in paleontology such as the importance of punctuated equilibrium and whether unique Cambrian phyla have survived to the present

  13. Large-scale trends in the evolution of gene structures within 11 animal genomes.

    Directory of Open Access Journals (Sweden)

    Mark Yandell

    2006-03-01

    Full Text Available We have used the annotations of six animal genomes (Homo sapiens, Mus musculus, Ciona intestinalis, Drosophila melanogaster, Anopheles gambiae, and Caenorhabditis elegans together with the sequences of five unannotated Drosophila genomes to survey changes in protein sequence and gene structure over a variety of timescales--from the less than 5 million years since the divergence of D. simulans and D. melanogaster to the more than 500 million years that have elapsed since the Cambrian explosion. To do so, we have developed a new open-source software library called CGL (for "Comparative Genomics Library". Our results demonstrate that change in intron-exon structure is gradual, clock-like, and largely independent of coding-sequence evolution. This means that genome annotations can be used in new ways to inform, corroborate, and test conclusions drawn from comparative genomics analyses that are based upon protein and nucleotide sequence similarities.

  14. Luminescence of quartz and feldspar fingerprints provenance and correlates with the source area denudation in the Amazon River basin

    DEFF Research Database (Denmark)

    Sawakuchi, A.O.; Jain, M.; Mineli, T.D.

    2018-01-01

    The Amazon region hosts the world's largest watershed spanning from high elevation Andean terrains to lowland cratonic shield areas in tropical South America. This study explores variations in optically stimulated luminescence (OSL) and infrared stimulated luminescence (IRSL) signals in suspended...... silt and riverbed sands retrieved from major Amazon rivers. These rivers drain Pre-Cambrian to Cenozoic source rocks in areas with contrasting denudation rates. In contrast to the previous studies, we do not observe an increase in the OSL sensitivity of quartz with transport distance; for example...... shield areas (denudation rate ξ=0.04 mmyr−1), while low sensitivity quartz occurs in less stable Andean terrains (ξ=0.24 mmyr−1). An apparent linear correlation between quartz OSL sensitivity and denudation rate suggests that OSL sensitivity may be used as a proxy for erosion rates in the Amazon basin...

  15. Study pf apatite accurrence from Gaviao and Serra de Jacabina gold deposit by scintillometry and gamma spectrometry

    International Nuclear Information System (INIS)

    Barreto, P.T.

    1974-01-01

    This work presents the results of radiogeologic reconnaissance in the Cenozoic, Mesozoic and Pre-Cambrian formations, localized between Salvador and Miguel Calmon, and of the radiogeologic detail study from areas of the radioactive anomalies: Gaviao in the Riacho do Lacuipe and Canavieira Mine, in the Jacobina, Bahia States Scintilometry and gamma spectrometry results make possible to conclude by the association, in the Gaviao's apatite mineralization with throrium and the gold of the Serra de Corrego's conglamerate with uranium, make possible in the both case, orient the Search and the mining by scintilometry. The petrographic study and the radiactivity elements dispersion, suggest a sedimentary primary origin to the regional metamorphic rocks. In the Canavieiras mine was evident the stratigraphic control of the gold, associated to uranium and pirite in the conglomerates. (C.D.G.) [pt

  16. National uranium resource evaluation: Sheridan Quadrangle, Wyoming and Montana

    Energy Technology Data Exchange (ETDEWEB)

    Damp, J N; Jennings, M D

    1982-04-01

    The Sheridan Quadrangle of north-central Wyoming was evaluated for uranium favorability according to specific criteria of the National Uranium Resource Evaluation program. Procedures consisted of geologic and radiometric surveys; rock, water, and sediment sampling; studying well logs; and reviewing the literature. Five favorable environments were identified. These include portions of Eocene Wasatch and Upper Cretaceous Lance sandstones of the Powder River Basin and Lower Cretaceous Pryor sandstones of the Bighorn Basin. Unfavorable environments include all Precambrian, Cambrian, Ordovician, Permian, Triassic, and Middle Jurassic rocks; the Cretaceous Thermopolis, Mowry, Cody, Meeteetse, and Bearpaw Formations; the Upper Jurassic Sundance and Morrison, the Cretaceous Frontier, Meseverde, Lance, and the Paleocene Fort Union and Eocene Willwood Formations of the Bighorn Basin; the Wasatch Formation of the Powder River Basin, excluding two favorable areas and all Oligocene and Miocene rocks. Remaining rocks are unevaluated.

  17. The Potosi Reservoir Model 2014

    Energy Technology Data Exchange (ETDEWEB)

    Smith, Valerie; Adushita, Yasmin; Leetaru, Hannes

    2014-09-30

    As a part of a larger project co-funded by the United States Department of Energy (US DOE) to evaluate the potential of formations within the Cambro-Ordovician strata above the Mt. Simon Sandstone as potential targets for carbon sequestration in the Illinois and Michigan Basins, the Illinois State Geological Survey (ISGS) requested Schlumberger to evaluate the potential injectivity and carbon dioxide (CO2) plume size of the Cambrian Potosi Formation. The evaluation of this formation was accomplished using wireline data, core data, pressure data, and seismic data from this project as well as two other separately funded projects: the United States Department of Energy-funded Illinois Basin – Decatur Project (IBDP) being conducted by the Midwest Geological Sequestration Consortium (MGSC) in Macon County, Illinois, and the Illinois Industrial Carbon Capture and Sequestration (IL-ICCS) project funded through the American Recovery and Reinvestment Act.

  18. Neoproterozoic stratigraphic framework of the Tarim Craton in NW China: Implications for rift evolution

    Science.gov (United States)

    Wu, Lin; Guan, Shuwei; Zhang, Shuichang; Yang, Haijun; Jin, Jiuqiang; Zhang, Xiaodan; Zhang, Chunyu

    2018-06-01

    The Tarim Craton is overlain by thick Neoproterozoic sedimentary successions in rift tectonic setting. This study examines the latest outcrop, seismic, and drilling core data with the objective of investigating the regional stratigraphy to deeply recognize the evolution of rifting in the craton. Cryogenian to Lower Ediacaran successions are mainly composed of clastic rocks with thicknesses of 2000-3000 m, and the Upper Ediacaran successions are composed of carbonate rocks with thicknesses of 500-800 m. The rift basins and stratigraphic zones are divided into northern and southern parts by a central paleo-uplift. The northern rift basin extends through the northern Tarim Craton in an E-W direction with two depocenters (Aksu and Kuruktag). The southern rift basin is oriented NE-SW. There are three or four phases of tillites in the northern zone, while there are two in the southern zone. Given the north-south difference of the stratigraphic framework, the northern rift basin initiated at ca. 740 Ma and the southern rift basin initiated at ca. 780 Ma. During the Cryogenian and Ediacaran, the northern and southern rift basins were separated by the central paleo-uplift, finally connecting with each other in the early Cambrian. Tectonic deformation in the Late Ediacaran led to the formation of a parallel unconformity in the rift basins and an angular unconformity in the central paleo-uplift. The Neoproterozoic rift basins continued to affect the distribution of Lower Cambrian hydrocarbon source rocks. The north-south distribution and evolution of the rift basins in the Tarim Craton have implications for reconstructions of the Rodinia supercontinent.

  19. A new perspective on the significance of the Ranotsara shear zone in Madagascar

    Science.gov (United States)

    Schreurs, Guido; Giese, Jörg; Berger, Alfons; Gnos, Edwin

    2010-12-01

    The Ranotsara shear zone in Madagascar has been considered in previous studies to be a >350-km-long, intracrustal strike-slip shear zone of Precambrian/Cambrian age. Because of its oblique strike to the east and west coast of Madagascar, the Ranotsara shear zone has been correlated with shear zones in southern India and eastern Africa in Gondwana reconstructions. Our assessment using remote sensing data and field-based investigations, however, reveals that what previously has been interpreted as the Ranotsara shear zone is in fact a composite structure with a ductile deflection zone confined to its central segment and prominent NW-SE trending brittle faulting along most of its length. We therefore prefer the more neutral term “Ranotsara Zone”. Lithologies, tectonic foliations, and axial trace trajectories of major folds can be followed from south to north across most of the Ranotsara Zone and show only a marked deflection along its central segment. The ductile deflection zone is interpreted as a result of E-W indentation of the Antananarivo Block into the less rigid, predominantly metasedimentary rocks of the Southwestern Madagascar Block during a late phase of the Neoproterozoic/Cambrian East African Orogeny (c. 550-520 Ma). The Ranotsara Zone shows significant NW-SE striking brittle faulting that reactivates part of the NW-SE striking ductile structures in the flexure zone, but also extends along strike toward the NW and toward the SE. Brittle reactivation of ductile structures along the central segment of the Ranotsara Zone, confirmed by apatite-fission track results, may have led to the formation of a shallow Neogene basin underlying the Ranotsara plain. The present-day drainage pattern suggests on-going normal fault activity along the central segment. The Ranotsara Zone is not a megascale intracrustal strike-slip shear zone that crosscuts the entire basement of southern Madagascar. It can therefore not be used as a piercing point in Gondwana

  20. Magnetic stratigraphy of the Ordovician in the lower reach of the Kotuy River: the age of the Bysy-Yuryakh stratum and the rate of geomagnetic reversals on the eve of the superchron

    Science.gov (United States)

    Pavlov, V. E.; Tolmacheva, T. Yu.; Veselovskiy, R. V.; Latyshev, A. V.; Fetisova, A. M.; Bigun, I. V.

    2017-09-01

    Until recently, the existing data prevented the geophysicists from accurately dating the Bysy-Yuryakh stratum, which outcrops in the middle reach of the Kotuy River, constraining the time of its formation to a wide interval from the end of the Late Cambrian to the beginning of the Silurian. The obtained paleomagnetic data unambiguously correlate the Bysy-Yuryakh stratum to the Nyaian regional stage and constrain its formation, at least a considerable part of it, by the Tremadocian. This result perfectly agrees with the data on the Bysy-Yuryakh conodonts studied in this work and yields a spectacular example of the successful application of paleomagnetic studies in solving important tasks of stratigraphy and, correspondingly, petroleum geology. Within the Bysy-Yuryakh stratum, we revealed a large normal-polarity interval corresponding to the long (>1 Ma) period when the geomagnetic reversals were absent. This result, in combination with the data for the Tremadocian and Middle-Upper Cambrian sequences of the other regions, indicates that (1) the rate of occurrence of the geomagnetic reversals on the eve of the Ordovician Moyero superchron of reversed polarity was at most one reversal per Ma; (2) the superchron does not switch on instantaneously but is preceded by a certain gradual change in the operation conditions of the dynamo mechanism which, inter alia, manifests itself by the reduction of the frequency of geomagnetic reversals with the approach of the superchron. This finding supports the views according to which a process preparing the establishment of the superchrons takes place at the core-mantle boundary.