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Sample records for cambrian metaclastic sediments

  1. 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

    Formation) and the Puncoviscana Formation of the Cordillera Oriental. The goal was the characterisation of the different domains in the study area and to give insights to the location of the source rocks. An active continental margin setting with typical composition of the upper continental crust is...

  2. Extensive Cambrian braidplain sedimentation: Insights from the southwestern Cordillera, U. S. A

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    Fedo, C.M. (Virginia Polytechnic Inst. and State Univ., Blacksburg (United States)); Prave, A.R. (City College of New York, NY (United States))

    1991-02-01

    The Lower to Middle Cambrian time-transgressive coarse terrigenous clastic rocks that form the basal part of the Cordilleran cratonal (Tapeats Sandstone) to miogeoclinal (Wood Canyon Formation, Zabriskie Quartzite) succession have long been though of as products of marine sediment dispersion processes. The authors' recent facies analyses and reinterpretation suggest, instead, that those strata record an extensive continental braidplain which interacted with marine environments. Marine deposits are distinguished by the presence of trace fossils and abundant wave- and tide-influenced sedimentary structures. The most abundant braidplain facies are those assigned a fluvial origin. Coarser, more poorly sorted deposits are feldspathic, whereas finer, better sorted deposits are quartzitic. Beds typically are wedge- and channel-shaped and their width ranges inversely to grain size; channels in conglomeratic layers are relatively narrow (< 20 m wide), whereas those in sand-dominated intervals are shallow (< 1 m) and wide (tens of meters) with broadly concave-up bases. Trough cross-strata and flat laminations are common with planar cross-strata less common. Basal lags and cyclic arrangement of sedimentary structures are rare, although thinning- and fining-upward intervals are developed locally. Paleocurrent indicators across the entire region are west directed and of low variance. They suggest that the dominant mode of sediment transport was by down-channel migrating dunes and that subordinate processes included sheet flow (flat laminated sandstones) and eolian deflation (textural bimodality). These consistent paleocurrent directions attest to the remarkable longevity (Early through Middle Cambrian) of an extensive, westward-draining fluvial system.

  3. Paleomagnetism of the Cambrian Sediments in Bornholm (Denmark) and Southern Sweden and Implications for Paleogeography of Baltica

    Science.gov (United States)

    Lewandowski, M.; Abrahamsen, N.

    2001-12-01

    In Bornholm the Phanerozoic sedimentary succession overlying Precambrian basement starts with the Lower Cambrian (ca. 545 Ma) Nekso Sandstone Fm (NSF) that, in the earlier paleomagnetic analyses, have yielded characteristic magnetization (ChRM) similar to the Permian direction for Baltica. Here, we present paleomagnetic results from other Lower Cambrian formations in Bornholm (Balka Sandstone, Broens Odde siltstone) and in southern Sweden (Hardebega, Mickwitzia and Lingula Sandstones). Lithologically, most of these formations are very similar to the NSF and they are all considered stratigraphically younger. The intention was to check, whether a Permian paleomagnetic overprint occured on a regional scale and could it be attributed to secondary magnetic phases originating from fluids, which possibly traveled laterally along the contact between the basement and the Lower Cambrian sediments. In this report we show results of this regional test, followed by a comprehensive re-analysis of our Nekso data, including new results obtained after supplementary sampling and new petrologic information, which appeared recently. We have found that the NSF possessed a unique ChRM. The well-grouped and stable characteristic magnetization of the Nekso Sandstone contrasts with fairly chaotic, soft and badly preserved magnetization of the Balka, the Hardeberga, the Mickwitzia and the Lingulid sandstones of Bornholm and southern Sweden. A regional geological context, including the inferred diagenetic evolution of Lower Cambrian sediments, points to a syndepositional/early diagenetic origin of the characteristic remanence of the Nekso Sandstone, revealing a stable remanence applicable for plate tectonic interpretations. Similarity of the characteristic remanence of the NSF to the Permian direction for Baltica has been confirmed, but it is supposed to be casual, because of lack of any sign of a regional Permian remagnetization within the other Cambrian deposits of Southern Scandinavia

  4. Strontium isotopic signature of hydrothermal sedimentation from Early Cambrian barite deposits in east Guizhou, China

    Institute of Scientific and Technical Information of China (English)

    XIA Fei; MA Dongsheng; PAN Jiayong; SUN Zhanxue; CAO Shuanglin; NIE Wenming; WU Kai

    2004-01-01

    The ore genesis model for barite deposits in east Guizhou Province has been in dispute and the major debate focuses on whether they are product of the submarine hydrothermal sedimentation. This note presents new strontium isotope data from 19 samples of Dahebian and Yuping barite deposits, and their 87Sr/86Sr ratios are significantly lower than that of the coeval seawater. The 87Sr/86Sr ratios of 17 samples out of 19 samples rang from 0.708310 to 0.708967, indicating that they might be related to the mantel admixture. Two isotopic ratios in this study are higher than those of coeval seawater (0.7090), collected from late-stage barite mineral vein of interpenetrative strata and a barite nodule bearing hypidiomorphic granular pyrite, which indicates that they might be related to the continental admixture. The study provides Sr isotopic evidence not only for the submarine hydrothermal exhalative genesis of Dahebian and Yuping barite deposits, but also for distinguishing the barite mineralization of late stage.

  5. 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

  6. Cambrian fans

    OpenAIRE

    Reading, Nathan; Speyer, David E.

    2006-01-01

    For a finite Coxeter group W and a Coxeter element c of W, the c-Cambrian fan is a coarsening of the fan defined by the reflecting hyperplanes of W. Its maximal cones are naturally indexed by the c-sortable elements of W. The main result of this paper is that the known bijection cl_c between c-sortable elements and c-clusters induces a combinatorial isomorphism of fans. In particular, the c-Cambrian fan is combinatorially isomorphic to the normal fan of the generalized associahedron for W. Th...

  7. Paleomagnetic results from the Cambrian and Ordovician sediments of Bornholm (Denmark) and Southern Sweden and paleogeographical implications for Baltica

    Science.gov (United States)

    Lewandowski, Marek; Abrahamsen, Niels

    2003-11-01

    If apparent polar wander paths (APWP) cross, the question arises how to prove the older magnetization to be primary and not just a younger overprint. This problem is typically met in areas affected by percolating mineralizing fluids and/or heating due to a younger regional igneous activity. The Permian magnetic overprint is the classical example. Earlier paleomagnetic studies over the Lowermost Cambrian Nekso Sandstone Fm (NSF) of Bornholm (Denmark) yielded a characteristic remanent magnetization (ChRM) similar to the Permian directions for Baltica. Since a possible reason could be a chemical overprint, we checked whether this phenomenon did take place on a regional scale. Some samples therefore were collected from other Lower Cambrian clastics of Bornholm and Southern Scandinavia. In result we show that the well-grouped and stable ChRM of the NSF contrasts with fairly chaotic, soft, and badly preserved magnetizations of the Balka, Hardeberga, Mickwitzia, and Lingulid sandstones of Bornholm and Southern Sweden, thus not indicating widespread paleomagnetic overprint. We demonstrate that the ChRM of the NSF is most probably of syndepositional/early diagenetic origin and its similarity to the Permian direction for Baltica is only casual. We propose a normal polarity and a near-equatorial position on the Southern Hemisphere for Baltica in the early Cambrian time, as well as a more complicated trend of the APWP for this paleocontinent than envisaged by other authors. Paleomagnetic results from the Arenigian limestones of the Laesaa Formation (Bornholm) that yield excellently defined but most probably only secondary components are also presented.

  8. 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

  9. Soft-sediment deformation structures in Cambrian Series 2 tidal deposits (NW Estonia): implications for identifying endogenic triggering mechanisms in ancient sedimentary record

    Science.gov (United States)

    Põldsaar, Kairi

    2015-04-01

    Soft-sediment deformation structures (SSDS) are documented in several horizons within silt- and sandstones of the Cambrian Series 2 (Dominopolian Stage) Tiskre Formation, and some in the below-deposited argillaceous deposits of the Lükati Formation (northern part of the Baltoscandian Palaeobasin, NW Estonia). The aim of this study was to map, describe, and analyze these deformation features, discuss their deformation mechanism and possible triggers. Load structures (simple load casts, pillows, flame structures, convoluted lamination) with varying shapes and sizes occur in the Tiskre Fm in sedimentary interfaces within medium-bedded peritidal rhythmites (siltstone-argillaceous material) as well as within up to 3 m thick slightly seaward inclined stacked sandstone sequences. Homogenized beds, dish-and-pillar structures, and severely deformed bedding are also found within these stacked units and within a large tidal runoff channel infill. Autoclastic breccias and water-escape channels are rare and occur only in small-scale -- always related to thin, horizontal tidal laminae. Profound sedimentary dykes, sand volcanoes, and thrust faults, which are often related to earthquake triggered soft sediment deformation, were not observed within the studied intervals. Deformation horizon or horizons with large flat-topped pillows often with elongated morphologies occur at or near the boundary between the Tiskre and Lükati formations. Deformation mechanisms identified in this study for the various deformation types are gravitationally unstable reversed density gradient (especially in case of load features that are related to profound sedimentary interfaces) and lateral shear stress due to sediment current drag (in case of deformation structures that not related to loading at any apparent sedimentary interface). Synsedimentary liquefaction was identified as the primary driving force in most of the observed deformation horizons. Clay thixotropy may have contributed in the

  10. Cambrian small shelly fossils from the Çal Tepe Formation, Taurus Mountains, Turkey

    OpenAIRE

    Sarmiento, Graciela N.; Fernández Remolar, David Carlos; Göncüoglu, M. Cemal

    2001-01-01

    [EN] Lower and Middle Cambrian carbonate rocks of the Çal Tepe Formation, cropping out in the western Taurus Mountains, yielded a large number of microfossil remains. Small shelly fossils from a single level in the upper Lower Cambrian represent a high diversity biota that could be related to the «Cambrian explosion». Microfossil association from the lower Middle Cambrian sediments of the Çal Tepe Formation is taxonomically very reduced and a dominant taxon is Hadimopanella GEDIK. Th...

  11. Cambrian small shelly fossils from the Çal Tepe Formation, Taurus Mountains, Turkey

    OpenAIRE

    Sarmiento, Graciela; Fernández Remolar, David Carlos; Göncüoglu, M. Cemal

    2001-01-01

    Lower and Middle Cambrian carbonate rocks of the Çal Tepe Formation, cropping out in the western Taurus Mountains, yielded a large number of microfossil remains. Small shelly fossils from a single level in the upper Lower Cambrian represent a high diversity biota that could be related to the «Cambrian explosion». Microfossil association from the lower Middle Cambrian sediments of the Çal Tepe Formation is taxonomically very reduced and a dominant taxon is Hadimopanella GEDIK. This sudden chan...

  12. The Cambrian explosion.

    Science.gov (United States)

    Briggs, Derek E G

    2015-10-01

    The sudden appearance of fossils that marks the so-called 'Cambrian explosion' has intrigued and exercised biologists since Darwin's time. In On the Origin of Species, Darwin made it clear that he believed that ancestral forms 'lived long before' their first fossil representatives. While he considered such an invisible record necessary to explain the level of complexity already seen in the fossils of early trilobites, Darwin was at a loss to explain why there were no corresponding fossils of these earlier forms. In chapter 9 of the Origin, entitled 'On the imperfection of the geological record', he emphasized the 'poorness of our palaeontological collections' and stated categorically that 'no organism wholly soft can be preserved'. Fortunately much has been discovered in the last 150 years, not least multiple examples of Cambrian and Precambrian soft-bodied fossils. We now know that the sudden appearance of fossils in the Cambrian (541-485 million years ago) is real and not an artefact of an imperfect fossil record: rapid diversification of animals coincided with the evolution of biomineralized shells. And although fossils in earlier rocks are rare, they are not absent: their rarity reflects the low diversity of life at this time, as well as the low preservation potential of Precambrian organisms (see Primer by Butterfield, in this issue). PMID:26439348

  13. Reconstruction of early Cambrian ocean chemistry from Mo isotopes

    Science.gov (United States)

    Wen, Hanjie; Fan, Haifeng; Zhang, Yuxu; Cloquet, Christophe; Carignan, Jean

    2015-09-01

    The Neoproterozoic-Cambrian transition was a key time interval in the history of the Earth, especially for variations in oceanic and atmospheric chemical composition. However, two conflicting views exist concerning the nature of ocean chemistry across the Precambrian-Cambrian boundary. Abundant geochemical evidence suggests that oceanic basins were fully oxygenated by the late Ediacaran, while other studies provide seemingly conflicting evidence for anoxic deep waters, with ferruginous conditions [Fe(II)-enriched] persisting into the Cambrian. Here, two early Cambrian sedimentary platform and shelf-slope sections in South China were investigated to trace early Cambrian ocean chemistry from Mo isotopes. The results reveal that early Cambrian sediments deposited under oxic to anoxic/euxinic conditions have δ98/95Mo values ranging from -0.28‰ to 2.29‰, which suggests that early Cambrian seawater may have had δ98/95Mo values of at least 2.29‰, similar to modern oceans. The heaviest and relatively homogeneous δ98/95Mo values were recorded in siltstone samples formed under completely oxic conditions, which is considered that Mn oxide-free shuttling was responsible for such heavy δ98/95Mo value. Further, combined with Fe species data and the accumulation extent of Mo and U, the variation of δ98/95Mo values in the two studied sections demonstrate a redox-stratified ocean with completely oxic shallow water and predominantly anoxic (even euxinic) deeper water having developed early on, which eventually became completely oxygenated. This suggests that oceanic circulation at the time became reorganized, and such changes in oceanic chemistry may have been responsible for triggering the "Cambrian Explosion" of biological diversity.

  14. High continental weathering rate during Early Cambrian: Evidence from Os isotopic composition of Early Cambrian Ocean

    Science.gov (United States)

    Jiang, S.-Y.; Yang, J.-H.; Ling, H.-F.; Feng, H.-Z.; Chen, Y.-Q.; Chen, J.-H.

    2003-04-01

    The paleo-ocean environmental change during the Precambrian-Cambrian transition is a key issue related to the causes for an explosive radiation of different metazoan phyla during Early Cambrian. The chemical and isotopic compositions of marine sediments and chemical precipitates such as carbonates, phosphorites, siliceous rocks, and black shales record the changing composition and physical conditions of the seawater in which these rocks accumulated. Organic carbon-rich black shales from marine environments are commonly enriched in a number of trace elements such as Ni, Mo, V, Co, Cr, Au, U, As, Pb, Zn, Cu, Re, and platinum-group-elements (PGE). Recent researches have demonstrated that Re-Os isotopes and PGE contents in black shales are useful proxies for seawater chemistry. It is believed that Re and Os in orgainc-carbon rich black shales are mostly hydrogeneous in origin which were largely sequestered from seawater at the time of deposition. In South China, the Lower Cambrian black shale sequence of the Niutitang Formation (and lateral equivalents) exists broadly several thousands kilometers. The lowermost sequence of this formation contain a thin sulfide ore horizon with an apparently unique and extreme case of metal enrichments such as Mo, Ni, Se, Re, Os, As, Hg, Sb, Ag, Au, Pt, and Pd. In this study, we conducted a preliminary investigation of Re-Os isotopes and Plantium Group Element (PGE) distribution patterns of the balck shales and intercalated Ni-Mo polymetallic sulfide bed from Guizhou and Hunan Provinces. The high rOs(t) values of the black shales indicate that the Early Cambrian ocean in Yangtze Platform had a highly radiogenic Os, possibly as a result of high continental weathering rate at that time. The Ni-Mo polymetallic sulfide ores within the black shales have lower rOs(t) values than the black shales, and they show similar REE and PGE patterns as the hydrothermal siliceous rocks within the Lower Cambrian strata, which suggest that the Ni

  15. Did homeobox gene duplications contribute to the Cambrian explosion?

    OpenAIRE

    Holland, Peter W. H.

    2015-01-01

    The Cambrian explosion describes an apparently rapid increase in the diversity of bilaterian animals around 540–515 million years ago. Bilaterian animals explore the world in three-dimensions deploying forward-facing sense organs, a brain, and an anterior mouth; they possess muscle blocks enabling efficient crawling and burrowing in sediments, and they typically have an efficient ‘through-gut’ with separate mouth and anus to process bulk food and eject waste, even when burrowing in sediment. ...

  16. Umbrella structure and channel-wall stoping in the Cambrian St. Roch Formation, Quebec Appalachians: significance for particle support mechanisms and turbulence development in hyper-concentrated sediment gravity flows

    Science.gov (United States)

    Hesse, Reinhard; Fong, Christopher

    2014-03-01

    Umbrella structure is a newly recognized sedimentary structure associated with large platy clasts in resedimented boulder-bearing pebble conglomerate with a sandy matrix. It consists of a sand rim that lacks pebbles on parts or the entire underside of platy boulders, whereas on the upper side, pebbles are in direct contact with the boulders. The depositing processes were high- to hyper-concentrated sediment gravity flows in a submarine channel or canyon on the Cambrian continental slope of North America bordering the Iapetus Ocean. The structure occurs predominantly where clasts dip moderately in the down-current direction. Based on the association of the structure with slightly forward dipping slabs, it is proposed that these down-current dipping slabs may have been in the process of counter-clockwise rotation that was aborted and may have generated a pressure shadow on the underside enabling the inrush of fluid and the infiltration of sand into the anomalous low-pressure zone. The structure has implications for particle support mechanisms in high- to hyper-concentrated sedimentary gravity flows, in that it redirects attention to the much debated mechanism of dispersive pressure and alternatives. It provides an observable sediment structure that supports dispersive pressure which so far depended on experimental evidence and theoretical arguments alone. Vrolijk and Southard's (1997) concept of a `laminar sheared layer' is here for the first time interpreted as having an upward-moving `free-surface' layer effect during deposition from hyper-concentrated flows. Channel-wall stoping involves unlithified turbiditic spillover sand in the levee sediment of the canyon wall that was washed out by the upper diluted parts of the high-concentration flows coming down the channel and leaving a niche in the wall that was filled with coarser channel-axis facies by the same flow (or later flows) when its aggradation reached the level of the niche. The contact between turbidite and

  17. The Cambrian impact hypothesis

    CERN Document Server

    Zhang, Weijia

    2008-01-01

    After a thorough research on the circumstantial changes and the great evolution of life in the Cambrian period, the author propounds such a hypothesis: During the Late Precambrian, about 500-600Ma, a celestial body impacted the Earth. The high temperature ended the great glaciation, facilitated the communication of biological information. The rapid change of Earth environment enkindled the genesis-control system, and released the HSP-90 variations. After the impact, benefited from the protection of the new ozone layer and the energy supplement of the aerobic respiration, those survived underground life exploded. They generated carapaces and complex metabolism to adjust to the new circumstance of high temperature and high pressure. This article uses a large amount of analyses and calculations, and illustrates that this hypothesis fits well with most of the important incidences in astronomic and geologic discoveries.

  18. Sortable elements and Cambrian lattices

    OpenAIRE

    Reading, Nathan

    2005-01-01

    We show that the Coxeter-sortable elements in a finite Coxeter group W are the minimal congruence-class representatives of a lattice congruence of the weak order on W. We identify this congruence as the Cambrian congruence on W, so that the Cambrian lattice is the weak order on Coxeter-sortable elements. These results exhibit W-Catalan combinatorics arising in the context of the lattice theory of the weak order on W.

  19. Sponge fossil assemblage from the Early Cambrian Hetang Formation in southern Anhui

    Institute of Scientific and Technical Information of China (English)

    CHEN Zhe; HU Jie; ZHOU Chuanming; XIAO Shuhai; YUAN Xunlai

    2004-01-01

    Abundant well-preserved large articulated sponge fossils and isolated spicules have been reported from the Early Cambrian Hetang Formation, southern Anhui Province. This unique epifaunal fossil assemblage dominated by articulated sponge fossils is called the Xidi Sponge Fauna.The sponge fauna lived in a quiet oxygenic environment below the storm wave base. Bloom of phytoplankton and rapid sedimentation rate resulted in the deposition of the black shales. Sufficient food supply, lack of other competitors,abundant ecological niches, and demand for oxygen during early Cambrian were in favor of the diversification and evolution of large sponges in the Early Cambrian.

  20. Provenance shift in Cambrian mid-Baltica: detrital zircon chronology of Ediacaran–Cambrian sandstones in Estonia

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    Yukio Isozaki

    2014-12-01

    Full Text Available In order to clarify the tectono-sedimentary history of Paleozoic Baltica, age spectra of detrital zircon grains from the Ediacaran (Kotlin Regional Stage and Lower Cambrian sandstones (lowermost Lontova and Lükati formations in western Estonia in central Baltica were analyzed by LA-ICPMS. The abundant occurrence of Archean to Mesoproterozoic (2800–1000 Ma zircon grains was confirmed in all samples. The new data provided the following information on the provenance of siliciclastic material as well as a major change in the sedimentary regime of the Paleo-Baltic basin during the Early Cambrian: (1 the Ediacaran–Lower Cambrian Paleo-Baltic basin received abundant terrigenous clastics from the core of Baltica underlain by the Archean–Mesoproterozoic crystalline crust, (2 the exposed surface area of the 1600 Ma Rapakivi granites apparently was more extensive during the Ediacaran–Early Cambrian than at present, (3 a major re-organization of the basin geometry occurred in the middle Early Cambrian (ca 530–515 Ma in central Baltica, inducing a change in the sediment supply system, (4 in contrast to the total absence of Neoproterozoic detrital zircon grains before the middle Early Cambrian, their sudden appearance at this time, together with consistent occurrence at least until the mid-Devonian, suggests a significant uplift event located in southeast Baltica and/or in a more easterly land domain (e.g., in Sarmatia, (5 possible sources for the Neoproterozoic zircon grains include the peripheral mobile belts with pan-African signatures around Baltica, e.g., the so-called Gondwanan fragments along the Tornquist margin to the southwest and the Timanian belt along the northeastern margin.

  1. Oceanic anoxia at the Precambrian-Cambrian boundary

    Science.gov (United States)

    Kimura, Hiroto; Watanabe, Yoshio

    2001-11-01

    The Precambrian-Cambrian (PC-C) boundary separates fossils representing two discrete evolutionary phases: the Neoproterozoic soft-bodied Ediacarian biotas and Cambrian small shelly faunas. The biological discontinuity is suspected to have been a result of mass extinction; however, recent discoveries of the Ediacarian biotas in Cambrian sediments have led to an understanding that the faunal change was gradual through the PC-C transition. Th/U ratios, which are high in oxidizing conditions and low in reducing conditions, show a considerable positive correlation with δ13C values at all studied sites of the PC-C boundary. This correlation indicates that reported δ13C variation across the PC-C boundary from numerous localities corresponds to redox variation in the depositional environment. The negative δ13C anomaly that occurs worldwide at the PC-C boundary, therefore, corresponds to the widespread development of an oxygen-deficient shallow marine environment. This finding suggests that widespread oceanic oxygen deficiency, which has been interpreted to reflect Phanerozoic mass extinction events, also occurred immediately before the Cambrian explosion.

  2. 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

  3. Causes of the Cambrian Explosion.

    OpenAIRE

    Smith, M P; Harper, D.A.T.

    2013-01-01

    In the last decade, at least thirty individual hypotheses have been invoked to explain the Cambrian Explosion, ranging from starbursts in the Milky Way to intrinsic genomic reorganization and developmental patterning. It has been noted (1) that recent hypotheses fall into three categories: a) developmental/genetic, b) ecologic and c) abiotic environmental, with geochemical hypotheses forming an abundant and distinctive subset of the last. With a few notable exceptions, a significant majority ...

  4. Ichnofossil from the Cambrian succession of Parahio Valley, Spiti Basin, India: Their stratigraphic and paleoenvironmental significance

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    Pandey, Shivani; Parcha, Suraj Kumar

    2013-04-01

    The Spiti Basin exposes an excellent section of Neoproterozoic- Cretaceous rocks in the Tethyan Himalaya of Himachal Pradesh. The diverse assemblage of ichnofossils is present in the Cambrian succession of Parahio Valley in the Spiti Basin. In the present study nineteen ichnofossils are reported from the Cambrian succession of Parahio Valley. The ichnofossils includes Bergaueria, Chondrites, Cruziana, Didymaulichnus, Dimorphichnus, Diplichnites, Helminthorhaphe, Merostomichnites, ?Monocraterion, Monomorphichnus, Nereites, Palaeopascichnus, Palaeophycus, Phycodes, Planolites, Rusophycus, Skolithos, Scolicia, Treptichnus etc. along with annelid worm, burrow and scratch marks. The described ichnofossil assemblage indicates that the ichnocenosis is dominated by a high behavioral diversity ranging from suspension to deposit feeders. It seems that the ichnofauna present in the Cambrian succession of this section were mostly produced by trilobite and arthropods, whereas some of them were produced by crustacean, priapulid worm, polychaetes and polyphyletic vermiforms. The distribution pattern of ichnofossils shows increase in taxonomic and morphological diversity up in the section. It further indicates that the availability of nutrients significantly increased their abundance as well as spatial distribution during Cambrian. The presence of Chondrites, Treptichnus, and Phycodes at the basal part of the Cambrian indicates shallow to deep environment with anaerobic condition. Whereas, the complex forms like Rusophycus, Cruziana, Monomorphichnus and Nereites represent shelf to slope environment. The appearance of Skolithos in the upper part reflects well oxygenated high energy condition. The environmental changes in the Parahio Valley during Cambrian period was distinctly marked by an anaerobic to aerobic condition and by a faunal change from endobenthic, soft - bodied, deposit feeders to epibenthic grazers. The present ichnofossils indicates that these sediments were

  5. Magmatism in a Cambrian Laurentian Plate Rift

    Science.gov (United States)

    Gilbert, M. C.

    2008-12-01

    Evidences of the Cambrian Southern Oklahoma Aulacogen extend over 1000km from about Dallas out to the Uncompahgre Plateau in SW Colorado. The signature of this originally extensional feature can be traced geophysically, and in some places at the present surface, petrologically and temporally, by the presence of mafic rock. It appears to have been the intracontinental third arm of a plume-generated? triple junction which helped to dismember the southern part of Laurentia on the final break-up of a Neoproterozoic supercontinent. Other parts of Laurentia rifted away and are now found in the Precordillera of Argentina. Rift magmatism appears to have been concentrated nearer the plate edge during the breakup. Perhaps as much as 40,000 km3 of mostly subaerial silicic volcanics and shallow-seated granites overlay and filled the top of the rift in the area of SW Oklahoma. The rift fill below the silicic rocks is large, layered mafic complexes and smaller, layered, hydrous gabbros, the whole set appearing as a shallow AMCG complex. Unusually, direct rift sediments are not obvious. Furthermore, silicic and mafic rocks have identical Nd signatures. Finally, about 20 Ma after rifting ceased and later into the Paleozoic during sea incursion, overlying sediments are thickened 4X compared to equivalent units 100's of kms to the rift sides. This rift appears distinct from most modern rifts. Conclusions are 1) This was a hot, narrow rift; 2) Basaltic magmatism , not sedimentation, filled the rift; 3) Magmatic intensity varied along the rift strike; 4) Silicic rocks were generated mostly directly from new mantle-derived basalt liquids through fractionation, not melting of older crustal rocks; 5) Laurentian lithosphere was weak allowing centering of the Early/Middle Paleozoic large "Oklahoma" basin (pre-Anadarko) over the rift.

  6. The base of the Cambrian in Morocco

    Science.gov (United States)

    Sdzuy, K.; Geyer, G.

    The paper summarizes problems of datings of Latest Precambrian to Early Cambrian rocks of Morocco. The known palaeontological data are reviewed briefly. Characteristics and correlatability of the earliest trilobites of Morocco are discussed. Additional remarks concern the appearance of hard part animals at the beginning of the Cambrian.

  7. Did homeobox gene duplications contribute to the Cambrian explosion?

    Science.gov (United States)

    Holland, Peter W H

    2015-01-01

    The Cambrian explosion describes an apparently rapid increase in the diversity of bilaterian animals around 540-515 million years ago. Bilaterian animals explore the world in three-dimensions deploying forward-facing sense organs, a brain, and an anterior mouth; they possess muscle blocks enabling efficient crawling and burrowing in sediments, and they typically have an efficient 'through-gut' with separate mouth and anus to process bulk food and eject waste, even when burrowing in sediment. A variety of ecological, environmental, genetic, and developmental factors have been proposed as possible triggers and correlates of the Cambrian explosion, and it is likely that a combination of factors were involved. Here, I focus on a set of developmental genetic changes and propose these are part of the mix of permissive factors. I describe how ANTP-class homeobox genes, which encode transcription factors involved in body patterning, increased in number in the bilaterian stem lineage and earlier. These gene duplications generated a large array of ANTP class genes, including three distinct gene clusters called NK, Hox, and ParaHox. Comparative data supports the idea that NK genes were deployed primarily to pattern the bilaterian mesoderm, Hox genes coded position along the central nervous system, and ParaHox genes most likely originally specified the mouth, midgut, and anus of the newly evolved through-gut. It is proposed that diversification of ANTP class genes played a role in the Cambrian explosion by contributing to the patterning systems used to build animal bodies capable of high-energy directed locomotion, including active burrowing. PMID:26605046

  8. Phosphate Biomineralization of Cambrian Microorganisms

    Science.gov (United States)

    McKay, David S.; Rozanov, Alexei Yu.; Hoover, Richard B.; Westall, Frances

    1998-01-01

    As part of a long term study of biological markers (biomarkers), we are documenting a variety of features which reflect the previous presence of living organisms. As we study meteorites and samples returned from Mars, our main clue to recognizing possible microbial material may be the presence of biomarkers rather than the organisms themselves. One class of biomarkers consists of biominerals which have either been precipitated directly by microorganisms, or whose precipitation has been influenced by the organisms. Such microbe-mediated mineral formation may include important clues to the size, shape, and environment of the microorganisms. The process of fossilization or mineralization can cause major changes in morphologies and textures of the original organisms. The study of fossilized terrestrial organisms can help provide insight into the interpretation of mineral biomarkers. This paper describes the results of investigations of microfossils in Cambrian phosphate-rich rocks (phosphorites) that were found in Khubsugul, Northern Mongolia.

  9. Did Gamma Ray Burst Induce Cambrian Explosion?

    OpenAIRE

    Chen, Pisin; Ruffini, Remo

    2014-01-01

    One longstanding mystery in bio-evolution since Darwin's time is the origin of the Cambrian explosion that happened around 540 million years ago (Mya), where an extremely rapid increase of species occurred. Here we suggest that a nearby GRB event ~500 parsecs away, which should occur about once per 5 Gy, might have triggered the Cambrian explosion. Due to a relatively lower cross section and the conservation of photon number in Compton scattering, a substantial fraction of the GRB photons can...

  10. Diversity partitioning during the Cambrian radiation

    OpenAIRE

    Na, Lin; Kiessling, Wolfgang

    2015-01-01

    Many mechanisms of the Cambrian Explosion have been proposed, but rigorous quantitative analyses of biodiversity dynamics are scarce, although they may shed light on important factors. Using a comprehensive database and sampling standardization, we dissect global diversity patterns. The trajectories of within-community, between-community, and global diversity during the main phase of the Cambrian radiation revealed a low-competition model, which was probably governed by niche contraction and ...

  11. Is a Cambrian Explosion Coming for Robotics?

    OpenAIRE

    Gill A. Pratt

    2015-01-01

    About half a billion years ago, life on earth experienced a short period of very rapid diversification called the "Cambrian Explosion." Many theories have been proposed for the cause of the Cambrian Explosion, one of the most provocative being the evolution of vision, allowing animals to dramatically increase their ability to hunt and find mates. Today, technological developments on several fronts are fomenting a similar explosion in the diversification and applicability of robotics. Many of ...

  12. Geochemistry of the Ediacaran-Early Cambrian transition in Central Iberia: Tectonic setting and isotopic sources

    Science.gov (United States)

    Fuenlabrada, José Manuel; Pieren, Agustín P.; Díez Fernández, Rubén; Sánchez Martínez, Sonia; Arenas, Ricardo

    2016-06-01

    A complete Ediacaran-Early Cambrian stratigraphic transition can be observed in the southern part of the Central Iberian Zone (Iberian Massif). Two different stratigraphic units, underlying Ordovician series, display geochemical and Sm-Nd isotopic features in agreement with an evolving geodynamic setting. Pusa Shales (Early Cambrian) rest unconformably on greywackes of the Lower Alcudian Formation (Late Ediacaran). Both sequences present minor compositional variations for major and trace element contents and similar REE patterns, close to those of PAAS (Post Archean Australian Shale). Trace element contents and element ratios suggest mixed sources, with intermediate to felsic igneous contributions for both units. Tectonic setting discrimination diagrams for the Ediacaran greywackes indicate that these turbiditic series were deposited in a sedimentary basin associated with a mature active margin (volcanic arc). However, the compositions of the Cambrian shales fit better with a more stable context, a back-arc or retro-arc setting. εNd(T) and TDM ages are compatible with dominance of a similar cratonic source for both sequences, probably the West Africa Craton. εNd565 values for the Ediacaran greywackes (- 3.0 to - 1.4) along with TDM ages (1256-1334 Ma) imply a significant contribution of juvenile material, probably derived from the erosion of the volcanic arc. However, εNd530 values in the Cambrian shales (- 5.2 to - 4.0) together with older TDM ages (1444-1657 Ma), suggest a higher contribution of cratonic isotopic sources, probably derived from erosion of the adjacent mainland. Coeval with the progressive cessation of arc volcanism along the peri-Gondwanan realm during the Cambrian, there was a period of more tectonic stability and increasing arrival of sediments from cratonic areas. The geochemistry of the Ediacaran-Cambrian transition in Central Iberia documents a tectonic switch in the periphery of Gondwana, from an active margin to a more stable context

  13. Ouachita trough: Part of a Cambrian failed rift system

    Science.gov (United States)

    Lowe, Donald R.

    1985-11-01

    Pre-flysch (Cambrian-Mississippian) strata of the Ouachita Mountains of Arkansas and Oklahoma include two main sandstone lithofacies: (1) a craton-derived lithofacies made up largely of mature medium- to coarse-grained quartzose and carbonate detritus and, in some units, sediment eroded from exposed basement rocks and (2) an orogen-derived facies made up mainly of fine-grained quartzose sedimentary and metasedimentary debris and possibly, in lower units, a volcaniclastic component. Paleocurrent and distribution patterns indicate that detritus of facies I in the Benton uplift was derived from north and detritus of facies II throughout the Ouachitas was derived from south and east of the depositional basin. Overall sedimentological results suggest that the Ouachita trough was a relatively narrow, two-sided basin throughout most and probably all of its existence and never formed the southern margin of the North American craton. Regional comparisons suggest that it was one of several basins, including the Southern Oklahoma aulacogen, Reelfoot Rift, Illinois Basin, and Rome trough, that formed as a Cambrian failed rift system 150 to 250 m.y. after initial rifting along the Appalachian margin of the North American craton.

  14. Mineralogy and Chemistry of Coronadite from Middle Cambrian Manganese Deposits at Wadi Dana, Southern Jordan

    OpenAIRE

    Ahmad Al-Malabeh; Tayel El-Hasan

    2009-01-01

    Coronadite was reported from the upper-most horizons of the Middle Cambrian sediments at two locations in Wadi Dana, central Wadi Araba and Jordan. The unit is composed of dolomite, limestone and shale. Geochemical investigations show appreciable variations in Mn, Pb, Fe, K and Ba contents in the coronadite between the two studied sites. Pb was found to increase downward in both sites in spite of the lateral distance between them. Fe does not vary vertically, but its concentration decreases e...

  15. Possible impact event in the Late Cambrian

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The repeated investigation of the Batyrbay section has been done by the authors. Today we see increasing of interest to revising of volumes and boundaries of Stages and Series in the Cambrian and Ordovician,as well as to the events of this time. In this work the description of iron spherules and particles, found in the deep-water limestone layer of the conodont Cordylodus primitivus Zone in the middle Upper Cambrian of the Batyrbay section, Malyi Karatau of South Kazakhstan, and formed during the time of global sea-level changes known as a world-wide Lange Ranch Eustatic event, have been done. From our point of view, finds of iron spherules and particles may evidence about new unknown yet Event of cosmic origin, i.e. falling of a meteorite on Earth in the middle Late Cambrian.

  16. An Early Cambrian tunicate from China.

    Science.gov (United States)

    Shu, D G; Chen, L; Han, J; Zhang, X L

    2001-05-24

    Like the Burgess Shales of Canada, the Chengjiang Lagerstätte from the Lower Cambrian of China is renowned for the detailed preservation as fossils of delicate, soft-bodied creatures, providing an insight into the Cambrian explosion. The fossils of possible hemichordate chordates and vertebrates have attracted particular attention. Tunicates, or urochordates, comprise the most basal chordate clade, and details of their evolution could be important in understanding the sequence of character acquisition that led to the emergence of chordates and vertebrates. However, definitive fossils of tunicates from the Cambrian are scarce or debatable. Here we report a probable tunicate Cheungkongella ancestralis from the Chengjiang fauna. It resembles the extant ascidian tunicate genus Styela whose morphology could be useful in understanding the origin of the vertebrates. PMID:11373678

  17. Cambrian paleomagnetism of the Llano Uplift, Texas

    Science.gov (United States)

    Watts, Doyle R.; van der Voo, Rob; Reeve, Scott C.

    1980-10-01

    Late Cambrian sandstones and limestones sampled from various members of the Riley and Wilberns formations of the Llano uplift show a progression of paleomagnetic pole positions as a function of age. The members, ages, and poles are the following for the Riley Formation: the Hickory Sandstone, Lower Dresbachian, 34°N, 145°E; the Cap Mountain Limestone, Dresbachian, 33°N, 140°E; the Lion Mountain Limestone, Upper Dresbachian, 24°N, 146°E. For, the Wilberns Formation they are the following: the Welge Sandstone/Morgan Creek Limestone, Lower and Middle Franconian, 24°N, 151°E; and the Point peak Shale, Upper Franconian, 6°N, 159°E. These poles are based on thermal, chemical, and alternating field demagnetizations and on vector analysis. Most directions are interpreted to be of reversed polarity, but the Cap Mountain Limestone also yielded normal polarity directions; all directions resided in hematite with blocking temperatures up to 680°C. Almost all Cambrian poles appear to fall in a broad streak between the equator at about 155°E (e.g., the poles from the Tapeats Sandstone and from the Late Cambrian Point Peak Shale of the Wilberns Formation) and about 60°N, 90°E, where Cambrian poles have been obtained by Elston and Bressler (1977) and French et al. (1977). Although, at the present time, partial to complete remagnetization or nondipole behavior of the geomagnetic field are adequate ad hoc hypotheses to explain some of the data, it is suggested that the simplest and most unifying hypothesis to explain all data involves a Cambrian loop of apparent polar wander with respect to North America. This loop occurs before the middle Late Cambrian, with the poles from the Llano uplift falling on the return track.

  18. Gut contents as direct indicators for trophic relationships in the Cambrian marine ecosystem.

    Science.gov (United States)

    Vannier, Jean

    2012-01-01

    Present-day ecosystems host a huge variety of organisms that interact and transfer mass and energy via a cascade of trophic levels. When and how this complex machinery was established remains largely unknown. Although exceptionally preserved biotas clearly show that Early Cambrian animals had already acquired functionalities that enabled them to exploit a wide range of food resources, there is scant direct evidence concerning their diet and exact trophic relationships. Here I describe the gut contents of Ottoia prolifica, an abundant priapulid worm from the middle Cambrian (Stage 5) Burgess Shale biota. I identify the undigested exoskeletal remains of a wide range of small invertebrates that lived at or near the water sediment interface such as hyolithids, brachiopods, different types of arthropods, polychaetes and wiwaxiids. This set of direct fossil evidence allows the first detailed reconstruction of the diet of a 505-million-year-old animal. Ottoia was a dietary generalist and had no strict feeding regime. It fed on both living individuals and decaying organic matter present in its habitat. The feeding behavior of Ottoia was remarkably simple, reduced to the transit of food through an eversible pharynx and a tubular gut with limited physical breakdown and no storage. The recognition of generalist feeding strategies, exemplified by Ottoia, reveals key-aspects of modern-style trophic complexity in the immediate aftermath of the Cambrian explosion. It also shows that the middle Cambrian ecosystem was already too complex to be understood in terms of simple linear dynamics and unique pathways. PMID:23300612

  19. Gut contents as direct indicators for trophic relationships in the Cambrian marine ecosystem.

    Directory of Open Access Journals (Sweden)

    Jean Vannier

    Full Text Available Present-day ecosystems host a huge variety of organisms that interact and transfer mass and energy via a cascade of trophic levels. When and how this complex machinery was established remains largely unknown. Although exceptionally preserved biotas clearly show that Early Cambrian animals had already acquired functionalities that enabled them to exploit a wide range of food resources, there is scant direct evidence concerning their diet and exact trophic relationships. Here I describe the gut contents of Ottoia prolifica, an abundant priapulid worm from the middle Cambrian (Stage 5 Burgess Shale biota. I identify the undigested exoskeletal remains of a wide range of small invertebrates that lived at or near the water sediment interface such as hyolithids, brachiopods, different types of arthropods, polychaetes and wiwaxiids. This set of direct fossil evidence allows the first detailed reconstruction of the diet of a 505-million-year-old animal. Ottoia was a dietary generalist and had no strict feeding regime. It fed on both living individuals and decaying organic matter present in its habitat. The feeding behavior of Ottoia was remarkably simple, reduced to the transit of food through an eversible pharynx and a tubular gut with limited physical breakdown and no storage. The recognition of generalist feeding strategies, exemplified by Ottoia, reveals key-aspects of modern-style trophic complexity in the immediate aftermath of the Cambrian explosion. It also shows that the middle Cambrian ecosystem was already too complex to be understood in terms of simple linear dynamics and unique pathways.

  20. Collective behavior in an early Cambrian arthropod.

    Science.gov (United States)

    Hou, Xian-Guang; Siveter, Derek J; Aldridge, Richard J; Siveter, David J

    2008-10-10

    Examples that indicate collective behavior in the fossil record are rare. A group association of specimens that belong to a previously unknown arthropod from the Chengjiang Lagerstätte, China, provides evidence that such behavior was present in the early Cambrian (about 525 million years ago), coincident with the earliest extensive diversification of the Metazoa, the so-called Cambrian explosion event. The chainlike form of these specimens is unique for any arthropod, fossil or living, and most likely represents behavior associated with migration. PMID:18845748

  1. Cambrian Research in the New Century—the Fourth International Symposium on the Cambrian System

    Institute of Scientific and Technical Information of China (English)

    Peng Shanchi; Zhu Maoyan; L.E.Babcock

    2006-01-01

    @@ The International Subcomission on Cambrian Stratigraphy (ISCS) of the International Commission on Stratigraphy (ICS)held its Fourth International Symposium on the Cambrian System in Nanjing, the capital city of Jiangsu Province, China, on 18-24August, 2005. The Symposium was held in conjunction with the Tenth Field Conference of the Cambrian Stage Subdivision Working Group of the ISCS. Technical sessions were held in the conference center of Southeast University, and hosted by the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, the Geological Institute, Chinese Academy of Geological Sciences, and Guizhou University. Associated with the meeting were five field excursions to classical Cambrian localities in North China and South China.

  2. The significance of 24-norcholestanes, triaromatic steroids and dinosteroids in oils and Cambrian-Ordovician source rocks from the cratonic region of the Tarim Basin, NW China

    Science.gov (United States)

    Li, Meijun; Wang, T.-G.; Lillis, Paul G.; Wang, Chunjiang; Shi, Shengbao

    2012-01-01

    Two oil families in Ordovician reservoirs from the cratonic region of the Tarim Basin are distinguished by the distribution of regular steranes, triaromatic steroids, norcholestanes and dinosteroids. Oils with relatively lower contents of C28 regular steranes, C26 20S, C26 20R + C27 20S and C27 20R regular triaromatic steroids, dinosteranes, 24-norcholestanes and triaromatic dinosteroids originated from Middle–Upper Ordovician source rocks. In contrast, oils with abnormally high abundances of the above compounds are derived from Cambrian and Lower Ordovician source rocks. Only a few oils have previously been reported to be of Cambrian and Lower Ordovician origin, especially in the east region of the Tarim Basin. This study further reports the discovery of oil accumulations of Cambrian and Lower Ordovician origin in the Tabei and Tazhong Uplifts, which indicates a potential for further discoveries involving Cambrian and Lower Ordovician sourced oils in the Tarim Basin. Dinosteroids in petroleum and ancient sediments are generally thought to be biomarkers for dinoflagellates and 24-norcholestanes for dinoflagellates and diatoms. Therefore, the abnormally high abundance of these compounds in extracts from the organic-rich sediments in the Cambrian and Lower Ordovician and related oils in the cratonic region of the Tarim Basin suggests that phytoplankton algae related to dinoflagellates have appeared and might have flourished in the Tarim Basin during the Cambrian Period. Steroids with less common structural configurations are underutilized and can expand understanding of the early development history of organisms, as well as define petroleum systems.

  3. Formation of the 'Great Unconformity' as a trigger for the Cambrian explosion.

    Science.gov (United States)

    Peters, Shanan E; Gaines, Robert R

    2012-04-19

    The transition between the Proterozoic and Phanerozoic eons, beginning 542 million years (Myr) ago, is distinguished by the diversification of multicellular animals and by their acquisition of mineralized skeletons during the Cambrian period. Considerable progress has been made in documenting and more precisely correlating biotic patterns in the Neoproterozoic-Cambrian fossil record with geochemical and physical environmental perturbations, but the mechanisms responsible for those perturbations remain uncertain. Here we use new stratigraphic and geochemical data to show that early Palaeozoic marine sediments deposited approximately 540-480 Myr ago record both an expansion in the area of shallow epicontinental seas and anomalous patterns of chemical sedimentation that are indicative of increased oceanic alkalinity and enhanced chemical weathering of continental crust. These geochemical conditions were caused by a protracted period of widespread continental denudation during the Neoproterozoic followed by extensive physical reworking of soil, regolith and basement rock during the first continental-scale marine transgression of the Phanerozoic. The resultant globally occurring stratigraphic surface, which in most regions separates continental crystalline basement rock from much younger Cambrian shallow marine sedimentary deposits, is known as the Great Unconformity. Although Darwin and others have interpreted this widespread hiatus in sedimentation on the continents as a failure of the geologic record, this palaeogeomorphic surface represents a unique physical environmental boundary condition that affected seawater chemistry during a time of profound expansion of shallow marine habitats. Thus, the formation of the Great Unconformity may have been an environmental trigger for the evolution of biomineralization and the 'Cambrian explosion' of ecologic and taxonomic diversity following the Neoproterozoic emergence of animals. PMID:22517163

  4. Developmental sequence of Cambrian embryo Markuelia

    Institute of Scientific and Technical Information of China (English)

    DONG XiPing

    2007-01-01

    Based on more exquisitely preserved specimens of Markuelia hunanensis recently recovered from Middle and Upper Cambrian in western Hunan and in the light of Synchrotron radiation X-ray tomographic microscopy, the developmental sequence from cleavage through organogenesis to the pre-hatching of Cambrian embryo Markuelia, especially the developmental sequence during the pre-hatching stage, i.e. from the earliest period when the scalids and tail spines only took shape to the latest period (just about hatching), is established. This developmental sequence provides a pattern of embryonic development during the pre-hatching stage, which has not been established in the living scalidophorans (priapulids, Ioriciferans and kinorhynchs). Thus, it not only enriches our knowledge on the embryonic development of the extant descendants of Markuelia, but also opens a new window to the evolution and development of the animal.

  5. A new formal perspective on 'Cambrian explosions'.

    Science.gov (United States)

    Wallace, Rodrick

    2014-01-01

    The 'Cambrian explosion' 500 Myr ago saw a relatively sudden proliferation of organism Bauplan and ecosystem niche structure that continues to haunt evolutionary biology. Here, adapting standard methods from information theory and statistical mechanics, we model the phenomenon as a noise-driven phase transition, in the context of deep-time relaxation of current path-dependent evolutionary constraints. The result is analogous to recent suggestions that multiple 'explosions' of increasing complexity in the genetic code were driven by rising intensities of available metabolic free energy. In the absence of severe path-dependent lock-in, 'Cambrian explosions' are standard features of blind evolutionary process, representing outliers in the ongoing routine of evolutionary punctuated equilibrium. PMID:24439546

  6. The notion of the Cambrian pananimalia genome.

    OpenAIRE

    Ohno, S.

    1996-01-01

    The toil by photosynthesizing cyanobacteria and blue-green algae of nearly three billion years appeared to have finally resulted in the sufficient accumulation of molecular oxygen. So, the stage was set for the emergence, at the ocean bottom, of diverse animals that were consumers of molecular oxygen. It now appears that this Cambrian explosion, during which nearly all the extant animal phyla have emerged, was of an astonishingly short duration, lasting only 6-10 million years. Inasmuch as on...

  7. Tubicolous enteropneusts from the Cambrian period.

    Science.gov (United States)

    Caron, Jean-Bernard; Morris, Simon Conway; Cameron, Christopher B

    2013-03-28

    Hemichordates are a marine group that, apart from one monospecific pelagic larval form, are represented by the vermiform enteropneusts and minute colonial tube-dwelling pterobranchs. Together with echinoderms, they comprise the clade Ambulacraria. Despite their restricted diversity, hemichordates provide important insights into early deuterostome evolution, notably because of their pharyngeal gill slits. Hemichordate phylogeny has long remained problematic, not least because the nature of any transitional form that might serve to link the anatomically disparate enteropneusts and pterobranchs is conjectural. Hence, inter-relationships have also remained controversial. For example, pterobranchs have sometimes been compared to ancestral echinoderms. Molecular data identify enteropneusts as paraphyletic, and harrimaniids as the sister group of pterobranchs. Recent molecular phylogenies suggest that enteropneusts are probably basal within hemichordates, contrary to previous views, but otherwise provide little guidance as to the nature of the primitive hemichordate. In addition, the hemichordate fossil record is almost entirely restricted to peridermal skeletons of pterobranchs, notably graptolites. Owing to their low preservational potentials, fossil enteropneusts are exceedingly rare, and throw no light on either hemichordate phylogeny or the proposed harrimaniid-pterobranch transition. Here we describe an enteropneust, Spartobranchus tenuis (Walcott, 1911), from the Middle Cambrian-period (Series 3, Stage 5) Burgess Shale. It is remarkably similar to the extant harrimaniids, but differs from all known enteropneusts in that it is associated with a fibrous tube that is sometimes branched. We suggest that this is the precursor of the pterobranch periderm, and supports the hypothesis that pterobranchs are miniaturized and derived from an enteropneust-like worm. It also shows that the periderm was acquired before size reduction and acquisition of feeding tentacles, and

  8. Oxygen Requirements for the Cambrian Explosion

    Institute of Scientific and Technical Information of China (English)

    Xingliang Zhang; Linhao Cui

    2016-01-01

    Hypoxic tolerance experiments may be helpful to constrain the oxygen requirement for animal evolution. Based on literature review, available data demonstrate that fishes are more sensitive to hypoxia than crustaceans and echinoderms, which in turn are more sensitive than annelids, whilst mollusks are the least sensitive. Mortalities occur where O2 concentrations are below 2.0 mg/L, equivalent to saturation with oxygen content about 25% PAL (present atmospheric level). Therefore, the minimal oxygen requirement for maintaining animal diversity since Cambrian is determined as 25% PAL. The traditional view is that a rise in atmospheric oxygen concentrations led to the oxygenation of the ocean, thus triggering the evolution of animals. Geological and geochemical studies suggest a constant increase of the oxygen level and a contraction of anoxic oceans during Ediacaran–Cambrian transition when the world oceans experienced a rapid diversification of metazoan lineages. However, fossil first appearances of animal phyla are obviously asynchronous and episodic, showing a sequence as:basal metazoans>lophotrochozoans>ecdysozoans and deuterostomes. According to hitherto known data of fossil record and hypoxic sensitivity of animals, the appearance sequence of different animals is broadly consistent with their hypoxic sensitivity:animals like molluscs and annelids that are less sensitive to hypoxia appeared earlier, while animals like echinoderms and fishes that are more sensitive to hypoxia came later. Therefore, it is very likely that the appearance order of animals is corresponding to the increasing oxygen level and/or the contraction of anoxic oceans during Ediacaran–Cambrian transition.

  9. Did Gamma Ray Burst Induce Cambrian Explosion?

    CERN Document Server

    Chen, Pisin

    2014-01-01

    One longstanding mystery in bio-evolution since Darwin's time is the origin of the Cambrian explosion that happened around 540 million years ago (Mya), where an extremely rapid increase of species occurred. Here we suggest that a nearby GRB event ~500 parsecs away, which should occur about once per 5 Gy, might have triggered the Cambrian explosion. Due to a relatively lower cross section and the conservation of photon number in Compton scattering, a substantial fraction of the GRB photons can reach the sea level and would induce DNA mutations in organisms protected by a shallow layer of water or soil, thus expediting the bio-diversification. This possibility of inducing genetic mutations is unique among all candidate sources for major incidents in the history of bio-evolution. A possible evidence would be the anomalous abundance of certain nuclear isotopes with long half-lives transmuted by the GRB photons in geological records from the Cambrian period. Our notion also imposes constraints on the evolution of ...

  10. Did gamma ray burst induce Cambrian explosion?

    Science.gov (United States)

    Chen, Pisin; Ruffini, R.

    2015-06-01

    One longstanding mystery in bio-evolution since Darwin's time is the origin of the Cambrian explosion that happened around 540 million years ago (Mya), where an extremely rapid increase of species occurred. Here we suggest that a nearby GRB event 500 parsecs away, which should occur about once per 5 Gy, might have triggered the Cambrian explosion. Due to a relatively lower cross section and the conservation of photon number in Compton scattering, a substantial fraction of the GRB photons can reach the sea level and would induce DNA mutations in organisms protected by a shallow layer of water or soil, thus expediting the bio-diversification. This possibility of inducing genetic mutations is unique among all candidate sources for major incidents in the history of bio-evolution. A possible evidence would be the anomalous abundance of certain nuclear isotopes with long half-lives transmuted by the GRB photons in geological records from the Cambrian period. Our notion also imposes constraints on the evolution of exoplanet organisms and the migration of panspermia.

  11. Yochelcionella (Mollusca, Helcionelloida) from the lower Cambrian of North America

    OpenAIRE

    Atkins C J; Peel J S

    2008-01-01

    Five named species of the helcionelloid mollusc genus Yochelcionella Runnegar & Pojeta, 1974 are recognized from the lower Cambrian (Cambrian Series 2) of North America: Yochelcionella erecta (Walcott, 1891), Y. americana Runnegar &Pojeta, 1980, Y. chinensis Pei, 1985, Y. greenlandica Atkins & Peel, 2004 and Y. gracilis Atkins & Peel, 2004, linking lower Cambrian o...

  12. The Cambrian “explosion”: Slow-fuse or megatonnage?

    OpenAIRE

    Conway Morris, Simon

    2000-01-01

    Clearly, the fossil record from the Cambrian period is an invaluable tool for deciphering animal evolution. Less clear, however, is how to integrate the paleontological information with molecular phylogeny and developmental biology data. Equally challenging is answering why the Cambrian period provided such a rich interval for the redeployment of genes that led to more complex bodyplans.

  13. Trilobite biogeography and Cambrian tectonic models

    Science.gov (United States)

    Burrett, Clive; Richardson, Robert

    1980-03-01

    The biogeographic patterns of Cambrian trilobites are almost impossible to explain on an Early Palaeozoic Pangaea but may be explained by relative movements of several continental blocks separated by wide ocean basins. Realms, regions, provinces and sub-provinces are recognised by progressively agglomerating 450 faunal lists, based on 1371 genera, distributed through eleven time segments. The agglomerating method proposed, is a simple one that may be performed by hand or computer and provides Medial Cambrian results similar to those of Jell (1974) who used principal components and cluster analyses. Simplified results are obtained when time segments are combined or when only the largest list from each 10° (lat. × long.) tessera is used or when only illustrated papers are used or when only lists containing ⩾ 3, 5 or 10 genera are used. The program was also run with all of the presumably planktonic miomerids removed resulting in smaller, better defined provinces with few links between tectonic blocks. The number of polymerid-only realms is three in Albertella Zone times, four in Glossopleura Zone and Eluinia/Conaspis Zone times and five in all other time segments. The average five realms recognised tend to be restricted to one (or rarely two) of the major tectonic blocks: America (excluding Boston and maritime Canada), Europe (including Morocco), Siberia, China and Australia. The existence of the American realm in Argentina through most of the Cambrian and the unlikelihood of a dismembered Gondwanaland necessitates using the latitudinal control hypothesis of Palmer (1972). This hypothesis places the European realm in high palaeolatitudes, the American realm in low palaeolatitudes in the Southern Hemisphere, the Australian realm in low palaeolatitudes in the Northern Hemisphere and the Siberian realm in temperate palaeolatitudes in the Southern Hemisphere. When the miomerids are included, connections between the peripheral ocean-facing regions of one tectonic block

  14. Cambrian Fossil Embryos from Western Hunan,South China

    Institute of Scientific and Technical Information of China (English)

    DONG Xiping

    2009-01-01

    The exquisitely preserved fossil embryos of Markuelia recovered from the limestones of the Middle Cambrian Haoqiao Formation and Upper Cambrian Bitiao formation in western Hunan,South China are described and illustrated in detail for the first time.A new species Markuelia elegans sp.nov.is established based mainly on embryos from the Upper Cambrian.A few of animal's resting eggs,which are comparable with those of the Ediacaran Doushantuo Formation,have been also found in the Upper Cambrian of western Hunan.The membrane of oue egg from the uppermost Cambrian has been replaced by pyrite and the overgrowth of the pyrite crystals exhibits a unique inorganic reducing conditions promoted the excellent preservation for the Markuelia specimens.The study of Markuelia provides not only constraint on the anatomy,affinity,embryonic development and phylogenetic significance of this wormlike animal and but also opens a new window onto the evolution and development of the earliest animals.

  15. Decoupled evolution of soft and hard substrate communities during the Cambrian Explosion and Great Ordovician Biodiversification Event.

    Science.gov (United States)

    Buatois, Luis A; Mángano, Maria G; Olea, Ricardo A; Wilson, Mark A

    2016-06-21

    Contrasts between the Cambrian Explosion (CE) and the Great Ordovician Biodiversification Event (GOBE) have long been recognized. Whereas the vast majority of body plans were established as a result of the CE, taxonomic increases during the GOBE were manifested at lower taxonomic levels. Assessing changes of ichnodiversity and ichnodisparity as a result of these two evolutionary events may shed light on the dynamics of both radiations. The early Cambrian (series 1 and 2) displayed a dramatic increase in ichnodiversity and ichnodisparity in softground communities. In contrast to this evolutionary explosion in bioturbation structures, only a few Cambrian bioerosion structures are known. After the middle to late Cambrian diversity plateau, ichnodiversity in softground communities shows a continuous increase during the Ordovician in both shallow- and deep-marine environments. This Ordovician increase in bioturbation diversity was not paralleled by an equally significant increase in ichnodisparity as it was during the CE. However, hard substrate communities were significantly different during the GOBE, with an increase in ichnodiversity and ichnodisparity. Innovations in macrobioerosion clearly lagged behind animal-substrate interactions in unconsolidated sediment. The underlying causes of this evolutionary decoupling are unclear but may have involved three interrelated factors: (i) a Middle to Late Ordovician increase in available hard substrates for bioerosion, (ii) increased predation, and (iii) higher energetic requirements for bioerosion compared with bioturbation. PMID:27247396

  16. Remagnetized cratonic Cambrian strata from southern Nevada

    Science.gov (United States)

    Gillett, Stephen L.

    1982-08-01

    Stratigraphic sections of Cambrian strata in southeastern Nevada are akin to thin, cratonic facies exposed in the Grand Canyon; their structural setting is much more complicated, however, from Mesozoic and Cenozoic tectonism. Paleomagnetic samples from two sections through these strata appear to have been completely remagnetized. Coarse-grained, lightcolored sandstone from the Tapeats Sandstone yields scattered magnetizations, residing in hematite, that appear to reflect protracted diagenetic acquisition of remanence. A hematitic sandstone in the Bright Angel Shale yields relatively consistent `Paleozoic' directions of magnetization, but petrographic study shows that the hematite results from diagenetic oxidation, and stratigraphic arguments suggest that the oxidation was not penecontemporaneous. Gray limestones of the Jangle and Muav Limestones yield a magnetization, residing in magnetite, that may reflect late Tertiary remagnetization, being imposed during uplift related to the onset of Basin and Range deformation. In any case, this magnetization differs greatly in direction from a hematite magnetization reported from slightly younger Muav Limestone in the Grand Canyon. Both the sampling sites also appear to have been tectonically rotated, but whether this rotation is true or a geometric artifact of the tilt correction cannot be determined from the present data. These results suggest that paleomagnetic data from rocks as old as Cambrian must be scrutinized very carefully before their magnetizations can be accepted as penecontemporaneous, and such scrutiny must include geologic data.

  17. Segmentation, metamerism and the Cambrian explosion.

    Science.gov (United States)

    Couso, Juan Pablo

    2009-01-01

    Data on the molecular and genetic basis of animal development, and on genome sequences, have been challenging our established assumptions about animal evolution for the last decade. Recent such data in animals of particular phylogenetic importance beg us to take another look at whether similarities in developmental and genetic mechanisms in current animals are the product of a common inheritance (homology) or convergent evolution (analogy). The evolution of segmentation, in particular whether segmentation and metameric bodies have arisen just once or several times in evolution, is a prime concern. Segmentation and metamerism are striking developmental and body organisations that exist, in varying degrees, in many complex animals, but the traditional view holds that this is the result of convergent evolution. Here, I review recent palenotological and developmental information and conclude that a metameric body plan is not only a likely ancestral character of bilaterian animals, but also a possible trigger for the Cambrian explosion in body morphology and complexity. This conclusion is supported by the phylogenetic distribution and prevalence of metameric phyla in the Cambrian, and the similarity of the genomes and segmentation mechanisms across current bilaterian phyla. PMID:19247939

  18. Upper Cambrian (Furongian) biostratigraphy in Scandinavia revisited

    DEFF Research Database (Denmark)

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

    2014-01-01

    , 73–87], are resurrected and elevated to superzonal rank. These superzones are usually readily recognized in the field, even by non-specialists, and for general correlation and mapping the more wide-ranging biozones are considerably more practicable than the very detailed zonation (formerly......, Parabolina and Leptoplastus (super)zones as well as the recently introduced Acerocarina Superzone ( = Acerocare Zone of older literature) are maintained and formalized. The Protopeltura praecursor, Peltura minor and Peltura scarabaeoides zones are abandoned and replaced by two new units, named 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 to the...

  19. At the Origin of Animals: The Revolutionary Cambrian Fossil Record

    OpenAIRE

    Budd, Graham E.

    2013-01-01

    The certain fossil record of animals begins around 540 million years ago, close to the base of the Cambrian Period. A series of extraordinary discoveries starting over 100 years ago with Walcott’s discovery of the Burgess Shale has accelerated in the last thirty years or so with the description of exceptionally-preserved Cambrian fossils from around the world. Such deposits of “Burgess Shale Type” have been recently complemented by other types of exceptional preservation. Together with a rema...

  20. An Early Cambrian problematic fossil: Vetustovermis and its possible affinities

    OpenAIRE

    Chen, Jun-Yuan; Huang, Di-Ying; Bottjer, David J.

    2005-01-01

    The Early Cambrian problematic fossil Vetustovermis (Glaessner 1979 Alcheringa 3, 21–31) was described as an annelid or arthropod. Anatomical analysis of 17 new specimens from the Lower Cambrian Maotianshan Shale at Anning, Kunming (South China) does not support its affinities with annelids or arthropods. Anatomical features instead resemble other animal groups including modern flatworms, nemertines and molluscs. The presence of a pelagic slug-like form and ventral foot, as well as a head wit...

  1. Global standard names for the Lowermost Cambrian Series and Stage

    Institute of Scientific and Technical Information of China (English)

    Ed Landing; Shanchi Peng; Loren E.Babcock; Gerd Geyer; Malgorzata Moczydlowska-Vidal

    2007-01-01

    @@ The GSSP marking the base of the Cambrian System was ratified by the IUGS in 1992.Ratification of the GSSP point at the base of the Trichophycus pedum Ichnozone in the Fortune Head section,eastern Newfoundland,Canada,automatically defined the conterminant base of the lowermost series and stage of the Cambrian although names for those subdivisions were not proposed at the time of the decision.

  2. Tectonic Events May Have Triggered the Cambrian Explosion

    Science.gov (United States)

    Wendel, JoAnna

    2014-11-01

    Major geological changes causing sea level rise at the start of the Cambrian period (540-490 million years ago) could have kick-started the Cambrian Explosion—a geological time period when most major phyla of life suddenly appeared in the fossil record. A paper published in the November issue of Geology (doi:10.1130/G35886.1) proposes a new geological mechanism for this event.

  3. Pulse of atmospheric oxygen during the late Cambrian

    OpenAIRE

    Saltzman, Matthew R.; Young, Seth A.; Kump, Lee R.; Gill, Benjamin C.; Lyons, Timothy W.; Runnegar, Bruce

    2011-01-01

    A rise in atmospheric O2 has been linked to the Cambrian explosion of life. For the plankton and animal radiation that began some 40 million yr later and continued through much of the Ordovician (Great Ordovician Biodiversification Event), the search for an environmental trigger(s) has remained elusive. Here we present a carbon and sulfur isotope mass balance model for the latest Cambrian time interval spanning the globally recognized Steptoean Positive Carbon Isotope Excursion (SPICE) that i...

  4. Primitive soft-bodied cephalopods from the Cambrian.

    Science.gov (United States)

    Smith, Martin R; Caron, Jean-Bernard

    2010-05-27

    The exquisite preservation of soft-bodied animals in Burgess Shale-type deposits provides important clues into the early evolution of body plans that emerged during the Cambrian explosion. Until now, such deposits have remained silent regarding the early evolution of extant molluscan lineages-in particular the cephalopods. Nautiloids, traditionally considered basal within the cephalopods, are generally depicted as evolving from a creeping Cambrian ancestor whose dorsal shell afforded protection and buoyancy. Although nautiloid-like shells occur from the Late Cambrian onwards, the fossil record provides little constraint on this model, or indeed on the early evolution of cephalopods. Here, we reinterpret the problematic Middle Cambrian animal Nectocaris pteryx as a primitive (that is, stem-group), non-mineralized cephalopod, based on new material from the Burgess Shale. Together with Nectocaris, the problematic Lower Cambrian taxa Petalilium and (probably) Vetustovermis form a distinctive clade, Nectocarididae, characterized by an open axial cavity with paired gills, wide lateral fins, a single pair of long, prehensile tentacles, a pair of non-faceted eyes on short stalks, and a large, flexible anterior funnel. This clade extends the cephalopods' fossil record by over 30 million years, and indicates that primitive cephalopods lacked a mineralized shell, were hyperbenthic, and were presumably carnivorous. The presence of a funnel suggests that jet propulsion evolved in cephalopods before the acquisition of a shell. The explosive diversification of mineralized cephalopods in the Ordovician may have an understated Cambrian 'fuse'. PMID:20505727

  5. Marine Redox Conditions in the Early Cambrian Ocean:Insights from the Lower Cambrian Phosphorite Deposits, South China

    Institute of Scientific and Technical Information of China (English)

    Haifeng Fan; Hanjie Wen; Xiangkun Zhu

    2016-01-01

    ABSTRACT:It is generally considered that a significant change in oceanic redox conditions occurred during the Ediacaran–Cambrian transition. However, there are currently two major conflicting views on the degree of oxygenation of deep water (oxic vs. ferruginous) during this interval. To date, the oxygenation conditions of the Early Cambrian ocean have not been well constrained. The oxygenation magnitude and mechanism of the Early Cambrian ocean could be critical to the significant biological evolution of the“Cambrian Explosion”. To constrain the Early Cambrian oceanic redox environment, we conducted an integrated study on iron and sulfur isotopes and redox-sensitive elements (Mo, U, and V) of Lower Cambrian phosphorite deposits from two shallow sections (Meishucun and Gezhongwu) and a deeper water section (Zunyi) from the Yangtze Platform, South China. The near zero δ56Fe values from the two shallow sections studied here reflect oxic conditions in the lower phosphorite deposition. An obvious positive shift inδ56Fe and redox-sensitive element content was observed in the middle parts of the two shallow water sections, which might reflect loss of light iron by dissimilatory iron reduction during early diagenesis under suboxic shallow water in the platform. However, the highly positiveδ56Fe values in the deep section could reflect a lower oxidation degree of dissolved Fe(II) under anoxic deep water. The data suggest redox-stratified oceanic conditions during the Early Cambrian, in which completely oxygenated shallow water (platform) coexisted with anoxic deep water (slope). We propose that prolonged upwelling of dissolved organic carbon (DOC)-, Fe(II)- and phosphorus-rich anoxic deep water in a redox-stratified ocean could have increased exchange with the open ocean, resulting in major phosphorite deposition in oxic-suboxic conditions. The progressive oxygenation of the ocean may have facilitated the Early Cambrian biotic diversification.

  6. Lithofacies palaeogeography of the Cambrian in Tarim area

    Institute of Scientific and Technical Information of China (English)

    FENG Zengzhao; BAO Zhidong; WU Maobing; JIN Zhenkui; SHI Xiaozhang

    2007-01-01

    The Tarim area in this paper refers to the present Tarim Basin and its surrounding mountains, bounded on the north by the Middle Tianshan Mountains, on the south by the Kunlun Mountains, on the west by the national boundary of China, and on the east by the Altun Mountains. It covers an area of more than 1 000 000 km2. Based on the quantitative and qualitative data from the stratigraphy and petrology of outcrop and well sections, and according to the single factor analysis and multifactor comprehensive mapping method,the single factor maps of the Lower, Middle and Upper Cambrian, and the lithofacies palaeogeography maps of the Early, Middle and Late Cambrian of the Tarim area, are com-piled. The most important character of these lithofacies pal-aeogeography maps is quantification, I.e. The determination of each palaeogeography unit based on accurate quantitativedata and the quantitative single factor maps. The study marksthe first time that this quantitative method has been appliedin the Tarim area. In the Early Cambrian, the present TarimBasin was mainly a carbonate platform, in which there werepenebank, dolostone flats, and gypsum-halite lake. The South Tianshan Basin and East Tarim Basin were siliceous rock-limestone-mudstone basins. The Kunlun Platform was situ-ated in the south, where there were two small lands. The AltunLand was situated in the southeast. In the Middle and Late Cambrian, the framework of lithofacies palaeogeography was similar to that in the Early Cambrian; the land area was gradually reduced; the basin area was enlarged; while the Tarim Carbonate Platform changed little. The transgression continued from the Early Cambrian to the Late Cambrian.

  7. Explaining the Cambrian "Explosion" of Animals

    Science.gov (United States)

    Marshall, Charles R.

    2006-05-01

    The Cambrian "explosion" is a unique episode in Earth history, when essentially all the animal phyla first appear in the fossil record. A variety of environmental, developmental (genetic), and ecological explanations for this complex and somewhat protracted event are reviewed, with a focus on how well each explains the observed increases in disparity and diversity, the time of onset of the radiation, its duration, and its uniqueness. The increase in disparity (the origin of the phyla) and diversity are best understood as being the result of the interplay of the combinatorial bilaterian developmental system and the increase in the number of needs the first bilaterians had to meet as complex ecological interactions developed. The time of onset is constrained by the evolution of the environment, whereas its duration appears to be controlled primarily by rates of developmental innovation. The uniqueness of the event is either due to ensuing developmental limitation, to ecological saturation, or simply to the exhaustion of ecologically viable morphologies that could be produced by the nascent bilaterian developmental system.

  8. Evidence for microbial dissolution of pyrite from the Lower Cambrian oolitic limestone, South China

    Directory of Open Access Journals (Sweden)

    W. Liu

    2011-03-01

    Full Text Available The oxidative dissolution of the sulphide mineral pyrite (FeS2 has been of significant interest since it affects global geochemical cycles, generates acid mine drainage, and is used in industrial metal extraction. Several different groups of prokaryotes are known to catalyze the dissolution of pyrite and use the free energy generated from the oxidation, which may result in the dissolution of the mineral and the precipitation of the secondary ferric iron minerals either on the cell surface or is separated from the cells. However, straightforward evidence for such metabolic process in the ancient sediments is rare. Here we report pyrite crystals from the Lower Cambrian oolitic limestones that show indications of microbial erosion in various degrees. Erosion pits and tubular micro-tunnels with characteristic shapes and sizes in our samples are generally similar to those obtained from the laboratory studies on the oxidative dissolution of pyrite by iron-oxidizing bacteria. Diagenetic examination demonstrates that the bioerosion predates the consolidation of the limestone. In addition, bacillus-sized and -shaped microfossils encrusted with iron oxides are present in our samples, which are very likely to be fossilized sheaths produced by iron-oxidizing bacteria. Our findings indicate that the microbial oxidative dissolution of pyrite existed in the Cambrian shallow marine carbonate sediments. Furthermore, we suggest that characteristic pitting patterns on the pyrite crystals from ancient sediments are an important clue to trace the evolution of life, in particular, the evolution of metabolism like microbial iron oxidation in the remote past on our planet, independent of biomarkers, isotopic signals and body fossils as well.

  9. Discussions on the sedimentary-tectonic event and tectonic setting of the North Tarim Basin in Cryogenian-Cambrian

    Science.gov (United States)

    Zhou, X. B.; Li, J. H.; Li, W. S.

    2012-04-01

    Across the Tarim Basin, limited surface outcrops of Cryogenian to Cambrian sedimentary succession are completely exposed in the vicinity of Aksu area(Northwest Tarim), Kuruktag(Northeast Tarim)and Southwest Tarim, thus provides a unique, well preserved and accessible means by which to study the early development of the north Tarim Basin. Based on the field geological investigation in the northwestern and northeastern of Tarim Basin, with the referencing of paleomagnetism mapping and previous research, basin evolution process in Cryogenian-Cambrian is discussed according to sedimentary-tectonic event and other evidences. The major lithological types of Cryogenian-Cambrian system in Northeast Tarim are: tillite, clastic rocks(rich in organic matter) and carbonate ,with interbeds of volcanic rocks while in Northwest Tarim, the calstic rocks and carbonate are the common rock type, with tillite and volcanic interbeds in a small amount. The north margin of Tarim Block, which was a part of Rodinia supercontinent, neighboring the northwestern margin of Australia, was deeply rifted in Cryogenian-Ediacaran and developed into two rifts in the northwestern and northeastern margin, while formed a thick layer of the rift-passive margin deposits and the layer in the northwestern rift was not completely developed as the northeastern. The deepest rift-passive magin sediment which can be observed is Cryogenian-Middle Ordovician strata, and the period can be divided into Cryogenian faulted period (supercontinent rifting stage) and Ediacaran-Middle Ordovician subsidence period (plate drifting stage).

  10. Sm-Nd isotopic compositions of Cambrian-Ordovician strata at the Jinggangshan area in Jiangxi Province:Tectonic implications

    Institute of Scientific and Technical Information of China (English)

    SHEN WeiZhou; LING HongFei; SHU LiangShu; ZHANG FangRong; XIANG Lei

    2009-01-01

    Whole-rock Sm-Nd Isotopes were investigated for Cambrian-Ordovician strata from the Jinggangshan area beTween the Yangtze Block and Cathysla Block in South China. These strata were deposited as a greatly thick unit of muddy-sandy laminas with intercalated carbonate and organic carbon-bearing layers. They have low ε(t) values of -13.9 to -7.9 and old Nd model ages of 1842 to 2375 Ma. In t-tdiagram, they are far away from the concordant line but fall within the evolution zone of the Proterozoic crust of South China. This indicates that the Cambrian-Ordovician strata are mainly composed of mat-ters eroded from ancient Paleoproterozoic crust that may mainly consist of continental-derived detrital sediments with high maturity in the Cathyaia Block. However, the Ordovician Jueshangou Formation and Dui'erehi Formation have ε(t) values of -10.5 and -7.9 at the higher end of the above range and Nd model ages of 1842 to 2059 Ma at the lower end of the above range. This suggests involvement of more detritus that were eroded from the relatively juvenile crust from Late Paleoproterozoic to the Early Neoproterozoic. All the Nd model ages for the Cambrian-Ordovlcian sedimentary rocks in the Cathysia Block and the southeastern margin of the Yangtze Block are older than 1800 Ma, suggesting that no material from the Early Paleozoic depleted mantle-derived magmas was involved in these regions.

  11. A suspension-feeding anomalocarid from the Early Cambrian.

    Science.gov (United States)

    Vinther, Jakob; Stein, Martin; Longrich, Nicholas R; Harper, David A T

    2014-03-27

    Large, actively swimming suspension feeders evolved several times in Earth's history, arising independently from groups as diverse as sharks, rays and stem teleost fishes, and in mysticete whales. However, animals occupying this niche have not been identified from the early Palaeozoic era. Anomalocarids, a group of stem arthropods that were the largest nektonic animals of the Cambrian and Ordovician periods, are generally thought to have been apex predators. Here we describe new material from Tamisiocaris borealis, an anomalocarid from the Early Cambrian (Series 2) Sirius Passet Fauna of North Greenland, and propose that its frontal appendage is specialized for suspension feeding. The appendage bears long, slender and equally spaced ventral spines furnished with dense rows of long and fine auxiliary spines. This suggests that T. borealis was a microphagous suspension feeder, using its appendages for sweep-net capture of food items down to 0.5 mm, within the size range of mesozooplankton such as copepods. Our observations demonstrate that large, nektonic suspension feeders first evolved during the Cambrian explosion, as part of an adaptive radiation of anomalocarids. The presence of nektonic suspension feeders in the Early Cambrian, together with evidence for a diverse pelagic community containing phytoplankton and mesozooplankton, indicate the existence of a complex pelagic ecosystem supported by high primary productivity and nutrient flux. Cambrian pelagic ecosystems seem to have been more modern than previously believed. PMID:24670770

  12. Rates of phenotypic and genomic evolution during the Cambrian explosion.

    Science.gov (United States)

    Lee, Michael S Y; Soubrier, Julien; Edgecombe, Gregory D

    2013-10-01

    The near-simultaneous appearance of most modern animal body plans (phyla) ~530 million years ago during the Cambrian explosion is strong evidence for a brief interval of rapid phenotypic and genetic innovation, yet the exact speed and nature of this grand adaptive radiation remain debated. Crucially, rates of morphological evolution in the past (i.e., in ancestral lineages) can be inferred from phenotypic differences among living organisms-just as molecular evolutionary rates in ancestral lineages can be inferred from genetic divergences. We here employed Bayesian and maximum likelihood phylogenetic clock methods on an extensive anatomical and genomic data set for arthropods, the most diverse phylum in the Cambrian and today. Assuming an Ediacaran origin for arthropods, phenotypic evolution was ~4 times faster, and molecular evolution ~5.5 times faster, during the Cambrian explosion compared to all subsequent parts of the Phanerozoic. These rapid evolutionary rates are robust to assumptions about the precise age of arthropods. Surprisingly, these fast early rates do not change substantially even if the radiation of arthropods is compressed entirely into the Cambrian (~542 mega-annum [Ma]) or telescoped into the Cryogenian (~650 Ma). The fastest inferred rates are still consistent with evolution by natural selection and with data from living organisms, potentially resolving "Darwin's dilemma." However, evolution during the Cambrian explosion was unusual (compared to the subsequent Phanerozoic) in that fast rates were present across many lineages. PMID:24035543

  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. A vanished history of skeletonization in Cambrian comb jellies.

    Science.gov (United States)

    Ou, Qiang; Xiao, Shuhai; Han, Jian; Sun, Ge; Zhang, Fang; Zhang, Zhifei; Shu, Degan

    2015-07-01

    Ctenophores are traditionally regarded as "lower" metazoans, sharing with cnidarians a diploblastic grade of organization. Unlike cnidarians, where skeletonization (biomineralization and sclerotization) evolved repeatedly among ecologically important taxa (for example, scleractinians and octocorals), living ctenophores are characteristically soft-bodied animals. We report six sclerotized and armored ctenophores from the early Cambrian period. They have diagnostic ctenophore features (for example, an octamerous symmetry, oral-aboral axis, aboral sense organ, and octaradially arranged ctene rows). Unlike most modern counterparts, however, they lack tentacles, have a sclerotized framework, and have eight pairs of ctene rows. They are resolved as a monophyletic group (Scleroctenophora new class) within the ctenophores. This clade reveals a cryptic history and sheds new light on the early evolution of this basal animal phylum. Skeletonization also occurs in some other Cambrian animal groups whose extant members are exclusively soft-bodied, suggesting the ecological importance of skeletonization in the Cambrian explosion. PMID:26601209

  15. Cambrian explosion triggered by geosphere-biosphere feedbacks

    Science.gov (United States)

    von Bloh, Werner; Bounama, Christine; Franck, Siegfried

    2003-09-01

    A new hypothesis for the cause of the Cambrian explosion is presented. For that the evolution of the planet Earth is described by the co-evolution of the geosphere-biosphere system. Here we specify our previously published Earth system model for the long-term carbon cycle by introducing three different types of biosphere: procaryotes, eucaryotes, and complex multicellular life. They are characterized by different global temperature tolerance windows. The biotic enhancement of silicate weathering by complex multicellular life adds an additional feedback to the system and triggers the Cambrian explosion. The Cambrian explosion is characterized by a sudden increase of biomass and a rapid cooling, which amplified the spread of complex multicellular life. Cooling events in the Neoproterozoic, however, could force a premature appearance of complex multicellular life.

  16. Ediacarian sponge spicule clusters from southwestern Mongolia and the origins of the Cambrian fauna

    Science.gov (United States)

    Brasier, Martin; Green, Owen; Shields, Graham

    1997-04-01

    Carbon and strontium isotopic data are used to show that the earliest sponge spicule clusters and associated phosphatic sediments (with Anabarites) from southwestern Mongolia are of Ediacarian age. Spicule morphologies include bundles of oxeas arranged in three-dimensional quadrules, linked together at junctions by tetracts, pentacts, hexacts, or polyactines. All are referred to the Phylum Porifera, Class Hexactinellida. These sponge spicules provide the oldest remains that can be assigned without question to an extant phylum, and also the first firm evidence for filter feeding and metazoan silica biomineralization in the fossil record. It is suggested that siliceous and phosphatic members of the “Cambrian fauna” may have had their origins in eutrophic and outer shelf facies of the Late Proterozoic.

  17. Darwin's dilemma: the realities of the Cambrian ‘explosion’

    OpenAIRE

    Conway Morris, Simon

    2006-01-01

    The Cambrian ‘explosion’ is widely regarded as one of the fulcrum points in the history of life, yet its origins and causes remain deeply controversial. New data from the fossil record, especially of Burgess Shale-type Lagerstätten, indicate, however, that the assembly of bodyplans is not only largely a Cambrian phenomenon, but can already be documented in fair detail. This speaks against a much more ancient origin of the metazoans, and current work is doing much to reconcile the apparent dis...

  18. Dr. Cooper Curtice - Unknown worker in interpreting the Cambrian of Alabama

    Science.gov (United States)

    Yochelson, E.L.; Osborne, W.E.

    1999-01-01

    Cooper Curtice was an assistant to C. D. Walcott from 1883-1886. In 1885, he spent four months, mostly in Alabama, measuring sections of Paleozoic rocks and searching for fossils, mainly in the Cambrian. In 1888, Walcott concurred with foreign authorities that the rocks called Middle Cambrian in North America were Early Cambrian in age and vice versa, requiring a new interpretation of Cambrian strata. Curtice returned to Alabama for geologic investigations in 1892, and again briefly with Walcott in 1895. Since that time Cambrian stratigraphy in the southeastern United States has remained virtually unchanged.

  19. 内蒙古阿尔山地区下寒武统苏中组混合沉积特征及形成环境研究%Depositional Characteristics and Environment of Mixing Sediments of Lower Cambrian Suzhong Formation in Aershan Area, Inner Mongolia

    Institute of Scientific and Technical Information of China (English)

    曹桐生; 田景春; 朱迎堂; 赵荣华; 解惠; 田江飞; 杨辰雨

    2011-01-01

    Depositional characteristics and environment of the Lower Cambrian Suzhong Formation in Aershan area of Inner Mongolia are analyzed through integrating areal stratum, lithology, section characteristics, and distribution of the grain size. Grain size of the sandstone in the Suzhong Formation presents the following characters: with double or multimodal anisomerous peaks in grain size distribution frequency curves; mainly in positive skewed distribution; numerous but low peak values; poor sorting and most of the grain consists of those of coarse materials. Based on the size parameters, we located in the Sahu diagram and calculated with discriminate function, it is ascertained that the sandstone in the Lower Cambrian Suzhong Formation which lies in Aershan area of Inner Mongolia are deposited in marine delta environment. Nevertheless, most clastic deposits of the Suzhong Formation is macrograin materials with their grain size distribution similar to wave sand of neritic, and with larger suspension population as well; the mixing deposited sandstone and limestone appears lenticular bedding and rhythmic bedding; so we conclude that the sandstone of this area is deposited in the mixed flat of tide dominate delta. The limestone in the area studied mainly are Greyish white sandy limestone, dolomitic limestone, being recrystallized, with honeycombed surface and horizontal bedding, through these, we draw the following conclusion that limestone of the Lower Cambrian Suzhong Formation in Aershan area of Inner Mongolia are deposited in limemud flat.%以内蒙古阿尔山地区下寒武统苏中组为研究对象,综合区域地层、岩石结构、剖面特征、粒度分布特征,对苏中组碳酸盐岩夹碎屑岩的沉积环境进行了深入分析.从粒度分布特征来看,苏中组砂岩粒度分布表现出双峰和多峰不对称,偏度以正偏为主,峰度数值多且比较低,分选性差,以粗粒物质为主等特征;运用萨胡图解投点、判别函数计算

  20. Contribution of Oxygenic Photosynthesis to Palaeo-Oceanic Organic Carbon Sink Fluxes in Early Cambrian Upper Yangtze Shallow Sea:Evidence from Black Shale Record

    Institute of Scientific and Technical Information of China (English)

    Kunyu Wu; Tingshan Zhang; Yang Yang; Yuchuan Sun; Daoxian Yuan

    2016-01-01

    ABSTRACT:The extensive transgression that occurred on the Yangtze Plate in Early Cambrian led to a massive organic carbon pool in the Niutitang Formation. A black shale core section from 3 251.08 to 3 436.08 m beneath the Earth’s surface was studied to estimate the contribution of oxygenic photosyn-thesis to organic carbon sink fluxes in Early Cambrian Upper Yangtze shallow sea. Results indicate that the oxygenic photosynthesis played the most important role in carbon fixation in Early Cambrian. Or-ganic carbon sink was mainly contributed by photosynthetic microorganisms, e.g., cyanobacteria, algae and archaea. The Niutitang Formation was formed in a deep anoxic marine shelf sedimentary envi-ronment at a sedimentation rate of ~0.09±0.03 mm/yr. The initial TOC abundance in Niutitang shale ranged from 0.18%to 7.09%, with an average of 2.15%. In accordance with the sedimentation rate and initial TOC abundance, organic carbon sink fluxes were calculated and found to range from 0.21 to 8.10×103 kg/km2·yr-1, especially the organic carbon sink fluxes in depth between 3 385 and 3 470 m range from 3.80 to 8.10×103 kg/km2·yr-1, with an average of~6.03×103 kg/km2·yr-1, which is much high-er than that of contemporary marine sediments. The organic carbon sink fluxes of Niutitang shale are equal to 0.56 to 21.61×103 kg/km2·yr-1 net oxygen emitted into the Early Cambrian ocean and atmos-phere, this emitted oxygen may have significantly promoted the oxygen level of the Earth’s surface and diversification of metazoans.

  1. 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

  2. New Evidence for Pre-Cambrian Development of Complex Animals

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    @@ Much mystery surrounds the sudden and mushrooming appearance of animals in the fossil record about 540 million years ago. Known as the "Cambrian explosion," the change took place from zero evidence to all the basic types of creatures in today's world within a few million years.

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

    DEFF Research Database (Denmark)

    Mangano, M. Gabriela; Bromley, Richard Granville; Harper, David A.T.; Nielsen, Arne Thorshøj; Smith, M. Paul; Vinther, Jakob

    2012-01-01

    Widespread microbial mats and the absence of significant bioturbation resulted in a poorly developed mixed layer and extensive cohesive substrates during the Ediacaran-Cambrian transition. Large nonbiomineralized arthropod carapaces overprinted with trails, interconnected burrow systems, narrow-c...... served as the primary food for small macrofauna and meiofauna....

  4. Fossils, molecules and embryos: new perspectives on the Cambrian explosion

    Science.gov (United States)

    Valentine, J. W.; Jablonski, D.; Erwin, D. H.

    1999-01-01

    The Cambrian explosion is named for the geologically sudden appearance of numerous metazoan body plans (many of living phyla) between about 530 and 520 million years ago, only 1.7% of the duration of the fossil record of animals. Earlier indications of metazoans are found in the Neoproterozic; minute trails suggesting bilaterian activity date from about 600 million years ago. Larger and more elaborate fossil burrows appear near 543 million years ago, the beginning of the Cambrian Period. Evidence of metazoan activity in both trace and body fossils then increased during the 13 million years leading to the explosion. All living phyla may have originated by the end of the explosion. Molecular divergences among lineages leading to phyla record speciation events that have been earlier than the origins of the new body plans, which can arise many tens of millions of years after an initial branching. Various attempts to date those branchings by using molecular clocks have disagreed widely. While the timing of the evolution of the developmental systems of living metazoan body plans is still uncertain, the distribution of Hox and other developmental control genes among metazoans indicates that an extensive patterning system was in place prior to the Cambrian. However, it is likely that much genomic repatterning occurred during the Early Cambrian, involving both key control genes and regulators within their downstream cascades, as novel body plans evolved.

  5. A vanished history of skeletonization in Cambrian comb jellies

    OpenAIRE

    Ou, Qiang; Xiao, Shuhai; Han, Jian; Sun, Ge; Zhang, Fang; Zhang, Zhifei; Shu, Degan

    2015-01-01

    Ctenophores are traditionally regarded as “lower” metazoans, sharing with cnidarians a diploblastic grade of organization. Unlike cnidarians, where skeletonization (biomineralization and sclerotization) evolved repeatedly among ecologically important taxa (for example, scleractinians and octocorals), living ctenophores are characteristically soft-bodied animals. We report six sclerotized and armored ctenophores from the early Cambrian period. They have diagnostic ctenophore features (for exam...

  6. A New Landmark for Exploration of the Cambrian Explosion

    Institute of Scientific and Technical Information of China (English)

    Zhao Baohua; Song Jianlan; Guo Haiyan

    2002-01-01

    @@ New studies suggest that the Kaili Biota in southwestern China's Guizhou Province could be the third revealing evidence for the spectacular Cambrian Explosion of life about 530 million years ago, next to the Burgess Shale Biota of Canada, found in 1909,and the Chengjiang Biota, brought to light in Yunnan Province, China,in 1984.

  7. The First Paleomagnetic data from the Cambrian basalts of Henrietta Island (De Long Archipelago, Arctic Ocean)

    Science.gov (United States)

    Metelkin, D. V.; Zhdanova, A.; Vernikovskiy, V. A.; Matushkin, N. Y.

    2015-12-01

    Henrietta Island in De Long archipelago (East-Siberian sea) still remains poorly studied geologically but last investigations show that its volcano-sedimentary sequences can help reconstruct tectonic evolution of East Russian Arctic in Early Paleozoic stage. The deposits lying on Precambrian basements are deformed to varying degrees and intruded by mafic dykes.The study was carried out on two basaltic lava flows whose 40Ar/39Ar age is 520.6±9.5 Ma. Previously the age of these basalts was assumed Cretaceous. According to available data the underlaying sediments contain zircons with Cambrian and Ordovician ages but all boundaries between these basalts and other strata are tectonic. So we suppose the age of basalts as Middle Cambrian but more precise geochronological data are required. All magnetic measurements were performed at the Laboratory of Geodynamics and Paleomagnetism of Institute of Petroleum Geology and Geophysics (Novosibirsk). Basalt samples has relatively high magnetic susceptibility values varying from 5x10-4 to 180x10-4SI units. NRM values range is from 3 to 170 mA/m. Petromagnetic parameters including also coercive characteristics point at the good potentially preserving primary magnetization. Stepwise thermal demagnetization permits to isolate characteristic components of magnetization and calculate mean directions in two lava flows: 1. Ds=294.3°, Is=29.1°, K=81.1, α95=5.1; 2. Ds=301.0°, Is=28.3°, K=34.4, α95=7.9). The mean paleomagnetic pole has coordinates: Plat=20.9°, Plong = 42.6°, dp/dm=14.3/7.9. Paleolatitude was defined as 15.3° but the question of the hemisphere for De Long Islands is open yet. In case of south hemisphere in Middle Cambrian according to available paleomagnetic data De Long islands could be placed close to Taimyr margin of Siberia and in case of northern hemisphere they may be located near south (in present-day coordinates) margin of Siberia. The work was supported by grant RFBR 14-05-31399 and Russian Research Fund

  8. 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

  9. Detrital zircon geochronology of Neoproterozoic to Middle Cambrian miogeoclinal and platformal strata: Northwest Sonora, Mexico

    Science.gov (United States)

    Gross, E.L.; Stewart, John H.; Gehreis, G.E.

    2000-01-01

    Eighty-five detrital zircon grains from Mesoproterozoic and/or Neoproterozoic to Middle Cambrian sedimentary strata in northwest Sonora, Mexico, have been analyzed to determine source terranes and provide limiting depositional ages of the units. The zircon suites from the Mesoproterozoic and/or Neoproterozoic El Alamo Formation and El Aguila unit yield ages between 1.06 Ga and 2.67 Ga, with predominant ages of 1.1 to 1.2 Ga. Zircons from the Lower? and Middle Cambrian Bolsa Quartzite show age groups from 525 Ma to 1.63 Ga, with a dominant population of 1.1 to 1.2 Ga grains. Grains older than 1.2 Ga in the samples were most likely derived from basement terranes and ???1.4 Ga granitic bodies of the southwest U.S. and northwest Mexico. It is also possible that the sediments were transported from the south, although source rocks of the appropriate age are not presently exposed south of the study area in northern Mexico. Three possibilities for the dominant 1.1 to 1.2 Ga grains include derivation from: (I) exposures of the Grenville belt in southern North America, (2) local 1.1-1.2 Ga granite bodies, or (3) a southern source, such as the Oaxaca terrane, that was subsequently rifted away. Sampling of additional units in the western U.S. and northern Mexico may help resolve the ambiguity surrounding the source of the 1.1 to 1.2 Ga grains.

  10. 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.

  11. Reconstructing redox conditions of mesoproterozoic-early Cambrian seawater using δ98/95Mo

    International Nuclear Information System (INIS)

    Full text: Mo isotope composition of seawater is determined by its relative removal in oxic and anoxic sinks as Mo isotope fractionates during its removal from seawater in oxic sediments whereas it remains invariable during its precipitation in reducing sediments. Hence, Mo isotope composition of reducing sediments can be used to track the temporal variation in redox condition of the global ocean. In this study an attempt is being made to reconstruct the redox conditions during Mesoproterozoic-Early Cambrian period using δ98/95∼Mo in black shales from Vindhyan and Outer belt of Lesser Himalaya. This time span witnessed the important evolutionary changes in the early earth such as rise in atmospheric oxygen and changes in the biosphere. Samples processed for this study were collected from Bijaigarh Shales of Kaimur formation of the Vindhyan and Lower Tal formation of the Lesser Himalaya. The depositional ages of these formations was estimated to be -1200 Ma and -540 Ma for Bijaigarh and Tal formations respectively. Mo isotope composition of black shales were determined by their complete acid digestion in presence of 97Mo-100Mo double spike followed by column chromatography separation. Mo isotope composition in purified samples were analysed using Finnigan Neptune MC-ICP-MS at Physical Research Laboratory. δ98/95% Mo measured in Bijaigarh Shales indicate variation from 0.4 to 1.35% with concentration ranging from 1.6-34 ppm whereas the Tal black shales display variability of 0.3-1.5%0 with concentration 16-80 ppm. In general, higher 09%sMo in Bijaigarh shales are associated with higher Mo concentration indicating the dominance of seawater Mo. Lower δ99/95%Mo in some samples could result from detrital component. Based on these data it can be inferred that Mesoproterozoic ocean was more anoxic compared to that of Early Cambrian and the contemporary ocean. More work is underway to track and further quantify the anoxicity of the ocean with time

  12. New Vetulicoliids from the Lower Cambrian Guanshan Fauna,Kunming

    Institute of Scientific and Technical Information of China (English)

    LUO Huilin; FU Xiaoping; HU Shixue; LI Yong; CHEN Liangzhong; YOU Ting; LIU Qi

    2005-01-01

    The Guanshan Fauna, a soft-bodied fauna intermediate between the Chengjiang Fauna and the Kaili Fauna and also the Burgess Shale Fauna stratigraphically, consists of trilobites, trilobitoides, Tuzoia, Vetulicola, Paleoscolex, brachiopods and sponges. The discovery and research of this fauna is of great significance in understading the "Cambrian Explosion" and the evolution of early life. The occurrence of vetulicoliids from the Guanshan Fauna not only adds new members to the taxonomic list, but also provides new information to the evolution of this animal group. This paper describe Vetulicola gantoucunensis Luo, Fu et Hu sp. nov. from the Lower Cambrian Wulongqing Formation in the Kunming area. Also presented are the amended description of Vetulicola and the comparisons with related genera within Vetulicoliids. The affinity, distribution, as well as evolution of vetulicoliids are discussed.

  13. New and extraordinary Early Cambrian sponge spicule assemblage from China

    Science.gov (United States)

    Zhang, Xi-Guang; Pratt, Brian R.

    1994-01-01

    The fossil record of siliceous sponges, compared with that of other skeleton- secreting Metazoa, is poorly known, based as it is on disarticulated spicules and sporadically preserved body fossils. Abundant spicules recovered from Lower Cambrian strata in Shaanxi, China, essentially double the known morphological diversity of siliceous sponges for that interval of geologic time. These fossils, along with a comparable coeval fauna from South Australia, have a remarkably modern aspect, thereby demonstrating that the principal siliceous sponge groups and styles of body architecture were established quickly in the earliest Phanerozoic as part of the Cambrian "explosion" and that they inhabited a variety of low-energy, relatively deep water settings. The similarity of spicule shape and variation to that of younger assemblages reflects a conservative architecture for the siliceous sponges.

  14. Cambrian extensional tectonics and magmatism within the Southern Oklahoma aulacogen

    Science.gov (United States)

    McConnell, D. A.; Gilbert, M. C.

    1990-03-01

    The tectonic evolution of the Southern Oklahoma aulacogen is partially constrained by the petrological consequences of a bimodal igneous suite associated with the Cambrian rift. Mineralogical and compositional layers and erosional surfaces are recognized as initially subplanar, subhorizontal markers. The progressive rotation of these horizons can be explained by uniform-sense normal faulting. Magmatism, confined to the aulacogen trend, elevated the thermal gradient producing a crustal strength-anisotropy. This ensured the localization of the extension throughout the Cambrian rifting event. The presence of a substantial volume of mafic igneous rocks within the crust along the aulacogen's trend suggests that crustal attenuation was compensated for by the addition of mantle derived material during extension.

  15. Upper Cambrian chitons (Mollusca, polyplacophora) from Missouri, USA

    Science.gov (United States)

    Pojeta, J., Jr.; Vendrasco, M.J.; Darrough, G.

    2010-01-01

    Numerous new specimens reveal a greater presence of chitons in Upper Cambrian rocks than previously suspected. Evidence is presented showing that the chiton esthete sensory system is present in all chiton species in this study at the very beginning of the known polyplacophoran fossil record. The stratigraphic occurrences and paleobiogeography of Late Cambrian chitons are documented. The 14 previously-named families of Cambrian and Ordovician chitons are reviewed and analyzed. Aulochitonidae n. fam. is defined, based on Aulochiton n. gen.; A. sannerae n. sp. is also defined. The long misunderstood family Preacanthochitonidae and its type genus Preacanthochiton Bergenhayn, 1960, are placed in synonymy with Mattheviidae and Chelodes Davidson & King, 1874, respectively; Eochelodes Marek, 1962, also is placed in synonymy with Chelodes, and Elongata Stinchcomb & Darrough, 1995, is placed in synonymy with Hemithecella Ulrich & Bridge, 1941. At the species level, H. elongata Stinchcomb & Darrough, 1995, and Elongata perplexa Stinchcomb & Darrough, 1995, are placed in synonymy with H. eminensis Stinchcomb & Darrough, 1995. The Ordovician species H. abrupta Stinchcomb & Darrough, 1995, is transferred to the genus Chelodes as C. abrupta (Stinchcomb & Darrough, 1995). The Ordovician species Preacanthochiton baueri Hoare & Pojeta, 2006, is transferred to the genus Helminthochiton as H. ? baueri (Hoare & Pojeta, 2006). The Ordovician species H. marginatus Hoare & Pojeta, 2006, is transferred to the genus Litochiton as L. marginatus (Hoare & Pojeta, 2006). Matthevia walcotti Runnegar, Pojeta, Taylor, & Collins, 1979, is treated as a synonym of Hemithecella expansa Ulrich & Bridge, 1941. In addition, other multivalved Cambrian mollusks are discussed; within this group, Dycheiidae n. fam. is defined, as well as Paradycheia dorisae n. gen. and n. sp. Cladistic analysis indicates a close relationship among the genera here assigned to the Mattheviidae, and between Echinochiton Pojeta

  16. Contributions to the Proterozoic and Cambrian Evolution of Eukaryotes

    OpenAIRE

    Dong, Lin

    2007-01-01

    This thesis makes several contributions to improve our understanding of Proterozoic-Cambrian evolution of eukaryote life. Chapter 1 provides, for the first time, a quantitative characterization of the evolutionary trends of Proterozoic macroalgae. The analysis reveals that morphological disparity of Paleoproterozoic macroalgae was low but increased in the Mesoproterozoic and Ediacaran, with a plateau in between. There was also a significant increase in thallus surface/volume ratio and maxi...

  17. 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

    2015-01-01

    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. PMID:26610151

  18. Early-Middle Cambrian Palynomorph Microfossils and Related Geochemical Events in South China

    Institute of Scientific and Technical Information of China (English)

    Leiming Yin; Chunjiang Wang; Yuanlong Zhao; Zhiji Ou

    2016-01-01

    The earliest Cambrian acritarch ‘Asteridium–Heliosphaeridium–Comasphaeridium’ assemblage and the Early Cambrian (‘Chiungchussuan’) acritarch ‘Skiagia ornate–Fimbriaglomerella membranacea’ assemblage in South China can be correlated with assemblages from synchronous strata elsewhere in the world. Recent geochemical study and biomarker evidence further confirm a biostratigraphic change between Cambrian Series 2 and Series 3 and support the recognition of a major geological and biotic event during this time interval.

  19. First report of Crumillospongia (Demospongea) from the Cambrian of Europe (Murero biota, Spain)

    OpenAIRE

    García-Bellido D C; Dies Álvarez M E; Gámez Vintaned J A Liñán E; Gozalo R

    2011-01-01

    The demosponge genus Crumillospongia, originally described from the Burgess Shale (middle Cambrian of Canada), has only been cited from lower and middle Cambrian localities of North America and China. The taxon is now also described from uppermost lower Cambrian rocks of the Murero Lagerstätte (Zaragoza Province, NE Spain). Crumillospongia mureroensis sp. nov. is a small to medium sized sack-shaped to elongate demosponge characterized by the presence of d...

  20. Lower Cambrian polychaete from China sheds light on early annelid evolution

    OpenAIRE

    Liu, Jianni; Ou, Qiang; Han, Jian; Li, Jinshu; Wu, Yichen; Jiao, Guoxiang; He, Tongjiang

    2015-01-01

    We herein report a fossilized polychaete annelid, Guanshanchaeta felicia gen. et sp. nov., from the Lower Cambrian Guanshan Biota (Cambrian Series 2, stage 4). The new taxon has a generalized polychaete morphology, with biramous parapodia (most of which preserve the evidence of chaetae), an inferred prostomium bearing a pair of appendages, and a bifid pygidium. G. felicia is the first unequivocal annelid reported from the Lower Cambrian of China. It represents one of the oldest annelids among...

  1. 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

  2. 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

  3. Giant submarine landslide grooves in the Neoproterozoic/Lower Cambrian Phe Formation, northwest Himalaya: Mechanisms of formation and palaeogeographic implications

    Science.gov (United States)

    Draganits, E.; Schlaf, J.; Grasemann, B.; Argles, T.

    2008-04-01

    Giant groove casts have been found in the upper Proterozoic to Lower Cambrian Phe Formation (Haimanta Group), a siliciclastic sandstone/shale succession in the Tethyan Zone of the Higher Himalaya tectonic unit. The grooves are among the largest linear erosion structures related to submarine mass-movements observed in the geologic record. They are up to 4 m wide, about 0.2 m deep and can be traced for more than 35 m without changing their character. The grooves are straight, subparallel to cross-cutting striations with shallow semi-circular cross-sections and well-defined superimposed minor ridges and grooves. Groove casts exist on the soles of several sandstone beds within a 73 m thick logged section, commonly associated with flute casts. Their characteristics were compared with several other types of ancient and modern submarine linear erosion structures. A sand-rich, non-channelized basin floor depositional environment is inferred from the lithofacies, the combination of sedimentary structures, the lack of coarse-grained pebbly facies, the lateral continuity of beds, and the lack of channel structures. The grooves probably formed by laminar debris flows/concentrated density flows dragging blocks of already lithified sediment across the basin floor. When the bedding is structurally rotated back to horizontal, the groove casts show consistent North-South oriented palaeocurrent trends, with South-directed palaeocurrent directions indicated by flute casts. These palaeocurrent orientations contrast with previous palaeogeographic reconstructions of this area, which propose sediment delivery from the South. We therefore suggest a new "double provenance" model for the spatial relationship of late Proterozoic to Early Cambrian strata of the Himalaya, in which Lesser and Tethyan Himalayan age-equivalent sediment was deposited in a connected basin, where the former received detritus from the South, and the latter from a hitherto unknown source in the North. One possible

  4. Isotopic evolution of the terminal Neoproterozoic and early Cambrian carbon cycle on the northern Yangtze Platform, South China

    Institute of Scientific and Technical Information of China (English)

    GUO Qingjun; LIU Congqiang; Harald STRAUSS; Tatiana GOLDBERG

    2003-01-01

    Profound geotectonic, climatic and biological changes occur during the terminal Neoproterozoic and its transition into the early Cambrian. These are reflected in temporal variations of the chemical and isotopic composition of seawater. We are studying a sequence of sedimentary rocks at the Shatan section, northern Yangtze Platform, Sichuan Province of China. This succession comprises, in ascending stratigraphic order, predominantly calcareous sediments of the Sinian upper Dengying Formation and black shales of the lower Cambrian Guojiaba Formation (time equivalent of Niutitang Fm.). Paleoenvironmental setting represents shallow-water shelf deposits. The objective of our study is to provide temporal records for the isotopic compositions of organic and carbonate carbon throughout this time interval. Organic carbon isotope values display a range between -35.8‰ and -30.1‰ with clear stratigraphic variations. Carbonate carbon isotope data vary between -3.5‰ and +0.5‰. These secular variations are interpreted to reflect perturbations of the global carbon cycle, specifically changes in the fractional burial of organic carbon. However, local conditions have further affected the isotopic signals.

  5. A Euxinic-Wedge Model for Mo Cycling in the Early Cambrian Oceans

    Science.gov (United States)

    Li, C.; Cheng, M.; Zhou, L.; Algeo, T. J.; Jin, C. S.; Lei, L. D.; Feng, L. J.; Jiang, S. Y.

    2015-12-01

    Ocean redox conditions during the early Cambrian, a critical period in Earth history marked by rapid evolution of animals, are uncertain. Previous studies have suggested well oxic conditions based on Mo isotopes and stratified, anoxic deep waters based on Fe-S-C and trace metal data. The Niutitang Formation (529-514 Ma) at Yangjiaping (South China) consists of a lower black shale member (LM, 0-18 m) and an upper gray silty shale member (UM, 24-80 m). The LM is moderately to strongly enriched in Mo, U and V, and heterogeneous in Mo-isotopic compositions (δ98Mo = ‒0.65‰ to +2.14‰), while the UM shows lesser enrichment of Mo, U and V, higher Mo/U ratios, and intermediate and more uniform δ98Mo (+1.16‰ to +1.71‰). The metal data and previously reported Fe-speciation data suggest a redox change from dominantly euxinic conditions for the LM to suboxic or weakly anoxic-euxinic conditions for the UM, consistent with a shift of the chemocline from the water column to the sediment during a eustatic fall. We propose an "euxinic wedge" model for the δ98Mo patterns observed here. In this model, the early Cambrian ocean exhibited a lateral transition from ferruginous conditions in nearshore areas to euxinic conditions at mid-depths and back to ferruginous conditions in offshore areas. This pattern was the result of terrigenous Fe-Mnox reduction, sulfate resupply via rivers, and hydrothermal inputs of reactive Fe into the deep basin. Within this framework, sedimentary δ98Mo variation in the study units can be explained through the combined effects of Mo isotopic fractionation associated with Fe-Mnox adsorption and depth-dependent H2S concentrations. Importantly, the heaviest δ98Mo values, which were previously interpreted to reflect full oxygenation, can be explained by the operation of a globally widespread Fe-Mn particulate shuttle that removed large quantities of isotopically light Mo to the sediment, leaving seawater enriched in 98Mo.

  6. 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

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

    DEFF Research Database (Denmark)

    Topper, Timothy P.; Skovsted, Christian B.; Peel, John S.; Harper, David A. T.

    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...

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

    Science.gov (United States)

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

    2013-09-22

    Burgess Shale-type deposits are renowned for their exquisite preservation of soft-bodied organisms, representing a range of animal body plans that evolved during the Cambrian 'explosion'. However, the rarity of these fossil deposits makes it difficult to reconstruct the broader-scale distributions of their constituent organisms. By contrast, microscopic skeletal elements represent an extensive chronicle of early animal evolution--but are difficult to interpret in the absence of corresponding whole-body fossils. Here, we provide new observations on the dorsal spines of the Cambrian lobopodian (panarthropod) worm Hallucigenia sparsa from the Burgess Shale (Cambrian Series 3, Stage 5). These exhibit a distinctive scaly microstructure and layered (cone-in-cone) construction that together identify a hitherto enigmatic suite of carbonaceous and phosphatic Cambrian microfossils--including material attributed to Mongolitubulus, Rushtonites and Rhombocorniculum--as spines of Hallucigenia-type lobopodians. Hallucigeniids are thus revealed as an important and widespread component of disparate Cambrian communities from late in the Terreneuvian (Cambrian Stage 2) through the 'middle' Cambrian (Series 3); their apparent decline in the latest Cambrian may be partly taphonomic. The cone-in-cone construction of hallucigeniid sclerites is shared with the sclerotized cuticular structures (jaws and claws) in modern onychophorans. More generally, our results emphasize the reciprocal importance and complementary roles of Burgess Shale-type fossils and isolated microfossils in documenting early animal evolution. PMID:23902914

  9. Community structure and composition of the Cambrian Chengjiang biota

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Based on previously published species data(228 species in over 18 phyla) and field sampling(114 species and 18406 individuals) in the Chengjiang-Haikou-Anning area,we analyzed quantitatively the paleocommunity composition and structure of the Cambrian Chengjiang biota(Cambrian Series 2,eastern Yunnan,China).Arthropods dominate the community both in species diversity(species:37%) and in abundance(individuals:51.8%).Priapulids(individuals:22.6%) and brachiopods(individuals:16.3%) follow in abundance rank.The arthropod Kunmingella douvillei(26.2%),the priapulid Cricocosmia jinning-ensis(15.4%),and the brachiopod Diandongia pista(11%) are the three most abundant species.Ecological analyses show that the community was dominated by epifaunal organisms(species:63%,individuals:68.4%) followed by infaunal organisms(species:11.9%,individuals:25.9%),nektobenthic organisms(species:11.5%,individuals:2.6%),and pelagic organisms(species:5.3%,individuals:3.1%).The diverse feeding strategies,dominated by suspension feeders(species:35.6%,individuals:26.1%) and hunter/scavengers(species:31.1%,individuals:40.4%),indicate the former existence of a complex food chain and intense competition.Epifaunal vagrant omnivores(28.2%),infaunal vagrant hunter/scavengers(19.8%),epifaunal sessile suspension feeders(17.7%),and epifaunal vagrant hunter/scavengers(15.3%) were the most abundant ecological groups,represented primarily by arthropods,poriferans,priapulids,and brachiopods.Ecological group analyses reveal that the early Cambrian Chengjiang biota is similar in community patterns and functional relations to modern biotas in shallow marine settings.

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

    Directory of Open Access Journals (Sweden)

    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 (

  11. Nomenclature of Cambrian epochs and series based on GSSPs-Comments on an alternative proposal by Rowland and Hicks

    Institute of Scientific and Technical Information of China (English)

    Shanchi Peng; Loren E. Babcock; Gerd Geyer; Malgorzata Moczydlowska

    2006-01-01

    @@ In this issue, Rowland & Hicks advocate a nomenclature for the four epochs of the Cambrian Period that carries over the terms Early, Middle, and Late Cambrian from previous usage (but with new definitions) and introduces a non-geographically-based term, Ichnocambrian, for the earliest Cambrian epoch.

  12. A Precambrian-Cambrian oil play in southern Utah

    Energy Technology Data Exchange (ETDEWEB)

    Lillis, P.G.; Palacas, J.G.; Warden, A. [Geological Survey, Denver, CO (United States)

    1995-06-01

    The potential of the Precambrian Chuar Group as a petroleum source rock in southern Utah and northern Arizona resulted in the drilling of two wildcat wells in 1994. Both wells penetrated the Cambrian Tapeats Sandstone (the target reservoir rock) and presumably Precambrian rocks. The first well, Burnett Federal 36-1, was drilled east of Kanab, Utah (sec.36, T.34S., R.3W.) to a total depth of 5,365 ft and encountered Precambrian (?) reddish-brown sedimentary rocks at 4,790 ft. The Tapeats Sandstone had live oil shows and minor CO{sub 2} (?) gas shows. The second well, BHP Federal 28-1, was drilled near Capitol Reef (sec.28, T.33S., R.7E.) to a total depth of 6,185 ft and encountered the Tapeats Sandstone at 5,922 ft and Precambrian (?) phyllite at 6,125 ft. The upper Paleozoic rocks had abundant live oil/tar shows, and the Cambrian Bright Angel Shale and Tapeats Sandstone had numerous oil shows. There were no gas shows in the well except for a large CO{sub 2} gas kick in the Tapeats Sandstone. A drill-stem test from 5,950 to 6,185 ft yielded mostly CO{sub 2} (92%) and nitrogen gas (6%) and minor amounts of helium, argon, hydrogen, and methane. The {delta}{sup 13}C of the CO{sub 2} is -3.9 per mil PDB. The chemical composition of the extracted oil in the Cambrian sandstones is significantly different than oils produced from the Upper Valley field (upper Paleozoic reservoirs) and the tar sands that are widespread throughout southern and central Utah. However, the oil composition is similar in several aspects to the composition of some of the Precambrian Chuar Group bitumen extracts from the Grand Canyon area in Arizona. The encouraging features of both wells are the good reservoir characteristics and oil shows in the Tapeats Sandstone. In the BHP well the oil appears to be a new oil type, possibly derived from Precambrian or Cambrian source rocks.

  13. The Cambrian explosion triggered by critical turning point in genome size evolution.

    Science.gov (United States)

    Li, Dirson Jian; Zhang, Shengli

    2010-02-01

    The Cambrian explosion is a grand challenge to science today and involves multidisciplinary study. This event is generally believed as a result of genetic innovations, environmental factors and ecological interactions, even though there are many conflicts on nature and timing of metazoan origins. The crux of the matter is that an entire roadmap of the evolution is missing to discern the biological complexity transition and to evaluate the critical role of the Cambrian explosion in the overall evolutionary context. Here, we calculate the time of the Cambrian explosion by a "C-value clock"; our result quite fits the fossil records. We clarify that the intrinsic reason of genome evolution determined the Cambrian explosion. A general formula for evaluating genome size of different species has been found, by which the genome size evolution can be illustrated. The Cambrian explosion, as a major transition of biological complexity, essentially corresponds to a critical turning point in genome size evolution. PMID:20074549

  14. 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.

  15. Source tracing of noble metal elements in Lower Cambrian black rock series of Guizhou-Hunan Provinces, China

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The Lower Cambrian black rock series of South China is abnormally rich in noble metal elements. According to the concentrations, the ratios, the relations, the distribution and partition patterns of noble metal elements, the authors think that the noble metals and other elements are neither directly from extraterrestrial materials, nor from the products of normal marine sedimentation. The abnormal enrichment of noble metal elements is closely related with hydrothermal fluid that flew out on the sea floor through deep cycling and reaction with Proterozoic ultramafic-mafic igneous rocks forming noble metal rich fluid. It is possible to form industrial multiple-element- ore-deposits, especially hydrothermal type platinum-group-element-ore-deposits in the region with strong hydrothermal action.

  16. Source tracing of noble metal elements in Lower Cambrian black rock series of Guizhou-Hunan Provinces, China

    Institute of Scientific and Technical Information of China (English)

    李胜荣; 高振敏

    2000-01-01

    The Lower Cambrian black rock series of South China is abnormally rich in noble metal elements. According to the concentrations, the ratios, the relations, the distribution and partition patterns of noble metal elements, the authors think that the noble metals and other elements are neither directly from extraterrestrial materials, nor from the products of normal marine sedimentation. The abnormal enrichment of noble metal elements is closely related with hydrothermal fluid that flew out on the sea floor through deep cycling and reaction with Proterozoic ultramafic-mafic igneous rocks forming noble metal rich fluid. It is possible to form industrial multiple-element-ore-deposits, especially hydrothermal type platinum-group-element-ore-deposits in the region with strong hydrothermal action.

  17. A New Ichnogenus Kailidiscus Produced by Attachment from the Middle Cambrian Kaili Formation in Taijiang, Guizhou Province, China

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Over 190 specimens of an attachment ichnofossil Kailidiscus (n. ichnogen.) have been found in the Kaili Bitoa, a Burgess Shale-type biota, from the middle Kaili Formation (early Middle Cambrian) in Taijiang County, Guizhou Province, southern China. Kailidiscus is an epichnia with a circular to oval attachment platform, on which there is a carbonaceous film probably formed by the body of the living organism. Structures such as a marginal furrow, an inner and outer marginal ride, many convex fold-ridges, and a large caved peripheral furrow on the attachment platform may be the result of basal tissues of a sessile organism that wrinkled to increase the attachment's surface area. The Kailidiscus organism may have been a sessile cnidarian attached to the muddy seafloor. Kailidiscus organisms lived in relatively quiet water,and were buried by a sudden influx of sediment.

  18. Development, triploblastism, physics of wetting and the Cambrian explosion.

    Science.gov (United States)

    Fleury, Vincent

    2013-09-01

    The Cambrian explosion is characterized by the sudden outburst of organized animal plans, which occurred circa 530 M years ago. Around that time, many forms of animal life appeared, including several which have since disappeared. There is no general consensus about "why" this happened, and why it had any form of suddenness. However, all organized animal plans share a common feature: they are triploblastic, i.e., composed of 3 layers of tissue, endoderm, ectoderm and mesoderm. I show here that, within simple hypotheses, the formation of the mesoderm has intrinsically a physical exponential dynamics, leading rapidly to triploblastism, and eventually, to animal formation. A novel physico-mathematical framework including epithelium-mesenchyme transition, visco-elastic constitutive equations, and conservation laws, is presented which allows one to describe gastrulation as a self-wetting phenomenon of a soft solid onto itself. This phenomenon couples differentiation and migration during gastrulation, and leads in a closed form to an exponential scaling law for the formation of the mesoderm. Therefore, the Cambrian explosion might have started, actually, by a true viscoelastic "explosion": the exponential run-away of mesenchymal cells. PMID:23959076

  19. Preservational Pathways of Corresponding Brains of a Cambrian Euarthropod.

    Science.gov (United States)

    Ma, Xiaoya; Edgecombe, Gregory D; Hou, Xianguang; Goral, Tomasz; Strausfeld, Nicholas J

    2015-11-16

    The record of arthropod body fossils is traceable back to the "Cambrian explosion," marked by the appearance of most major animal phyla. Exceptional preservation provides crucial evidence for panarthropod early radiation. However, due to limited representation in the fossil record of internal anatomy, particularly the CNS, studies usually rely on exoskeletal and appendicular morphology. Recent studiesshow that despite extreme morphological disparities, euarthropod CNS evolution appears to have been remarkably conservative. This conclusion is supported by descriptions from Cambrian panarthropods of neural structures that contribute to understanding early evolution of nervous systems and resolving controversies about segmental homologies. However, the rarity of fossilized CNSs, even when exoskeletons and appendages show high levels of integrity, brought into question data reproducibility because all but one of the aforementioned studies were based on single specimens. Foremost among objections is the lack of taphonomic explanation for exceptional preservation of a tissue that some see as too prone to decay to be fossilized. Here we describe newly discovered specimens of the Chengjiang euarthropod Fuxianhuia protensa with fossilized brains revealing matching profiles, allowing rigorous testing of the reproducibility of cerebral structures. Their geochemical analyses provide crucial insights of taphonomic pathways for brain preservation, ranging from uniform carbon compressions to complete pyritization, revealing that neural tissue was initially preserved as carbonaceous film and subsequently pyritized. This mode of preservation is consistent with the taphonomic pathways of gross anatomy, indicating that no special mode is required for fossilization of labile neural tissue. PMID:26526373

  20. Carbon isotope fluctuations through the neoproterozoic-lower cambrian Birmania basin, Rajasthan, India

    International Nuclear Information System (INIS)

    The paleogeographic reconstruction of the end phase of Neoproterozoic assumes a significance due to the fact that the interactions between the biosphere and the atmosphere, hydrosphere and geosphere during this period of time strongly influenced the evolution of life and initiated a remarkable phase of organic evolution well documented in the rocks of this age (Banerjee and Majumdar, 1999). Time related changes in these carbon reservoirs and processes during the end Proterozoic have played an important role in the evolution of the environment and of life (Des Marais, 1997). Brasier (1992) discussed at length various factors that pushed shallow marine ecosystem of the late Neoproterozoic-Cambrian towards P-limitation and suggested that nitrate fixation, density stratification and massive removal of P in the sediments were responsible for the formation of phosphatic deposits within this time interval. East Gondwana assembly of continents provide fine examples of stratigraphic successions in which the ideas related to oceanic stratification, phosphate deposition, enhanced organic production and carbon isotope fluctuations can be verified and correlated from continent to continent (Banerjee and Majumdar, 1999). The Birmania basin is an oval shaped isolated remnant of the Marwar basin (Neo-proterozoic-Early Palaeozoic) located in the heart of the Thar desert of western Rajasthan, India. It is underlain by Malani Igneous Suite of rocks which range in age from 780 to 680Ma (Rathore et al., 1999).The Birmania basin comprises around 900 metre thick sedimentary sequence of siliciclastic, carbonate and phosphorite facies. These sequences are unconformably overlain by La-thi conglomerate of Jurassic age in north-ern flank of the basin. Global Neoproterozoic glacial activity in the western Rajasthan is also reported and is represented by Pokaran Boulder Bed, few kms away from study area. The Pokaran Boulder Bed overlies the Malani Igneous Suite and is mainly consist of boulders

  1. Sulfur and Oxygen Isotopes of Sulfate Extracted from Early Cambrian Phosphorite Nodules:Implications for Marine Redox Evolution in the Yangtze Platform

    Institute of Scientific and Technical Information of China (English)

    Wenlang Qiao; Xianguo Lang; Yongbo Peng; Kaiyuan Jiang; Wu Chen; Kangjun Huang; Bing Shen

    2016-01-01

    ABSTRACT:Phosphorite nodule beds are discovered in the black shale of basal Niutitang Formation throughout the Yangtze Platform in South China, recording an important phosphorite-generation event. Platform-wide phosphorite precipitation requires special oceanographic and geochemical conditions, thus the origin of the Niutitang phosphorite nodules may provide valuable information about the ocean chemistry in the Early Cambrian. In this study, we measured sulfur and oxygen isotopic compositions of sulfate extracted from phosphorite nodules collected from the basal Niutitang Formation. Phosphorite associated sulfate (PAS) is a trace amount of sulfate that incorporates into crystal lattice during phosphorite precipitation, accordingly PAS records the geochemical signals during phosphorite nodule formation. Sulfur isotopic composition of PAS (δ34SPAS) ranges from -1.16‰ to +24.48‰(mean=+8.19‰, n=11), and oxygen isotopic value (δ18OPAS) varies between -5.3‰ and +26.3‰(mean=+7.0‰, n=8). Most phosphorite nodules have low δ34SPAS and low δ18OPAS values, suggesting PAS mainly derived from anaerobic oxidation of H2S within suboxic sediment porewater. We propose that phosphate was delivered to the Yangtze Platform by a series of upwelling events, and was scavenged from seawater with the precipitation of FeOOH. The absorbed phosphate was released into suboxic porewater by the reduction of FeOOH at the oxic-suboxic redox boundary in sediments, and phosphorite nodule precipitated by the reaction of phosphate with Ca2+ diffused from the overlying seawater. The platform-wide deposition of phosphorite nodules in the basal Niutitang Formation implies the bottom water might be suboxic or even oxic, at least sporadically, in Early Cambrian. We speculate that the intensified ocean circulation as evident with frequent occurrences of upwelling events might be the primary reason for the episodic oxidation of the Yangtze Platform in Early Cambrian.

  2. Fossil Association from the Lower Cambrian Yanjiahe Formation in the Yangtze Gorges Area, Hubei, South China

    Institute of Scientific and Technical Information of China (English)

    GUO Junfeng; Tsuyoshi KOMIYA; LI Yong; HAN Jian; ZHANG Xingliang; ZHANG Zhifei; OU Qiang; LIU Jianni; SHU Degan; Shigenori MARUYAMA

    2008-01-01

    Apart from previously reported Small Shelly Fossils (SSFs), a macroscopic fossil assemblage, comprising abundant algae, cone-shaped tubular fossil forms, and probable impressions of a megascopic metazoan, comes from the Lower Cambrian Yanjiahe Formation in the Yangtze Gorges area of western Hubei Province, south China. The visible fossils are preserved in thin-laminated siltstone or muddy siltstone intercalated between 8-15 mm-thick carbonate deposits, probably representing sedimentary settings of a constrained local depression in the shallow water carbonate platform during the Early Cambrian Meishucunian Stage. The macroscopic fossil association provides significant fossil evidence about the evolution of life from the late Precambrian to the 'Cambrian explosion' interval.

  3. Occurrence of Highly Mature Organic Matter in Marine Black Shale Petroleum Source Rocks of Basal Cambrian from Northern Tarim Basin, China

    Institute of Scientific and Technical Information of China (English)

    YU Bingsong (于炳松); Hailiang DONG; CHEN Jianqiang (陈建强); CHEN Xiaolin (陈晓林); LIANG Shiyou (梁世友)

    2004-01-01

    More and more evidence indicates that organic matter (OM) in immature organic-rich sediments and sedimentary rocks is chemically adsorbed onto the outer surfaces of minerals and into interlayer (inner) surfaces of smectitic clay minerals in the form of amorphous molecular-scale carbon. But there have been few reports about the occurrence of highly mature OM in marine black shales (petroleum source rocks). The occurrence of highly mature OM in the black shales of basal Cambrian from northern Tarim Basin is studied in this paper. Based on the comprehensive analyses of total organic carbon contents (TOC), maximum thermolysis temperatures (T max ) of OM, mineral surface areas (MSA), and scanning electronic microscopic (SEM) and transmission electronic microscopic (TEM) observations of the black shales, it is concluded that the highly mature OM in the marine black shales of the basal Cambrian from northern Tarim Basin occurs in particulates ranging in size from 1 to 5 μm in diameter. Through the contrast of the occurrence of the highly mature OM in the black shales with that of the immature ones in modern marine continental margin sediments, some scientific problems are proposed, which are worth to study further in detail.

  4. Pulse of atmospheric oxygen during the late Cambrian.

    Science.gov (United States)

    Saltzman, Matthew R; Young, Seth A; Kump, Lee R; Gill, Benjamin C; Lyons, Timothy W; Runnegar, Bruce

    2011-03-01

    A rise in atmospheric O(2) has been linked to the Cambrian explosion of life. For the plankton and animal radiation that began some 40 million yr later and continued through much of the Ordovician (Great Ordovician Biodiversification Event), the search for an environmental trigger(s) has remained elusive. Here we present a carbon and sulfur isotope mass balance model for the latest Cambrian time interval spanning the globally recognized Steptoean Positive Carbon Isotope Excursion (SPICE) that indicates a major increase in atmospheric O(2). We estimate that this organic carbon and pyrite burial event added approximately 19 × 10(18) moles of O(2) to the atmosphere (i.e., equal to change from an initial starting point for O(2) between 10-18% to a peak of 20-28% O(2)) beginning at approximately 500 million years. We further report on new paired carbon isotope results from carbonate and organic matter through the SPICE in North America, Australia, and China that reveal an approximately 2‰ increase in biological fractionation, also consistent with a major increase in atmospheric O(2). The SPICE is followed by an increase in plankton diversity that may relate to changes in macro- and micronutrient abundances in increasingly oxic marine environments, representing a critical initial step in the trophic chain. Ecologically diverse plankton groups could provide new food sources for an animal biota expanding into progressively more ventilated marine habitats during the Ordovician, ultimately establishing complex ecosystems that are a hallmark of the Great Ordovician Biodiversification Event. PMID:21368152

  5. 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

  6. Germanium/silicon of the Ediacaran-Cambrian Laobao cherts: Implications for the bedded chert formation and paleoenvironment interpretations

    Science.gov (United States)

    Dong, Lin; Shen, Bing; Lee, Cin-Ty A.; Shu, Xu-jie; Peng, Yang; Sun, Yuanlin; Tang, Zhuanhong; Rong, Hong; Lang, Xianguo; Ma, Haoran; Yang, Fan; Guo, Wen

    2015-03-01

    Sedimentary strata of the terminal Ediacaran (635-542 Ma) to early Cambrian (542-488 Ma) Laobao-Liuchapo bedded cherts in the South China Block include the Ediacaran Oxidation Event and the Cambrian explosion. Understanding the origin and depositional environment of the bedded cherts may provide insight into how the Earth's surface environment changed between the Proterozoic and Phanerozoic. We measured major and trace element compositions and Ge/Si ratios of the Laobao cherts from northern Guangxi province. The Laobao cherts were deposited in the deep basinal environment of the South China Block. We show that the composition of the Laobao cherts is determined by a mixture of four components: quartz, clay, carbonate, and pyrite/iron-oxide. The quartz component is the dominant component of the Laobao cherts. The maximum estimated Ge/Si of the quartz component is between 0.4 and 0.5 μmol/mol, which is close to the Ge/Si of modern seawater and biogenic silica but 1 order of magnitude lower than that of hydrothermal fluids. These Ge/Si systematics suggest that normal seawater rather than mid-ocean ridge hydrothermal fluids is the primary Si source for the Laobao cherts. The Ge/Si of the clay component varies between 1 and 10 μmol/mol, which is comparable to the Ge/Si of typical marine clays, but 10-100 times lower than that of chert nodules from early Ediacaran beds (the Doushantuo Formation) predating the terminal Ediacaran Laobao cherts studied here. Our observations indicate that the clay component Ge/Si ratio decreased from the early Ediacaran to the late Ediacaran. We speculate that high Ge/Si ratios in clays reflect the preferential chelation of Ge by dissolved organic compounds adsorbed onto clays. If so, this suggests that the decrease in Ge/Si ratio of the clay component in the Ediacaran signifies a decrease in the total dissolved organic carbon content of seawater toward the Ediacaran-Cambrian transition, consistent with oxidation of the oceans during the

  7. Discovery of hydrothermal venting community at the base of Cambrian barite in Guizhou Province, Western China:Implication for the Cambrian biological explosion

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The barite deposit in the Niutitang Formation of Lower Cambrian, in Tianzhu County, Guizhou Province, western China, is a superlarge barite deposit with about 2 × 109 tons of reserves: Mineral, petrological and geochemical studies reveal that this barite deposit belongs to a hydrothermal sedimentary deposit. Microscopic observations indicate that a lot of algae, sponge spicules and tube-type fossils are well-preserved in this barite section, and moreover, those fossils share most characteristics of the deep-sea hydrothermal venting community in the modern Pacific. We suggest that the hydrothermal venting community was thriving in hydrothermal vent in early Cambrian, and it is of great significance for elucidating the geological background of the "Cambrian explosion".

  8. Early Cambrian origin of modern food webs: evidence from predator arrow worms

    OpenAIRE

    Vannier, J; Steiner, M.; Renvoisé, E; Hu, S.-X.; Casanova, J.-P

    2006-01-01

    Although palaeontological evidence from exceptional biota demonstrates the existence of diverse marine communities in the Early Cambrian (approx. 540–520 Myr ago), little is known concerning the functioning of the marine ecosystem, especially its trophic structure and the full range of ecological niches colonized by the fauna. The presence of a diverse zooplankton in Early Cambrian oceans is still an open issue. Here we provide compelling evidence that chaetognaths, an important element of mo...

  9. The Precambrian–Cambrian nonconformity at the Ercall Quarries, The Wrekin, Shropshire, UK

    OpenAIRE

    Pringle, JK; Stimpson, IG

    2013-01-01

    The Precambrian–Cambrian boundary is iconic, marking the first appearance of shelly fauna in the fossil record, and opening the Phanerozoic Eon. In England and Wales, the transition from predominantly Precambrian igneous rocks to Cambrian sedimentary strata is generally unconformable. An exceptional exposure of this transition can be observed in the Ercall Quarries in Shropshire, a classic locality in all senses of the word.

  10. Exceptionally preserved brachiopods from the Chengjiang Lagerstatte (Yunnan, China) : Perspectives on the Cambriane explosion of metazoans

    OpenAIRE

    Zhang, Zhifei; Holmer, L. E.

    2013-01-01

    The Cambrian explosion was coined to describe the geologically sudden appearance of numerous bilaterian body plans (Phyla) around the Ediacaran-Cambrian transition, around 565-520 million years ago. Many explanations and conjectures have been postulated in order to explain the pattern and duration of this explosive radiation of many different phyla of early metazoans. Here, we focus on the evolution of a phylum of marine suspension-feeding animals – the brachiopods, as exemplified by the exce...

  11. The Genetic Response to Snowball Earth: Role of HSP90 in the Cambrian Explosion

    OpenAIRE

    Baker, Michael E.

    2006-01-01

    The events that shaped the Cambrian explosion from 545 to 530 myr ago, when multicellular animals suddenly appeared in the fossil record, are not fully understood. It is likely that the evolution of new transcription factors and other signal transduction proteins that regulated developmental networks were important in the emergence of diverse animal phyla seen in the Cambrian. I propose that one or both extensive glaciations that ended about 670 myr and 635 myr ago were important in the evo...

  12. The C-value enigma and timing of the Cambrian explosion

    OpenAIRE

    Li, Dirson Jian; Zhang, Shengli

    2008-01-01

    The Cambrian explosion is a grand challenge to science today and involves multidisciplinary study. This event is generally believed as a result of genetic innovations, environmental factors and ecological interactions, even though there are many conflicts on nature and timing of metazoan origins. The crux of the matter is that an entire roadmap of the evolution is missing to discern the biological complexity transition and to evaluate the critical role of the Cambrian explosion in the overall...

  13. A sclerite-bearing stem group entoproct from the early Cambrian and its implications

    OpenAIRE

    Zhifei Zhang; Holmer, Lars E.; Skovsted, Christian B; Glenn A. Brock; Graham E. Budd; Dongjing Fu; Xingliang Zhang; Degan Shu; Jian Han; Jianni Liu; Haizhou Wang; Aodhán Butler; Guoxiang Li

    2013-01-01

    The Lophotrochozoa includes disparate tentacle-bearing sessile protostome animals, which apparently appeared in the Cambrian explosion, but lack an uncontested fossil record. Here we describe abundant well preserved material of Cotyledion tylodes Luo et Hu, 1999, from the Cambrian (Series 2) Chengjiang deposits, reinterpreted here as a stem-group entoproct. The entoproct affinity is supported by the sessile body plan and interior soft anatomy. The body consists of an upper calyx and a lower e...

  14. Lower Cambrian polychaete from China sheds light on early annelid evolution

    Science.gov (United States)

    Liu, Jianni; Ou, Qiang; Han, Jian; Li, Jinshu; Wu, Yichen; Jiao, Guoxiang; He, Tongjiang

    2015-06-01

    We herein report a fossilized polychaete annelid, Guanshanchaeta felicia gen. et sp. nov., from the Lower Cambrian Guanshan Biota (Cambrian Series 2, stage 4). The new taxon has a generalized polychaete morphology, with biramous parapodia (most of which preserve the evidence of chaetae), an inferred prostomium bearing a pair of appendages, and a bifid pygidium. G. felicia is the first unequivocal annelid reported from the Lower Cambrian of China. It represents one of the oldest annelids among those from other early Paleozoic Lagerstätten including Sirius Passet from Greenland (Vinther et al., Nature 451: 185-188, 2008) and Emu Bay from Kangaroo island (Parry et al., Palaeontology 57: 1091-1103, 2014), and adds to our increasing roll of present-day animal phyla recognized in the early Cambrian Guanshan Biota. This finding expands the panorama of the Cambrian `explosion' exemplified by the Guanshan Biota, suggesting the presence of many more fossil annelids in the Chengjiang Lagerstätte and the Kaili Biota. In addition, this new taxon increases our knowledge of early polychaete morphology, which suggests that polychaete annelids considerably diversified in the Cambrian.

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

    Science.gov (United States)

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

    2008-06-01

    Animal-like multicellular fossils appeared towards the end of the Precambrian, followed by a rapid increase in the abundance and diversity of fossils during the Early Cambrian period, an event also known as the 'Cambrian explosion'. Changes in the environmental conditions at the Precambrian/Cambrian transition (about 542 Myr ago) have been suggested as a possible explanation for this event, but are still a matter of debate. Here we report molybdenum isotope signatures of black shales from two stratigraphically correlated sample sets with a depositional age of around 542 Myr. We find a transient molybdenum isotope signal immediately after the Precambrian/Cambrian transition. Using a box model of the oceanic molybdenum cycle, we find that intense upwelling of hydrogen sulphide-rich deep ocean water best explains the observed Early Cambrian molybdenum isotope signal. Our findings suggest that the Early Cambrian animal radiation may have been triggered by a major change in ocean circulation, terminating a long period during which the Proterozoic ocean was stratified, with sulphidic deep water. PMID:18509331

  16. The Cambrian Evolutionary Explosion: Novel Evidence from Fossils Studied by X-ray Tomography

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Jun-Yuan [Nanjing University, China

    2011-06-01

    The Cambrian explosion (from 542 million years to 488 million years ago) is one of the greatest mysteries in evolutionary biology. It wasn't until this period that complex organisms became common and diverse. the magnitude of the event can be understood based on the contrast between the biota and the degree of diversity of the fossils from both sides. great advances have been made in Cambrian palaeontology over the past century, especially the discovery of the well-preserved soft-bodied fauna from the Middle Cambrian Burgess Shale and the Lower Cambrian Maotianshan Shale deposits. The Cambrian side of the "Cambrian explosion" is richly illustrated and contrasts greatly with the Precambrian side. The study of these extraordinarily preserved fossil biota is extremely difficult. A major challenge is 3-D reconstruction and determining the patter of the cell organization in Weng'an embryos and their buried structures in Maotianshan Shale fossils. This talk will show that two recent technological approaches, propagation phase contrast synchrotron x-ray microtomography and microtomography, provide unique analytical tools that permit the nondestructive computational examination and visualization of the internal and buried characters in virtual sections in any plane, and virtual 3-D depictions of internal structures.

  17. The Ordovician Radiation: A Follow-up to the Cambrian Explosion?

    Science.gov (United States)

    Droser, Mary L; Finnegan, Seth

    2003-02-01

    There was a major diversification known as the Ordovician Radiation, in the period immediately following the Cambrian. This event is unique in taxonomic, ecologic and biogeographic aspects.While all of the phyla but one were established during the Cambrian explosion, taxonomic increases during the Ordovician were manifest at lower taxonomic levels although ordinal level diversity doubled. Marine family diversity tripled and within clade diversity increases occurred at the genus and species levels. The Ordovician radiation established the Paleozoic Evolutionary Fauna; those taxa which dominated the marine realm for the next 250 million years. Community structure dramatically increased in complexity. New communities were established and there were fundamental shifts in dominance and abundance.Over the past ten years, there has been an effort to examine this radiation at different scales. In comparison with the Cambrian explosion which appears to be more globally mediated, local and regional studies of Ordovician faunas reveal sharp transitions with timing and magnitudes that vary geographically. These transitions suggest a more episodic and complex history than that revealed through synoptic global studies alone.Despite its apparent uniqueness, we cannot exclude the possibility that the Ordovician radiation was an extension of Cambrian diversity dynamics. That is, the Ordovician radiation may have been an event independent of the Cambrian radiation and thus requiring a different set of explanations, or it may have been the inevitable follow-up to the Cambrian radiation. Future studies should focus on resolving this issue. PMID:21680422

  18. A submarine welded ignimbrite-crystal-rich sandstone facies association in the Cambrian Tyndall Group, western Tasmania, Australia

    Science.gov (United States)

    White, Matthew J.; McPhie, Jocelyn

    1997-04-01

    Three occurrences of rhyolitic welded ignimbrite are intercalated within a submarine, below-storm-wave-base sedimentary succession in the Cambrian Tyndall Group, Mount Read Volcanics, western Tasmania. These occurrences are closely associated with very thick crystal-rich sandstone facies that is present at this stratigraphic level throughout the Tyndall Group. This facies is interpreted to comprise deposits from syn-eruptive, crystal-rich, submarine sediment gravity flows that were generated by interaction of subaerial pyroclastic flows with seawater. Removal of fine ash and pumice from the submarine flows by hydraulic sorting and flotation resulted in marked crystal enrichment in the deposits. Rapid, essentially syn-eruptive aggradation of crystal-rich sand led to temporary shoaling so that in some cases, subsequent pyroclastic flows deposited welded ignimbrite in shallow marine or possibly subaerial settings (e.g., Zig Zag Hill welded ignimbrite). Breccia units composed of welded ignimbrite clasts and crystal-rich matrix (e.g., Comstock and Anthony Road ignimbrite breccias) imply that some welded ignimbrite was submerged, providing clasts to syn-eruptive, submarine, crystal-rich sediment gravity flows. One example of welded ignimbrite (Cradle Mountain Link Road) may have been deposited in an entirely below-storm-wave-base environment. The distinctive facies association of welded ignimbrite, crystal-rich sandstone and ignimbrite-clast breccia in the Tyndall Group exemplifies the submarine record of a major rhyolitic explosive eruption in the source volcanic terrane.

  19. The geobiology of the extremely enriched polymetallic sulfides in the black shale of the lower Cambrian Niutitang formation, Southwestern China

    OpenAIRE

    Xu, Jun; 徐俊

    2014-01-01

    The Precambrian-Cambrian transition is a period with enormous geological and biological changes. There is a wide distribution of black shale sequence in the Late Sinian and Early Cambrian strata along the passive southern margin of the Yangtze Platform in South China. The remarkable polymetallic sulfide extremely enriched ore layer is embedded at the bottom of the Lower Cambrian Niutitang Formation, but its genesis remains highly disputable. Known mechanisms can hardly explain the extreme enr...

  20. Nonlinear geosphere-biosphere interactions and the Cambrian explosion

    Science.gov (United States)

    von Bloh, W.; Bounama, C.; Franck, S.

    2003-04-01

    A conceptual model for the global carbon cycle of the Earth containing the reservoirs mantle, ocean floor, continental crust, continental biosphere, the kerogen , as well as the aggregated reservoir ocean and atmosphere is presented. In this study the evolution of the mean global surface temperature, the biomass, and reservoir sizes over the whole history and future of the Earth under a maturing Sun is investigated. Reasonable values for the present distribution of carbon in the surface reservoirs of the Earth are obtained and a pronounced global minimum of mean surface temperature at the present state of the Earth is found. Furthermore, three different biosphere types are introduced: procaryotes, eucaryotes, and higher metazoa. They all differ in their temperature tolerance interval and their biogenic enhancement of silicate rock weathering. Around 500 Myr in the past we find a rise of higher metazoa caused by the nonlinear feedback between biosphere and climate. Biotic amplifying of weathering provides and maintains the environment of higher life forms. Such a mechanism may explain the so-called Cambrian explosion.

  1. Rapid Polar Wander in North America During the Early Cambrian: Paleomagnetic and Magnetostratigraphic Constraints from the Peurto Blanco Volcanics from Caborca, and the Tapeats Sandstone of the Grand Canyon.

    Science.gov (United States)

    Kirschvink, J. L.; Elston, D. P.; Petterson, R.; Hagadorn, J. W.; Raub, T. D.; Evans, D. A.; Rose, E. C.; Weiss, B. P.; Barr, T. D.

    2006-12-01

    rich sediments along the Cordilleran margin of North America as compared to the Appalachian margin, predicts the observed age transgression in the appearance of archaeocyathid faunas across the North American craton, and supports the hypothesis of one or more rapid true polar wander events during Ediacaran and Cambrian time.

  2. Three-step modernization of the ocean:Modeling of carbon cycles and the revolution of ecological systems in the Ediacaran/Cambrian periods

    Institute of Scientific and Technical Information of China (English)

    Miyuki Tahata; Yusuke Sawaki; Yuichiro Ueno; Manabu Nishizawa; Naohiro Yoshida; Toshikazu Ebisuzaki; Tsuyoshi Komiya; ,Shigenori Maruyama

    2015-01-01

    Important ecological changes of the Earth (oxidization of the atmosphere and the ocean) increase in nutrient supply due to the break-up of the super continent (Rodinia) and the appearance of multi-cellular organisms (macroscopic algae and metazoan) took place in the Ediacaran period, priming the Cambrian explosion. The strong perturbations in carbon cycles in the ocean are recorded as excursions in carbonate and organic carbon isotope ratio (d13Ccarb and d13Corg) from the Ediacaran through early Cambrian periods. The Ediacaraneearly Cambrian sediment records of d13Ccarb and d13Corg, obtained from the drill-core samples in Three Gorges in South China, are compared with the results of numerical simulation of a sim-ple one-zone model of the carbon cycle of the ocean, which has two reservoirs (i.e., dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC). The fluxes from the reservoirs are assumed to be proportional to the mass of the carbon reservoirs. We constructed a model, referred to here as the Best Fit Model (BFM), which reproduce d13Ccarb and d13Corg records in the Ediacaraneearly Cambrian period noted above. BFM reveals that the Shuram excursion is related to three major changes in the carbon cycle or the global ecological system of the Earth:(1) an increase in the coefficient of remineralization by a factor of ca. 100, possibly corresponding to a change in the dominant metabolism from anaerobic respiration to aerobic respiration, (2) an increase of carbon fractionation index from 25&to 33&, possibly corresponding to the change in the primary producer from rock-living cyanobacteria to free-living macro algae, and (3) an in-crease in the coefficient of the organic carbon burial by a factor of ca. 100, possibly corresponding to the onset of a biological pump driven by the flourishing metazoan and zooplankton. The former two changes took place at the start of the Shuram excursion, while the third occurred at the end of the Shuram excursion. The other

  3. Reconstruction of Cambrian Global Paleo-plates and Paleogeography%寒武纪全球板块构造与古地理环境再造

    Institute of Scientific and Technical Information of China (English)

    周肖贝; 李江海; 王洪浩; 李文山

    2014-01-01

    during the whole Cambrian, the global plates were generally in epeiric sea environments which promoted the Early Cambrian organic-rich deposits and dominant carbonate deposits and provided good conditions for Cambrian life explosion, which were characterized by low climate zone gradients and widely-distributing drought climate zones that led to Lower and Middle Cambrian evaporate and salt deposits. In Gondwana supercontinent, carbonate deposits were mainly in the north part, sandstone deposits in the south and volcanic activities mainly in the east while good source rocks and petroleum resources were commonly distributed in the carbonate and sandstone deposits along the west margin of the central part. Laurentia was characteristic of band sedimentation, outer of which carbonate deposits existed. Huge evaporate rock deposited in the Siberia plate during the Middle-Lower Cambrian and only a few hundreds meter thickness of carbonate deposits did in the late Cambrian, which improved the development of reservoirs and seals under the setting of passive margin. Sandstone and shale were commonly deposited in Baltica plate at relatively high latitude.

  4. Geochemical characteristics of organic matter-rich strata of lower Cambrian in Tarim Basin and its origin

    Institute of Scientific and Technical Information of China (English)

    CHEN; Jianfa; SUN; Shengli; LIU; Wenhui; ZHENG; Jianjing

    2004-01-01

    The organic matter-rich strata of the Yurtusi Formation of Lower Cambrian are wildly spread and steady in the Tarim Basin, in which cherts are developed, companied with phosphorite. Al/(Al+Fe+Mn) ratio and Si/(Si+Al+Fe) ratio of cherts range from 0.0023 to 0.0046 and 0.965 to 0.98, respectively, suggesting that cherts are formed in submarine hydrothermal activity and far away from terrestrial. Trace elements, such as As, Hg, Pb, Zn, Cu, Co, P, V, Ba, etc., are markedly rich in organic matter-rich sedimentary rocks of which Ba/Sr ratios are between 21.2 and 158.1. Compared with modern hydrothermal sediments, their Ba/Sr ratios are similar, it indicates that the organic matter-rich strata have the geochemical feature of submarine hydrothermal sediments. The total content of rare earth elements (ЕREE) in cherts is from 8.81 to 56.682 μg/g, on average 31.41 μg/g and the ΕREE of cherts is between continental margin chert's and abyssal chert's. The LREE/HREE ratio of cherts varies from 1.01 to 3.56, which reveals the characteristics of hydrothermal sediments. There is positive correlation between the total organic content (TOC) and Ba/Sr ratio which is geochemical index of submarine hydrothermal activity, which indicates that the submarine hydrothermal activity obviously influences the richness of organic matter in the Yurtusi Formation.

  5. Ichnology of the Early Cambrian Tal Group, Mussoorie Syncline, Lesser Himalaya, India

    Indian Academy of Sciences (India)

    Meera Tiwari; S K Parcha; Rajita Shukla; Harshita Joshi

    2013-12-01

    The Lesser Himalayan sequence is considered as one of the best developed sections of Cambrian successions, exposed in five different synclines. Mussoorie Syncline, being one of the five synclines, exposes the Cambrian Tal Group. This paper describes nine ichnotaxa, viz., Dimorphichnus isp., ?Diplichnites isp., Monomorphichnus isp., Nereites isp., Palaeopasichnus isp., Palaeophycus isp., Planolites montanus, Planolites isp., Skolithos isp., Treptichnus isp. from the Dhaulagiri Formation of the Tal Group. A detailed analysis of the ichnofossils indicates that the entire succession of Tal Group reflects shallow marine conditions in general and Mussoorie Syncline in particular. The above ichnofossil assemblage along with earlier ichnofossils and other faunal occurrences substantiates the assignment of Early Cambrian age to the Dhaulagiri Formation.

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

    DEFF Research Database (Denmark)

    Servais, Thomas; Perrier, Vincent; Danelian, Taniel;

    2016-01-01

    The 'Great Ordovician Biodiversification Event' comprises the rapid diversification of marine organisms during the Ordovician Period. It is now clear that this adaptive radiation started for some organisms already in the Cambrian and continued for others beyond the end of the Ordovician, making...... the 'Great Ordovician Biodiversification Event' part of a long-term late Proterozoic and Early Palaeozoic radiation, that in part is expressed by the fossil record as the 'Cambrian Explosion.' A significant diversification of different groups of the plankton is observed in the late Cambrian-Early Ordovician...... interval, leading to the subsequent 'Ordovician Plankton Revolution.' The possible causes of this 'plankton revolution' are currently debated. They include changes in palaeoclimate, palaeogeography or tectonic and volcanic activity, as well as a modified nutrient supply. In this context, the Steptoean...

  7. Ichnology of the Early Cambrian Tal Group, Mussoorie Syncline, Lesser Himalaya, India

    Science.gov (United States)

    Tiwari, Meera; Parcha, S. K.; Shukla, Rajita; Joshi, Harshita

    2013-12-01

    The Lesser Himalayan sequence is considered as one of the best developed sections of Cambrian successions, exposed in five different synclines. Mussoorie Syncline, being one of the five synclines, exposes the Cambrian Tal Group. This paper describes nine ichnotaxa, viz., Dimorphichnus isp., ? Diplichnites isp., Monomorphichnus isp., Nereites isp., Palaeopasichnus isp., Palaeophycus isp., Planolites montanus, Planolites isp., Skolithos isp., Treptichnus isp. from the Dhaulagiri Formation of the Tal Group. A detailed analysis of the ichnofossils indicates that the entire succession of Tal Group reflects shallow marine conditions in general and Mussoorie Syncline in particular. The above ichnofossil assemblage along with earlier ichnofossils and other faunal occurrences substantiates the assignment of Early Cambrian age to the Dhaulagiri Formation.

  8. Cambrian Sequence Stratigraphy and Sea Level Cycles of North China Platform

    Institute of Scientific and Technical Information of China (English)

    1999-01-01

    The Cambrian of the North China platform consists chiefly of shallow water deposits and shows the sedimentary characters of an epicontinental sea basin. Controlled mainly by global sea level changes and sedimentary influx, the depositional sequences all exhibit as composite sequences. From bottom upward, 14 sequences (3rd order) are recognized, which may be grouped into 5 sequence sets and further into 2 mesosequences (2nd order). It is suggested herein that the Cambrian/Ordovician boundary may better be set at the MFS (maximum flooding surface) of the sequence OSq1, above which the conodont Cordylodus lindstroemi occurs. This position is about 40 m above the traditional Cambrian/Ordovician boundary and is within the Yeli Formation.

  9. Sponge spicules in phosphorites of the Early Cambrian Gezhongwu Formation, Zhijin, Guizhou

    Institute of Scientific and Technical Information of China (English)

    YANG Ruidong; QIAN Yi; ZHANG Jie; ZHANG Weihua; JIANG Lijun; GAO Hui

    2004-01-01

    Phosphorites occurring at the bottom of the Cambrian system contain abundant small shelly fossils, which are the product of the first episode of life explosion in the Cambrian. It was previously reported that the small shelly fossils are dominated by hyolithids, olivooids, zhijinitids, conodontomorphs, yubelichitids, camenitids and algae, with minor amounts of sponge fossils. Large amounts of sponge spicules, diverse in form, have been found for the first time in the Gezhongwu Formation phosphorites at Shixing, Zhijin County, Guizhou Province, of which such spicules as diaxon-triactins, diaxon-tetractins, pentaxon-pentactins and hexon-hexactins account for 30%. These spicules constitute the sponge clastic phosphorites made up of sponge clastics. Meanwhile, it is also expected that the radiation and diversity of sponge animals started as early as in the earliest Early Cambrian. Habit and burying environment of sponge animal are discussed in the paper.

  10. MicroRNAs and metazoan macroevolution: insights into canalization, complexity, and the Cambrian explosion.

    Science.gov (United States)

    Peterson, Kevin J; Dietrich, Michael R; McPeek, Mark A

    2009-07-01

    One of the most interesting challenges facing paleobiologists is explaining the Cambrian explosion, the dramatic appearance of most metazoan animal phyla in the Early Cambrian, and the subsequent stability of these body plans over the ensuing 530 million years. We propose that because phenotypic variation decreases through geologic time, because microRNAs (miRNAs) increase genic precision, by turning an imprecise number of mRNA transcripts into a more precise number of protein molecules, and because miRNAs are continuously being added to metazoan genomes through geologic time, miRNAs might be instrumental in the canalization of development. Further, miRNAs ultimately allow for natural selection to elaborate morphological complexity, because by reducing gene expression variability, miRNAs increase heritability, allowing selection to change characters more effectively. Hence, miRNAs might play an important role in shaping metazoan macroevolution, and might be part of the solution to the Cambrian conundrum. PMID:19472371

  11. Articulated Wiwaxia from the Cambrian Stage 3 Xiaoshiba Lagerstätte

    Science.gov (United States)

    Yang, Jie; Smith, Martin R.; Lan, Tian; Hou, Jin-Bo; Zhang, Xi-Guang

    2014-04-01

    Wiwaxia is a bizarre metazoan that has been interpreted as a primitive mollusc and as a polychaete annelid worm. Extensive material from the Burgess Shale provides a detailed picture of its morphology and ontogeny, but the fossil record outside this lagerstätte is scarce, and complete wiwaxiids are particularly rare. Here we report small articulated specimens of Wiwaxia foliosa sp. nov. from the Xiaoshiba fauna (Cambrian Stage 3, Hongjingshao Formation, Kunming, south China). Although spines are absent, the fossils' sclerites - like those of W. corrugata - are symmetrically arranged in five distinct zones. They form rows across the body, and were individually added and shed throughout growth to retain an approximately symmetrical body shape. Their development pattern suggests a molluscan affinity. The basic body plan of wiwaxiids is fundamentally conserved across two continents through Cambrian Stages 3-5 - revealing morphological stasis in the wake of the Cambrian explosion.

  12. A sclerite-bearing stem group entoproct from the early Cambrian and its implications.

    Science.gov (United States)

    Zhang, Zhifei; Holmer, Lars E; Skovsted, Christian B; Brock, Glenn A; Budd, Graham E; Fu, Dongjing; Zhang, Xingliang; Shu, Degan; Han, Jian; Liu, Jianni; Wang, Haizhou; Butler, Aodhán; Li, Guoxiang

    2013-01-01

    The Lophotrochozoa includes disparate tentacle-bearing sessile protostome animals, which apparently appeared in the Cambrian explosion, but lack an uncontested fossil record. Here we describe abundant well preserved material of Cotyledion tylodes Luo et Hu, 1999, from the Cambrian (Series 2) Chengjiang deposits, reinterpreted here as a stem-group entoproct. The entoproct affinity is supported by the sessile body plan and interior soft anatomy. The body consists of an upper calyx and a lower elongate stalk with a distal holdfast. The soft anatomy includes a U-shaped gut with a mouth and aboral anus ringed by retractable marginal tentacles. Cotyledion differs from extant entoprocts in being larger, and having the calyx and the stalk covered by numerous loosely-spaced external sclerites. The description of entoprocts from the Chengjiang biota traces the ancestry of yet another lophotrochozoan phylum back to the Cambrian radiation, and has important implications for the earliest evolution of lophotrochozoans. PMID:23336066

  13. Biodiversity and taphonomy of the Early Cambrian Guanshan biota,eastern Yunnan

    Institute of Scientific and Technical Information of China (English)

    Michael; STEINER

    2010-01-01

    The Guanshan biota from eastern Yunnan(Cambrian Series 2,early Stage 4) is a Burgess Shale-type fossil biota with abundant exceptionally preserved soft-bodied fossils after the discovery of the well-known Cambrian Chengjiang fauna and Kaili biota in South China.The geological settings,sedimentology,taphonomy,and the fossil assemblage of the Guanshan biota are briefly summarized here.The Guanshan biota consists of about 60 taxa belonging to more than 10 metazoan groups and algae,among which the lobopods,eldonids,hyolithids with helens,and green algae are reported for the first time.The common occurrence of soft-bodied preservation in many groups,notably the trilobites and brachiopods,makes the Guanshan biota a significant fossil lagersttte for understanding the metazoan evolution during Cambrian explosion and taphonomy of the Burgess Shale-type fossils.

  14. Comparative analysis of methods used to define eustatic variations in outcrop: Late Cambrian interbasinal sequence development

    Energy Technology Data Exchange (ETDEWEB)

    Osleger, D. (Univ. of California, Riverside (United States)); Read, J.F. (Virginia Polytechnic Inst. and State Univ., Blacksburg (United States))

    1993-03-01

    Interbasinal correlation of Late Cambrian cyclic carbonates from the Appalachian and Cordilleran passive margins, the Texas craton, and the southern Oklahoma aulacogen defines six major third-order depositional sequences. Graphic correlation of biostratigraphically-constrained strata was used to establish equivalency of stratigraphic sequences between the individual sections. Relatively isochronous biomere boundaries were used as time datums for lithostratigraphic correlation. Although the individual sections are composed of different types of meter-scale cycles and component lithofacies that reflect the various environmental settings of the localities, the overall upward-shallowing character of individual sequences is evident. The sequences are: late Cedaria, mid-Crepicephalus, late Crepicephalus, Aphelaspis to earliest Elvinia, Elvinia to early Saukia, and Saukia to the Cambrian-Ordovician boundary. Interbasinal correlation of stratigraphic sequences permits an evaluation of quantitative techniques for determining accommodation history. Correlation of Fischer plots of cyclic successions from separate basins supports a eustatic control of Late Cambrian sequence development. R2/R3 curves derived from subsidence analysis of the Late Cambrian sections provide good resolution of the second- and third-order scales of accommodation change, and interbasinal correlations of R2/R3 curves also support eustatic control on sequence development. Comparing the accomodation curves and subsidence analysis with paleobathymetric trends of Late Cambrian cyclic strata suggests that the curves may approximate the form of the eustatic sealevel signal. A composite eustatic sealevel curve for Late Cambrian time in North America was created by qualitatively combining the accommodation curves defined by the different techniques for each of the four localities. 129 refs., 16 figs., 3 tabs.

  15. Biological and Molecular Geochemical Evidence for Dinoflagellate Ancestors in the Upper Sinian-Cambrian

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Dinoflagellates are single celled organisms that reflect the ecological conditions in modem oceans and lakes. Their earliest undisputed fossil record suggests that dinoflagellates originated from the Middle Triassic (c.240 Ma ago). However, the presence of molecular biomarkers (dinosterane, 4α-methyl-24-ethylcholestane and triaromatic dinosteroids) in rock extracts and coccoid dinoflagellate fossils from the upper Sinian to Cambrian of the Tarim basin confirms the hypothesis that dinoflagellates have an ancient origin, and predate the oldest undisputed dinoflagellate fossils at least by 300 Ma, as early as the late Sinian-Cambrian.

  16. Discovery of sponge body fossils from the late Meishucunian (Cambrian) at Jinsha, Guizhou, south China

    Institute of Scientific and Technical Information of China (English)

    YANG Xinglian; ZHAO Yuanlong; WANG Yue; WANG Pingli

    2005-01-01

    Here we report discovery of a sponge body fossil Triticispongia sp. from the base of lower Cambrian Niutitang Formation at Jinsha, Guizhou. Stratigraphically, the fossil horizon is located below Ni-Mo ore layer with the Niutitang Biota above, and is equivalent to the late Meishucunian. The species is global in shape with skeletons composed of stauractins and monaxons. Triticispongia sp. reported here may be the earliest sponge body fossils of Cambrian, which provides new informationfor understanding early evolution and radiation of sponge animals.

  17. Extraordinary fossils reveal the nature of Cambrian life: a commentary on Whittington (1975) 'The enigmatic animal Opabinia regalis, Middle Cambrian, Burgess Shale, British Columbia'.

    Science.gov (United States)

    Briggs, Derek E G

    2015-04-19

    Harry Whittington's 1975 monograph on Opabinia was the first to highlight how some of the Burgess Shale animals differ markedly from those that populate today's oceans. Categorized by Stephen J. Gould as a 'weird wonder' (Wonderful life, 1989) Opabinia, together with other unusual Burgess Shale fossils, stimulated ongoing debates about the early evolution of the major animal groups and the nature of the Cambrian explosion. The subsequent discovery of a number of other exceptionally preserved fossil faunas of Cambrian and early Ordovician age has significantly augmented the information available on this critical interval in the history of life. Although Opabinia initially defied assignment to any group of modern animals, it is now interpreted as lying below anomalocaridids on the stem leading to the living arthropods. This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society. PMID:25750235

  18. Extraordinary fossils reveal the nature of Cambrian life: a commentary on Whittington (1975) ‘The enigmatic animal Opabinia regalis, Middle Cambrian, Burgess Shale, British Columbia’

    Science.gov (United States)

    Briggs, Derek E. G.

    2015-01-01

    Harry Whittington's 1975 monograph on Opabinia was the first to highlight how some of the Burgess Shale animals differ markedly from those that populate today's oceans. Categorized by Stephen J. Gould as a ‘weird wonder’ (Wonderful life, 1989) Opabinia, together with other unusual Burgess Shale fossils, stimulated ongoing debates about the early evolution of the major animal groups and the nature of the Cambrian explosion. The subsequent discovery of a number of other exceptionally preserved fossil faunas of Cambrian and early Ordovician age has significantly augmented the information available on this critical interval in the history of life. Although Opabinia initially defied assignment to any group of modern animals, it is now interpreted as lying below anomalocaridids on the stem leading to the living arthropods. This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society. PMID:25750235

  19. Combined Microfacies-Log-Analysis of Cambrian and Ordovician Carbonate Rocks (Upper Cambrian, Western Hills, Bejing; TZ-162 well, Tarim Basin, Western China)

    OpenAIRE

    Wang, Anjia

    2014-01-01

    The Tarim Basin in northwestern China is the second largest petroleum field in China. The reservoirs are predominantly Palaeozoic (Devonian, Ordovician, and Cambrian) carbonate rocks buried at a depth of 5000 m – 6000 m. Ordovician carbonate rocks are one of the main topics in recent hydrocarbon drilling projects. This great depth and a complex inhomogeneous geological and tectonic development results in many problems in hydrocarbon exploration and production. The Ordovician sequence is do...

  20. Extraordinary fossils reveal the nature of Cambrian life: a commentary on Whittington (1975) ‘The enigmatic animal Opabinia regalis, Middle Cambrian, Burgess Shale, British Columbia’

    OpenAIRE

    Briggs, Derek E G

    2015-01-01

    Harry Whittington's 1975 monograph on Opabinia was the first to highlight how some of the Burgess Shale animals differ markedly from those that populate today's oceans. Categorized by Stephen J. Gould as a ‘weird wonder’ (Wonderful life, 1989) Opabinia, together with other unusual Burgess Shale fossils, stimulated ongoing debates about the early evolution of the major animal groups and the nature of the Cambrian explosion. The subsequent discovery of a number of other exceptionally preserved ...

  1. On the evolution and histology of some Cambrian protoconodonts, paraconodonts and primitive euconodonts

    Institute of Scientific and Technical Information of China (English)

    DONG Xiping

    2004-01-01

    Previous reports on the morphological evolution of protoconodonts and paraconodonts are reviewed. The evolutionary trends exhibited by species of the protoconodont genus Gapparodus and the paraconodont genus Westergaadodina are discussed. Based on the present study on histology, genus Paibiconus is protoconodont, while genus Yongshunella is paraconodont (fig. 1 (a)). However, the nature of Huayuanodontus has not been fully understood so far.Recently, the transitional form New Gen. Sensu Miller, 1980 of late Late Cambrian has been found in Hunan Province, South China. It is considered as the Sister-Group of Proconodontus.Moreover, another kind of transitional form of middle Late Cambrian and late Late Cambrian between Prooneotodus rotundatus and Proconodontus, which looks like Prooneotodus rotundatus in gross morphology, but has anterior and posterior costae, has also been found in Hunan,South China. This kind of transitional form is believed to be probably the real intermediate link between Prooneotodus rotundatus and Proconodontus, and Prooneotodus rotundatus is most probably the ancestor of Proconodontus. The two transitional forms noted above are all euconodonts by the study of their histology. Unlike the euconodonts of Post-Cambrian, the evolutionary relationships among the species of protoconodonts, paraconodonts and the primitive euconodonts could not be made clear without the histological study on them.

  2. The sudden appearance of diverse animal body plansduring the Cambrian explosion.

    Science.gov (United States)

    Chen, Jun-Yuan

    2009-01-01

    Beautifully preserved organisms from the Lower Cambrian Maotianshan Shale in central Yunnan, southern China, document the sudden appearance of diverse metazoan body plans at phylum or subphylum levels, which were either short-lived or have continued to the present day. These 530 million year old fossil representatives of living animal groups provide us with unique insight into the foundations of living animal groups at their evolutionary roots. Among these diverse animal groups, many are conservative, changing very little since the Early Cambrian. Others, especially Panarthropoda (superphylum), however, evolved rapidly, with origination of novel body plans representing different evolutionary stages one after another in a very short geological period of Early Cambrian time. These nested body plans portray a novel big picture of pararthropod evolution as a progression of step-wise changes both in the head and the appendages. The evolution of the pararthropods displays how the head/trunk boundary progressively shifted to the posterior, and how the simple annulated soft uniramous appendages progressively changed into stalked eyes in the first head appendages, into whip-like sensorial and grasping organs in the second appendage, and into jointed and biramous bipartite limbs in the post-antennal appendages. Haikouella is one of most remarkable fossils representing the origin body plan of Cristozoa, or crest animals (procraniates+craniates). The anatomy of Early Cambrian crest animals, including Haikouella and Yunnanozoon, contributes to novel understanding and discussion for the origins of the vertebrate brain, neural crest cells, branchial system and vertebrae. PMID:19557680

  3. Progress and significance in research on the early Middle Cambrian Kaili Biota, Guizhou Province,China

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Important progress in research on the Kaili Biota has been made recently. Many interesting components from Chengjiang Biota and Burgess Shale Biota have been discovered, e.g. Microdictyon of lobopodia; Ottoia, Palaeoscolex of worms; Naraoia, Marrella of Trilobitioidea, Mollisonia, anamalocarids and other non-trilobite arthropods; and new sorts of echinoder-mas, macroalage fossils and so on. Recent work on the Kaili Biota has resulted in the following developments: (i) an increase in the number of animal genera, up to more than 100 genera in total, so that the Kaili Biota has become the third most diverse of the Burgess Shale-type Biota after the Burgess Shale and Chengjiang Biotas; and (ii) the most noteworthy fossils in the Kaili Biota are echinoderms, non-trilobite arthropods and soft-bodied medusiform fossils, especially the most diverse echinoderms. The progress provides envidence for the biodiversity of marine organisms presented after the "Cambrian Explosion" and serves as a link between the earlist Cambrian Chengjiang Biota and late early Middle Cambrian Burgess Shale Biota. It is of great significance in the reconstruction of the Cambrian palaeoplate, palaeongeography and in research on taphonomy.

  4. The distribution of the oil derived from Cambrian source rocks in Lunnan area, the Tarim Basin, China

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    There are great differences in biomarks between Cambrian oil and Middle-Upper Ordoviclan oil. In this stuty, the authors analyzed 40 oils found in Lunnan area by GC-MS and calculated the content of Cambrian oil in the 40 oils according to the steroid indexes of typical oil mixture and match experiment. The results show that it is a general phenomenon in Ordovician reservoir that the oil derived from Cambrian source rock mixed with the oil derived from Middle-Upper Ordovician source rock in Lunnan area, the mixture degree of the two oils is lower in Carboniferous reservoir than in Ordovician reservoir, and the oils kept in Triassic reservoir have single source, Middle-Upper Ordovician source rock. The mixture oils mainly composed of Cambrian oil (>50%) distributed in Sangtamu fault zone, and the oils found in Lunnan fault zone are Middle-Upper Ordovician oil. This distribution of oils in Lunnan area is owing to that Lunnan fault zone is located in anticline axis part, Lunnan fault zone underwent serious erosion, and the oils from Cambrian source rock accumulated in Lunnan fault zone were degraded completely during Caledonian-Hercynian movement. But the Cambrian oil accumulated in Sangtamu fault zone was not degraded completely and some of them were left for the location of Sangtamu fault zone is lower than Lunnan fault zone. Later, the oil derived from Middle-Upper Ordovician source rock mixed with the remained Cambrian oil, and the mixture oil formed in Sangtamu fault zone.

  5. Geological features of Sinian-Early Cambrian intracratonic rift of the Sichuan Basin

    Directory of Open Access Journals (Sweden)

    Guoqi Wei

    2015-01-01

    Full Text Available With the major breakthrough in Sinian-Cambrian gas exploration in the Sichuan Basin, the geologic understanding on this formation has changed. One change concerns the discovery of a nearly SN negative structure in the west of Gaoshiti-Moxi area, but there is controversy over the nature, boundary features and distribution scope, sedimentary features, formation stage and evolution of the structure [11–14]. Since the negative structure belt is closely related to the formation of the Anyue Sinian-Cambrian giant gas field, it is necessary to get a better understanding of its geological features in order to guide the gas exploration in Sinian-Cambrian of the Sichuan Basin in the future. Through an analysis of the drilling data of Sinian-Cambrian in this area, an observation of outcrop profiles and the use of 27000 km 2D seismic data and latest drilling data (Well Gaoshi 17, and in combination with regional structure background, the boundary and distribution scope, sedimentary features and evolution of the Mianzhu-Changning rift in craton were investigated. The results showed that: ① the rift in overall SN direction had a steep and fairly stable eastern boundary, and gentler western boundary with variable positions in different stages; ② at the end of Sinian Deng2 member, the rift was a nearly symmetrical depression with an area of 3 × 104 km2; ③ at the end of Deng4 member, it was a fault depression which was steep in the east and gentle in the west controlled by its eastern boundary fault with an area of 8 × 104 km2; and ④ the evolution of the rift can be divided into four stages: embryonic stage in Deng1-Deng2, formation stage in Deng3-Deng4, filling and subsidence stage in Early Cambrian Maidingping-Qiongzhusi Formation, shrinkage and disappearing stage in Early Cambrian Canglangpu-Longwangmiao Formation. Through the study, it was concluded that both sides of the rift are in good Sinian-Cambrian gas-reservoir-forming conditions

  6. Marine Mo biogeochemistry in the context of dynamically euxinic mid-depth waters: A case study of the lower Cambrian Niutitang shales, South China

    Science.gov (United States)

    Cheng, Meng; Li, Chao; Zhou, Lian; Algeo, Thomas J.; Zhang, Feifei; Romaniello, Stephen; Jin, Cheng-Sheng; Lei, Li-Dan; Feng, Lian-Jun; Jiang, Shao-Yong

    2016-06-01

    Molybdenum (Mo) concentrations and Mo isotopes have been widely used as proxies for local and global redox conditions in early oceans (>520 Ma) that were stratified and characterized by dynamically euxinic mid-depth waters. However, the nature of the Mo cycle and accompanying isotopic fractionations in such oceans remain poorly known. To fill this gap, we conducted an integrated study of Mo isotopes and redox-sensitive trace element (RSTE) abundances in the Lower Cambrian Niutitang Formation at Yangjiaping, South China. This section accumulated on the northern shelf margin of the Nanhua Basin, a failed intracontinental rift basin with a good connection to the open ocean during the early Cambrian. The Niutitang Formation contains a ∼18-m-thick lower black shale member, and a ∼56-m-thick upper gray silty shale member. The lower member (LM) is moderately to strongly enriched in Mo, U and V, and heterogeneous in Mo isotopic composition (δ98Mo = -0.65‰ to +2.14‰), indicative of dominantly euxinic depositional conditions punctuated by ferruginous episodes (as shown by previously reported Fe speciation data). The upper member (UM) shows lesser enrichment of Mo, U and V, higher Mo/U ratios, and intermediate and more uniform Mo-isotopic compositions (δ98Mo = +1.16‰ to +1.71‰), indicative of weakly oxic to anoxic-euxinic depositional conditions. Geochemical profiles suggest that the LM-to-UM transition reflects a shift of the O2/H2S chemocline from the water column to the sediment. Large δ98Mo fluctuations in the LM may record variations of H2S concentrations in the mid-depth euxinic waters. The intermediate and relatively uniform δ98Mo values of the UM are attributed to the effects of a local Fe-Mn particulate shuttle. In light of the observations at Yangjiaping and other contemporaneous sections in the Nanhua Basin, we propose a new marine Mo biogeochemical model for the early Cambrian ocean. In this model, an Fe-Mn reduction zone may have developed above

  7. Timing and evolution of ocean anoxic event during Early Cambrian in south China

    Science.gov (United States)

    Yang, J.; Jiang, S.; Pi, D.; Ling, H.

    2008-12-01

    The Precambrian/Cambrian (PC-C) interval is one of the most interesting intervals in the evolution of life because of the sudden diversification of animals with mineralized skeletons, known as "Cambrian Explosion". The Yangtze Platform in south China is one of the best occurrences that can provide excellent insights into the palaeo-environmental and biological changes across the PC-C boundary. Our study show that the ocean anoxia were widespread during the Early Cambrian period, however, the start of this anoxic event was not from the PC-C boundary (i.e., 542 Ma), but some 7 Ma later (~535 Ma) when the Niutitang Formation black rock series (black phosphorite, chert, and black shale) deposited along a thousand kilometer long NEE zone in the transitional facies in the Yangtze Platform, while the major Cambrian radiation (Changjiang fauna) took place during 521-511 Ma. During the Niutitang period, the depositional environment of the Early Cambrian sedimentary sequence in south China have evolved from an initial oxic/dysoxic to a major anoxic/euxinic environment, and then back to dysoxic/oxic environment. A Ni-Mo sulfide layer occurred in the lower part of the Niutitang black shales which contains extremely enrichments of many metals, and can serve as a marker layer in south China when the depositional environment turned into euxinic condition. Re-Os isotope study of the sulfide ores and host black shales show an age of 535 Ma. Initial Os isotopic compositions, Mo isotopic compositions, and rare earth elements and Pt group element geochemistry suggest involvement of submarine hydrothermal fluids during the metal enrichments in black shale.

  8. 四川盆地中—上寒武统层序地层划分与沉积模式%Division and Sedimentary Model of Middle-Upper Cambrian Sequence Strata in Sichuan Basin

    Institute of Scientific and Technical Information of China (English)

    袁立; 姚君波; 李国蓉; 彭博; 麻宇杰

    2013-01-01

    According to the observation of the field outcrop profiles at Fandian,Yankong and Sanhuichang,and the sequence boundary characters and succession analysis of two connecting well sections cross Sichuan Basin,the Cambrian strata can be divided into 12 third-order sequences,named as SQ1 to SQ12 from lower to upper,which include SQ1 to SQ6 in lower Cambrian Series and SQ7 to SQ12 in middle to upper Cambrian Series.Several shallowing-upward cycles develop in the middle-upper Cambrian strata,which include lagoons to platform inner shoals,lagoons to tidal flats,and platform inner shoals to tidal flats.The middle-upper Cambrian sediments are the tidal flat-platform inner shoals-lagoon facies from west to east and the thickness of sediments show a varying pattern that is thick in the east and thin in the west,which is complementary to Lower Cambrian sediments.The total thickness of HST is thicker than that of TST in middle-upper Cambrian strata (SQ7-SQ12) so that it is generally characterized of fast transgression and slow regression.Semi-closed shallow-water carbonate platform gradually formed in the east and shoreline developed in the west in the SQ7 during middle Cambrian epoch.The middle Cambrian sedimentary model was inherited in SQ8 to SQ12 during upper Cambrian but more platform inner shoals developed in the west due to the weakening influence of the terrestrial detritus input and shallowing water.The platform inner shoals generally develop in the middle to top parts of HST invertical and in the center and eastern parts of Sichuan Basin in plan.%据对四川盆地范店、岩孔以及三汇场等3个野外寒武系剖面的观察,特别是根据岩孔单井剖面和女基井—宫深1井等连井剖面的层序界面特征和序列分析,将四川盆地寒武系自下而上划分为SQ1、SQ2、……、SQ12共12个三级层序,其中下寒武统6个(SQ1-SQ6),中—上寒武统6个(SQ7-SQ12).中—上寒武统发育多个潟湖→台内滩、潟湖→潮坪、台内

  9. An Early Cambrian archaeocyath–trilobite fauna in limestone erratics from the Upper Carboniferous Fitzroy Tillite Formation, Falkland Islands

    OpenAIRE

    Stone, P; Thomson, M.R.A; Rushton, A.W.A.

    2012-01-01

    Rare clasts of limestone contained in the uppermost Carboniferous Fitzroy Tillite Formation of the Falkland Islands contain a rich Cambrian fauna of archaeocyaths together with a radiocyath and a few trilobites. Neither Cambrian strata nor limestone are present in the indigenous rock succession and the clasts are regarded as exotic erratics, introduced during the Permo-Carboniferous glaciation of southern Gondwana, prior to its Mesozoic break-up. Nineteen archaeocyath taxa have been identifie...

  10. Eocrinoid echinoderms from the Lower Cambrian Guanshan Fauna in Wuding, Yunnan, China

    Institute of Scientific and Technical Information of China (English)

    HU ShiXue; LUO HuiLin; HOU ShuGuang; Bernd-Dietrich ERDTMANN

    2007-01-01

    This is a brief report of a new occurrence of eocrinoids from the Early Cambrian Wulongqing Formation in Yunnan, China. The eocrinoids from the Guanshan fauna are among the earliest known eocrinoids. Different from many other Early and Middle Cambrian eocrinoids, the Guanshan eocrinoids are characterized by the absence of sutural pores and epispires, the long and spiral brachioles, the extremely long stalk, and the ratio of the length of the stalk versus that of the calyx. The discovery of the eocrinoids from the Guanshan fauna not only provides new information to the investigation of the early evolution of this animal group, but also shed new light on the occurrence and migration of early eocrinoids.

  11. Lower Cambrian yolk-pyramid embryos from Southern Shaanxi,China

    Institute of Scientific and Technical Information of China (English)

    CHEN Junyuan; Andreas BRAUN; Dieter WALOSZEK; PENG Qingqing; Andreas MAAS

    2004-01-01

    Phosphatized globules with radially arranged pillars were recently recorded from the Lower Cambrian phosphate deposit, Ningqiang, Shaanxi by Yue and Bengtson. These authors interpreted the globules as blastula stage of embryos and the pillars as blastomeres. On the basis of new additional material, we reinterpret these structures as yolk-pyramid stages of possible arthropod eggs. The 20 embryos under present study range from 380 μm to 600 μm in diameter and contain about 120 pyramids. Some embryos having a higher number of pyramids are tentatively interpreted as slightly later developmental stages of the same animal. These 543-million-year-old embryos may push back the evolutionary history of the arthropods to a deeper time and also suggest that one important pattern of arthropod development was already present at the beginning of the Cambrian.

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

    Science.gov (United States)

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

    2012-05-01

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

  13. Rise to modern levels of ocean oxygenation coincided with the Cambrian radiation of animals.

    Science.gov (United States)

    Chen, Xi; Ling, Hong-Fei; Vance, Derek; Shields-Zhou, Graham A; Zhu, Maoyan; Poulton, Simon W; Och, Lawrence M; Jiang, Shao-Yong; Li, Da; Cremonese, Lorenzo; Archer, Corey

    2015-01-01

    The early diversification of animals (∼ 630 Ma), and their development into both motile and macroscopic forms (∼ 575-565 Ma), has been linked to stepwise increases in the oxygenation of Earth's surface environment. However, establishing such a linkage between oxygen and evolution for the later Cambrian 'explosion' (540-520 Ma) of new, energy-sapping body plans and behaviours has proved more elusive. Here we present new molybdenum isotope data, which demonstrate that the areal extent of oxygenated bottom waters increased in step with the early Cambrian bioradiation of animals and eukaryotic phytoplankton. Modern-like oxygen levels characterized the ocean at ∼ 521 Ma for the first time in Earth history. This marks the first establishment of a key environmental factor in modern-like ecosystems, where animals benefit from, and also contribute to, the 'homeostasis' of marine redox conditions. PMID:25980960

  14. Cambrian spiral-plated echinoderms from Gondwana reveal the earliest pentaradial body plan.

    Science.gov (United States)

    Smith, Andrew B; Zamora, Samuel

    2013-08-22

    Echinoderms are unique among animal phyla in having a pentaradial body plan, and their fossil record provides critical data on how this novel organization came about by revealing intermediate stages. Here, we report a spiral-plated animal from the early Cambrian of Morocco that is the most primitive pentaradial echinoderm yet discovered. It is intermediate between helicoplacoids (a bizarre group of spiral-bodied echinoderms) and crown-group pentaradiate echinoderms. By filling an important gap, this fossil reveals the common pattern that underpins the body plans of the two major echinoderm clades (pelmatozoans and eleutherozoans), showing that differential growth played an important role in their divergence. It also adds to the striking disparity of novel body plans appearing in the Cambrian explosion. PMID:23804624

  15. A superarmored lobopodian from the Cambrian of China and early disparity in the evolution of Onychophora.

    Science.gov (United States)

    Yang, Jie; Ortega-Hernández, Javier; Gerber, Sylvain; Butterfield, Nicholas J; Hou, Jin-Bo; Lan, Tian; Zhang, Xi-guang

    2015-07-14

    We describe Collinsium ciliosum from the early Cambrian Xiaoshiba Lagerstätte in South China, an armored lobopodian with a remarkable degree of limb differentiation including a pair of antenna-like appendages, six pairs of elongate setiferous limbs for suspension feeding, and nine pairs of clawed annulated legs with an anchoring function. Collinsium belongs to a highly derived clade of lobopodians within stem group Onychophora, distinguished by a substantial dorsal armature of supernumerary and biomineralized spines (Family Luolishaniidae). As demonstrated here, luolishaniids display the highest degree of limb specialization among Paleozoic lobopodians, constitute more than one-third of the overall morphological disparity of stem group Onychophora, and are substantially more disparate than crown group representatives. Despite having higher disparity and appendage complexity than other lobopodians and extant velvet worms, the specialized mode of life embodied by luolishaniids became extinct during the Early Paleozoic. Collinsium and other superarmored lobopodians exploited a unique paleoecological niche during the Cambrian explosion. PMID:26124122

  16. Aquatic Sediments.

    Science.gov (United States)

    Sanville, W. D.; And Others

    1978-01-01

    Presents a literature review of aquatic sediments and its effect upon water quality, covering publications of 1976-77. This review includes: (1) sediment water interchange; (2) chemical and physical characterization; and (3) heavy water in sediments. A list of 129 references is also presented. (HM)

  17. Precambrian-Cambrian Sedimentology, Stratigraphy, and Paleontology in the Great Basin (Western United States)

    OpenAIRE

    Sappenfield, Aaron Dale

    2015-01-01

    Thick accumulations of Neoproterozoic and early Phanerozoic strata are distributed throughout much of the arid continental interior of western North America, providing an expansive and well-exposed archive of this important time in Earth’s history. The information presented herein supplements evaluations regarding the utility and limitations of this archive by providing an integrated sedimentological, paleontological, and geochronological description for Precambrian-Cambrian strata exposed i...

  18. The Middle Cambrian fossil Pikaia and the evolution of chordate swimming

    OpenAIRE

    Lacalli Thurston

    2012-01-01

    Abstract Conway Morris and Caron (2012) have recently published an account of virtually all the available information on Pikaia gracilens, a well-known Cambrian fossil and supposed basal chordate, and propose on this basis some new ideas about Pikaia’s anatomy and evolutionary significance. Chief among its chordate-like features are the putative myomeres, a regular series of vertical bands that extends the length of the body. These differ from the myomeres of living chordates in that boundari...

  19. Cambrian Series 3 carbonate platform of Korea dominated by microbial-sponge reefs

    Science.gov (United States)

    Hong, Jongsun; Lee, Jeong-Hyun; Choh, Suk-Joo; Lee, Dong-Jin

    2016-07-01

    Metazoans have been considered as negligible components of Cambrian Series 3 and Furongian microbial-dominated reefs, in contrast to their presence in earlier Terreneuvian-Cambrian Series 2 microbial-archaeocyath reefs. However, recent discoveries of sponges in Cambrian Series 3-Furongian reefs of Australia, China, Iran, USA, and Korea have raised question regarding their contribution in terms of carbonate platform development, which have never been assessed. This study examines Cambrian Series 3 deposits of the Daegi Formation, Korea to elucidate this question. The 100-m-thick middle part of the Daegi Formation is dominated by boundstone facies, which occupies 45% of the study interval, as well as bioclastic wackestone to packstone, bioclastic grainstone, and ooid packstone to grainstone facies. The Daegi reefs are primarily thrombolitic in composition, with 90% (n = 26/29) of the reefs containing an average of 9% sponges in aerial percentage calculated from thin sections. Lithistid sponges composed of peloidal fabrics, some desma spicules, and spicule networks commonly occupy the interstitial space in microbial clusters, are encrusted by mesoclots and Epiphyton, and are surrounded by micrite. Subordinate non-lithistid demosponges occur within clusters of microbial elements. The middle Daegi Formation can be largely subdivided into shoal environment dominated by grainstone to packstone facies and shallow subtidal platform interior environment located behind shoal with wackestone to packstone facies. The microbial-sponge reefs mainly developed around platform interior as patch reefs. The current study indicates that metazoans in the form of lithistid and non-lithistid demosponges are nearly ubiquitously incorporated in Daegi reefs and contributed greatly to the formation of microbial-sponge reefs as well as carbonate platform during the time. Study of these microbial-sponge reefs and their distribution within the carbonate platform may help us to understand how

  20. 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/

  1. Cambrian spiral-plated echinoderms from Gondwana reveal the earliest pentaradial body plan

    OpenAIRE

    Smith, Andrew B.; Zamora, Samuel

    2013-01-01

    Echinoderms are unique among animal phyla in having a pentaradial body plan, and their fossil record provides critical data on how this novel organization came about by revealing intermediate stages. Here, we report a spiral-plated animal from the early Cambrian of Morocco that is the most primitive pentaradial echinoderm yet discovered. It is intermediate between helicoplacoids (a bizarre group of spiral-bodied echinoderms) and crown-group pentaradiate echinoderms. By filling an important ga...

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

    OpenAIRE

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

    2013-01-01

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

  3. Decoding the fossil record of early lophophorates : Systematics and phylogeny of problematic Cambrian Lophotrochozoa

    OpenAIRE

    Butler, Aodhán D.

    2015-01-01

    The evolutionary origins of animal phyla are intimately linked with the Cambrian explosion, a period of radical ecological and evolutionary innovation that begins approximately 540 Mya and continues for some 20 million years, during which most major animal groups appear. Lophotrochozoa, a major group of protostome animals that includes molluscs, annelids and brachiopods, represent a significant component of the oldest known fossil records of biomineralised animals, as disclosed by the enigmat...

  4. Testing the Cambrian explosion hypothesis by using a molecular dating technique

    OpenAIRE

    Bromham, L.; Rambaut, A; Fortey, R; Cooper, A.; Penny, D

    1998-01-01

    Molecular studies have the potential to shed light on the origin of the animal phyla by providing independent estimates of the divergence times, but have been criticized for failing to account adequately for variation in rate of evolution. A method of dating divergence times from molecular data addresses the criticisms of earlier studies and provides more realistic, but wider, confidence intervals. The data are not compatible with the Cambrian explosion hypothesis as an explanation for the or...

  5. Articulated Wiwaxia from the Cambrian Stage 3 Xiaoshiba Lagerstätte.

    OpenAIRE

    Yang, J.; Smith, M. R.; Lan, T.; Hou, J.-B.; Zhang, X.-G.

    2014-01-01

    Wiwaxia is a bizarre metazoan that has been interpreted as a primitive mollusc and as a polychaete annelid worm. Extensive material from the Burgess Shale provides a detailed picture of its morphology and ontogeny, but the fossil record outside this lagerstätte is scarce, and complete wiwaxiids are particularly rare. Here we report small articulated specimens of Wiwaxia foliosa sp. nov. from the Xiaoshiba fauna (Cambrian Stage 3, Hongjingshao Formation, Kunming, south China). Although spines ...

  6. A superarmored lobopodian from the Cambrian of China and early disparity in the evolution of Onychophora

    OpenAIRE

    Yang, Jie; Ortega-Hernández, Javier; Gerber, Sylvain; Butterfield, Nicholas J.; Hou, Jin-bo; Lan, Tian; Zhang, Xi-guang

    2015-01-01

    Paleozoic lobopodians constitute a diverse assemblage of worm-like organisms that are known from various exceptional fossil deposits and were among the earliest animals to develop skeletonized body parts for protection. Here, we describe Collinsium ciliosum gen. et sp. nov., an armored lobopodian from the early Cambrian Xiaoshiba Lagerstätte (South China). Collinsium belongs to an extinct clade of superarmored lobopodians characterized by supernumerary dorsal spines, and specialized limbs for...

  7. Gut Contents as Direct Indicators for Trophic Relationships in the Cambrian Marine Ecosystem

    OpenAIRE

    Vannier, Jean

    2012-01-01

    Present-day ecosystems host a huge variety of organisms that interact and transfer mass and energy via a cascade of trophic levels. When and how this complex machinery was established remains largely unknown. Although exceptionally preserved biotas clearly show that Early Cambrian animals had already acquired functionalities that enabled them to exploit a wide range of food resources, there is scant direct evidence concerning their diet and exact trophic relationships. Here I describe the gut...

  8. Response to "Discussion on the systematic position of the Early Cambrian priapulomorph worms"

    Institute of Scientific and Technical Information of China (English)

    HAN Jian; HU Shixue

    2006-01-01

    @@ Due to the combination of complex states of preservation and taphonomies in Chengjiang fossils, Huang et al.[1] expressed different opinions to those of Han et al.[2] on the morphology and systematic position of the fossil priapulomorph worms (Priapulomorpha) based on their additional materials. These diverse opinions are critical in any investigation of the diversity of the Introverta in the Cambrian explosion. However, some of their ideas need to be discussed in further detail.

  9. Can fast early rates reconcile molecular dates with the Cambrian explosion?

    OpenAIRE

    Bromham, L D; Hendy, M D

    2000-01-01

    Molecular dates consistently place the divergence of major metazoan lineages in the Precambrian, leading to the suggestion that the 'Cambrian explosion' is an artefact of preservation which left earlier forms unrecorded in the fossil record. While criticisms of molecular analyses for failing to deal with variation in the rate of molecular evolution adequately have been countered by analyses which allow both site-to-site and lineage-specific rate variation, no analysis to date has allowed the ...

  10. Adaptive walks in a gene network model of morphogenesis: insights into the Cambrian explosion

    OpenAIRE

    Sole, Ricard V.; Fernandez, Pau; Kauffman, Stuart A.

    2003-01-01

    The emergence of complex patterns of organization close to the Cambrian boundary is known to have happened over a (geologically) short period of time. It involved the rapid diversification of body plans and stands as one of the major transitions in evolution. How it took place is a controversial issue. Here we explore this problem by considering a simple model of pattern formation in multicellular organisms. By modeling gene network-based morphogenesis and its evolution through adaptive walks...

  11. 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.

  12. Paleobiology of the Early Cambrian Yanjiahe Formation in Hubei Province of South China

    OpenAIRE

    Broce, Jesse

    2013-01-01

    Fossils recovered from limestones of the lower Cambrian (Stage 2-3) Yanjiahe Formation in Hubei Province, South China, recovered using acetic acid maceration, fracturing, and thin sectioning techniques were examined using a combination of analytical techniques, including energy dispersive spectroscopic (EDS) elemental mapping and micro-focus X-ray computed tomography (micro-CT). One important fossil recovered and analyzed with these techniques is a fossilized embryo. Fossilized animal embryos...

  13. Cyclostratigraphy of Late Cambrian cyclic carbonates: an interbasinal field and modelling study, U.S.A.

    OpenAIRE

    Osleger, David Allen

    1995-01-01

    An interbasinal study of Late Cambrian cyclic carbonate successions in the Appalachian and Cordilleran passive margins, the Texas cratonic embayment and the southern Oklahoma aulacogen has provided controls on the simultaneous development of peritidal to subtidal meter-scale cycles and the larger scale depositional sequences on which they are superimposed. Fining-upward peritidal cycles grade seaward into coarsening-upward, shallow to deep subtidal cycles that form a continuum across...

  14. Why is construction of an Ediacaran-Cambrian global paleogeography so difficult?

    Science.gov (United States)

    Evans, D. A.; Raub, T. D.; Maloof, A. C.

    2004-05-01

    The foremost answer to the above question is that high-precision global biostratigraphy extends only to Early Cambrian time. A more challenging issue concerns paleomagnetic data from the Ediacaran (proposed terminal Proterozoic period) and earliest Cambrian intervals: each paleocontinent's apparent polar wander path shows a large spread in poles, intriguingly distributed around a great circle (excepting Baltica, see below), and implying rates of paleolatitude translation or rotation far exceeding typical values from the Cenozoic. Oscillatory true polar wander (TPW) has been proposed to explain these great-circle distributions, but as more data are gathered the number of required episodes increases steadily. Another mechanism to explain such jumpy datasets is a persistently nonaxial geomagnetic field, with greatly amplified paleosecular variation; however, such an interpretation is unattractive to many geodynamicists. A third approach to explain the anomalous data is to discount them altogether; this is unsatisfactory because some of the most reliable results (e.g., Grenville dykes B component and Bunyeroo Formation pole) must be discarded in order to simplify the paths. We propose a new technique for Ediacaran-Cambrian continental reconstruction, which uses these intriguing great circle pole paths regardless of how they were generated. Each paleocontinent's path yields a best-fit great circle and corresponding pole. In the TPW interpretation, that pole describes the long-lived, common (equatorial) axis to the oscillatory rotations. Given that age constraints on the poles is generally so poor, we may reconstruct each continent to this axis with azimuthal freedom. This is topologically identical to the longitudinal degeneracy of standard paleomagnetic reconstructions, but in the case of TPW uncertainties in positions along the great circle represent uncertainties in paleolatitudes, hence climate zones. Analysis of the global Ediacaran-Cambrian paleomagnetic database

  15. Geosphere-Biosphere Feedbacks as a Trigger for the Cambrian explosion

    Science.gov (United States)

    von Bloh, W.; Bounama, C.; Franck, S.

    2003-12-01

    A new hypothesis for the cause of the Cambrian explosion is presented. The Cambrian explosion 542 Myr ago is characterized by a sudden increase of biomass and a rapid cooling, which amplified the spread of complex multicellular life. The evolution of the planet Earth is described by the co-evolution of the geosphere-biosphere system. A conceptual model for the global carbon cycle of the Earth containing the reservoirs mantle, ocean floor, continental crust, continental biosphere, the kerogen, as well as the aggregated reservoir ocean and atmosphere is presented. In this study the evolution of the mean global surface temperature, the biomass, and reservoir sizes over the whole history and future of the Earth under a maturing Sun is investigated. Here we specify our previously published Earth system model (Franck et al., 2002) by introducing three different types of biosphere: procaryotes, eucaryotes, and complex multicellular life. They are characterized by different temperature tolerance windows and biotic amplification factors of silicate weathering. The biotic enhancement of weathering by complex multicellular life adds an additional feedback to the system and triggers the Cambrian explosion. The Cambrian explosion was mainly driven by extrinsic environmental causes, i.e. a gradual cooling of the Earth. The Cambrian explosion was so rapid because of a positive feedback between the spread of biosphere, increased silicate weathering, and a consequent cooling of the climate. The environment itself has been actively changed by the biosphere maintaining the temperature conditions for its existence. Furthermore, it can be shown that the coupled geosphere-biosphere system exhibit s bistability: there exist two stable model solutions for a certain interval of the biotic enhancement factor, one solution with and one without complex multicellular life. In particular, cooling events in the Neoproterozoic, could force a premature appearance of complex multicellular life

  16. 早寒武世初期沂沭断裂带地震效应%Seismic effects from Yishu Fault Zone during the earlier Early Cambrian

    Institute of Scientific and Technical Information of China (English)

    田洪水; 张邦花; 祝介旺; 张增奇; 李洪奎

    2011-01-01

    In the earlier Early Cambrian, with the proceeding of the marine invasion from the Paleo-Yishu Strait to west, uneven thick deposits of sandstone, mudstone and carbonate rock of littoral, lagoon and neritic facies were deposited in western Shandong Province. The horizon of these layers belongs to the bottom part of Lower Cambrian consisting of the Liguan and Zhushadong Formations. Together with the depositional and formation processes, tectonic rift-depression was taking place in the Yishu Fault Zone, characterized by frequent submarine earthquakes with different seismic effects within 200 km range from the Yishu Fault Zone to west. Various seismogenetic syndepositional deformation structures are formed in the seismic records. Seismic effect records developed in the Zhushadong Formation are mainly soft-sediment deformations such as diapir structure, carbonate lime-mud volcano, liquefied vein, liquefied brec cia , seismic fold, graded-fault, siliceous vein etc., besides a few brittle deformation of semi-consolidated sediments. Those preserved in the Liguan Formation are not only slump fold, load structure and ball-and pillow structure, but also some seismo-turbidite. Magnitude reflected by submarine seismic effects might be Richater magnitude of 5. 0 ~ 8. 9. These evidences indicate that strong tectonic activities occurred along the Yishu Fault Zone in the Early Cambrian. Analyses from the viewpoint of marine engineering geology show that seismic effects mentioned above are destructive forms of sediment layers caused by earthquake at the sea-bottom. This paper has provided intuitive materials for understanding earthquake destruction to rock-soil layers of seafloor-engineering foundation.%早寒武世初期,随着从古沂沭海峡向西海侵的发展,鲁西地区沉积了厚度不等的主要由砂岩、泥岩和碳酸盐岩组成的滨海、潟湖及浅海相沉积,其层位属下寒武统底部的李官组和朱砂洞组.在它们沉积过程中,沂沭断裂带

  17. The Late Cambrian Takaka Terrane, NW Nelson, New Zealand: Accretionary-prism development and arc collision followed by extension and fan-delta deposition at the SE margin of Gondwana

    Science.gov (United States)

    Pound, K. S.

    2013-12-01

    convergence, but is reinterpreted here as a ';true' fan-delta deposit, sedimentologically similar to deposits associated with extension. Textural and compositional data for the Lockett Conglomerate indicates rapid supply of new material (including quartzite, granite, gabbro, and amphibolitic metavolcanics). The Lockett Conglomerate is proposed here to record the initiation of extension, during which basement faults in the hinterland exposed previously buried source rocks. This new interpretation of the Lockett Conglomerate places that initiation of extension and subsequent passive margin sedimentation (Mt. Ellis and Mt. Arthur Groups) earlier (late Middle Cambrian) than previous work has suggested (Late Cambrian or Early Ordovician). These new interpretations provide input useful for correlations and interpretations of the complex mosaic that preserves a record of tectonic activity and processes at the Antarctic, Tasmanian and SE Australian portions of the Cambrian Gondwana margin.

  18. A new U/Pb date for the basal Meishucun section and implications for the age of the Cambrian explosion

    Science.gov (United States)

    Brooks, B. J.; Crowley, J. L.; Bowring, S. A.; Cervato, C.; Jin, Y.

    2006-12-01

    The Early Cambrian of southern China has long been recognized to record the spectacular transition from microscopic small shelly fossils to a fauna characterized by large, diverse higher bilaterians during part of the Early Cambrian evolutionary explosion. Understanding the timing and rate of this evolutionary transition has been aided through the integration of U/Pb geochronology into Cambrian fossil biozones, which has established strong tie-points between platforms. The Meishucun section (Yunnan, China) is one of the units that best preserves what could be considered the prelude to the Cambrian explosion. Several attempts at dating volcanic horizons within this section have resulted in U/Pb zircon dates that range from 538 to 525 Ma, making correlations to sections further afield problematic. This new high-precision U/Pb date of 533 Ma for Meishucun's Bed 5 is in broad agreement but considerably more precise than previous U/Pb ages. This indicates that the low diversity fauna of the Anabarites trisulcatus--Protohertzina anabarica zone persisted for no less than the first 9 m.y. of the Cambrian in China, and sets an additional lower bracket age for the emergence of higher bilaterians (e.g. trilobites, soft-bodied fauna).

  19. Sediment Transport

    DEFF Research Database (Denmark)

    Liu, Zhou

    Flow and sediment transport are important in relation to several engineering topics, e.g. erosion around structures, backfilling of dredged channels and nearshore morphological change. The purpose of the present book is to describe both the basic hydrodynamics and the basic sediment transport...... mechanics. Chapter 1 deals with fundamentals in fluid mechanics with emphasis on bed shear stress by currents, while chapter 3 discusses wave boundary layer theory. They are both written with a view to sediment transport. Sediment transport in rivers, cross-shore and longshore are dealt with in chapters 2...

  20. A Cambrian micro-lobopodian and the evolution of arthropod locomotion and reproduction

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The evolutionary success of arthropods, the most abundant and diverse animal group, is mainly based on their segmented body and jointed appendages, features that had evolved most likely already before the Cambrian. The first arthropod-like animals, the lobopodians from the Early Cambrian, were unsclerotized and worm-like, and they had unjointed tubular legs. Here we describe the first three-dimensionally preserved Cambrian lobopodian. The material presented of Orstenotubulus evamuellerae gen. et sp. nov. is the smallest and youngest of a lobopodian known. O. evamuellerae shows strikingly detailed similarities to Recent tardigrades and/or onychophorans in its cellular-structured cuticle and the telescopic spines. It also shows similarities to other, longer known lobopodians, but which are ten times as large as the new form. These similarities include the finely annulated body and legs, which is characteristic also for Recent onychophorans, and paired humps continuing into spines situated dorsally to the leg insertions, a feature lacking in the extant forms. The morphology of O. evamuellerae not only elucidates our knowledge about lobopodians, but also aids in a clearer picture of the early evolution of arthropods. An example is the single ventral gonopore between a limb pair of O. evamuellerae, which indicates that a single gonopore, as developed in onychophorans, tardigrades, pentastomids, myriapods and insects, might represent the plesiomorphic state for Arthropoda, while the paired state in chelicerates and crustaceans was convergently achieved. Concerning life habits, the lateral orientation of the limbs and their anchoring spines of the new lobopodian imply that early arthropods were crawlers rather than walkers.

  1. Molecular Fossils for Understanding Biodiversity During the Neoproterozoic-Cambrian Transition in China

    Science.gov (United States)

    Pi, Y.; Tuo, J.; McFadden, K.; Xiao, S.; Zhang, C. L.

    2005-12-01

    Neoproterozoic-Cambrian rocks in South China contain an extraordinary fossil record, including exceptionally well preserved animal embryos, acritarchs, and multi-cellular algae. The goal of this study was to evaluate the microbial diversity associated with these remarkably preserved fossil assemblages at the Neoproterozoic-Cambrian transition. Rock samples of 520-632 Ma in age were collected in the Yangtze Gorges area and southern Anhui Province, China. Samples were powdered and extracted for organic biomarkers. The content of bitumen A accounted for 4-16% of the rock material and most of it (49-79%) was asphaltenes. Saturated and aromatic hydrocarbons accounted for 2-6% and 1-3%, respectively. Analysis using GC-MS indicated the predominance of n-alkanes and less abundant isoprenoid alkanes in the saturated fractions. The n-alkanes were characterized by homologues dominated by C15-C17, which is consistent with the result of high thermal-evolution (Brocks et al., 2003. GCA 67:4321-4335). Hopanoids were present in less abundance and ranged from C29 to C32. A smaller amount of heavy-molecular-weight n-alkanes (C23-C39) was also detected, which indicated a source of high plants and must be contamination from younger organic matter. Still, patterns of variation can be detected among these samples. For example, the ratio of pristane to phytane was all greater than 1.0 except for one sample (JLW9.3) from Yangtze Gorges area. The results indicate that sample JLW9.3 might have been deposited in a reducing environment whereas the other samples might have been formed in relatively oxidative environments. The overall results, however, suggest that rock samples from the Neoproterozoic-Cambrian transition in China have gone through significant metamorphism; thus, understanding of microbial communities using molecular biomarkers in such altered rocks needs to be cautiously executed.

  2. The Urbilateria: Insights From Comparative Developmental Biology Into The Cambrian Radiation

    Science.gov (United States)

    Erwin, D. H.

    2004-12-01

    A critical issue in understanding the patterns of morphological and developmental evolution during the Cambrian radiation of animal body plans is the morphological complexity of the last common ancestor of the two great bilaterian clades, the protostomes and deuterostomes. Often known as the Urbilateria or the protostome-deuterostome ancestor (PDA) this node in metazoan phylogeny distinguishes the sponges and cnidarians from the bilaterian clades. Highly conserved developmental genes and complexes suggests that the PDA was a relatively complex organism, with dorsal-ventral and anterior-posterior patterning, eyes, appendages, heart, central nervous system, segmentation and other relatively complex morphological features. If this view of the PDA is correct, it has important implications for understanding the Cambrian radiation, for such a complex animal is likely to leave traces in the sedimentary record even if it lacked a durable skeleton. However, this interpretation of conserved developmental sequences may overestimate the extent to which homologies of developmental sequences implies morphological conservation. In other words, does the presence of the Nkx 2.5 gene in the PDA necessitate the presence of a heart, or simple the appearance of contractile muscles? If the latter, then the PDA may have been a much less complex organism. This latter view of developmental evolution suggests the PDA possessed a developmental toolkit, but that the specific implementation of these tools in specific body plans occurred after the PDA, within specific clades. Moreover, this view also strongly suggests that changes in the physical environment, or in ecological relationships, was primarily responsible for the evolutionary innovations seen in the Cambrian, rather than developmental innovations.

  3. Preliminary basin analysis of late Proterozoic-Cambrian post-rift strata, southeast Idaho thrust belt

    Energy Technology Data Exchange (ETDEWEB)

    Link, P.K.; Jansen, S.T.; Halimdihardja, P.; Lande, A.C.; Zahn, P.D.

    1987-08-01

    Strata of the Brigham Group in the Paris-Putnam plate of the southeastern Idaho thrust belt span the late Proterozoic-Cambrian boundary and consist of quartzose sandstone with subordinate pebble conglomerate and siltstone. The Brigham Group is overlain by fossiliferous Cambrian carbonate units that represent the transition from siliciclastic to carbonate deposition in the Cordilleran miogeocline. The Brigham Group contains four stratigraphic sequences bounded by regional disconformities. The lower sequence includes strata below the Brigham group (upper member, Pocatello Formation), plus the Papoose Creek Formation and most of the overlying Caddy Canyon Quartzite. This sequence is dominantly marine with shoreface and braided fluvial strata at the top. The first sequence is overlain disconformably by offshore sub-wave base marine strata of the upper Caddy Canyon Quartzite and Inkom Formation. This second sequence is entirely marine and is composed dominantly of siltstone with sandstone-filled channels. The third sequence comprises the Mutual Formation, an entirely braided fluvial and lacustrine unit. The fourth sequence (Sauk sequence) locally overlies the Mutual Formation with an erosional unconformity and consists of dominantly marine strata of the Camelback Mountain Quartzite, Gibson Jack Formation, Windy Pass Argillite, Twin Knobs Formation, and Sedgwick peak Quartzite. Correlations of these sequences to the McCoy Creek Group of eastern Nevada suggests uniform conditions of sea level and subsidence across the late Proterozoic-Cambrian Cordilleran miogeocline. This preliminary synthesis suggests the Brigham and McCoy Creek Groups are post-rift deposits, as indicated by regional persistence of facies, paleocurrents, and quartzose petrology.

  4. 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

  5. Vermicular fossils in the Early Cambrian Xidashan Formation in the Quruqtagh region of Xinjiang, China

    Institute of Scientific and Technical Information of China (English)

    YANG Ruidong; ZHANG Chuanlin; SONG Guoqi; LUO Xinrong

    2006-01-01

    Large amounts of vermicular fossils and a minor amount of sponge animal fossils have been found in the Early Cambrian Xidashan Formation in the region of Quruqtagh, Xinjiang. Vermicular fossils are generally more than 50 mm long and 0.3-1.4 mm wide; their wrinkled lamellae are microfine with 3-10 pieces within the length of every each millimeter. The fossils are considered to be Sabellidites cambriensis Sokolov (1965). The Xidashan Formation is the highest stratum in which Sabellidites occur, as has been so far reported.

  6. Organic carbon isotopes of the Sinian and Early Cambrian black shales on Yangtze Platform, China

    Institute of Scientific and Technical Information of China (English)

    李任伟; 卢家烂; 张淑坤; 雷加锦

    1999-01-01

    Organic matter of the Sinian and early Cambrian black shales on the Yangtze Platform belongs to the light carbon group of isotopes with the δ13C values from - 27 % to -35 % , which are lower than those of the contemporaneously deposited carbonates and phosphorites. A carbon isotope-stratified paleooceanographic model caused by upwelling is proposed, which can be used not only to interpret the characteristics of organic carbon isotopic compositions of the black shales, but also to interpret the paleogeographic difference in the organic carbon isotope compositions of various types of sedimentary rocks.

  7. Early Cambrian phosphatized blastula-and gastrula-stage animal fossils from southern Shaanxi

    Institute of Scientific and Technical Information of China (English)

    HUA Hong; CHEN Zhe; ZHANG Luyi

    2004-01-01

    Marine invertebrate animal embryos and their early developmental products are of great significance to the study of taxonomy and phylogeny of early animals. A great number of phosphatized globular fossils were collected from the early Cambrian Kuanchuanpu Member (upper Dengying Formation), southern Shaanxi, and a nearly complete developmental sequence--from a fertilized egg, via blastodisc formation, blastula development, blastodisc enlargement toward gastrulae, to tissue differentiation--can be discerned in this collection. This discovery provides unmatchable material for studies on the origin, taxonomy, radiation,and ontogeny of early metazoans.

  8. Neo proterozoic Cambrian in Uruguay: Dom Feliciano belt against Cuchilla Dionisio Terrane

    International Nuclear Information System (INIS)

    After an exhaustive bibliographic research about the subject, its was detected two opinion groups that beleive different evolution processes during Neoproterozoic Cambrian period in Uruguay.One of them beleives that litho-structural arrangement was generated in an unique Wilson cycle, the other one, supports that the genesis of nowaday structure is a tangential collision near 520 Ma; this point of view coincides with authors thinking 62 papers were consulted and many geological as some geochronological unpublished data were used in the analysis of the subject

  9. Origin and variability of the late Precambrian-Cambrian Athel Silicilyte, South Oman Salt Basin

    OpenAIRE

    Al Rajaibi, Ibrahim Mohamed amur

    2011-01-01

    The Precambrian-Cambrian Athel Silicilyte is an enigmatic chert unit of up to 390 m thick found as slabs (each slab typically 2 × 6 km across) entrapped within salt domes at a depth of 4-5 km in the South Oman Salt Basin. This formation is a prolific self-charged reservoir with high porosity (up to 34 %) and high oil saturation (80 %). Despite its economic value, the origin and the variability of this formation are not fully understood. This study therefore aims to investigate the variability...

  10. Rise to modern levels of ocean oxygenation coincided with the Cambrian radiation of animals.

    OpenAIRE

    Chen, X.; Ling, HF; Vance, D.; Shields-Zhou, GA; Zhu, M.; Poulton, SW; Och, LM; Jiang, SY; Li, D.; Cremonese, L; Archer, C.

    2015-01-01

    The early diversification of animals (∼630 Ma), and their development into both motile and macroscopic forms (∼575–565 Ma), has been linked to stepwise increases in the oxygenation of Earth's surface environment. However, establishing such a linkage between oxygen and evolution for the later Cambrian ‘explosion' (540–520 Ma) of new, energy-sapping body plans and behaviours has proved more elusive. Here we present new molybdenum isotope data, which demonstrate that the areal extent of oxygenat...

  11. A molecular and isotopic study of palaeoenvironmental conditions through the middle Cambrian in the Georgina Basin, central Australia

    Science.gov (United States)

    Pagès, Anais; Schmid, Susanne; Edwards, Dianne; Barnes, Stephen; He, Nannan; Grice, Kliti

    2016-08-01

    The Cambrian period marks an important point in Earth's history with profound changes in the ocean's biogeochemistry and the occurrence of the most significant evolutionary event in the history of life, the Cambrian explosion. The Cambrian explosion is described as a succession of complex cycles of extinctions and radiations. This study integrates biomarkers and their compound-specific stable carbon isotopes to investigate the palaeoenvironmental depositional conditions in middle Cambrian (Series 3) sedimentary rocks (Thorntonia Limestone, Inca Formation and Currant Bush Limestone) from two drillholes in the Undilla Sub-basin in the eastern Georgina Basin, central Australia. The occurrence of photic zone euxinia (PZE) was detected throughout these three formations by the identification of green sulfur bacteria Chlorobiaceae-derived biomarkers, including a series of 2,3,6-aryl isoprenoids and the intact biomarker isorenieratane. Pulses of enhanced PZE conditions were detected in two core intervals (90-110 mKB, Currant Bush Limestone and 170-200 mKB, Inca Formation) by an increase in the 2,3,6-aryl isoprenoids and C19 biphenyl concentrations. These enhanced PZE conditions were followed by blooms of phytoplankton, as demonstrated by the increase in algal-derived biomarker (i.e. pristane, phytane and the C19n-alkane) concentrations and compound-specific isotopes. These observations confirm that palaeoenvironmental conditions were similar to those reported for the Permian/Triassic and Triassic/Jurassic mass extinction events. The sterane distributions varied across the three formations reflecting possible changes in the phytoplanktonic communities through time. Although a rise in atmospheric oxygen during the Cambrian has been previously associated with the rapid evolution of metazoans, the ecological challenges related to widespread anoxia must have had a major influence on the evolution of life in Cambrian oceans.

  12. 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

  13. Isotopic compositions of small shelly fossil Anabarites from Lower Cambrian in Yangtze Platform of South China: Implications for palaeocean temperature

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Anabarites belong to small shelly fossils (SSF), which occur widely in the Lower Cambrian strata of Yangtze Platform in South China. They are phosphate shell in composition and represent the earliest stage of the Cambrian bioradiation of Bilateria, the socalled "Cambrian Explosion". In this study, we attempted to separate Anabarites fossils from Lower Cambrian dolostones, and we obtained samples of both the fossils (SSF) and the granular phosphates (GP). Isotopic analyses were performed on samples of SSF, GP, and matrix dolostone (DH-23). The results showed that the δ30 Si values of the quartz filling in fossils celoms, and the siliceous materials in granular phosphates are -0.6‰ and -0.7‰, which is different from normal sedimentary siliceous rocks from the Lower Cambrian strata (0-0.7‰) as reported by Li et al., but is consistent with the data for siliceous rocks and cherts of submarine hydrothermal origin. It is likely that a later hydrothermal replacement could have taken place in the SSF-bearing sedimentary rocks. The oxygen isotope values of the phosphate of SSF and GP are 16.8‰ and 17.0‰, respectively. These are significantly higher than the Neoproterozoic phosphate ores (10.9‰-13.9‰) as reported by Ling et al., hence, late diagenesis and hydrothermal replacement may not have caused a significant change in the oxygen isotope compositions of the small shelly fossils, and the calculated temperatures (25.4-26.3 ℃ ) for palaeo-seawater using a SSF phosphate oxygen isotope thermometer are therefore considered here as the upper limit of seawater temperature in the Early Cambrian ocean of the Yangtze Platform.

  14. Early colonization of metazoans in the deep-water: Evidences from the lowermost Cambrian black shales of South China

    Science.gov (United States)

    Zhu, M.-Y.; Yang, A.-H.; Zhang, J.-M.; Li, G.-X.; Yang, X.-L.

    2003-04-01

    Diversity of metazoans is high in the deep-water of the present ocean. But it is unknown that when the metazoans began to colonize in the deep-water and what kinds of metazoans first colonized in the deep-water since origin and radiation of metazoans during the Precambrian-Cambrian transition interval. Up to the present, colonization of the deep-sea began in the Ordovician. Although it is suggested that animals were penetrated into the intermediate water depth during the Precambrian, evidences support such suggestion are based on the problematic Ediacaran-grade fossils. However, almost fossil materials that support the Cambrian Explosion hypothesis were discovered from the lowermost Cambrian shallow-water deposits. The abundant earliest Cambrian mineralized small shelly fossils (SSF) are globally from the shallow-water deposits, and the well-known Chengjiang fauna that may records most complete features of metazoans in the ocean after the Cambrian Explosion, occurs as well in the shallow basin near an old land on the Yangtze Platform. In order to understand ecology of the Cambrian Explosion time interval and how happened of the onshore-offshore trends of metazoans, we focused our attention on collecting fossils in the lowermost Cambrian deposits under the varied facies on the Yangtze Platformm during recent years. Investigations of the shallow-water carbonate facies and the oxygen-depleted deep-water black shale facies revealed additional biological and ecological information that are not recorded in the Chengjiang fauna in the siliclastic shallow-water facies. Here we report our discovery of a particular fossil association from more than 10 sections in the deep-water black shales (Qiongzhusian) in the out shelf and slope area of the Yangtze Platform. The fossil association is composed of pelagic and sessile organisms, including abundant sponges, 3 types of bivalved arthropods, 3 types of tubular animals and few problematic organisms. The fossils have either

  15. Sinian-Cambrian stratigraphic framework for shallow- to deep-water environments of the Yangtze Platform: an integrated approach

    Institute of Scientific and Technical Information of China (English)

    ZHU Maoyan; ZHANG Junming; Michael STEINER; YANG Aihua; LI Guoxiang; Bernd D. ERDTMANN

    2003-01-01

    The Sinian (Terminal Proterozoic) and Early Cambrian shallow- to deep-water sequences of the Yangtze Platform were investigated. Based on integrated lithostratigraphic, biostratigraphic, and other approaches, the shallow-water sequence from the base of the Sinian (base of the Doushantuo Formation) to the top of the Qiongzhusian (top of the Yu'anshan Formation) was subdivided into 12 stratigraphic intervals. These 12 intervals were applied in turn to the subdivision and correlation of the sequences present in various facies of the Yangtze Platform. The high-resolution stratigraphic framework here developed can serve as a time frame for ongoing multidisciplinary analyses of the "Cambrian explosion".

  16. Experimental mineralization of crustacean eggs: new implications for the fossilization of Precambrian–Cambrian embryos

    Directory of Open Access Journals (Sweden)

    D. Hippler

    2012-05-01

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

  17. Brachiopods hitching a ride: an early case of commensalism in the middle Cambrian Burgess Shale

    Science.gov (United States)

    Topper, Timothy P.; Holmer, Lars E.; Caron, Jean-Bernard

    2014-10-01

    Ecological interactions, including symbiotic associations such as mutualism, parasitism and commensalism are crucial factors in generating evolutionary novelties and strategies. Direct examples of species interactions in the fossil record generally involve organisms attached to sessile organisms in an epibiont or macroboring relationship. Here we provide support for an intimate ecological association between a calcareous brachiopod (Nisusia) and the stem group mollusc Wiwaxia from the Burgess Shale. Brachiopod specimens are fixed to Wiwaxia scleritomes, the latter showing no signs of decay and disarticulation, suggesting a live association. We interpret this association as the oldest unambiguous example of a facultative ectosymbiosis between a sessile organism and a mobile benthic animal in the fossil record. The potential evolutionary advantage of this association is discussed, brachiopods benefiting from ease of attachment, increased food supply, avoidance of turbid benthic conditions, biofoul and possible protection from predators, suggesting commensalism (benefiting the symbiont with no impact for the host). While Cambrian brachiopods are relatively common epibionts, in particular on sponges, the association of Nisusia with the motile Wiwaxia is rare for a brachiopod species, fossil or living, and suggests that symbiotic associations were already well established and diversified by the ``middle'' (Series 3, Stage 5) Cambrian.

  18. Mantle insulation beneath the West African craton during the Precambrian-Cambrian transition

    Science.gov (United States)

    Doblas, Miguel; López-Ruiz, José; Cebriá, José-María; Youbi, Nasrrddine; Degroote, Eugenio

    2002-09-01

    At the time of the Precambrian-Cambrian transition, the West African craton underwent widespread magmatism, hydrothermal activity, and thermal rejuvenation. This tectonothermal event gave rise to an anorogenic “ring of fire” along the rim of this craton, following the Pan-African Brasiliano belt that was reactivated by extension and transtension. The thermal phenomena were due to the progressive peripheral release of mantle heat that had built up beneath this craton because of strong insulating conditions. The West African craton at the Precambrian-Cambrian transition can thus be envisioned in terms of a gigantic pressure-cooker with a thick blanketing lithospheric lid. These insulation processes triggered an unusually hot mantle that was channeled by edge-driven convection toward the peri West African craton extensional corridors and released through magmatic pressure-relief valves. Massive ice melting and outgassing of volcanic CO2 gave rise to a planet-scale sea-level rise, a greenhouse effect, and the end of the icehouse snowball Earth. These processes played an important role in the Phanerozoic explosion of life on Earth.

  19. The evolution of associative learning: A factor in the Cambrian explosion.

    Science.gov (United States)

    Ginsburg, Simona; Jablonka, Eva

    2010-09-01

    The Cambrian explosion is probably the most spectacular diversification in evolutionary history, and understanding it has been a challenge for biologists since the time of Darwin. We propose that one of the key factors that drove this great diversification was associative learning. Although the evolutionary emergence of associative learning required only small modifications in already existing memory mechanisms and may have occurred in parallel in several groups, once this type of learning appeared on the evolutionary scene, it led to extreme diversifying selection at the ecological level: it enabled animals to exploit new niches, promoted new types of relations and arms races, and led to adaptive responses that became fixed through genetic accommodation processes. This learning-based diversification was accompanied by neurohormonal stress, which led to an ongoing destabilization and re-patterning of the epigenome, which, in turn, enabled further morphological, physiological, and behavioral diversification. Our hypothesis combines several previous ideas about the dynamics of the Cambrian explosion and provides a unifying framework that includes both ecological and genomic factors. We conclude by suggesting research directions that would clarify the timing and manner in which associative learning evolved, and the effects it had on the evolution of nervous systems, genomes, and animal morphology. PMID:20558182

  20. Preliminary estimate of crustal extension during Cambrian rifting in the southern midcontinent

    Energy Technology Data Exchange (ETDEWEB)

    McConnell, D.A.; Gilbert, M.

    1985-01-01

    The Southern Oklahoma Aulacogen is a prominent rift extending 500+ km NW into the southern Midcontinent from the probably Cambrian plate margin. The biomodal igneous floor of the rift has been strongly structurally inverted and is now partially exposed in the core of the Wichita Mountains. Utilizing structural and stratigraphic patterns, and character of the igneous sequence, the style of tectonism and magnitude of displacement can be inferred for the initiation of the rift. Five possible extensional pulses can be related to specific igneous features although these could be part of one continuous episode lasting from about 565 to 525 mybp. Pennsylvanian transpressive faults are assumed to be reactivated Cambrian normal faults (and they may even have an earlier parentage). Using known thickness of continuous rhyolite (1.4 km), an initial width of 60 km, and a half-graben configuration, an estimate of extension is possible independent of bounding fault dip. For a brittle-ductile transition between 10 to 15 km, the brittle extension in the upper crust varies between 8-5%. Using the minimum mafic volume needed within the ductile lower crust (40,000 km/sup 3/), and a total crustal thickness of 35 to 45 km, the lower crust was extended 8-6% to 10-7%. The upper and lower crustal estimates of extension are in good agreement confirming a relatively shallow brittle-ductile transition. This is consistent with concomitant igneous activity and an enhanced geothermal gradient.

  1. Origin of Middle Cambrian and Late Silurian potassic granitoids from the western Kunlun orogen, northwest China: a magmatic response to the Proto-Tethys evolution

    Science.gov (United States)

    Liu, Zheng; Jiang, Yao-Hui; Jia, Ru-Ya; Zhao, Peng; Zhou, Qing; Wang, Guo-Chang; Ni, Chun-Yu

    2014-02-01

    This paper presents new SHRIMP zircon U-Pb chronology, major and trace element, and Sr-Nd-Hf isotopic data of two Early Paleozoic granitic plutons (Yierba and North Kudi) from the western Kunlun orogen, in attempt to further constrain the Proto-Tethys evolution. SHRIMP zircon U-Pb dating shows that the Yierba pluton was emplaced in the Middle Cambrian (513 ± 7 Ma) and the North Kudi pluton was emplaced in the Late Silurian (420.6 ± 6.3 Ma). The Yierba pluton consists of quartz monzodiorite, quartz monzonite and granodiorite. These granitoids are metaluminous and potassic, with initial 87Sr/86Sr ratios of 0.7072-0.7096, ɛNd (T) of -0.2 to -1.6 and ɛHf (T) (in-situ zircon) of -1.2. Elemental and isotopic data suggest that they were formed by partial melting of subducted sediments, with subsequent melts interacting with the overlying mantle wedge in an oceanic island arc setting in response to the intra-oceanic subduction of Proto-Tethys. The North Kudi pluton consists of syenogranite and alkali-feldspar granite. These granites are metaluminous to weakly peraluminous and potassic. They show an affinity of A1 subtype granite, with initial 87Sr/86Sr ratios of 0.7077-0.7101, ɛNd (T) of -3.5 to -4.0 and ɛHf (T) (in-situ zircon) of -3.9. Elemental and isotopic data suggest that they were formed by partial melting of the Precambrian metamorphic basement at a shallow depth (<30 km) during the post-orogenic regime caused by Proto-Tethyan oceanic slab break-off. Our new data suggest that the subduction of the Proto-Tethyan oceanic crust was as early as Middle Cambrian (˜513 Ma) and the final closure of Proto-Tethys was not later than Late Silurian (˜421 Ma), most probably in Middle Silurian.

  2. The paleomagnetism of the salt pseudomorph beds of middle cambrian age from the salt range, West Pakistan

    NARCIS (Netherlands)

    Wensink, H.

    1972-01-01

    Oriented cores for a paleomagnetic investigation were collected from ten sites in the sedimentary redbeds of the Salt Pseudomorph Beds of Middle Cambrian age m the Salt Range near Khcwra. All samples were subjected to progressive, thermal demagnetization procedures which revealed the characteristic

  3. The paleomagnetism of the Salt Pseudomorph Beds of Middle Cambrian age from the Salt Range, West Pakistan

    NARCIS (Netherlands)

    Wensink, H.

    1972-01-01

    Oriented cores for a paleomagnetic investigation were collected from ten sites in the sedimentary redbeds of the Salt Pseudomorph Beds of Middle Cambrian age in the Salt Range near Khewra. All samples were subjected to progressive, thermal demagnetization procedures which revealed the characteristic

  4. Diversification of skeletal microstructures of organisms through the interval from the latest Precambrian to the Early Cambrian

    Institute of Scientific and Technical Information of China (English)

    FENG; Weimin(冯伟民); CHEN; Zhe(陈哲); SUN; Weiguo(孙卫国)

    2003-01-01

    Research on early skeletal fossils of southern Shaanxi Province and eastern Yunnan Province shows that the interval from the latest Precambrian to the Early Cambrian was an important period of significant changes in biomineralization of various organisms. The latest Precambrian skeletal fossils, represented by Cloudina, are characterized by cone-in-cone structures, relatively high content of organic matter, and various shell shapes with obvious plastic deformation. In the Early Cambrian the skeletal organisms, consisting of phosphatic, carbonate and siliceous minerals, began to appear in great abundance and to distribute widely. Moreover, microstructure of these skeletal organisms appeared to have been diversified, for example, main types of recent molluscan microstructures, such as prismatic, lamello-fibrillar and regular foliated structures, were already developed at that time; fibrous structures further diversified, such as lamello-fibrillas indicative of mollusks and fibre bundles of hyoliths; there were at least two layers in a shell. This shows that biologically controlled biomineralization had played the main role in the Early Cambrian and it laid a key foundation for formation of the true shell of diverse invertebrates, giving rise to the "Cambrian explosion".

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

    International Nuclear Information System (INIS)

    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)

  6. The structure and sedimentary sequence of intracratonic rift from Late Sinian to Early Cambrian in the Sichuan Basin, South China

    Science.gov (United States)

    Gu, Zhidong; Zhang, Baomin; Lu, Weihu; Zhai, Xiufen; Jiang, Hua

    2016-04-01

    Sichuan Basin is located in the northwest of Upper Yangtze craton of South China, and there is developed an intracratonic rift from Late Sinian to Early Cambrian in the middle of Sichuan Basin, and the paper systematically discusses the structure and sedimentary sequence of the intracratonic rift based on the fields, drilling and seismic data, and so on. Detailed structural interpretation of 2D and 3D seismic profiles displays the development of two stages of intracratonic rift due to regional extension with the depth of 2000m, and plane distribution of intracratonic rift presents the V-pattern from the northwest to the southeast in the middle of Sichuan Basin with the width from 100km to 20km. The drilling data from the intracratonic rift shows the obvious thinning of Upper Sinian and thickening of Lower Cambrian. And field outcrops situated in the intracratonic rift reveal that the Upper Sinian is mainly composed of siliceous rock, shale and carbonate, with the thickness of less than 100m, but the thickness of Upper Sinian on the platform reaches 1000m by contrast; They also reveals that Lower Cambrian is mainly composed of shale, mudstone, and siltstone with the development of gravity current, and the thickness of Lower Cambrian reaches 2000m. The formation of intracratonic rift may be initiated by pre-existing basement weakness zone and deep mantle dynamics.

  7. 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

    the deposits belong to the Lower Cambrian Norretorp Member of the Læså Formation. The shallow marine deposits are strongly bioturbated, but only a single ichnoassociation is represented. The ichnogenus is referable to either Trichophycus Miller and Dyer, 1878 or Teichichnus Seilacher, 1955. Rare...

  8. 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

  9. 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

    2014-04-01

    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. PMID:24523279

  10. Lower Cambrian Black Rock Series and Associated Stratiform Deposits in Southern China

    Institute of Scientific and Technical Information of China (English)

    陈南生; 范德廉; 等

    1990-01-01

    Widespread in more than ten provinces of southern China are the Lower Cambrian black argillaceous-arenaceous rock series consisting of black carbonaceous shales,black carbonaceousargillo-siliceous rocks,black carbonaceous silicolite and black silicolite and black carbonaceous argillaceous siltstone.The Ni,Mo,V,Cu,U,Ba,Ag,P contents of these series are usually several to tens of times higher than their average values in shales.As viewed from lithological sequence,element association and evolution,these black series can be diveided into two types.There occur a variety of deposits in the black rock series,such as phosphorite deposits,Ni-Mo-V polymetal deposits and "Stone coal" seams.According to ore composition,texture and structure,the phosphorite deposits fall into three types,i.e.,thick-bedded,lenticular and nodular,The Ni-Mo-V polymetal deposits,V deposits and reworked sedimentary CU-U-Cd polymetal deposits in terms of their element assiciation and ore genesis.As for the stratiform deposits in the black rock series,three mineralization stages have been recognized,i.e.,the formation of phosphorite deposits,of Ni-Mo polymetal deposits and of V-Cu-U-Cd polymetal deposits as well as of ":stone coal" seams.Evidence strongly suggests that lower organisms have played an important role in mineralization. Our studies indicate that the Lower Cambrian black argillaceous-arenaceous rock series in southern China and their associated stratiform deposits occur generally in the basal parts of a big sedimentary cycle,i.e.,the initial period of a transgression,or in the fine detrital-siliceous formation between two carbonate formatons,formed in a humid climatic zone between two arid ones.As for the environment of deposition,it is suggested that the Lower Cambrian black argillaceous-arenaceous rock series and associated stratiform deposits(excluding thick-bedded phosphorite deposits)were formed mainly in a restricted and poorly-fed sea basin of stagnant shallow water containing

  11. A highly redox-heterogeneous ocean in South China during the early Cambrian (˜529-514 Ma): Implications for biota-environment co-evolution

    Science.gov (United States)

    Jin, Chengsheng; Li, Chao; Algeo, Thomas J.; Planavsky, Noah J.; Cui, Hao; Yang, Xinglian; Zhao, Yuanlong; Zhang, Xingliang; Xie, Shucheng

    2016-05-01

    The "Cambrian Explosion" is known for rapid increases in the morphological disparity and taxonomic diversity of metazoans. It has been widely proposed that this biological event was a consequence of oxygenation of the global ocean, but this hypothesis is still under debate. Here, we present high-resolution Fe-S-C-Al-trace element geochemical records from the Jinsha (outer shelf) and Weng'an (outer shelf) sections of the early Cambrian Yangtze Platform, integrating these results with previously published data from six correlative sections representing a range of water depths (Xiaotan, Shatan, Dingtai, Yangjiaping, Songtao, and Longbizui). The integrated iron chemistry and redox-sensitive trace element data suggest that euxinic mid-depth waters dynamically coexisted with oxic surface waters and ferruginous deep waters during the earliest Cambrian, but that stepwise expansion of oxic waters commenced during Cambrian Stage 3 (∼ 521- 514 Ma). Combined with data from lower Cambrian sections elsewhere, including Oman, Iran and Canada, we infer that the global ocean exhibited a high degree of redox heterogeneity during the early Cambrian, consistent with low atmospheric oxygen levels (∼ 10- 40% of present atmospheric level, or PAL). A large spatial gradient in pyrite sulfur isotopic compositions (δ34Spy), which vary from a mean of - 12.0 ‰ in nearshore areas to + 22.5 ‰ in distal deepwater sections in lower Cambrian marine units of South China imply low concentrations and spatial heterogeneity of seawater sulfate, which is consistent with a limited oceanic sulfate reservoir globally. By comparing our reconstructed redox chemistry with fossil records from the lower Cambrian of South China, we infer that a stepwise oxygenation of shelf and slope environments occurred concurrently with a gradual increase in ecosystem complexity. However, deep waters remained anoxic and ferruginous even as macrozooplankton and suspension-feeding mesozooplankton appeared during

  12. 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.

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

    DEFF Research Database (Denmark)

    Stein, Martin

    2013-01-01

    evidence for variability of head segment counts in Cambrian arthropods, and to falsify the hypothesis of a head with three postantennular segments in the euarthropod ground pattern. Restudy of a substantial amount of material of S. inexpectans shows that previous interpretations of a short head were based...... understood, but the exopod seemed to differ from that of other artiopodans, except for the shared presence of lamellae. The head was considered to comprise only the ocular and antennular segments, these being covered entirely on the ventral side by a large doublure. This short head was often taken as an...... 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...

  14. Preliminary notes on soft-bodied fossil concentrations from the Early Cambrian Chengjiang deposits

    Institute of Scientific and Technical Information of China (English)

    HAN Jian; SHU Degan; ZHANG Zhifei; LIU Jianni; ZHANG Xingliang; YAO Yang

    2006-01-01

    The efforts of labor-intensive collecting in the Early Cambrian Chengjiang deposits in eastern Yunnan Province, China led to the discovery of many horizons containing exceptionally well preserved soft-bodied fossil concentrations, many of which can be assigned to either monospecific concentrations or paucispecific concentrations. The features of these fossil concentrations support the hypothesis that frequent storm events producing tempestites mainly contributed to the preservation of abundant softbodied fossils in the Chengjiang deposits, and indicate that the balance of the ecological web in this region was probably frequently destroyed or upset by such storm events during that geological time. Animals in a fossil assemblage in such fossil concentrations probably occupied similar ecological biotopes.

  15. 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.; Jiang, C.; Goodsite, M. E.

    2014-01-01

    degradation of labile kerogen by radiation from uranium-rich minerals. The higher degree of aromaticity in Alum shale suggests lower than expected oil-proneness. The results of this study suggest that the Alum Shale is a gas-prone source producing aromatic hydrocarbon mixtures with an unexpectedly low......This paper presents an integrated geochemical and petrological study of the Hällekis-1 core from the Furongian (upper Cambrian) Alum shales in central Sweden to characterise organic matter composition, depositional environment, and potential hydrocarbon generation capability. The results show 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...

  16. 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....... The burial history modelling points to development of most of the dolomite cement during rapid Silurian-Devonian subsidence and Carboniferous-early Permian uplift. A wide range of precipitation temperatures indicate that temperature was not a major factor in triggering the carbonate cementation. Dolomite...

  17. Origin of northern Gondwana Cambrian sandstone revealed by detrital zircon SHRIMP dating

    Science.gov (United States)

    Avigad, D.; Kolodner, K.; McWilliams, M.; Persing, H.; Weissbrod, T.

    2003-01-01

    Voluminous Paleozoic sandstone sequences were deposited in northern Africa and Arabia following an extended Neoproterozoic orogenic cycle that culminated in the assembly of Gondwana. We measured sensitive high-resolution ion microprobe (SHRIMP) U-Pb ages of detrital zircons separated from several Cambrian units in the Elat area of southern Israel in order to unravel their provenance. This sandstone forms the base of the widespread siliciclastic section now exposed on the periphery of the Arabian-Nubian shield in northeastern Africa and Arabia. Most of the detrital zircons we analyzed yielded Neoproterozoic concordant ages with a marked concentration at 0.55–0.65 Ga. The most likely provenance of the Neoproterozoic detritus is the Arabian-Nubian shield; 0.55–0.65 Ga was a time of posttectonic igneous activity, rift-related volcanism, and strike-slip faulting there. Of the zircons, 30% yielded pre-Neoproterozoic ages grouped at 0.9–1.1 Ga (Kibaran), 1.65–1.85 Ga, and 2.45–2.7 Ga. The majority of the pre-Neoproterozoic zircons underwent Pb loss, possibly as a consequence of the Pan-African orogeny resetting their provenance. Rocks of the Saharan metacraton and the southern Afif terrane in Saudi Arabia (∼1000 km south of Elat) are plausible sources of these zircons. Kibaran basement rocks are currently exposed more than 3000 km south of Elat (flanking the Mozambique belt), but the shape of the detrital zircons of that age and the presence of feldspar in the host sandstone are not fully consistent with such a long-distance transport. Reworking of Neoproteorozoic glacial detritus may explain the presence of Kibaran detrital zircons in the Cambrian of Elat, but the possibility that the Arabian-Nubian shield contains Kibaran rocks (hitherto not recognized) should also be explored.

  18. The Meers Fault in Southern Oklahoma: Holocene Movements on a Fault with Pennsylvanian and Cambrian Linages

    Science.gov (United States)

    Keller, G. R.; Holland, A. A.; Luza, K.; Oldow, J. S.; Crain, K.

    2011-12-01

    The Meers fault and subparallel fault strands in southern Oklahoma is the southernmost element of the complex and massive (>10 km of throw) frontal fault zone that forms the boundary between the Anadarko basin, which is the deepest intra-continental basin in the United States, and the uplifted Cambrian igneous rocks of the Wichita Mountains. The Wichita uplift is evidence of extraordinary Pennsylvanian intra-plate deformation along the trend of the Southern Oklahoma aulacogen, which is a classic example of a failed and massively inverted rift. The Meers Fault is the best-documented Holocene fault scarp east of Colorado and probably represents reactivation of a Pennsylvanian oblique thrust that in turn is likely to be an inverted Cambrian normal fault. The magnitude of these structures is shown on images from 3-D industry seismic reflection data ~25 km northwest of the northwestern mapped extent of the Meers fault that indicate the Pennsylvanian structure, or a northern strand of it, has a reverse throw of ~6km at depth. The fault displays a conspicuous and continuous scarp that is at least 25 km long and is evident in air photos and 1:100,000 scale geologic mapping, but this feature is not well mapped in detail beyond the area of trenching studies conducted in the 1980's. In the Holocene, 3-5 m of vertical surface displacement has been documented and left-lateral strike slip displacement on the fault is 2-3 times greater than the vertical displacement. During this movement, Quaternary soils along the fault were folded and ruptured, and the scarp has dammed small gullies where fine-grained alluvium has collected and has been used in the dating efforts. The most recent movement occurred (1100-1300 y ago) with a variety of earlier events having been proposed. As such, this fault represents one of the highest potential seismic hazards in the central/eastern United States.

  19. Geodatabase of the datasets used to represent the four aquifer subunits of the Cambrian-Ordovician aquifer system, Illinois, Iowa, Michigan, Minnesota, and Wisconsin

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — This geodatabase includes spatial datasets that represent the Cambrian-Ordovician aquifer system in the States of Wisconsin, Michigan, Minnesota, Iowa, and...

  20. "The Chengjiang Fauna and the Cambrian Explosion" Sponsord by NSFC won the first-class award of National Natural Sciences Award

    Institute of Scientific and Technical Information of China (English)

    Liu Y.; Yao Y.P.

    2004-01-01

    @@ "The Chengjiang Fauna and the Cambrian explosion'' sponsord by NSFC won the first-class award of National Natural Sciences Award. The Awarding ceremony was held in the Great Hall of the People in Beijing on February 20, 2004. "The Chengjiang Fauna and the Cambrian explosion" was sponsord by NSFC and carried out by several groups led by Prof. Chen Junyuan of the Nanjing Institute of Geology and Palaeontology,CAGS, Prof. Hou Xianguang of Yunnan University and Prof.

  1. Microthermometric measurement of fluid inclusions and its constraints on genesis of PGE-polymetallic deposits in Lower Cambrian black rock series, southern China

    Institute of Scientific and Technical Information of China (English)

    WANG Min; SUN Xiaoming; MA Mingyang

    2005-01-01

    Systematic microthermometric measurements of fluid inclusions in the PGE-polymetallic deposits hosted in the Lower Cambrian black rock series in southern China were performed, and the results suggest: (1) there exist two types of fluid inclusions. TypeⅠis of NaCl-H2O system with low-medium salinity, and its homogenization temperatures (Th) and salinities are 106.9- 286.4℃ and ( 0.8- 21.8) wt%NaCl eq. respectively; TypeⅡ is of CaCl2-NaCl-H2O system with medium-high salinities, and its homogenization temperatures and salinities range from 120.1℃ to 269.6℃ and ( 11.4- 31.4) wt%NaCl eq., respectively. The typeⅡ fluid inclusions have been discovered for the first time in this kind of deposits; (2) two generations of ore-forming fluids were recognized. Characteristics of fluid inclusions in the PGE-polymetallic ores and carbonate-quartz stockworks in the underlying phosphorites are almost of no difference, they may represent ore-forming fluids at the main metallogenic stage. The peak value of homogenization temperature of those fluid inclusions is about 170℃, while their salinities possess a remarkable bimodal distribution pattern with two peak values of (27-31) wt%NaCl eq. and (4-6) wt%NaCl eq. On the contrary, fluid inclusions in the carbonate-quartz veins in the hanging wall may represent ore-forming fluids at the post-metallogenetic stage. The homogenization temperatures and the peak values of salinities are mostly 130-170℃ and (12-14) wt%NaCl eq., respectively; (3) nobel gas isotopic composition analyses in combination with the microthermometric measurements of fluid inclusions suggest that the ore-forming fluids at the main metallogenetic stage were probably derived from mixing of basinal hot brines with the CaCl2-NaCl-H2O system and seawater with the NaCl-H2O system; (4) in the Early Cambrian, the basinal hot brines were trapped in the Caledonian basins, which were distributed along the southern margin of the Yangtze Craton, and where giant thick

  2. 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).

  3. A New Arthropod, Guangweicaris Luo, Fu et Hu gen. nov.from the Early Cambrian Guanshan Fauna, Kunming, China

    Institute of Scientific and Technical Information of China (English)

    LUO Huilin; FU Xiaoping; HU Shixue; LI Yong; HOU Shuguang; YOU Ting; PANG Jiyuan; LIU Qi

    2007-01-01

    The Guanshan Fauna is a soft-bodied fauna dominated by arthropods (including trilobites,trilobitoides, Tuzoia, Isoxys, and bradorids) in association with priapulids, brachiopods,anomalocaridids, vetulicoliids, sponges, chancellorids, and echinoderms. This paper reports and describes a new arthropod from the yellowish green mudstone at the lower part of the Wulongqing Formation, Canglangpuan Stage, Lower Cambrian in Kunming, Yunnan, China. The stratigraphic and geographic distribution, classification, fossil preservation, life style of this new arthropod and comparisons with other fossil arthropods are also discussed in details. The discovery and research of the non-mineralized arthropod, Guangweicaris Luo, Fu et Hu gen. nov. from the Guanshan Fauna adds new members to the taxonomic list and provides new information to the evolution of early arthropods.Furthermore, this study would shed new light into the "Cambrian Explosion" and the evolution of early life.

  4. The demosponge Leptomitus cf. L. lineatus, first occurence from the Middle Cambrian of Spain (Murero Formation, Western Iberian Chain)

    OpenAIRE

    García-Bellido, Diego

    2003-01-01

    The Middle Cambrian Murero Formation in the Iberian Chain (NE Spain) has yielded a small collection of softbodied fossils (palaeoscolecid worms, onychophorans, algae), a host of fossils from organisms with mineralized skeletons such as trilobites and brachiopods, and some trace fossils. This paper deals with the description of the only specimen of the demosponge Leptomitus known so far from Spain and its association with the brachiopod Micromitra, showing a probable case of commensalism by th...

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

    OpenAIRE

    Mángano, M. Gabriela; Luis A. Buatois

    2014-01-01

    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 behav...

  6. On gamma-ray bursts and their biological effects :a case for an extrinsic trigger of the Cambrian explosion ?

    CERN Document Server

    Horváth, J E

    2003-01-01

    We discuss some the effects of local gamma-ray bursts on the earth's atmosphere. A rough calculation of the fraction of ozone destruction by catalytic $NO_{x}$ cycles is given, which in turn serves to argue how the large flux of gammas from these events would have indirectly provoked major extinction of living organisms. We give specific examples of these features, and tentatively identify the Cambrian explosion seen in the actual fossil record as an event caused by a GRB.

  7. A new vetulicolian from Australia and its bearing on the chordate affinities of an enigmatic Cambrian group

    OpenAIRE

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

    2014-01-01

    Background Vetulicolians are one of the most problematic and controversial Cambrian fossil groups, having been considered as arthropods, chordates, kinorhynchs, or their own phylum. Mounting evidence suggests that vetulicolians are deuterostomes, but affinities to crown-group phyla are unresolved. Results A new vetulicolian from the Emu Bay Shale Konservat-Lagerstätte, South Australia, Nesonektris aldridgei gen. et sp. nov., preserves an axial, rod-like structure in the posterior body region ...

  8. The Sirius Passet Lagerstatte : silica death masking opens the window on the earliest matground community of the Cambrian explosion.

    OpenAIRE

    Strang, K.M.; Armstrong, H.A.; Harper, D.A.T.; Trabucho-Alexandre, João P.

    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 preserved as complete, three-dimensional, concave hyporelief external moulds and convex epirelief casts. External moulds are shown to consist of a thin veneer of authigenic silica. The casts are for...

  9. From snowball earth to the cambrian explosion: the interpretative potential of the isotope record

    Science.gov (United States)

    Shields, G.

    2003-04-01

    The interval in Earth history between 750 Ma and 530 Ma represents the erratic transition between the distinctly different "Earth systems" of the Proterozoic and the Phanerozoic. Geologists have developed several indirect methods to study this key interval but perhaps none with as much wanton enthusiasm as isotope geochemistry. Here I attempt a review of the isotope record across this key transition period, with special emphasis on the interpretative role that isotopes can play in understanding events such as the "Snowball Earth" glaciations and the "Cambrian Explosion". The marine isotope record reveals the Proterozoic-Phanerozoic transition to have been a unique period in Earth history with first-order features in all three of the major isotope proxies: 87Sr/86Sr, 34S/32S and 13C/12C ratios. Seawater 87Sr/86Sr, increased sharply between about 900 Ma and 500 Ma from 0.704 to 0.709, the largest rise ever. Although attributed to increasing rates of continental erosion, this remains only the most plausible explanation because few aspects of the rise have been satisfactorily linked to particular tectonic events. Much of the uncertainty surrounding the Proterozoic 87Sr/86Sr record is due to poor age dating and discrepancies in stratigraphic correlation schemes, which together with diagenetic alteration have led to the current inability to realise the potential of the 87Sr/86Sr record for global stratigraphic correlation. Carbon isotopes have played a key role in recent palaeoenvironmental interpretations of the Proterozoic-Phanerozoic transition, most of which have already been discarded or merely forgotten. Nevertheless, it is clear that the extraordinary δ13C values of the later Neoproterozoic (and the earliest Cambrian) demand extraordinary explanations, for which there is still much scope for future invention. Carbon isotopes may also play an important supporting role in correlation, however, the role that δ13C may play in global stratigraphic correlation has

  10. Molecular fossils and sources of Cambrian heavy oil of Well Tadong-2 in theTarim Basin, Xinjiang, China

    Institute of Scientific and Technical Information of China (English)

    TANG Youjun; ZAN Ling

    2009-01-01

    Research on the molecular fossil characteristics of heavy oil from Well Tadong-2 is of great importance to constrain the source of marine crude oils in the Tarim Basin, Xinjiang, China. The authors synthetically applied the isotope mass spectrograph, chromatography and chromatography-mass spectrography to the studies of molecular fossil characteristics of heavy oil from Well Tadong-2 in the Tarim Basin, and the results obtained revealed that heavy oil from Well Tadong-2 is characterized by high gammacerane, high C28 sterane, low rearranged sterane and high C27-triaromatic steroid, these characteristics are similar to those of Cambrian-Lower Ordovician source rocks, demonstrating that Cambrian crude oils came from Cambrian-Lower Ordovician source rocks; condensed compounds (fluoranthene, pyrene, benzo[a]anthracene, bow, benzo fluoranthene, benzopyrene) of high abundance were detected in heavy oil from Well Tadong-2, and the carbon isotopic values of whole oil are evidently heavy, all the above characteristics revealed that hydrocarbons in the crude oils became densified in response to thermal alteration.

  11. Ichnofossils and their significance in the Cambrian successions of the Parahio Valley in the Spiti Basin, Tethys Himalaya, India

    Science.gov (United States)

    Parcha, S. K.; Pandey, Shivani

    2011-11-01

    The Spiti Basin exposes well preserved Cambrian successions in the Tethys Himalaya. The present ichnofossil assemblage is reported from the Debsakhad Member of the Kunzum La Formation. The ichnofossils includes the ichnogenera Bergaueria, Chondrites, Cruziana, Didymaulichnus, Dimorphichnus, Diplichnites, Helminthorhaphe, Merostomichnites, ?Monocraterion, Monomorphichnus, Nereites, Palaeopascichnus, Palaeophycus, Phycodes, Planolites, Rusophycus, Skolithos, Scolicia, Treptichnus, etc. along with annelid worm, burrow and scratch marks. These ichnogenera can be assigned to cubichnial, repichnial, pascichnial to fodinichnial behaviors. The ichnofossils reported from this section provide evidence regarding the developmental patterns during the early phase of life. In absence of trilobites, the present assemblage of ichnofossils is very significant in assigning the age of the Debsakhad Member. The abundance of ichnofossils in sandstone, siltstone and in shale beds indicate that the ichnocenosis is dominated by a high behavioral diversity ranging from the suspension to deposit feeders. Three lithofacies were observed in this section, they show a vertical disposition, which further reflects general upward coarsening trend. Ichnofossils are mostly produced by arthropods along with crustacean, polychaetes and polyphyletic vermiforms. Due to the paucity of body fossil, as well as microbiota in the lowermost beds of the Debsakhad Member, the Precambrian-Cambrian boundary could not be demarcated. However, the presence of Treptichnus and Phycodes can be considered as a horizon marker for the beginning of Lower Cambrian in this section.

  12. Quartz cementation mechanisms between adjacent sandstone and shale in Middle Cambrian, West Lithuania

    Science.gov (United States)

    Zhou, Lingli; Friis, Henrik

    2013-04-01

    Quartz is an important cementing material in siliciclastic sandstones that can reduce porosity and permeability severely. For efficiently predicting and extrapolating petrophysical properties such as porosity and permeability, the controls on the occurrence and the degree of quartz cementation need to be better understood. Because it is generally difficult to identify specific sources for quartz cement, many models attempting to explain quartz cementation conclude that external sources of silica are needed to explain the observed quantity of quartz cement, such as the mass transfer between sandstone and shale. Cambrian sandstones in Lithuania have abundant quartz cement which has significant effect on reservoir properties. The detrital quartz grains have been dissolved extensively along the shale-quartz contacts zones, making it a natural laboratory to study the influence of mass transfer between sandstone and shale to quartz cementation on petrophysical properties and reservoir quality. Our Cambrian shale samples in west Lithuania are mainly silty shale or siltstone (sample locations vary from 330 to 2090 m of burial depth). They are composed of quartz, clay and traces of feldspars, sericite, calcite, and pyrite. The clay minerals are mainly illite, with variable content of kaolinite and traces of chlorite. In the sandstone lamina, authigenic illite occurs as pore-filling cement which was composed of fibrous illite; pore-filling kaolinite is generally well crystallized and occurs as hexagonal plates arranged in booklets; quartz overgrowth are obvious in these sandstone laminas, especially in the contact zones between sandstone and shale. Dolomite and pyrite cementation are also present in some sandstone laminas but with few quartz overgrowth. Depositional facies and architecture played an important role in the precipitation of silica. Three different possible sources are distinguished for the quartz overgrowths in the intercalated sandstones: 1) Pressure

  13. Radiometric dating of sediments using fission tracks in conodonts

    Science.gov (United States)

    Sachs, H.M.; Denkinger, M.; Bennett, C.L.; Harris, A.G.

    1980-01-01

    Conodonts are microfossils which are commonly found in marine rocks of Cambrian to Triassic age. Although their biological affinities are difficult to assess, conodonts are valuable stratigraphical indices for much of their geological range1. Recent work has also established that conodont colour alteration indices (CAI) are useful guides to diagenetic temperatures and hence burial depth2. Fission tracks3 in conodonts allow measurement of uranium concentrations and estimates of 'age' to be made using isotopic methods4. We report here that fission tracks counted in irradiated, thermally unaltered (as indicated by CAI) middle Palaeozoic conodonts indicate typical uranium concentrations of ???1 part in 10 9, with some samples higher. A single specimen of Siphonodella from the Lower Mississippian yielded an age estimate of 380??140 Myr consistent with conventional interpolations. This method may also allow the unroofing of deeply buried sediments to be dated. ?? 1980 Nature Publishing Group.

  14. 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

  15. Early Cambrian eodiscoid trilobites of the Yangtze Platform and their stratigraphic implications

    Institute of Scientific and Technical Information of China (English)

    YANG Aihua; ZHU Maoyan; ZHANG Junming; LI Guoxiang

    2003-01-01

    Analysis of the taxonomy and stratigraphic distribution of the Early Cambrian eodiscoid trilobites of the Yangtze Platform indicates that species of Tsunyidiscus and Hupeidiscus can be used for biostratigraphic correlation. T. aclis occurs only in the lower Qiongzhusian, T. armatus occurs in the lower and middle Qiongzhusian, while T. niutitangensis and T. tingi occur mainly in the middle and upper Qiongzhusian, with only T. tingi extending upward into the lower Canglangpuian. H. orientalis first appears in the upper Qiongzhusian, reaching peak abundance in the lower Canglangpuian and becoming extinct above the Drepanuroides Zone. Biostratigraphic and lithostratigraphic correlations indicate that the limestone in the lower part of the Mingxinsi Formation, the Upper Member of Jiumenchong Formation, and the upper part of the Middle Member of the Huangbailing Formation, can be correlated with each other as Hupediscus, an index fossil of the lower Canglangpuian, is abundant in all these units. The lower part of the Niutitang and Jiumenchong formations in eastern Guizhou, which mainly represent Qiongzhusian strata, can be correlated with the Lower Member of the Huangbailing Formation. The basal part of the Niutitang Formation, which may be equivalent to the Upper Meishucunian Shiyantou Formation in eastern Yunnan, is very condensed. Well-preserved sponge faunas and non-mineralized fossils in the lower part of the Niutitang and Hetang formations are not older than Qiongzhusian in age.

  16. 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.

  17. The newly-developed Cambrian biostratigraphic succession and chronostratigraphic scheme for South China

    Institute of Scientific and Technical Information of China (English)

    PENG ShanChi

    2009-01-01

    Biostratigraphy and chronostratigraphy are common means of subdividing rock strata.The biostratigraphic succession and chronostratigraphic scheme are regarded as the basis for the subdivision and correlation of regional and global stratigraphic units.This paper reviews research on the biostratigraphy and chronostratigraphy carried out in the Jiangnan Slope Belt,South China since 1978,and,in particular,the biostratigraphic succession and chronostratigraphic scheme developed in the last decade.The updated biostratigraphic succession of South China includes 36 biozones,the base of each of which is defined by the first appearance of a single taxon (index fossil),and a poorly fossiliferous interzone.The updated chronostratigraphic scheme of South China comprises 4 series and 10 stages,embracing 3 global chronostratigraphic units,the Guzhangian Stage,Furongian Series,and Paibian Stage,and 2 GSSPa,all of which are erected in northwestern Hunan and 2 International Tie Points recognized in sections also in northwestern Hunan and each was accepted by the International Subcommission on Cambrian Stratigraphy for defining the base of the global stage.The biostratigraphic and chronostratigraphic systems are recognized as Chinese standards both domestically and worldwide.Future research is suggested for improving the two sets of stratigraphic standards.

  18. Body Size Evolution in Conodonts from the Cambrian through the Triassic

    Science.gov (United States)

    Schaal, E. K.; Morgan, D. J.; Payne, J.

    2013-12-01

    The size of an organism exercises tremendous control over its physiology, life history, and ecology, yet the factors that influence body size evolution remain poorly understood. One major limitation is the lack of appropriate datasets spanning long intervals of evolutionary time. Here, we document size trends in conodonts (tooth-like microfossils from marine chordates) because they evolved rapidly and are known to change size during intervals of environmental change. By measuring photographs from the Catalogue of Conodonts (Ziegler 1982), we compiled a database of conodont P1 element measurements for 575 species and subspecies from the Cambrian through Triassic periods. Because tooth size correlates with body size in conodont animals and their extant relatives, conodont element length can serve as a proxy for the size of the conodont animal. We find that mean and maximum size across species increased during the early Paleozoic, peaked during the Devonian-Mississippian, and then generally decreased until conodonts went extinct at the end of the Triassic. We used regression analyses to compare conodont mean size trends to potential environmental predictors, such as changing atmospheric pO2, atmospheric pCO2, and sea level. Conodont size exhibited poor correlation with these environmental factors, suggesting that conodont evolution may have been more strongly influenced by other environmental covariates or ecological variables such as predation and competition.

  19. Phylogeny and evolutionary significance of vermiform animals from the Early Cambrian Chengjiang Lagersttte

    Institute of Scientific and Technical Information of China (English)

    David; BAINES

    2010-01-01

    The Early Cambrian Chengjiang Biota of China has preserved many species of vermiform animals in exquisite detail,which provide a unique window into the origin and early evolution of different vermiform phyla.This article reviews and discusses the forty-five Chengjiang vermiform animals discovered so far,and specifically comments on the phylogeny,modes of life,evolutionary significance as well as existing debates concerning the Chengjiang priapulid and lobopodian phyla.This article analyzes existing problems with Chengjiang vermiform morphological research and highlights various factors that affect the final preserved fossil morphology,including taphonomy and shape change caused by vermiform movement,as well as proposing that Anningvermis multispinosa and Corynetis brevis are synonymous.Chengjiang vermiform animals displayed a great diversity of morphologies and ecological roles,which is significant for understanding the origin and evolution of early metazoans;the potential for future research is enormous but needs to be broadened by interdisciplinary work involving taphonomy,geochemistry,cladistics,and genetics.

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

    Science.gov (United States)

    Sansom, Robert S

    2016-01-01

    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. PMID:27595908

  1. Geochemical investigations on some of the Infra Cambrian Acid intrusive and volcanic rocks in Iran

    International Nuclear Information System (INIS)

    Geochemical investigations on some of the acid intrusive and volcanic rocks of Iran, which are attributed to the Infra cambrian, have been carried out to reveal their possible genetic relationships. These igneous rocks include: Do ran, Shah-Bolaghi, Sarve-Jahan, NE Ardakan - Yazd (Darbastegoon), south Mahabad, Bornavard (Tak nar), Zarigan, Narigan, Chardormaloo granites, Rizo and De zoo micro granites and volcanic rocks, Ga chin rhyolites (Bandar-Abass), and Ghareh-Dash (east of Sae en-De j). These intrusive s, except south Mahabad granodiorite, belong to the class of the alkali feldspathic granite to granitic rocks. Most of these rocks are hololeucocratic and devoid of ferro magnesian minerals. The volcanic rocks are mainly felsic (Rhyolite and Quartz porphyra) associated with vacillation's rocks. These suites of rocks plot on the chemical diagrams in sub alkaline field. Regarding to variations of Na2O, K2O and Ca O contents, they can further be subdivided into sodi c, potas sic, sodi-potas sic and sodi-calci c subgroups. The normalized values (MORB and chondritic) of their trace elements on the spider diagrams overlap each other indicates that some genetic relations ships exist among samples of white Doran Granite, Shahbolaghi, Sarve-Jahan and some Darbastegoon, in one hand, and Taknar, Narigan Granites, Gachin, Rizoo and Dezoo Rhyolites, on the other hand. The overlap also shows that the mentioned igneous bodies have been originated from continental crust and the samples of each groups, at least belong to a distinct tectonic al regime

  2. Original molluscan radula: comparisons among Aplacophora, Polyplacophora, Gastropoda, and the Cambrian fossil Wiwaxia corrugata.

    Science.gov (United States)

    Scheltema, Amélie H; Kerth, Klaus; Kuzirian, Alan M

    2003-08-01

    As the original molluscan radula is not known from direct observation, we consider what the form of the original radula may have been from evidence provided by neomenioid Aplacophora (Solenogastres), Gastropoda, Polyplacophora, and the Cambrian fossil Wiwaxia corrugata (Matthews). Conclusions are based on direct observation of radula morphology and its accessory structures (salivary gland ducts, radular sac, anteroventral radular pocket) in 25 species and 16 genera of Aplacophora; radula morphogenesis in Aplacophora; earliest tooth formation in Gastropoda (14 species among Prosobranchia, Opisthobranchia, and Pulmonata); earliest tooth formation in four species of Polyplacophora; and the morphology of the feeding apparatus in W. corrugata. The existence of a true radula membrane and of membranoblasts and odontoblasts in neomenioids indicates that morphogenesis of the aplacophoran radula is homologous to that in other radulate Mollusca. We conclude from p redness of salivary gland ducts, a divided radular sac, and a pair of anteroventral pockets that the plesiomorphic state in neomenioids is bipartite, formed of denticulate bars that are distichous (two teeth per row) on a partially divided or fused radula membrane with the largest denticles lateral, as occurs in the genus Helicoradomenia. The tooth morphology in Helicoradomenia is similar to the feeding apparatus in W. corrugata. We show that distichy also occurs during early development in several species of gastropods and polyplacophorans. Through the rejection of the null hypothesis that the earliest radula was unipartite and had no radula membrane, we conclude that the original molluscan radula was similar to the radula found in Helicoradomena species. PMID:12833382

  3. The importance of preadapted genomes in the origin of the animal bodyplans and the Cambrian explosion.

    Science.gov (United States)

    Marshall, Charles R; Valentine, James W

    2010-05-01

    The genomes of taxa whose stem lineages branched early in metazoan history, and of allied protistan groups, provide a tantalizing outline of the morphological and genomic changes that accompanied the origin and early diversifications of animals. Genome comparisons show that the early clades increasingly contain genes that mediate development of complex features only seen in later metazoan branches. Peak additions of protein-coding regulatory genes occurred deep in the metazoan tree, evidently within stem groups of metazoans and eumetazoans. However, the bodyplans of these early-branching clades are relatively simple. The existence of major elements of the bilaterian developmental toolkit in these simpler organisms implies that these components evolved for functions other than the production of complex morphology, preadapting the genome for the morphological differentiation that occurred higher in metazoan phylogeny. Stem lineages of the bilaterian phyla apparently required few additional genes beyond their diploblastic ancestors. As disparate bodyplans appeared and diversified during the Cambrian explosion, increasing complexity was accommodated largely through changes in cis-regulatory networks, accompanied by some additional gene novelties. Subsequently, protein-coding genic richness appears to have essentially plateaued. Some genomic evidence suggests that similar stages of genomic evolution may have accompanied the rise of land plants. PMID:19930449

  4. Neoproterozoic Land Colonisation, Rising Oxygen, Global Cooling and the Cambrian Explosion

    Science.gov (United States)

    Lenton, T. M.; Watson, A. J.

    2004-12-01

    The Neoproterozoic (1000-542 Ma BP) was a time of severe glaciations and a major transition from microscopic to macroscopic life forms. We develop the hypothesis that a rise in atmospheric oxygen in the Neoproterozoic was driven by the biological colonization of the land surface. If early forms of photosynthetic land life selectively weathered continental rock in order to extract nutrients, this would have led to an increase in the flux of biologically available phosphorus to the ocean. We show that recent models for coupled biogeochemical cycles, despite differences in the feedback mechanisms represented, predict this would lead to a rise in atmospheric oxygen concentration, consistent with biological and geochemical evidence. Increased weathering of silicate rocks would also have caused a decline in atmospheric carbon dioxide, which could have been a causal factor in the Neoproterozoic glaciations. A rise in oxygen may have provided a necessary condition for the evolution of animals with hard skeletons seen in the Cambrian explosion. Furthermore, an increase in phosphorus supply to the ocean may have driven an increase in the phosphorus content of marine primary producers. This would have represented an increase in food quality for grazing animals, which have a high phosphorus requirement, and may thus have removed a further limitation on their evolutionary radiation.

  5. 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

  6. From Cycles to Sequences: Sequence Stratigraphy and Relative Sea Level Change for the Late Cambrian of the North China Platform

    Institute of Scientific and Technical Information of China (English)

    MEI Mingxiang; MA Yongsheng; DENG Jun; CHEN Huijun

    2005-01-01

    In the Late Cambrian, the North China Platform was a typical carbonate ramp platform. The Upper Cambrian of the northern part of the North China Platform is famous for the development of bioherm limestones and storm calcirudites and can be divided from bottom to top into the Gushan, Changshan and Fengshan formations. In this set of strata, the deep-ramp mudstone and marls and the shallow-ramp packstones and grainstones constitute many carbonate meter-scale cycles of subtidal type. More tidal-flat dolomites are developed in the Upper Cambrian of the southern margin of the North China platform, in which limestone and dolomite beds also constitute many carbonate meter-scale cycles of the peritidal type. These cycles are marked by a variety of litho-facies successions. There are regularly vertical stacking patterns of meter-scale cycles in long-term third-order sequences, which is the key to discerning such sequences. Thirdorder sequence is marked by a particular sedimentary-facies succession that is the result of the environment-changing process of deepening and shoaling, which is genetically related to third-order sea level changes. Furthermore, four thirdorder sequences can be grouped in the Upper Cambrian of the North China Platform. The main features of these four thirdorder sequences in the northern part of the platform can be summarized as follows: firstly, sequence-boundaries are characterized by drowning unconformities; secondly, the sedimentary-facies succession is generally constituted by one from deep-ramp facies to shallow-ramp facies; thirdly, a succession of "CS (?)+HST" (i.e., "condensed section and highstand system") forms these four third-order sequences. The chief features for the third-order sequences in the southern part of the North China Platform comprises: more dolomites are developed in the HSTs of third-order sequences and also developed more carbonate meter-scale cycles of peritidal types; the sedimentary-facies succession of the third

  7. Effects of fracture reactivation and diagenesis on fracture network evolution: Cambrian Eriboll Formation, NW Scotland

    Science.gov (United States)

    Hooker, J. N.; Eichhubl, P.; Xu, G.; Ahn, H.; Fall, A.; Hargrove, P.; Laubach, S.; Ukar, E.

    2011-12-01

    The Cambrian Eriboll Formation quartzarenites contain abundant fractures with varying degrees of quartz cement infill. Fractures exist that are entirely sealed; are locally sealed by bridging cements but preserve pore space among bridges; are mostly open but lined with veneers of cement; or are devoid of cement. Fracture propagation in the Eriboll Formation is highly sensitive to the presence of pre-existing fractures. Fracture reactivation occurs in opening mode as individual fractures repeatedly open and are filled or bridged by syn-kinematic cements. As well, reactivation occurs in shear as opening of one fracture orientation coincides with shear displacement along pre-existing fractures of different orientations. The tendency for pre-existing fractures to slip varies in part by the extent of cement infill, yet we observe shear and opening-mode reactivation even among sealed fractures. Paleotemperature analysis of fluid inclusions within fracture cements suggests some fractures now in outcrop formed deep in the subsurface. Fractures within the Eriboll Formation may therefore affect later fracture propagation throughout geologic time. With progressive strain, fault zones develop within fracture networks by a sequence of opening-mode fracture formation, fracture reactivation and linkage, fragmentation, cataclasis, and the formation of slip surfaces. Cataclasite within fault zones is commonly more thoroughly cemented than fractures in the damage zone or outside the fault zone. This variance of cement abundance is likely the result of (1) continued exposure of freshly broken quartz surfaces within cataclasite, promoting quartz precipitation, and (2) possibly more interconnected pathways for mass transfer within the fault zone. Enhanced cementation of cataclasite results in strengthening or diagenetic strain hardening of the evolving fault zone. Further slip is accommodated by shear localization along discrete slip surfaces. With further linkage of fault segments

  8. The Middle Cambrian fossil Pikaia and the evolution of chordate swimming

    Directory of Open Access Journals (Sweden)

    Lacalli Thurston

    2012-07-01

    Full Text Available Abstract Conway Morris and Caron (2012 have recently published an account of virtually all the available information on Pikaia gracilens, a well-known Cambrian fossil and supposed basal chordate, and propose on this basis some new ideas about Pikaia’s anatomy and evolutionary significance. Chief among its chordate-like features are the putative myomeres, a regular series of vertical bands that extends the length of the body. These differ from the myomeres of living chordates in that boundaries between them (the myosepta are gently curved, with minimal overlap, whereas amphioxus and vertebrates have strongly overlapping V- and W-shaped myomeres. The implication, on biomechanical grounds, is that myomeres in Pikaia exerted much less tension on the myosepta, so the animal would have been incapable of swimming as rapidly as living chordates operating in the fast-twitch mode used for escape and attack. Pikaia either lacked the fast-twitch fibers necessary for such speeds, having instead only slow-twitch fibers, or it had an ancestral fiber type with functional capabilities more like modern slow fibers than fast ones. The first option is supported by the sequence of development in zebrafish, where both myoseptum formation and fast fiber deployment show a dependence on slow fibers, which develop first. For Pikaia, the absence of fast fibers has both behavioral and anatomical implications, which are discussed. Among the latter is the possibility that a notochord may not have been needed as a primary stiffening device if other structures (for example, the dorsal organ could perform that role.

  9. 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.

  10. The evolutionary and genetic origins of consciousness in the Cambrian Period over 500 million years ago

    Directory of Open Access Journals (Sweden)

    Todd E Feinberg

    2013-10-01

    Full Text Available Vertebrates evolved in the Cambrian Period before 520 million years ago, but we do not know when or how consciousness arose in the history of the vertebrate brain. Here we propose multiple levels of isomorphic or somatotopic neural representations as an objective marker for sensory consciousness. All extant vertebrates have these, so we deduce that consciousness extends back to the group’s origin. The first conscious sense may have been vision. Then vision, coupled with additional sensory systems derived from ectodermal placodes and neural crest, transformed primitive reflexive systems into image forming brains that map and perceive the external world and the body’s interior. We posit that the minimum requirement for sensory consciousness and qualia is a brain including a forebrain (but not necessarily a developed cerebral cortex/pallium, midbrain and hindbrain. This brain must also have 1 hierarchical systems of intercommunicating, isomorphically organized, processing nuclei that extensively integrate the different senses into representations that emerge in upper levels of the neural hierarchy; and 2 a widespread reticular formation that integrates the sensory inputs and contributes to attention, awareness, and neural synchronization. We propose a two-step evolutionary history, in which the optic tectum was the original center of multi-sensory conscious perception (as in fish and amphibians: step 1, followed by a gradual shift of this center to the dorsal pallium or its cerebral cortex (in mammals, reptiles, birds: step 2. We address objections to the hypothesis and call for more studies of fish and amphibians. In our view, the lamprey has all the neural requisites and is likely the simplest extant vertebrate with sensory consciousness and qualia. Genes that pattern the proposed elements of consciousness (isomorphism, neural crest, placodes have been identified in all vertebrates. Thus, consciousness is in the genes, some of which are

  11. Enigmatic Connection Between Rhyolites and Shallow Granites in a Cambrian Rift

    Science.gov (United States)

    Gilbert, M. C.

    2007-12-01

    The Cambrian Southern Oklahoma Aulacogen (SOA) exposes shallow-seated, A-type sheet granites emplaced on top of layered mafic bodies and under cover of A-type rhyolites, this gabbro-rhyolite boundary being a crustal magma trap. Granites and rhyolites appear to overlap in age, although rhyolites built up first, with the rhyolite pile thickening as later granites coarsened texturally to medium-grained types from earlier fine-grained sheets. Outcrop relations + widespread subsurface data, including regional gravity, indicate rhyolite volume exceeds granite volume. Both silicic and mafic members of the SOA sequence have the same positive Nd signature showing a fundamental genetic relationship between the rifting process and the development of new crust in the SOA. Major element geochemistry of rhyolites (~76% SiO2) and granites (73-76% SiO2) is similar, as are many trace element abundances and signatures. However, some indices are different: Zr in rhyolites is ~600-700ppm, in granites ~300-500; Zr/Nb in rhyolites 8-11, in granites 4-8; K/Rb in rhyolites 300's, in granites 200's. In only one locality can a continuous connection between fine-grained granite and a texturally rhyolitic lobe be seen. Thus, it is clear that none of the rhyolites and granites are directly related at their emplacement level. Conclusions: 1)Silicic magma, both rhyolitic and granitic, was fractionated from mafic sources in the middle rift crust. 2)Magma driving pressures for silicic liquids must have been higher for those becoming rhyolites than for those that became granites. 3)These differences imply that rhyolitic magma generally came from a deeper depth in the mid-crust, although the ultimate mafic sources may have been similar. 4)More generally as this case shows, spatially near, and chemically similar, rhyolite and granite bodies in the same tectonic setting may not be directly related.

  12. Proterozoic sequences and their implications for precamorian and cambrian geologic evolution of Western Kentucky: Evidence from seismic-reflection data

    Science.gov (United States)

    Drahovzal, J.A.

    1997-01-01

    Analyses of two seismic-reflection lines in western Kentucky indicate the presence of two Proterozoic, unconformity-bounded sequences. One is autochthonous and of probable Late Proterozoic age; the other is allochthonous and of probable Middle Proterozoic age. Reflector patterns and apparent relationships to similar sequences elsewhere in the region suggest that the two sequences are of continental-rift origin. The two Proterozoic sequences lie beneath and adjacent to rocks of the Cambrian rift sequence in the Rough Creek Graben. The oldest sequence, the pre-Grenville sequence, was apparently folded and thrust faulted by the Grenville compressional event, implying that it is older than ???0.975 Ga (Middle Proterozoic). Two seismic-reflection pattern types are present in the western Kentucky data that may relate to the Middle Run (lithic arenite) and volcanic sequences defined farther east near the Grenville Front. The presence of imbricate, thrust-belt geometries in the pre-Grenville sequence extends the known westward limit of Grenville compressional structures into western Kentucky. The younger, post-Grenville sequence is less deformed and was apparently formed after the Grenville compressional event; several lines of evidence indicate that it is Late Proterozoic (0.7 to 0.6 Ga) in age. This probable siliciclastic and volcanic-rift sequence is represented by only thin remnants in western Kentucky and has no equivalent near the Grenville Front in southwestern Ohio and central Kentucky. Rocks of the better documented Cambrian rifting event belong to the thick, pre-Knox sequence in the Rough Creek Graben of western Kentucky and lie unconformably above these earlier sequences. A previously undocumented, northward-thickening interval within the lower part of the Cambrian pre-Knox sequence is recognized north of the Rough Creek Graben.

  13. Geochemical comparison of a Cambrian alginite potential source rock, and hydrocarbons from the Colville/Tweed Lake area, Northwest Territories

    Energy Technology Data Exchange (ETDEWEB)

    Wielens, J.B.W.; Fowler, M.G.; Brooks, P.W. (Inst. of Sedimentary and Petroleum Geology, Calgary, AB (Canada)); Dick, H. Von der (Canadian Hunter Exploration Ltd., Calgary, AB (Canada)); Monnier, F. (Chevron Oil Field Research, CA (USA))

    1990-06-01

    The reservoir for gas discoveries in the Colville/Tweed Lake area is the Lower Cambrian Mount Clark sandstone. Heavy oils are also found in this area in Cretaceous formations for which no source rock has previously been assigned. A comparison and correlation of reservoir and oil seep hydrocarbons is presented, and a potential source rock discussed. The gasoline range composition of Tweed Lake condensate shows an unusual distribution, distinguished by a very high abundance of n-alkanes and iso-alkanes and an extremely low abundance of benzene and toluene. The C{sub 15+} saturate fraction gas chromatograms of the condensate and of bitumens found with the Mount Clark reservoir also show many similarities to Ordovidian oils sourced from kukersite intervals. Geochemical screening of samples from several wells indicates that only the Middle Cambrian Mount Cap Formation is sufficiently organic-rich to be a probable source rock. Microscopic examination of one particularly rich interval shows dominance by alginite of a species resembling Gloeocapsomorpha prisca, the predominant contributor to kukersites. The organic matter is Type I, known to generate hydrocarbons at higher maturities. Organic geochemical investigations indicate that a source rock similar to this sample is responsible for the hydrocarbons in the Mount Clark reservoirs. The actual source rocks must be present in areas which have not been drilled to date. Bitumens recovered from surface seeps in the area are very biodegraded and cannot be correlated with any specific source rock, but they were not derived from the Cambrian source rock. 24 refs., 7 figs., 3 tabs.

  14. Self-recognition and Ca2+-dependent carbohydrate-carbohydrate cell adhesion provide clues to the cambrian explosion.

    Science.gov (United States)

    Fernàndez-Busquets, Xavier; Körnig, André; Bucior, Iwona; Burger, Max M; Anselmetti, Dario

    2009-11-01

    The Cambrian explosion of life was a relatively short period approximately 540 Ma that marked a generalized acceleration in the evolution of most animal phyla, but the trigger of this key biological event remains elusive. Sponges are the oldest extant Precambrian metazoan phylum and thus a valid model to study factors that could have unleashed the rise of multicellular animals. One such factor is the advent of self-/non-self-recognition systems, which would be evolutionarily beneficial to organisms to prevent germ-cell parasitism or the introduction of deleterious mutations resulting from fusion with genetically different individuals. However, the molecules responsible for allorecognition probably evolved gradually before the Cambrian period, and some other (external) factor remains to be identified as the missing triggering event. Sponge cells associate through calcium-dependent, multivalent carbohydrate-carbohydrate interactions of the g200 glycan found on extracellular proteoglycans. Single molecule force spectroscopy analysis of g200-g200 binding indicates that calcium affects the lifetime (+Ca/-Ca: 680 s/3 s) and bond reaction length (+Ca/-Ca: 3.47 A/2.27 A). Calculation of mean g200 dissociation times in low and high calcium within the theoretical framework of a cooperative binding model indicates the nonlinear and divergent characteristics leading to either disaggregated cells or stable multicellular assemblies, respectively. This fundamental phenomenon can explain a switch from weak to strong adhesion between primitive metazoan cells caused by the well-documented rise in ocean calcium levels at the end of Precambrian time. We propose that stronger cell adhesion allowed the integrity of genetically uniform animals composed only of "self" cells, facilitating genetic constitutions to remain within the metazoan individual and be passed down inheritance lines. The Cambrian explosion might have been triggered by the coincidence in time of primitive animals

  15. Trilobites from the Çal Tepe Formation (Cambrian), Near Seydişehir, Central Taurides, Southwestern Turkey

    OpenAIRE

    DEAN, WILLIAM T.

    2005-01-01

    The type section of the Çal Tepe Formation, near Seydişehir, is reviewed. The basal dolomite member is unfossiliferous, but the succeeding black limestone member (24 m), light-grey limestone member (10.15 m), and red nodular limestone member (46.7 m) are subdivided into thirty-seven numbered, often fossiliferous beds. Trilobites from the black limestone member, late Early Cambrian, exhibit affinities with Morocco, Spain and northwestern Europe; they include one new genus and species (Pamphyli...

  16. 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

  17. From Basin Black Shales to Platform Carbonate Rocks: A Study on Sequence Stratigraphy for the Lower Cambrian of the Upper-Yangtze Region in South China

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    In the Upper-Yangtze region, especially in Guizhou Province and its adjacent areas, the Lower Cambrian is well developed and is marked by a succession from black shales of the basin facies to carbonate rocks of the platform facies. The drowning event of the platform occurring at the turn from Sinian to Cambrian resulted in a set of black shales, i.e. the Niutitang Formation, which makes up the bottom part of the Lower Cambrian. With the shoaling of the sedimentary environment, a set of carbonate rocks, i.e. the Qingxudong Formation, was formed in the top part of the Lower Cambrian. Thus, the Lower Cambrian in the study area makes up one second-order sequence that can be further subdivided into five third-order sequences, and forms a regularly cyclic succession of transgression-regression. There is a regularly vertical stacking pattern for the third-order sequences in the second-order sequence. From bottom to top, the succession of the "CS (condensed section)+HST (high-stand system tract)" of the third-order sequences is changed into the succession of the "TST (transgressive system tract)+CS+HST". Correspondingly, the drowning-type sequence boundary is changed into the exposure-type one. Therefore, both the second-order and the third-order sequences have similar sedimentary-facies architectures. A concomitant with these temporal changes,the Lower Cambrian with a thickness of 1000 m that contains five third-order sequences is changed into a condensed succession that cannot identify third-order sequences toward the southeast with the deepening of the sedimentary environment. According to the elementary features of the third-order sequences, i.e. the regularity o sedimentary-facies successions in space and the synchronism of sedimentary-environment changes in time, the detailed division of the third-order sequences at main logged sections in different paleogeographical background becomes the basis to establish the sequence-stratigraphic framework that can demonstrate

  18. Paleoceangraphic significance of redox-sensitive metals of black shales in the basal Lower Cambrian Niutitang Formation in Guizhou Province,South China

    Institute of Scientific and Technical Information of China (English)

    YANG Jinghong; JIANG Shaoyong; LING Hongfei; FENG Hongzhen; CHEN Yongquan; CHEN Jianhua

    2004-01-01

    Black shales of the Lower Cambrian Niutitang Formation occur widely on the Yangtze Platform. In this study, we analyzed black shales from two sections (Zhongnan and Zhijin) in Guizhou Province. The redox-sensitive metal concentration and distribution of black shales from the two sections provide good evidence for the anoxic conditions of the basal Cambrian ocean on the Yangtze Platform. Our geochemical data suggest that the black shales from the Zhongnan section may have deposited in a more strongly anoxic environment than the black shales in the Zhijin section.

  19. "The Chengjiang Fauna and the Cambrian Explosion" Sponsord by NSFC won the first-class award of National Natural Sciences Award

    Institute of Scientific and Technical Information of China (English)

    Liu; Y.; Yao; Y.P.

    2004-01-01

      "The Chengjiang Fauna and the Cambrian explosion'' sponsord by NSFC won the first-class award of National Natural Sciences Award. The Awarding ceremony was held in the Great Hall of the People in Beijing on February 20, 2004. "The Chengjiang Fauna and the Cambrian explosion" was sponsord by NSFC and carried out by several groups led by Prof. Chen Junyuan of the Nanjing Institute of Geology and Palaeontology,CAGS, Prof. Hou Xianguang of Yunnan University and Prof.……

  20. Dam sediment tracking using spectrometry and Landsat 8 satellite image, Taleghan Basin, Iran.

    Science.gov (United States)

    Afshar, Sirous; Shamsai, Abolfazl; Saghafian, Bahram

    2016-02-01

    Sedimentation in reservoirs, in addition to reducing water storage capacity, causes serious environmental impacts including intensification of river erosion. Detection of sediment origins plays a determining role in control and prevention of sedimentation. Nowadays, with the help of studies on sedimentation and erosion, sediment origins can be detected with high accuracy. This research integrated geographic information system (GIS) and remote sensing (RS) techniques to detect the primary source of sediment to Taleghan Dam in northern Iran. After collecting samples of sediment from the basin outlet, they were divided into two parts. One part was sent to the Mineralogy Laboratory in order to determine the percentage of each mineral in the samples using X-ray. A few were sent to the Spectroscopy Laboratory to determine their spectral signature using the spectrometer. The laboratory test results determined the wavelength of the minerals. In the next step, those spots on the satellite image whose spectral reflectance fell within the spectral signature of the minerals were detected and enhanced by mixture-tuned matched filtering (MTMF) method. These spots were overlapped with the map of geological formations. Accordingly, the origin of the minerals was detected. The greatest proportion of trace minerals was found in sample 4 including 6% of Illite trace mineral, while sample 2 contains only 2% of trace minerals. Accordingly, the origin of the minerals was detected. The obtained results revealed that mudstone, red siltstone, and conglomerate formations, Karaj formation in section Poldokhtar, acidic tuffs, alcanic lavas of Karaj Formation, mudstone and gypsum of upper red formation, and Cambrian dolomites were recognized as the most possible origins of the dam sediments. These formations are vulnerable to erosion and should be conserved so as to substantially prevent the volume of sedimentation in the reservoir. PMID:26790431

  1. Organic Carbon Isotopic Evolution during the Ediacaran-Cambrian Transition Interval in Eastern Guizhou, South China: Paleoenvironmental and Stratigraphic Implications

    Institute of Scientific and Technical Information of China (English)

    YANG Xinglian; ZHU Maoyan; GUO Qingjun; ZHAO Yuanlong

    2007-01-01

    Secular variations of carbon isotopic composition of organic carbon can be used in the study of global environmental variation, the carbon cycle, stratigraphic delimitation, and biological evolution, etc. Organic carbon isotopic analysis of the Nangao and Zhalagou sections in eastern Guizhou reveals a negative excursion near the Precambrian-Cambrian boundary that correlates with a distinct carbonate carbon isotopic negative excursion at this boundary globally. Our results also demonstrate that several alternating positive and negative shifts occur in the Meishucunian, and an obvious negative anomaly appears at the boundary between the Meishucunian and Qiongzhusian. The isotope values are stable in the middle and lower parts but became more positive in the upper part of the Qiongzhusian. Evolution of organic carbon isotopes from the two sections in the deepwater facies can be well correlated with that of the carbonate carbon isotopes from the section in the shallow water facies. Integrated with other stratigraphic tools, we can precisely establish a lower Cambrian stratigraphic framework from shallow shelf to deep basin of the Yangtze Platform.

  2. 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 <4 m.y. Existing hypotheses suggest that the 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.

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

    Directory of Open Access Journals (Sweden)

    D. Hippler

    2011-12-01

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

  4. Cambrian magmatism, Variscan high-grade metamorphism and imposed greenschist facies shearing in the Central Sredna Gora basement units (Bulgaria

    Directory of Open Access Journals (Sweden)

    Lazarova Anna

    2015-12-01

    Full Text Available Gneisses from the deep structural levels of the European Variscan Belt are well exposed in the Central Sredna Gora in Bulgaria. In general, migmatites predominate, but unmigmatized domains (or domains with incipient migmatization are also documented in this area. This paper presents new structural, petrographic and U-Pb isotope geochronological data from such an unmigmatized part of the Variscan high-grade metamorphic basement (the Koprivshtitsa Unit. A predominant part of this unit represents an alternation of metagranitoids and metabasites. The protolith crystallization age of the metagranitoids is constrained at 491.5 ± 7.6 Ma by U-Pb laser ablation method on zircons. This age coincides with the previously available Late Cambrian protolith ages of metabasic rocks that crop out within the adjacent migmatitic unit. The Korpivshtitsa Unit comprises also lesser orthogneisses with Late Neoproterozoic protoliths. Based on the available local and regional paleogeographic reconstruction schemes, we suggest that the Upper Cambrian magmatic rocks intruded Upper Neoproterozoic crust during the initial opening stages of the Rheic Ocean or a related basin. Subsequently, both were involved in the Variscan high-grade deformation. The contact of the Koprivshitsa Unit with the migmatitic part of the metamorphic complex coincides with a north-vergent greenschist facies thrust zone – the Chuminska Shear Zone. The exact time of the shearing is still not well constrained but it clearly postdates the Variscan high-temperature metamorphism of the gneisses.

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

    Science.gov (United States)

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

    2011-12-01

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

  6. Proterozoic-Cambrian detrital zircon and monazite ages from the Anakie lnlier, central Queensland: Grenville and Pacific-Gondwana signatures

    International Nuclear Information System (INIS)

    The Anakie Metamorphic Group is a complexly deformed, dominantly metasedimentary succession in central Queensland. Metamorphic cooling is constrained to ca 500 Ma by previously published K-Ar ages. Detrital-zircon SHRIMP U-Pb ages from three samples of greenschist facies quartz-rich psammites (Bathampton Metamorphics), west of Clermont, are predominantly in the age range 1300-1000Ma (65-75%). They show that a Grenville-aged orogenic belt must have existed in northeastern Australia, which is consistent with the discovery of a potential Grenville source farther north. The youngest detrital zircons in these samples are ca 580 Ma, indicating that deposition may have been as old as latest Neoproterozoic. Two samples have been analysed from amphibolite facies pelitic schist from the western part of the inlier (Wynyard Metamorphics). One sample contains detrital monazite with two age components of ca 580-570 Ma and ca 540 Ma. The other sample only has detrital zircons with the youngest component between 510Ma and 700Ma (Pacific-Gondwana component), which is consistent with a Middle Cambrian age for these rocks. These zircons were probably derived from igneous activity associated with rifting events along the Gondwanan passive margin. These constraints confirm correlation of the Anakie Metamorphic Group with latest Neoproterozoic - Cambrian units in the Adelaide Fold Belt of South Australia and the Wonominta Block of western New South Wales. Copyright (2001) Geological Society of Australia

  7. Phylogenomic insights into the cambrian explosion, the colonization of land and the evolution of flight in arthropoda.

    Science.gov (United States)

    Wheat, Christopher W; Wahlberg, Niklas

    2013-01-01

    The timing of the origin of arthropods in relation to the Cambrian explosion is still controversial, as are the timing of other arthropod macroevolutionary events such as the colonization of land and the evolution of flight. Here we assess the power of a phylogenomic approach to shed light on these major events in the evolutionary history of life on earth. Analyzing a large phylogenomic dataset (122 taxa, 62 genes) with a Bayesian-relaxed molecular clock, we simultaneously reconstructed the phylogenetic relationships and the absolute times of divergences among the arthropods. Simulations were used to test whether our analysis could distinguish between alternative Cambrian explosion scenarios with increasing levels of autocorrelated rate variation. Our analyses support previous phylogenomic hypotheses and simulations indicate a Precambrian origin of the arthropods. Our results provide insights into the 3 independent colonizations of land by arthropods and suggest that evolution of insect wings happened much earlier than the fossil record indicates, with flight evolving during a period of increasing oxygen levels and impressively large forests. These and other findings provide a foundation for macroevolutionary and comparative genomic study of Arthropoda. PMID:22949483

  8. Thermal evidence of Caledonide foreland, molasse sedimentation in Fennoscandia

    International Nuclear Information System (INIS)

    The Phanerozoic rocks present on the Fennoscandian Shield are dominantly of Cambrian to Silurian age. They represent a relatively thin sedimentary cover. The question is: why do we not see any remnants of younger sedimentary rocks? Did they ever exist, have they been eroded, transported and redeposited elsewhere? δ18O and δ13C analyses of Ordovician limestones from different places in Sweden and from the Oslo region in Norway show modification of their original marine signature according to the δ18O concentrations, while the δ13C concentrations generally are typical for marine limestones. In some cases the modifications can be explained by intrusions of dykes or by metamorphic events, but in most areas the redistribution of the oxygen isotopes indicates burial diagenesis. From a number of published investigations, raised temperatures at the present surface during the late Palaeozoic, are indicated by different temperature indicators. We suggest that these increased temperatures were due to a sedimentary cover of mainly Devonian sediments deposited on top of the Cambrian-Silurian sequence. This palaeo-cover caused raised temperatures at the present rock surface. In the Proterozoic basement, annealing of fission tracks in apatite and mobility of radiogenic lead also give evidence of increased temperatures. A model where the thickness of the Upper Paleozoic cover of the Caledonian foreland is 2-4 kilometers thick is suggested. This cover mainly consisted of late Silurian-Devonian erosion products from the Caledonides, the latter formed during a Silurian continent-continent collision. A major Permian to Triassic uplift and erosion reduced the cover significantly. 94 refs, 9 figs

  9. Geochronological Constraints on Neoproterozoic Glaciations, the first appearance of Metazoans, and the Cambrian Explosion.

    Science.gov (United States)

    Bowring, S.; Condon, D.; Ramezani, J.; Myrow, P.; Landing, E.

    2004-05-01

    the timing of the first appearance of animal fossils (south China and Newfoundland) relative to the last global glaciation and whether a major extinction occurred at the Cambrian/Precambrian boundary. These important issues will only be resolved by the integration of high-resolution geochronology and stratigraphy.

  10. Hydrogeochemical and stream sediment reconnaissance basic data for Lawton NTMS quadrangle, Oklahoma; Texas

    International Nuclear Information System (INIS)

    Field and laboratory data are presented for 703 groundwater and 782 stream sediment samples. Statistical and areal distributions of uranium and possible uranium-related variables are displayed. Groundwater data indicate that the most promising areas for potential uranium mineralization occur in the Lower Permian units surrounding the granite outcrops of the Wichita Mountains. Waters from the Hennessey and Clearfork Groups and the Garber Sandstone contain the highest uranium values. Elements associated with the uranium are arsenic, boron, barium, molybdenum, sodium, selenium, and vandium. Stream sediment data indicate that the promising areas for potential uranium mineralization occur around the Wichita Mountains where stream sediments are derived from the Lower Permian Post Oak Conglomerate, Hennessey Group, and Garber Sandstone and from the Cambrian igneous rocks. Other areas of interest occur (1) in the western part of the quadrangle where the sediments are derived from rocks of the El Reno Group, and (2) along the southern border of the quadrangle where the sediments are derived from the Wichita Group

  11. OU3 sediment dating and sedimentation rates

    International Nuclear Information System (INIS)

    Environmental Technologies at Rocky Flats Environmental Technology Site (RFS) investigated the sediment history of Standley Lake, Great Western Reservoir, and Mower Reservoir using 137Cs and 239,240Pu global fall-out as dating indicators. These Colorado Front Range reservoirs have been the subject of study by various city, state and national agencies due to suspected Department of Energy Rocky Flats Plant impacts. We performed sediment dating as part of the RCRA Facility Investigation/Remedial Investigation Report for Operable Unit 3. A sediment chronology profile assists scientist in determining the year of sedimentation for a particular peak concentration of contaminants. Radioisotope sediment dating for the three reservoirs indicated sedimentation rates of 0.7 to 0.8 in./yr. for Standley Lake (SL), 0.9 in./yr. for Great Western Reservoir (GWR), and 0.3 in./yr. in Mower Reservoir (MR). RFS sediment dating for Operable Unit 3 compared favorably with the Hardy, Livingston, Burke, and Volchok Standley Lake study. This report describes the cesium/plutonium sediment dating method, estimates sedimentation rates for Operable Unit 3 reservoirs, and compares these results to previous investigations

  12. 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; Fallick, Anthony E.; Ellam, Rob M.

    2014-01-01

    peneplanation. An 40Ar/39Ar age of 542.62 ± 0.38 Ma (1 sigma, full external precision, Renne et al., 2011) for metalliferous alteration clays in Scotland shows that this event occurred immediately prior to the Precambrian–Cambrian boundary. A negative δ53Cr isotopic signature for the clay is consistent with...

  13. Substrate as test of behaviour and as the ichnotaxonomical problem: predation and scavenging traces on trilobite exosceletons, Middle Cambrian, Czech Republic

    Czech Academy of Sciences Publication Activity Database

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

    Moscow : PIN RAN, 2010. s. 39-40. [Workshop on Ichnotaxonomy /4./. 21.06.2010-26.06.2010, Moscow - St. Petersburg] R&D Projects: GA ČR GA205/09/1521 Institutional research plan: CEZ:AV0Z30130516 Keywords : Cambrian * ichnology * ichnotaxonomy * ichnofossils * predation traces * scavening traces * palaeontology Subject RIV: DB - Geology ; Mineralogy

  14. U-Pb zircon ages and structural development of metagranitoids of the Teplá crystalline complex: evidence for pervasive Cambrian plutonism within the Bohemian massif (Czech Republic)

    Czech Academy of Sciences Publication Activity Database

    Dörr, W.; Fiala, Jiří; Vejnar, Zdeněk; Zulauf, G.

    1998-01-01

    Roč. 87, č. 1 (1998), s. 135-149. ISSN 0016-7835 R&D Projects: GA AV ČR KSK1012601 Grant ostatní: DFG(DE) Zu73/1-3 Keywords : Cambrian plutonism * U-Pb analyses * Bohemian massif Subject RIV: DB - Geology ; Mineralogy Impact factor: 0.841, year: 1998

  15. Center for Contaminated Sediments

    Data.gov (United States)

    Federal Laboratory Consortium — The U.S. Army Corps of Engineers Center for Contaminated Sediments serves as a clearinghouse for technology and expertise concerned with contaminated sediments. The...

  16. Electrodialytic remediation of sediments

    DEFF Research Database (Denmark)

    Jensen, Pernille Erland

    Sediments of harbors and freshwaters are regularly dredged for various reasons: maintenance of navigational depths, recovery of recreational locations, and even environmental recovery. In the past, sediments dredged from harbors have been dumped at sea, however, environmental regulations now, in ...

  17. Ocean Sediment Thickness Contours

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Ocean sediment thickness contours in 200 meter intervals for water depths ranging from 0 - 18,000 meters. These contours were derived from a global sediment...

  18. National Geochemical Database: Sediment

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Geochemical analysis of sediment samples from the National Geochemical Database. Primarily inorganic elemental concentrations, most samples are of stream sediment...

  19. The Kalkarindji Large Igneous Province and the Early-Middle Cambrian Extinction.

    Science.gov (United States)

    Jourdan, Fred; Evins, Lena

    2010-05-01

    Despite being one of the largest large igneous provinces (LIP) on Earth, the recently discovered Kalkarindji LIP, Australia, has received only very little attention (e.g., Glass & Philips, 2005; Evins et al., 2009). This province is located across the Northern Territories and Western Australia and covers a currently known area of ≥ 2.1x106 km² (Evins et al., 2009) with hints that it stretches as far as the southernmost part of South Australia (equivalent to a total area of ≥ 3x106 km²). The province includes flows, intrusions and volcanic tuffs. The age of the province is currently based only on three robust 40Ar/39Ar apparent ages ranging from 504.6 ± 2.5 to 507.5 ± 1.6 Ma (Glass & Philips, 2005; Evins et al., 2009). This province is of particular interest as it seems to coincide with a global anoxic event (Hough et al., 2006) and more importantly, the Early-Middle Cambrian (EMC) extinction where 50% of the genera (e.g. Archeocyaths, Trilobites) went extinct. The age of the EMC extinction has been estimated at ~510 Ma according to the revised timescale of 2009 but so far, attempts to date the extinction level have not yielded any precise date. Considering the now well-established 40K decay constant bias (Min et al., 2000), the 40Ar/39Ar ages obtained so far suggest an emplacement age of the Kalkarindji province between ~509 and ~512 Ma, thus apparently synchronous with the EMC extinction. However, due to the paucity of available ages, it is still not clear if the Kalkarindji LIP was emplaced during only few hundred ka, or rather was more sluggish over few Ma. The Kalkarindji basalts are overlapping thick sulfate-rich evaporite layers and carbonate rocks of the Precambrian central Australia basins. Evaporite and carbonate metamorphism might have been responsible for a significant source of CO2, SO2 and halocarbons as demonstrated for the Siberian traps (Svensen et al., 2009). In addition, the occurrence of pyroclastics eruptions as indicated by the presence

  20. Detrital zircon provenance of Mesoproterozoic to Cambrian arenites in the Western United States and Northwestern Mexico

    Science.gov (United States)

    Stewart, John H.; Gehrels, G.E.; Barth, A.P.; Link, P.K.; Christie-Blick, N.; Wrucke, C.T.

    2001-01-01

    U-Pb isotopic dating of detrital zircon from supracrustal Proterozoic and Cambrian arenites from the western United States and northern Mexico reveal three main age groups, 1.90 to 1.62 Ga, 1.45 to 1.40 Ga, and 1.2 to 1.0 Ga. Small amounts of zircons with ages of 3.1 to 2.5 Ga, 1.57 Ga, 1.32 Ga, 1.26 Ga, 0.7 Ga, and 0.5 Ga are also present. Detrital zircons ranging in age from 1.90 to 1.62 Ga and from 1.45 to 1.40 Ga are considered to have been derived from Proterozoic crystalline basement rocks of these known ages, and probably in part from reworked Proterozoic supracrustal sedimentary rocks, of the western United States. The 1.2 to 1.0 Ga detrital zircon ages from California, Arizona, and Sonora are characterized by distinct spikes (1.11 Ga, in particular) in the age-probability plots. These spikes are interpreted to indicate the influx of zircon from major silicic volcanic fields. Igneous rocks such as the Pikes Peak Granite (1.093 Ga) of Colorado, and the Aibo Granite (1.110 Ga) of Sonora, Mexico, may represent the deeply eroded roots of such volcanic fields. Samples from farther north along the Cordilleran margin that contain abundant 1.2-1.0 Ga detrital zircons do not show spikes in the age distribution, but rather ages spread out across the entire 1.2-1.0 Ga range. These age spectra resemble those for detrital zircons from the Grenville province, which is considered their source. Less common detrital zircons had a variety of sources. Zircons ranging in age from 3.36 to 2.31 Ga were apparently derived from inland parts of the North American continent from Wyoming to Canada. Zircons of about 1.577 Ga are highly unusual and may have had an exotic source; they may have come from Australia and been deposited in North America when Australia and North America were juxtaposed as part of the hypothetical Rodinian supercontinent. Detrital zircon of ??1.320 Ga apparently had the same source as that for tuff (1.320 Ga) in the Pioneer Shale of the Apache Group in Arizona

  1. 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

    cementation is derived from internal sources. Rather, in spite of large variation in porosity and quartz cement content, a regular pattern of porosity decrease is related to increasing temperature or depth. The observed heterogeneity is due to local factors that influence the precipitation of quartz cement......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. The......, including sandstone architecture, i.e., distribution of shales within the sandstone bodies, and sandstone thickness. Heterogeneity is inherent to sandstone architecture and to the fact that silica for quartz cementation is derived from heterogeneously distributed local pressure solution. Models predicting...

  2. Speciation of the genus Arthricocephalus Bergeron, 1899 (Trilobita) from the late Early Cambrian and its stratigraphic significance

    Institute of Scientific and Technical Information of China (English)

    YUAN Jinliang; ZHAO Yuanlong; YANG Xinglian

    2006-01-01

    The genus Arthricocephalus Bergeron,1899 is revised, and Halipanktos Balker & Peel, 1997 is suggested here as a senior synonym. The subgenus Arthricocephalus (Arthricocephalites) Chien & Lin in Lu et al., 1974 is considered as a separate genus.Of the 20 previously assigned species of Arthricocephalus ( Arthricocephalus ) Bergeron, 1899, Arthricocephalus ( Arthricocephalites )Chien & Lin in Lu et al., 1974, Arthricocephalus (Euarthricocephalus) Ju, 1983 are lumped into eight species. The speciation trend of Arthricocephalus and Arthricocephalites is demonstrated based on their stratigraphic occurrences. It not only enhances the resolution of the biostatigraphic zonation in the uppermost Lower Cambrian, but also represents a potential candidate to define the Duyunian stage. The base of the stage is suggested at the first appearance datum (FAD) of Arthricocephalus chauveaui Bergeron, 1899 within the evolutionary lineage from Ar. jiangkouensis Yin in Yin & Li, 1978 to Ar. chauveaui in a global scale.

  3. Chengjiang fauna & the Cambrian taxonomic explosion%澄江动物群与寒武纪大爆发

    Institute of Scientific and Technical Information of China (English)

    赵生才

    1998-01-01

    @@ 1984年,中国学者在云南澄江寒武纪地层发现一批丰富多彩的古化石群,迅速在世界上引起强烈反响,美国据世界一些著名科学家联合建议,将此列入本世纪最惊人的发现之一.德国古生物学家赛拉赫(Seilacher)等著名学者认为,"寒武纪大爆发(Cambrian Explosion)"是生命历史中最伟大、但也是了解最少的一次生物事件,而中国澄江动物群拥有解开这个谜的线索.

  4. Phosphatized Punctatus with mouthparts and its embryo fossils from the Lower Cambrian of Ningqiang, south Shaanxi, China

    Institute of Scientific and Technical Information of China (English)

    LIU Yunhuan; LI Yong; SHAO Tiequan; ZHU Zhixin; YU Bo; WANG Zhuo; ZHANG Wanqian; LI Rongxi

    2007-01-01

    The appearance of coelenterates marks the real beginning ofmetazoan evolution. It therefore has a prominent position in the origin and evolutionary history of organisms,and is also a pivotal question of evolutionary biology.Punctatus is an extinct, ancient marine animal from the early stage of the Cambrian explosion, occurring at. The lowermost Cambrian of both Kuanchuanpu (Ningqiang, Shaanxi) and Maidiping (Emei, Sichuan) areas. Punctatus has been studied for many years since the discovery of its fragments. System-atic and phylogenetic analysis has long been limited because of the rarity of complete specimens. In order to improve research into Punctatus, more than ten thousand globular fossils were recovered by means of "Chemistry Retting". On the basis of the study of these globular fossils, a series of Punctatus fossils with cone parts and finely preserved soft-tissue mouthparts and fossilized metazoan embryo were recovered. Through research on characteristics such as shape,modality and structure of these fossils symbiotic with Punctatus emeiensis, the author found many possible embryo fossils including the evidence of gastrula-stage animal fossils.The sequence of fetation might have appeared on the corol-liform oral region of Punctatus emeiensis. A study of the soft tissues, functional morphology and the sequence of embryo fossils shows evidence that Punctatus resembles coelenterate polyps in systematic classification. Perhaps it also represents an ancestor of the coelenterate with an original tentacle. A comparison with the real "tentacle animal" found in the Chengjiang Fauna, shows that the original tentacle is very tiny and its function range is limited. This reveals the primi-tive nature of the animal. Although the original tentacle is so small, it does exist, representing the first big step towards the real flexible tentacle with a strong function from the early evolving tentacle.

  5. The noble gas isotope geochemical composition of chert at the bottom of Cambrian in Tarim Basin,China

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    In the Tarim Basin,black shale series at the bottom of Cambrian is one of the important marine facies hydrocarbon source rocks. This research focuses on the analysis of the isotope of noble gas of 11 cherts. The R/Ra ratio of chert in the Keping area is 0.032―0.319,and 40Ar/36Ar is 338―430. In Quruqtagh the R/Ra ratio is 0.44―10.21,and 40Ar/36Ar is 360―765. The R/Ra ratio of chert increases with 40Ar/36Ar from the west to the east accordingly. They have evolved from the crust source area to the mantle source area in a direct proportion. Surplus argon 40ArE in chert is in direct proportion to the R/Ra ratio,indicating that it has the same origin of excess argon as in fluid and mantle source helium. Comparison of the R/Ra ratios between the west and the east shows that the chert in the eastern part formed from the activity system of the bottom hydrothermal venting driven by the mantle source,where the material and energy of crust and mantle had a strong interaction in exchange;whereas in the western part,chert deposited from the floating of hydrothermal plume undersea bottom,which is far away from the centre of activities of the hydrothermal fluid of ocean bottom. In addition,from noble gas isotope composition of chert,it is suggested that the ocean anoxia incident happened at the black shale of the Cambrian bottom probably because of the large-scaled ocean volcanoes and the followinghydrothermal activities.

  6. The geological significance of the boundary between the Fort Sill and Signal Mountain Formations in the lower Arbuckle Group (Cambrian)

    Energy Technology Data Exchange (ETDEWEB)

    Hosey, R.; Donovan, R.N. (Texas Christian Univ., Ft Worth, TX (United States). Geology Dept.)

    1993-02-01

    During the upper Cambrian, a transgression inundated the Southern Oklahoma aulacogen enveloping a landscape that consisted of hills of Cambrian-aged rhyolite up to 350 m in height. Initial deposits on this topography--the Reagan Formation--consist of siliciclastics that were deposited as alluvium and succeeding tidally-influenced marine sandstones and shales. The siliciclastics grains are made up of local rhyolite, quartz and authigenic glauconite. The overlying Honeycreek Formation is defined by the addition of carbonated detritus in the form of tidally-influenced pelmatozoan grainstones. The passage from the Honeycreek to the overlying Fort Sill Formation of the Arbuckle Group is marked by the incoming of beds of lime mudstone and the gradual disappearance of grainstones and siliciclastics. The contact between the Fort Sill and the overlying thinly-bedded dark grey bioclastic limestones of the Signal Mountain Formation is one of the most distinctive horizons in the Arbuckle Group. The contact evidently marks a substantial change in depositional environment. In detail the contact is sharp and shows evidence of minor erosion, although no karsting has been detected. The authors suggest that the contact surface records a regression, perhaps associated with dolomitization and followed by some erosion. A regression is also indicated by the local occurrence of a laminated tidal flat unit with traces of evaporites that outcrops in the far west of the Slick Hills immediately below the formation contact. They suggest that the Signal Mountains as a transgressive unit, incorporating siliciclastics transported into the area during the regression. It has been suggested that the unconformity reflects localized tectonism associated with the evolution of the Southern Oklahoma aulacogen. On the other hand the surface may correlate with a craton--wide Sauxian' hiatus.

  7. Sediment supply to beaches

    DEFF Research Database (Denmark)

    Aagaard, Troels

    2014-01-01

    Many beaches have been built by an onshore supply of sand from the shoreface, and future long-term coastal evolution critically depends on cross-shore sediment exchange between the upper and the lower shorefaces. Even so, cross-shore sediment supply remains poorly known in quantitative terms and...... this reduces confidence in predictions of long-term shoreline change. In this paper, field measurements of suspended sediment load and cross-shore transport on the lower shoreface are used to derive a model for sediment supply from the lower to the upper shoreface at large spatial and temporal scales....... Data collection took place at five different field sites that exhibit a wide range of wave conditions and sediment characteristics. Data analysis shows that both suspended sediment load and cross-shore sediment transport scale with the grain-related mobility number which ranged up to ψ ≈ 1000 in the...

  8. Santos estuarine sediments, Brazil - metal and trace element assessment by neutron activation analysis

    International Nuclear Information System (INIS)

    The Santos estuary system is an intricate pattern of tidal channels and small rivers originating from the adjacent Pre-Cambrian slopes. These two major estuaries share a common area in the upper portion of the region which interacts with each other. The largest harbor in Latin America is located at the eastern outlet of the Santos estuary. This intricate and sensitive ecosystem is highly susceptible to human impact from industrial activities, urban sewage and polluted solid wastes disposal. Due to its high vulnerability CETESB (Environmental Control Agency of the Sao Paulo State) sporadically monitors the contamination levels of water, sediment and marine organisms in this region. The present study reports results concerning the distribution of some major, trace and rare earth elements in the Santos estuarine marine sediments. Thirty two bottom sediment samples (SS0601 to SS0616 (summer) and SW0601 to SW0616 (winter) were collected in this estuary, including regions of Sao Vicente, Santos, Cubatao and Vicente de Carvalho, by a vanVeen sampler in the summer and winter of 2006. Multielemental analysis was carried out by instrumental neutron activation analysis (INAA). The concentration values obtained for As and metals Cr and Zn in the sediment samples were compared to Canadian Council of Minister of the Environment (CCME) oriented values (TEL and PEL values) and are adopted by CETESB. (author)

  9. Proposed GSSP for the base of Cambrian Stage 9, coinciding with the first appearance of Agnostotes orientalis, at Duibian, Zhejiang, China

    Institute of Scientific and Technical Information of China (English)

    Loren; E.; BABCOCK; Gabriella; BAGNOLI

    2009-01-01

    Exposed in natural outcrops near the Duibian Village, Jiangshan County, Zhejiang Province, China, the Duibian B section is proposed as the boundary stratotype for the base of an unnamed stage termed provisionally Cambrian Stage 9. The proposed position of the GSSP is 108.12 m above the base of the Huayansi Formation, at a horizon coinciding with the first appearance of the cosmopolitan agnostoid trilobite Agnostotes orientalis. This horizon coincides also with the first appearance of the cosmopoli-tan polymerid trilobite Irvingella angustilimbata. The section fulfills all the requirements for a GSSP, and the horizon can be constrained not only by the primary stratigraphic marker (A. orientalis) but also with secondary biostratigraphic, chemostratigraphic, and sequence-stratigraphic correlation tools. The first appearance of A. orientalis is one of the most readily recognizable levels in Cambrian, and can be correlated with precision to all paleocontinents.

  10. A Protocol for Diagnosing the Effect of Calibration Priors on Posterior Time Estimates: A Case Study for the Cambrian Explosion of Animal Phyla.

    Science.gov (United States)

    Battistuzzi, Fabia U; Billing-Ross, Paul; Murillo, Oscar; Filipski, Alan; Kumar, Sudhir

    2015-07-01

    We present a procedure to test the effect of calibration priors on estimated times, which applies a recently developed calibration-free approach (RelTime) method that produces relative divergence times for all nodes in the tree. We illustrate this protocol by applying it to a timetree of metazoan diversification (Erwin DH, Laflamme M, Tweedt SM, Sperling EA, Pisani D, Peterson KJ. 2011. The Cambrian conundrum: early divergence and later ecological success in the early history of animals. Science 334:1091-1097.), which placed the divergence of animal phyla close to the time of the Cambrian explosion inferred from the fossil record. These analyses revealed that the two maximum-only calibration priors in the pre-Cambrian are the primary determinants of the young divergence times among animal phyla in this study. In fact, these two maximum-only calibrations produce divergence times that severely violate minimum boundaries of almost all of the other 22 calibration constraints. The use of these 22 calibrations produces dates for metazoan divergences that are hundreds of millions of years earlier in the Proterozoic. Our results encourage the use of calibration-free approaches to identify most influential calibration constraints and to evaluate their impact in order to achieve biologically robust interpretations. PMID:25808541

  11. Lead and barium sources in Cambrian siliciclastics and sediment provenance of a sector of the Taconic Orogen, Quebec: a mixing scenario based on Pb-isotopic evidence

    Science.gov (United States)

    Schrijver, K.; Zartman, R.E.; Williams-Jones, A. E.

    1994-01-01

    To test the hypothesis that siliciclastic rocks constituted the major source of Pb and Ba in barite-galena deposits of the Taconic Orogen, we determined Pb-isotope ratios in galena, barren rocks and contained minerals, as well as concentrations of Pb, U, Th and Ba in the latter (detrital feldspars, sandstones, mudstones, rock clasts and carbonate cements and clasts). Ranges in 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb of 28 galena samples are 17.96-18.05, 15.56-15.59 and 37.75-37.93, respectively; ranges for 41 barren rocks and minerals are 16.17-23.31, 15.26-15.86 and 35.98-42.51, respectively. The lowest ratios are in feldspar, and the highest in carbonate and mudstone. Values of the mudstones samples overlap those of galena when corrected for in situ decay of U and Th since galena precipitation (???450 Ma). We thus propose that mudstones constituted a source of lead. Corrected ratios for anomalously Pb-rich mudstones are virtually identical to galena-Pb ratios and may be due to contamination by lead-bearing brines. Assuming that burial diagenesis did not disturb the Pb-isotope values of sandstones, these rocks contributed only a minor fraction of lead to the galena, estimated at ???20% for one deposit. The source of barite-Ba was probably perthite. Low Ba and Pb concentrations of sandstone adjacent to this deposit, compared to high concentrations remote from it, support leaching of barium (and minor lead) from feldspar penecontemporaneous with feldspar dissolution. Geological data indicate that the provenance of the siliciclastic rocks was mainly from Grenville terrane. A comparison of our Pb-isotopic data for Taconic perthite with those of Grenville K-feldspar, as well as ratios of trace elements, support this provenance for both sandstones and mudstones. The presence of carbonate platforms peripheral to the orogen, and the Middle Ordovician-Middle Devonian depositional range of the studied and Mississippi Valley type deposits north (Newfoundland) and south (U.S.A. Appalachians) of our study area suggest targets for exploration in these platforms. ?? 1994.

  12. Dynamics of Cohesive Sediments

    DEFF Research Database (Denmark)

    Johansen, Claus

    The present thesis considers the transport processes of cohesive sediments. The cohesive sediment used in the laboratory experiments was kaolinite, a clay mineral, in order to be able to reproduce the individual experiments. In the first part of the thesis, the theoretical considerations regarding...

  13. Pb-Pb isotope dating of black shales from the Lower Cambrian Niutitang Formation, Guizhou Province, South China

    Institute of Scientific and Technical Information of China (English)

    CHEN Yongquan; JIANG Shaoyong; LING Hongfei; FENG Hongzhen; YANG Jinghong; CHEN Jianhua

    2003-01-01

    The Lower Cambrian black shales of the Niutitang Formation and their lateral equivalents occur widely on the Yangtze Platform, South China. In this study, we examine two sections of the Niutitang Formation in Guizhou Province. We employ a stepwise acid-leaching technique to obtain Pb-isotope compositions of the black shales. At the Zhongnan section, the black shales display large Pb isotope variations, with 206Pb/204Pb of 20.5396~33.5709, and 207Pb/204Pb of 15.8407~16.5782. In contrast, Pb isotope data show a relatively limited range in 206Pb/204Pb (18.2797~18.5972) and 207Pb/204Pb (15.6813~15.7159) at the Zhijin section. Data for all acid-leached black shale samples from the two sections yield a Pb-Pb isochron age of 531±24 Ma. This age may represent the sedimentary age of the black shales. The initial Pb-isotope composition of the black shales falls near the upper-crust evolution curve in a Zartman Pb-Pb evolution diagram. Hence, it is likely that the Pb in the black shales may have been derived from an upper continental crustal source.

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

    Directory of Open Access Journals (Sweden)

    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.

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

    Directory of Open Access Journals (Sweden)

    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.

  16. New observations of the lobopod-like worm Facivermis from the Early Cambrian Chengjiang Lagerst(a)tte

    Institute of Scientific and Technical Information of China (English)

    LIU Jianni; HAN Jian; SIMONETTA A. M.; HU Shixue; ZHANG Zhifei; YAO Yang; SHU Degan

    2006-01-01

    Facivermis yunnanicus (Hou & Chen, 1989), from the Early Cambrian Chengjiang Lagerst(a)tte, a worm-like fossil with 5 pairs of tentacles and a perceived shrunken end, has been regarded as related to polychaetes, later it has been variously interpreted as lobopods, Pentastoma and lophophorates. Newly discovered complete specimens by the ELI field team show that the taxon has, in addition to the 5 pairs of appendages, a pear-shaped trunk end bearing two or three circles of hooks. Accordingly, based on these important morphological characters, reconsideration of its affinities is provided and the taxonomy is remedied herein. Because the five pairs of appendages of Facivermis yunnanicus resemble the appendages of the fore-trunk of lobopod Miraluolishania (Liu & Shu, 2004), it seems that they are homologous structures. Therefore, the affinities of Facivermis are regarded here as being close to the lobopods, in addition, the lobe-like appendages of Facivermis are very crucial to exploring the origin of the appendages of lobopods and arthropods.

  17. The Guarguaraz Complex and the Neoproterozoic-Cambrian evolution of southwestern Gondwana: Geochemical signatures and geochronological constraints

    Science.gov (United States)

    López de Azarevich, Vanina L.; Escayola, Mónica; Azarevich, Miguel B.; Pimentel, Márcio M.; Tassinari, Colombo

    2009-12-01

    The Guarguaraz Complex, in western Argentina, comprises a metasedimentary assemblage, associated with mafic sills and ultramafic bodies intruded by basaltic dikes, which are interpreted as Ordovician dismembered ophiolites. Two kinds of dikes are recognized, a group associated with the metasediments and the other ophiolite-related. Both have N-MORB signatures, with ɛNd between +3.5 and +8.2, indicating a depleted source, and Grenville model ages between 0.99 and 1.62 Ga. A whole-rock Sm-Nd isochron yielded an age of 655 ± 76 Ma for these mafic rocks, which is compatible with cianobacteria and acritarchae recognized in the clastic metasedimentary platform sequences, that indicate a Neoproterozoic (Vendian)-Cambrian age of deposition. The Guarguaraz metasedimentary-ophiolitic complex represents, therefore, a remnant of an oceanic basin developed to the west of the Grenville-aged Cuyania terrane during the Neoproterozoic. The southernmost extension of these metasedimentary sequences in Cordón del Portillo might represent part of this platform and not fragments of the Chilenia terrane. An extensional event related to the fragmentation of Rodinia is represented by the mafic and ultramafic rocks. The Devonian docking of Chilenia emplaced remnants of ocean floor and slices of the Cuyania terrane (Las Yaretas Gneisses) in tectonic contact with the Neoproterozoic metasediments, marking the Devonian western border of Gondwana.

  18. Characteristics of sulfur species and their implications in Lower Cambrian black shales from southern margin of Yangtze Platform

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    There are different sulfur forms in the black shales from theEarly Cambrian of the Yangtze platform. With its emphasis on pyrite and organosulfur, this paper discusses their distribution and formation. The research shows that sulfur phases take regular variations laterally as well as vertically in the research areas. In western researched profile with high terrigenous supply at the time it formed, there exists a larger amount of pyrite and less organosulfur, and pyrite amount declines while organosulfur content increases upwards along the profile. This black shale profile is characterized by relatively light sulfur isotope composition with evolution trend of becoming heavier both for pyrite and organosulfur from bottom to top along the profile. Opposite situation occurs in eastern profiles which were located farther away from terrigenous land. Here pyrite amount obviously decreases and organic matter has combined more sulfur, although these two kinds of sulfur species take similar trend in content variation along profiles to that for western profile. At the same time more 34S is accumulated in sulfur species of black shale samples from eastern profile, and sulfur isotope composition gradually turns lighter from bottom to top. In combination with other information of iron, organic carbon contents and petrographic features, it can be established that sea-level change, supply of terrigenous matters, tectonic background and natures of paleoceanic chemistry have exerted great influence on the distribution of sulfur species in these black shales.

  19. The earliest-known ancestors of Recent Priapulomorpha from the Early Cambrian Chengjiang Lagerst(``a)tte

    Institute of Scientific and Technical Information of China (English)

    HAN Jian; SHU Degan; ZHANG Zhifei; LIU Jianni

    2004-01-01

    The taxonomy of an early ancestor of Recent Priapulidae, Xiaoheiqingella peculiaris (= Yunnanpriapulus halteroformis Huang et al., 2004) from the Early Cambrian Chengjiang fossil LagerstStte, is revised. Morphological characters comprise a pair of caudal appendages rather than a single appendage flanking the trunk end and a possible urogenital duct found inside the preanal region. An additional extremely rare fossil priapulid worm, Paratubiluchus bicaudatus gen. nov., sp. nov. is also described herein. Its diagnostic characters are: an introvert bearing 25 longitudinal rows of scalids, a distinct neck region, no annulus on the oval trunk, and a pair of caudal appendages. The proportion of body parts is similar in size to that of loricate larvae of Recent priapulids and larva-formed Palaeopriapulitidae. Taking account of the features of Xiaoheiqingella, bicaudal appendages are considered to be a synapomorphy of Priapulidae and Tubiluchidae. Paratubiluchus gen. nov. is most likely a candidate for the ancestor of the Tubiluchidae; it probably originated from a larva-formed priapulid with 25 rows of scalids, thus representing an intermediate link between the priapulids in mature-form and the priapulids with Iorica.

  20. The Vendian (Ediacaran) in the geological record: Enigmas in geology's prelude to the Cambrian explosion

    Science.gov (United States)

    McCall, G. J. H.

    2006-07-01

    Up to the 1950s, the Precambrian was regarded as unrewardingly unfossiliferous, records of fossils being isolated, few in number and dubious. The change came with the discovery by Reg Sprigg of body fossils in latest Proterozoic sediments in South Australia. Although there had been descriptions of isolated fossils (now recognised as Ediacaran) from rocks of this age in the nineteenth century and at the start of the twentieth century, in Newfoundland and Namibia, respectively, the Ediacara finds stimulated researches and now, at the start of the twenty-first century, diversified fossil assemblages are known, all over the world, from the period 600-543 Ma, known formerly as the Vendian and now officially as the Ediacaran. In this account, a brief description of the history of these finds is given, followed by descriptions of the most important provinces [South Australia, Leicestershire, Namibia, Russia (Podolia, the White Sea Coast, Urals and Siberia), Newfoundland (Avalon Peninsula) and Northwest Canada]: then of 27 other known occurrences of this dominantly soft-bodied and perplexing fauna(?)-it seems certain that some, at least of the fossils, are animal fossils, although some, even the greater part, could be a unique form of life, not animals or plants ("Vendobionta"). These descriptions, derived in the course of a literature search lasting over a year, are followed by discussions of important special aspects: trace fossils; geochronology and correlation; geotectonics; glaciation (the "Snowball Earth" concept applied to the Varangian/Laplandian/Marinoan glaciation, which ushered in this last subdivision of the Proterozoic); the evidence for Ediacaran and other life forms existing in the Proterozoic prior to its last, Ediacaran, chronological subdivison; the Vendozoa concept. The last section consists of short summary of conclusions. This text essentially constitutes an objective record of what has been published to 2005 on the Ediacaran System.

  1. Thermoluminescence dating of sediments

    International Nuclear Information System (INIS)

    Thermoluminescence (TL) dating of sediments is based on the observation that exposure of quartz and feldspar to sunlight rapidly reduces the TL level to a small residual value. Therefore, sediments transported by air or water will usually be deposited with a very small TL level. When the sediment has been covered as a result of subsequent sedimentation, the TL level again increases with time as a result of exposure of the minerals to the natural background radiation. The TL level is thus a measure of the accumulated radiation dose (the palaeodose), and the time elapsed since sedimentation is given by the ratio of the palaeodose to the annual dose. Techniques for determining the palaeodose are described including the regeneration, additive dose and R-GAMMA methods. Insufficient bleaching during transport, instability of the latent TL signal and non-linear dose response for older samples pose particular problems which are discussed. In several respects, TL dating of sediments is still at the experimental stage, but the method has a great potential for dating sediments within the last 500,000 years, a period for which there are few other absolute dating methods. (author)

  2. Geochemistry of sediments

    Digital Repository Service at National Institute of Oceanography (India)

    Nath, B.N.

    chemistry, isotope geochemistry, rare-earth element fractionation and patterns to delineate the southern limits of influence of Ganges-Brahmaputra river system are described. Other sources of sediments to the northern and central Indian Ocean identified from...

  3. Offshore Surficial Sediment

    Data.gov (United States)

    California Department of Resources — This data layer (PAC_EXT.txt and PAC_PRS.txt) represents two of five point coverages of known sediment samples, inspections, and probes from the usSEABED data...

  4. Risk management of sediments

    International Nuclear Information System (INIS)

    Sediment management nowadays is often concerned around sediments that have been polluted in former times, posing the following questions: what risks remain after time has passed concerning the persistence, ageing and bioavailability of the polluting substances; where does the risk apply regarding the transport of contaminated sediments and the management objectives in the different zones of a river basin; how can solutions be found; who is responsible for paying the management measures. This publication reflects on the discussions in the SedNet Working Group on risk management and communication claiming that sustainable sediment management needs to be risk based and oriented towards the river basin scale. Results of two case studies are recounted, which roughly followed the site prioritization approach that was suggested by the participants of the working group and gives an example on a decision making module that could help in communicating interests and the resulting priorities of measures, after areas of risks have been identified in a river basin

  5. Sediment Oxygen Demand Kinetics

    OpenAIRE

    Olinde, Lindsay

    2007-01-01

    Hypolimnetic oxygen diffusers increase sediment oxygen demand (SOD) and, if not accounted for in design, can further exacerbate anoxic conditions. A study using extracted sediment cores, that included both field and laboratory experiments, was performed to investigate SOD kinetics in Carvinâ s Cove Reservoir, a eutrophic water supply reservoir for Roanoke, Virginia. A bubble-plume diffuser is used in Carvinâ s Cove to replenish oxygen consumed while the reservoir is thermally stratified. ...

  6. Plutonium in Baltic sediments

    International Nuclear Information System (INIS)

    Marine sediments accumulate the bulk of plutonium produced by nuclear tests. The nuclear power industry will form an additional source of plutonium, and it is important to determine the present background levels of plutonium in sediments and to compare the accumulation rate in the Baltic with that in other areas of the world. Plutonium was determined on four sediment cores collected from the Baltic Sea in 1974 and 1975. Two of the samples were from oxygenated coastal sediment with benthic life and two cores were collected from deep basins in the Baltic at depths of 183 m and 164 m where the bottoms were anoxic, with no benthic life, and where the rate of sedimentation is rather high. Data are presented on the Pu-239,240 content of the sediment cores as is pCi/kg dry wt in the different core sections. The highest plutonium concentrations were found near the surface, at depths of 0 to 8 cm. In all cores the plutonium concentration decreases sharply at a depth of about 6 to 8 cm

  7. Maps showing petroleum exploration intensity and production in major Cambrian to Ordovician reservoir rocks in the Anadarko Basin

    Science.gov (United States)

    Henry, Mitch; Hester, Tim

    1996-01-01

    The Anadarko basin is a large, deep, two-stage Paleozoic basin (Feinstein, 1981) that is petroleum rich and generally well explored. The Anadarko basin province, a geogrphic area used here mostly for the convenience of mapping and data management, is defined by political boundaries that include the Anadarko basin proper. The boundaries of the province are identical to those used by the U.S. Geological Survey (USGS) in the 1995 National Assessment of United Stated Oil and Gas Resources. The data in this report, also identical to those used in the national assessment, are from several computerized data bases including Nehring Research Group (NRG) Associates Inc., Significant Oil and Gas Fields of the United States (1992); Petroleum Information (PI), Inc., Well History Control System (1991); and Petroleum Information (PI), Inc., Petro-ROM: Production data on CD-ROM (1993). Although generated mostly in response to the national assessment, the data presented here arc grouped differently and arc displayed and described in greater detail. In addition, the stratigraphic sequences discussed may not necessarily correlate with the "plays" of the 1995 national assessment. This report uses computer-generated maps to show drilling intensity, producing wells, major fields, and other geologic information relevant to petroleum exploration and production in the lower Paleozoic part of the Anadarko basin province as defined for the U.S. Geological Survey's 1995 national petroleum assessment. Hydrocarbon accumulations must meet a minimum standard of 1 million barrels of oil (MMBO) or 6 billion cubic feet of gas (BCFG) estimated ultimate recovery to be included in this report as a major field or revoir. Mapped strata in this report include the Upper Cambrian to Lower Ordovician Arbuckle and Low Ordovician Ellenburger Groups, the Middle Ordovician Simpson Group, and the Middle to Upper Ordovician Viola Group.

  8. A transgression-regression event during the deposition of the Upper Cambrian Honey Creek formation in the southern Oklahoma aulacogen

    Energy Technology Data Exchange (ETDEWEB)

    McElmoyl, C.; Donovan, R.N. (Texas Christian Univ., Ft. Worth, TX (United States). Geology Dept.)

    1993-02-01

    The transgression that inundated the Southern Oklahoma aulacogen during the upper Cambrian enveloped a landscape that consisted of hills of rhyolite up to 350 m in high. Initial deposits on this topography have been interpreted as alluvium. These, together with succeeding tidally-influenced marine siliciclastics form the Reagan Formation. The siliciclastics grains are made up of fragments of local origin (i.e., rhyolite), quartz (derived from a distal source) and authigenic glauconite. The upward passage from the Reagan to the Honeycreek Formation is defined by the addition to the siliciclastics of carbonate detritus in the form of tidally-influenced grainstones, mostly composed of pelmatozoan fragments. The passage from the Honeycreek to the overlying Fort Sill Formation of the Arbuckle Group is marked by the incoming of beds of lime mudstone and the gradual disappearance of grainstones and siliciclastics. Evidence of the existence of rhyolite topography (i.e., an archipelago) can be detected to within 50 m of the top of the Fort Sill. While the overall facies pattern undoubtedly records a widespread transgression, a newly-discovered slightly angular unconformity within the lower part of the Honeycreek is best interpreted as a record of a temporary regression. Three distinctive lithologies are involved in this relationship: the lowest beds are light grey cross-bedded pelmatozoan grainstones with minor amounts of quartz and rhyolite grains. Syntaxial cements at the base of this unit are homogenous under cathode luminescence, while cements near the top display up to 27 zones of reflectance, interpreted as a fluctuating marine-meteoric groundwater imprint. The overlying bed is a red-brown mud-supported limestone that contains abundant angular rhyolite pebbles and a rich trilobite fauna. Some of the pebbles are coated by pelmatozoans.

  9. Cambrian Magmatism Along the Southern Laurentian Margin: New Petrologic Constraints from Well Cuttings in the Southern Oklahoma Aulacogen (USA)

    Science.gov (United States)

    Hobbs, J. M.; Brueseke, M. E.; Mertzman, S. A.; Puckett, R. E., Jr.

    2014-12-01

    Magmatism in the Southern Oklahoma aulacogen (SOA) is associated with >250,000 km3 of early Cambrian aged mafic-silicic intrusives and effusive products possibly related to the opening of the Iapetus Ocean. In the vicinity of the Arbuckle Mts., thick mafic to intermediate lava packages interbedded with rhyolite lavas and sedimentary strata are exposed in the subsurface and penetrated by oil and gas exploration wells. We have sampled cuttings from six wells exposed along the strike of the SOA with the aim of petrographically, geochemically, and isotopically characterizing the rocks to better understand their tectonomagmatic affinity. Cuttings were observed under a binocular microscope to ensure textural homogeneity; XRF bulk chemistry from these samples show that they are relatively unaltered based on analytical totals and alteration indices. The samples plot as basalts to andesites (e.g., 47-64 wt. % SiO2) and are primarily tholeiitic. On discrimination diagrams, these samples fall in "intraplate" fields, consistent with continental basalt volcanism, including flood basalt eruptions. These lavas show Zr/Nb values ranging from 6.8 to 11.1, K/Nb values ranging from 300-600, and Ba/Nb values ranging from 10-20, which are similar to EM1 OIB. The samples also show trace element patterns consistent with OIB-like mantle sources when normalized to primitive mantle, and similar geochemical traits to the Roosevelt Gabbros that crop out along strike of the SOA in the Wichita Mts.. Sr, Nd, and Pb isotope analysis is ongoing. Chemostratigraphic variations show the possibility of several lava packages. The geochemical analyses of the SOA lava flows provide insight into how these magmas formed as well as what tectonic regime (e.g., lower-mantle derived plume, upper-mantle extension, or "leaky" transform fault) produced the volcanism that affected the southern margin of Laurentia during the formation of the SOA; we favor the involvement of a deep mantle plume.

  10. 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

  11. 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 Thorshoj

    2014-01-01

    A newly collected trilobite fauna from the lowermost part of the Alum Shale Formation at Øleå, Bornholm, Denmark, demonstrates the presence of a thin but richly fossiliferous Middle Cambrian Acidusus atavus Zone (Paradoxides paradoxissimus Superzone). The lower part of the zone (the Tomagnostus...... designation and reillustration of relevant lectotypes. The abundance of polymerid trilobites in comparison with nearby Scania, southern Sweden, where 25 agnostid and nine polymerid species have been reported from equivalent strata, is indicative of a less dysoxic environment in the Bornholm area, which was...

  12. Limitations of metazoan 18S rRNA sequence data : implications for reconstructing a phylogeny of the animal kingdom and inferring the reality of the cambrian explosion

    OpenAIRE

    Abouheif, Ehab; Zardoya, Rafael; Meyer, Axel

    1998-01-01

    We document the phylogenetic behavior of the 18S rRNA molecule in 67 taxa from 28 metazoan phyla and assess the effects of among-site rate variation on reconstructing phylogenies of the animal kingdom. This empirical assessment was undertaken to clarify further the limits of resolution of the 18S rRNA gene as a phylogenetic marker and to address the question of whether 18S rRNA phylogenies can be used as a source of evidence to infer the reality of a Cambrian explosion. A notable degree of am...

  13. Evaluating the primary and/or diagenetic origin of rare earth element abundances in Ediacaran to early Cambrian phosphate deposits, Yangtze Platform (South China) by LA-ICPMS

    Science.gov (United States)

    Hippler, Dorothee; Klügel, Andreas; Biedermann, Nicole; Guo, Qingjun; Franz, Gerhard

    2014-05-01

    The Precambrian-Cambrian time interval represents one of the greatest phosphogenic episodes in Earth's history with giant and well-preserved phosphate deposits occurring on the Yangtze Platform in South China. We investigated concentrations of rare earth elements (REE) and yttrium of shallow and deep-water sedimentary phosphate deposits of the Ediacaran Doushantou Formation and the early Cambrian Zhongyicun Formation by using LA-ICP mass spectrometry. The aim is to examine the temporal and spatial variability of seawater chemistry in conjunction with the conditions of phosphate formation and the evaluation of the extent of diagenetic modification. The mineralogical and textural composition of the samples was pre-screened using SEM and XRD, and polished thick sections were prepared for subsequent high-resolution LA-ICPMS analyses. Overall concentrations in REE range between 18 and 657 ppm, with elevated concentrations (> 200 ppm) in apatite from the deep-water phosphate deposits. REE+Y patterns of shallow-water phosphate deposits exhibit the evolution from flat shale-like to gently inclined seawater-derived patterns, with the early Cambrian phosphate deposits revealing distinct negative Ce- and positive Y-anomalies indicative for oxygenated surface waters. REE+Y patterns of phosphate deposits of the deep-water facies are flat to highly enriched in MREE, which is manifested in variably pronounced concave-down patterns. In detail, these patterns display different Ce-anomalies, as well as small positive Eu-anomalies. We propose that REE+Y patterns of Ediacaran and early Cambrian sedimentary phosphate deposits can inherit both primary and secondary signatures reflecting either seawater composition or diagenetic modification and fluid flow. The combination of imaging techniques and in-situ LA-ICPMS thereby enables a more sophisticated examination of the potential sources and processes than whole rock determinations. Placing the results in stratigraphic order and assuming

  14. 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).

  15. Influenza-Sediment Interactions

    Science.gov (United States)

    Trusiak, A.; Block, K. A.; Katz, A.; Gottlieb, P.; Alimova, A.; Galarza, J.; Wei, H.; Steiner, J. C.

    2013-12-01

    A typical water fowl can secrete 1012 influenza virions per day. Therefore it is not unexpected that influenza virions interact with sediments in the water column. The influence of sediments on avian influenza virions is not known. With the threat of avian influenza emerging into the human population, it is crucial to understand virus survivability and residence time in a body of water. Influenza and clay sediments are colloidal particles and thus aggregate as explained by DLVO (Derjaguin & Landau, Verwey & Overbeek) theory. Of great importance is an understanding of the types of particulate or macromolecular components that bind the virus particles, and whether the virus remains biologically active. We present results of hetero-aggregation and transmission electron microscopy experiments performed with influenza A/PR8/38. Influenza particles are suspended with sediment and minimal nutrients for several days, after which the components are evaluated to determine influenza concentration and survivability. Transmission electron microscopy results are reported on the influenza-sediment aggregates to elucidate structure and morphology of the components.

  16. The oceanic sediment barrier

    International Nuclear Information System (INIS)

    Burial within the sediments of the deep ocean floor is one of the options that have been proposed for the disposal of high-level radioactive waste. An international research programme is in progress to determine whether oceanic sediments have the requisite properties for this purpose. After summarizing the salient features of this programme, the paper focuses on the Great Meteor East study area in the Northeast Atlantic, where most oceanographic effort has been concentrated. The geological geochemical and geotechnical properties of the sediments in the area are discussed. Measurements designed to determine the rate of pore water movement through the sediment column are described. Our understanding of the chemistry of both the solid and pore-water phases of the sediment are outlined, emphasizing the control that redox conditions have on the mobility of, for example, naturally occurring manganese and uranium. The burial of instrumented free-fall penetrators to depths of 30 m beneath the ocean floor is described, modelling one of the methods by which waste might be emplaced. Finally, the nature of this oceanic environment is compared with geological environments on land and attention is drawn to the gaps in our knowledge that must be filled before oceanic burial can be regarded as an acceptable disposal option. (author)

  17. Transport Model of Underground Sediment in Soils

    OpenAIRE

    Sun Jichao; Wang Guangqian

    2013-01-01

    Studies about sediment erosion were mainly concentrated on the river channel sediment, the terrestrial sediment, and the underground sediment. The transport process of underground sediment is studied in the paper. The concept of the flush potential sediment is founded. The transport equation with stable saturated seepage is set up, and the relations between the flush potential sediment and water sediment are discussed. Flushing of underground sediment begins with small particles, and large pa...

  18. Petrophysics of Palaeogene sediments

    DEFF Research Database (Denmark)

    Awadalkarim, Ahmed

    ) the siliceous ooze sediments from the Norwegian Sea, and 3) the Palaeogene shale from both the Atlantic and the Danish basins. The three geological settings differ in water depths, temperature, effective stress and pressure. If the factors governing physical properties of the studied lithologies are...... predict the geomechanical behaviour of shale. Biot’s coefficient (β) for elastic deformation is an important parameter involves in the estimation of effective stress. However, engineers usually assume β equal to one when estimating in-situ vertical effective stress on buried sediments, but, this...... especially on deep-sea sediments; to establish a relationship between static and dynamic modulus of shale which could be used to estimate geotechnical drained elastic modulus from bulk density and sonic velocity. The influence of burial depth on physical properties of Atlantic Palaeogene shale and Eocene...

  19. Correlation for aerosol sedimentation

    International Nuclear Information System (INIS)

    The fission product source term from a postulated light water reactor (LWR) accident has several components. One of these components is the suspended aerosols present in the atmosphere during containment degradation and failure. Sedimentation, inertial impaction, and Stefan-Nusselt flows are the dominant natural removal mechanisms in the containment atmosphere for the majority of the postulated LWR severe accidents. The sedimentation correlation described was developed for conditions applicable to the primary coolant system and containment under severe accident conditions. The correlation exists as a result of a unique nondimensional mass concentration versus nondimensional particle volume

  20. Sediment trap methodology

    International Nuclear Information System (INIS)

    The processes by which dissolved pollutants from atmospheric or tributary inputs are deposited in local regions of the bottom sediments of Lake Michigan are known only in part. Settling particulate material must play a major role in these processes, but sediment traps have been used only rarely in the Great Lakes. The trap and mooring designs developed during the plutonium study in Lake Michigan are presented, and the experience with their use is summarized. the traps used were right circular cylinders, and the mooring arrangement an adaptation of the U system often used in current-meter studies

  1. An Ediacaran–Cambrian thermal imprint in Rajasthan, western India: Evidence from 40Ar-39Ar geochronology of the Sindreth volcanics

    Indian Academy of Sciences (India)

    Archisman Sen; Kanchan Pande; Hetu C Sheth; Kamal Kant Sharma; Shraboni Sarkar; A M Dayal; Harish Mistry

    2013-12-01

    The Sindreth Group exposed near Sirohi in southern Rajasthan, western India, is a volcanosedimentary sequence. Zircons from Sindreth rhyolite lavas and tuffs have yielded U–Pb crystallization ages of ∼768–761 Ma, suggesting that the Sindreth Group is a part of the Malani magmatic event. Earlier 40Ar-39Ar studies of other Malani volcanic and plutonic rocks yielded disturbed argon release spectra, ascribed to a ∼550 Ma thermal event possibly related to the Pan-African orogeny. To test and confirm this possibility, we dated two whole-rock and three feldspar separate samples of the Sindreth volcanics by the 40Ar-39Ar method. All samples yield disturbed argon release spectra suggesting radiogenic argon loss and with plateau segments at 550 Ma or 490 Ma. We interpret these as events of argon loss at 550–490 Ma related to an Ediacaran–Cambrian thermal event, possibly related to the Malagasy orogeny. The combined older and new 40Ar-39Ar results are significant in showing that whereas Ediacaran–Cambrian magmatic and metamorphic events are well known from many parts of India, they left thermal imprints in much of Trans-Aravalli Rajasthan as well. The overall evidence is consistent with a model of multiphase assembly of Gondwanaland from separate continental landmasses.

  2. Phosphatized rare star-like mouth disc of Punctatus and its functional morphology from the earliest Cambrian of the South Shaanxi China

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The Meishucun stage is the prelude in decipher-ing the Cambrian Explosion. In this prominent stage, rapid radioactive evolution and body-plan innovation have taken place and different associations of organism have been shaped. In this paper we report several 3D-preserved rare star-like fossils with finely preserved soft tissues which were recovered from the Kuanchuanpu Member of the Dengying Formation in South Shaanxi, China in 2003. By studying on functional morphology and analogy with mouthpart of Punctatus, there are evidences that this star-like organism approaches the coelenterates in systematic classification and the centre of star-like organism is its mouth. The appearance of coelenterates marks the real beginning of metazoan evolution. Therefore, it has the prominent position in the origin and evolutionary history of organisms. Perhaps the star-like organism represents the early types of coelenterate with original tentacles. These new materials provide new evidence for the origin, evolution and the functional evolution of the metazoan during the early stage of the Cambrian Explosion.

  3. Research progress and prospects of Cambrian medusae from South China%寒武纪水母化石研究现状与展望

    Institute of Scientific and Technical Information of China (English)

    韩健; 李国祥; 久保田信; 王星; 欧强

    2014-01-01

    We introduced the fossil records of medusa in brief and discussed the radial symmetry, body plan, life history, and exoskeleton of ancestral medusae. It is hypothesized that major clades of superclass medusa should have derived prior to that of ballerinas at the dawn of Cambrian explosion. The Cambrian medusae should be classified as sessile benthic and pelagic forms.%简述了水母的早期化石记录,并根据华南寒武系发现的立方水母干群化石,讨论了祖先型水母的辐射对称、躯体构型、生活史、生活习性,以及外骨骼的形成特征,推测水母类在寒武纪大爆发初期先于两侧对称动物基本完成其高级分类单元的宏演化。寒武纪的水母在生活习性上可以分为底栖固着型和游泳型两种。

  4. Elasto-Plastic Constitutive Behavior in Three Lithofacies of the Cambrian Mt. Simon Sandstone, Illinois Basin, USA

    Science.gov (United States)

    Dewers, T.; Newell, P.; Broome, S. T.; Heath, J. E.; Bauer, S. J.

    2012-12-01

    The Mt. Simon Formation, a basal Cambrian sandstone underlying the Illinois Basin in the Central US, is a target for underground storage and waste injection which require an assessment of geomechanical behavior. The range of depositional environments, from braided streams and minor eolean features in the lower Mt Simon, to tidally-influenced near- and on-shore sands in the upper Mt. Simon, yield a heterogeneous formation with a range in porosity, permeability, and mechanical properties. We examine the experimental deformational behavior of three distinct Mt. Simon lithofacies via axisymmetric compressional testing. Initial yielding is confirmed with acoustic emissions in many of the tests and failure envelopes are determined for each lithofacies. The evolution of (assumed) isotropic elastic moduli are examined during testing by use of unload-reload cycles, which permit the separation of total measured strains into elastic and plastic (permanent) strains. The upper Mt Simon samples deform largely elastically at stresses encountered in the Illinois Basin, with very little modulus degradation. The lower Mt. Simon facies are weaker and deform plastically, with varying amounts of modulus degradation. Results are interpreted via petrographic observation of textural contrasts. This range in constitutive response is captured up to failure with a phenomenological elasto-plasticity model. Essential aspects to describe observed behavior used in the model include non-associative plasticity, stress-invariant dependent failure, an elliptical cap surface capturing shear effects on pore collapse, kinematic and isotropic hardening, nonlinear elasticity and elastic-plastic coupling, among other features. Static moduli derived from laboratory tests are compared to dynamic moduli from wellbore log response which can allow experimental results and model to be extrapolated to Mt. Simon occurrences across the basin. This work was funded in part by the Center for Frontiers of Subsurface

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

    Directory of Open Access Journals (Sweden)

    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

  6. Contaminated Aquatic Sediments.

    Science.gov (United States)

    Jaglal, Kendrick

    2016-10-01

    A review of the literature published in 2015 relating to the assessment, evaluation and remediation of contaminated aquatic sediments is presented. The review is divided into the following main sections: policy and guidance, methodology, distribution, fate and transport, risk, toxicity and remediation. PMID:27620103

  7. Soils and organic sediments

    International Nuclear Information System (INIS)

    The organic component of soils is basically made up of substances of an individual nature (fats, waxes, resins, proteins, tannic substances, and many others), and humic substances (Kononova, 1966). These are complex polymers formed from breakdown products of the chemical and biological degradation of plant and animal residues. They are dark coloured, acidic, predominantly aromatic compounds ranging in molecular weight from less than one thousand to tens of thousands (Schnitzer, 1977). They can be partitioned into three main fractions:(i) Humic acid, which is soluble in dilute alkaline solution, but can be precipitated by acidification of the alkaline extract.(ii) Fulvic acid, which is soluble in alkaline solution, but is also soluble on acidification.(iii) Humin that cannot be extracted from the soil or sediment by dilute acid or alkaline solutions. It has mostly been assumed that the humic and fulvic acid components of the soil are part of the mobile, or 'active' component, and the humin component is part of the 'passive' component. Other types of organic sediments are likely to contain chemical breakdown products of plant material, plant fragments and material brought in from outside sources. The outside material can be contemporaneous with sediment deposition, can be older material, or younger material incorporated into the sediment long after deposition. Recognition of 'foreign' material is essential for dating, but is not an easy task. Examples of separation techniques for humic and non humic components are evaluated for their efficiency

  8. Sediment Erosion in Hydro turbines

    OpenAIRE

    Neopane, Hari Prasad

    2010-01-01

    Sediment erosion is caused by the dynamic action of sediment flowing along with water impacting against a solid surface. Hydraulic turbine components operating in sediment-laden water are subject to abrasive and erosive wear. This wear not only reduces the efficiency and the life of the turbine but also causes problems in operation and maintenance, which ultimately leads to economic losses. This is a global operation and maintenance problem of hydropower plants. The high sediment concentratio...

  9. Cable Bacteria in Freshwater Sediments

    OpenAIRE

    Risgaard-Petersen, Nils; Kristiansen, Michael; Frederiksen, Rasmus B.; Dittmer, Anders Lindequist; Bjerg, Jesper Tataru; Trojan, Daniela; Schreiber, Lars; Damgaard, Lars Riis; Schramm, Andreas; Nielsen, Lars Peter

    2015-01-01

    In marine sediments cathodic oxygen reduction at the sediment surface can be coupled to anodic sulfide oxidation in deeper anoxic layers through electrical currents mediated by filamentous, multicellular bacteria of the Desulfobulbaceae family, the so-called cable bacteria. Until now, cable bacteria have only been reported from marine environments. In this study, we demonstrate that cable bacteria also occur in freshwater sediments. In a first step, homogenized sediment collected from the fre...

  10. The sediment delivery problem revisited

    OpenAIRE

    de Vente, Joris; Poesen, Jean; Arabkhedri, M; Verstraeten, Gert

    2007-01-01

    Understanding the sediment delivery process at the drainage basin scale remains a challenge in erosion and sedimentation research. In the absence of reliable spatially distributed process-based models for the prediction of sediment transport at the drainage basin scale, area-specific sediment yield (SSY, t km(-2) y(-1)) is often assumed to decrease with increasing drainage basin area (A). As the measurement of A is relatively simple, this assumption is frequently used for prediction of SSY in...

  11. Terminal suturing of Gondwana along the southern margin of South China Craton: Evidence from detrital zircon U-Pb ages and Hf isotopes in Cambrian and Ordovician strata, Hainan Island

    Science.gov (United States)

    Xu, Yajun; Cawood, Peter A.; Du, Yuansheng; Zhong, Zengqiu; Hughes, Nigel C.

    2014-12-01

    Hainan Island, located near the southern end of mainland South China, consists of the Qiongzhong Block to the north and the Sanya Block to the south. In the Cambrian, these blocks were separated by an intervening ocean. U-Pb ages and Hf isotope compositions of detrital zircons from the Cambrian succession in the Sanya Block suggest that the unit contains detritus derived from late Paleoproterozoic and Mesoproterozoic units along the western margin of the West Australia Craton (e.g., Northampton Complex) or the Albany-Fraser-Wilkes orogen, which separates the West Australia and Mawson cratons. Thus, in the Cambrian the Sanya Block was not part of the South China Craton but rather part of the West Australian Craton and its environs. In contrast, overlying Late Ordovician strata display evidence for input of detritus from the Qiongzhong Block, which constituted part of the southeastern convergent plate margin of the South China Craton in the early Paleozoic. The evolving provenance record of the Cambrian and Ordovician strata suggests that the juxtaposition of South China and West Australian cratons occurred during the early to mid-Ordovician. The event was linked with the northern continuation of Kuungan Orogeny, with South China providing a record of final assembly of Gondwana.

  12. A review of undulated sediment features on Mediterranean prodeltas: distinguishing sediment transport structures from sediment deformation

    OpenAIRE

    Urgeles, Roger; Cattaneo, Antonio; PUIG Pere; Liquete, Camino; Mol, Ben; Amblas, David; Sultan, Nabil; Trincardi, Fabio

    2011-01-01

    Most Mediterranean prodeltas show undulated sediment features on the foresets of their Holocene wedges. These features have been described all along the Mediterranean for the last 30 years and interpreted as either soft sediment deformation and incipient landsliding, and more recently, as sediment transport structures. We perform a review and detailed analysis of these undulated sediment features using ultrahigh-resolution seismic and bathymetric data as well as geotechnical information and h...

  13. A discussions on the Cryogenian-Cambrian tectonic-sedimentary event and tectonic setting of northern Tarim Basin%塔里木盆地北缘南华纪—寒武纪构造背景及构造-沉积事件探讨

    Institute of Scientific and Technical Information of China (English)

    周肖贝; 李江海; 傅臣建; 李文山; 王洪浩

    2012-01-01

    Based on field geological investigation in northwestern and northeastern Tarim Basin, in combination with paleomagnetic mapping and previous researches, this paper has discussed the evolution process of the basin in Cryogenian-Cambrian period according to sedimentary-tectonic event and other evidence. Across the Tarim Basin, surface outcrops of Cryogenian to Cambrian sedimentary succession are completely exposed in the vicinity of Aksu area (northwest Tarim), Kuruktag (northeast Tarim) and southwest Tarim, thus providing a unique, well preserved and accessible means with which researchers can study the early development of northern Tarim Basin. The major lithologic types of Cryogenian-Cambrian strata in northeast Tarim include tillite, clastic rocks (rich in organic matter) and carbonate intercalated with volcanic rocks; in northwest Tarim, calstic rocks and carbonate are the common rock types, intercalated with small amounts of tillite and volcanic rocks. The north margin of Tarim block, which was a part of Rodinia supercontinent and neighbored the northwestern margin of Australia, was deeply rifted in Cryogenian-Ediacaran period and developed into two rifts in the northwestern and northeastern margin, forming a thick layer of rift-passive margin deposits, but the layer in the northwestern rift was not so completely developed as the layer in the northeastern margin. The earliest rift-passive margin sediments which can be observed are Cryogenian-Middle Ordovician strata, and the period can be divided into Cryogenian faulted period (supercontinent rifting stage) and Ediacaran-Middle Ordovician subsidence period (plate drifting stage).%以塔里木盆地西北缘和东北缘南区南华系—寒武系野外地质调查为基础,结合古地磁成图及前人研究资料,针对构造-沉积事件等探讨盆地北缘南华纪—寒武纪成盆演化过程.研究区保存了完整的南华纪—寒武纪地层,其中塔东北缘以冰碛岩、碎屑岩(富含有机

  14. Sediment problems in reservoirs. Control of sediment deposits

    Energy Technology Data Exchange (ETDEWEB)

    Jacobsen, Tom

    1997-12-31

    When a reservoir is formed on a river, sediment will deposit in the reservoir. Such processes are unfortunate, for instance, for the implementation of hydroelectric energy. This thesis studies the problem of reservoir sedimentation and discusses methods of removing the sediments. Various aspects of reservoir sedimentation are discussed. Anthropogenic impacts seem to greatly affect the erosion processes. Temporal distribution is uneven, mainly because of the very large flood events. A world map showing the Reservoir Capacity: Annual Sediment Inflow ratio for reservoirs with volume equal to 10% of annual inflow has been prepared. The map shows that sedimentation is severe in the western parts of North and South America, eastern, southern and northern Africa, parts of Australia and most of Asia. The development of medium-sized reservoirs is difficult, as they are too large for conventional flushing technique and too small to store the sediment that accumulates during their economic lifetime. A computer model, SSIIM, was used with good results in a case study of two flood drawdown trials in Lake Roxburg, New Zealand. Two techniques have been developed that permits controlled suction of sediment and water into a pipe: the Slotted Pipe Sediment Sluicer (SPSS) and the Saxophone Sediment Sluicer (SSS). The techniques exploit the inflow pattern in through a slot in a pipe. An equation describing this inflow pattern was derived and verified experimentally. The SPSS is fixed near the reservoir bed, and sediment that deposits on top of it is removed in the sluicing process. The SSS sluices sediment from the surface of the sediment deposits. Some technical and economic conditions affecting the economics of sediment removal from reservoirs have been identified and studied. 79 refs., 112 figs., 14 tabs.

  15. Cambrian intermediate-mafic magmatism along the Laurentian margin: Evidence for flood basalt volcanism from well cuttings in the Southern Oklahoma Aulacogen (U.S.A.)

    Science.gov (United States)

    Brueseke, Matthew E.; Hobbs, Jasper M.; Bulen, Casey L.; Mertzman, Stanley A.; Puckett, Robert E.; Walker, J. Douglas; Feldman, Josh

    2016-09-01

    The Southern Oklahoma Aulocogen (SOA) stretches from southern Oklahoma through the Texas panhandle and into Colorado and New Mexico, and contains mafic through silicic magmatism related to the opening of the Iapetus Ocean during the early Cambrian. Cambrian magmatic products are best exposed in the Wichita Mountains (Oklahoma), where they have been extensively studied. However, their ultimate derivation is still somewhat contentious and centers on two very different models: SOA magmatism has been suggested to occur via [1] continental rifting (with or without mantle plume emplacement) or [2] transform-fault related magmatism (e.g., leaky strike-slip faults). Within the SOA, the subsurface in and adjacent to the Arbuckle Mountains in southern Oklahoma contains thick sequences of mafic to intermediate lavas, intrusive bodies, and phreatomagmatic deposits interlayered with thick, extensive rhyolite lavas, thin localized tuffs, and lesser silicic intrusive bodies. These materials were first described in the Arbuckle Mountains region by a 1982 drill test (Hamilton Brothers Turner Falls well) and the best available age constraints from SOA Arbuckle Mountains eruptive products are ~ 535 to 540 Ma. Well cuttings of the mafic through intermediate units were collected from that well and six others and samples from all but the Turner Falls and Morton wells are the focus of this study. Samples analyzed from the wells are dominantly subalkaline, tholeiitic, and range from basalt to andesite. Their overall bulk major and trace element chemistry, normative mineralogy, and Srsbnd Nd isotope ratios are similar to magmas erupted/emplaced in flood basalt provinces. When compared with intrusive mafic rocks that crop out in the Wichita Mountains, the SOA well cuttings are geochemically most similar to the Roosevelt Gabbros. New geochemical and isotope data presented in this study, when coupled with recent geophysical work in the SOA and the coeval relationship with rhyolites, indicates

  16. Algal stabilisation of estuarine sediments

    International Nuclear Information System (INIS)

    The presence of benthic microalgae can increase the stability of intertidal sediments and influence sediment fluxes within an estuarine environment. Therefore the relative importance of algal stabilisation needs to be understood to help predict the effects of a tidal barrage. The biogenic stabilisation of intertidal estuarine sediments by epipelic diatom films and the macrophyte Vaucheria was studied at three sites on the Severn Estuary. The cohesive strength meter (CSM) was developed to measure surface critical shear stress with varied algal density. A number of techniques have been used to determine the general in situ erodibility of cohesive estuarine sediments. The measurements of sediment shear strength and critical erosion velocity were investigated. Field experiments were undertaken to investigate the effect of algae on binding sediments, and a predictive method for the assessment of sediment stabilisation by algal binding was developed. (author)

  17. Sediments of Ypacarai Lake

    International Nuclear Information System (INIS)

    Bottom and sestonic sediments of Ypacarai Lake were investigated with XRF and Moessbauer techniques. The 120 km2 lake, depth averages 1.8 m. In addition to the lakes use for recreation, its basin has economic significance. Sediments play an important role in the distribution of trace elements in the aquatic system and as a sink for metals. Bottom and seston samples were taken from 4 different sampling stations which were selected according the morphology and population sites on the shore. The concentration of toxic metals was found to be low and no adverse ecological impact should be expected. The main metallic ion component is iron (1.68%). Moessbauer studies showed this element appears as Fe3+. Iron2+ was not detected. We suggest that Fe3+ acts as the limiting element which controls the eutrophication process. (author) 13 refs.; 2 tabs

  18. Alluvial-eolian interaction in a Cambrian rift margin: the Pedra das Torrinhas and Pedra Pintada formations (Guaritas Group, RS

    Directory of Open Access Journals (Sweden)

    André Marconato

    2009-12-01

    Full Text Available This work presents a study of selected outcrops from the Pedra das Torrinhas Formation of the Guaritas Group (Cambrian, Camaquã Basin, near the basin bordering Encantadas Fault Zone. The studied succession includes alluvial fan deposits that pass laterally into eolian deposits. Sedimentary facies and architectural element analysis were performed, followed by sedimentary petrography and microscopic porosity analysis, aiming to characterize the porosity of the deposits and its spatial distribution. The main objective was to contribute to a better understanding of the porosity spatial distribution in depositional systems characterized by the interaction between alluvial and eolian processes, with special reference to deposits formed prior to the development of terrestrial plants. Porosity values are related to depositional processes, with higher porosities associated to eolian dune deposits (mean of 8.4%, and lower porosity related to interdunes (mean of 3.4% and alluvial fans (mean of 4.3%. Architectural elements analysis revealed the spatial relationships of these deposits, a response to the interplay of the eolian and alluvial processes. The integration of porosity data reveals that the interaction of alluvial and eolian processes results in heterogeneous distribution of porosity at the facies association scale. Eolian reworking of alluvial facies increases porosity whereas sheet-flood and other alluvial processes in the interdune areas reduce porosity.O presente trabalho consiste no estudo de afloramentos da Formação Pedra das Torrinhas do Grupo Guaritas (Cambriano, Bacia Camaquã, próximo à Zona de Falha das Encantadas. As sucessões estudadas incluem depósitos de leques aluviais que passam lateralmente para depósitos eólicos. Foram realizadas análises de fácies e de elementos arquiteturais, seguidos de petrografia sedimentar e análise microscópica de porosidade, com o objetivo de caracterizar a porosidade da unidade e sua

  19. Two new species of Vestrogothia (Phosphatocopina, Crustacea) of Orsten-type preservation from the Upper Cambrian in western Hunan, South China

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Although fossils of Orsten-type preservation represented by Skaracarida and Phosphatocopina were first reported from the Middle and Upper Cambrian in western Hunan, South China in 2005, diversified phosphatocopine species have never been appropriately described and elucidated in terms of their evolutionary relationships. Here, we described two new species of Phosphatocopina, Vestrogothia anterispinata sp. nov. and V. bispinata sp. nov. The evolutionary relationship among all the valid species of Phosphatocopina is discussed and the phylogeny of Phosphatocopina is reestablished using cladistic analysis. Accordingly, phosphatocopines primitively evolved along two lineages: one evolved towards the emergence of lobes; the other evolved towards the emergence of dorsal spines. Respectively, lobes originated independently three times, and dorsal spines originated only once. With regard to the dorsal rims, interdorsum originated first, whereas dorsal furrow originated independently twice on the basis of interdorsum. Probably Hesslandona may represent a polyphyletic group, whereas Vestrogothia a monophyletic group.

  20. A comparison of the biological,geological events and environmental backgrounds between the Neoproterozoic-Cambrian and Permian-Triassic transitions

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The Neoproterozoic-Cambrian(N-C) and Permian-Triassic(P-T) transitions have been regarded the two most critical transitions in earth history because of the explosive biological radiation in the early Cambrian(the Cambrian Explosion) and the largest mass extinction at the end-Permian.Previous studies suggest that these two critical transitions showed certain comparability in major evolutionary events.In other words,a series of biological,geological,and geochemical events that had happened in the N-C transition occurred repeatedly during the P-T transition.Those events included continental re-configuration related to the deep mantle dynamics,global-scale glaciations,large C-,Sr-,and S-isotope perturbations indicating atmospheric and oceanic changes,abnormal precipitation of carbonates,and associated multiple biological radiations and mass extinctions.The coupling of those events in both N-C and P-T transitions suggests that deep mantle dynamics could be a primary mechanism driving dramatic changes of environment on the earth’s surface,which in turn caused major biological re-organizations.A detailed comparison of those events during the two critical transitions indicates that despite their general comparability,significant differences do exist in magnitude,duration,and frequency.The supercontinent Rodinia began to rift before the Snowball Earth time.By contrast,the supercontinent Pangea entered the dispersal stage after the greatest glaciation from the Late Carboniferous to Cisuralian.Quantitative data and qualitative analyses of different fossil groups show a more profound mass extinction during the N-C transition than at the end-Permian in terms of ecosystem disruption.This is indicated by the disappearance of the whole Ediacaran biota at the N-C boundary.The subsequent appearances of many new complex animals at phylum level in the early Cambrian mark the establishment of a brand new ecosystem.However,the end-Permian mass extinction is manifested mainly by the

  1. The origin of life near deep-sea hydrothermal systems during the Cambrian explosion: data from the Kyzyl Tashtyg sulphide deposit (Central Asia)

    Science.gov (United States)

    Simonov, Vladimir; Terleev, Alexander; Safonova, Inna; Kotlyarov, Alexey; Stupakov, Sergey; Tokarev, Dmitry

    2015-04-01

    On Earth the solar radiation and the hydrothermal circulation both affect life evolution. Recent extensive studies of the World Ocean have shown that the biodiversity of Earth is linked with hydrothermal activity on the oceanic floor. These deep-sea ecosystems use chemical energy, not solar radiation. In the last quarter of the XX century, a new type of hydrothermal systems, so-called black smokers, was discovered in mid-oceanic ridges. As black smokers form sulfide ores and are surrounded by abundant bio-oases or symbioses, identification of their analogues in ancient orogenic belts is necessary for studying life origin and evolution. Of special importance are problems of life associated with deep-sea hydrothermal systems acted at the Precambrian-Cambrian boundary - the time of Cambrian explosion (Maruyama et al., 2013). During that explosion life significantly evolved and diversified due to dramatic changes of Earth's environment. Consequently, the early Cambrian - late Precambrian Kyzyl Tashtyg sulphide deposit of East Tuva in the Central Asian Orogenic Belt is of special interest. This deposit was formed on the bottom of ancient back-arc deep-sea basin as a result of black smoker hydrothermal activity and is hosted by volcanogenic-sedimentary rocks altered by the high temperature solutions. The altered Kyzyl Tashtyg basalts have an amygdules (filled by albite, epidote and carbonates), contain brown-green microfossils, often attached to their walls. The microfossils are thin tubes 5 to 25 microns in diameter and 500 microns long. This tubes are empty and have straight, curved or branching shape. Chemically, the tube material is close to epidote. In consideration of microscopic dimensions, simple morphology and similarity with modern tubular microorganisms, the studied tube-shaped microfossils can be related to cyanobacteria. Almost the same fossils, associated with oceanic basalt complexes, were described earlier (Furnes et al., 2007; Mcloughlin et al., 2007

  2. 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.

  3. Sediment management for reservoir

    International Nuclear Information System (INIS)

    All natural lakes and reservoirs whether on rivers, tributaries or off channel storages are doomed to be sited up. Pakistan has two major reservoirs of Tarbela and Managla and shallow lake created by Chashma Barrage. Tarbela and Mangla Lakes are losing their capacities ever since first impounding, Tarbela since 1974 and Mangla since 1967. Tarbela Reservoir receives average annual flow of about 62 MAF and sediment deposits of 0.11 MAF whereas Mangla gets about 23 MAF of average annual flows and is losing its storage at the rate of average 34,000 MAF annually. The loss of storage is a great concern and studies for Tarbela were carried out by TAMS and Wallingford to sustain its capacity whereas no study has been done for Mangla as yet except as part of study for Raised Mangla, which is only desk work. Delta of Tarbala reservoir has advanced to about 6.59 miles (Pivot Point) from power intakes. In case of liquefaction of delta by tremor as low as 0.12g peak ground acceleration the power tunnels I, 2 and 3 will be blocked. Minimum Pool of reservoir is being raised so as to check the advance of delta. Mangla delta will follow the trend of Tarbela. Tarbela has vast amount of data as reservoir is surveyed every year, whereas Mangla Reservoir survey was done at five-year interval, which has now been proposed .to be reduced to three-year interval. In addition suspended sediment sampling of inflow streams is being done by Surface Water Hydrology Project of WAPDA as also some bed load sampling. The problem of Chasma Reservoir has also been highlighted, as it is being indiscriminately being filled up and drawdown several times a year without regard to its reaction to this treatment. The Sediment Management of these reservoirs is essential and the paper discusses pros and cons of various alternatives. (author)

  4. APPLICABILITY OF SEDIMENT TRANSPORT FORMULAS

    Institute of Scientific and Technical Information of China (English)

    Chih Ted YANG; Caian HUANG

    2001-01-01

    The paper provides a comprehensive testing of the applicability of 13 sediment transport formulas under different flow and sediment conditions. The dimensionless parameters used for testing the reliability and sensitivity of formulas are dimensionless particle diameter, relative depth, Froude number, relative shear velocity, dimensionless unit stream power, and sediment concentration. A total of 3,391 sets of laboratory and river data are used in the tests. Engineers may find the test results useful to their selection of formulas under different flow and sediment conditions.

  5. Mineral potential for sediment-hosted copper deposits in the Islamic Republic of Mauritania (phase V, deliverable 75): Chapter K in Second projet de renforcement institutionnel du secteur minier de la République Islamique de Mauritanie (PRISM-II)

    Science.gov (United States)

    Taylor, Cliff D.; Giles, Stuart A.

    2015-01-01

    The presence of Neoproterozoic through Cambrian, continental, siliciclastic sedimentary rocks interbedded with dolomitic carbonates, shales, and glacial tillites similar to the Katanga Supergroup host rocks of the Central African Copperbelt and other sediment-hosted copper-bearing Proterozoic sequences worldwide, is first order criteria for consideration of the Neoproterozoic units of the Taoudeni Basin in Mauritania as prospective for sediment-hosted copper deposits. Review of the National Mineral Occurrences Database (Marsh and Anderson, 2015) and previous literature suggest that only a handful of small sediment-hosted copper occurrences have been found to date in Mauritania and that the resource potential for this deposit type is low. In the northern Taoudeni Basin, the most important occurrence is at Taradent. This occurrence consists of three mineralized horizons in the lower Neoproterozoic Char Group in three outcrop areas separated by alluvium over a strike length of 12 kilometers (km). The most extensively mineralized horizon consists of malachite and disseminated copper sulfides, and is concentrated at the base of a dolomitic interval, consistent with a reduced faciestype sediment-hosted copper deposit model. Additional and poorly described copper occurrences in the Taoudeni Basin margin sedimentary rocks in northeastern Mauritania, such as Chegga Guettatira and Sidi Bara, may be sediment-hosted copper occurrences and extend the potential throughout this portion of the Basin.

  6. National Uranium Resource Evaluation Program. Hydrogeochemical and stream sediment reconnaissance basic data for Green Bay NTMS Quadrangle, Wisconsin

    International Nuclear Information System (INIS)

    Field and laboratory data are presented for 695 groundwater samples, 546 stream sediment samples, and 401 stream water samples. Statistical and areal distributions of uranium and other possibly uranium-related variables are displayed. A generalized geologic map of the survey area is provided, and pertinent geologic factors which may be of significance in evaluating the potential for uranium mineralization are briefly discussed. Greater than 85th percentile concentrations of uranium in all sample types define an area of about 2,000 km2 (780 mi2) in the central and north central portions of the survey area as the most probable area for potential uranium mineralization within the quadrangle. Bedrock of the area includes granitic and monzonitic batholiths of Precambrian age. A 500 km2 area is also outlined by uranium in groundwater samples coincident with a Precambrian fault-shear zone in Marathon County. Anomalous uranium concentrations occur in stream sediments from Marathon, Wood, and Portage Counties; however, other associated variables suggest that the uranium is associated with refractory minerals which are less favorable for commercial potential. Concentrations of uranium above the 85th percentile are also found in Waushara, Winnebago, Outagamie, and Shawano Counties within the area of Cambrian sandstone and Prairie du Chien outcrop. Groundwater and stream water representing the Sinnipee and Ancell Rock Groups, and the Richmond and Silurian Formations are characterized by high conductivity, calcium, magnesium, sulfate, total alkalinity, and pH, but moderate to low concentrations of uranium

  7. Targeting sediment management strategies using sediment quantification and fingerprinting methods

    Science.gov (United States)

    Sherriff, Sophie; Rowan, John; Fenton, Owen; Jordan, Phil; hUallacháin, Daire Ó.

    2016-04-01

    Cost-effective sediment management is required to reduce excessive delivery of fine sediment due to intensive land uses such as agriculture, resulting in the degradation of aquatic ecosystems. Prioritising measures to mitigate dominant sediment sources is, however, challenging, as sediment loss risk is spatially and temporally variable between and within catchments. Fluctuations in sediment supply from potential sources result from variations in land uses resulting in increased erodibility where ground cover is low (e.g., cultivated, poached and compacted soils), and physical catchment characteristics controlling hydrological connectivity and transport pathways (surface and/or sub-surface). Sediment fingerprinting is an evidence-based management tool to identify sources of in-stream sediments at the catchment scale. Potential sediment sources are related to a river sediment sample, comprising a mixture of source sediments, using natural physico-chemical characteristics (or 'tracers'), and contributions are statistically un-mixed. Suspended sediment data were collected over two years at the outlet of three intensive agricultural catchments (approximately 10 km2) in Ireland. Dominant catchment characteristics were grassland on poorly-drained soils, arable on well-drained soils and arable on moderately-drained soils. High-resolution (10-min) calibrated turbidity-based suspended sediment and discharge data were combined to quantify yield. In-stream sediment samples (for fingerprinting analysis) were collected at six to twelve week intervals, using time-integrated sediment samplers. Potential sources, including stream channel banks, ditches, arable and grassland field topsoils, damaged road verges and tracks were sampled, oven-dried (Soil and sediment samples were analysed for mineral magnetics, geochemistry and radionuclide tracers, particle size distribution and soil organic carbon. Tracer data were corrected to account for particle size and organic matter selectivity

  8. 寒武纪早期大气-海洋氧含量与生命大爆发%Atmosphere-Ocean Oxygen Levels and Biotic Explosion in the Early Cambrian

    Institute of Scientific and Technical Information of China (English)

    李超; 金承胜

    2015-01-01

    寒武纪早期(541~510,Ma)地球环境与这一时期生命大爆发之间的关系一直是地球生物学研究的热点问题之一。本文系统总结了目前寒武纪早期大气-海洋氧含量与这一时期生命辐射之间关系的3种假说:大气-海洋的氧含量增加导致了寒武纪生命大爆发;寒武纪生命大爆发导致了大气-海洋氧化以及二者之间没有因果关系。3种假说均有相应的支持证据,但也存在与寒武纪早期海洋化学记录、与现代海洋观察不符和上述假说均未考虑寒武纪早期生命演化所展示的时空差异性等问题。在上述3种假说的基础之上,本文通过对寒武纪构造活动、陆源输入、海洋化学和生命演化等最新资料的综合讨论和分析表明:寒武纪早期地球环境与生命辐射之间很可能是相互作用与协同演化关系,而非简单的单向关系。%The relationship between the Earth environment and the biotic explosion in early Cambrian (ca.541 -5 10,Ma) is one top geobiological issue.Here,we systematically summarized three major hypotheses for the relationship between the atmosphere-ocean oxygen level and the biotic evolution in early Cambrian,including that (1)increasing oxygenation of at-mosphere and ocean caused the Cambrian explosion,(2)the emergence and evolution of lives resulted in oxygenation of atmosphere and ocean,(3)the atmosphere-ocean oxygen level and the evolution of lives are not interrelated.Although each hypothesis is supported by specific evidences,these hypotheses show significantly inconsistent with partial ocean chemistry records in early Cambrian and investigations of lives in modern ocean analogues.In addition,the spatiotemporal heterogeneity of early Cambrian life evolution is not considered in these hypotheses.By synthesizing these major hypotheses with available data on Cambrian tectonic activities,terrestrial fluxes,ocean chemistry and life evolution patterns,we dis

  9. Geochemistry of Sediments from the PLUTO Database

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Geochemical data for unconsolidated sediments (stream sediments, lake sediments, etc.) collected in the US and analyzed by the USGS. These data were originally...

  10. 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

    OpenAIRE

    Yuman Wang; Dazhong Dong; Xiangzhi Cheng; Jinliang Huang; Shufang Wang; Shiqian Wang

    2014-01-01

    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...

  11. The Occurrence of Longfengshania in the Early Cambrian from Haikou, Yunnan, China%龙凤山藻在澄江早寒武世生物群中的发现

    Institute of Scientific and Technical Information of China (English)

    徐兆良

    2002-01-01

    Well preserved Early Cambrian small individual megascopic carbonaceous algal fossils have been found from the Chengjiang Biota. This paper deals with the new megascopic algal fossils in the Early Cambrian also from Chengjiang Biota at Ercai Village, Haikou, Kunming, Yunnan, southwest China. Two new taxa, Longfengshania cordata sp. nov. and Plantulaformis sinensis gen. et sp. nov. are described here in detail. These new findings show that the Chengjiang Biota is high in species diversity of fossil algae and might offer new evidence for a better understanding of the Cambrian explosive biological evolution. Moreover, the fossils described here might belong to the megaalgal fossils according to detailed morphological study on the relationships of Longfengshania. Additionally, the occurrence of Longfengshania in the early Cambrian and the Neoproterozoic probably indicates a wide ecological tolerance and flexibility and apparently reflects its evolutionary conservation and a high degree of inherent genetic stability.%主要报道了产自云南昆明海口耳材村早寒武世筇竹寺组玉案山段澄江生物群中可能为自由漂浮生长的宏观藻类化石--心型龙凤山藻(新种)(Longfengshania cordata sp. nov.)和中华豆芽藻(新属、新种)(Plantulaformis sinensis gen. et sp. nov.).这些化石的发现进一步显示了澄江生物群物种多样性,为揭示该生物群爆发性演化提供了新的证据.通过对龙凤山藻属亲缘关系的深入比较研究,进一步证明该类化石应归属宏观藻类以及它们遗传上的稳定性、演化上的保守性和环境上的适应性.

  12. FGMs by sedimentation

    International Nuclear Information System (INIS)

    Simple sedimentation in organic solvents followed by hot-pressing is used to produce alumina-NiAl functionally graded materials (FGMs). Varying degrees of agglomeration influenced the phase arrangement in the mixed layer(s) producing microstructural variation. The authors discovered a pronounced structural dependence on NiAl stoichiometry. Slight variations in Al content are known to influence Tdb and these apparently lead to large increases in residual stress. Zirconia-NiAl FGMs were better able to accommodate these levels of residual stress possibly due to accommodation by enhanced tetragonal phase retention. However, these FGMs undergo transformation of the tetragonal phase to the monoclinic form, starting from the surface. Finally, variable microstructures result in detectable changes in the stress-strain behavior of alumina-NiAl FGMs. 47 refs., 11 figs

  13. Targeting sediment management strategies using sediment quantification and fingerprinting methods

    Science.gov (United States)

    Sherriff, Sophie; Rowan, John; Fenton, Owen; Jordan, Phil; hUallacháin, Daire Ó.

    2016-04-01

    Cost-effective sediment management is required to reduce excessive delivery of fine sediment due to intensive land uses such as agriculture, resulting in the degradation of aquatic ecosystems. Prioritising measures to mitigate dominant sediment sources is, however, challenging, as sediment loss risk is spatially and temporally variable between and within catchments. Fluctuations in sediment supply from potential sources result from variations in land uses resulting in increased erodibility where ground cover is low (e.g., cultivated, poached and compacted soils), and physical catchment characteristics controlling hydrological connectivity and transport pathways (surface and/or sub-surface). Sediment fingerprinting is an evidence-based management tool to identify sources of in-stream sediments at the catchment scale. Potential sediment sources are related to a river sediment sample, comprising a mixture of source sediments, using natural physico-chemical characteristics (or 'tracers'), and contributions are statistically un-mixed. Suspended sediment data were collected over two years at the outlet of three intensive agricultural catchments (approximately 10 km2) in Ireland. Dominant catchment characteristics were grassland on poorly-drained soils, arable on well-drained soils and arable on moderately-drained soils. High-resolution (10-min) calibrated turbidity-based suspended sediment and discharge data were combined to quantify yield. In-stream sediment samples (for fingerprinting analysis) were collected at six to twelve week intervals, using time-integrated sediment samplers. Potential sources, including stream channel banks, ditches, arable and grassland field topsoils, damaged road verges and tracks were sampled, oven-dried (stream banks, roads - road verges and tracks, fields - grassland and arable topsoils) were statistically un-mixed using FR2000, an uncertainty-inclusive algorithm, and combined with sediment yield data. Results showed sediment contributions

  14. Dating of sediments and determination of sedimentation rate. Proceedings

    International Nuclear Information System (INIS)

    The Second NKS (Nordic Nuclear Safety Research)/EKO-1 Seminar was held at the Finnish Centre for Radiation and Nuclear Safety (STUK) on April 2-3, 1997. The work of the NKS is based on 4-year programmes; the current programme having been planned for the years 1994-1997. The programme comprises 3 major fields, one of them being environmental effects (EKO). Under this umbrella there are 4 main projects. The EKO-1 project deals with marine radioecology, in particular bottom sediments and sediment processes. The programme of the second seminar consisted of 8 invited lecturers and 6 other scientific presentations. Dating of sediments and determination of sedimentation rate are important in all types of sedimentological study and model calculations of fluxes of substances in the aquatic environment. In many cases these tasks have been closely related to radioecological studies undertaken in marine and fresh water environments, because they are often based on measured depth profiles of certain natural or artificial radionuclides present in the sediments. During recent decades Pb-210 has proved to be very useful in dating of sediments, but some other radionuclides have also been successfully used, e.g. Pu-239,240, Am-241 and Cs-137. The difficulties existing and problems involved in dating of sediments, as well as solutions for resolving these problems are discussed in the presentations

  15. Dating of sediments and determination of sedimentation rate. Proceedings

    Energy Technology Data Exchange (ETDEWEB)

    Illus, E. [ed.

    1998-08-01

    The Second NKS (Nordic Nuclear Safety Research)/EKO-1 Seminar was held at the Finnish Centre for Radiation and Nuclear Safety (STUK) on April 2-3, 1997. The work of the NKS is based on 4-year programmes; the current programme having been planned for the years 1994-1997. The programme comprises 3 major fields, one of them being environmental effects (EKO). Under this umbrella there are 4 main projects. The EKO-1 project deals with marine radioecology, in particular bottom sediments and sediment processes. The programme of the second seminar consisted of 8 invited lecturers and 6 other scientific presentations. Dating of sediments and determination of sedimentation rate are important in all types of sedimentological study and model calculations of fluxes of substances in the aquatic environment. In many cases these tasks have been closely related to radioecological studies undertaken in marine and fresh water environments, because they are often based on measured depth profiles of certain natural or artificial radionuclides present in the sediments. During recent decades Pb-210 has proved to be very useful in dating of sediments, but some other radionuclides have also been successfully used, e.g. Pu-239,240, Am-241 and Cs-137. The difficulties existing and problems involved in dating of sediments, as well as solutions for resolving these problems are discussed in the presentations

  16. Zircon dating of Neoproterozoic and Cambrian ophiolites in West Mongolia and implications for the timing of orogenic processes in the central part of the Central Asian Orogenic Belt

    Science.gov (United States)

    Jian, Ping; Kröner, Alfred; Jahn, Bor-ming; Windley, Brian F.; Shi, Yuruo; Zhang, Wei; Zhang, Fuqin; Miao, Laicheng; Tomurhuu, Dondov; Liu, Dunyi

    2014-06-01

    , we re-subdivide West Mongolia into: a latest Neoproterozoic-early Cambrian, arc-microcontinent collision zone north of the MML; a Cambrian Gobi Altai ophiolite-microcontinent collision zone and a Cambrian Trans-Altai forearc complex south of the MML. The central CAOB evolved in five phases: subduction initiation and arc formation (ca. 573 to > ca. 540 Ma); arc-microcontinent collision (ca. 535-524 Ma); a continuum of slab delamination, overthrusting, crustal thickening and surface uplift (ca. 519-482 Ma) in Northwest Mongolia; initiation of new subduction zones in South Mongolia (ca. 523-511 Ma); and continuing orogeny with local surface uplift. Overall, the current, documented timing of orogenic development in the central CAOB is largely consistent with a W/SW-Pacific style of evolution in terms of subduction initiation, short timescales of individual orogenies, and episodic subduction-collision during a continuing migration of subduction zones.

  17. Estimating sediment discharge: Appendix D

    Science.gov (United States)

    Gray, John R.; Simões, Francisco J. M.

    2008-01-01

    Sediment-discharge measurements usually are available on a discrete or periodic basis. However, estimates of sediment transport often are needed for unmeasured periods, such as when daily or annual sediment-discharge values are sought, or when estimates of transport rates for unmeasured or hypothetical flows are required. Selected methods for estimating suspended-sediment, bed-load, bed- material-load, and total-load discharges have been presented in some detail elsewhere in this volume. The purposes of this contribution are to present some limitations and potential pitfalls associated with obtaining and using the requisite data and equations to estimate sediment discharges and to provide guidance for selecting appropriate estimating equations. Records of sediment discharge are derived from data collected with sufficient frequency to obtain reliable estimates for the computational interval and period. Most sediment- discharge records are computed at daily or annual intervals based on periodically collected data, although some partial records represent discrete or seasonal intervals such as those for flood periods. The method used to calculate sediment- discharge records is dependent on the types and frequency of available data. Records for suspended-sediment discharge computed by methods described by Porterfield (1972) are most prevalent, in part because measurement protocols and computational techniques are well established and because suspended sediment composes the bulk of sediment dis- charges for many rivers. Discharge records for bed load, total load, or in some cases bed-material load plus wash load are less common. Reliable estimation of sediment discharges presupposes that the data on which the estimates are based are comparable and reliable. Unfortunately, data describing a selected characteristic of sediment were not necessarily derived—collected, processed, analyzed, or interpreted—in a consistent manner. For example, bed-load data collected with

  18. Trace fossils and sedimentary facies from a Late Cambrian-Early Ordovician tide-dominated shelf (Santa Rosita Formation, northwest Argentina): Implications for ichnofacies models of shallow marine successions

    Science.gov (United States)

    Mangano, M.G.; Buatois, L.A.; Acenolaza, G.F.

    1996-01-01

    The Santa Rosita Formation is one the most widely distributed lower Paleozoic units of northwest Argentina. At the Quebrada del Salto Alto section, east of Purmamarca, Jujuy Province, it is represented by four sedimentary facies: thick-bedded planar cross-stratified quartzose sandstones (A), thin-bedded planar cross-stratified quartzose sandstones and mudstones (B), wave-rippled sandstones and bioturbated mudstones (C), and black and greenish gray shales (D). Paleocurrent data, sandstone architecture, and sedimentary structures from facies A and B indicate bipolar/bimodal paleoflows, suggesting the action of tidal currents. The succession is interpreted as that of a tide-dominated shelf, with only secondary influence of wave processes. Trace fossils are restricted to facies B and C. The Cruziana ichnocoenosis is preserved on the soles of thin-bedded planar cross-stratified quartzose sandstones (facies B). This ichnocoenosis consists of Conostichus isp., Cruziana omanica, C. semiplicata, C. cf. tortworthi, Cruziana isp. Helminthopsis abeli, Monomorphichnus bilinearis, M. multilineatus, Palaeophycus tubularis, Rusophycus carbonarius, R. latus, and R. isp. The occurrence of Cruziana semiplicata, C. omanica, C. cf. tortworthi, and Rusophycus latus supports a Late Cambrian-Tremadoc age. Slabbing of Cruziana shows complex interactions between biologic and sedimentologic processes, and suggests a predominance of exhumed traces, washed out and recast by tractive sand deposition. Sandstone soles are densely packed with biogenic structures and exhibit distinctive clusters of Rusophycus isp. that most likely represent trilobite nesting burrows. The Cruziana ichnocoenosis records the resident fauna of a protected, lower intertidal to subtidal interbar setting. The Skolithos ichnocoenosis is represented by high to low density vertical burrows of Skolithos linearis, which extend downwards to the quartzose sandstone soles of facies B and cross the Cruziana ichnocoenosis. The

  19. The early Cambrian Chahmir shale-hosted Zn-Pb deposit, Central Iran: an example of vent-proximal SEDEX mineralization

    Science.gov (United States)

    Rajabi, Abdorrahman; Rastad, Ebrahim; Canet, Carles; Alfonso, Pura

    2015-06-01

    The Chahmir zinc-lead deposit (1.5 Mt @ 6 % Zn + 2 % Pb) in Central Iran is one among several sedimentary-exhalative Zn-Pb deposits in the Early Cambrian Zarigan-Chahmir basin (e.g., Koushk, Darreh-Dehu, and Zarigan). The deposit is hosted by carbonaceous, fine-grained black siltstones, and shales interlayered with volcaniclastic sandstone beds. It corresponds to the upper part of the Early Cambrian volcano-sedimentary sequence (ECVSS), which was deposited on the Posht-e-Badam Block during back-arc rifting of the continental margin of Central Iran. Based on crosscutting relationships, mineralogy, and texture of sulfide mineralization, four different facies can be distinguished: stockwork (feeder zone), massive ore, bedded ore, and distal facies (exhalites with barite). Silicification, carbonatization, sericitization, and chloritization are the main wall-rock alteration styles; alteration intensity increases toward the proximal feeder zone. Fluid inclusion microthermometry was carried out on quartz associated with sulfides of the massive ore. Homogenization temperatures are in the range of 170-226 °C, and salinity is around 9 wt% NaCl eq. The size distribution of pyrite framboids of the bedded ore facies suggests anoxic to locally suboxic event for the host basin. δ34S(V-CDT) values of pyrite, sphalerite, and galena range from +10.9 to +29.8 ‰. The highest δ34S values correspond to the bedded ore (+28.6 to +29.8 ‰), and the lowest to the massive ore (+10.9 to +14.7 ‰) and the feeder zone (+11.3 and +12.1 ‰). The overall range of δ34S is consistent with a sedimentary environment where sulfide sulfur was derived from two sources. One of them was corresponding to early ore-stage sulfides in bedded ore and distal facies, consistent with bacterial reduction from coeval seawater sulfate in a closed or semiclosed basin. However, the δ34S values of late ore-stage sulfides, observed mainly in massive ore, interpreted as a hydrothermal sulfur component, leached

  20. Fluvial sediment transport: Analytical techniques for measuring sediment load

    International Nuclear Information System (INIS)

    Sediment transport data are often used for the evaluation of land surface erosion, reservoir sedimentation, ecological habitat quality and coastal sediment budgets. Sediment transport by rivers is usually considered to occur in two major ways: (1) in the flow as a suspended load and (2) along the bed as a bed load. This publication provides guidance on selected techniques for the measurement of particles moving in both modes in the fluvial environment. The relative importance of the transport mode is variable and depends on the hydraulic and sedimentary conditions. The potential user is directed in the selection of an appropriate technique through the presentation of operating principles, application guidelines and estimated costs. Techniques which require laboratory analysis are grab sample, pump sample, depth sample, point integrated and radioactive tracers. Techniques which will continuously record data are optical backscattering, nuclear transmission, single frequency acoustic and laser diffraction

  1. DESIGN OF SEDIMENT FLUSHING OUTLETS

    Institute of Scientific and Technical Information of China (English)

    Prabhata K.SWAMEE

    2002-01-01

    Flushing pipe outlets are provided at the floor of sedimentation basins for flushing out of the deposited sediments. These outlets have to be positioned in such a way so as to remove the deposited sediments effectively. In the absence of rational method for the location, presently the outlets are located by judgment. A review of literature indicated that there is no judicious method available for obtaining the outlet diameter. Presented herein are the design equations for the flushing outlets. It is hoped that the equation will be useful to the design engineers.

  2. Elwha River Restoration: Sediment Management

    Science.gov (United States)

    Kimbrel, S.; Bountry, J.; Randle, T. J.; Ritchie, A.; Huginin, H.; Torrance, A.

    2013-12-01

    The removal of Elwha and Glines Canyon Dams on the Elwha River relies on controlled reservoir drawdown increments and natural river flows to erode and redistribute the reservoir sediment, estimated to be a total of 23 (× 3) million m3. To mitigate for the predicted sediment effects, facilities have been constructed for water quality and flood protection. A sediment monitoring program is being implemented by an interdisciplinary team from Reclamation and National Park Service to integrate real-time measurements with continually updated numerical model predictions. The most recent numerical reservoir modeling and monitoring results indicate about 20 to 25 percent of the reservoir sediment has been released since the start of dam removal. Monitoring results in 2012 and early 2013 confirmed that controlled reservoir drawdown increments have induced sufficient vertical and lateral erosion of delta surfaces behind both dams. Predam channel and floodplain surface has been exposed in numerous portions of Lake Aldwell, with the release of coarse and fine sediment in the first few pools below Elwha Dam. The material released from Lake Aldwell has included organic material. With the removal of about three quarters of Glines Canyon Dam and the disappearance of Lake Mills, coarse bedload sediment has been continually released into the downstream river since late fall 2012. Field measurements and numerical modeling are being used to track the progression of the sediment wave downstream to the Elwha River mouth. Initial findings are that the aggradation was greatest immediately downstream of Glines Canyon Dam, and filled pools and transformed river planform from step-pool to glide for most of the 7 mile reach between Lake Mills and Lake Aldwell. Although there has not been a major flood, winter flows and spring snowmelt have significantly reworked the released sediment and remnants of the pre-sediment release pools and rapids have re-emerged. Large wood and organics have also

  3. Sedimentation rate control on diagenesis, East China Sea sediments

    Science.gov (United States)

    Zheng, Yan; Zheng, Hongbo; Kissel, Catherine; Laj, Carlo

    2011-08-01

    Diagenesis of ferrimagnetic minerals can alter the magnetic properties, erasing partially or entirely the original paleomagnetic and paleoclimatic signals, especially on continental margins where sedimentation rates are usually high. Understanding the mechanisms by which magnetic particles are affected by diagenesis is therefore critical for retrieving paleomagnetic and paleoclimatic information from sediments. High-resolution magnetic analysis was carried out on rapidly deposited (0.4-20 mm/year) Holocene sediments from the East China Sea (ECS) inner continental shelf. The primary magnetic mineral assemblage in the sediment core contains ferrimagnetic minerals, such as magnetite, with minor contributions from hematite. The magnetic properties vary down-core in two steps, due to post-depositional reductive diagenesis. The first occurs at depths of 0.15-1.1 m and is characterized by reduction of both magnetite and hematite in suboxic sediments. The suboxic-sulfate boundary (SSB) is therefore located at 1.1 m. We demonstrate that the depth of the SSB has negative relation to the average sedimentation rate in Chinese marginal seas. The second step change in magnetic properties occurs at 3.2-5.8 m, and contains two intervals with extremely low magnetic mineral content, each corresponding to dissolution fronts associated with the former and present position of the sulfate-methanic transition (SMT). These two intervals correlate well with abrupt changes in sedimentation rate and separate the anoxic zone into two parts: the sulfidic zone and the methanic zone. Our study suggests that sedimentation rate provides a dominant control on magnetic mineral diagenesis, at least in the Chinese marginal seas, which controls not only the type of redox zonation, but also the thicknesses of diagenetic zones.

  4. Two new species of Vestrogothia (Phosphatocopina,Crustacea) of Orsten-type preservation from the Upper Cambrian in western Hunan,South China

    Institute of Scientific and Technical Information of China (English)

    ZHANG HuaQiao; DONG XiPing

    2009-01-01

    Although fossils of Orsten-type preservation represented by Skaracarida and Phosphatocopina were first reported from the Middle and Upper Cambrian in western Hunan,South China in 2005,diversified phosphatocopine species have never been appropriately described and elucidated in terms of their evolutionary relationships.Here,we described two new species of Phosphatocopina,Vestrogothia anterispinata sp.nov.and V.bispinata sp.nov.The evolutionary relationship among all the valid spe-cies of Phosphatocopina is discussed and the phylogeny of Phosphatocopina is reestablished using cladistic analysis.Accordingly,phosphatocopines primitively evolved along two lineages:one evolved towards the emergence of lobes; the other evolved towards the emergence of dorsal spines.Respec-tively,lobes originated independently three times,and dorsal spines originated only once.With regard to the dorsal rims,interdorsum originated first,whereas dorsal furrow originated independently twice on the basis of interdorsum.Probably Hesslandona may represent a polyphyletic group,whereas Vestrogothia a monophyletic group.

  5. Late-stage sulfides and sulfarsenides in Lower Cambrian black shale (stone coal) from the Huangjiawan mine, Guizhou Province, People's Republic of China

    Science.gov (United States)

    Belkin, H.E.; Luo, K.

    2008-01-01

    The Ni-Mo Huangjiawan mine, Guizhou Province, People's Republic of China, occurs in Lower Cambrian black shale (stone coal) in an area where other mines have recently extracted ore from the same horizon. Detailed electron microprobe (EMPA) and scanning electron microscope (SEM) analyses of representative thin sections have revealed a complex assemblage of sulfides and sulfarsenides. Early sulfidic and phosphatic nodules and host matrix have been lithified, somewhat fractured, and then mineralized with later-stage sulfides and sulfarsenides. Gersdorffite, millerite, polydymite, pyrite, sphalerite, chalcopyrite, galena, and clausthalite have been recognized. EMPA data are given for the major phases. Pyrite trace-element distributions and coeval Ni-, As-sulfides indicate that in the main ore layer, the last sulfide deposition was Ni-As-Co-rich. Mo and V deposition were early in the petrogenesis of these rocks. The assemblages gersdorffite-millerite-polydymite (pyrite) and millerite-gersdorffite (pyrite) and the composition of gersdorffite indicate a formation temperature of between 200?? and 300??C suggesting that the last solutions to infiltrate and mineralize the samples were related to hydrothermal processes. Environmentally sensitive elements such as As, Cd, and Se are hosted by sulfides and sulfarsenides and are the main source of these elements to residual soil. Crops grown on them are enriched in these elements, and they may be hazardous for animal and human consumption. ?? Springer-Verlag 2007.

  6. THE "CAMBRIAN EXPLOSION" IN THE EVOLUTION OF METAZOA AND ITS CAUSES%"寒武纪爆发"事件及其成因述评

    Institute of Scientific and Technical Information of China (English)

    郝家胜

    2003-01-01

    主要后生动物门类化石在寒武纪初期的突然出现记录了生命史中一个从未有过的快速演化时期,这一事件被称为"寒武纪爆发(Cambrian explosion)".多年来有关"寒武纪爆发"成因的各种猜测从未间断过.但是,将古生物化石记录看成是生物进化过程中种系形成的真实过程已遭到许多研究者的非议,这主要取决于以下二方面的证据:一是对早期后生动物系统发生关系的重新评估;二是来自于分子系统学和分子钟的研究.现在看来,"寒武纪爆发"事件的产生,一方面归因于化石体积的明显增加及其伴随的骨骼化过程,另一方面可能是其时的进化革新事件所导致.

  7. Cable Bacteria in Freshwater Sediments

    DEFF Research Database (Denmark)

    Risgaard-Petersen, Nils; Kristiansen, Michael; Frederiksen, Rasmus;

    2015-01-01

    In marine sediments cathodic oxygen reduction at the sediment surface can be coupled to anodic sulfide oxidation in deeper anoxic layers through electrical currents mediated by filamentous, multicellular bacteria of the Desulfobulbaceae family, the so-called cable bacteria. Until now, cable...... bacteria have only been reported from marine environments. In this study, we demonstrate that cable bacteria also occur in freshwater sediments. In a first step, homogenized sediment collected from the freshwater stream Giber Å, Denmark, was incubated in the laboratory. After 2 weeks, pH signatures and...... marine cable bacteria, with the genus Desulfobulbus as the closest cultured lineage. The results of the present study indicate that electric currents mediated by cable bacteria could be important for the biogeochemistry in many more environments than anticipated thus far and suggest a common evolutionary...

  8. SEDIMENT MANAGEMENT IN HYDROELECTRIC PROJECTS

    Institute of Scientific and Technical Information of China (English)

    K.G.RANGA RAJU; U.C.KOTHYARI

    2005-01-01

    Withdrawal of water from a river into a canal involves the construction of a barrage or a dam across the river depending on whether the river is perennial or not. The design of the reservoir upstream of the dam and of the canal requires consideration of the sediment load carried by the river in case the river is sediment-laden. The basic equations concerning morphological changes in such rivers are discussed with particular reference to computation of reservoir sedimentation. The hydraulics of lined canals carrying wash load is examined from the point of view of limiting transport capacity and changes in frictional resistance. Lastly,the methods of design of sediment extraction devices like settling basins and vortex chambers are presented.

  9. Haw River sediment quality assessment

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This report documents an evaluation of chemical contaminants in, and toxicity of, sediments collected from impoundments created by dams on the Haw River in Alamance...

  10. 7 CFR 58.134 - Sediment content.

    Science.gov (United States)

    2010-01-01

    ... 7 Agriculture 3 2010-01-01 2010-01-01 false Sediment content. 58.134 Section 58.134 Agriculture... Milk § 58.134 Sediment content. (a) Method of testing. Methods for determining the sediment content of... for the Examination of Dairy Products. Sediment content shall be based on comparison with...

  11. The kinetics of denitrification in permeable sediments

    DEFF Research Database (Denmark)

    Evrard, Victor; Glud, Ronnie N.; Cook, Perran L. M.

    2013-01-01

    Permeable sediments comprise the majority of shelf sediments, yet the rates of denitrification remain highly uncertain in these environments. Computational models are increasingly being used to understand the dynamics of denitrification in permeable sediments, which are complex environments to...... environment experienced in permeable sediments. In contrast to previous studies, we did not observe any significant rates of oxic denitrification....

  12. Mathematical theory of sedimentation analysis

    CERN Document Server

    Fujita, Hiroshi; Van Rysselberghe, P

    1962-01-01

    Mathematical Theory of Sedimentation Analysis presents the flow equations for the ultracentrifuge. This book is organized into two parts encompassing six chapters that evaluate the systems of reacting components, the differential equations for the ultracentrifuge, and the case of negligible diffusion. The first chapters consider the Archibald method for molecular weight determination; pressure-dependent sedimentation; expressions for the refractive index and its gradient; relation between refractive index and concentration; and the analysis of Gaussian distribution. Other chapters deal with th

  13. Geophysical constraints on sediment dispersal systems

    OpenAIRE

    Johnstone, Elizabeth Anne Carruthers

    2012-01-01

    Geophysical and geological approaches were employed to understand sediment dispersal systems and their response to various forcing functions (i.e., sea level fluctuations, tectonic deformation, sediment supply, and climate change). Two end member marine environments were studied; one with high precipitation and sediment discharge (Gulf of Papua, Papua New Guinea) and the other with low precipitation and sediment discharge (Oceanside Littoral Cell). The high-sedimentation rate in the Gulf of P...

  14. River sediment supply, sedimentation and transport of the highly turbid sediment plume in Malindi Bay, Kenya

    Institute of Scientific and Technical Information of China (English)

    JOHNSON U.Kitheka

    2013-01-01

    The paper presents results of a study on the sediment supply and movement of highly turbid sediment plume within Malindi Bay in the Northern region of the Kenya coast.The current velocities,tidal elevation,salinity and suspended sediment concentrations (TSSC)were measured in stations located within the bay using Aanderaa Recording Current Meter (RCM-9),Turbidity Sensor mounted on RCM-9,Divers Gauges and Aanderaa Temperature-Salinity Meter.The study established that Malindi Bay receives a high terrigenous sediment load amounting to 5.7 × 106 ton·yr-1.The river freshwater supply into the bay is highly variable ranging from 7 to 680 m3·s-1.The high flows that are > 150 m3·s-1 occurred in May during the South East Monsoon (SEM).Relatively low peak flows occurred in November during the North East Monsoon (NEM) but these were usually <70 m3·s-1.The discharge of highly turbidity river water into the bay in April and May occurs in a period of high intensity SEM winds that generate strong north flowing current that transports the river sediment plume northward.However,during the NEM,the river supply of turbid water is relatively low occurring in a period of relatively low intensity NEM winds that result in relatively weaker south flowing current that transports the sediment plume southward.The mechanism of advection of the sediment plume north or south of the estuary is mainly thought to be due to the Ekman transport generated by the onshore monsoon winds.Limited movement of the river sediment plume southward towards Ras Vasco Da Gama during NEM has ensured that the coral reef ecosystem in the northern parts of Malindi Marine National Park has not been completely destroyed by the influx of terrigenous sediments.However,to the north there is no coral reef ecosystem.The high sediment discharge into Malindi Bay can be attributed to land use change in the Athi-Sabaki River Basin in addition to rapid population increase which has led to clearance of forests to open land

  15. Extraterrestrial Matter Chronometry of Sediments

    Science.gov (United States)

    Peucker-Ehrenbrink, B.; Waters, C. A.; Hoffman, P. F.; Kurz, M. D.

    2010-12-01

    Tracer records of extraterrestrial matter (ET) accumulation in sediments suggest that ET accretion rates are reasonable constant on time scales relevant to sediment accumulation in terrestrial and marine environments (1000-100,000 years), except during impact events. Geochemical tracers of ET matter in sediments are therefore informative rate indicators applicable to individual samples. This alleviates the need for interpolating rates between known chronometric tie points. The most sensitive tracers of ET accretion include noble gases, particularly helium, and the heavy platinum group elements osmium, iridium and platinum. Helium and osmium have tell-tale isotope signatures that are sensitive indicators of terrestrial vs. extraterrestrial pedigree. Here we investigate the use of coupled helium-osmium isotope and helium, osmium, iridium and platinum concentration analyses to determine sedimentation rates across Neoproterozoic glacial terminations. Bodiselitsch et al. (Science 308, 2005, 239ff) suggested that significant iridium anomalies at transitions from glacial to postglacial sediments constrain the duration of Neoproterozoic Marinoan glaciation to at least 3, and most likely 12 million years. Our data on Marinoan sections from NW Canada and Namibia reveal no large ET matter anomaly, and support a more nuanced interpretation of coupled geochemical indicators of accretion of ET matter across those transitions. Our records provide insights into environmental changes during periods of Neoproterozoic climate change.

  16. Cable Bacteria in Freshwater Sediments.

    Science.gov (United States)

    Risgaard-Petersen, Nils; Kristiansen, Michael; Frederiksen, Rasmus B; Dittmer, Anders Lindequist; Bjerg, Jesper Tataru; Trojan, Daniela; Schreiber, Lars; Damgaard, Lars Riis; Schramm, Andreas; Nielsen, Lars Peter

    2015-09-01

    In marine sediments cathodic oxygen reduction at the sediment surface can be coupled to anodic sulfide oxidation in deeper anoxic layers through electrical currents mediated by filamentous, multicellular bacteria of the Desulfobulbaceae family, the so-called cable bacteria. Until now, cable bacteria have only been reported from marine environments. In this study, we demonstrate that cable bacteria also occur in freshwater sediments. In a first step, homogenized sediment collected from the freshwater stream Giber Å, Denmark, was incubated in the laboratory. After 2 weeks, pH signatures and electric fields indicated electron transfer between vertically separated anodic and cathodic half-reactions. Fluorescence in situ hybridization revealed the presence of Desulfobulbaceae filaments. In addition, in situ measurements of oxygen, pH, and electric potential distributions in the waterlogged banks of Giber Å demonstrated the presence of distant electric redox coupling in naturally occurring freshwater sediment. At the same site, filamentous Desulfobulbaceae with cable bacterium morphology were found to be present. Their 16S rRNA gene sequence placed them as a distinct sister group to the known marine cable bacteria, with the genus Desulfobulbus as the closest cultured lineage. The results of the present study indicate that electric currents mediated by cable bacteria could be important for the biogeochemistry in many more environments than anticipated thus far and suggest a common evolutionary origin of the cable phenotype within Desulfobulbaceae with subsequent diversification into a freshwater and a marine lineage. PMID:26116678

  17. 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

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

    Directory of Open Access Journals (Sweden)

    G. A. Shields

    2007-07-01

    Full Text Available 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 87Sr/86Sr curve to trace globally integrated chemical weathering rates has not been fully realised because ocean 87Sr/86Sr is also influenced by the isotopic evolution of Sr sources to the ocean. A preliminary attempt is made here to normalise the seawater 87Sr/86Sr curve to plausible trends in the 87Sr/86Sr 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 87Sr/86Sr curve, a published seawater δ34S curve and atmospheric pCO2 models is used here to argue that elevated chemical weathering rates were a major contributing factor to the steep rise in seawater 87Sr/86Sr 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 87Sr/86Sr curves will, it is hoped, help to improve future geochemical models of Earth System dynamics.

  19. The Neoproterozoic-Cambrian Paraguay Belt, central Brazil: Part I - New structural data and a new approach on the regional implications

    Science.gov (United States)

    Silva, Luiz José Homem D'el-Rey; Walde, Detlef Hans-Gerd; Saldanha, Davi Oliveira

    2016-04-01

    Together with the Araguaia and Brasília belts, the Paraguay belt forms in central Brazil, the Tocantins Province that is one of the largest orogens of western Gondwana. The Corumbá area occupies the site where the northern and southern parts of the Paraguay belt form, together with the Chiquitos-Tucavaca aulacogen (stretching E-W in the adjacent Bolivian territory) an R-R-R basin system opened-filled in the ~ 700/650-540 Ma interval within the Amazon-Rio Apa paleo-continent. The sedimentary (volcanic) rocks of the Jacadigo and Corumbá Groups found around the Corumbá city record part of the Neoproterozoic-Cambrian passive margin precursor of the Paraguay belt. Our pioneer structural analysis reveals that these rocks experienced progressive deformation (phases D1-D2-D3) and low-grade metamorphism during the Brasiliano Cycle (540-513 Ma). The crystalline basement was also involved, according to structural data and K-Ar ages in the literature. The paleo-passive margin was thickened during the D1-D2 deformation and was lately shortened (D3) in two orthogonal directions, SE-NW (D3P) and SW-NE (D3T). Developed co-axially and verging to NW, D1-D2-D3P structures record the closure of the basin precursor of the Paraguay belt, whereas D3T structures seem related to the inversion of the aulacogen. Although the tectonic transport to NW, as observed in the Corumbá area, matches the reported transport of Paraguay belt's supracrustal rocks towards the eastern margin of the Rio Apa block and Araguaia belt's rocks towards the Amazon craton, the transport direction is opposite in other parts of the Paraguay belt. Our comprehensive discussion of these facts brings to light profound regional implications.

  20. Petroleum source rock evaluation of the Alum and Dictyonema Shales (Upper Cambrian-Lower Ordovician) in the Baltic Basin and Podlasie Depression (eastern Poland)

    Science.gov (United States)

    Kosakowski, Paweł; Kotarba, Maciej J.; Piestrzyński, Adam; Shogenova, Alla; Więcław, Dariusz

    2016-05-01

    We present geochemical characteristics of the Lower Palaeozoic shales deposited in the Baltic Basin and Podlasie Depression. In the study area, this strata are represented by the Upper Cambrian-Lower Ordovician Alum Shale recognized in southern Scandinavia and Polish offshore and a equivalent the Lower Tremadocian Dictyonema Shale from the northern Estonia and the Podlasie Depression in Poland. Geochemical analyses reveal that the Alum Shale and Dictyonema Shale present high contents of organic carbon. These deposits have the best source quality among the Lower Palaeozoic strata, and they are the best source rocks in the Baltic region. The bituminous shales complex has TOC contents up to ca. 22 wt%. The analysed rocks contain low-sulphur, oil-prone Type-II kerogen deposited in anoxic or sub-oxic conditions. The maturity of the Alum and Dictyonema Shales changes gradually, from the east and north-east to the west and south-west, i.e. in the direction of the Tornquist-Teisseyre Zone. Samples, located in the seashore of Estonia and in the Podlasie region, are immature and in the initial phase of "oil window". The mature shales were found in the central offshore part of the Polish Baltic Basin, and the late mature and overmature are located in the western part of the Baltic Basin. The Alum and Dictyonema Shales are characterized by a high grade of radioactive elements, especially uranium. The enrichment has a syngenetic or early diagenetic origin. The measured content of uranium reached up to 750 ppm and thorium up to 37 ppm.

  1. Contaminated sediment transport during floods

    International Nuclear Information System (INIS)

    Over the past 48 years, operations and waste disposal activities at Oak Ridge National Laboratory have resulted in the contamination of parts of the White Oak Creek catchment. The contaminants presenting the highest risk to human health and the environment are particle reactive and are associated with the soils and sediments in the White Oak Creek drainage system. The erosion of these sediments during floods can result in the transport of contaminants both within the catchment and off-site into the Clinch River. A data collection program and a modeling investigation are being used to evaluate the probability of contaminated sediment transport during floods and to develop strategies for controlling off-site transport under present and future conditions

  2. Creep behavior of submarine sediments

    Science.gov (United States)

    Silva, Armand J.; Booth, J.S.

    1984-01-01

    A series of experiments on drained creep of marine sediment indicates that strength degradation results from the creep process, which implies an associated reduction in slope stability. Furthermore, the highest creep potential of a sediment may be at its preconsolidation stress. Results from the experiments on samples from Georges Bank continental slope were also used in conjunction with a preliminary theoretical model to predict creep displacements. For the case illustrated in this report, steep slopes (>20??) and thick sections (>30 m) give rise to substantial creep and probable creep rupture; as angles or thicknesses decrease, displacements rapidly become negligible. Creep may be a significant geologic process on many marine slopes. Not only can it cause major displacements of surface sediment, but it may also be the precursor to numerous slope failures. ?? 1985 Springer-Verlag New York Inc.

  3. Radionuclide interactions with marine sediments

    International Nuclear Information System (INIS)

    A critical review of the literature on the subject of the interactions of radionuclides with marine sediments has been carried out. On the basis of the information available, an attempt has been made to give ranges and 'best estimates' for the distribution ratios between seawater and sediments. These estimates have been based on an understanding of the sediment seawater system and the porewater chemistry and mineralogy. Field measurements, laboratory measurements and estimates based on stable-element geochemical data are all taken into account. Laboratory measurements include distribution-ratio and diffusion-coefficient determinations. The elements reviewed are carbon, chlorine, calcium, nickel, selenium, strontium, zirconium, niobium, technetium, tin, iodine, caesium, lead, radium, actinium, thorium, protactinium, uranium, neptunium, plutonium, americium and curium. (author)

  4. Corrigendum to "Isotopic and geochemical characterization of fossil brines of the Cambrian Mt. Simon sandstone and Ironton-Galesville formation from the Illinois Basin, USA" [Geochim. Cosmochim. Acta 165 (2015) 342-360

    Science.gov (United States)

    Labotka, Dana M.; Panno, Samuel V.; Locke, Randall A.; Freiburg, Jared T.

    2016-08-01

    The original Fig. 4 incorrectly represented data from Clayton et al. (1966). The deuterium values were reported in percent deuterium and mistaken by the authors as per mille. The corrected Fig. 4 Corrigendum is given and shows the data from Clayton et al. (1966) plotting in a similar manner as other published data for groundwater in the Illinois Basin. The data from Clayton et al. (1966) was not used in the discussion of the deep-seated Cambrian brines, and, therefore, this misrepresentation does not affect the conclusions of the original manuscript. The authors apologize for the oversight.

  5. STUDY ON TOTAL SEDIMENT TRANSPORT BY FLOW

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Total sediment transport under the action of flow includes generally three forms of sediment transport, suspended load, density current and bed load. How to realize simultaneously these three forms of sediment movement in an identical physical model was studied in this paper. For the suspended load, fall and pickup similarities were used to design sediment gradation, and similarities of sediment-carrying capacity and scouring and depositing time were be insured. For the density current its occurrence condition should be similar, and similarities of sediment concentration and depositing time were insured. For the bed load, sediment gradation was designed by the similarity of incipient motion, and similarities of sediment discharge and scouring and depositing time were satisfied. And a physical model test was conducted.

  6. Sedimentation measurements of apple pectins molecular weight

    International Nuclear Information System (INIS)

    The article is described the sedimentation measurements of a number of apple pectin's molecular weight using only sedimentation diagrams through computer program. This approach has good readability and some advantages over others

  7. Longshore sediment transport along the Indian coast

    Digital Repository Service at National Institute of Oceanography (India)

    Chandramohan, P.; Nayak, B.U.

    An empirical sediment transport model has been developed based on longshore energy flux equation. Ship reported waves, published in Indian Daily Weather Reports, are compiled for 19 y and used for estimation of sediment transport. Annual gross...

  8. Biota-Sediment Accumulation Factor Data

    Data.gov (United States)

    U.S. Environmental Protection Agency — The Biota-Sediment Accumulation Factor contains approximately 20,000 biota-sediment accumulation factors (BSAFs) from 20 locations (mostly Superfund sites) for...

  9. Green PCB Remediation from Sediment Systems Project

    Data.gov (United States)

    National Aeronautics and Space Administration — The GPRSS technology is an in situ remediation technique for PCB-contaminated sediments. The technique provides an effective and safe method for sediment cleanup...

  10. SEDIMENT TRANSPORT AND STREAM POWER

    Institute of Scientific and Technical Information of China (English)

    Chih Ted YANG

    2002-01-01

    This paper provides a step-by-step derivation of the sediment transport functions by Engelund and Hansen (1967) and by Ackers and White (1973). The theoretical derivations demonstrate that these two functions are closely related to Bagnold's (1966) stream power and efficiency concepts.

  11. Sediment transport under breaking waves

    DEFF Research Database (Denmark)

    Christensen, Erik Damgaard; Hjelmager Jensen, Jacob; Mayer, Stefan

    2000-01-01

    generated at the surface where the wave breaks as well as the turbulence generated near the bed due to the wave-motion and the undertow. In general, the levels of turbulent kinetic energy are found to be higher than experiments show. This results in an over prediction of the sediment transport. Nevertheless...

  12. Flocculation Dynamics of cohesive sediment

    NARCIS (Netherlands)

    Maggi, F.

    2005-01-01

    Cohesive sediment suspended in natural waters is subject not only to transport and deposition processes but also to reactions of flocculation, \\textit{i.e.} aggregation of fine particles, and breakup of aggregates. Although aggregation and breakup occur at small and very small length scales compared

  13. Black carbon in marine sediments

    NARCIS (Netherlands)

    Middelburg, J.J.; Nieuwenhuize, J.; Van Breugel, P.

    1999-01-01

    Concentrations of black carbon were determined for a number of marine sediments. A comparison of black carbon based on thermal oxidation and hot concentrated nitric acid pretreatments revealed that the latter significantly overestimates combustion derived carbon phases. Black carbon accounts for abo

  14. Radionuclide sorption by marine sediments

    International Nuclear Information System (INIS)

    The effect of the solid/solution ratio on distribution ratios measured using a standard batch technique was investigated. Two different deep-sea sediments and the actinides americium, neptunium and plutonium were studied. It is shown that the apparent drop in distribution ratio with increasing sediment concentration can frequently be explained by the presence of a small amount of non-separable or 'low-Rsub(d)' species and that by measuring the Rsub(d) at different solid/solution ratios it is possible to estimate the proportion of low-Rsub(d) species present. These may be colloids or stable complexes. Plutonium exhibited anomalous behaviour with the high-carbonate sediment and the distribution ratio dropped from > 104 to 102 as the solid/soln ratio increased from 2g/l to 20g/l. At high sediment concentrations the plutonium in solution was mainly in the oxidised Pu(V + VI) form and it is postulated that Pu-VI carbonates were the main species present. (author)

  15. Karst sediments age in Slovenia

    Czech Academy of Sciences Publication Activity Database

    Zupan Hajna, N.; Mihevc, A.; Pruner, Petr; Bosák, Pavel

    Prague : Czech Speleological Society, 2009. s. 54-55. ISBN 978-80-254-4928-8. [International Congress of Speleology /15./ : Karst Horizons. 11.07.2009-26.07.2009, Kerrville] Institutional research plan: CEZ:AV0Z30130516 Keywords : karst * caves * karst sediments Subject RIV: DB - Geology ; Mineralogy

  16. Prediction of bedload sediment transport for heterogeneous sediments in shape

    Science.gov (United States)

    Durafour, Marine; Jarno, Armelle; Le Bot, Sophie; Lafite, Robert; Marin, François

    2015-04-01

    Key words: Particle shape, in-situ measurements, bedload transport, heterogeneous sediments Bedload sediment transport in the coastal area is a dynamic process mainly influenced by the type of hydrodynamic forcings involved (current and/or waves), the flow properties (velocity, viscosity, depth) and sediment heterogeneity (particle size, density, shape). Although particle shape is recognized to be a significant factor in the hydrodynamic behavior of grains, this parameter is not currently implemented in bedload transport formulations: firstly because the mechanisms of initiation of motion according to particle shape are still not fully understood, and secondly due to the difficulties in defining common shape parameters. In March 2011, a large panel of in-situ instruments was deployed on two sites in the Eastern English Channel, during the sea campaign MESFLUX11. Samples of the sediment cover available for transport are collected, during a slack period, per 2cm thick strata by divers and by using a Shipeck grab. Bedload discharges along a tidal cycle are also collected with a Delft Nile Sampler (DNS; Gaweesh and Van Rijn, 1992, 1994) on both sites. The first one is characterized by a sandy bed with a low size dispersion, while the other study area implies graded sediments from fine sands to granules. A detailed analysis of the data is performed to follow the evolution of in-situ bedload fluxes on the seabed for a single current. In-situ measurements are compared to existing formulations according to a single fraction approach, using the median diameter of the mixture, and a fractionwise approach, involving a discretization of the grading curve. Results emphasize the interest to oscillate between these two methods according to the dispersion in size of the site considered. The need to apply a hiding/exposure coefficient (Egiazaroff, 1965) and a hindrance factor (Kleinhans and Van Rijn, 2002) for size heterogeneous sediments is also clearly highlighted. A really good

  17. Geophysical Constraints on Sediment Dispersal Systems

    OpenAIRE

    Johnstone, Elizabeth Anne Carruthers

    2012-01-01

    Geophysical and geological approaches were employed to understand sediment dispersal systems and their response to various forcing functions (i.e., sea level member marine environments were studied; one with high precipitation and sediment discharge (Gulf of Papua, Papua New Guinea) and the other with low precipitation and sediment discharge (Oceanside Littoral Cell). The high-sedimentation rate in the Margins Source-to-Sink (S2S) program, we acquired CHIRP and core data across the GoP contin...

  18. SEDIMENT MANAGEMENT IN FLOOD CONTROL DAMS

    OpenAIRE

    Pattanapanchai, Maneechit; Shah, Farhed A.; Annandale, George

    2002-01-01

    Reservoir sedimentation reduces economic value and longevity of flood control dams. Periodic sediment removal allows extension of reservoir life. An optimal control model is developed to evaluate alternative sediment management strategies for flood control dams. An illustrative empirical analysis shows that sustainable management is economically desirable for a wide range of parameter values.

  19. Sediment Characteristic Studies in the Surface Sediment from Kemaman Mangrove Forest, Terengganu, Malaysia

    Directory of Open Access Journals (Sweden)

    M.C. ONG

    2012-12-01

    Full Text Available 43 surface sediment samples from Kemaman mangrove forest, Terengganu were analyzed for sediment characteristic (mean, sorting and skewness off two seasons (dry season and wet season by using the Particle Size Analyzer (PSA after digest the sample with Hydrogen Peroxide (H2O2 and Hydrochloric Acid (HCl. There is a significant (P<0.05 relationship between sediment characteristic with the seasonal changes with the increasing mean particle size occurring during the wet season. Finer sediments dominate the mangrove sediment during monsoon season while coarser sediments dominate during the dry season. Meanwhile, sediment mean size for each transect tends to be coarser towards the back mangrove.

  20. 四川盆地南部地区寒武系油气勘探前景%Oil and Gas Exploration Prospects of Cambrian in Southern Sichuan Basin

    Institute of Scientific and Technical Information of China (English)

    王佳; 刘树根; 黄文明; 张长俊; 曾祥亮

    2011-01-01

    为明确四川盆地南部地区寒武系常规油气和页岩气的勘探前景,应用岩相学和地球化学分析手段相结合,对研究区中上寒武统娄山组和下寒武统清虚洞组的厚度、孔隙度、渗透率、孔隙类型和下寒武统筇竹寺组的厚度、总有机碳质量分数w(TOC)、镜质体反射率Ro、矿物组分等进行了深入剖析.结果表明:①川南地区烃源岩厚度大(80~100m),w(TOC)高(3%~5%),为一套中—好的过成熟后期阶段烃源岩(Ro为3.0%~4.8%),矿物组分与美国重要页岩气产层Barnett页岩相似,其中石英、长石和黄铁矿的体积分数为31%~50%,黏土矿物体积分数为29%~53%;②威远地区下寒武统九老洞组黑色页岩含气量达0.43~0.86 m3/t;微孔隙发育,主要为粒间孔,孔隙直径达5~10μm,裂缝密度一般为30~50条/m;③中上寒武统娄山组和下寒武统清虚洞组总体上是寒武系最重要的常规储层,储层内部沥青质量分数一般为3%~6%,储集空间主要为粒间溶孔—晶间孔等,平均孔隙度为1.85%,平均渗透率为2.25×10-3μm2;④在川东南地区靠近盆地边缘的斜坡带,寒武系具有较好的常规油气藏勘探前景,而川东南缘和川西南地区筇竹寺组下部具有较大的页岩气勘探潜力.%In order to identify the exploration prospect of Cambrian conventional oil and gas and shale gas in southern Sichuan Basin, this paper, combining the petrographic and geochemical methods, makes a tho-rugh analysis of the thickness, porosity, permeability, porosity type of Middle-Upper Cambrian Loushan-guan Formation and Lower Cambrian Qingxudong Formation, as well as the thickness, TOC, Ro, mineral composition of Lower Cambrian Qiongzhusi Formation. The results show that: (1) The hydrocarbon source rocks in southern Sichuan Basin are thick(80 -100 m)and of high organic matter content (3%-5%). It is a set of general-good late-mature stage of hydrocarbon source

  1. Concentrations of heavy metals in river sediments of the Canes River Basin, the state of Rio de Janeiro, Brazil

    International Nuclear Information System (INIS)

    Research about chimism in the Bengalas river basin was performed as a part of the environmental study project developed in the area, encompassing several knowledge fields. Among these, Environmental Geochemistry played an important role. This work presents the results related to heavy metals in stream sediments, indicating its origins (natural or anthropic) and its availability for aquatic biota. The basin under study has 135.07 Km2, laying in the oriental portion of the Teresópolis country, 100 Km far from the of Rio de Janeiro city. The rivers forming the Bengalas basin cut Pre-Cambrian terrain, formed by Orthognaiss takes 70% of the area, post-tectonic granite(20%), migmatite gneiss (10%) and gabro dikes. The methodology used was the determination of the content of heavy metals through sequencial extraction technique, consisting in the selective remove of metals in the geochemical fractions found in the sediments, cation exchange (bioavailable), carbonaceous, reducible and organic (potentially bioavailable) and residual (non available).The analyze of the results showed that iron was present in all sequential phases and predominated in the residual phase The same behavior was verified for zinc and copper. Manganese had the best distribution through the fractions due to its redox character, allowing bigger solubility and transportation; it appeared in the exchange, residual, organic and carbonaceous phases. Cadmium was found only in the carbonaceous phase, confirming its geochemical tendency. Chrome, on the other hand, was present in the residual and organic phase, while lead was found in the residual and carbonaceous phase

  2. NUMERICAL SIMULATION OF SEDIMENT RELEASE FROM RESERVOIRS

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    For the computation of the sediment quantity released from reservoirs, a vertical two-dimensional hydrodynamic model is combined with a sediment transport model. The hydrodynamic model is based on the equations of mass and momentum conservation along with a k - ε model for closure of the Reynolds stresses. The sediment transport model is based on the convection-diffusion equation of sediment concentration and the sediment continuity equation. Both the hydrodynamic and sediment transport models are developed in a boundary-fitted curvilinear co-ordinate system. Comparison of the predicted mean velocity field with laboratory results indicates that the present model captures most experimental trends with reasonable accuracy. Also good agreement is found in comparison of the sediment transport results for the numerical model and the experimental model.

  3. Review of sediment stabilisation techniques

    International Nuclear Information System (INIS)

    The best sites for tidal power schemes are found in estuaries with high tidal ranges which have complex ecosystems and include a wide and diverse range of habitats. If the tidal power is to be developed, therefore, it is important to determine the likely effect on the environment and any ameliorative measures which may be necessary. One possible change is likely to be the erosion of material from the bed or shoreline of the estuary, and possibly the adjacent coast. This is of particular concern if intertidal sandflats, mudflats and saltmarsh are affected, as these are important wildlife habitats. Moreover, largescale movement of sediments would be undesirable. Results of a desk study of methods of preventing the erosion of sediment deposits in or near an estuary in the conditions that may occur following the construction of a tidal power barrage are presented. (author)

  4. Bottom sediments of Ypacarai Lake

    International Nuclear Information System (INIS)

    Bottom sediments of Ypacarai Lake was investigated with XRF and Mossbauer techniques. The lake of about 120 Km2, is a shallow one, medium deep of about 1.8m. In addition to its use for recreation, its basin has a wide area of influence and of economical significance. Bottom sediments play an important role in the overall distribution of trace elements in the aquatic system and act as a sink for metals. Bottom samples were taken from 5 different sampling stations, selected according to the morphology and population sites in the shore. The concentration of toxic metals was found to be low and no negative ecological impact should be expected. The main metallic ion component is iron (1.69%). Mossbauer studies showed this element appears as Fe+3 and no Fe+2 was detected. It is here suggested that Fe+3 acts as the limiting element which controls eutrophication process

  5. Vertical distribution of sediment concentration

    Institute of Scientific and Technical Information of China (English)

    Sai-hua HUANG; Zhi-lin SUN; Dan XU; Shan-shan XIA

    2008-01-01

    A simple formula is proposed to predict the vertical distribution of a suspended load concentration in a 2D steady turbulent flow.The proposed formula significantly improves the well-known Rouse formula where sediment concentration has an infinitely large value at the channel bottom and a zero value at the water surface.Based on this formula and the logarithmic ve-locity profile,a theoretical elementary function for the transport rate of a suspended load is developed.This equation improves the Einstein equation in which the unit-width suspended sediment discharge must be solved by numerical integration and a contra-diction between the lower limit of the integral and that of velocity distribution exists.

  6. SEDIMENT TRANSPORT EXPERIMENTSIN UNSTEADY FLOWS

    Institute of Scientific and Technical Information of China (English)

    DE SUTTER R.; HUYGENS M.; VERHOEVEN R.

    2001-01-01

    By means of a test flume with semi-circular cross-section, bedload and suspended-sediment transport of non-cohesive material have been studied in transient flow. The experimental facility enables us to investigate the time evolution of friction and transport parameters. Preliminary measurements with a fixed bottom instead of a sediment bed yield a reliable assessment of flow and friction characteristics. Time sequence in unsteady flow of the relevant parameters is revealed. The influence of turbulence variation and shear stress variation on the transport is investigated. As existing transport equations are found to be in poor agreement with experimental data, a new "engineering" concept is constructed which relates friction velocity to transport.

  7. Machine learning in sedimentation modelling.

    Science.gov (United States)

    Bhattacharya, B; Solomatine, D P

    2006-03-01

    The paper presents machine learning (ML) models that predict sedimentation in the harbour basin of the Port of Rotterdam. The important factors affecting the sedimentation process such as waves, wind, tides, surge, river discharge, etc. are studied, the corresponding time series data is analysed, missing values are estimated and the most important variables behind the process are chosen as the inputs. Two ML methods are used: MLP ANN and M5 model tree. The latter is a collection of piece-wise linear regression models, each being an expert for a particular region of the input space. The models are trained on the data collected during 1992-1998 and tested by the data of 1999-2000. The predictive accuracy of the models is found to be adequate for the potential use in the operational decision making. PMID:16530383

  8. Using sediment particle size distribution to evaluate sediment sources in the Tobacco Creek Watershed

    Science.gov (United States)

    Liu, Cenwei; Lobb, David; Li, Sheng; Owens, Philip; Kuzyk, ZouZou

    2014-05-01

    Lake Winnipeg has recently brought attention to the deteriorated water quality due to in part to nutrient and sediment input from agricultural land. Improving water quality in Lake Winnipeg requires the knowledge of the sediment sources within this ecosystem. There are a variety of environmental fingerprinting techniques have been successfully used in the assessment of sediment sources. In this study, we used particle size distribution to evaluate spatial and temporal variations of suspended sediment and potential sediment sources collected in the Tobacco Creek Watershed in Manitoba, Canada. The particle size distribution of suspended sediment can reflect the origin of sediment and processes during sediment transport, deposition and remobilization within the watershed. The objectives of this study were to quantify visually observed spatial and temporal changes in sediment particles, and to assess the sediment source using a rapid and cost-effective fingerprinting technique based on particle size distribution. The suspended sediment was collected by sediment traps twice a year during rainfall and snowmelt periods from 2009 to 2012. The potential sediment sources included the top soil of cultivated field, riparian area and entire profile from stream banks. Suspended sediment and soil samples were pre-wet with RO water and sieved through 600 μm sieve before analyzing. Particle size distribution of all samples was determined using a Malvern Mastersizer 2000S laser diffraction with the measurement range up to 600μm. Comparison of the results for different fractions of sediment showed significant difference in particle size distribution of suspended sediment between snowmelt and rainfall events. An important difference of particle size distribution also found between the cultivated soil and forest soil. This difference can be explained by different land uses which provided a distinct fingerprint of sediment. An overall improvement in water quality can be achieved by

  9. Flocculation Dynamics of cohesive sediment

    OpenAIRE

    Maggi, F.

    2005-01-01

    Cohesive sediment suspended in natural waters is subject not only to transport and deposition processes but also to reactions of flocculation, \\textit{i.e.} aggregation of fine particles, and breakup of aggregates. Although aggregation and breakup occur at small and very small length scales compared to transport and deposition, flocculation can effectively have an impact on the large scale as well. Some phenomena that are correlated to (or find roots in) flocculation reactions are, for instan...

  10. MITIGATION OF SEDIMENTATION HAZARDS DOWNSTREAM FROM RESERVOIRS

    Institute of Scientific and Technical Information of China (English)

    Ellen WOHL; Sara RATHBURN

    2003-01-01

    Many reservoirs currently in operation trap most or all of the sediment entering the reservoir,creating sediment-depleted conditions downstream. This may cause channel adjustment in the form of bank erosion, bed erosion, substrate coarsening, and channel planform change. Channel adjustment may also result from episodic sediment releases during reservoir operation, or from sediment evacuation following dam removal. Channel adjustment to increased sediment influx depends on the magnitude, frequency, duration and grain-size distribution of the sediment releases, and on the downstream channel characteristics. Channel adjustment may occur as a change in substrate sizedistribution, filling of pools, general bed aggradation, lateral instability, change in channel planform,and/or floodplain aggradation. The increased sediment availability may alter aquatic and riparian habitat, reduce water quality, distribute adsorbed contaminants along the river corridor, and provide germination sites for exotic vegetation. Mitigation of these sedimentation hazards requires: (1)mapping grain-size distribution within the reservoir and estimating the grain-size distributions of sediment that will be mobilized through time; (2) mapping shear stress and sediment transport capacity as a function of discharge on the basis of channel units for the length of the river likely to be affected; (3) mapping potential depositional zones, and aquatic habitat and "acceptable losses," along the downstream channel, and comparing these volumes to the total sediment volume stored in the reservoir as a means of estimating total transport capacity required to mobilize reservoir sediment delivered to the channel; (4) designing discharge and sediment release regime (magnitude, frequency,duration) to minimize adverse downstream impacts; and (5) developing plans to remove, treat, contain,or track contaminants, and to restrict establishment of exotic vegetation. The North Fork Poudre River in Colorado is used to

  11. Evidence for multi-cycle sedimentation and provenance constraints from detrital zircon U-Pb ages: Triassic strata of the Lusitanian basin (western Iberia)

    Science.gov (United States)

    Pereira, M. F.; Gama, C.; Chichorro, M.; Silva, J. B.; Gutiérrez-Alonso, G.; Hofmann, M.; Linnemann, U.; Gärtner, A.

    2016-06-01

    Laser ablation ICP-MS U-Pb analyses were conducted on detrital zircons of Triassic sandstone and conglomerate from the Lusitanian basin in order to: i) document the age spectra of detrital zircon; ii) compare U-Pb detrital zircon ages with previous published data obtained from Upper Carboniferous, Ordovician, Cambrian and Ediacaran sedimentary rocks of the pre-Mesozoic basement of western Iberia; iii) discuss potential sources; and iv) test the hypothesis of sedimentary recycling. U-Pb dating of zircons established a maximum depositional age for this deposit as Permian (ca. 296 Ma), which is about sixty million years older compared to the fossil content recognized in previous studies (Upper Triassic). The distribution of detrital zircon ages obtained points to common source areas: the Ossa-Morena and Central Iberian zones that outcrop in and close to the Porto-Tomar fault zone. The high degree of immaturity and evidence of little transport of the Triassic sediment suggests that granite may constitute primary crystalline sources. The Carboniferous age of ca. 330 Ma for the best estimate of crystallization for a granite pebble in a Triassic conglomerate and the Permian-Carboniferous ages (age spectra found in Triassic strata are also the result of recycling from the Upper Carboniferous Buçaco basin, which probably acted as an intermediate sediment repository. U-Pb data in this study suggest that the detritus from the Triassic sandstone and conglomerate of the Lusitanian basin is derived from local source areas with features typical of Gondwana, with no sediment from external sources from Laurussia or southwestern Iberia.

  12. Sediment load reduction in Chinese rivers

    Institute of Scientific and Technical Information of China (English)

    Cheng LIU; Jueyi SUI; Zhao-Yin WANG

    2008-01-01

    In this Paper,the changes in the annual runoff and sediment transport have been assessed by using the long term observation data from 10 gauging stations on 10 large rivers across China from far north to far south.It is found that the annual sediment yield has generally had a decreasing trend in the past half century.According to the changes in annual runoff and the sediment yield per area.rivers in China can be classified into the following three groups:1)rivers with decreasing annual sediment transport and stable runoff:2)rivers with both decreasing annual sediment transport and runoff and 3)rivers with greatly reduced annual sediment transport and decreasing annual runoff.The results indicate that,in all southern rivers(to the south of the Huaihe River including the Huaihe River),there has been little change in average annual runoff but a dramatic decrease in annual sediment transport.In the northern rivers.however,both the annual sediment yield and the runoff show significant evidence of reduction.To further investigate the recent changes in annual runoff and sediment transport.the short-term observation data from these 10 gauging stations in the recent 10 years have been assessed.Results show that both the annual sediment transport and the runoff have decreased significantly in the northern rivers in the past 10 years.Using the Yellow River at the Lijin Station as an example,the average annual runoff for the last 10 years is only 1/3 of the long term average value and the average annual sediment yield of the last 10 years is only 1/4 of the long term average value.More unusually,in the Yongding River the annual sediment yield has approached zero and the runoff has decreased significantly.In addition,the impacts of human activities on the changes in both runoff and sediment transport have been discussed.

  13. Sediment supply versus local hydraulic controls on sediment transport and storage in a river with large sediment loads

    Science.gov (United States)

    Dean, David; Topping, David; Schmidt, John C.; Griffiths, Ronald; Sabol, Thomas

    2016-01-01

    The Rio Grande in the Big Bend region of Texas, USA, and Chihuahua and Coahuila, Mexico, undergoes rapid geomorphic changes as a result of its large sediment supply and variable hydrology; thus, it is a useful natural laboratory to investigate the relative importance of flow strength and sediment supply in controlling alluvial channel change. We analyzed a suite of sediment transport and geomorphic data to determine the cumulative influence of different flood types on changing channel form. In this study, physically based analyses suggest that channel change in the Rio Grande is controlled by both changes in flow strength and sediment supply over different spatial and temporal scales. Channel narrowing is primarily caused by substantial deposition of sediment supplied to the Rio Grande during tributary-sourced flash floods. Tributary floods have large suspended-sediment concentrations, occur for short durations, and attenuate rapidly downstream in the Rio Grande, depositing much of their sediment in downstream reaches. Long-duration floods on the mainstem have the capacity to enlarge the Rio Grande, and these floods, released from upstream dams, can either erode or deposit sediment in the Rio Grande depending upon the antecedent in-channel sediment supply and the magnitude and duration of the flood. Geomorphic and sediment transport analyses show that the locations and rates of sand erosion and deposition during long-duration floods are most strongly controlled by spatial changes in flow strength, largely through changes in channel slope. However, spatial differences in the in-channel sediment supply regulate sediment evacuation or accumulation over time in long reaches (greater than a kilometer).

  14. Watershed sediment yield modeling for data scarce areas

    OpenAIRE

    Habtamu Itefa Geleta

    2011-01-01

    The sustainability and service life of reservoirs depends on the amount of sediment storage. Reservoir sedimentation is a critical problem in reducing the service life of dams. The sedimentation problem is the consequence of watersheds sediment supply to the river networks and then to the reservoir. River bank sediment deposition is another consequence of excess sediment supply from the upstream watersheds. The deposition of sediment on bank of a river causes change in flow regime and as resu...

  15. Oldest entirely preserved sponges and other fossils from the Lowermost Cambrian and a new facies reconstruction of the Yangtze platform (China)

    OpenAIRE

    Steiner, M; Mehl, D.; Reitner, Joachim; Erdtmann, B.-D.

    1993-01-01

    Eine Faziesrekonstruktion W1d Korrelation obersinischer-unterkambrischer Schichten der Yangtze-Plattform (Südchina) wird vorgestellt. Dabei wird zwischen geschütztem Becken, Schwelle W1d tiefem Becken unterschieden. Die unterkambrische Schwarzschiefer-Transgression, der "Badaowan" Event, wird als diachron gekennzeichnet. Nach Untersuchungen der Lithologie W1d Geochemie der unterkambrischen Sedimente, vorwiegend Schwarzschiefer des Profils Sansha (nahe Dayong. N-Hunan), kann zwischen ...

  16. PROFILE: Management of Sedimentation in Tropical Watersheds.

    Science.gov (United States)

    NAGLE; FAHEY; LASSOIE

    1999-05-01

    / The sedimentation of reservoirs is a serious problem throughout the tropics, yet most attempts to control sedimentation in large river basins have not been very successful. Reliable information on erosion rates and sources of sediments has been lacking. In regions where geologically unstable terrain combines with high rainfall, natural erosion rates might be so high that the effects of human activity are limited. Estimates of natural erosion in these situations often have been poor because of the episodic nature of most erosion during large storms and because mass-wasting may supply much of the sediment. The predominance of mass-wasting in some watersheds can result in an unexpectedly high ratio of bedload to suspended load, shifting sedimentation to "live" rather than "dead" storage within reservoirs. Furthermore, the inappropriate use of the Universal Soil Loss Equation to assess the effectiveness of erosion control measures has led to inaccurate estimates of the sediment reduction benefits that could accrue to watershed treatment efforts. Although reducing erosion from cultivated areas is desirable for other reasons, efforts aimed at reducing reservoir sedimentation by controlling agricultural sources of erosion may have limited benefits if the principal sources are of natural origin or are associated with construction of the dams and reservoirs and with rural roads and trails. Finally, the most appropriate locations for watershed rehabilitation depend on the magnitude of temporary storage of colluvium and alluvium within the river basin: Where storage volume is large and residence time of sediment very long, reducing agricultural erosion may have limited impacts on sedimentation within the expected life of a reservoir. Systematic development and analysis of sediment budgets for representative watersheds is needed to address these limitations and thereby improve both the planning of river basin development schemes and the allocation of resources towards

  17. 137Cs in northern Adriatic sediments

    International Nuclear Information System (INIS)

    The activity of 137Cs in shallow northern Adriatic sediments was obtained on the basis of measurement results from 25 sediment box cores, sampled during the Adriatic Scientific COoperation Program (ASCOP) 16 cruise in the summer 1990. 137Cs was determined in surface sediments (0-3 cm) and 12-15 cm-deep sediment. It was found that the lowest caesium concentrations correspond to sands, which are spread along the Croatian coast. Parallel to the Italian coast, 137Cs concentrations in pelites are the highest. It seems that the influence of Po River is significant for 137Cs activities in recent marine sediments along Italian coast south of Po River delta. Significantly higher 137Cs activities in 0-3 cm sediment layer can be attributed to the deposition caused by Chernobyl accident. (author)

  18. Sedimentation

    Digital Repository Service at National Institute of Oceanography (India)

    Rixen, T.; Guptha, M.V.S.; Ittekkot, V.

    through the water column but their trapping efficiency, and thus, their accuracy can be biased by hydrodynamic and biological effects (Lee et al., 1988; Gust et al., 1992; 1994). Scholten et al. (2001) showed that the 230 Thorium trapping efficiency... (Lee et al. 1998; Honjo et al., 1999) and off Somalia (Broerse et al., 2000). In the southern open Arabian Sea this pattern is only weakly evident and the peak organic carbon fluxes are even lower than those during the Intermonsoon periods at the other...

  19. Continental margin sedimentation: from sediment transport to sequence stratigraphy

    Science.gov (United States)

    Nittrouer, Charles A., (Edited By); Austin, James A.; Field, Michael E.; Kravitz, Joseph H.; Syvitski, James P.M.; Wiberg, Patricia L.

    2007-01-01

    This volume on continental margin sedimentation brings together an expert editorial and contributor team to create a state-of-the-art resource. Taking a global perspective, the book spans a range of timescales and content, ranging from how oceans transport particles, to how thick rock sequences are formed on continental margins. - Summarizes and integrates our understanding of sedimentary processes and strata associated with fluvial dispersal systems on continental shelves and slopes - Explores timescales ranging from particle transport at one extreme, to deep burial at the other - Insights are presented for margins in general, and with focus on a tectonically active margin (northern California) and a passive margin (New Jersey), enabling detailed examination of the intricate relationships between a wide suite of sedimentary processes and their preserved stratigraphy - Includes observational studies which document the processes and strata found on particular margins, in addition to numerical models and laboratory experimentation, which provide a quantitative basis for extrapolation in time and space of insights about continental-margin sedimentation - Provides a research resource for scientists studying modern and ancient margins, and an educational text for advanced students in sedimentology and stratigraphy

  20. Analysis of sedimentation of canals

    Directory of Open Access Journals (Sweden)

    Agunwamba, J.C.,

    2013-03-01

    Full Text Available The dredged canals in the Niger Delta coastal flood plain are being threatened by siltation. This study is limited to those canals in Rivers State of Nigeria, which are under the influence of tidal waves. A total of eight canals were considered with four each from Ekulama and Cawthorne Channel. Different approaches were used to carry out this study, which includes field reconnaissance survey, hydrographic survey, soil sample analysis and collection of all available data and information. The typical bed materials size (D50 is approximately 0.01mm; which gives a settling velocity of 0.09mm/sec using stroke’s law. Hydrographic survey of the canals from 1992 to 1996 revealed an average siltation rate of 2.35m/yr. A regression equation was also derived which relates the cost of dredging to canal area, rate of siltation and average aggregation. A plot of canal centre profile; entrance, middle and end cross sections showing sediment distribution along the canal profile, shows that majority of the particles that form the sediment enter the canal from the rivers. The sedimentation is caused by the reduction in water current, which has average value of 0.0145m/sec. The bathyorographical check on the canals revealed that the sum of the two exterior angles of the canal with the river at the point of connection has to lie within 1800 + 50 for an effective flow that will minimize settlement of particles. In addition, the canals should be constructed to start and terminate on a moving water body, to avoid dead ends. A regression equation was determined which relates the cost of dredging to canal area, rate of siltation and average aggradations.

  1. DYNAMIC RESOURCES OF RIVER SEDIMENTS

    Institute of Scientific and Technical Information of China (English)

    George GERGOV; Tzviatka KARAGIOZOVA

    2005-01-01

    The currently enforced Bulgarian water legislation [the Water Act (1999),the Environmental Protection Act (2002),etc.] requires conducting special studies for accurate assessments of sand and gravel flux along the rivers,prior to the issue of the license for operation of the quarries,where they will be dredged. The activity of a quarry necessitates special investigations because of the large dimensions of the damages inflicted on the environment. Ours studies have shown that there are two types of river reaches,in which abstracion of sand and gravel is performed. The first one refers usually to the plain area river reaches. The other type is mountainous with high rate of sediment load,which consists of coarse solid matter. The "on-the-spot" study on the environmental impact of the sand and gravel dredging has revealed that in the area of the quarry the riverbed cuts into the alluvial sediments to about 6-7 m and this ditch has spread by attenuation at a distance of more than 25 km upstream. Downstream the pit the picture is replicated and at the 8th km a local scour on the riverbed,amounting to more than 1.80 - 2.00 m,has been measured near the foundation of a massive bridge in the centre of city of Plovdiv. Such assessments of dynamic resources of sand and gravel materials are expected to serve for the purposes of gradual limitation of this activity in river sections close to renewable resources. The amount of sediment load,which may be abstracted in the area of the Orizare quarry in Bulgaria on a yearly basis has been calculated as 6000 m3/a. It ensures that the resources will not be exhausted and irreversible distortion of the riverbed will be prevented. This is an environmentally safe limit.

  2. Long distance electron transmission in marine sediment

    DEFF Research Database (Denmark)

    Risgaard-Petersen, Nils; Nielsen, Lars Peter

    Geochemical observations in marine sediment have recently shown that electric currents may intimately couple spatially separated biogeochemical processes like oxygen reduction at the sediment surface and hydrogen sul-phide oxidation in anoxic layers centimeters below 1. Further experimental studi...... the system. Long distance electron transmission may flourishes in marine sediments exposed to tran-sient oxygen depletion, leaving distinct signatures of such events in the geological record....

  3. Flux saturation length of sediment transport

    OpenAIRE

    Pähtz, T.; Kok, JF; Parteli, EJR; Herrmann, HJ

    2013-01-01

    Sediment transport along the surface drives geophysical phenomena as diverse as wind erosion and dune formation. The main length-scale controlling the dynamics of sediment erosion and deposition is the saturation length $L_\\mathrm{s}$, which characterizes the flux response to a change in transport conditions. Here we derive, for the first time, an expression predicting $L_\\mathrm{s}$ as a function of the average sediment velocity under different physical environments. Our expression accounts ...

  4. Luminescence dating of storm-surge sediment

    OpenAIRE

    Cunningham, A. C.

    2011-01-01

    Geological evidence of storm surges has the potential to provide vital information on storm-surge risk. Sediment from the coastal dunes of the Netherlands contains evidence of extreme floods that occurred before reliable measurements of water level began. For these sediments to be useful in flood-risk analysis, they need to be reliably dated. This thesis investigates the use of Luminescence dating for storm-surge sediment. Luminescence dating is a radiometric dating method, which uses tiny li...

  5. Biodegradation of petroleum in marine seep sediments

    OpenAIRE

    Mishra, Sonakshi

    2016-01-01

    This study presented for the first time the use of intact sediment cores in a continuous sediment-oil-flow-through (SOFT) system for investigating the degradation of petroleum under a simulated petroleum seepage.The biogeochemical response of sediments from hydrocarbon adapted sites like the Caspian Sea, North Alex Mud Volcano in the Eastern Mediterranean, the Santa Barbara Channel and non-adapted site like the Eckernfoerde Bay in the Baltic Sea to petroleum seepage was investigated and compa...

  6. Sulfate reduction and methanogenesis in marine sediments

    Science.gov (United States)

    Oremland, R. S.; Taylor, B. F.

    1978-01-01

    Methanogenesis and sulfate-reduction were followed in laboratory incubations of sediments taken from tropical seagrass beds. Methanogenesis and sulfate-reduction occurred simultaneously in sediments incubated under N2, thereby indicating that the two processes are not mutually exclusive. Sediments incubated under an atmosphere of H2 developed negative pressures due to the oxidation of H2 by sulfate-respiring bacteria. H2 also stimulated methanogenesis, but methanogenic bacteria could not compete for H2 with the sulfate-respiring bacteria.

  7. Improving Fishpond Sediment by Aquatic Vegetable Rotation

    OpenAIRE

    Ling Tao; Chun-Xue Zhang; Jian-Qiang Zhu; Shi-Yang Zhang; Xiao-Li Li; Gu Li

    2012-01-01

    Continuously intensive fish farming results in pond degradation that needs to be improved. Therefore, the experiment rotating intensive fish culture with two aquatic vegetables lotus (Nelumbo nucifera) and water chestnuts (Eleocharis dulcis) cultivation is conducted aiming at determining the effect of rotation as a sediment management technique on improving the pond sediment and assessing the food safety risk of the vegetables cultivated in the pond sediment from the aspects of heavy metal. T...

  8. Meiofauna Metabolism in Suboxic Sediments: Currently Overestimated

    OpenAIRE

    Braeckman, U.; Vanaverbeke, J.; Vincx, M.; van Oevelen, D.; Soetaert, K.

    2013-01-01

    Oxygen is recognized as a structuring factor of metazoan communities in marine sediments. The importance of oxygen as a controlling factor on meiofauna (32 µm-1 mm in size) respiration rates is however less clear. Typically, respiration rates are measured under oxic conditions, after which these rates are used in food web studies to quantify the role of meiofauna in sediment carbon turnover. Sediment oxygen concentration ([O2]) is generally far from saturated, implying that (1) current estima...

  9. Reservoir quality and petrophysical properties of Cambrian sandstones and their changes during the experimental modelling of CO2 storage in the Baltic Basin

    Directory of Open Access Journals (Sweden)

    Kazbulat Shogenov

    2015-08-01

    Full Text Available The objectives of this study were (1 to review current recommendations on storage reservoirs and classify their quality using experimental data of sandstones of the Deimena Formation of Cambrian Series 3, (2 to determine how the possible CO2 geological storage (CGS in the Deimena Formation sandstones affects their properties and reservoir quality and (3 to apply the proposed classification to the storage reservoirs and their changes during CGS in the Baltic Basin. The new classification of the reservoir quality of rocks for CGS in terms of gas permeability and porosity was proposed for the sandstones of the Deimena Formation covered by Lower Ordovician clayey and carbonate cap rocks in the Baltic sedimentary basin. Based on permeability the sandstones were divided into four groups showing their practical usability for CGS (‘very appropriate’, ‘appropriate’, ‘cautionary’ and ‘not appropriate’. According to porosity, eight reservoir quality classes were distinguished within these groups. The petrophysical, geochemical and mineralogical parameters of the sandstones from the onshore South Kandava and offshore E6 structures in Latvia and the E7 structure in Lithuania were studied before and after the CO2 injection-like alteration experiment. The greatest changes in the composition and properties were determined in the carbonate-cemented sandstones from the uppermost part of the South Kandava onshore structure. Partial dissolution of pore-filling carbonate cement (ankerite and calcite and displacement of clay cement blocking pores caused significant increase in the effective porosity of the samples, drastic increase in their permeability and decrease in grain and bulk density, P- and S-wave velocity, and weight of the dry samples. As a result of these alterations, carbonate-cemented sandstones of initially ‘very low’ reservoir quality (class VIII, ‘not appropriate’ for CGS, acquired an ‘appropriate’ for CGS

  10. Geochemistry of major and trace elements and Pb–Sr isotopes of a weathering profile developed on the Lower Cambrian black shales in central Hunan, China

    International Nuclear Information System (INIS)

    Highlights: • The chemical changes during black shale weathering are geochemically estimated. • Chemical changes and Pb–Sr data suggest four types of chemical reactions. • There were two stages of geochemical processes during black shale weathering. • Early stage of chemical differentiation led elements leaching and redistribution. • Soil was formed by later chemical homogenisation after the early differentiation. - Abstract: This paper reports a geochemical study on the major and trace elements and Pb–Sr isotopes of a weathering profile developed in the Lower Cambrian black shales in central Hunan (China). Six weathering horizons were identified and sampled vertically throughout the profile. The chemical composition of the profile consists of variable concentrations of the major elements Fe2O3, FeO, MnO, MgO, CaO, Na2O, and P2O5 and of less variable concentrations of SiO2, TiO2, Al2O3, and K2O. The chemical change caused by weathering is estimated by mass-balance calculations, and the results show that the element mobility is characterised by substantial loss of SiO2, FeO, CaO, K2O, Na2O, LOI, Cr, V, Ba, Cs, Rb, Sr, U, and Th, and moderate loss of Al2O3, MgO, Fe2O3, Ni, Cu, Pb, Tl, Sn, Sc, Ge and REE (Y). The high field strength elements TiO2, Sn, Sc, U, Ga, Ge, Zr, Hf, Nb, and Ta were immobile during weathering. The chemical changes and the Pb–Sr isotopic data suggest that four types of chemical reactions occurred: the oxidation of sulphide minerals (e.g., pyrite) and organic carbon (OS), the dissolution of less resistant clinochlore-Ia, calcite, and P-bearing minerals (DL), the dissolution of detrital albite and microcline (DA), and the transformation of clay (TC) minerals (e.g., muscovite and illite–smectite). These chemical reactions then led to two stages of geochemical processes, an early stage of chemical differentiation and a later stage of chemical homogenisation. The chemical differentiation dominated by the OS, DL, and DA reactions

  11. Thermoluminescence dating of pleistocene sediments

    International Nuclear Information System (INIS)

    After a short introduction on recent trends in quaternary geochronology, this article focuses on the thermoluminescence dating of sediments, whose principles and present limits and prospects are discussed. Results are presented for the TL behaviour of sands from various geological contexts in Brazil. They show that the coarse (approx. 100-200μm) quartz fraction of coastal and intra continental, eolian and fluvial-type deposits, might be datable by TL from the upper Holocene to at least the basis of the upper Pleistocene, with a precision of + - 10-15%. (Author)

  12. Sedimentation rate in Ariake Sea

    International Nuclear Information System (INIS)

    The Ariake Sea is a shallow and almost enclosed sea located in western Kyushu, Japan with an area of about 1,700 km2 and the deepest up to 30 m at north area. The most inner part of the bay area is very shallow and during low tide big mudflats tideland appears and extends up to several km. The tidal range is the highest in Japan with a maximum of about 6 m. The area is one of Japan's most important area for fishery, with over 40% of the total seaweed production in Japan In the year 2001, due to environmental conditions, the seaweed population decreased substantially with a production drop of about 50%. This was caused by an earlier winter outbreak of red tide that affected the seaweed quality. One proposed cause for this decline might be the land reclamation project in the western part of Ariake Sea, Isahaya Bay. This project started in April 1997 were more than 3,000 ha of the bay where closed by a 7 km long seawall. Contaminated water is regularly discharged from the reservoir inside the dike, which have resulted in changes in water flows and perhaps a decrease in tidal range. In 2002, the gates at the dike were open for two months for a survey campaign and the seaweed harvest in the winter 2002-2003 was quite good. However, the problem may be linked to totally different causes, e.g. increase in industrial pollution discharge, chemicals used in the disinfection methods of washing seaweed, or change in water pH after the volcanic eruptions of the Unzen mountain in 1992 and 1993. The purpose of the research is to elucidate present condition of the Ariake Sea and past history using by radiometric methods, and obtained useful information will resolve the environmental status of Ariake Sea and give us answers way to save the Ariake Sea. Sea sediment cores were taken on board in 2003 at several points covering the Ariake sea. Two cores taken in inner area of the sea were sectioned at every 2 cm intervals and subjected to gamma spectrometry to determine sedimentation

  13. Crenarchaeota in Lake Michigan sediment.

    OpenAIRE

    MacGregor, B.J.; Moser, D. P.; Alm, E W; Nealson, K. H.; Stahl, D. A.

    1997-01-01

    RNA from Lake Michigan sediment was hybridized with a DNA probe for archaeal 16S rRNA. There was a peak of archaeal rRNA abundance in the oxic zone and another immediately below it. Six contributing species were identified by PCR amplification of extracted DNA with primers specific for archaeal rDNA: two related to Methanosarcina acetivorans and four related to marine crenarchaeotal sequences. rRNA quantification using a DNA probe specific for this crenarchaeotal assemblage showed it is most ...

  14. Thermoluminescence dating of pleistocene sediments

    International Nuclear Information System (INIS)

    After a short introduction on recent trends in quaternary geochronology, this article focuses on the thermoluminescence (TL) dating of sediments, whose principles, present limits and prospects are discussed. Results are presented for TL behavior of sands from various geological contexts in Brazil. They show that the coarse (approx. 100-200 μm) quartz fraction of coastal and intracontinental, eolian and fluvial - type deposits, might be datable by TL from the upper Holocene to at least the base of the upper Pleistocene, with a precision of +- 10-15%. (Author)

  15. Arsenic mobility in contaminated lake sediments

    International Nuclear Information System (INIS)

    An arsenic contaminated lake sediment near a landfill in Maine was used to characterize the geochemistry of arsenic and assess the influence of environmental conditions on its mobility. A kinetic model was developed to simulate the leaching ability of arsenic in lake sediments under different environmental conditions. The HM1D chemical transport model was used to model the column experiments and determine the rates of arsenic mobility from the sediment. Laboratory studies provided the information to construct a conceptual model to demonstrate the mobility of arsenic in the lake sediment. The leaching ability of arsenic in lake sediments greatly depends on the flow conditions of ground water and the geochemistry of the sediments. Large amounts of arsenic were tightly bound to the sediments. The amount of arsenic leaching out of the sediment to the water column was substantially decreased due to iron/arsenic co-precipitation at the water-sediment interface. Overall, it was found that arsenic greatly accumulated at the ground water/lake interface and it formed insoluble precipitates. - Arsenic accumulates at the ground water/lake interface, where it forms insoluble precipitates

  16. Release of metals from anoxic sediment

    DEFF Research Database (Denmark)

    Larsen, Martin Mørk; Jacobsen, Gitte

    sediment surface and the top of the water column on day 1, 4, 8 and 12, and the results for V, Mn, Co, Ni, Cu, Zn, Cd, Pb and Fe will be presented, together with indication of statistically significant increase in concentration between the different groups of treatment. The water was clear over both groups...... without crabs, but cloudy, indicating re-suspension in the group with crabs. The metal release from sediments will be discussed in the context of re-oxygenation of anoxic or low-oxic sediments and the effect of organism that digs into the sediment in recently re-oxidised bottom waters....

  17. Incipient motion of surf zone sediments

    Science.gov (United States)

    Frank, Donya; Foster, Diane; Sou, In Mei; Calantoni, Joseph

    2015-08-01

    Incipient motion experiments were conducted with natural gravel, acetate beads, and coarse-gravel-sized electronic grains called Smart Sediment Grains in a Small-Oscillatory Flow Tunnel. Measurements of fluid velocity were made using Particle Image Velocimetry. The strength of the fluid shear stresses and the pressure gradients were examined for a range of oscillatory flow conditions at the onset of motion of the sediment particles to determine which mechanism had induced particle motion. The three sediment types utilized in these experiments facilitated an assessment of the effects of sediment grain size diameter, shape, and density on incipient motion. Results suggested that the onset of sediment motion was dominated by the pressure gradients for flows with small orbital excursion amplitudes, by the shear stresses for flows with large orbital excursion amplitudes and by the combined effects for intermediate flows. The denser, angular gravel required greater free-stream accelerations to trigger sediment motion than the spherical, less dense acetate beads, and Smart Sediment Grains. A combined parameter for incipient motion that accounts for the simultaneous effects of both shear stresses and pressure gradients while depending on the static coefficient of friction and the packing concentration of the mobile bed layer was evaluated for accuracy using a range of sediment types. The results suggested that the combined parameter may be a better indicator of sediment mobilization under oscillatory flows than the typically assumed shear stress criterion.

  18. Suspended sediments limit coral sperm availability

    Science.gov (United States)

    Ricardo, Gerard F.; Jones, Ross J.; Clode, Peta L.; Humanes, Adriana; Negri, Andrew P.

    2015-01-01

    Suspended sediment from dredging activities and natural resuspension events represent a risk to the reproductive processes of coral, and therefore the ongoing maintenance of reefal populations. To investigate the underlying mechanisms that could reduce the fertilisation success in turbid water, we conducted several experiments exposing gametes of the corals Acropora tenuis and A. millepora to two sediment types. Sperm limitation was identified in the presence of siliciclastic sediment (230 and ~700 mg L−1), with 2–37 fold more sperm required to achieve maximum fertilisation rates, when compared with sediment-free treatments. This effect was more pronounced at sub-optimum sperm concentrations. Considerable (>45%) decreases in sperm concentration at the water’s surface was recorded in the presence of siliciclastic sediment and a >20% decrease for carbonate sediment. Electron microscopy then confirmed sediment entangled sperm and we propose entrapment and sinking is the primary mechanism reducing sperm available to the egg. Longer exposure to suspended sediments and gamete aging further decreased fertilisation success when compared with a shorter exposure. Collectively, these findings demonstrate that high concentrations of suspended sediments effectively remove sperm from the water’s surface during coral spawning events, reducing the window for fertilisation with potential subsequent flow-on effects for recruitment. PMID:26659008

  19. Sediment Sources in the Persian Gulf

    Science.gov (United States)

    Mahoutian, Mehrab

    2014-05-01

    Sediment Constituent Analysis is an effective tool for identifying sediment sources. Based on several sediment samples taken from different sites all over the Iranian coastlines, we have been able to show that an important portion of sediment on the beaches in the Persian Gulf is bio-clastic; that is, biologically created from the coral environment as well as other marine habitats. Unlike mineral (clastic) sediments, carbonate sediments are born not made. Furthermore, carbonate sand constituents are generally less durable than their quartz and mineral counterparts, and break down relatively quickly. Therefore, destruction of reefs and degradation of marine habitat are certain to reduce the sand supply to the shoreline in the Persian Gulf that is necessary to maintain beaches. Carbonate sands are also found on the coastline of the Oman Sea. One of the striking things about the sediments along the coastline of Iran is the high percentage of carbonate material. Molluscan debris is common, even ubiquitous. This reflects the populations living in the offshore waters. Some molluscs thrive in high-energy sandy environments, others like finer sediments. Some live at the surface, while some burrow down as much as a half-metre. A great deal of information can be gained from the study of the species of mollusk and their distribution in the sediments. This paper introduces a few case studies done in different parts of the Persian Gulf by using this method as a general assessment toolbox.

  20. Sediment reservoirs and sediment fluxes in high mountain environments: how does sediment move through the system at the decadal scale?

    Science.gov (United States)

    Micheletti, Natan; Lambiel, Christophe; Lane, Stuart N.

    2016-04-01

    Faced with rapid climate warming over recent decades, high mountain systems are likely to respond dramatically because of: (1) the vulnerability of permafrost, glacial and nival processes to temperature and precipitation changes; (2) the ample availability of unconsolidated, potentially mobile sediments left after deglaciation; and (3) steep slopes, that potentially aid sediment mobilization. We no surprisingly know little about these processes over the decadal scale because the geomorphic response is often complex, spatially and temporally, and there is little history of decadal scale measurement of these systems. In this paper, we focus upon a number of basins in the Southern Swiss Alps, with a wide range of primary sediment transfer mechanisms and altitude ranges up to 1,800 to 3,600 m asl. We are able to combine a set of unique data on: (1) erosion/deposition processes (derived from combined geomorphological maps and photogrammetrically-derived Digital Elevation Models); (2) sediment flux based upon tracking sediment using image correlation; (3) sediment connection quantified using a new approach to handle DEM noise; (4) changing stream sediment transport capacity derived from hydrodynamic modeling applied to long time series of river flow; and (5) sediment export measured at intakes flushed periodically as part of hydropower management. Results suggest a distinct landscape response to climatic forcing. A progressive acceleration of surface displacements for different landforms is observed throughout the last five decades. We observed that, with the beginning of a warmer period in the 1980s, glacier retreat and enhanced snowmelt caused water yield to increase considerably for various watersheds. This translates into enhancement of sediment transport capacities, which in combination with the intensification of landscape dynamics (greater erosion rates) explains the increase flushing frequency and hence sediment export registered in the basins. However, whilst

  1. Upstream sediment input effects on experimental dune trough scour in sediment mixtures

    OpenAIRE

    Kleinhans, M. G.

    2005-01-01

    Understanding causes of dune irregularity, especially dune trough scour, is important for the modeling of vertical sorting of sediment mixtures in morphological models of rivers with sediment mixtures. Sediment in dunes is generally sorted in a fining-upward manner, which affects the sediment transport composition depending on the scour depth distribution of the dunes. Why dunes become more irregular and develop deep scour holes in some conditions is only partially understood. Moreover, there...

  2. Development of a reference artificial sediment for chemical testing adapted to the MELA sediment contact assay

    OpenAIRE

    Le Bihanic, Florane; Perrichon, Prescilla; Landi, Laure; Clerandeau, Christelle; Le Menach, Karyn; Budzinski, Helene; Cousin, Xavier; Cachot, Jerome

    2014-01-01

    Most persistent organic pollutants, due to their hydrophobic properties, accumulate in aquatic sediments and represent a high risk for sediment quality. To assess the toxicity of hydrophobic pollutants, a novel approach was recently proposed as an alternative to replace, refine and reduce animal experimentation: the medaka embryo–larval sediment contact assay (MELAc). This assay is performed with Japanese medaka embryos incubated on a natural sediment spiked with the compound being tested. Wi...

  3. Dating sediment in a fast sedimentation reservoir using 137Cs and 210Pb

    Science.gov (United States)

    Over 10,000 reservoirs have been constructed in agricultural watersheds in the United States since the 1940s to control floods and sediments. Reservoir sedimentation records provide a unique opportunity to retrospectively study the effects of land use changes and climate variations on sediment produ...

  4. Evaluating sediment storage dams: structural off-site sediment trapping measures in northwest Ethiopia

    NARCIS (Netherlands)

    Mekonnen, M.M.; Keesstra, S.D.; Baartman, J.E.M.; Ritsema, C.J.; Melesse, A.M.

    2015-01-01

    Reservoir and lake sedimentation is a vital problem in Ethiopia. Constructing small and medium size dams at the outlets of sub-catchments within larger catchment helps to reduce the transport of sediment downstream to reservoirs or lakes. This study assessed the sediment trapping efficacy (STE) of s

  5. Auto consolidated cohesive sediments erosion

    International Nuclear Information System (INIS)

    Pollutants and suspended matters of a river can accumulate into the sedimentary column. Once deposited, they are submitted to self-weight consolidation processes, ageing and burying, leading to an increase of their erosion resistance. Pollutant fluxes can be related to sedimentary fluxes, determined by threshold laws. In this work, an erosion threshold model is suggested by introducing a cohesion force into the usual force balance. A model of cohesion is developed on the basis of interactions between argillaceous cohesive particles (clays), particularly the Van der Waals force, whose parameterization is ensured by means of granulometry and porosity. Artificial erosion experiments were performed in a recirculating erosion flume with natural cored sediments where critical shear stress measurements were performed. Other analyses provided granulometry and porosity. The results obtained constitute a good database for the literature. The model is then applied to the experimental conditions and gives good agreement with measurements. An example of the accounting for self-weight consolidation processes is finally suggested, before finishing on a Mohr like diagram dedicated to soft cohesive sediment erosion. (author)

  6. The Cambrian initiation of intra-oceanic subduction in the southern Paleo-Asian Ocean: Further evidence from the Barleik subduction-related metamorphic complex in the West Junggar region, NW China

    Science.gov (United States)

    Liu, Bo; Han, Bao-Fu; Xu, Zhao; Ren, Rong; Zhang, Jin-Rui; Zhou, Jing; Su, Li; Li, Qiu-Li

    2016-06-01

    In this study, we present new evidence from the Barleik subduction-related metamorphic complex in the southern West Junggar region, northwestern China, for the Cambrian initiation of intra-oceanic subduction in the southern Paleo-Asian Ocean. The Barleik metamorphic complex is mainly composed of blueschist and amphibolite blocks within an ophiolitic mélange and their protoliths are calc-alkaline andesite and alkali and tholeiitic basalts. The calc-alkaline andesite has a zircon U-Pb age of 502 ± 2 Ma, obtained from magmatic cores of zircon grains, and shares geochemical features similar to the 515-485 Ma intra-oceanic arc magmatic rocks in the West Junggar region. By contrast, the alkali and tholeiitic basalts have trace element features similar to ocean island and enriched mid-ocean ridge basalts, respectively. Rutile and sodic-calcic amphibole from the amphibolite have a U-Pb age of 502 ± 25 Ma and a 40Ar/39Ar age of ∼504 Ma, respectively, which are in good agreement within errors with a 40Ar/39Ar age of 492 ± 4 Ma for phengite from the blueschist. These metamorphic ages of ∼500 Ma are interpreted to represent the timing of Pacific-type subduction-related metamorphism and are also compatible with ages of the oldest supra-subduction zone ophiolites (531-512 Ma) and intra-oceanic arc plutons (515-485 Ma) in the southern West Junggar region. Being one of the oldest subduction-related metamorphic complexes (509-490 Ma) in the southern Central Asian Orogenic Belt, the Barleik metamorphic complex, together with the oldest arc plutons, definitely indicate the initial intra-oceanic subduction in the southern Paleo-Asian Ocean at least in the Early Cambrian.

  7. New Discoveries of Phaeophycean Fossils in the Early Cambrian,Haikou, Kunming,Yunnan, Southwest China%云南海口早寒武世褐藻化石新知

    Institute of Scientific and Technical Information of China (English)

    徐兆良

    2001-01-01

    主要报道了产自云南海口耳材村早寒武世筇竹寺组玉案山段澄江生物群中的褐藻化石——拟点叶藻(Punctariopsis latifolia gen. et sp. nov.)、简单拟点叶藻(Punctariopsis simplex gen. et sp. nov.)和古文德带藻(Vendotaenia cf. antiqua Gnilovskaya) 3种.这些化石丰富了澄江生物群物种的多样性,为研究该群生物爆发性演化提供了新的证据.同时通过对现生褐藻和褐藻化石形态学的比较研究,表明化石属和现代属在系统演化上可能有较密切的亲缘关系,并进一步证明了澄江生物群在云南海口地区发生于一个潮间带和亚潮带的海水环境.%The paper deals with the new phaeophycean fossils in the Early Cambrian from Chengjiang Biota at Ercai Village of Haikou, Kunming, Yunnan, Southwest China. Three new taxa, Punctariopsis latifolia gen. et sp. nov., P.simplex gen. et sp. nov. and Vendotaenia cf. antiqua Gnilovskaya are described here in detail. These new findings show that the Chengjiang Biota is high in species diversity of fossil algae and might offer new evidence for a better understanding of the Cambrian explosive biological evolution. The fossil genus described here is found to have a close relationship with the living Punctaria based on similar morphology. The results suggest that the Chengjiang Biota in Haikou area of Kunming was living in an intertidal and subtidal seawater environment.

  8. 昆明海口早寒武世澄江生物群中叶状红藻化石%Leaf-like Rhodophycean Fossils in the Early Cambrian from Haikou,Kunming,Yunnan of China

    Institute of Scientific and Technical Information of China (English)

    徐兆良

    2004-01-01

    This paper deals with the new leaf-like rhodophycean fossils in the Early Cambrian from Chengjiang Biota at Mafang Village of Haikou, Kunming, Yunnan, Southeast China. The new taxa Paradelesseria sanguinea gen. et sp. nov. is found to have a close relationship with the living Delesseria according to detailed morphological study between the fossil and modern Delesseria. These new findings show that the Chengjiang Biota is high in species diversity of fossil algae and might offer new evidence for a better understanding of the Cambrian explosive biological evolution and its paleoenvironment. The Biota in Haikou district of Kunming was living in subtidal and lower intertidal marine environment, up to 30 m below surface of the water based on the comparative study of extant red algae.%主要报道了采自云南省昆明市海口马房村鞍山早寒武世筇竹寺组玉案山段澄江生物群中的叶状红藻-似红叶藻(新属、新种)(Paradelesseria sanguinea Xu,gen.et sp.Nov.).通过比较形态学研究,探讨了该宏观化石藻类的分类归属与亲缘关系,进一步丰富了澄江生物群生物物种多样性的认识,并为研究早寒武世生物演化及其古环境提供了新的化石证据.同时,通过对现生红藻的比较研究,进一步证明了澄江生物群在云南海口地区发生于一个水深在30 m以上的亚潮带和下潮间带的海水环境.

  9. Suspended sediment yield in Texas watersheds

    Science.gov (United States)

    Coonrod, Julia Ellen Allred

    The Texas Water Development Board collected suspended sediment samples across the state of Texas for approximately 60 years. Until this research, no comprehensive analysis of the data had been conducted. This study compiles the suspended sediment data along with corresponding streamflow and rainfall. GIS programs are developed which characterize watersheds corresponding to the sediment gauging stations. The watersheds are characterized according to topography, climate, soils, and land use. All of the data is combined to form several SAS data sets which can subsequently be analyzed using regression. Annual data for all of the stations across the state are classified temporally and spatially to determine trends in the sediment yield. In general, the suspended sediment load increases with increasing runoff but no correlation exists with rainfall. However, the annual average rainfall can be used to classify the watersheds according to climate, which improves the correlation between sediment load and runoff. The watersheds with no dams have higher sediment loads than watersheds with dams. Dams in the drier parts of Texas reduce the sediment load more than dams in the wetter part of the state. Sediment rating curves are developed separately for each basin in Texas. All but one of the curves fall into a band which varies by about two orders of magnitude. The study analyzes daily time series data for the Lavaca River near Edna station. USGS data are used to improve the sediment rating curve by the addition of physically related variables and interaction terms. The model can explain an additional 41% of the variability in sediment concentration compared to a simple bivariate regression of sediment load and flow. The TWDB daily data for the Lavaca River near Edna station are used to quantify temporal trends. There is a high correlation between sediment load and flowrate for the Lavaca River. The correlation can be improved by considering a flow-squared term and by

  10. Estimation of sediment loading in Asian coastal area using 210Pb inventory in mangrove sediment

    International Nuclear Information System (INIS)

    Full text: Concentrations of 210Pb in coastal sediment are generally controlled by local atmospheric 210Pb flux and fine sediment input to coastal area, because the 210Pb has high affinity to inorganic fine particles and 210Pb inventory in coastal sediment is coincided with sediment loading to the area. Thus the 210Pb level in coastal sediment is good index of sediment loading to coastal zones. However, in subtropical/tropical coastal area, such as S-E Asian coast, sediment loading is widely variable due to seasonal difference of precipitation and coastal sediment discharge among rainy/dry season. Secondly, the S-E Asian coastal areas are mostly covered with mangroves those entrap the sediment particle supplied from river to adjacent coastal waters. Since the entrapped fine sediment particles include not only the excess 210Pb supplied from local atmosphere but also the accumulated sediment particles by terrestrial input, thus the 210Pb inventory exceeds largely compared to the atmospheric supply. Thus the 210Pb inventory balance in mangrove area is expected to reflect drastically the local sediment loading conditions in S-E Asia. We studied the 210Pb balance in subtropical mangrove coastal water in Japan and found that the 210Pb was useful natural tracer to evaluate the coastal sediment load. However, limited data are reported about the mangrove coastal area. In this study, we collected mangrove sediment cores at the Japan and Viet Nam and analyzed the 210Pb concentrations in sections of different depth and location. By comparing with the atmospheric flux, we estimate the balance of the 210Pb in the area and evaluate the sediment loading to the studied mangrove area. (author)

  11. Accumulation and effects of sediment-associated silver nanoparticles to sediment-dwelling invertebrates

    DEFF Research Database (Denmark)

    Ramskov, Tina; Forbes, Valery E; Gilliland, Douglas;

    2015-01-01

    Sediment is increasingly recognized as the major sink for contaminants including nanoparticles (NPs). Thus, sediment-living organisms are especially susceptible to NP exposure. Studies of the fate and effects of NPs in the sediment matrix are still in their infancy, and data from such studies are...... in high demand. Here, we examine the effects of exposure to sediment mixed with either aqueous Ag (administered as AgNO3) or Ag NPs (13 nm, citrate-capped) at a nominal exposure concentration of 100 μg Ag/g dry weight sediment on four benthic invertebrates: two clones of the gastropod Potamopyrgus...

  12. Sediment transport capacity of hyperconcentrated flow

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    As one of the most important components of river mechanics,sediment transport capacity of sediment-laden flows has attracted much attention from many researchers working on river mechanics and hydraulic engineering. Based on the time-averaged equation for a turbulent energy equilibrium in solid and liquid two-phase flow,an expression for the efficiency coefficient of suspended load movement was derived for the two-dimensional,steady,uniform,fully-developed turbulent flow. A new structural expression of sediment transport capacity was achieved. Using 115 runs of flume experimental data,which were obtained through two kinds of sediment transport experiments in the state of equilibrium,in combination with the basic rheological and sediment transporting characteristics of hyperconcentrated flow,the main parameters in the structural expression of sediment transport capacity were calibrated,and a new formula of sediment transport capacity for hyperconcentrated flow was developed. A large amount of field data from the Yellow River,Wuding River,and Yangtze River,etc. were adopted to verify the new formula and good agreement was obtained. These results above contribute to an improved theoretical system of river mechanics and a reliable tool for management of rivers carrying high concentration of sediments.

  13. PORTABLE DEVICE FOR MEASURING SEDIMENT RESUSPENSION

    Science.gov (United States)

    A portable device for measuring sediment resuspension has been developed. he device consists of a cylindrical chamber inside of which a horizontal grid oscillates vertically. he sediments whose properties are to be determined are placed at the bottom of the chamber with water ove...

  14. Mean sediment residence time in barchan dunes

    Science.gov (United States)

    Zhang, D.; Yang, X.; Rozier, O.; Narteau, C.

    2014-03-01

    When a barchan dune migrates, the sediment trapped on its lee side is later mobilized when exposed on the stoss side. Then sand grains may undergo many dune turnover cycles before their ejection along the horns, but the amount of time a sand grain contributes to the dune morphodynamics remains unknown. To estimate such a residence time, we analyze sediment particle motions in steady state barchans by tracking individual cells of a 3-D cellular automaton dune model. The overall sediment flux may be decomposed into advective and dispersive fluxes to estimate the relative contribution of the underlying physical processes to the barchan shape. The net lateral sediment transport from the center to the horns indicates that dispersion on the stoss slope is more efficient than the convergent sediment fluxes associated with avalanches on the lee slope. The combined effect of these two antagonistic dispersive processes restricts the lateral mixing of sediment particles in the central region of barchans. Then, for different flow strengths and dune sizes, we find that the mean residence time of sediment particles in barchans is equal to the surface of the central longitudinal dune slices divided by the input sand flux. We infer that this central slice contains most of the relevant information about barchan morphodynamics. Finally, we initiate a discussion about sediment transport and memory in the presence of bed forms using the advantages of the particle tracking technique.

  15. On luminescence bleaching of tidal channel sediments

    DEFF Research Database (Denmark)

    Fruergaard, Mikkel; Pejrup, Morten; Murray, Andrew S.;

    2015-01-01

    We investigate the processes responsible for bleaching of the quartz OSL signal from tidal channel sediment. Tidal dynamics are expected to play an important role for complete bleaching of tidal sediments. However, no studies have examined the amount of reworking occurring in tidal channels and o...

  16. PHYSICS OF SUSPENED SEDIMENT TRANSPORT IN ANNAGNPS

    Science.gov (United States)

    The physics of suspended sediment transport as used in the continuous-simulation version of AnnAGNPS is explained. The fine sediment loading from sheet & rill erosion on agricultural lands is both a primary source of wash load within stream systems and a significant non-point source of pollutants. ...

  17. Iron-oxide Magnetic, Morphologic, and Compositional Tracers of Sediment Provenance and Ice Sheet Extent in the ANDRILL AND-1B Drill Core, Ross Sea, Antarctica (Invited)

    Science.gov (United States)

    Brachfeld, S. A.; Pinzon, J.; Darley, J. S.; Sagnotti, L.; Kuhn, G.; Florindo, F.; Wilson, G. S.; Ohneiser, C.; Monien, D.; Joseph, L. H.

    2013-12-01

    The first drilling season of the Antarctic Drilling Program (ANDRILL) recovered a 13.57 million year Miocene through Pleistocene record of paleoclimate change (core AND-1B) within the Ross Sea. The magnetic mineral assemblage records the varying contributions of biological productivity, changing sediment sources, the emergence of volcanic centers, and post-depositional diagenesis. Characterization of bedrock samples from the McMurdo Volcanic Group (MVG) and Transantarctic Mountain (TAM) lithologic units allows us to construct fingerprints for the major source rocks bordering the Ross Sea, and identify their signatures within the AND-1B sediment. Key parameters that can be traced from source rock to sediment for the MVG-derived sediment include a 100-200 C order-disorder transition, titanomaghemite grains with homogenous textures but with substantial Al and Mg content, Fe-spinels with substantial Al, Cr, Mg, and Ti content, and titanomagnetite host grains with 1-3 swarms of ilmenite lamellae (both with variable amounts of oxidation). Distinctive signatures in TAM lithologies include low S-ratios in Koettlitz Group gneisses and Fe-sulfides with magnetite intergrowths in Byrd Glacier basement samples. The Cambrian Granite Harbor Intrusive Complex is characterized by coarse, homogeneous Mn-bearing ilmenite and nearly pure magnetite. The Jurassic dolerites and basalts of the Ferrar Group contain pseudo single domain to stable single domain-sized Fe-oxides with low-Ti content and homogeneous textures. Cu-Fe sulfides are also present in the Ferrar Group. Diamictites in the Pliocene-Pleistocene section of the AND-1B drill core contains Fe-oxide assemblages with MVG-type rock magnetic and textural characteristics, while the Miocene diamictites contain TAM-type signatures. These observations can be explained by increased ice flow from the west during the Miocene and/or the absence of MVG volcanic centers, which had not yet reached a significant size. During the Pliocene and

  18. A MATHEMATICAL MODEL OF RESERVOIR SEDIMENTATION

    Institute of Scientific and Technical Information of China (English)

    HUANG Jinchi

    2001-01-01

    Reliable quantitative estimation of bed aggradation or degradation is important for river-training and water management projects. With the development of water resources, sediment problems associated with a dam are becoming more severe. This paper describes some special problems in mathematical model for calculation of degradation and aggradation in a reservoir. The main efforts of this study are on the treatment of some physical processes of fine sediment transport (<0.05 mm). Problems in a reservoir are obviously different from a natural stream, such as the turbid current flow, orifice sediment flushing;and the initiation and consolidation of cohesive sediment deposition. The case of Liujiaxia Reservoir,which is located in the upper reaches of the Yellow River, is employed to verify the model. The results show that the model is applicable in the evaluation of an engineering planing with plenty of fine sediment movement.

  19. Bubble growth and rise in soft sediments

    Science.gov (United States)

    Boudreau, Bernard P.; Algar, Chris; Johnson, Bruce D.; Croudace, Ian; Reed, Allen; Furukawa, Yoko; Dorgan, Kelley M.; Jumars, Peter A.; Grader, Abraham S.; Gardiner, Bruce S.

    2005-06-01

    The mechanics of uncemented soft sediments during bubble growth are not widely understood and no rheological model has found wide acceptance. We offer definitive evidence on the mode of bubble formation in the form of X-ray computed tomographic images and comparison with theory. Natural and injected bubbles in muddy cohesive sediments are shown to be highly eccentric oblate spheroids (disks) that grow either by fracturing the sediment or by reopening preexisting fractures. In contrast, bubbles in soft sandy sediment tend to be spherical, suggesting that sand acts fluidly or plastically in response to growth stresses. We also present bubble-rise results from gelatin, a mechanically similar but transparent medium, that suggest that initial rise is also accomplished by fracture. Given that muddy sediments are elastic and yield by fracture, it becomes much easier to explain physically related phenomena such as seafloor pockmark formation, animal burrowing, and gas buildup during methane hydrate melting.

  20. Incipient motion of sediment by waves

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    In this paper, the forces acting on sediment particles are analyzed in all the aspects. Considering the cohesive force between particles, the additional static water pressure induced by the solid-body characteristics of film water and the inertia force of waves, a unified formula of the incipient motion for both coarse and fine particles is defined. The formula can reflect the variation in the initial velocity of fine particles with the volume weight of sediment. The verification of the formula is carried out by use of both experimental data and field observation data accumulated by experts at home and abroad. The verification shows that the formula expresses the law governing the incipient motion of sediment of all particle sizes inclusive of natural sediment and light-weight materials, and thus a basic formula for the study and solution of sediment problems in estuarine and coastal regions is provided.

  1. Diversity, Persistence and Evolution in Marine Sediments

    DEFF Research Database (Denmark)

    Starnawski, Piotr

    2016-01-01

    . No evidence for selection of repair and recombination functions in the deeper sediment was found, and high number of motility and chemotaxis was detected through the sediment column. This work casts new light on marine sediment communities, describes their vertical structure and assembly in detail......72 % of our planet is covered by saline water, which at its bottom gradually forms a layer of deposited material. This layer of marine sediments harbors active and diverse prokaryotic communities, of which we know little more than just the phylogenetical associ- ation with their often distant...... treat the whole community as equal, not knowing who and what are the contributions of hydrolyzers, fermenters and terminal oxidizers. In order to address these unknowns I have focused my work on three main aspects of the marine sediments: (i) systematic, analytical description of the microbial...

  2. Particle reworking in Great Lakes sediments

    International Nuclear Information System (INIS)

    Pollen grain distributions and radioactive fallout horizons observed in sediment cores collected over the past decade have served as tracers of sediment reworking and burial rates for both the marine and lacustrine environments. Errors associated with the analysis of these cores, attributable to biogenic sediment reworking and shipboard handling, have necessitated the development of more precise techniques to measure sediment transport rates. The authors utilize a rare earth element tracer technique, which takes advantage of the high neutron-capture cross-section of samarium oxide, and neutron activation analysis, to trace the burial and lateral transport rates of surficial sediments in the littoral (SCUBA diver depths) and profundal (manned submersible depths) of the Great Lakes

  3. Sediment transport in rivers, estuaries and harbours

    International Nuclear Information System (INIS)

    Proper understanding of sediment transport phenomena both in terms of quality i.e. direction of sediment transport and quantity i.e. rate of sediment transport and deposition is necessary in : (1) development and maintenance of coastal harbours and appurtenance works such as approach channels, location of sand traps and selection of spoil dumping grounds, (2) deepening of harbours and dredging of channels in estuarine environment, (3) assessing life of a reservoir of a power/irrigation project and (4) silting study of irrigation system. Radioactive tracers have been mainly used in studying the movement of sediment in the coastal areas. Techniques are being developed for quantitative estimation of sediment transport. These techniques and their limitations are discussed. (M.G.B.)

  4. Effects of oil sands sediments on fish

    Energy Technology Data Exchange (ETDEWEB)

    Parrott, J.; Colavecchia, M.; Hewitt, L.; Sherry, J.; Headley, J. [Environment Canada, Ottawa, ON (Canada); Turcotte, D.; Liber, K. [Saskatchewan Univ., Regina, SK (Canada)

    2010-07-01

    This paper described a collaborative project organized by Natural Resources Canada (NRCan) Panel of Energy Research and Development (PERD) with researchers from Environment Canada and the University of Saskatchewan. The 4-year study was conducted to assess the toxicity of oil sands sediments and river waters, and reclamation ponds and sediments on laboratory-raised fish. Three sediments from rivers were evaluated for their potential to cause adverse impacts on fathead minnow eggs and larvae for a period of 18 days. The study monitored hatching, larval survival, development, and growth. Naphthenic acids (NA), polycyclic aromatic hydrocarbons (PAHs) and metals were measured in the sediments to determine if the compounds can be correlated with observed toxicity. The study will also assess walleye eggs exposed to sediments, and in situ fish exposures. Toxicity identification and evaluation (TIE) studies will be conducted to isolate the fractions that may affect fish development and growth.

  5. Effects of oil sands sediments on fish

    International Nuclear Information System (INIS)

    This paper described a collaborative project organized by Natural Resources Canada (NRCan) Panel of Energy Research and Development (PERD) with researchers from Environment Canada and the University of Saskatchewan. The 4-year study was conducted to assess the toxicity of oil sands sediments and river waters, and reclamation ponds and sediments on laboratory-raised fish. Three sediments from rivers were evaluated for their potential to cause adverse impacts on fathead minnow eggs and larvae for a period of 18 days. The study monitored hatching, larval survival, development, and growth. Naphthenic acids (NA), polycyclic aromatic hydrocarbons (PAHs) and metals were measured in the sediments to determine if the compounds can be correlated with observed toxicity. The study will also assess walleye eggs exposed to sediments, and in situ fish exposures. Toxicity identification and evaluation (TIE) studies will be conducted to isolate the fractions that may affect fish development and growth.

  6. Evaluation of upland disposal of Oakland Harbor, California, sediment; Volume I: Turning basin sediments. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Lee, C.R.; Tatem, H.E.; Simmers, J.W.; Skogerboe, J.G.; Folsom, B.L.

    1992-10-01

    This report describes testing and evaluation performed by the Environmental Laboratory of the US Army Engineer Waterways Experiment Station on sediment from the turning basin of Oakland Inner Harbor, Oakland, CA. Test protocols from the Corps' Management Strategy for Disposal of Dredged Material were used in the present evaluation to determine the potential for migration of contaminants into effluent, surface runoff, leachates, plants, and animals at an upland disposal site. Two sediments from the turning basin of Oakland Inner Harbor were tested: a composite sample of cores taken from the surface to 38-ft depth (upper sediment) and a composite sample of cores taken from 38- to 45-ft depth (lower sediment). In addition, two potential disposal site soils were tested: Twitchell Island and 7th Street disposal site. Sediment characterization indicated that the Oakland upper sediment contained higher concentrations of most contaminants than the lower sediment. Metal concentrations in the Oakland lower sediment were in the range of values found at the Twitchell Island disposal site. The Oakland upper sediment contained levels of cadmium and arsenic similar to those in Twitchell Island levee soils, but higher levels of zinc, nickel, lead, and copper.... Contaminant migration, Sediment testing, Contaminated sediments, Upland disposal, Dredged material.

  7. [Distributions of phosphorus fractions in suspended sediments and surface sediments of Tiaoxi mainstreams and cause analysis].

    Science.gov (United States)

    Chen, Hai-Long; Yuan, Xu-Yin; Wang, Huan; Li, Zheng-Yang; Xu, Hai-Yan

    2015-02-01

    Phosphorus is a primary nutrient showing the water quality status of river and inducing eutrophication, and a different phosphorus fraction can make diverse contributions to water quality. Four phosphorus forms of suspended sediments and surface sediments in Tiaoxi mainstreams were measured using a sequential extraction procedure, and the distributions of their forms were discussed. The results showed that the tropic status of Xitiaoxi River was inferior to that of Dongtiaoxi River as a whole, and the water quality in the middle reach of Dongtiaoxi River was better than that in the upper and lower reaches. The contents of nutrient elements in suspended sediments were significantly higher than those in surface sediment, which indicated an enrichment of nutrient in fine sediment. The percentages of the loosely absorbed phosphorus ( NH4Cl-P), the reductant phosphorus (BD-P) and the metal oxide bound phosphorus (NaOH-P) in the suspended sediment were higher than those in surface sediment, while the percentage of the calcium bound phosphorus (HCl-P) showed a reverse trend. Correlation analyses between phosphorus forms and chemical compositions of suspended sediments and surface sediments were performed. The results showed the phosphorus forms in suspended sediments and surface sediments of Xitiaoxi River had weak relationships with mineral components, while those in the Dongtiaoxi River had strong relationships with mineral, especially OM and clay mineral. The cause was associated with the geological setting and material sources in Tiaoxi watershed. PMID:26031071

  8. Sediment varve counting with PIXE

    International Nuclear Information System (INIS)

    The feasibility of the particle induced X-ray emission (PIXE) technique for varve counting of vertically taken marine and lacustrine sediments was studied aiming at its possible use as a dating procedure by observing the yearly variation of the constituent elements. The samples were impregnated with a low viscosity epoxy resin to obtain slabs with preserved layered structure suitable for the PIXE analyses. PIXE-spectra were taken as a function of depth distance and the normalized X-ray peak area variations were determined. Especially, concentration changes of silicon and iron were found to be clear. Due to the employed sample preparation technique the observed chlorine concentration corresponds to the amount of water in the initial sample. Maximum chlorine concentration appeared at positions where the Si and Fe concentrations were near minimum. By plotting the Si/Cl or Fe/Cl peak area ratios, an even more distinct position dependent variation was noted. (author)

  9. Optical dating: insufficiently bleached sediments

    International Nuclear Information System (INIS)

    Although infrared-stimulated luminescence (IRSL) signals in feldspars can be bleached rapidly by sunlight, there could still be a small amount of IRSL signal remaining in sediment grains if they have experienced only relatively short sunlight exposure before deposition. This remaining signal results in a ''remnant dose'' stored in the grain and is important for young samples but negligible for old samples. Several methods have been introduced to detect insufficient bleaching, and some of them can provide information on the extent of the bleaching. Others can only distinguish between samples bleached for a very long time and for a short time. Empirical methods are introduced to evaluate the possible values of equivalent dose accumulated since the grains were deposited. These methods involve the analysis of the equivalent doses and the natural IRSL signals obtained using single-disc dose determination methods. (author)

  10. Fluctuations and Instability in Sedimentation

    KAUST Repository

    Guazzelli, Élisabeth

    2011-01-21

    This review concentrates on the fluctuations of the velocities of sedimenting spheres, and on the structural instability of a suspension of settling fibers. For many years, theoretical estimates and numerical simulations predicted the fluctuations of the velocities of spheres to increase with the size of the container, whereas experiments found no such variation. Two ideas have increased our understanding. First, the correlation length of the velocity fluctuations was found experimentally to be 20 interparticle separations. Second, in dilute suspensions, a vertical variation in the concentration due to the spreading of the front with the clear fluid can inhibit the velocity fluctuations. In a very dilute regime, a homogeneous suspension of fibers suffers a spontaneous instability in which fast descending fiber-rich columns are separated by rising fiber-sparse columns. In a semidilute regime, the settling is hindered, more so than for spheres. © 2011 by Annual Reviews. All rights reserved.

  11. Settling velocities in batch sedimentation

    International Nuclear Information System (INIS)

    The sedimentation of mixtures containing one and two sizes of spherical particles (44 and 62 μm in diameter) was studied. Radioactive tracing with 57Co was used to measure the settling velocities. The ratio of the settling velocity U of uniformly sized particles to the velocity predicted to Stokes' law U0 was correlated to an expression of the form U/U0 = epsilon/sup α/, where epsilon is the liquid volume fraction and α is an empirical constant, determined experimentally to be 4.85. No effect of viscosity on the ratio U/U0 was observed as the viscosity of the liquid medium was varied from 1x10-3 to 5x10-3 Pa.s. The settling velocities of particles in a bimodal mixture were fit by the same correlation; the ratio U/U0 was independent of the concentrations of different-sized particles

  12. Assessing the potential toxicity of resuspended sediment

    Energy Technology Data Exchange (ETDEWEB)

    Bonnet, C.; Babut, M.; Ferard, J.F.; Martel, L.; Garric, J.

    2000-05-01

    Two moderately contaminated freshwater sediments (Sorel Harbour, St. Lawrence River, Canada) were subjected to a suspension event. The objective was to assess the environmental impact of the disposal of dredged material in water, in particular, the short-term effects of dumping on the water column and the long-term effects of dredged sediment deposits. In a series of microcosms, the sediments were left to stand for 25 d under flow-through conditions. In a second series of microcosms, sediments were vigorously suspended for 15 min before being left to settle and were submitted to the same treatment as reference sediments during the following 25 d. Physicochemical and biological parameters (Daphnia magna and Hydra attenuata survival) were measured in overlying water throughout the experiment. Sediment toxicity was assessed with Chironomus tentans and Hyalella azteca exposed to sediments collected at both the beginning and end of the 25-d period. Pore-water toxicity was evaluated with D. magna. During the suspension process, in the Sorel Harbour mixed sediment overlying water, the authors observed effects on H. attenuata survival and ammonia and metals (chromium, copper, and zinc) releases. Meanwhile, in reference (nonmixed) and mixed sediments as well as in associated pore waters, there were no significant chemical modifications no biological effects after the 25-d experiments. The developed approach, which attempts to simulate a dumping process, aims at allowing the assessment of the short- and long-term hazards resulting from a resuspension process in overlying water and in resettled sediments using both chemical and biological measurements.

  13. Sediment suppresses herbivory across a coral reef depth gradient

    OpenAIRE

    Goatley, Christopher H. R.; Bellwood, David R.

    2012-01-01

    Sediments are a ubiquitous feature of all coral reefs, yet our understanding of how they affect complex ecological processes on coral reefs is limited. Sediment in algal turfs has been shown to suppress herbivory by coral reef fishes on high-sediment, low-herbivory reef flats. Here, we investigate the role of sediment in suppressing herbivory across a depth gradient (reef base, crest and flat) by observing fish feeding following benthic sediment reductions. We found that sediment suppresses h...

  14. Hanford contaminated sediment stabilization studies

    Energy Technology Data Exchange (ETDEWEB)

    Bruns, L.E.; Key, K.T.; Higley, B.A.

    1977-03-01

    The major problems with radionuclide waste sites in the 200 Area plateau on the Hanford Reservation is the high degree of toxicity or Hazard Index (HI). Transport Factors (TF) are fortunately low but can increase with time and certainly with episodic events such as explosions or earthquakes. Two major tests involving surface affixation were sponsored by the Atlantic Richfield Hanford Company, one by Dowell using M-166 and the other by Battelle-Northwest comparing many different surface affixants. The latex emulsion, M-166, appeared to be well suited for the Hanford desert type area. Of the many surface affixants tested by Battelle-Northwest, Coherex and Aerospray appeared to be the best. As an emergency precaution, 200 barrels of M-166 were purchased for surface affixation in case of a range fire. The subsurface affixants laboratory and field tests include organic polymers, asphalt emulsions, concrete, AM-9, and sodium silicate-calcium chloride-foramide grouts. The applications were second containment (or leak prevention) of subsurface waste tanks and piping, grouting water wells to prevent contamination leaking to the water table, and encompassing cribs, trenches, burial grounds, and other subsurface sediment contaminations. Organic polymers added strength to the soil, but penetration of the viscous liquid was not as deep as desired; it may be good for situations requiring only a few inches penetration, such as well grouting. The asphalt emulsion looked promising as an easily injected well grouting material and it may also be good for encompassing subsurface contaminated sediment plumes. The sodium silicate-calcium chloride-foramide affixant appeared best for second containment of waste tanks but may require the help of asphalt emulsion to ensure good coverage.

  15. Estimating suspended sediment yield, sedimentation controls and impacts in the Mellah Catchment of Northern Algeria

    International Nuclear Information System (INIS)

    This paper is an assessment of the suspended sediment yield in the Mellah Catchment of northern Algeria. We use discharge-sediment load relationships to explore the variability of water discharge and sediment load, and to investigate the impact of geomorphic factors disturbance on erosion and sedimentation. Suspended sediment load was analyzed in the Mellah Catchment (550 squre kms ) which was controlled by a gauging station to measure discharge and sediment transport. The relations between daily mean sediment concentration and daily mean water discharge were analyzed to develop sediment rating curves. For storms with no water samples, a sediment rating curve was developed. The technique involves stratification of data into discharge-based classes, the mean of which are used to fit a rating curve according to single flow data and season to provide various rating relationships. The mean annual sediment yield during the 24 years of the study period was 562 T km -2 in the Mellah Catchment. This drainage basin had high rainfall and runoff, the erosion was high. The high sediment yield in the Mellah basin could be explained by a high percentage of sparse grassland and cultivation developed on shallow marly silty-clayey soils with steep slopes often exceeding 12%. Almost all suspended sediment loads are transported during storm events that mainly occur in the winter and spring heavy and medium downpours. The scarceness of these events leads to a very large interseasonal variability of the wadi sediment fluxes. The negative impacts of this enhanced sediment mobility are directly felt in the western part of the basin which shows many mass movements, bank and gully erosion because cultivated areas are often bared during autumnal brief flash floods and furrowed downslope during the winter season. (author)

  16. Controls on flood and sediment wave propagation

    Science.gov (United States)

    Bakker, Maarten; Lane, Stuart N.; Costa, Anna; Molnar, Peter

    2015-04-01

    The understanding of flood wave propagation - celerity and transformation - through a fluvial system is of generic importance for flood forecasting/mitigation. In association with flood wave propagation, sediment wave propagation may induce local erosion and sedimentation, which will affect infrastructure and riparian natural habitats. Through analysing flood and sediment wave propagation, we gain insight in temporal changes in transport capacity (the flood wave) and sediment availability and transport (the sediment wave) along the river channel. Heidel (1956) was amongst the first to discuss the progressive lag of sediment concentration behind the corresponding flood wave based on field measurements. Since then this type of hysteresis has been characterized in a number of studies, but these were often based on limited amount of floods and measurement sites, giving insufficient insight into associated forcing mechanisms. Here, as part of a project concerned with the hydrological and geomorphic forcing of sediment transfer processes in alpine environments, we model the downstream propagation of short duration, high frequency releases of water and sediment (purges) from a flow intake in the Borgne d'Arolla River in south-west Switzerland. A total of >50 events were measured at 1 minute time intervals using pressure transducers and turbidity probes at a number of sites along the river. We show that flood and sediment wave propagation can be well represented through simple convection diffusion models. The models are calibrated/validated to describe the set of measured waves and used to explain the observed variation in wave celerity and diffusion. In addition we explore the effects of controlling factors including initial flow depth, flood height, flood duration, bed roughness, bed slope and initial sediment concentration, on the wave propagation processes. We show that the effects of forcing mechanisms on flood and sediment wave propagation will lead to different

  17. Temporal variability of suspended sediment sources in an alpine catchment combining river/rainfall monitoring and sediment fingerprinting

    OpenAIRE

    Navratil, O.; O. Evrard; Esteves, Michel; C. Legout; Ayrault, S.; Nemery, J.; Mate-Marin, A.; Ahmadi, M; Lefevre, I.; Poirel, A.; Bonte, P.

    2012-01-01

    Influence of the rainfall regime on erosion and transfer of suspended sediment in a 905-km(2) mountainous catchment of the southern French Alps was investigated by combining sediment monitoring, rainfall data, and sediment fingerprinting (based on geochemistry and radionuclide concentrations). Suspended sediment yields were monitored between October 2007 and December 2009 in four subcatchments (22-713km(2)). Automatic sediment sampling was triggered during floods to trace the sediment origin ...

  18. Prediction of sediment load by sediment rating curve and neural network (ANN) in El Kebir catchment, Algeria

    OpenAIRE

    Boukhrissa, Z A; Le Bissonnais, Yves; Tourki, Mahmoud

    2013-01-01

    The annual sediment load of a river is generally determined either from direct measurements of the sediment load throughout the year or from any of the many sediment transport equations that are available today. Due to lack of a long-term sediment concentration data, sediment rating curves and flux estimation are the most widely applied. This paper has investigated the abilities of statistical models to improve the accuracy of streamflow–suspended sediment relationships in daily and annual...

  19. APPLICATION OF SEDIMENT QUALITY GUIDELINES IN THE ASSESSMENT OF MANGROVE SURFACE SEDIMENT IN MENGKABONG LAGOON, SABAH, MALAYSIA

    OpenAIRE

    S. M. Praveena, M. Radojevic, M. H. Abdullah, A. Z. Aris

    2008-01-01

    There have been numerous sediment quality guidelines developed to monitor the sediments. Sediment quality guidelines are very useful to screen sediment contamination by comparing sediment contaminant concentration with the corresponding quality guideline, provide useful tools for screening sediment chemical data to identify pollutants of concern and prioritise problem sites and relatively good predictors of contaminations. However, these guidelines are chemical specific and do not include bio...

  20. Using sediment 'fingerprints' to assess sediment-budget errors, north Halawa Valley, Oahu, Hawaii, 1991-92

    Science.gov (United States)

    Hill, B.R.; DeCarlo, E.H.; Fuller, C.C.; Wong, M.F.

    1998-01-01

    Reliable estimates of sediment-budget errors are important for interpreting sediment-budget results. Sediment-budget errors are commonly considered equal to sediment-budget imbalances, which may underestimate actual sediment-budget errors if they include compensating positive and negative errors. We modified the sediment 'fingerprinting' approach to qualitatively evaluate compensating errors in an annual (1991) fine (<63 ??m) sediment budget for the North Halawa Valley, a mountainous, forested drainage basin on the island of Oahu, Hawaii, during construction of a major highway. We measured concentrations of aeolian quartz and 137Cs in sediment sources and fluvial sediments, and combined concentrations of these aerosols with the sediment budget to construct aerosol budgets. Aerosol concentrations were independent of the sediment budget, hence aerosol budgets were less likely than sediment budgets to include compensating errors. Differences between sediment-budget and aerosol-budget imbalances therefore provide a measure of compensating errors in the sediment budget. The sediment-budget imbalance equalled 25% of the fluvial fine-sediment load. Aerosol-budget imbalances were equal to 19% of the fluvial 137Cs load and 34% of the fluval quartz load. The reasonably close agreement between sediment- and aerosol-budget imbalances indicates that compensating errors in the sediment budget were not large and that the sediment-budget imbalance as a reliable measure of sediment-budget error. We attribute at least one-third of the 1991 fluvial fine-sediment load to highway construction. Continued monitoring indicated that highway construction produced 90% of the fluvial fine-sediment load during 1992. Erosion of channel margins and attrition of coarse particles provided most of the fine sediment produced by natural processes. Hillslope processes contributed relatively minor amounts of sediment.