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Facies sedimentares e ambientes deposicionais da Formação Barbalha no vale do cariri, bacia do araripe, nordeste do Brasil

Chagas, Daniel Bezerra das; Assine, Mário Luís; Freitas, Francisco Idalécio de
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 313-322
POR
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The Aptian Barbalha Formation represents the first unit of the post-rift sequence of the Araripe Basin and crops out at the slopes of the Aranpe plateau in the eastern part ot Aranpe Basin. The unit has also been named Kio da Batateira Formation, but this name is here used in its original definition as Batateira Beds, an interval of great lateral continuity and characterized by the presence of bituminous shales of the Alagoas Stage (P-270 palynological biozone). This paper presents the results of a stratigraphic analysis carried out along the outcrop belt in order to establish the facies architecture and to interpret deposicional environments of the siliciclastic Barbalha Formation. Detailed stratigraphic vertical sections were measured and correlated. They allowed the recognition of two depositional sequences characterized by fining upward arrangement of facies, beginning with fluvial deposits and ending with lacustrine deposits at their tops. The end of the first cycle is represented by black shales and brecciated limestones of the Batateira Beds that record a geologic event of regional magnitude and serve as meaningful long-distance stratigraphic mark. The second deposicional sequence overlies disconformably the Batateira Beds and begins with clast-supported conglomerates...

Alternative interpretations of some earliest ediacaran fossils from China

Iten, Heyo Van; Leme, Juliana de M.; Marques, Antonio C.; Simões, Marcello G.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 111-113
ENG
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In a letter to Nature (February, 2011), Xunlai Yuan and collaborators recorded carbon compression fossils from black shales of the Lantian Formation (Ediacaran), southern Anhui Province, South China. The new fossils, described under five morphological types (Types A to E), exhibit degrees of morphological differentiation suggesting that they were multicellular eukaryotes. Some of the Lantian macrofossils were interpreted as algae, but others are of unknown affinities. For reasons noted in this discussion, Type A fossils attracted our particular attention, and we suggest an alternative interpretation of their affinities. According to our view, some of them (at least those with three faces and no globose holdfast at their base) may represent conulariid cnidarians or close medusozoan relatives. The undistorted organism probably was a three-sided cone in life. We believe that our suggested alternative interpretations of the anatomy and affinities of the fossils in question can be useful in guiding future research on the oldest currently known fossil assemblage of multicellular organisms. Copyright © 2012.

Ocorrencia de mercurio na Bacia do Rio Iguaçu, Estado do Parana, Brasil; Mercury occorrence at the Iguaçu River Basin, State of Parana, Brasil

Rafael Andre Belotto Plawiak
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 24/07/2007 PT
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A anomalia geoquímica de mercúrio em sedimento de corrente da bacia hidrográfica do rio Iguaçu, Estado do Paraná, delimitada por um levantamento prévio de geoquímica regional, foi investigada através de determinações das concentrações do metal em rochas, solo e sedimento fluvial. O rio Iguaçu está inserido no contexto geológico da Bacia do Paraná e a porção correspondente ao alto vale, no município de Curitiba e vizinhanças, compreende rochas gnáissico-migmatíticas do embasamento cristalino (Arqueano-Proterozóico Inferior) e sedimentos pleistocênicos da Bacia de Curitiba. Na área de estudo ocorrem rochas vulcânicas da Formação Serra Geral, Grupo São Bento (Cretáceo) e folhelhos negros da Formação Irati, Grupo Passa Dois (Permiano-Triássico). Os teores de Hg foram determinados através de Espectrometria de Absorção Atômica por decomposição térmica com correção do efeito Zeeman. Foram obtidos teores de Hg em rochas vulcânicas (0,2 a 0,4 ng/g), folhelho negro (286 e 430 ng/g), solo (média de 103±57 ng/g, fração < 177 µm), sedimento fluvial (média de 37±18 ng/g, fração < 177 µm). Para caracterização química nas rochas e no solo, os teores de óxidos maiores e elementos traço foram determinados por Espectrometria de Fluorescência de Raios-X. A qualidade das águas do rio Iguaçu foi avaliada através de análises por Cromatografia de Íons...

Pyro-expanded black slate in sculptural art

Costa,J. C. e; Almeida,T.; Gomes,C. S. F.
Fonte: Associação Brasileira de Cerâmica Publicador: Associação Brasileira de Cerâmica
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2013 EN
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Black slate transformed through a pyroplastic process named pyro-expansion or exfoliation has been explored in the present work in order to be used as sculptural material. Black slate is a highly fissile, fine grained and organic matter rich rock that is the product of the action of low-grade regional metamorphism on black shale (a sedimentary clay and organic matter rich, also fissile and fine grained rock). Black slate if fired at an adequate firing rate up to the temperature range 1000 ºC-1240 ºC shows great potential for the manufacture of sculptural pieces. The technical possibilities of the shaping or conformation of pyro-expanded black slate have also been studied, including the reactions that take place when two different black slate pieces are closely associated with each other, or when black slate pieces are closely associated to other materials, such as metals and ceramics. These interactions, while associating different materials that react with each other, emphasize the unique characteristics of new sculptural compositions increasing the plastic capacities of the pyro-expanded black slate. Some examples of the associations referred to will be shown, which highlight the close functional relationship between art and science; research involves the approach to new techniques and materials...

Geochemical Mass Balance and Elemental Transport during the Weathering of the Black Shale of Shuijingtuo Formation in Northeast Chongqing, China

Ling, Sixiang; Wu, Xiyong; Zhao, Siyuan; Liao, Xin; Ren, Yong; Zhu, Baolong
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
EN
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46.36%
An understanding of the processes that control the behavior of major elements with respect to weathering profile is essential to calculate the mobility, redistribution, and mass fluxes of elements. Hence, this study aims to determine the geochemical mass balance, strain, elemental correlation, and transport in weathering profiles. We constructed three weathering profiles for the black shale of Shujingtuo formation. As per the principal component analysis of major elements, density, and pH values, the first component represents the “elemental factor” and the second denotes the “external factor.” The “depletion” pattern is a mass transportation pattern, and Na, K, and Mg are depleted along transect relative to the composition of fresh rock. Fe is redeposited at the bottom half of the saprock zone, whereas Al is accumulated at the regolith zone. The Fe and Al patterns are attributed to the “depletion–addition” and “addition” patterns, respectively. The strain in profiles A and B demonstrates the expansion at the regolith zone and part of the saprock zone. In profile C, however, these zones collapsed at all depths. In chemical weathering, Na, K, Ca, Mg, and Si are depleted in the following order: valley (C) > near mountaintop (B) > ridge (A).

Diversity and role of plasmids in adaptation of bacteria inhabiting the Lubin copper mine in Poland, an environment rich in heavy metals

Dziewit, Lukasz; Pyzik, Adam; Szuplewska, Magdalena; Matlakowska, Renata; Mielnicki, Sebastian; Wibberg, Daniel; Schlüter, Andreas; Pühler, Alfred; Bartosik, Dariusz
Fonte: Frontiers Media S.A. Publicador: Frontiers Media S.A.
Tipo: Artigo de Revista Científica
Publicado em 03/03/2015 EN
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26.36%
The Lubin underground mine, is one of three mining divisions in the Lubin-Glogow Copper District in Lower Silesia province (Poland). It is the source of polymetallic ore that is rich in copper, silver and several heavy metals. Black shale is also significantly enriched in fossil organic matter in the form of long-chain hydrocarbons, polycyclic aromatic hydrocarbons, organic acids, esters, thiophenes and metalloporphyrins. Biological analyses have revealed that this environment is inhabited by extremophilic bacteria and fungi. Kupfershiefer black shale and samples of water, bottom and mineral sediments from the underground (below 600 m) Lubin mine were taken and 20 bacterial strains were isolated and characterized. All exhibited multi-resistant and hypertolerant phenotypes to heavy metals. We analyzed the plasmidome of these strains in order to evaluate the diversity and role of mobile DNA in adaptation to the harsh conditions of the mine environment. Experimental and bioinformatic analyses of 11 extrachromosomal replicons were performed. Three plasmids, including a broad-host-range replicon containing a Tn3 family transposon, carried genes conferring resistance to arsenic, cadmium, cobalt, mercury and zinc. Functional analysis revealed that the resistance modules exhibit host specificity...

Elemental, isotopic and molecular signatures of Early Cambrian marine sediments and a phantom petroleum system in South Australia.

Hall, Philip Anthony
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2012
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The aim of the research study is to apply mass spectrometric geochemical techniques to the investigation of palaeoenvironmental, chemostratigraphic and provenance questions from several South Australian Phanerozoic basins. Results of a multi-pronged palaeoenvironmental investigation of Early Cambrian marine sediments, employing trace and REE abundances, TOC and stable isotopes (C, S) are reported from three formations in the Stansbury Basins; Heatherdale Shale, Emu Bay Shale and Talisker Formation. The multiproxy approach in conjunction with sedimentological information provides a powerful tool for interpreting palaeoenvironmental conditions. Prevalent palaeoredox conditions of the Heatherdale Shale and Talisker Formation were dysoxic, evolving progressively more reducing natures up section. The Emu Bay Shale conversely demonstrates consistently aerobic interpretations for the redox proxies. Comparison of trace element and REE distributions to similar sequences of the Yangtze platform, South China shows striking similarities, Analogous basinal environments and common provenance may have lead to the seawater trace element chemistry of the Palaeo Pacific & Asian oceans exhibiting a homogenous nature. The Emu Bay Shale biota is the richest Burgess Shale-type (BST) fauna in the southern hemisphere. The implied oxic water column during accumulation appears difficult to reconcile with the exceptional preservation exhibited. Micro-scale sealed vessel (MSSV) pyrolysis of isolated kerogen and δ¹³Corg values provided confirmation of its redox status and implicate cyanobacteria in the preservation mechanism. Molecular signatures diagnostic of Gloeocapsomorpha prisca were identified...

Direct evidence for organic carbon preservation as clay-organic nanocomposites in a Devonian black shale; from deposition to diagenesis

Kennedy, M.; Löhr, S.; Fraser, S.; Baruch, E.
Fonte: Elsevier Science Publicador: Elsevier Science
Tipo: Artigo de Revista Científica
Publicado em //2014 EN
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Abstract not available; Martin John Kennedy, Stefan Carlos Löhr, Samuel Alex Fraser, Elizabeth Teresa Baruch

Hochauflösende Untersuchungen von Biomarkern an epikontinentalen Schwarzschiefern des Unteren Toarciums (Posidonienschiefer, Lias e) von SW-Deutschland; High-resolution biomarker investigations of Lower Toarcian epicontinental black shales (Posidonia Shale, SW-Germany)

Frimmel, Andreas
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
DE_DE
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Die detaillierte Beprobung eines Komposit-Profils des Posidonienschiefers (Unteres Toarcium) aus dem Raum Dotternhausen (SW-Deutschland) hat einen hochauflösenden organisch-geochemischen Datensatz geliefert. Im Vordergrund der Untersuchungen stand die genaue Charakterisierung und Beschreibung der Zusammensetzung des organischen Materials anhand von Biomarkern und stabilen Isotopen. Ziel dieser Arbeit war es, die Kopplung klimatischer und ozeanographischer Faktoren mit der Sauerstoffverfügbarkeit und damit die Lebensbedingungen am Meeresboden und in der nahen Wassersäule der epikontinentalen Schwarzschiefer zu rekonstruieren. Die sequenzstratigraphische Entwicklung des Meeresspiegels im Posidonienschiefer von SW-Deutschland, die sich anhand des C27/C29-Steran-Verhältnisses sowie durch sedimentologische und palökologische Beobachtungen ableiten lässt, steht im engen Zusammenhang mit den Veränderungen der Sauerstoffverfügbarkeit im Posidonienschiefer-Meer. Verschiedene Redox- und Alkalinitätsparameter folgen dem Verlauf der Meeresspiegelkurve 3. Ordnung und lassen sich gut mit den untergeordneten Zyklen 4. Ordnung korrelieren. Erstmals konnten neben sulfatreduzierenden Bakterien durch langkettige Isoprenoide auch methanogene Archaebakterien im Posidonienschiefer von SW-Deutschland identifiziert werden. Das Zusammenwirken methanoxidierender und sulfatreduzierender Bakterien im Bereich der anaeroben Methanoxidations-Zone führte zu einer Zunahme der Alkalinität im Porenwasser...

VARIATIONS IN ORGANIC GEOCHEMISTRY OF ANOXIC-OXIC BLACK SHALE - CARBONATE SEQUENCES IN THE PENNSYLVANIAN OF THE MIDCONTINENT, USA (KANSAS, OKLAHOMA)

WENGER, LLOYD MILLER, JR.
Fonte: Universidade Rice Publicador: Universidade Rice
ENG
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Two cores containing thin organic-rich phosphatic black shale members, the Excello and Little Osage shales, and transitional lithologies from Pennsylvania cyclothems of southeast Kansas and northeast Oklahoma were characterized by geochemical and organic petrographic methods by very detailed sampling. Variations in relative amount of primary organic material, i.e. liptinitic versus humic, exerts a major control on the nature and quality of the organic profiles. Organic petrography, Rock-Eval pyrolysis, n-alkane and isoprenoid distributions, and C$sb{27}$/C$sb{29}$-sterane ratios indicate that shallow-water, more oxic facies (e.g. fossiliferous shales and limestones) contain dominantly terrestrial organic matter while "deep" water phosphatic organic-rich black shales contain significant proportions of marine algal organic matter. Pyrolysis Transformation Ratios ${ m (Ssb 1/Ssb 1 + Ssb 2)}$ were lower for facies with significant marine components sugesting differential kinetics of bitumen generation for marine versus terrestrially-derived kerogen. Vitrinite reflectance (%R$sb{ m o}$) values were suppressed in liptinite-rich anoxic black shale facies relative to the coal "benchmark." Anoxia levels varied within the sequences and had significant influence on several geochemical parameters. Oxidized facies...

The New Albany Shale gas play in southern Indiana

Comer, J. B.; Hasenmueller, N. R.; Mastalerz, M. D.; Rupp, J. A.; Shaffer, N. R; Zuppann, C. W
Fonte: Universidade de Indiana Publicador: Universidade de Indiana
Tipo: Conferência ou Objeto de Conferência Formato: 30458158 bytes; application/pdf
EN_US
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This poster was presented at the 2006 Eastern Section American Association of Petroleum Geologists, 35th Annual Meeting, in Buffalo, N.Y., October 8-11, 2006.; The New Albany Shale (Devonian and Mississippian) in Indiana is mostly brownish-black organic-rich shale with lesser greenish-gray shale. The formation is 100 to 140 feet thick in southeastern Indiana and dips and thickens to the southwest into the Illinois Basin, where it attains a thickness of more than 360 feet in Posey County. Gas production from New Albany Shale began in 1885 and drilling activity continued into the 1930s, when interest waned in favor of more lucrative opportunities elsewhere. Renewed activity, driven by higher gas prices, has been brisk since the mid-1990s, witnessed by the completion of more than 400 productive wells. The majority of these wells were drilled in Harrison County, where production typically occurs at depths from 500 to 1,100 feet and production rates generally range from 20 to 450 MCFGPD. In the past 2 years, Daviess County and surrounding areas have become the focus of New Albany exploration after the El Paso Production No. 2-10 Peterson horizontal discovery well was rumored to have tested 1.3 MMCFGPD at an approximate measured depth of 2...

Reservoir Characteristics and Gas Production Potential of Woodford Shale in the Southern Midcontinent

Comer, John B.
Fonte: Universidade de Indiana Publicador: Universidade de Indiana
Tipo: Conferência ou Objeto de Conferência Formato: 3474944 bytes; application/vnd.ms-powerpoint
EN_US
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This PowerPoint presentation was presented at the “Woodford Gas Shale Conference” held on May 23, 2007, in Oklahoma City, Okla. The conference was sponsored by the Oklahoma Geological Survey, which is located in Norman, Okla. A black and white version of the PowerPoint was printed and distributed at the meeting. Notes for this presentation are also provided.; Woodford Shale is a prolific hydrocarbon source rock throughout the Southern Midcontinent of the United States, and in south-central Oklahoma it produces both oil and natural gas. The characteristic and dominant Woodford lithology is black shale, but chert, siltstone, sandstone, dolostone, and light-colored shale are common locally. In general, proximal lithofacies and basin depocenters contain more silt and sand and distal lithofacies more chert. The highest concentrations of organic carbon are found in intermediate settings remote from clastic source areas and bypassed by bottom flows. High concentrations of marine organic matter coexist with abundant biogenic silica, indicating that high biological productivity in surface waters was supported mainly by dynamic upwelling. The primary sites of hydrocarbon generation coincide mostly with the principal depocenters of the Delaware and Anadarko Basins; however...

Woodford Shale in Southern Midcontinent, USA - Transgressive System Tract Marine Source Rocks on an Arid Passive Continental Margin with Persistent Oceanic Upwelling

Comer, John B.
Fonte: Universidade de Indiana Publicador: Universidade de Indiana
Tipo: Conferência ou Objeto de Conferência Formato: 35595120 bytes; application/pdf
EN_US
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This poster was presented at the 2008 Annual Convention and Exhibition of the American Association of Petroleum Geologists (AAPG) in San Antonio, Texas, from April 20-23, 2008. John B. Comer won an AAPG Award of Excellence "Top 10" Poster Presentation for the poster.; Woodford Shale (Givetian to Kinderhookian) is a prolific hydrocarbon source rock in the southern USA Midcontinent and is locally an unconventional oil and gas reservoir. Woodford sediments were deposited in epeiric seas as anaerobic and dysaerobic biofacies recording widespread bottom-water anoxia and strongly density-stratified water columns. High concentrations of marine organic matter coexist with abundant biogenic silica, indicating that high biological productivity in surface waters was supported by dynamic upwelling. Hypersalinity, recorded as anhydrite in burrows and syneresis cracks, suggests an arid paleoclimate and indicates that density stratification was due in part to accumulation of hypersaline bottom water. Plate-tectonic reconstructions consistent with an arid paleoclimate and dynamic upwelling place this region on the western passive continental margin of North America in the dry tropics near 15 degrees south latitude. Here, southeasterly trade winds and Ekman circulation force surface water westward toward the open ocean and countercurrents with upwelled oceanic water eastward onto the craton. The strong net flow of ocean water into the epeiric seas developed because of the high rate of evaporation during a period of eustatic sea level rise. Transgressive system tracts along west-facing...

High-resolution organic petrography of the Toarcian Posidonia Shale of Germany and the western Netherlands: Study of the organo-mineral microfacies variations, reconstruction of the depositional environments and construction of a depositional model

Gorbanenko, Olga
Fonte: Universität Tübingen Publicador: Universität Tübingen
Tipo: Dissertation; info:eu-repo/semantics/doctoralThesis
EN
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46.68%
High-resolution organic petrological analysis was carried out on more than 150 core bituminous shale samples of the Posidonia Shale (Toarcian, Lower Jurassic) from three sedimentary basins: the West Netherlands Basin, the Lower Saxony Basin and the South German Basin. This study is subdivided into three main parts: the identification of the organic microfacies variations in order to reconstruct paleoenvironmental conditions of the Posidonia Shale sedimentation, the maturity evaluation of the Posidonia Shale from three sedimentary basins and the construction of the deposition model of the Posidonia Shale. The results of the organic petrography reveal that the organo-mineral microfacies defined by maceral composition and associated mineral groundmass show a wide range of variations related to the content of individual liptinite of marine origin and terrestrial macerals (macerals of vitrinite and inertinite groups and sporinite). The modifications in composition are considered as a potential indicator of different changes in depositional environments. In addition, much attention has been paid to the origin of the bituminite, which comprises most of the hydrocarbon-rich source rocks. All defined organo-mineral microfacies are poorly correlated laterally between sedimentary basins. Only those from wells E and M (the West Netherlands Basin) show a resemblance. Organo-mineral microfacies from each investigated area contain a specific type of bituminite. Particularly...

Mechanisms of carbon sequestration within the organic rich Miocene Monterey Formation

Collett, R. L.
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2011 EN
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36.36%
Carbon preservation in the geological past has been an important process for global climate and the onset of glacial events. The majority of carbon preservation occurs in marine continental margin settings that consist of fine grained sediments like the Monterey Formation, California, USA. The mechanisms driving carbon preservation remain highly controversial and the Monterey Formation has served as a prominent test case used to determine these mechanisms. Organic-carbon rich deposits in this formation have been attributed to high organic productivity enhanced fluxes of organic matter (OM) to the sea floor and/or enhanced OM preservation through anoxia. In this study, the Monterey Formation was used as a natural experiment to focus on a new mechanism of carbon preservation, in the form of mineral surface area (MSA) as a control on total organic carbon (TOC). Mineral surface area was determined using the Ethylene Glycol Monoethyl Ether free surface procedure and TOC was derived from high temperature combustion. The relationship between the OM and the surface of the shale samples was viewed using an environmental scanning electron microscope (ESEM) with micron resolution. The major findings indicate a first-order relationship between MSA and TOC...

Chemical and carbon isotopic evolution of hydrocarbons during prograde metamorphism from 100°C to 550°C: Case study in the Liassic black shale formation of Central Swiss Alps

Schwab, Valérie; Spangenberg, Jorge E.; Grimalt, Joan O.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 22195 bytes; application/pdf
ENG
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16 pages, 8 figures.; Hydrocarbon distributions and stable isotope ratios of carbonates (δ13Ccar, δ18Ocar), kerogen (δ13Cker), extractable organic matter (δ13CEOM) and individual hydrocarbons of Liassic black shale samples from a prograde metamorphic sequence in the Swiss Alps were used to identify the major organic reactions with increasing metamorphic grade. The studied samples range from the diagenetic zone (<100°C) to amphibolite facies (~ 550°C). The samples within the diagenetic zones (<100 and 150°C) are characterized by the dominance of C<20 n-alkanes, suggesting an origin related with marine and/or bacterial inputs. The metamorphic samples (200 to 550°C) have distributions significantly dominated by C12 and C13 n-alkanes, C14, C16 and C18 n-alkylcyclopentanes and to a lesser extend C15, C17 and C21 n-alkylcyclohexanes. The progressive 13C-enrichment (up to 3.9‰) with metamorphism of the C>17 n-alkanes suggests the occurrence of cracking reactions of high molecular weight compounds. The isotopically heavier (up to 5.6‰) C<17 n-alkanes in metamorphic samples are likely originated by thermal degradation of long-chain homologous with preferential release of isotopically light C1 and C2 radicals. The dominance of specific even C-number n-alkylcyclopentanes suggests an origin related to direct cyclization mechanism (without decarboxylation step) of algal or bacterial fatty acids occurring in reducing aqueous metamorphic fluid conditions. The regular increase of the concentrations of n-alkylcycloalkanes vs. C>13 n-alkanes with metamorphism suggests progressive thermal release of kerogen-linked fatty acid precursors and degradation of n-alkanes. Changes of the steroid and terpenoid distributions are clearly related to increasing metamorphic temperatures. The absence of 18α(H)-22...

Correlation of Sturtian diamictite successions in southern Australia and northwestern Tasmania by Re–Os black shale geochronology and the ambiguity of “Sturtian”-type diamictite–cap carbonate pairs as chronostratigraphic marker horizons

Kendall, Brian; Creaser, Robert A.; Calver, Clive R.; Raub, Timothy D.; Evans, David A. D.
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /08/2009
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Recent geochronological studies have raised concerns regarding the accuracy of regional and global correlations of Neoproterozoic sedimentary successions using relative dating methods such as carbon isotope chemostratigraphy and glaciogenic diamictite–cap carbonate lithological and geochemical characteristics. Precise and accurate radio-isotopic age constraints for Neoproterozoic sedimentary rocks thus remain a high priority for establishing a reliable Neoproterozoic chronostratigraphy. Here, we present a new Re–Os age of 640.7 ± 4.7 Ma from black shales of the upper Black River Dolomite (Togari Group, northwestern Tasmania) that represents a minimum age for deposition of the immediately underlying, diamictite-bearing Julius River Member. The upper Black River Dolomite Re–Os age is statistically identical to a Re–Os age of 643.0 ± 2.4 Ma previously determined for the Sturtian post-glacial Tindelpina Shale Member (Umberatana Group, Adelaide Rift Complex, southern Australia). Consistent with previous lithostratigraphic and stromatolite biostratigraphic evidence, the Re–Os ages suggest broadly coeval deposition of the Julius River Member and Sturtian diamictites and overlying organic-rich marine shales. Consideration of the Neoproterozoic geochronological database suggests that “Sturtian”-type diamictite–cap carbonate pairs cannot be used as chronostratigraphic marker horizons for global correlation of the Neoproterozoic rock record.

Mo-Cr isotope evidence for a reducing Archean atmosphere in 3.46-2.76Ga black shales from the Pilbara, Western Australia

Wille, Martin; Nebel, Oliver; Van Kranendonk, Martin; Schoenberg, Ronny; Kleinhanns, Ilka C.; Ellwood, Michael
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
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36.12%
The distribution of redox-sensitive elements and their stable isotope variations in marine sediments has been employed to track the possible oxygenation of the atmosphere at, and before, the Great Oxidation Event (GOE; 2.4-2.2. Ga). Contrasting datasets have been used to advocate for and against the rise of free oxygen in the atmosphere prior to 2.4. Ga based on various geochemical tracers, and evidence for a partially oxidized environment remains elusive.Herein, we present stable isotope datasets for Mo and Cr, in conjunction with major and trace elements from four black shale horizons spanning a time interval from 3.46 to 2.76. Ga in order to ascertain atmospheric oxygen levels through the Archean. The Mo, Cr and U elemental signatures within all sedimentary units are dominated by continental input. Both Mo isotopic values and Mo and U elemental signatures suggest anoxic conditions with no indication of redox cycling of these elements. This contradicts previous interpretations of an oxidized atmosphere based on published sulfur isotopic data (Ohmoto et al., 2006) and oxidized hematite occurrences at ~. 3.45. Ga (Hoashi et al., 2009).Cr concentration patterns within the sample suites are controlled by continental provenance composition rather than by an authigenic Cr seawater contribution. This interpretation is supported by the relatively homogeneous Cr isotopic compositions across all sample suites and is consistent with high temperature controlled Cr isotopic ratios. Identification of redox cycling processes within detrital dominated sediments with Cr isotopes is likely to be less sensitive compared to Mo isotopes...

Late Ordovician stratigraphy, zircon provenance and tectonics, Lachlan Fold Belt, southeastern Australia

Fergusson, Christopher Lloyd; Fanning, Christopher
Fonte: Blackwell Publishing Ltd Publicador: Blackwell Publishing Ltd
Tipo: Artigo de Revista Científica
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Ordovician quartz turbidites of the Lachlan Fold Belt in southeastern Australia accumulated in a marginal sea and overlapped an adjoining island arc (Molong volcanic province) developed adjacent to eastern Gondwana. The turbidite succession in the Shoalhaven River Gorge, in the southern highlands of New South Wales, has abundant outcrop and graptolite sites. The succession consists of, from the base up, a unit of mainly thick-bedded turbidites (undifferentiated Adaminaby Group), a unit with conspicuous bedded chert (Numeralla Chert), a unit with common thin-bedded turbidites (Bumballa Formation (new name)) and a unit of black shale (Warbisco Shale). Coarse to very coarse sandstone in the Bumballa Formation is rich in quartz and similar to sandstone in the undifferentiated Adaminaby Group. Detrital zircons from sandstone in the Bumballa Formation, and from sandstone at a similar stratigraphic level from the upper Adaminaby Group of the Genoa River area in eastern Victoria, include grains as young as 453-473 Ma, slightly older than the stratigraphic ages. The dominant detrital ages are in the interval 500-700 Ma (Pacific Gondwana component) with a lessor concentration of Grenville ages (1000-1300 Ma). This pattern resembles other Ordovician sandstones from the Lachian Fold Belt and also occurs in Triassic sandstones and Quaternary sands from eastern Australia. The Upper Ordovician succession is predominantly fine grained...

Impacts – The Key to Understand Earth

Hua Huang
Fonte: Nature Preceedings Publicador: Nature Preceedings
Tipo: Conferência ou Objeto de Conferência
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A significant factor, where are the major elements e.g. Mg, Fe, Si, Al, Ca, P, Ni that make up the asteroid or comet after the impact, has been ignored since the proposal of the impact events. In a striking contrast, there are many remaining unanswered or poorly answered questions regarding the formation and nature of banded iron formation (BIF), iron stone, phosphorite, bedded manganese ore, dolomite and carbonaceous black shales. The appearance of Lake Superior type banded ion formation associated with dolomite, quartzite, and black shale, the deposition of manganese ore and the occurrence of large phosphate repository during the Plaeoproterozoic; the onset of BIF with phosphate deposition and sedimentary manganese deposits and cap dolomite during the Neoproterozoic; the penecontemporary formation of oolitic iron stone taking place of the BIF, bedded manganese deposit, phosphorite, dolomite, and black shale during the Phanerozoic, which suggest a genetic link among them from the perspective of chemical elements. Actually, during hypervelocity impact cratering events, the main part of the asteroid or comet and target material are vaporizing, which forms a mushroom cloud of vapor in the atmosphere. The previous study shows that the calcite...