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Petrography and stable isotopic variations in Dalmiapuram Formation of Cauvery Basin, South India: implication on OAE1d

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Chinese Journal Of Geochemistry 2015年第3期34卷 447-458页

作者： J.Madhavaraju A.N.Sial S.M.Hussain R.Nagarajan S.Ramasamy Estación Regional del Noroeste Instituto de GeologíaUniversidad Nacional Autónoma de México Nucleo de Estudos Geoquímicos e Laborató rio de Isótopos Estáveis (neg - labise) Departmento de GeologiaUniversidade Federal de Pernambuco Department of Geology University of Madras Department of Applied Geology School of Engineering and Science Curtin University

Petrography, carbon and oxygen isotopic study was carried out to interpret isotopic variations on the predominant carbonate sequence of the Dalmiapuram Formation of the Cauvery Basin, South India. The common petrographic types identified in the Dalmiapuram Formation range from wackestone to boundstone. The gray shale and limestone members show large variations in d13 C and d18 O values(Gray shale member: +1.44 to +2.40 %VPDB,-3.05 to-5.92 % VPDB, respectively; Limestone member:-6.07 to +2.93 % VPDB;-7.08 to-0.39 %VPDB; respectively). In the present study, the carbon and oxygen values are not correlated, which supports the fact that these limestones retain their primary isotopic signatures. In carbon isotope curve, one negative shift is identified in the gray shale member and a positive isotopic excursion is detected in the coral algal limestone(CAL).The observed positive isotopic excursion in the lower part of the CAL correlates with OAE1 d and suggests the global nature of the late Albian OAE1 d in the Cauvery Basin.

关键词：稳定同位素岩相学盆地印度蕴涵碳酸盐岩氧同位素偏移检测

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Sedimentary Organic Matter Characterization on a Tropical Continental Shelf in Northeastern Brazil

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International Journal of Geosciences 2020年第6期11卷 393-419页

作者： Roberto Lima Barcellos Maria Cristina da Silva Sales de Melo Alcides Nobrega Sial Valdir do Amaral Vaz Manso Labogeo/GSGMar Oceanography Department Federal University of Pernambuco Recife Brazil LGGM Geology Department Federal University of Pernambuco Recife Brazil neg-labise Geology Department Federal University of Pernambuco Recife Brazil

In continental shelf areas works where the focus is Geochemistry are widely relevant, due to the vast complexity and uses of these relief features (social, environmental and economic). On the Brazilian Northeast tropical shelves, with emphasis on the Pernambuco Continental Shelf (PCS), the published studies are limited and have aimed at portions closer to the coastline. The objective of the present work is the description of the characteristics and origin of sedimentary organic matter (SOM) in the inner and middle Pernambuco shelf, defining and classifying the local geochemical sedimentary facies. The sampling stations (136) were collected in the study area, and the grain-size, contents of total organic matter (TOM), calcium carbonate (CaCO3) were analyzed. The samples were processed in an elemental analyzer coupled with a mass spectrometer after the elimination of calcium carbonate. The obtained data were the grain-size, TOM, CaCO3, elemental (C, N) and the stable isotopic ratios of δ13C e δ15N of SOM. Based on the measured values of carbon and nitrogen, the C/N ratio, associated to δ13C e δ15N, is observed that in the PCS predominates an organic matter of marine origin along its entire length: C < 1%, N < 1%, C/N < 5, <

关键词： Biogenic Sediments Total Nitrogen δ13C Stable Isotopic Ratio Geochemical Facies Pernambuco

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A shift in redox conditions near the Ediacaran/Cambrian transition and its possible influence on early animal evolution,CorumbáGroup,Brazil

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Geoscience Frontiers 2024年第4期15卷 148-158页

作者： Fabricio A.Caxito Erik Sperling Gabriella Fazio Rodrigo Rodrigues Adorno Matheus Denezine Dermeval Aparecido Do Carmo Martino Giorgioni Gabriel J.Uhlein Alcides N.Sial CPMTC Research Center and Programa de Pós-graduação em Geologia Departamento de GeologiaInstituto de GeociênciasUniversidade Federal de Minas GeraisBelo HorizonteMG 31270-901Brazil Department of Earth and Planetary Sciences Doerr School of SustainabilityStanford UniversityCA 94305USA Instituto de Geociências Universidade de BrasíliaBrasíliaDF 70910-900Brazil Center for Applied Geosciences(CGA)of the Geological Survey of Brazil(SBG/CPRM) BrasíliaDistrito Federal 70040-904Brazil neg labise Universidade Federal de PernambucoRecife-PE 50740-530Brazil

The Ediacaran-Cambrian transition witnessed some of the most important biological,tectonic,climatic and geochemical changes in Earth's *** utmost importance for early animal evolution is the likely shift in redox conditions of bottom waters,which might have taken place in distinct pulses during the late Ediacaran and early *** track redox changes during this transition,we present new trace element,total organic carbon and both inorganic and organic carbon isotopes,and the first iron speciation data on the Tamengo and Guaicurus formations of the CorumbáGroup in western Brazil,which record important paleobiological changes between 555 Ma to<541 *** stratigraphically older Tamengo Formation is composed mainly of limestone with interbedded marls and mudrocks,and bears fragments of upper Ediacaran biomineralized fossils such as Cloudina lucianoi and Corumbella *** younger Guaicurus Formation represents a regional transgression of the shallow carbonate platform and is composed of a homogeneous fine-grained siliciclastic succession,bearing meiofaunal bilateral *** new iron speciation data reveal predominantly anoxic and ferruginous(non-sulfidic)bottom water conditions during deposition of the Tamengo Formation,with FeHR/FeT around 0.8 and FePy/FeHR below *** transition from the Tamengo to the Guaicurus Formation is marked by a stratigraphically rapid drop in FeHR/FeT to below 0.2,recording a shift to likely oxic bottom waters,which persist ***-sensitive element(RSE)concentrations are muted in both formations,but consistent with non-sulfidic bottom water conditions *** interpret the collected data to reflect a transition between two distinct paleoenvironmental *** Tamengo Formation represents an environment with anoxic bottom waters,with fragments of biomineralized organisms that lived on shallower,proba-bly mildly oxygenated surficial waters,and that were then transported *** to coeval suc

关键词： Atmospheric oxygenation Gondwana Redox proxies Iron speciation Ediacaran biota Redox-sensitive elements

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