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Palaeoenvironmental and biostratigraphic implications of microbial mat-related structures:Examples from the modern Gulf of Cambay and the Precambrian vindhyan basin,India

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Journal of Palaeogeography 2014年第2期3卷 127-144页

作者： Santanu Banerjee Subir Sarkar Patrick G.Eriksson Department of Earth Sciences Indian Institute of Technology Bombay Department of Geological Sciences Jadavpur University Department of Geology University of Pretoria

A stretch of the modern hypersaline coastal plain of the Gulf of Cambay was chosen to examine the distribution of the microbial mat-related structures(MRS) on siliciclastic sediments in the intertidal and supratidal *** abundance of MRS increases from the lower intertidal zone to the upper supratidal zone while the type of MRS records a systematic *** the lower intertidal zone exhibits wrinkle structures,sieve-like surfaces and patchy ripples in places,the upper intertidal zone exhibits diverse MRS related to reduced current activity on the mat layer and intermittent *** in the upper intertidal zone include wrinkle structures,sieve-like surfaces,gas domes,reticulated surfaces,multi-directional ripples,patchy ripples,rolled-up mat fragments,setulfs and occasional petee ridges and cracked mat *** lower supratidal zone is characterized by increased occurrence of petee ridges,gas domes and cracked mat surfaces compared to the upper intertidal *** upper supratidal zone is distinguished by the presence of abundant cracked mat surfaces,petee ridges,gas domes and wrinkle *** presence of cm-scale,disc-shaped microbial colonies(DMC) with a variety of internal structures is a unique feature of the Gulf of Cambay study *** wrinkle structures occur in all the coastal zones,setulfs occur close to the boundary between the upper intertidal and lower supratidal *** attempt has been made to compare the distribution of MRS in this modern environment with those in the ~1.6 Ga Chorhat Sandstone of the vindhyan Supergroup for high-resolution palaeoenvironmental *** upper part of the intertidal segment of the Chorhat Sandstone is distinguished from its lower part by the presence of abundant cracked mat surfaces,petee ridges and gas domes in the former,while wrinkle structures,Kinneyia,rolled-up mat fragments,patchy ripples and multi-directional ripples are equally abundant in both *** lower part of the inter

关键词： microbial mat discoidal microbial colony setulf petee ridge gas dome Precambrian vindhyan basin Gulf of Cambay India

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Diagenesis,facies and palaeocurrent analysis of Upper Rewa Sandstone around Sagar,Central India

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Journal of Palaeogeography 2023年第4期12卷 546-563页

作者： Gaurav K.Singh Ashish K.Rai Arvind K.Singh Department of Applied Geology Dr.Harisingh Gour VishwavidyalayaSagar 470003Madhya PradeshIndia Geological Survey of India ShillongIndia

The stratigraphic surface represented by a major contact between the Archean Bundelkhand Granite and the extensive Proterozoic vindhyan sediments is a regional basement cover *** crystalline—sedimentary interface reflects an intense weathering of continental crust during marine *** time-transgressive sand deposition events ***,Rewa and Bhander are mainly witnessed during the entire vindhyan ***,the Upper Rewa Sandstone comprises one of these events in the vindhyan *** progress has been made in interpreting these sandstones as a function of entirely marine process to a combination of tidal—fluvio—eolian *** the results have so far been attained on the basis of sedimentary facies,provenance,palaeocurrent analysis,and some of petrography.A distinct differentiation between marine and fluvial components of the Upper Rewa Sandstone still remains ***,we use diagenesis as a parameter for the first time along with facies and palaeocurrent analysis to acquire a clear comprehension of marine-and fluvial-dominated *** present study spans 27 square kilometer area covering 15 stratigraphic sections with a collection of 571directional data from the facies specific sedimentary structures,and 28 samples obtained for the thin section *** lower unit of the Upper Rewa Sandstone shows facies association typical of tidal environment,along with polymodal *** rocks are well sorted and dominantly lithified by authigenic *** development of a complex of syntaxial,passive pore fills,and grain replacive cements reflect normally pressured nature of the lower unit *** upper unit of the Upper Rewa Sandstone however,reveals a facies pattern resembling fluvial processes and unimodal palaeocurrent *** exhibit poor sorting,siliceous,and ferruginous matrix,and development of intense ***,pressure solution is a dominant mode of l

关键词： Palaeocurrent Diagenesis Facies Upper Rewa Sandstone vindhyan basin

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Soft-sediment deformation structures in the Mesoproterozoic Kaimur Sandstone,vindhyan Supergroup(Central India),and their seismotectonic implications

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Journal of Palaeogeography 2023年第3期12卷 463-486页

作者： Jayanta Kumar Pati Anuj Kumar Singh Department of Earth and Planetary Sciences Faculty of ScienceUniversity of AllahabadPrayagraj211002India National Centre of Experimental Mineralogy and Petrology 14 Chatham LinesUniversity of AllahabadPrayagraj211002India

The unequivocal identification of soft-sediment deformation structures(SSDS)is a significant attribute to constrain the effect of transient geological events in the spatio-temporal evolution of ancient sedimentary *** paper reports and discusses,for the first time,the occurrence of several cm-to dm-scale SSDS within sandstone successions of the Mesoproterozoic Kaimur Group(vindhyan Supergroup),exposed at the Hanumandhara Hill of Chitrakoot-Satna border region,Madhya Pradesh State,*** SSDS are confined to a deformed interval comprising seven individual sedimentary units of variable composition and texture,which are sandwiched between nearly horizontally undeformed sandstone *** SSDS consist of load structures(load casts,flame structures,pseudonodules and ball-and-pillow structures),contorted lamination,convolute lamination,boudins and pinch-and-swell structures,deformed cross-stratification,slump structures,clastic injections,fluid escape structures,and syn-sedimentary fractures/*** pre-sent study suggests that the formation of these SSDS is essentially related to a combination of processes(gravitational instability,liquefaction,fluidization,and fluid escape)predominantly induced by seismic *** addition,the restricted occurrence of fractures/faults in these deformed layers emphasizes the passage of seismically-induced Rayleigh *** the observed types of SSDS,their lateral homo-geneity and geographic distribution along with the geodynamic framework of the vindhyan basin,the whole area can be tentatively attributed to having experienced moderate-to high-magnitude(M≥5)*** present study combined with earlier reports of seismically-induced SSDS,from other regionally disposed formations belonging to the Lower(e.g.,Kajrahat Limestone,Chopan Porcellanite,Koldaha Shale,Rohtas Limestone,and Glauconitic Sandstone of the Semri Group)and Upper(e.g.,Bhander Limestone of the Bhander Group)vindhyan Supergroup,respectively,provi

关键词： Soft-sediment deformation structures SSDS Seismites Kaimur Group vindhyan basin Sand-stone Central India

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Geochemistry and hydrocarbon source rock potential of shales from the Palaeo-Mesoproterozoic vindhyan Supergroup, central India

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Energy Geoscience 2023年第3期4卷 276-295页

作者： Arvind Kumar Singh Partha Pratim Chakraborty Birbal Sahni Institute of Palaeosciences 53 University RoadLucknow226007India Department of Geology University of DelhiNew Delhi110007India Hiroshima Institute of Plate Convergence Region Research Hiroshima UniversityHigashi-Hiroshima7398526Japan

With increase in shale gas exploration, inorganic and organic geochemical investigations of shale have become extremely important. Here, we explore the six argillaceous (shale) intervals (Arangi, Koldaha, Rampur, Bijaygarh, Rewa and Sirbu shale) from Son valley sector, vindhyan basin with an aim to understand provenance conditions, palaeoclimate, tectonic setting and hydrocarbon generation potential. Whole rock geochemistry indicates vindhyan sediments derived from felsic source(s) except for Sirbu shale that indicates additional influx of mafic rocks with differentiated felsic source. A comparative study of vindhyan shale rare earth elements (REEs) points to Mahakoshals and Chhotanagpur gneissic complex (CGC) as probable sediment provenance for vindhyan sediments. CIA analysis, after necessary corrections for K-metasomatism, suggests evolution in weathering and palaeoclimate indicating a transformation from moderate weathering conditions with warm and humid climate during lower vindhyan deposition to intense weathering conditions with hot and humid climate during upper vindhyan deposition. Trace (La/Y vs. Sc/Cr) and REE analysis indicates passive margin setting for vindhyan sediments whereas a wide range spanning passive to active continental margin setting is also inferred using (Th-Sc-Zr/10) and (Th–La-Sc) ternary diagrams. However, these tectonic discriminant diagrams lack in explaining rift- or sag-related origin of any intracratonic basin such as the vindhyan basin. The total organic carbon (TOC) content in vindhyan shales ranges from 0.29% to 8.44%. The thermally liberated hydrocarbon (S1) values range from 0.01 to 0.18 mg HC/g rock (milligram hydrocarbon per gram of rock sample), whereas hydrocarbon from cracking of the kerogen (S2) shows values ranging from 0.04 to 0.47 mg HC/g rock. Based on modified Van Krevelen correlation (HI vs. Tmax) diagram, organic matter from Arangi and Bijaygarh shales is characterized as thermally mature, Type III kerogen of gas

关键词： Shale geocheristry Provenance Organic matter Hydrocarbon potential vindhyan basin

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