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Subir Sarkar ¹, Partha P. Chakraborty ¹, Pradip K. Bose ¹

Affiliations
1 Department of Geological Sciences, Jadavpur University, Calcutta-700 032, IN

Abstract

Breccia and pebbly massflow products are present in abundance in basin slope deposits of an unnamed marine Proterozoic fonnation in Maharashtra. Seven distinctive genetic modes have been identified and attributed to slump, slide, spring sapping and evaporite dissolution. The clasts are tabular in form and intraclastic in origin. The observations suggest caution against the prevailing tendency to equate occurrence of tabular intraclasts with shallow depositional regime. In order to ascertain their sedimentological significance, a clear understanding of their genetic processes is thus warranted.

Keywords

Sedimentary Structures, Carbonates, Proterozoic, Sedimentology, Maharashtra.

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Partha Pratim Chakraborty ¹, Subir Sarkar ²

Affiliations
1 Department of Applied Geology, Indian School of Mines, Dhanbad - 826 004, IN
2 Department of Geological Sciences, Jadavpur University, Kolkata - 700 032, IN

Abstract

Detailed facies analysis in late Proterozoic Rewa Shale reveals three physically distinctive facies that differ in their paleogeography. Between shoreface and outer shelf the facies types are distributed as (I) shale with thin siltstone/Fine sandstone interbeds of outer shelf, (II) shale interbedded with HCS bearing sheet sandstone of inner shelf within storm wave base and (III) sandstone interbedded with silty shale of distal shoreface paleogeography. High resolution facies succession analysis reveals three different orders of depositional cyclicity, the lowest of which may be correlated with third order depositional 'sequence'. Thin (av 3 5 cm) discrete levels of emergence with their invariable associations and sharp transitions from inner shelf to shoreface facies mark the subaerial discontinuities, which punctuate the apparently monotonous. Rewa Shale succession Far from the coastline on a siliciclastic ramp that lacks shelf slope break, these features, even though cryptic, can provide important clues for sea level falls in shale dominated successions.

Keywords

Depositional Cyclicity Emergence, Sequence, Rewa Shale, Son Valley, Central India.

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Asru K. Chaudhuri ¹, Somnath Dasgupta ², Goutam Bandyopadhyay ², Subir Sarkar ², P. C. Bandyopadhyay ², K. Gopalan ³

Affiliations
1 Geological Studies, Unit, Indian Statistical Institute, Calcutta, IN
2 Department of Geological Sciences, Jadavpur University, Calcutta 700032, IN
3 National Geophysical Research Institute, Hyderabad, IN

Abstract

The Proterozoic sequence around Adilabad, Andhra Pradesh comprises a distinct lithostratigraphic unit of 'Group' status and has been given the name Penganga Group. The Penganga Group has been classified into three Formations which are, in order of younging, Pranhita Sandstone, Chanda Limestone and Sat Nala Shale. The sequence is dominated by limestones and shales which were deposited in relatively deep water environment and, thus, contrast sharply with the conglomerate, sandstone and shallow water limestones of the Pakhal Group. Radiometric dating of fresh glauconites from middle part of the Penganga Group gives an age of 770 ± 30 Ma. Thus, the Penganga Group is the youngest of all other Proterozoic sequences in Pranhita-Godavari Valley.

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Lukasz Wiejaczka ¹, Anna Bucala ², Subir Sarkar ³

Affiliations
1 Polish Academy of Sciences, Institute of Geography and Spatial Organization, Św. Jana 22, 31-018 Cracow, PL
2 Polish Academy of Sciences, Institute of Geography and Spatial Organization, Św. Jana 22, 31-018 Cracow, IN
3 North Bengal University, Geography Department, Siliguri 734 430, IN

Abstract

The aim of the present study is to evaluate the hydromorphological state (the degree of naturalness and anthropogenic transformation) of Himalayan rivers and to determine the role of human activity in shaping their hydromorphology. The study was conducted in the valley of the Tista River in Darjeeling Himalaya. The field research was carried out in selected channel sections with and without noticeable human interference. The assessment of the hydromorphological state was conducted on the basis of the River Habitat Survey method. The analysis of research results shows that the habitat quality of the river sections with noticeable human interference is not significantly different from that in the sections without noticeable anthropogenic pressure.

Keywords

Darjeeling Himalaya, Hydromorphology, Human Impact, River Habit Survey Method, Tista River.

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Arvind K. Singh ¹, Partha Pratim Chakraborty ², Subir Sarkar ³

Affiliations
1 Birbal Sahni Institute of Palaeosciences, Lucknow 226 007, IN
2 Department of Geology, University of Delhi, Delhi 110 007, IN
3 Department of Geological Sciences, Jadavpur University, Kolkata 700 032, IN

Abstract

Trace metal concentration in black shales can hold valuable information regarding ancient deep-ocean redox state. The size of marine reservoir of redoxsensitive elements (particularly molybdenum and chromium) is principally controlled by the extent of anoxicity in marine conditions following the onset of oxidative weathering post Great Oxygenation Event (~2.5-2.3 Ga). Hence, it is considered that coupled analysis involving redox-sensitive element/s and primary organic productivity (total organic carbon) may provide a clue for redox behaviour of ancient deep ocean. Here, we use the redox behaviour of Mo and total organic carbon values of Vindhyan shales to show that the Vindhyan hydrosphere although initiated as a stratified sea with anoxic and sulphidic deep water as exemplified by the geochemical character of the Arangi Shale, the extent and veracity of anoxicity and euxinicity was never pervasive. It further suggests that the Vindhyan hydrosphere developed euxinic deep water only during deposition of Arangi, Rampur and Bijaygarh black shale and was anoxic but certainly not euxinic during Koldaha and Rewa sedimentation. The low concentration of Mo and Cr, in general, in argillaceous intervals suggests that the Vindhyan Sea behaved as a moderate Mo and depleted Cr reservoir. The consistent low concentration of Cr within the Vindhyan shales also suggests restriction in the availability of Cr in the water column in the absence of any significant detrital supply of Cr at very low atmospheric oxygen level (<0.1% PAL; present atmospheric level).

Keywords

Hydrosphere, Primary Organic Productivity, Total Organic Carbon, Transition Metals, Stable Isotope Chemistry.

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