Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Rajiv Sinha ¹, Asim Chatterjee ²

Affiliations
1 Engineering Geology Group, Department of Civil Engineering, Indian Institute of Technology, Kanpur, IN
2 BHP Minerals (India) Pvt. Ltd., Udaipur - 313 001, IN

Abstract

A mineralogical study of the lacustrine sediment cores from lakes and varve deposits of the lake shore in the Schirmacher Range of East Antarctica is presented. Fietd observations and laboratory analysis indicate quartz and feldspar as principal allogenic phases derived from local crystalline rocks surrounding the lake basin. Illite, chlorite and minor amount of mixed-layered minerals in the lacustrine sediments are interpreted to be products of weathering in the lake catchment. In general, the clay mineralogy of sediment cores and varve sediments is indicative of low-hydrolyzing depositional environment under high latitudes and subtle weathering.

Keywords

Mineralogy, Sedimentology, Clay Minerals, Schirmacher Hills, Antarctic Lakes.

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Rajiv Sinha ¹

Affiliations
1 Engineering Geology Group, Department of Civil Engineering, Indian Institute of Technology, Kanpur-208016, IN

Abstract

An account of sedimentolpgical characteristics such as grain size distribution, clay mineralogy, sand mineralogy and magnetic susceptibility of the alluvial sediments from the Gandak Kosi interfan area in the Indo-Gangetic plains of north Bihar is presented. Fine-grained sediments consisting of significant percentage of detrital clays and variable carbonate content are present in the plains and are distinctly derived from the Himalaya. Sedimentation in the interfan is episodic through overbank flooding forming thick muddy sequences. Changes in depositional regime occurred because of shifting of channels which, in turn, affected channel proximity of floodplain sites.

Keywords

Gandak-Kosi Interfan, Sedimentation, Quaternary, Bihar.

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Rajiv Sinha ¹

Affiliations
1 Indian Institute of Technology, Kanpur - 203016, IN

Abstract

No Abstract.

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Rajiv Sinha ¹, D. Stueben ², Zsolt Berner ²

Affiliations
1 Engineering Geosciences Group, Indian Institute of Technology, Kanpur 208016, IN
2 Institute of Mineralogy and Geochemistry, Karlsruhe University, 74131 Karlsruhe, DE

Abstract

The Sambhar Playa in western Rajasthan, India has been studied to understand its Tectono-Geomorphologic evolution and palaeohydrological reconstruction. The playa basin originated due to tectonic movements during the Quaternary, and was deepened by large scale deflation during arid periods. A dense network of ielict drainage reflects abundant supply it water and sediments during wetter phases. A deep core (∼23 m) raised from the center of the playa indicates an alternation of clastic and evaporitic sediments. Mineralogical assemblages and the geochemical characteristics have been used to decipher the palaeohydrological conditions in the region for a period extending over 25 ka. Evaporite mineralogy shows a major change in brine chemistry at ∼5 m depth, the lower part being rich in gypsum and the upper part completely devoid in gypsum. The vertical profile shows a correlation between Na/AI ratio, δ¹⁸0 values of carbonates, MgO/(MgO+CaO) ratio of insoluble fraction and dolomite content. We interpret these trends as changes in Evaporation/Inflow ratio which in turn would reflect Low/High stands of the lake.

Keywords

Palaeohydrology, Evaporites, Playa Sedimentology, Saline Lake.

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Rajiv Sinha ¹

Affiliations
1 Engineering Geoscience Group, IIT Kanpur-208018, IN

Abstract

No Abstract.

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Rajiv Sinha ¹, Peter F. Friend ²

Affiliations
1 Engineering Geology Group, Department of Civil Engineering, IIT Kanpur-208016, IN
2 Department of Earth Sciences, University of Cambridge, Cambridge CB23EQ, IN

Abstract

The Quaternary successions exposed by excavation in the top 1.5-3.0 m of alluvial tract along a traverse in parts of the Indo-Gangetic plains are analyzed. The traverse extends across some 100 km of the interfan area between the Gandak and Kosi megafans of northern Bihar, eastern India. Most of the successions exhibit a fining upward grain size distribution, bottoming in sand or silt. though the overlying silts or clays are often interrupted by beds of coarse silt and sands. Radiocarbon dating suggests that all of the material was deposited during the last 2500 years and post-depositional pedogenic alteration has taken place. Micromorphological study of this subtle alteration shows (a) weathering of primary grains, (b) decomposition of plant and shell material, (c) carbonate dissolution and precipitation, (d) iron oxide/hydroxide accumulation and (e) illuviation of clays. The minor degree of alteration is contrasted with that reported in other areas of the Indo-Gangetic plains and it is concluded that the north Bihar plains, with an average accumulation rate of the order of 1 mm/a over 10³ years has been an area of exceptionally high sedimentation.

Keywords

Quaternary, Soil Micromorphology, Pedogenesis, Overbanks, Indo-Gangetic Plains, Bihar.

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