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Himalayan Geology, Vol. 28 (2), 2007, pp.1-9 Printed in India

Mineral Magnetic Response to Climate Variability in the High Altitude Kioto Palaeolake, Spiti Valley, Northwestern Himalaya

Dept. of Geology, University of Pune, Ganeshkhind, Pune- 411 007
Wadia Institute of Himalayan Geology, 33, GMS Road, Dehra Dun -248 001

Concentration dependent and qualitative mineral magnetic parameters are analyzed in 2300 cm thick varved lake sedimentation of the Kioto palaeolake in Spiti valley, northwestern Himalaya, at a sampling interval of 20 cm. Empirical models based on mineral magnetic parameters indicate episodic influx of larger (> 40 micron) ferrimagnetic and antiferromagnetic mineral grains and occurrence of smaller (0.03 to 0.06 micron) in-situ magnetite grains in a background variation of the hard ferrimagnetic oxide minerals (titanomagnetites ~0.08 to 40 microns). The relative variations in the fundamental mineral magnetic parameters (clf, B(0)CR, cfd%, cARM: and S-Ratios) mainly in response to changes in catchment weathering style, detrital influx and in-situ productivity are used to indicate the variability between warm (oxidative) and cold (restricted) conditions in the overall high altitude Alpine climatic regime. The warm events in general show sharp drop in S-Ratios and B(0)CR and enhanced clf,, indicating increased catchment weathering. On the other hand the cold intervals are characterized by cARM: due to stable anoxic conditions of production of authigenic iron oxides. Significant warm events are noted at the tentative ages (based on varve counts) of ~43,000 yr, ~32,000 yr, ~27,500 yr, ~19,000 yr and ~12,800 yr. With a detailed framework of mineral magnetic approach combined with sediment dating we can envisage quantitative information on the magnitude and intensity of glaciation-deglaciation and glacial advancement/retreat in the tectonically modified topographic set up of the Himalaya.

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