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L. S. Chamyal ¹, N. Juyal ²

Affiliations
1 Department of Geology, The M S University of Baroda, Vadodara-390002, IN
2 Physical Research Laboratory, Navrangpura, Ahmedabad-380009, IN

Abstract

Indian Summer Monsoon (ISM) is the major climatic feature in the Indian sub continent. Since marine proxies used for monsoon reconstructions are the expressions of the wind strength that may or may not translate on land as rainfall, the continental records are the direct proxies of rainfall variability. We have made an attempt here to synthesize the available works aimed at past monsoon reconstruction using the chronologically constrained continental archives. The nature of geomorphic response of a fluvial system depends upon its environmental setting and the magnitude and duration of a climatic perturbation. In the present synthesis it was observed that events that lasted for ∼10⁴ years could imprint its signature particularly in the fluvial systems irrespective of their geographical location. Except few examples, there is virtually no evidence of short term climatic fluctuations coming out from the available fluvrial records. Could it be due to the fact that short lived climate instability (10² to 10³ years) are not sufficient enough to bring about major geomorphic changes in fluvial processes?

Climatic inferences drawn so far using the fluvial and aeolian archives are largely based on the field stratigraphy, sedimentology and chronometric studies from limited geographical areas. There is a need for wider coverage pertaining to the fluvial systems particularly in the peninsular and southern Indian rivers. Further, unless, the clitmate proxies like stable isotopes, geochemistry, and environmental magnetism are used the monsoonal inferences would remain qualitative. Lacustrine sequences provide uninterrupted record of monsoonal variability. This important continental archive has not been exploited to its potential, except for the Thar Desert Renewed efforts should be made to explore other areas including the Himalaya.

Keywords

Continental Deposits, Monsoon Variability, Late Quaternary.

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N. Juyal ¹, L. S. Chamyal ², S. Bhandari ², D. M. Maurya ², A. K. Singhvi ¹

Affiliations
1 Physical Research Laboratory, Navrangpura, Ahmedabad - 380 009, IN
2 Department of Geology, M S University of Baroda, Vadodara - 390 002, IN

Abstract

Chronometric and sedimentological data generated from the exposed Quaternary sequences of the Orsang River basin indicate close correspondence between the environmental changes and fluvial aggradation. The oldest and regionally extensive fine Silty-Clay occurring at the base of the successions is dated to >97 ka suggesting prevalence of high sinuosity suspended load fluvial regime. Its stratigraphics portion suggests that the deposition occurred during the enhanced southwest monsoon corresponding to the Marine isotopic Stage-5 (MIS-5). The gravel deposits that overlie provide an age of -60 ka indicating dominance of braided system (MIS-4) during the reduced southwest monsoon. The pluvial interstadial (MIS-3) is represented by flood plain facies that was deposited under the persistent fluvial system strengthened by enhanced southwest monsoon and assigned ages ranging between 50 and 30 ka. An extensive aeolian sand sheet that blankets the topography, is luminescence dated to 21 ka suggesting the onset of Last Glacial Maximum in the Orsang River basin.

Keywords

Late Pleistocene, Fluvial Aggradation, Environmental Change, Orsang River Basin, Western India.

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