Paleoclimate History and Antiquity of Thar

Abstract

The presence of climate-responsive landforms, namely lakes, aeolian and fluvial transported sediments termed sheetwash aggradations and relicts of pre-existing surfaces in the Thar Desert, have generated a wealth of paleoclimate information. Aeolian dynamism has dominated the past ~250 ka (kilo years before present) with episodes of aggradation at 17-13, 30-21, 70-60, 100-80, 140-130, 170-160 and ~250 ka. Most of these episodes were followed by extended periods of landscape stability and soil development, including redistribution of carbonates with in a stratigraphic context. The preceding period i.e., from ~250 to 600 ka was characterized by episodic sheetwash deposition. Deep sections show a stack of aggradations each generally with a discrete calcrete formation. Extensive spatial mobility of carbonates and pronounced pedogenic calcrete development suggest dominance of a distinctly semi-arid climate that was significantly wetter than the present. Relict surfaces are from ~600 ka to 1600 ka. Extraordinary landscape-scale mobility of carbonates is demonstrated by regoliths with massive carbonate enrichment and by the evolved nature of carbonate fabric. Both these attest to their extended antiquity and to a pronounced semiarid with possibility of even wetter episodes during this period. Summing up, studies suggest that for a major part of the past two million years this region enjoyed a semi-arid climate, significantly wetter than the present and that aeolian activity typical of a desertic environment appeared in a much later part of the of the Quaternary. Much has been learnt but scope exists for further refinement. Key words: Thar paleoclimate, desert antiquity, calcretes in Thar, climate-responsive surfaces of Thar.