LATE QUATERNARY CLIMATE AND SEISMICITY IN THE EVOLUTION OF FLUVIAL LANDFORMS IN SOUTHERN KACHCHH PENNINSULA, WESTERN INDIA

The tectonically active Kachchh peninsula in the western India lies in the southwest monsoon trajectory hence provides a rare opportunity to decipher the temporal changes in climate-tectonics interaction in the evolution of the fluvial landforms. Reconstruction based on geomorphology, sedimentology, geochemistry supported by optical chronology suggest that the fluvial aggradation in the region was initiated during the onset of the Indian Summer Monsoon (ISM) after the Last Glacial Maximum (LGM). The sedimentary characteristics and major elemental concentration suggests that the sediments are dominated by miliolite with subordinate contribution from the Mesozoic sandstone and shale. The miliolites were deposited during the glacial aridity as obstacle and valley fill dunes which were fluvially reworked with the initiation of the ISM after the LGM around 20 ka. A progressive strengthening of monsoon between 17 and 12 ka followed by an overall strengthening of monsoon with fluctuation between 12 ka and 7 ka is inferred. This was followed by a steady decline in the ISM until around 3 ka. However, presence of the younger fill sequences which occurs proximal to the present day river channel and dated to 1 ka suggests a short-lived phase of renewed strengthened ISM in the region.

Based on the nature and pattern of the fluvial landforms, two major events of enhanced seismicity can be suggested. The geomorphic expression of the older seismic event dated to >17 ka are preserved in the form of beveled Mesozoic bedrock surfaces which accommodated the post glacial fluvial aggradation. The younger event of enhanced seismicity is assigned <3 ka and was responsible for the re-incision of the fill sediments and the Mesozoic bedrock as also the evolution of the present day fluvial landforms. The time averaged incision/uplift rate indicates that the Katrol Hill Range is uplifting at a rate of ~4 mm per year implying seismically active nature of the terrain.