The influence of the South-west Indian monsoon on continental deposition over the past 130 kyr, Gujarat, western India

Abstract

Ocean and ice core records of the intensity of the South-west Indian Monsoon (SwIM) show rapid shifts in most proxy indicators of climate over the past 125 kyr on decadal to millenial scales. However, the responses of continental environments to such perturbations remain unknown due to the absence of a suitable long-term continental record. The stratigraphic record from Gujarat, western India, an area where all sedimentological processes are governed by the vagaries of the SwIM, reveals three aggradation phases that represent deposits of seasonal rivers (AP1), ephemeral rivers (AP2) and dust storms (AP3). Based on a review of available dates and new ESR dates on the oldest exposed calcretes from palaeovertisols these phases are assigned the time brackets 135-100 kyr bp (AP1), 100-20 kyr bp (AP2) and 20-6 kyr bp (AP3). These results suggest that continental depositional environments respond in a subdued manner and are separated by thresholds. For climate shifts to effect durable changes in the continental depositional environment, a period between < 5 kyr and 16 kyr is the minimum time required to permanently change the landscape of an area. Alternatively, catastrophic changes in terrestrial depositional environments may also be effected by abrupt climatic shifts that are beyond the tolerance limits of the depositional systems.