Continental record of the Southwest monsoon during the last 130 ka: evidence from the Southern margin of the Thar Desert, India

Abstract

Field stratigraphy, sedimentology and luminescence dating of the exposed fluvial and aeolian sequences from the southern desert margin were used to discern the pattern of southwest monsoon variability during the last 130 ka. The sedimentary architecture and textural attributes of the sediments belonging to the period 130-120 ka suggests the existence of a meandering river system consequent to enhanced southwest monsoon conditions. A shift from a meandering to a braided pattern during 120-100 ka indicates a phase of reduced precipitation. Presence of flood plain fines and bedded calcretes during ~100-70 ka suggest a period of enhanced monsoon with seasonality. Following this, a phase of weak monsoon activity was observed during 70-60 ka. Regional flood plain aggradation and pedogenesis during the period < 60-30 ka indicated enhanced southwest monsoon condition. Onset of fluvio-aeolian sedimentation after 30 ka and initiation of a regionally extent aeolian sedimentation during 20-11 ka indicates overall dry climatic condition. These observations accord well with the total organic carbon (TOC) data and suggest a vegetation/moisture control on the aeolian sedimentation in the region. Termination of a regional fluvial phase around 30 ka and incision of dunes dated to 20-11 ka suggest that the present rivers occupied their course between < 30 ka and > 11 ka. Drowned valleys in the estuarine zones suggest that the incision began during the low sea stand around 20 ka when the rivers were graded to the exposed shelf. The incision intensified with the re-establishment of monsoon during the early Holocene.