Impact of the Indian Summer Monsoon variability on the source area weathering in the Indo-Burman ranges during the last 21 kyr – A sediment record from the Andaman Sea

Abstract

The paleomonsoonal variations and their impact on the weathering patterns in the source regions of sediments of the Andaman Sea were investigated from a 21 kyr sedimentary record using environmental magnetic, clay mineralogical and geochemical techniques. The sediment provenance of the study area determined from the geochemical discrimination diagrams and available εNd records indicates that the Western Andaman Sea receives a considerable contribution from the Indo-Burman ranges (IBR) and local sources compared to the central and eastern Andaman Sea. The results illustrate a strong Indian Summer Monsoon (ISM) during the late glacial (16–13 kyr), early (10.5–8.5 kyr) and middle Holocene (5–3.5 kyr) and a weak ISM during the Younger Dryas (12.9–11.7 kyr) and late Holocene (3.5–0 kyr) periods. The mineral magnetic grain size parameters (χARM/SIRM, SIRM/χLF, χARM/χLF) show finer grain sizes during the strong ISM periods indicating the increased chemical weathering while cold and dry periods are marked by an increase in magnetic grain size indicating the shift from chemical to physical weathering in the source regions. The results from our study are in agreement with the global and local records of paleoclimate and weathering and exhibit a close correlation with the solar insolation data suggesting the major role played by the solar forcing on the ISM variability.