Middle to Late Holocene climate, vegetation and sea-level changes in NW Tripura, northeast India, based on palynological and mineral magnetic evidence

Abstract

The sediment deposits of northwestern Tripura, northeast India, revealed the enhanced proximity to the marginal marine environments, forest cover variations and anthropogenic infuences. We infer the palaeo-vegetation and palaeo-environmental conditions between 9900 and 1800 cal B.P. through a 1.80 m deep sediment profle, from the remote location of Charilam, Tripura, using biotic (fossil pollen) and abiotic (mineral magnetism) proxies. The sediment profle recorded warm and humid conditions between 8300 and 6200 cal B.P., which later shifted towards less humid phase until 4900 cal B.P. The lower part of the sediment profle provided evidence of enhanced sea-level in this region, as manifested by mangrove taxa found between 9900 and 4900 cal B.P. But later, these taxa were minimal and thereafter, diminished in the sediments during the Late Holocene (4100–1800 cal B.P.).The occurrence of fewer tree taxa and dominance of larger grass pollen signify the enhancement of anthropogenic activities in the region, during the recent times. The shifts in mineral magnetic content towards fne-grained anti-ferrimagnetic hematite components, as exhibited by relatively high Hard IRM, SIRM/ΧLF, ARM/SIRM ratio and low S–ratio towards the end of the Middle Holocene, resonate with the climate variations concurrent to the vegetation changes. These interpretations lead to the perception of a reduction in the Indian Summer Monsoon (ISM) strength during the Late Middle Holocene. The inception of anthropogenic activities has also induced the changes in the vegetation cover, leading to increased soil erosion and land-use changes during the Late Holocene in the region, which are well observed in the pollen and mineral magnetic records. This study focuses on multi-proxy analyses of the Holocene sediments in this part of northeast India, which has no such previous records.