Vegetation history and monsoonal fluctuations during the last 12,500 years BP inferred from pollen record at Lower Subansiri Basin, Assam, Northeast India

Abstract

A 120 cm sediment profile from 4.5 m deep exposed section of Lower Subansiri River Basin has been pollen analyzed to trace palaeovegetation and climate in relation to monsoonal activity since 12,500 years BP. The study has depicted the existence of tropical mixed tree–savannah type to tropical mixed deciduous type forest under four climatic regimes, viz. cold and dry to warm and relatively dry since 12,500 years BP followed by a palynologically barren zone indicating strong fluvial activity. Four sets of monsoon fluctuations, i.e. relatively low to considerably decline in monsoonal activities have been estimated by using pollen marker taxa during the period. The marker taxa signifying high monsoonal activity are – Dipterocarpaceae, Syzygium cumunii, Arecaceae and Moraceae. Melastoma malabathricum, the only taxa which is marked as low monsoonal activity and dry depositional environment. The consistent occurrences of high land taxa are suggestive of long distance pollen transport from higher elevation via strong wind and water source.