Tropical rainforest vegetation, climate and sea level during the Pleistocene in Kerala, India

摘要

The southwestern Ghats region of the Indian Peninsula is unique for its extant endemic rainforest flora supported by high rainfall throughout the year. The record of tropical rainforest corresponding to the dynamic series of Pleistocene interglacial/glacial cycles is poorly known from peninsular India. This communication discusses the palynological study of organic matter (OM) deposits (>40 ka BP) in two well sections (Chaganachery, Kerala) from the Indian Peninsula (west coast). A rich archive of tropical rainforest pollen/spores and marine dinoflagellate cysts indicates anoxic fluvio-marine/estuarine depositional environments during warmer climates with an intensified Asian monsoon. The geochemical fingerprinting of glass shards indicates the presence of Youngest Toba ash of ～74 ka from northern Sumatra, and therefore establishes a time-controlled stratigraphy. Thus, the depositional time period of the OM is related to the sea level highstand of Marine Isotopic Stage 5.1 (～80 ka) which was the host to the YTT shards. The Late Quaternary pollen/spores diversity suggests that the modern climatic conditions in the southwestern Ghats have facilitated the conservation of moist evergreen rainforest and dry/moist deciduous forest. The pollen grains show its lineage with the extant flora and some of the fossil pollen recorded during the mesic Tertiary period from the Indian peninsula. Thus, it appears that the tropical rainforest survived here as 'Plant Refugia' in xeric (glacial) Quaternary periods, perhaps as riparian vegetation, and was rejuvenated during the Holocene as modern extant flora.