Palaeoecology of the Lower Bengal Basin, Calcutta, India, during the Late Quaternary

Abstract

AbstractPalynological analysis was conducted in view of past ecological reconstruction trends of Calcutta, the Lower Bengal Basin (West Bengal), India. Floristic compositions were derived from peat samples collected from Garia, located at the southern extremity of the city. Garia, being one of the oldest settlements in this region, is situated by the ‘Tolly Nullah’ connecting Calcutta to the Vidhyadhari River at the east. Bore hole samples were radiocarbon dated and three successive peat layers of 7000 (+170) y. B.P. to 2650 (+150) y. B.P. were analyzed for their pollen composition. Pollen data indicates the existance of typical swampy vegetation of mangrove plant community in and around Calcutta, which are presently confined to the Sundarbans forest, the further south of the studied area. The lower most peat layer (ca. 7000–6500 y. B.P.) reveals that the vegetational sequence was comparatively uniform and mainly comprised of Heritiera, Rhizophora, Sonneratia, Excoecaria, Phoenix paludosa and grasses, implying insignificant fluctuations in climatic conditions. The middle layer indicates a mixed vegetational type of fern spores, mangroves and some terrestrial plants (e.g. Acanthus, Cynometra, Suaeda, and grasses). The lower part of the middle peat layer (ca. 6450–6100 y. B.P.) consisted of marshy habitat as evidenced by fern spores, whereas their absence in the upper part implies relatively dry environmental conditions. The upper peat layer (ca. 2600 y. B.P.) is dominated by grass, pollen grains terrestrial habitats (Typha, Cassia, Eucalyptus, Desmodium, Salicornia, and Rhamnaceae) and some of typical mangroves (Heritiera and Excoecaria). Low amounts of fern spores indicating Lower Bengal change towards the terrestrial habitats. The pollen/spore assemblages in the three successive peat layers indicate the presence of typical mangrove vegetation, of the type currently observed in the Sundarbans region. Frequent sea water inundation mixed with fresh water flow from the northern upstream at the low lying topography of Basin seems to have led to the formation of peat by deposition rather than by drifting. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)