A PALEO-BIOCLIMATOLOGICAL STUDY ON QUATERNARY PEAT DEPOSITS OF BANGLADESH REFLECTED BY PALYNOLOGICAL APPROACH

Environmental changes due to the Quaternary sea-level fluctuations had a profound impact on the distribution of mangrove habitats at both local and regional scales that kept their records on peat deposit. During Holocene time, Global rise and fall of Eustatic Sea level played an important role in the depositional environment. Sediments deposited beneath mangrove or salt marsh vegetation provide useful indications of present and past sea levels and paleoclimate. The research is focused to identify the climatic condition that persisted and its changes in Quaternary Period studying the peat deposits in and around Bangladesh and correlate them. It exquisitely preserves pollen and other microfossils that has been used to interpret the depositional environments, climatic conditions and sea level changes in Holocene period around Bangladesh. For this, pollen and other constitute microfossils in peat deposits of four different parts of Bangladesh has been analyzed. The presence of mangrove pollen specially Phoenix sylvestris, Prosopis grandis, Phoenix paludosa, Palmidites maximus, Palmidites plicatus, Avicennia sp, Corrugatisporites formosus found all over the study area indicate that mangrove community developed predominantly under saline facies with minor brackish condition around Bangladesh in Holocene time leading to the locally wide spread deposition of organic rich sediments. Recurrent occurrence of saline and brackish water mangrove in Bangladesh indicates that these areas undergone cyclic marine and non-marine influence. This verifies the transgression and regression pattern that was persisted during the delta progradation towards the south. During the Holocene transgression, Central and South-central regions were under the tidal influence. Saline water intruded in the river systems and floodplains. This environment facilitates the growth of tidal mangrove that has been found in the peat deposits. In addition, the prevalence of the marine mangrove pollen indicates that most of the Holocene time these areas were under marine influence. Lastly, paleo coastline reconstruction shows the direction and magnitude of delta progradation toward South-East. which the span of 8000 years the mega delta Ganges-Brahmaputra-Meghna (GBM) regressed more than 300 kilometer which indicates the rapid growth of the delta.