Micropalaeontological investigations on tsunamigenic sediments of Andaman Islands

In order to understand the type of microfauna (Foraminifera and Ostracoda), which might have been transported by tsunamigenic sediments that deposited on the beaches, estuaries/creeks and mangrove locations of Andaman Islands, a detailed fieldwork has been carried out from these islands. The main objective of this study is to record and document the calcareous microfaunal assemblage and its distribution pattern in the tsunamigenic sediment samples collected from Andaman group of Islands. The pre-tsunami foraminiferal fauna of Andaman Islands reported by earlier workers is also compared. A total of 46 surface and nine core samples have been collected from various coastal geomorphological features such as beaches, estuaries/creeks and mangrove areas of Andaman Islands. These samples are analysed for Foraminifera and Ostracoda, by applying standard micropalaeontological techniques. A total of 87 species belonging to 74 genera of Foraminifera and 29 species belonging to 22 genera of Ostracoda have been encountered. Among Foraminifera, Assilina ammonoides, Amphistegina radiata and Calcarina sp. are widely distributed. Most of the forms are highly to moderately abraded and appeared in milky white colour, may be due to churning action and transportation. However, the Ostracod population is scanty; of these only Macrocyprina sp. is comparatively a deep water form. Ostracod fauna is reported in this study based on the recent tsunamigenic sediments of Andaman Islands. All the forms recorded in the study area thrive in the shallow inner shelf (neritic) zone. From their distribution, it is inferred that the 26 December 2004 tsunamigenic sediments deposited on the coastal landforms in Andaman group of islands have been derived from shallow littoral to neritic depths and not from deeper bathyal territories.