BIOSTRATIGRAPHY OF THE POST KOPILI SEDIMENTS OF GARO HILLS, MEGHALAYA

The lithounits of post Kopili sediments constitute the Simsang, Baghma ra, Chengapara and Dupitila formations in that order of sequence. Base d on the present study five biostratigraphic zones have been recognise d in these rock stratigraphic units. The palyno-assemblage recovered f rom the Simsang formation consists of gemmate syncolpate grains, Spino spites acolporata Schizeaesporites knoxi, Polypodisporites tuberculens is, Polypodeaceaesporites, Lycopodiumsporites sp., together with a hos t of angiospermic pollen grains: Since such an assemblage is indicativ e of Oligocene age, the Simsang formation is, therefore, considered as the time and rock stratigraphic equivalent to the Barail Group in Ass am. From the Baghmara formation a palynozone of early Miocene age has been recorded, which is characterised by two winged conifer pollen, ri bbed trilete spores referable to Striatriletes, Lycopodiumsporites, an d frequent occurrence of fungal bodies and spores of Ascomycetae and F ungi Imperfectii. Two faunal biostratigraphic zones have been recognis ed in the fossiliferous beds occurring at the bottom of the Chengapara formation. The lower assemblage is characterised by the presence of A nadara, Cardium and Ostrea. The zone is unique for the occurrence of v ariety of pelecypods and gastropods. The upper assemblage zone is char acterised by the frequent presence of Tellinaceans and the absence of most of the gastropods occurring on the lower assemblage. The lower an d upper assemblage zones are of Aquitanian - Burdigalian age. The foss iliferous horizon occurring well within the Chengapara formation is co nsidered to represent probably the uppermost fossiliferous horizon in the Garo Hills. This horizon is characterised by the presence of elasm obranchs represented by Carcharadon carcharias and a few batoids. Carc haradon carcharias is not known to occur in the beds older to upper Bu rdigalian. Dupitila and Dihing formations have been found to be devoid of fossils.