Palynological investigation of the Siju Formation (middle eocene) in the type area, south Garo Hills, Meghalaya, India

Abstract

A palynofloral assemblage. consisting of 37 genera and 53 species, has been recorded from the Siju Formation (Middle Eocene) exposed along Simsang River near Siju, South Garo Hills, Meghalaya. The assemblage is dominated by dinoflagellate cysts and acritarchs (73%) followed by fungal remains (26%) whereas spores-pollen (I %) are rare. Predominant palynotaxa of the assemblage are Achomosphaera ramulifera, Cleistosphaeridium brevispinosum, C. sijuensis, Collumosphaera fruticosa, Homotryblium floripes, H. pallidum, H. tenuispinosum, Lingulodinium machaerophorum, Operculodium centrocarpum, O. major; etc. Three species. viz.. Cleistosphaeridium sijuensis. Collumosphaera garoellsis and Thalassiphora indica, are proposed as new. On the basis of frequency and distribution of palynotaxa, two cenozones, viz.. Homotryblium pallidum Cenozone and Cleistosphaeridium sijuensis Cenozone, have been proposed in the Siju Formation. These cenozones can be recognized by their characteristic and restricted palynotaxa. The palynoflora indicates prevalence of tropical (warm-humid) climate and presence of mangrove elements along the shore and also wet evergreen forest further inland. The environment of deposition has been interpreted as marginal marine. The palynoflora has been compared with the Eocene assemblages recorded from various sedimentary basins of India and has been assigned a Middle Eocene age.