Palaeontological Studies of Palaeogene Sediments in and around Thoubal Area

Palaeogene sediments consists of Palaeocene, Eocene and Oligocene age these are very well outcrop in and around Thoubal area (Lat. 24⁰ 39’ 67” N and Long. 94⁰ 00’ 57” E) is cover by survey of India Toposheet No. 83 L/2. Fossil yielding horizons are only two in number namely light grey fine grained sandstone (1.0m) and dark brown siltstone (0.3m) in ascending order. The fossils are collected from the Kabrang Hills of Thoubal area. The present paper deals with molluscan fauna, their biozonation and correlation with the known molluscan zone. All together 33 genera and subgenera of molluscs i.e. 26  bivalves and 7 gastropods taxa are recorded belonging to the class bivalvia and gastropoda the checklist are Nuculana, Aphrodina, Corbula, Bicorbula, Glycymeris, Musculus, Undatimusculus, Corbicula, Crassinella, Mytilus,Septifer, Lopha, Lucinoma, Lucina, Callista, Microcallista, Costacallista, Diplodonta, Venus, Eotrigonia, Pitar, Calpitaria, Meretrix, Tellina,Nucula and Lamellinucula (all are bivalves), Serratocerithium, Campanile, Seila, Mesalia, Turritella, Haustator and Telescopium (all are gastropods). Some of the assemblage is similar to that of the Pondung Sandstone and Yaw Stage of Myanmar which have been dated as Late Eocene (Eames,1975). It is also confirmed by recorded fauna of upper age limit of Disang group in Manipur is late Eocene (Kachhara et al., 2000). On basis of molluscan fauna the light grey fine grained sandstone bed derived its possible palaeoecology was shallow, sub-littoral habitat perhaps from 10-15m.deep with sandy substrate. Shore was very near and has luxurious vegetation as evident by the occurrence of wood fragments. And the dark brown siltstone bed is shallow water shelf environment with a water depth of between 10-30m.having sandy substrate. Bottom has experienced feeble currents and temperature of around 20⁰-25⁰C. In the later phase, sea started regressing resulting into fluvio-marine conditions indicated by the presence of fossils plants in the form of leaves. Overall strata is of Palaeocene to Eocene in age.