THE CASE STUDY OF PALEOCENE-EOCENE PLANKTONIC FORAMINIFERA IN A NEAR SHORE ENVIRONMENT (JAISALMER BASIN, RAJASTHAN, INDIA)

The neritic Paleogene sedimentary sequence in the Jaisalmer Basin, India is the eastward extension of the Indus Basin. A large number of studies on the Paleocene/Eocene thermal maximum have been carried out on mid-outer neritic to bathyal environment but the knowledge of PETM in inner neritic to middle neritic environment remains quite poor. The present study deals with the planktonic foraminiferal changes across the Paleocene/Eocene boundary in shallow marine inner neritic shelf environment. The studied sections include- RAM-1 well (Oil India Limited), boreholes JOGA-99 (drilled by Rajasthan State Department of Mines and Geology) & SDC-49 and the surface section at Khuiala, village located in Jaisalmer Basin. The sections are mostly composed of clay and marl along with some limestone and shale. The low latitude acarininids (Acarinina esnaensis, A. wilcoxensis, A. strabocella, A. nitida, A. mckanni, A. soldadoensis, A. pseudotopilensis) dominate the assemblages. The occurrence of the Initial Eocene excursion taxa namely Acarinina sibaiyaensis and A. africana and decrease in the planktonic/benthic (P/B) ratio indicates the Zone E1 which is related to the global P/E boundary warming event (PETM). Acarinina flooding occurs within the Zone E1.The maximum diversity of the acarininids occurs in the Zone E1 coincides with most of the P/E sections world over. In the studied sections morozovellids are rare to absent. The presence of Morozovella praeangulata, M. angulata, M. conicotruncata, M. velascoensis (Zone P2-P3) indicates an initial transgressional phase. In the Zone P4-P5 morozovellids are almost absent. The morozovellids are completely absent in the A. sibaiyaensis and Pseudohastigerina wilcoxensis Subzones. A few kilometers away towards the seaward, in Tanot-1 well (Oil India Ltd) the morozovellids are present throughout the Paleocene to early Eocene that signifies an open marine environment. Thus the absence of morozovellids can be referred as an indication of a near shoreline deposition. The occurrence of M. edgari at the topmost part of the Zone E2 signifies the reappearance of the morozovellids which indicates another transgressional phase.The co-occurrence of larger foraminifers( e.g. Nummulites, Assilina and Daviesina) along with planktonic foraminifers also signifies an inner neritic to middle neritic shelf environment.