BARTONIAN AGE CALCAREOUS NANNOFOSSIL BIOSTRATIGRAPHY OF TANOT WELL-1, JAISALMER BASIN AND ITS IMPLICATIONS

摘要

A fairly rich and moderately diversified nannofossil assemblage comprising thirty-eight species belonging to eighteen genera and one calcareous dinoflagellate species are described from subsurface samples of Tanot #1 well (Oil India Limited) representing the Bandah Formation of the Jaisalmer Basin. The assemblage though contains little overgrowth in delicate forms, yet displays exceptional preservation at some levels. The assemblage is dominated by reticulofenestrids specially Cribrocentrum reticulatum. The assemblage is typically indicative of low-latitude, near-shore, shallow and warm water environment and can be assigned to zone NP17 Discoaster saipanensis Zone. This is correlatable with parts of both P13 Orbulinoides beckmanni and P14 Truncorotaloides rohri planktonic foraminiferal Zones and a part of Dll dinoflagellate Zone of Bartonian age. This nannofossil data from subsurface of Jaisalmer is coeval with more diversified nannofossil assemblage from Kachchh and less diversified assemblages from the Dilni River section, Meghalaya. Though the entire Bartonian spans (41.3-37.my) ca. four million years, it appears that the nannofossil assemblages in both western and eastern sectors of India pertain only to 1.5 my. time slice (39.5-38.0 my) of global eustatic rise. The late Eocene (Priabonian) is hiatus both in the Kachchh and Jaisalmer basins of western India, whereas the sedimentation continued in Meghalaya in the eastern sector and the sea encroached on the Cambay Basin in western India in late Eocene.