Palynostratigraphy and depositional environment of Tura and Pre-Tura sedimentary successions in Dhansiri Valley of Upper Assam Shelf, Assam & Assam-Arakan Basin, Assam, India

Abstract

Detailed palynological investigations have been carried out to reconstruct stratigraphy and interpretation of depositional environment of Tura and Pre-Tura sedimentary sections in Dhansiri Valley of Upper Assam Shelf, Assam & Assam-Arakan Basin. Sediments of the Tura Formation dated as Early Eocene and interpreted to be deposited under subtidal to inner shelf environment. Pre-Tura sediments, developed in studied wells, led to the identification of Dergaon, Bamangaon and Moabund formations with intervening unconformities, having different tectonic history and distinct palynofossil assemblages. Early Permian sediments of the Dergaon Formation (=Talchir Formation), the oldest in the basin are deposited under the intracratonic phase, overlie the metamorphic basement complex. The sediments of the Dergaon Formation are unconformably overlain by the Bamangaon Formation deposited during the Early Cretaceous, whereas, in well DR-A, the sediments of the Dergaon Formation are directly overlain by the Moabund Formation corresponding to the Late Maastrichtian age. The sediments of the Tura Formation overlie the Maobund Formation in well DR-A, and they overlie the Bamangaon Formation in the rest of the wells in Dhansiri Valley.