A Record of Late Jurassic Dinoflagellate Cysts from Ariyalur-Pondicherry Sub-Basin of Cauvery Basin, Tamil Nadu

A detailed study was carried out on dinoflagellate cyst taxa in the interval between 4995 m and 4725 m in Andimadam Formation (Pre-Albian) of well Komarakshi # A of Ariyalur-Pondicherry Sub-Basin in the Cauvery Basin. The study recognises five dinoflagellate cyst biozones, ranging from Late Jurassic to Early Cretaceous (Early Oxfordian & older-Aptian) age. The stratigraphic order of these biozones are: Sentusidinium rioultii-Polystephanephorus calathus interval zone, Polystephanephorus calathus-Wanaea clathrata interval zone, Wanaea Clathrata-Gochteodinia mutabilis interval zone, Gochteodinia mutabilis - Egmontaoinium torynum interval zone and Odontochitina Operculata-Pseudoceratium pelliferumAssemblage zone.

The presence of dinoflagellate cysts throughout the study interval suggests that the marine influence was prevalent through Late Jurassic (Early Oxfordian) to Early Cretaceous (Aptian) period. The record of Late Jurassic dinoflagellate cysts in the well Komarakshi # A, amply suggests that the marine incursion had taken place during Early Oxfordian in the Cauvery Basin. This also leads to the hypothesis that the rifting of Gondwanaland and opening up of Indian Ocean might have begun during Late Jurassic (Early Oxfordian) period, which led to the first marine transgression into the basin.