Biostratigraphy and palaeoenvironmental analysis of subsurface Palaeogene sediments in western part of Ahmedabad Block, North Cambay Basin

Abstract

The western part of Ahmedabad Block is among the thrust areas for hydrocarbon exploration in Cambay Basin. Palynological studies of the Palaeogene sediments of Ahmedabad Block between Detroj and Wasnalava have been carried out to evaluate the palynostratigraphy and infer depositional environment to help in basin modelling for exploration of hydrocarbons. Based on palynofloral association three assemblage zones, viz. Polybrevicolporites cephalus Zone (Palynozone-I), Proxapertites cursus- Polycolpites flavatus Zone (Palynozone-II) and Palmaepollenites kutchensis Zone (Palynozone-III) have been identified. These zones are dated Early, Middle and Late Eocene in age. The sediments corresponding to Olpad Formation (?Palaeocene) exhibited poor palynofloral contents. The interpretation of depositional environment is based on the absolute pollen frequency and palynofloral associations. In Cambay and Kadi formations the coastal and back mangrove elements are common with sporadic occurrence of marine elements, suggestive of near shore environment of deposition. The overlying Kalol Formation has yielded rich back mangrove floral assemblage along with moderate occurrences of coastal elements and is suggestive of Littoral conditions. The dominance of marine phytoplankton in Tarapur Formation is indicative of shallow marine conditions of deposition.