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Biostratigraphy and Depositional Environment of Olpad and Ankleshwar Pays in Dabka - Padra Area, Cambay Basin, Gujarat, India

M. S. Murthy1, Raju Grover2, A. C. Baruah2, and Harswaroop S. Aswal1
1Oil & Natural Gas Corp. Ltd., Regional Geoscience Labs, Vadodara, India
2Oil & Natural Gas Corp. Ltd., KDMIPE, ONGC, Dehradun, India

The Dabka - Padra area in Cambay Basin has been drawing attention for the exploration of hydrocarbon since the discovery of oil in the basin margin area. The occurrence of oil in deeper pays in Olpad and Deccan trap formations necessitated generation of biostratigraphic and depositional model for the accelerated exploration of these deeper pays.

The biostratigraphic studies identified tapered age boundaries in the eastern margin area, suggesting minimum thicknesses for Olpad, Cambay Shale and Ankleshwar formations. Based on diagnostic and significant palynotaxa five Palynozones have been recognized in the studied Paleogene sections referable to Middle to Late Paleocene (Zone-I) corresponding to Olpad Formation, Early Eocene age (Zone-II) to Cambay Shale, Middle Eocene age (Zone-III), Late Eocene age (Zone-IV) and Oligocene (Zone-V) to undifferentiated Ankleshwar and Dadhar formations.

The distribution of the identified zones in time and space suggest narrowing of Paleogene sediments towards rift shoulders and eastern basin margin. The quantitative analysis of the microfloral assemblage along with palynofloral association and absolute pollen frequency plots suggest that the sediments belonging to Olpad and lower part of Cambay formation were deposited under tidal conditions in Padra area while towards Dabka area the subtidal condition prevailed up to lower part of Ankleshwar Formation. The upper part of Ankleshwar Formation is deposited under subtidal to inner shelf conditions and the Dadhar Formation was under brackish to tidal environment.

Understanding of the fluctuations in depositional setup with chronostratigraphy is vital for basin analysis. Through lateral correlation of the palynofloral associations the microenvironmental changes resulting in facies variations are helpful in identifying the prospective locales related to Olpad and Ankleshwar pays.

Presentation GEO India Expo XXI, Noida, New Delhi, India 2008©AAPG Search and Discovery