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Paleogene Biostratigraphy and Depositional Modeling in Limbodra - Gamij Area, Cambay Basin, Gujarat, India

M. Shanmukhappa1 and Raju Grover2
1Oil & Natural Gas Corporateion Ltd., Regional Geoscience Labs, Vadodara, India
2Palynology Labs, KDMIPE, ONGC, Dehradun, India

The Limbodra - Gamij area in Cambay Basin is the thrust area for hydrocarbon exploration. The study of this prospective area has been undertaken for reconstructing the biostratigraphy and depositional setup of Paleogene sediments to identify suitable locales for hydrocarbon exploration through geological modeling.

The qualitative analysis has been applied for dating and demarcation of age boundaries. The quantitative analysis, absolute pollen frequency and palynofloral associations helped in constructing the depositional model.

Based on qualitative analysis, four assemblage zones viz. Pelliceroipollis langenheimii, Early Eocene, Proxapertites cursus - Polycolpites flavatus, Middle Eocene, Palmaepollenites kutchensis - Proxapertites operculatus, Late Eocene and Couperipollis rarispinosus - Striatopollis bellus Zone of Oligocene have been established. These zones helped in demarcating Early / Middle Eocene, Middle / Late Eocene and Late Eocene / Oligocene boundaries.

The spatial and temporal distribution of palynoflora suggests thinning of the Paleogene sediments to the east towards the basin margin. The paleoenvironmental reconstruction suggests Early Eocene sediments (Cambay Shale) were deposited in inner shelf environment towards basin center while intertidal conditions prevailed towards basin margin. During Middle Eocene, overall shallowing of the area resulted in deposition of Kalol and lower part of Tarapur formations thereby developing the Limbodra pays under intertidal conditions. Late Eocene and Oligocene witnessed a transgression which resulted in deposition of middle - upper part of Tarapur Formation under shallow inner shelf conditions.

Understanding of the chronostratigraphic implications and lateral variations in depositional setup through correlation helped in constructing depositional model for Limbodra pays in Tarapur shale.