2019 AAPG Annual Convention and Exhibition:

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Tectonic and Climate Control on the Seismic Architecture of Palaeocene-Eocene Isolated Carbonate Banks of the Offshore Indus Basin, Pakistan


Investigation of the Offshore Indus Basin seismic survey provides an unprecedented example of an isolated Paleogene carbonate platform complex developed on Early Paleocene volcanic ridges and structural highs. The first study of its kind in the area therefore shows that the Offshore Indus Basin is a test laboratory for analyzing the depositional geometries and stratigraphic architecture of tropical carbonate platforms developed under the greenhouse climate conditions of the Paleocene and Eocene. The carbonate growth initiated following the submergence of the volcanic basement during the Paleocene. The topographic relief of the antecedent topography has determined the size, shape and locations of the carbonate banks which form the platform complex. It is further shown that the carbonate platform architecture is a result from the combined effects of regional and local tectonics, paleoclimate, paleoceanography, and eustatic changes. Continuous subsidence of the substratum allowed the carbonate banks to grow up to significant thicknesses with locally more than 1000 m. The minimal eustatic variations of the greenhouse world provided an ideal balance between the relative sea level fluctuations and rate of deposition. This explains the depositional response of the platform internal “parallel and layer cake” accumulations geometries with flat tops without development of any rigid rims or empty bucket geometries. The episodic synsedimentary reactivation of faults linked to the drifting and collision of the Indian Plate during deposition of the carbonate platforms also partially controlled the internal architecture and caused the backstepping of the bank margins. The growth of the carbonate platform complex coincided with the Paleocene-Eocene hyperthermal events. This early Paleogene episode is also known to correspond to a phase of major biotic changes of shallow-water reef assemblages. Findings are expected to improve our understanding for the depositional configuration and better constrain prediction of hydrocarbon reservoir facies in greenhouse carbonate platforms of Offshore Indus Basin Pakistan.