Controls on the Paleogene carbonate platform growth under greenhouse climate conditions (Offshore Indus Basin)

Abstract

During the Paleocene and Eocene, the western continental margin of the Indian Plate was an equatorial province characterized by widespread attached and isolated carbonate platforms. Using high-resolution seismic data combined with sedimentological data and log-motifs, this study presents the stratigraphic evolution, the morphological features, and the distributions of these isolated carbonate platforms which are located on NE-SW oriented basement highs and volcanic ridges linked to the Réunion Hotspot trace. Seismic stratigraphy allows defining seven seismic units in the platform succession. Stratal stacking patterns indicative of phases of aggradation and of large-scale backstepping alternate with horizons interpreted to indicate repeated phases of emersion. The onset of platform growth and the further platform development were mainly controlled by the subsidence following the Deccan Volcanism and the opening of Carlsberg Ridge. Platforms are asymmetrical in the section with the eastern aggrading margins interpreted as windward and the western margins as leeward. The leeward margins, which through time stepped back appear as structurally modified by basement induced faults. Fault blocks movement also partially influenced the internal platform geometries and the facies distribution. Change in the rate of subsidence possibly augmented the relative sea-level rise during the Early to Middle Eocene and hence contributed to the demise of the isolated carbonate platforms. Isolated carbonate platforms are stratigraphically age-equivalent to the Laki-Ghazij lithostratigraphic unit of the contemporaneous carbonate shelf. As per our knowledge, this carbonate system is the best-known seismic scale example of greenhouse carbonate system thriving during the Paleocene –Eocene.