Geodynamic evolution of the offshore Indus Basin Pakistan: the western Indian Plate Passive Continental Margin.

A complex Meso-Cenozoic history characterizes the offshore Indus Basin Pakistan, including rifting, drifting, collision, transpression and recent inverted extension that is poorly understood. We use reflection seismic data to document the geometry of the structures that accommodated the deformation and offshore well data to correlate the sedimentary sequences which were affected by the different tectonic episodes. Synthetic seismograms have been prepared for calibrating seismic data with well information for identification of key reflections representative of major lithological horizons. Seismic stratigraphy helped in dividing the sedimentary successions into rifted margin and transpressive margin sequences. Additionally, the basement represented by chaotic and semitransparent reflections, and Moho discontinuity by moderate amplitude bright reflections are also identified on seismic records. Syn-depositional normal faulting in extensional regime (Cretaceous–Oligocene) are identified on seismic profiles that converted into strike slip faults in Miocene and listric faults in Recent sediments forming inverted extensional regime. We infer that the basin inversion from extension to inverted extension and transpression occurred in recent times. Number of depositional features including shelves, deltaic deposits, canyons and channel levee complexes have been identified that developed in different tectonic episodes. Five tectonic subsidence curves using backstripping procedure have been calculated in order to constrain the geodynamic evolution of the Meso-Cenozoic sedimentary succession of the offshore Indus Pakistan. The analysis of tectonic subsidence curves, covering a time span of 140 Ma, allowed us to quantify the total subsidence and to document the activities of syn-rift and post-rift faulting systems. Different stages, in terms of duration and magnitude of subsidence-uplift trends, have been identified in the evolution of the basin. Two uplift events are prominent in Eocene (∼40 Ma) and Miocene time (∼12 Ma). A rapid resumption of subsidence with non-conformity in Early Palaeocene is seen along the margin. [ABSTRACT FROM AUTHOR]