Indications of uplift from seismic stratigraphy and backstripping of the well data in western Indus offshore Pakistan

Abstract

Two‐dimensional regional seismic reflection, oil well data, and biostratigraphic data have been used in integration to study the general structure, stratigraphic architecture, and subsidence history of the part of River Indus offshore Pakistan. The seismic data have been calibrated with the well data by generating the synthetic seismograms to identify the key reflectors indicative of major lithologic horizons. The sedimentary successions on the seismic sections are divided into passive and transpressive margin sediments on the basis of regional tectonics of the area. The western Indian margin is in oblique collision and transpression with Eurasian and Arabian plates creating Kirthar Range onshore and Murray Ridge offshore, respectively. Four mappable seismic sequences are identified within the passive margin sediments and two within the transpressive margin sediments. Due to the complex depositional setting of the basin, certain seismic sequences are not clear on the seismic records. In addition to depositional complexity, the seismic sequences are disturbed by the presence of normal faults generated probably under the action of gravity. It is interpreted from the seismic records that the normal faults were probably reactivated due to the movement of the basement blocks which have generated the push‐up structures within the offshore depression area. The subsidence curves show a gentle convex upward trend, which suggest an uplift around 40 Ma probably resulting from the reactivation of the basement blocks. The study could be helpful in understanding the tectonics of the worldwide passive margins dominated by rifting and transpression stages.