Presenting Meso-Cenozoic seismic sequential stratigraphy of the Offshore Indus Basin Pakistan

Abstract

Preserved deformed depositional sequences along passive continental margins are important repositories of natural resources as well as key laboratories for understanding rift-drift tectonics. With better post signal processing schemes, interpretation techniques, and potential data, imaging sedimentary basins along these margins has reached unique levels of refinement. This, in turn, has led to considerable improvement in unfolding the complex tectono-sedimentary history since rifting to basin development. In this paper, deep reflection seismic coupled with well data and biostratigraphic information have been used to decipher the third-order depositional sequences of Meso-Cenozoic succession in western parts of the Indian Plate Passive Continental Margin (Offshore Indus Basin) as pioneer research. Based on morpho-tectonic considerations, the depositional sequences are divided into syn-rift, passive margin, and post-rift stages deformed by steeply dipping normal faults. Using the principles of classic sequence stratigraphy, five third-order mappable depositional sequences have been recognized on seismic records that are controlled by regional tectonics and sea-level fluctuations coupled with sedimentation type and rates in the region. The associated system tracts were recognized and mapped based on genetic reflection terminations on seismic profiles and log motifs, and constraint surfaces include sequence boundaries (SBs), maximum flooding surfaces (MFSs) and transgressive surfaces (TSs). The depositional systems encompass lowstand system tracts (LSTs), transgressive system tracts (TSTs), and highstand system tracts (HSTs). The LSTs are composed of shallowing-upward lowstand deltas or terraces prograding in the basin-ward direction while pinches out landward at preceding depositional shoreline breaks. The sand units of TSTs are interpreted as shoreface sands deposited in the shelfal part during rising sea-levels and HSTs are characterized by coarsening and shallowing upward intervals, with both fluvial and laterally prograding deltaic deposits. A hydrocarbon entrapment model is proposed suggesting an interesting petroleum trap. Based on the entire course of this research, valuable recommendations have been made for answering past exploration failures and future efforts. Such studies can be applied to worldwide passive margins dominated by third-order sequences with complex sediments-tectonic interplay.