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AAPG Bulletin, V.
Prospect of hydrocarbon associated with fossil-rift structures of the
southern Indus basin, Pakistan
Nayyer Alam Zaigham,1 Khalil Ahmad
Mallick2
1Professor, Department of Geology, University of Karachi,
Karachi, Pakistan; email: [email protected]
2Professor, Department of Geology, University of Karachi, Karachi, Pakistan;
email: [email protected]
AUTHORS
Nayyer Alam Zaigham received his B.Sc., M.Sc., and Ph.D. from University of Karachi. He started his career as an exploration geophysicist in 1970 and has worked in various capacities with the Geological Survey of Pakistan. In connection with his professional activities, Zaigham has traveled extensively in the United States and Canada. Presently, he is working as professor in the Geology Department of Karachi University.
Khalil A. Mallick is professor and chairman of the Geology Department and also director of the Evening Program at the University of Karachi, Pakistan. He has 40 years of teaching and research experience at the university level. He received an M.S. degree in applied geochemistry from McGill University, Canada, a Ph.D. from Karachi University, and a postdoctoral scholarship from Technical University of Norway, Trondheim. He has directed 17 Ph.D. and M.Phil. students.
ACKNOWLEDGMENTS
We very much thank AAPG referees R. V. Ingersoll, H. J. White, and one who is anonymous for their painstaking reviews that helped to improve the quality of the manuscript. We also thank I. H. Quraishi of the Geological Survey of Pakistan for his useful comments.
ABSTRACT
The southern Indus basin (550 × 250 km) is characterized by tectonic upwarping on the western margin of the Indo-Pakistan subcontinent. Several hypotheses have so far been proposed to explain the origin of these crustal features, but these basement upwarps remain puzzling. Aeromagnetic data have been analyzed and interpreted, supplemented with seismicity and geological information. From the integrated study, we inferred basement configuration and developed models for tectonic evolution of these exotic crustal features and their impact on hydrocarbon potential associated with the southern Indus basin. The southern Indus basin is identified as an extension basin resulting from an inferred fossil-rift crustal feature overlain by a thick sedimentary sequence. Extension was a consequence of temporal divergence of the Indo-Pakistan subcontinent from Gondwanaland during the early Paleozoic. Based on magnetic-anomaly trends, the Indus basin fossil-rift feature is characterized by horst and graben structures, together with a system of transcurrent faults. The association of seismicity events and basement crustal features suggests that Tertiary reactivation of individual segments of the inferred rift structure has deformed overlying sequences of the Indus basin and also the surrounding areas, particularly the fold and thrust belt of Pakistan on the western side of the basin. The proposed geological models also illustrate the potential for appropriate environments for development of hydrocarbon source rocks, sufficient heat for thermal maturity, and structures for reservoirs and seals, suggesting more bright prospects in the southern Indus basin.