Structural Style and Its Implication to Hydrocarbon Potentiality of the Pishin Basin (Pakistan)

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Abstract The Pishin Basin in Pakistan is the younger and smaller sedimentary basin with 800 km length and variable width of 40‒175 km located on the northwestern extremity of the Indian Plate. It is bounded by the Chaman Fault and Ghazaband Fault and is connected to the Makran-Balochistan Basin towards the southwest. The Pishin Basin area (the Upper Cretaceous) is structurally limited to the recent flysch basin, deformed by sinistral transpression along the Chaman Fault System, between Eurasian and Indian tectonic plates. The Pishin Basin has immense potential for hydrocarbons. However, it still largely remains the geological frontier despite the availability of only reconnaissance-level regional surface mapping, sporadic detailed maps and low-quality seismic data acquired over some parts of the basin. Moreover, drill data from only one exploratory well are still insufficient to define the key elements of the petroleum system of the area of research. However, based on information inferred from the regional geodynamic evolution from gross crust structural development, regional and local tectonics, combined with available geological mapping and stratigraphic/sedimentary strata, integrated with seismic signatures (though feeble) and gravity data. A geological structural model along four cross-section lines has been developed that indicates the possibility of upper main decollement within the enormously thick shales of the Oligoene‒Miocene strata. The main elemental detachment from and within the basement rocks that instigated the ultimate ophiolitic obduction caused an eventual discordance between surface and subsurface structural geometry and tectonic framework. It is related to the development of large-scale folding and duplex systems involving antiformal stacks and pop-ups. Towards the south, the basin gets narrower and structures converge, the impact of strike-slip faulting due to the proximity of the Chaman strike-slip fault intensifies which is expressed in the form of its clustered fault splays.

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