Petroleum geology of Kohat-Bannu Plateau, Northwest Frontier Province, Pakistan.

摘要

The Kohat-Bannu basin originated due to the compressional tectonics at the northern margin of the Indian plate. The anticlinal structures of Marwat, Khisor, Surghar, and Bhittani Ranges, "the Trans-Indus Ranges," are the southernmost extension of the fold and thrust belt. These ranges were originally aligned with the Salt Range prior to the India-Eurasia collision, but because of compression, moulding of the sedimentary strata, obstruction by the Sargodha high, and rotation of the Indian plate, the Mianwali/Kalabagh and Bannu re-entrants were developed.; The seismic study suggests that the Kohat-Bannu plateau has been overthrust to the south along a sole thrust fault. Many thrust faults, mostly verging to the south and southeast, cut the sedimentary strata, implying that the Kohat-Potwar plateau was thrust southward and southeastward as a direct consequence of the crustal shortening resulting from north-south (post-Paleocene) and northwest-southeast (pre-Eocene) lateral compression. The Eocambrian Salt Range Formation is a thick evaporite sequence present beneath the foreland fold and thrust belt, which acts as a zone of decollement between the upper sedimentary belt and the lower basement rocks. The basement beneath the foreland fold and thrust belt is not involved in thrusting.; The anticlines and synclines in the Bannu area are generally gentle, broad structures compared to the overturned, faulted and imbricated structures in the Kohat folded zone. The Bannu depression is downfaulted along normal faults. The basement rocks are also downfaulted along normal faults, causing ramping of the sedimentary strata.; Source rocks are widespread throughout the Kohat-Potwar plateau. The best source rocks in this area are contained in the Salt Range Formation. A variety of carbonate and clastic origin rocks of Cambrian, Permian, Jurassic and Cretaceous age show good reservoir qualities.; The traps are anticlines, structures related to thrust faults, flower structures and/or triangle zones. The stratigraphic traps are also present.; The presence of the combination of source-reservoir-trap, oil seeps, the presence of thick deposits of sedimentary rocks and their location on continental margin makes the area favorable for hydrocarbon exploration.