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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
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Stable-shelf carbonate sedimentation along the northwestern edge of the Indian subcontinent preceded the post-mid-Eocene Indian-Asian collision. The early Eocene section in Pakistan displays very rapid facies changes controlled by a cycle of regression and transgression. Beginning with the Paleocene Patala Formation in the Kohat area, quiet-water offshore dark shales grade up-section to include increasingly thick, extensive, and common marly limestones, becoming a foraminiferal limestone sequence. This section then becomes shalier with progressively thinner and more argillaceous micrites and grades upward into the unfossiliferous green Panoba Shale, which then passes into the nearshore, medium-energy, fossiliferous, and bioturbated limestones of the Shekhan Formation. The upper Shekhan beds are mud-cracked, festoon-bedded, channel-form dolostones, presumably tidal deposits. The topmost dolostones contain zones of small disruptive anhydrite nodules and pass rapidly into gypsum laminated with varicolored clays. To the west, the Panoba Shale and the Shekhan Formation grade into a massive salt deposit; to the northeast they grade into deeper water limestone. The evaporites are interpreted as sabkha deposits. All are covered by the mostly continental, mammal-bearing Kuldana Formation red beds. Drowning of the coastline then caused rapid development of (1) local lacustrine dolomite and chert units, (2) oyster-rich lagoonal or estuarine limestones, and finally (3) open-bay nummulitic limestones and shales of the mid-Eocene Kohat Formation. The succession is trun ated by a regional unconformity that records uplift, erosion, and dolomitization of the underlying carbonate rocks. The unconformity is then buried by continental Himalayan molasse.
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