ABSTRACT: The Paleogene larger benthic foraminifera (LBF) of the Kohat and Potwar basins, Pakistan are very useful for dating shallow marine sediments and documenting cessation of marine sedimentation that provides constraint on the initial age of India-Asia collision. We record important Paleogene LBF species in multiple sections of the two basins. We performed biometric analysis of nummulitid species useful for taxonomic purposes. We recognize six Larger Benthic Foraminiferal Zones (BFZ Zones 1-6) in the Kohat Basin. The first three (BFZ Zones 1-3) also occur in the Potwar Basin and the adjoining Trans Indus Ranges (TIR). The correlation of BFZ 1-6 Zones with previous local and regional LBF biostratigraphic schemes in the Eastern Tethys (Pakistan-India) and Western Tethys (European Basins) resulted in recognition of useful index taxa for developing a regional stratigraphic framework during Paleogene. The last occurrence (LO) of Miscellanea miscella in the BFZ 1 Zone, and the first occurrence (FO) of Assilina dandotica in the BFZ 2 Zone mark the late Paleocene (Late Thenetian) - early Eocene (Lower Illerdian1) boundary. The co-occurrence of A. pustulosa, Al. vredenburgi, Al. globula and Al. pasticillata in the BFZ 2 Zone characterizes lower Eocene (Lower IlIerdian 1-Middle Illerdian 1) sediments. The synchronous FO of N. atacicus and N. globulus is an excellent global biostratigraphic marker of the early Eocene (Middle Illerdian 1- Middle Illerdian 2) boundary and the FO of O. complanatus is a useful biostratigraphic marker of Lower Cuisian 2-Middle Cuisian boundary in the BFZ 3 Zone. Mammalian bones found at the base of Koldana Formation in the Kohat Basin represent early Eocene (Upper Cuisian), which is in agreement with the LBF biostratigraphy of the underlying Middle Cuisian strata. The FO of A. exponens in the BFZ 4 Zone record middle Eocene (Middle Lutetian 1) sediments while the FO of N. beaumonti in the BFZ 5 Zone marks the middle Lutetian 1-middle Lutetian 2 boundary. The FO of A. cancellata in the BFZ 6 Zone marks Middle Lutetian 2-Upper Lutetian boundary. The implications of our LBF study are that cessation of marine sedimentation in both Pakistani basins occurred in early Eocene (Middle Cuisian ËœBFZ 3) around 50-49.5 Ma. Notably, marine conditions returned in the Kohat Basin in middle Eocene (Middle Lutetian 1 Ëœ BFZ 4) due to an eustatic sea level rise. The final cessation of marine sedimentation, causing closure of the Eastern Tethys seaway in the Kohat Basin occurred in middle Eocene (Upper Lutetian ËœBFZ 6) around 41.2 Ma, probably as a result of India-Asia post-collisional stresses.
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