Classification of planktonic and larger Benthic foraminifers and biozonation of Kohat formation, southern Kohat plateau, District Karak, Khyber Pakhtunkhwa, Pakistan (T-1445) (MFN 7019)

Abstract

The Eocene Kohat Formation is well exposed in the Karaat hills. At this locality the lower part is composed of light brown to khaki color shale. The limestone is contained in the upper and middle part of the Formation. The limestone is welldeveloped. medium to thin bedded and compact and medium to light grey in color. The middle part of the Formation is richly fossiliferous. These beds can be regarded as bio-lithite due to huge abundance of the micro-fossils. While, the upper part of the formation consists of well-bedded to slightly massive bedded cream-colored limestone. The upper part is also fossiliferous but the fossils abundance and their size decreases. The limestone unit of the formation is fractured and shattered at places which makes it devoid of fossils. The Kohat formation in the study area makes a conformable contact with underlying Kuldana Formation and unconformable contact with the overlying Kamlial Formation. Kohat Formation is almost entirely composed of larger benthic foraminifera belonging to the genera Nummulites, Assilina and Alveolina. Some excellent age diagnostic larger foraminiferal species of Nummulitids, Assilinids and Alveolinids have been found namely Nummulites mamillatus, N. atacicus, N.globulus, N. subirregularis, Assilina exponens, A. granulosa, Alveolina elliptica and Alveolina stercusmuris. The formation is divided into two biozones namely Nummulites globolus/Nummulites atacicus zone and Alveolinid zone. Using modern shallow benthic biozones (SB zones) the chronostratigraphy of the Kohat Formation is established based on Alveolinids. The presence of Alveolina elliptica and Alveolina stercusmeris from the middle and top parts of the Formation show the range of Kohat Formation from Alveolina stipes zone to Alveolina prorrecta zone. The Kohat Formation deposited in the shallow shelf environment as depicted by the fossil assemblage.