ALVEOLINID BIOSTRATIGRAPHY OF THE KOHAT FORMATION, NORTHERN KOHAT BASIN, HIMALAYAN FOLD AND THRUST BELT, NORTHERN PAKISTAN

The Kohat Formation of late early to early middle Eocene age is an important rock unit in the biostratigraphy of the Northern Pakistan. The formation marks the culmination of the rich marine realm encompassing a large time interval from Mesozoic to Cenozoic in the Upper Indus Basin with some small scale exceptions (deposition of parts of Kuldana Formation) followed by the deposition of thick sequence of Himalayan molasse deposits. The formation is highly rich in shallow benthic fauna including foraminifera, brachiopods, mollusks, echinoderms and algae. The formation has certain horizons, especially in the middle part, which seems to be almost entirely composed of shallow benthic larger foraminifera and can be termed as “Coquina”.

In present study, two sections of the formation from the northern part of the Kohat Basin, a sub-unit of the Upper Indus Basin, were selected and sampled systematically to identify and define the Alveolinid biostratigraphy. These sections are Shekhan Nala Section and the Hangu Section, located in the north eastern and north western part of the basin respectively. Sixty four (64) samples were collected from Shekhan Nala Section and ninety two (92) from the Hangu section. Out of these samples a total number of 200 thin sections were prepared for detailed biostratigraphic studies in the framework of Shallow Benthic Biozonation of Sierra Kiel et. al. (SB zonation). These thin sections have yielded some moderate to well preserved species of the Genus Alveolina including Alveolina elliptica, A. stercusmuris, A. violae, A.cosigena and A. kohatensis sp.nov. All foraminifers in general and the genus Alveolina in particular, is quite susceptible to the variations in climatic and energy conditions. The documented alveolinid assemblage indicates an age of SBZ 12 to 14 (Lutetian to Bartonian) of the Kohat Formation. It further shows that the environment of deposition of the formation might have been open marine, shallow shelf with moderate energy conditions.