EOCENE PLANKTIC FORAMINIFERAL BIOSTRATIGRAPHY OF THE SULAIMAN RANGE, INDUS BASIN, PAKISTAN

Abstract

Paleocene and Eocene marine sequences distributed in Rakhi Nala and Zinda Pir Anticline areas of the eastern part of the Sulaiman Range in Pakistan record the geological history and tectonic events during the last stage of collision between the Indian and Eurasian Plates and closure of the Tethyan Ocean. The Eocene sequences consist of siltstone and mudstone with some limestone intercalations, and are divided into the Shaheed Ghat, Baska and Kirthar Formations in ascending order. We studied the Eocene biostratigraphy of planktic foraminifers in this region to reveal the geological ages of the Eocene strata based on (international) correlation with standard tropical/subtropical zones. The planktic foraminiferal assemblages are composed of 78 species of 19 different genera, including many zonal markers of tropical to subtropical regions. We identified 8 biostratigraphic zones, Zone P7, Acarinina pentacamerata Partial Range Zone, Planorotalites palmerae Total Range Zone, A. soldadoensis Assemblage Zone, Zone P12, Zone P13, Orbulinoides beckmanni-Truncorotaloides rohri Interval Zone, and Truncorotaloides rohri-Turborotalia cerroazulensis cunialensis Interval Zone in ascending order. These zones correspond to Zones P7 to P15 of tropical/subtropical schemes. However, the upper part of Zone P10 to Zone P11 is not recognized because of an interval that is barren of planktic foraminifers in the Baska Formation. The geological age of the Shaheed Ghat Formation is assigned to the Early Eocene through early Middle Eocene (Zones P7 to P10, 52.3~45.8 Ma). The Baska Formation is apparently equivalent to Zone P10 (early Middle Eocene), although its direct age is uncertain as it is barren of planktic foraminifers. The fossiliferous micritic limestone forming the lowermost part of the Kirthar Formation yielded recrystallized planktic foraminifers and calcareous nannoplankton indicating an early Middle Eocene age spanning calcareous nannoplankton Zones NP14 to NP15 (48.5~43.4 Ma), while the upper part of the Kirthar Formation ranges in age from middle Middle Eocene to early Late Eocene (Zones P12 to P15, 43.6~35.2 Ma). Hence the strata of the Kirthar Formation spans in age from early Middle Eocene through early Late Eocene based on recognition of the planktic foraminiferal Zones P10 to P15 (49~35.2 Ma).