SMALLER FORAMINIFERAL ASSEMBLAGE OF THE KHIRTHAR FORMATION OF SUKKUR AND KOTDIJI AREA, SINDH

Abstract

Khirthar Limestone, the most prominent ridge-forming rock unit that has derived its name from the north-south stretching range of hills, the Khirthar Ranges, that attracted Blanford (1876) to name this well developed rock unit as "Khirthar Limestone", later formalized to Khirthar Formation. It extends towards the north east to Sulaiman Range and South Waziristan. The unit is about 1270m thick in the type section, the Gaj river section, but tapers to 15-30m towards south. However, inspite of its wide-spread occurrence no effort has been made at age-dating this unit and it is vaguely placed between 'Middle to Upper Eocene to Lower Oligocene'. As such the present study was initiated and to start with, detailed study of the smaller foraminifera of the Khirthar rocks exposed in Sukkur and Kotdiji areas was carried out with a view to determine the character of the faunal assemblage and to find out whether these rocks can be age-dated and correlated more accurately. The investigation enabled to identify 43 species, belonging to 15 genera. These include 15 Planktonic forms. Among the species identified 17 benthonic species and 7 planktonic species have been earlier reported from various Eocene rocks of Pakistan. The study reveals that foraminifera in rocks of Sukkur and Kotdiji areas probably represent reworked fauna derived intra-basinally. They include forms typical to both Eocene and Basal Oligocene. Further, the age of this outcrop of Khirthar Formation extends upto Lowest Oligocene.