Silurian-Devonian Reef Complex near Nowshera, West Pakistan

Abstract

The first Paleozoic reef belt on the Indo-Pakistan subcontinent has recently been recognized near the town of Nowshera (lat 34°00′ N., long 72°00′ E.) in northern West Pakistan. It consists of nine separate hills aligned in a 15-mile-long, east-west band rising out of the Peshawar alluvial plain. Each hill is composed of one or more reef cores whose thicknesses range from less than 100 feet to more than 700 feet. The reef cores are separated by relatively unfossiliferous carbonate rocks thinner than the reefs. The reef belt contains a fauna entirely new to Pakistan that has been dated as Early Devonian to to Late Silurian (Ludlovian to Gedinnian). The reef carbonates are the first sediments of possible Silurian age found anywhere in the country and the southernmost Devonian deposits in West Pakistan. Individual reef cores consist of faunal zones or layers that indicate a gradual growth of the reef mass from relatively quiet water upward into rough water. The presence of these reefs and correlative fossiliferous carbonate sediments in the Peshawar area suggests that in Silurian and Devonian times much of northern West Pakistan was covered by warm, shallow seas bordered by reefs or containing reef platforms. The association of these Paleozoic reefs with extensive deposits of fetid black limestones and porous dolomites may indicate economic potential for the accumulation of oil.