The Geology of the Attock-Cherate Range, West Pakistan

Abstract

The Attock-Cherat Range is exposed in an area of about 50 square miles in Attock district and 360 square miles in the Peshawar district, on both sides of the Indus River. Around Attock the relief is low; the elevations: range from 1300 to 2079 feet which on the other side of the Indus culminate to 4546 and 5033 feet .at Cherat .and Jalala Sar respectively, which are the commanding heights in the Peshawar Plain. Between. Attock and Mir Kalan village, the general trend of the range is east-west which coincides with the strike of the rocks. Beyond this point, the range swings to the south west and ultimately merges into Nizampur-Kohat mountains in Darra Adam Khel tribal territory. In the Attock plain, the slats are lost beneath the alluvium beyond Kamra hillock till they crop out again in southern Hazara.  In the west, the last slate outcrop mapped is exposed near Dag village, beyond which the slates are covered by thick alluvium till they crop cut in the Khyber mountains.

Two types of lithological elements, with a tectonic contact, are exposed in the Attock-Cherat Range. On comprises the Palaeozoic metasediments (phyllite, phyllite slate, slate and crys1alline limestone) forming the northern face of the range.

They are correlated with the rocks of Khyber in the west, Hazara in the east and Swabi­Lower Swat in the north. The dominantly sedimentary rocks belo11ging to the Mesozoic Tertiary eras, developed along the southern face of the Attock-Cherat Range, may be correlated with the rocks of Samana Range, Kala Chitta hill, Salt Range and Hazara.

The pelites of the Attock-Cherat Range are divided into two-part s on the basis of fossil evidences.  The older, Mallki Slate, is of Lower Silurian age and the younger, Attock Shale, has been placed in the middle Jurrasic-Cretaceous. Altogether, thirteen mappable lithological have been distinguished in the Attock cherat Ranges. Of these, four have been placed in Palaeozoic, four in the Messozoic and five in the Tertiary. The Shahkotbala Formation is the oldest lithological exposed in the area and is (?) Upper Ordivician to Lower Silurian in age. No Precambrian rocks have been recorded in the Attock-Cherat Range.

Two major thrust faults, running along the northern and southern fronts of the range, traverse the area in the east-west direction. The northern thrust is the results of overthrusting of the southern flank of an anticlinal fold. Another anticlinal fold strikes the Attock-Cherat Range on the south in the Nizampur valley. The northern limb of this fold is intact. The southern limb is eroded away and is buried under the alluvium. The Attock shales are folded into asymmetrical parallel isoclinal folds with their axes dipping towards the north. The faulting pattern in the Attock-Cherat Range yielded imbricate type structures which are conspicuously observed all over the area.