Late Proterozoic stratigraphy of the Swabi area, NWFP, N. Pakistan
Abstract
A succession of weakly metamorphosed unfossiliferous sedimentary rocks has been described in terms of lithostratigraphy from an area north of Swab. The succession unconformably underlies the Cambrian Ambar (Dolomite) Formation (=Abbotabad Formation) and represents the supra-crustal sediments of a probable Late Proterozoic age from the IndianPlate basement. A WNW plunging cylindrical anticline controls the disposition of stratigraphic units. The succession is divisible into two formations; Salkhala and Tanawal. The basal part of the Salkhala Formation, exposed at the west bank of the Tarbela dam, is classified as the Gandaf unit and comprises pelitic and graphitic schists, brown dolomite and white and grey-black marble. The upper part, exposed at the apex of the Kundal anticline, is predominantly argillaceous and contains black mud- and siltstone which grade upward into pebbly green phyllite. The overlying Tanawal Formation is conglomeratic at its base and comprises three units, two of which are quartzitic , while the one , in the middle , is argillaceous. It is suggested that the Tanaual Formation may be a time-equivalent facies change of the Hazara, Manki and Landikotal Slate formations, rather than being younger as suggested in the existing literature. This may explain some of the discrepancies in the existing regional tectonic framework of the Indian plate in northern Pakistan.
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