Precambrian lithostratigraphic units of Pakistan

Precambrian lithostratigraphic units of Pakistan, recorded in the first addition of the Stratigraphy of Pakistan (Shah, 1977), were only half a dozen in numbers. Since then researchers from different organizations working in different parts of the country have come up with more than two dozens of them. In some cases single formation originally known and described with wide distribution and facies variation has, hitherto been split up into different groups and formations. In most of these cases, it is justified but in a few cases unwarranted, multiple splitting of a previously named one unit into number of formations with the addition of new names has also been seen. They may also have some merit. However, at the time of the formalization of the rock units, many of these extra names are likely to be synonymised.
                A large number of radiometric ages dating data are now available for many of the igneous and metamorphic rocks of Pakistan, which have now placed some of them as old as Early Proterozoic. These Precambrian rocks provided basement for the lower Palaeozoic sediments and in certain cases, they served as the source of terrigenous elastics, a provenance for the younger rocks of the adjoining areas.
              In the southern half of Pakistan, the Precambrian assemblage within the Indus Basin constitutes volcano-plutonic rocks of Late Proterozoic age, which were earlier considered Indian Shield elements, and with the belief that the orogenic activities of this shield had ended during Precambrian age, thereupon, assuming the character of a stable mass. Detailed work on these rocks shows that the concept of stable Indian Shield is challengeable; details arc given in the succeeding topic of Indian Shield elements.
             The southern most exposures of this so-called shield cropout near Nagar Parkar, Sind, where granite arid basic igneous rocks represent the assemblage. The other exposures of the Proterozoic exposures are present in the isolated hills extending from Shahkot to Sargodha, Punjab. These rock units are composed
of meta sedimentary complex with acid and basic igneous rocks.
             Lastly, in the Indus Basin, the rocks close to the Precambrian-Cambrian boundary are exposed in the Salt Range,Punjab.They are composed mainly of marl, salt, dolomite and gypsum deposits.They occupy probably the sloping part of the Indian Platform and overly the metamorphic rocks of the Late Proterozoic age
             In the Northern areas beginning with the Axial Belt and Himalayan Tectono stratigraphic Basin, the
assemblage of Precambrian rocks occupies a large area in the Hazara Folded Belt. Here, they are composed mostly of sedimentary and metamorphic units and frequently intruded by acidic and basic igneous rocks. It is here that the largest expanse of Precambrian rocks has been recorded in Pakistan.
           The Hazara Formation occupies considerable part of the eastern Hazara area and represents lithologies of slate, phyllite and shale. In fact, in the northern part of the Hazara Folded Belt, the rocks are mostly comprised of phyllitc, quartzite with minor amount of limestone. Westwards, in the
Attock-Cherat Range, similar exposures have been recognized as Manki and Dakhner Formations. Earlier the later rocks were?collectively known as Attack slate.The age was highly problem, only  recently, the question of age has been settled and they are now considered mostly Precambrian similar to the rocks of Hazara area (Hussain et al., 1990).

           Further north in the upper Hazara, Salkhala and Tanawal Formations of Precambrian age had been recorded by earlier workers. These formations consist of schist, gneiss and marble with minor amount of carbonaceous material. A large part of the exposures of these formations have now been thoroughly revised and studied in detail, whereupon host of Precambrian basement rocks are now described to be present in the form of meta sedimentary, igneous and metamorphic complexes.