PETROGRPAHY, GEOCHEMISTRY AND PROVENANCE OF LATE PROTEROZOIC SALT RANGE FORMATION OF THE SALT RANGE PAKISTAN

The Neoproterozoic Salt Range Formation (SRF) of Salt Range Pakistan has been studied for the purpose of understanding its geochemistry, petrography, sedimentology, depositional environment, and the provenance. The SRF is composed of ferruginous and gypsiferrous claystone/marl, thick salt bodies, dolomite, shale, siltstone, oil-shale and euhedral authigenic quartz termed as Khewrites. In this paper we present the preliminary petrographic and geochemical data of the sandstone part of the SRF. The sandstone of the SRF is composed of subangular to subrounded, medium- to fine-grained, poory sorted detrital grains with some well rounded grains. Quartz is the dominant framework mineral followed by feldspar and lithic fragments. Both plagioclase and K-feldspar are present. The cement is mostly calcite with minor silica whereas matrix is mostly clay. Among cements calcite makes 5-17%, silica 3-5% and traces of iron oxide. Some samples contain upto 15% clay matrix. Recalculated point count data of the framework grains, when plotted in discrimination diagrams, indicate that sandstone is quartz arenites to subarkose. The detritus of SRF were originated from craton interior and deposited in a closed epicontinental basin that was intermittently connected to open marine continental margin environment.

The Chemical Index of Alteration (CIA) and Plagioclase Index of Alteration (PIA) values suggest moderate and steady state weathering in the source areas during most part of the Late Neoproterozoic. Moreover, higher CIA and PIA values, low K₂O/Al₂O₃ ratio, and index of compositional variability reflect the multiple sedimentary recycling. Major and trace element distribution and multi-element plots suggest that the sediments of SRF were derived mainly from a continental margin with minor contribution from old continental crust.