MODAL COMPOSITION AND PROVENANCE OF SHAIGALU SANDSTONES, PISHIN-KATAWAZ BASIN, NORTHERN BALOCHISTAN, PAKISTAN

The Oligocene Shaigalu member of the Khojak formation (Oligocene – Miocene), exposed in the Pishin basin, is dominated by sandstone with minor interbedded shale. Detailed petrographic analysis of the sandstones was carried out in order to determine mineral composition and provenance. Petrographic studies based on modal analysis of detrital modes revealed that the sandstones of the Shaigalu member of the Khojak formation in the study area are mostly composed of lithic fragments, quartz and minor proportion of feldspar. Among the main detrital modes, the quartz constitutes 5-50 %, feldspar 1-2 % and lithic fragments 23-75 %. These sandstones can be classified as lithic arenites with only one sample from Nisai section (Eocene) as quartz arenite having 94 % quartz. These sandstones are mostly fine grained, subrounded and moderately to well sorted, however a few samples are medium to coarse grained. These sandstones are compositionally immature and can be classified as lithic arenite. The QFL ternary plots show that the sandstones of the Shaigalu member of the Khojak formation were derived from recycled orogen, which probably derived from the early Himalaya highlands and Sulaiman thrust fold belt. Download Full Paper