Grain size analysis of the Oligocene Nari Formation sandstone in the Laki Range, southern Indus Basin, Pakistan: Implications for depositional setting

Abstract

This study investigates the depositional setting of the Oligocene sedimentary rocks of the southern Indus Basin according to grain size analysis of sandstones. Twelve sandstone samples were collected and studied from the Oligocene Nari Formation that distributes along the N‐S‐trending Laki Range in the Kirthar Province of Pakistan. The analysis results specify very fine to fine‐grained sediments and unimodal nature of grain size distribution. The sorting values of the studied sandstones vary from 0.66φ to 0.90φ, which indicates that the sediments are moderately to moderately well‐sorted. The skewness values of investigated samples vary from −0.04φ to 0.25φ, which indicate nearly symmetrical to fine‐skewed nature. The kurtosis of the studied samples varies between 0.73φ and 1.44φ which shows platykurtic, mesokurtic, and leptokurtic nature. Linear discriminant function and interpretation diagrams of sediments demonstrate that the Oligocene Nari Formation sediments from Lal Bagh section were being transported as bedload and suspended load with a bimodal to unimodal depositional mode that were deposited in a fluvial to shallow marine deltaic environment of a passive margin.