DefinePK

Abstract

The Miocene to Pliocene Hinglaj Formation dominantly composed of sandstone and shale is widely exposed in the southern Balochistan stretching from Nal to Bela area and extends upto southwest Ormara, Mekran. The present study aims at to document the depositional environment of the Hinglaj Formation near Nal.
Twelve facies in the 1443 m thick Hinglaj Formation of Nal section have been recognised. The detailed facies analyses indicate a foreshore beach environment. The facies of shale, shale with interbedded sandstone, arenaceous limestone and hummocky cross-stratified sandstone were deposited on the lower shoreface. Bioturbated sandstone and shale clasted sandstone were deposited on lower shoreface to transition zone, whereas the deposition of low angle cross-bedded sandstone, trough cross-bedded sandstone and turriform gastropod shell lag facies are interpreted to have been deposited in upper to middle shoreface environment. The herringbone cross-stratified sandstone with oyester shell fragments represents deposition in swash zone. The facies distribution of these silisiclastic rocks reflects the complex interaction of fluvial and marine processes. 
Seven zones of transgressive and regressive complexes have been identified. The transgressive complexes involve the shoreface retreat of the topographically higher parts of the beach during storms and continuous reworking of the sediment input by wave action during fair weather conditions. The shoreface retreat storm events produced shell lag beds of turriform gastropod and oyster which characterize the initial transgression and secondary transgression respectively. On the other hand the regressive complexes originated during the period of prolonged calm and quiescent intervals accompanied with lower reworking, reduced wave energy and sporadic subaerial exposures.