LATREALAND VERTICAL FACIES VARIATION IN THE JURASSIC DATTA FORMATION IN KASANWALA NALAAND KAOWAALI SECTION, WESTERN SALT RANGE, PAKISTAN.

Abstract

A mixture of lithologies consisting of basal conglomerates, sandstones, siltstones, shale/marl and dolostones represents the Lower Jurassic Datta Formation in the two studied sections. Mostly medium to thick planar beds occur. Sedimentary structures present are cross bedding, straight crested and bifurcating ripples and rarely climbing ripple lamination. Other diagnostic features are the presence of concretions of variable size (maximum size observed is 45cm) and rusty brown coloured tubular structures that may be up to 7 cm long and 2 cm wide. Overall, the formation represents a fining upward (conglomerate-sandstone siltstone-shale-carbonate) sequence. Oligomict conglomerates comprising of dominantly fractured, mostly monocrystalline quartz with unit extinction and showing cross bedding is considered to have formed in a fluvial channel as a channel bar deposit. The overlying thick cross bedded sandstone (QUaI1Z arenite) with monocrystalline quartz again predominating is also interpreted to be a part of the chaJU1el bar deposit. Other mixed siliciclastics comprising of siltstones and shales depict the associated subenvironments of channel fill, crevasse splays and/or delta top envirolU11ents. More work is needed to understand the dolomitization process. Repetition of the envirOlU11ents in the studied sections suggests channel migration. Kasanwala section in the east mostly represents a channel bar sequence, where as the Kaowaali section in the west mostly represents the delta top envirolU11ents thereby indicating flow of river from east to west.