Lithofacies, Sand-Bodies Geometry and Depositional Setting of the Datta Formation in Surghar Range, North Pakistan

Abstract

Thick Mesozoic sedimentary rocks are exposed over a wide area in the Lower andUpper Indus Basin of Pakistan, particularly along the western margin of theIndian Plate. The Mesozoic sequence is generally comprised of clastic facies inthe lower part, carbonate facies dominate in the upper part. In the SurgharRange the Datta Formation represents the lower part of the early Jurassicsequence. The formation is comprised dominantly of clastic facies withcarbonate interbeds at places. The Datta Formation of early Jurassic wasmeasured and described in the Chichali and Pannu gorge, Surghar Range. Thetotal thickness of Datta sediments at Chichali section is 161m while thicknessof the Pannu section is 225m. Sections were measured for sedimentologicalstudies and sand bodies were classified accordingly. On the basis oflithological variation and sedimentary structures eight lithofacies have beenrecognized. These lithofacies are; LF 8: Clay lithofacies, LF 7: Cross beddedsandstone lithofacies, LF 6: Siltstone lithofacies, LF 5: Interbedded limestoneand shale lithofacies, LF 4: Sandstone with intercalations of clay lithofacies, LF 3: Carbonaceous shale lithofacies, LF 2: Channelized sandstone lithofacies, LF 1: Interbedded sandstone and shale lithofacies. Three kinds of sand bodies were identified, these are mostly multistoreychannels but some simple ribbons as well as sheets are also present. Fossilsidentified are gastropods and pelecypodes. After collecting and interpreting the data acquired from the measuredsections and sandstone bodies' geometry analysis, it is interpreted that theDatta Formation was deposited along the delta plain and delta front setting bya fluvial-wave dominated delta. Continental, transitional to oceanic conditionsprevailed at the time of deposition of the Datta Formation and all the faciesshow prograding deltaic setting. Cross beds interpretation indicates east towest flowing channels.