Lithofacies paleogeography of Cambrian sequences in the Tarim Basin

Through sedimentary facies observations on coring and outcrop samples,seismic sequence interpretations and seismic facies analyses,the present paper,integrated regional geological data of ophiolite-melange belts with those of plate tectonic evolution,firstly compiled 4 lithofacies paleogeography maps of Cambrian sequences in the Tarim Basin under the third sequences stratigraphic framework.We discovered 3 Cambrian isolated carbonate platforms(the western Tarim platform,western Lop Nor platform and Kuruktag platform) and some inter-platform deepwater depositional regions within the Tarim plate and suggested that Cambrian deepwater basinal-facies depositional regions distributed in southwestern Tarim might be chief source rocks of marine oil-gas reservoirs represented by the Hetianhe gas field,this point of view is very important to marine oil gas exploration in the Tarim Basin,especially in the SW Tarim area.The continental riftogenesis of the northern margin of the Tarim plate occurred initially in Early Sinian and Early Cambrian,and the Sinian-Cambrian pull-apart structural condition controlled the formation of several isolated carbonate platforms and inter-platform deepwater depositional areas within the Tarim plate.From Early Cambrian to Late Cambrian,these isolated carbonate platforms represented by the western Tarim platform expanded universally due to progradation and aggradation though the paleogeographic framework as a whole did not change much within the Tarim plate,meanwhile,changes occurred in types and superimposition patterns of platform margins in different time-space domains,namely ramp to feebly rimmed platform margins were dominant in Early Cambrian,while feebly rimmed to rimmed platform margins became dominant in Middle-Late Cambrian.