Sedimentary Characteristics and Tectonic Setting of the Lower Cretaceous Strata in Jiuxi Basin, Gansu

Jiuquan Basin,located on the western part of the northern endge of Qilian orogenic belt,is a petroliferous basin on western end of the Corridor basin group.It is a subbasin of Jiuquan Basin.The exploration of several medium-to highcapacity industrial oil wells in the Lower Cretaceous strata indicates Jiuxi Basin the favourable geological conditions for hydrocarbon accumulation.People have never come to an agreement to the origin of the Jiuquan Basin.So,we studied the sedimentary facies of the Early Cretaceous strata at Hongliuxia Section of Jiuxi Basin and believe that sedimentary setting experienced four evolution stages are deep lake subfacies,pro fan-delta subfacies,fan-delta front subfacies,and fan-delta plain subfacies.Therefore the Jiuxi Basin can be divided into three evolutionary stage of embryonic rift,spread rift and basin shrinkage,having a bilayer structure of superposed sag and depression.By analyzing the exploration data and regional correlation,we propose that that tectonic setting of Cretaceous strata in Jiuxi Basin is similar to that of Mesozoic land facies basin in east China.Through comparing to the origin of early Cretaceous extensional rift basin group in east China,we think that the formation and evolution of the basin is affected by the subduction of Pacific Plate and the southward drift of Siberia Plate.