Sedimentary Facies of the Lower Cretaceous Xiagou and Zhonggou Formation in Hanxia, Northern Qilian Mountain, Gansu Province, Northwest China

Key words: 
• Northen Qilian Mountain /
• the Hanxia area /
• the Lower Cretaceous /
• XiagouZhonggou Formation /
• Sedimentary facies /

Abstract: Depositional succession of the Lower Cretaceous XiagouZhonggou Formations is widely distributed in Hanxia of the northern Qilian Mountain, and mainly composed of conglomerates, sandstones, calcareous siltstone, mudstone or shale. Gravels within conglomerates are poorly sorted and subrounded. Sandstones are characterized of poor or medium compositional maturities. Depositional succession lithological associations and facies indicate that both the Xiagou and Zhonggou Formations consist of lacustrine, fan delta or fluvial facies as well as gravity flow deposits. Lacustrine is mainly in the bottom of the Xiagou Formation and the Zhonggou Formation. Fan delta facies is dominantly in the middle and upper parts of the Xiagou Formation. Fluvial facies is common in the Zhonggou Formation. Correlation and synthesized analysis of stratigraphy, depositional facies and lithological associations in Hanxia and its adjacent areas(Changma basin and the western Jiuquan basin) illustrate that the Xiagou and Zhonggou Formations in Changma to the southwest of Hanxia, are interpreted as deposits of shallow lacustrine and meandering river facies, and then Hongliuxia to the north of Hanxia was shallow lacustrine environment, Xinminpu(to the northeast of Hanxia), however, is mainly    and meandering river facies. Based on the  huge stratigraphic thickness in Hanxia than the mentioned three areas else and deepening shallow lacustrine depositional subfacies as well, was regarded as a depocenter of the Jiuxi basin of midlate Early Cretaceous. Paleocurrent reconstruction show northeastwards in the Xiagou Formation and westward in the Zhonggou Formation. A dispositional model of the Lower Cretaceous Xiagou and Zhonggou Formations is synthesized finally. 