祁连山北缘旱峡早白垩世下沟组-中沟组沉积相研究

祁连山北缘旱峡地区发育完整的下白垩统下沟组-中沟组沉积序列；以陆源碎屑岩为主，发育砾岩、砂岩、钙质粉砂岩和页岩等；其中砾石分选差、磨圆一般、成分以灰白色砂岩为主，砂岩成分、结构成熟度中等-差。岩石组合、沉积序列和综合沉积特征研究表明，下沟组和中沟组主要由湖泊、扇三角洲、河流等3种类型沉积相、亚相与微相类型组成，发育了一系列重力流成因的沉积类型；湖泊沉积主要发育在下沟组底部和中沟组，扇三角洲沉积分布在下沟组中-上部，中沟组发育河流沉积。研究区早白垩世中期古流向以EN向为主，早白垩世晚期以W向为主，表明沉积沉降中心也由早期的旱峡西移至研究区西南侧。在综合分析的基础上，建立了研究区下白垩统下沟组-中沟组沉积相模式。

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

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. 