东海陆架盆地西湖凹陷渐新世花港组大型砂体碎屑锆石U-Pb测年：源区示踪、沉积充填模式及构造意义研究

Large-scale thick sandstone of Oligocene Huagang Formation was revealed by the latest drilling wells in the central reversal structure belt of Xihu Depression, East China Sea Shelf Basin. However, the geologic background, the depositional characteristics and the sedimentary-filling model, etc., of the large sandstone are still unclear. Given the problems above, we plan to trace the provenance of the sandstone by collecting and dating the detrital zircon samples systematically using the U-Pb geochronology as the key method. Together with the studies of syndepostional prototype basin, palaeo structural and geomorphologic frameworks, sedimentary environment analysis, sedimentary facies types and depositional characteristics, the palaeo structural and geomorphologic backgrounds, main controlling factors of the large sandstone will be analyzed. Furthermore, the mutual response relationship between the tectonics and deposition will be clarified，and the deposition-filling model of Xihu Depressionwill be built. Intensive study of the large sandstone will promote the understanding of the tectonics and deposition-filling evolutionary process of Xihu Depression, and provide the theoretical supporting for further petroleum exploration in Xihu depression. Meanwhile, this study is also significant on the constraints of the stress regime, basin dynamic background,and plate dynamic events of this region during the Oligocene period.

西湖凹陷最新钻井揭示凹陷中央反转构造带渐新世花港组普遍发育大型厚层砂体，出乎油气勘探的先期预料。目前，对该套大型砂体的发育背景、沉积特征、沉积充填模式等方面的认识非常薄弱。本课题以对该大型砂体的系统碎屑锆石U-Pb测年及源区示踪研究为主线，通过碎屑锆石U-Pb年龄谱和潜在源区的对比分析，明确花港组大型砂体的物源区。结合对花港组同沉积期的原型盆地性质、盆地古构造－地貌格局、大型砂体的沉积环境、沉积类型、沉积特征等方面的综合研究，分析大型砂体形成的构造-地貌背景和主要控制因素，阐明该时期盆地构造和沉积的相互响应关系，建立大型砂体发育的沉积充填模式。该研究成果将深化对西湖凹陷构造及沉积充填演化过程的认识，为西湖凹陷下一步油气勘探布署提供理论支撑，对渐新世时期该区的盆地应力体制、盆地动力学背景及板块构造响应事件提供约束和重要参考。

针对东海陆架盆地西湖凹陷渐新世花港组发育的大型厚层砂体，通过对花港组原型盆地性质、盆地古构造－地貌格局、大型砂体的源汇体系、沉积环境、沉积类型、沉积特征等方面的综合研究，主要取得以下三个方面的研究成果：（1）明确了西湖凹陷渐新世花港组大型单向挤压不对称坳陷型原型盆地的性质。恢复了盆地及西湖凹陷新生代以来的构造演化过程；（2）恢复了渐新世时期西湖凹陷同沉积古地貌特征，重建了西湖凹陷渐新世花港组沉积期的源汇系统，确定了以北侧长轴物源为主，东西两侧短轴物源为辅的大型轴向物源为主的源汇格局；（3）建立了西湖陷凹陷渐新花港组的层序对比格架，解析了该时期大型轴向辫状河-湖泊三角洲体系的空间发育模式及沉积构成特征。研究成果深化了西湖凹陷渐新世时期的构造特征及沉积充填演化过程的认识，为该时期的盆地应力体制、盆地动力学背景及板块构造响应事件提供约束和重要参考；为西湖凹陷渐新世大型砂体的下一步油气勘探部署提供重要理论支撑。同时对于存在轴向和测向物源供给的陆相坳陷型盆地在砂体的叠置模式、联通性等方面具有重要的借鉴意义。