渤海湾盆地东营凹陷利津洼陷古近系沙河街组湖相风暴沉积特征及控制因素

Sedimentary characteristics and controlling factors of lacustrine storm deposits of the Paleogene Shahejie Formation in Lijin sag,Dongying Depression,Bohai Bay Basin

渤海湾盆地东营凹陷利津洼陷古近系沙河街组第四上亚段风暴岩沉积构造类型丰富,包括风暴侵蚀形成的冲刷面、渠模、截切面构造,风暴涡流形成的撕裂构造,风暴重力流形成的递变、块状层理,风暴浪形成的丘状交错层理、平行层理、浪成沙纹交错层理及风暴后能量衰减阶段形成的准同生变形构造等。通过岩心观察统计,建立了适合于研究区风暴岩的理想垂向沉积序列,包括10个岩相单元,对应着3个主要的风暴作用阶段:风暴涡流作用阶段、风暴浪作用阶段和风暴作用衰减阶段。结合风暴岩沉积特征及沉积动力学机制,将研究区风暴岩归为4种类型:其中Ⅰ型风暴岩发育于正常浪基面之上,为原地侵蚀型风暴岩,Ⅱ型、Ⅲ型、Ⅳ型风暴岩发育于正常浪基面与风暴浪基面之间。根据以上4种风暴岩沉积特征,探讨了研究区风暴岩形成的主控因素,认为风暴岩的形成主要受风暴作用、物源、古地形以及湖平面变化的影响,并总结出4种类型风暴岩发育的有利条件。

Based on cores observation, abundant and diverse sedimentary structures were found in the upper part of Member 4 of Paleogene Shahejie Formation （Es4） in Lijin sag, Dongying Depression, Bohai Bay Basin. The main sedimentary structures of storm deposits identified included storm-erosional structures （scour surfaces, gutter casts and truncated structures）, storm-eddy structures （tear structures）, stormravity structures （graded bedding and blocky bedding）, storm-wave structures （hummocky cross-bedding, parallel bedding and wave ripples） , and penecontemporaneous deformation structures formed in the storm energy attenuated stage. An ideal vertical sedimentary sequence of storm deposits was constructed in the study area. It consisted ten lithofacies units, corresponding to three storm energy stages： Storm eddy stage, storm wave stage and storm energy attenuated stage. Storm deposits in the study area mainly developed between the fair-weather wave base and storm wave base, except type I （in-situ erosion storm deposits） developed above the fair-weather wave base. According to comprehensive analysis, it was acknowledged that the storm energy, provenance, palaeotopography as well as lake level change were controlling factors of storm deposits, and the favorable developing conditions for these four types of storm deposits were analyzed.