断陷湖盆重力流水道地震沉积学研究——以歧南地区沙一段为例

本文以歧口凹陷歧南地区沙一段为例，分析了断陷湖盆以沟道型砂质碎屑流为主体的重力流沉积的结构与构造、测井响应、地震相模式以及主水道的平面分布格局及纵向演化。研究发现：①以歧南地区沙一段为代表的陆相断陷湖盆重力流沉积至少包括砂质碎屑流、滑塌、浊流等3种成因沉积类型，以沟道化砂质碎屑流为主体，悬浮组分含量高。②断陷湖盆重力流水道横断面的地震相模式有U型或V型、碟片性、蠕虫型、纺锤型（透镜状）等4种类型，很可能依次与流体能量由强而弱的变化相对应。③构造活跃期湖盆底形较陡，沿洼槽发育的重力流水道窄而顺直，对下伏地层刻蚀显著；构造相对平静期湖盆底形平坦，水道宽度及弯曲度增大，对下伏地层侵蚀相对较弱。

Seismic sedimentology research on fault-depressed lacustrine basin gravity flow channels of Oligocene Es1 in Qi’nan area,Qikou Sag

Based on the first Member of Shahejie Formation (Es₁) in Qi'nan area, Qikou Sag, we conducted seismic sedimentology analysis, including sedimentary textures, well logging characteristics, seismic facies models, and channel distribution of a faulted-lacustrine basin gravity flow depositional system dominated by channel sandy debris flow. The following observations have been obtained: 1There are at least three types of gravity-flow deposits developed in the Oligocene fault-depressed lacustrine basin: sandy debris flow, slump, and turbidite, in which the sandy debris flow with considerable suspension content is the main depositional type. 2Seismic facies models of fault-depressed lacustrine basin gravity-flow channels can be divided into U-shaped (or V-shaped), saucer-like, worm-like, and spindle-shaped (lenticular-like) facies, which are probably related to the changes from strong fluid energy to weak fluid energy. 3When tectonic movement was active, the lacustrine basin was steep, and gravity-flow channels developed along valleys were narrow and straight with obvious erosion to underlain strata; when the tectonic movement was inactive, the lacustrine basin was flat, and channels were much wider with less erosion to underlain strata.