东营凹陷北带古冲沟古近系多物源沉积模式

Multi-provenance depositional model of paleo gully in north steep slope of Dongying depression of upper Es4 in Paleogene

利用地震反射结构、碎屑组分以及聚类分析等方法,提出东营凹陷北部陡坡带东部Y920古冲沟沙河街组沙四上亚段多物源叠加模式。研究结果表明:沙四上亚段沉积时期,Y920冲沟呈西陡东缓的不对称箕状构造形态。地震相呈东西分带的特点,冲沟西部发育楔形反射、东部发育前积反射、中部发育透镜状反射。冲沟内砂岩充填物的碎屑矿物组成在平面上具有明显的差异性,冲沟西部砂岩的石英含量低、岩屑含量高,岩屑以火成岩岩屑为主;冲沟东部,砂岩的长石和岩屑含量均较高,岩屑以变质岩岩屑为主;中部长石和石英含量较高,岩屑含量较低,含有较多的灰岩岩屑。Y920古冲沟存在3个方向的物源,分别为自北向南、沿冲沟长轴方向的北部物源以及来自冲沟西部和东部的短轴、侧向物源。冲沟西部发育近岸水下扇沉积,东部扇体以扇三角洲为主。

Based on seismic reflections, detrital composition analysis and cluster analysis, a multi-provenance depositional model of the Upper Fourth Member of the Shahejie Formation was proposed about the paleo-valley sedimentation controlled by well Y920 in the east of the northern abrupt slope belt in Dongying depression. The result shows that the paleogeomorphology of the Y920 gully develops asymmetrically as being abrupt in the west yet gentle in the east during this period. The seismic facies can be divided into two types： the west of the gully is dominated by the wedge-shape reflections, while the east is dominated by progradational reflections. And these two types are separated by the lens-shape reflections in the middle. The detrital composition planar distribution of the sand filling of the gully varies greatly： the west has a low content of quartz and a high content of rock fragment mainly in the type of volcanic; while the east has a relatively high abundance in both the feldspar and the rock fragment mainly in the type of metamorphic detritus; and in the central part the proportions of feldspar and quartz are overwhelming yet the content of detritus mainly in the type of limestone is low. There are three provenances for the Y920 gully including the northern one which provides sediments southward along the long axis and the western and the eastern ones on either side of the gully along the short axis. Thus, the nearshore subaqueous fan and fan delta mainly develop on the west and the east sides respectively .