渤海湾盆地车西洼陷陡坡带古近系沙河街组沙三下段“源-汇”系统

“Source-to-sink”system of the Lower Member 3 of Paleogene Shahejie Formation in steep slope zone of Western Chezhen sub-sag,Bohai Bay Basin

依据渤海湾盆地车镇凹陷车西洼陷陡坡带古近系沙河街组沙三下段岩心、测井以及三维地震资料,对研究区的"源-汇"系统进行了研究。结果表明:(1)车西洼陷沙三下段为一个三级层序,并可进一步划分为低位、湖侵与高位3个体系域,其陡坡带沙三下段发育杂基支撑中砾岩、碎屑支撑中砾岩、杂基支撑细砾岩、碎屑支撑细砾岩、砂质砾岩、含砾砂岩、粗砂岩、中砂岩、细砂岩、递变层理砂岩、滑塌岩等11种重力流成因岩石类型及深湖泥岩,表现为典型的近岸水下扇沉积;不同体系域时期扇体规模整体呈"由大变小,再变大"的演化趋势。(2)车西洼陷陡坡带自西向东识别出6套供源体系,可分为有沟道为主供源体系和滑塌为主供源体系,分别形成沟道供源为主近岸水下扇和滑塌供源为主近岸水下扇类型,其中滑塌供源为主近岸水下扇中的滑塌变形构造更发育、更普遍,但其扇体规模较沟道供源为主近岸水下扇小。(3)进一步的"溯源"分析结果表明,沙三下段沉积时期,研究区物源区母岩以碳酸盐岩为主,其在强烈的构造活动、湿热气候作用下,易于发育石漠化古地貌,剥蚀作用较为强烈,由此形成的频发的季节性重力流进入湖盆,形成该地区的近岸水下扇沉积;不同体系域时期扇体规模的差异主要受物源区气候和植被覆盖的控制。

Based on core observation, well logs and 3-D seismic data, the research in the ＂source- to-sink＂ system of the Lower Member 3 of Paleogene Shahejie Formation in the steep slope zone of Western Chezhen sub-sag of Chezhen sag, Bohai Bay Basin, is conducted. The results show that： （1） The Lower Member 3 of Shahejie Formation is a third-order sequence which can be divided into three system tracts, including the lowstand system tract, transgressive system tract and highstand system tract, and in the steep slope zone, 11 gravity flow rock types and deep-lacustrine mudstone can be identified, and the gravity flow rock types include matrix-supported medium-grained conglomerates, clast-supported medium-grained conglomerates, matrix-supported fine-grained conglomerates, clast-supported fine-grained conglomerates, sandy conglomerate, conglomeratic sandstones, coarse sandstones, medium sandstones, fine sandstones, graded bedding sandstones and slumps, they are all the typical characteristics of the near-shore subaque- ous fan. The evolution tendency of fan scales is from increasing to decreasing, and then increasing again as a whole. （2） Six provenance supplying systems can he identified in the steep slope zone of Western Chezhen sub-sag, and they can be divided into two types, namely, gully-dominated provenance suppl- ying systems and slump-dominated provenance supplying system. The slump structure are much more wide- ly developed in the fans associated with the slump-dominated provenance supplying systems than the fans associated with the gully-dominated provenance supplying systems, in addition, the scale of slump near- shore subaqueous fans is smaller than the fans associated with gully. （3） The further study on the ＂source＂ area＇s characteristics shows that, the parent rock developed in the depositional period of the Lower Member 3 of Shahejie Formation of the source area was mainly the carbonate rocks ; under the action of strong tectonic activities and warm-wet climate, the source area may developed stony desertification palaeogeomorphology and strong erosion, which would cause frequent seasonal gravity to be transported in- to the lacustrine and form the near-shore subaqueous fans ; the scale difference of the fans developed in dif- ferent system tracts were mainly controlled by the climatic variation and vegetation cover of the source area.