Sedimentary characteristics and seismic geomorphology of gravity-flow channels in a rift basin: Oligocene Shahejie Formation,Qinan Slope,Huanghua Depression of Bohai Bay Basin,China     

《Marine and Petroleum Geology》2016

Deep-water gravity-flow sandstones are important hydrocarbon exploration and production targets in the Bohai Bay Basin, a Paleogene intra-continental rift basin in eastern China. In this paper, the seismic-sedimentology techniques are used to characterize, in plan view, the temporal and spatial evolution of a gravity-flow-channel complex of the Paleogene Shahejie Formation (Es) on the Qinan faulted-monoslope (Qinan Slope), Bohai Bay Basin. The results show that two or three gravity-flow channels, 9–12 km long and 0.5–2 km wide, were successively developed in later Es (Es1z–Es1s). The channels initially experienced westward migration and then shifted eastward. The corresponding wireline logs of the channel-fill sequences mainly present blocky-shaped or bell-like configurations, whereas their seismic profile features are characterized by strong amplitude reflections, such as U-shaped, plate-like, spindle-shaped and lenticular configurations.The syndepositional activity of three normal faults, i.e., the Nandagang Fault to the northwest, the Zhangbei Fault to the northeast and the Zhaobei Fault to the east led to gradient changes of the Qinan Slope, which have controlled the plan morphology (width, curvature, and bifurcation) of the gravity-flow channels. In the medium-late period of Es1z, triggered by intensive faulting on the three faults, the gradient of the Qinan Slope was steepened abruptly, resulting in an increase of flow velocity and erosion amplitude to underlying deposits. As a result, channels exhibiting narrow and straight configurations in plan view were formed. During the stage of early Es1z and Es1s, tectonic activity intensity was relatively low and the gradient of the Qinan Slope was gentle, so channels with great width and curvature were bifurcated and merged downstream.Comparison of the faulting amplitude of the three syndepositional faults suggests that the Nandagang and Zhaobei faults were inversely strengthened in the Es1z and Es1s. The Nandagang Fault to the west was found to be more active than the Zhaobei Fault to the east in the Es1z stage. This condition was reversed in Es1s. For that reason, the channels migrated to the west in the Es1z stage and then went back to the east during Es1s.Core analysis shows that the channel fills are mainly composed of sandy-debrites, slumps and turbidites. Among them, sandy debrites dominate deposition in terms of reservoir volume and hydrocarbon potential. These units primarily consist of sandstones and gravel-bearing sandstones, with bed thicknesses ranging from 10 to 40 m, an average porosity of 11% and a permeability of 25 mD. Being mostly encased in organic-rich dark mudstones, these sandy debrites are significant hydrocarbon exploration targets.The results of this study are not only useful to the hydrocarbon exploration and development planning for the Qinan Slope, but also helpful when considering other faulted-depressions in the Bohai Bay Basin and other intra-continent rifted basins around the world, particularly in terms of gravity-flow hydrocarbon exploration and research.  相似文献   

江苏辐射沙洲水道垂线平均余流的计算与分析   总被引：3，自引：0，他引：3  

吴德安  张忍顺  沈永明 《海洋与湖沼》2007,38(4):289-295

根据辐射沙洲邻近主水道和中心沙洲滩面水道33个站次的准同步实测潮流资料, 计算了各站位垂线平均欧拉余流、斯托克斯余流、拉格朗日余流, 并分别进行了逐站位的分析和比较.各站位斯托克斯余流相对较小, 在水道口门处斯托克斯余流较大, 余流流向大都沿涨潮流向, 豆腐渣腰门水道及其以东站位的斯托克斯余流则大致沿落潮流向.欧拉余流和拉格朗日余流大小和流向基本一致.研究海域存在着半封闭的顺时针方向的海水净输移.西洋水道和条鱼港水道是辐射沙洲中心腹地的净进水通道, 而豆腐渣腰门水道、陈家坞槽水道、外王家槽水道、苦水洋海域水道则是净出水通道.  相似文献