Unconfined Flow Deposits in Front Sandbodies of Shallow Water Deltaic Distributary Systems
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摘要: 新近纪渤海湾盆地具有构造稳定、沉降缓慢、地形平缓、坡度小等特点；古气候资料证实渤海海域新近纪中期（明下段沉积时期）湿润亚热带到暖温带气候，广泛发育浅水三角洲及浅水湖泊沉积。应用层序地层学原理将黄河口凹陷新近纪明下段划分为1个三级层序、3个体系域，即低位域、湖侵域、高位域，识别出不同体系域内拼合板型、孤立型、席状型三种砂体结构，分别对应分流河道型、砂坝型及席状型浅水三角洲类型。同时借鉴现代浅水沉积、水槽实验模拟研究，探讨浅水三角洲沉积演化过程中砂体分布规律与湖平面相对变化之间响应关系，最终建立了黄河口凹陷新近纪明下段温凉型、湿热型两种浅水三角洲层序成因模式，认为古气候影响的湖平面相对变化控制了浅水三角洲前缘砂体的微相类型、结构及分布。Abstract: Bohai Basin is characterized by stable tectonics with steady and slow subsidence, which formed in low-relief and low gradient during the Neogene. The paleoclimate data confirmed that the Bohai area was humid subtropical to warm temperate climate and widely developed shallow-water delta and shallow lake sedimentation system in Middle Neogene (sedimentary period of the Lower Member of Minghuazhen Formation). Changes of palaeogeomorphology, palaeoclimate and ancient water depth controlled shallow water deltaic distributary systems’ front sandbodiesis’ architectures, distribution and evolution. Application of the principle of sequence stratigraphy, the lower member of Minghuazhen Formation in Huanghekou sag will be divided into one three order sequence and three system tracts which is LST, TST and HST. On the basic, recognized three kinds of sand body architectures include the stacked channel type, isolated channel type, sheeted channel type. According to core, logging, seismic, means of modern sediments and tank simulation experiment, we established depositional model of Huanghekou sag fluvial-dominated delta in the lower member of Minghuazhen Formation.
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