渤海西部晚第四纪地层层序特征及沉积响应

Late Quaternary Stratigraphic Sequence and Depositional Response in the Western Bohai Sea

渤海是一个仅通过渤海海峡与北黄海相接的半封闭陆架浅海,晚第四纪以来的地层演化过程复杂,目前尚不清楚,且海相地层的形成时代存在争议.为了研究渤海西部晚第四纪以来的地层层序,对高分辨率浅地层剖面声学地层与典型钻孔沉积地层的进行对比分析.研究表明:高分辨率浅地层剖面自下而上划定的7个声学地层单元(U5、U4-2、U4-1、U3、U2、U1-2、U1-1)与钻孔岩心划分的沉积地层单元具有良好的对应关系.与MIS4期、MIS2期低海面时期的沉积间断密切相关的两个层序界面R5、R3,将渤海西部晚第四纪(MIS5期)以来的地层层序自下而上划分为3个层序(SQ3、SQ2、SQ1):SQ3识别出下部海侵体系域与高水位体系域、上部海退体系域,分别对应MIS5期海平面相对较高时期的滨-浅海相交替沉积(U5)、MIS4期早期滨海相沉积(U4-2);SQ2自下而上由低水位体系域[MIS4期中晚期与黄河、滦河相关的河湖相沉积(U4-1)]与海侵体系域[MIS3期早中期滨海相沉积(U3)]组成;SQ1自下而上包括低水位体系域[末次冰盛期与滦河相关的河湖相沉积(U2)]、海侵体系域[全新世早中期滨海相沉积(U1-2)]高水位体系域[全新世高海面以来的浅海相沉积(U1-1)].研究区的地层发育受控于海平面变化、沉积物供应、渤海海峡地形及活动构造的共同作用.

The Bohai Sea(BS)is a semi-enclosed sea connected to the North Yellow Sea only via the Bohai Strait.Its stratigraphic evolution during the Late Quaternary has been complex and unresolved.Moreover,the timing of Late Quaternary transgression has been a matter of controversy.In order to study the stratigraphic sequence in the western BS during the Late Quaternary,highresolution seismic reflection data in conjunction with depositional stratigraphy of typical cores were analyzed.The results indicate that high-resolution seismic profiles from the study area were subdivided into seven seismic units(U5,U4-2,U4-1,U3,U2,U1-2,U1-1 in ascending order),which were clearly correLated with the depositional units of core TJC-1.These units constitute three distinctive sequences(SQ3,SQ2,SQ1 from bottom to up)bounded by two sequence boundaries(R5,R3)with obvious depositional hiatus,correLated with sea-level lowstands of MIS4 and MIS2,respectively.SQ3 consists of the lower transgressive systems tract(TST)and highstand systems tract(HST)(U5,interactive deposits of littoral and neritic facies in MIS5),and the upper regressive systems tract(RST)(U4-2,littoral facies in early MIS4).SQ2 is composed of lowstand systems tract(LST)(U4-1,fluvial and lacustrine facies in middle-Late MIS4 correlating with the Huanghe River and Luanhe River)and TST(U3,littoral facies during the early-middle MIS3)from the bottom up.SQ1 comprises LST(U2,fluvial and lacustrine during Last Glacial Maximum correlating with Luanhe River),TST(U1-2,littoral facies during the early-middle Holocene)and HST(U1-1,neritic facies since the sea-level highstand of Holocene).Stratigraphy development in the study area during the Late Quaternary was governed mainly by sea-level changes,provenance,the Bohai Strait topography and the active faults.