莱州湾第四系初步框架及环境意义  

Framework of Quaternary Stratigraphy in Laizhou Bay,Bohai Sea,and Its Paleoenvironmental Significance

作　　者：易亮[1] YI Liang(State Key Laboratory of Marine Geology,Tongji University,Shanghai 200092,China)

机构地区：[1]同济大学海洋地质国家重点实验室,上海200092

出　　处：《沉积学报》2023年第6期1739-1754,共16页Acta Sedimentologica Sinica

基　　金：国家自然科学基金项目(42177422,41888101)。

摘　　要：[目的]莱州湾位于渤海陆架的南端,是研究第四纪东北亚地理与环境重组的关键地点之一,较为连续地记录了渤海盆地陆—海转换时区域环境变化的历史。[方法]为揭示区域地层特征及其可能的环境意义,以莱州湾地区11支钻孔岩心为研究对象,详细分析了第四纪地层对比框架与沉积演化过程。[结果](1)通过布容正极性时和松山负极性时两个等时面的对比分析,推测莱州湾地区向海一侧在早更新世经历了显著的沉降过程,导致盆地向南(山区一侧)广泛扩张;(2)基于11支钻孔岩心的地层特征对比,初步构建了区域第四纪地层框架,识别出17个水退—水进旋回,包括全新统1个、中更新统上部—上更新统2个、下更新统上部—中更新统7个、下更新统7个;(3)开展环渤海地区地层对比研究,基于加拉米诺正极性亚时的等时面对比,推测中更新世渤海盆地向东、西北缘显著扩张。[结论]初步重建了渤海盆地陆—海转换的主要过程,包括晚上新世的泛湖—湖群环境,早更新世的大湖发育(最近一期“渤海古湖”),中更新世大湖萎缩—弱海侵过程,晚更新世大海侵—陆架沉积环境等阶段。因此,莱州湾第四系的初步框架为重构盆地演化和区域古环境过程提供了新证据,也为探讨更大区域内盆地演化的协同性积累了新素材;不过由于缺少生物化石序列等证据,这些推测仍需更多的检验。[Objective]Laizhou Bay is located in the southern Bohai Sea,where the Quaternary history of regional environmental changes during the transition from land to sea is continuously recorded in coastal sediments.Studying these geological records provides critical insights into the geographical and environmental reorganization of northeast-ern Asia during the Quaternary.Previous studies have reported a major transition from lacustrine to shelf environment in the Middle Pleistocene.Three transgression events have been dated to marine isotope stage(MIS)7-6,MIS 5-3,and the Holocene.However,the evolution of the Bohai paleolake was not clear,since the framework of these lacus-trine deposits had not yet been established.[Methods]To reveal the evolutional history of the Bohai paleolake/sea,analyses of the Quaternary sedimentary strata in 11 drilling cores from Laizhou Bay were carried out to establish a pre-liminary framework.These mainly included magnetostratigraphy,sediment grain size and stratigraphic correlation.[Results](1)The magnetostratigraphy of three new cores implied newly defined magnetozones generally correlated to the Brunhes,Matuyama and Gauss chrons in the geological polarity timescale,consistent with previous studies of Laizhou Bay.(2)Three major types of Quaternary sediment were identified(fluvial-alluvial,lacustrine,and continental-shelf);the sedimentary properties and the relationships of sediment grain-size parameters are distinctive and potentially useful for paleoenvironmental inferences.(3)Stratigraphic analyses and isochronous strata correlation(Brunhes and Matuyama chrons)found that Laizhou Bay may have experienced significant subsidence in the Early Pleistocene.(4)In establishing a stratigraphic framework for Quaternary sediments in Laizhou Bay,17 alternations between extension and shrinking of sea/lake water were identified:one in the Holocene;two in the Upper Pleistocene and latter part of the Middle Pleistocene;seven in the Middle Pleistocene;and seven in the Early Pleistocene.(5)The preliminary

关 键 词：磁性地层 莱州湾 渤海古湖 陆架演化 第四纪 

分 类 号：P512.2[天文地球—地质学]