沉积学报2023，Vol.41Issue(6)：1739-1754,16.DOI:10.14027/j.issn.1000-0550.2023.082
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
摘要
Abstract
[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 framework indicates predominant periodicities of 100 ka in the upper transgression-related strata and 200 ka in the lower lacustrine/fluvial strata,implying a dominant role of orbital eccentricity in these regional paleoenvironmental processes.(6)Correlations of Quaternary strata around the Bohai Basin and of isochronous strata based on the Jaramillo subchron indicated significant subsidence of the eastern and northwestern margins during the Middle Pleistocene.[Conclusions and Prospects]It is inferred that the land/sea transition of the Bohai Basin has ex-perienced the following processes:alluvial and diluvial systems in the Early Pliocene or earlier;a lake-group environ-ment prior to the early part of the Early Pleistocene;the latest stage of a Bohai paleolake in the Early Pleistocene;shrinking of the lake and weak transgression in the Middle Pleistocene;and shelf deposition since the Late Pleisto-cene.Preliminary correlation of these developmental stages of the Bohai Basin indicate the evolution of a series of paleolakes in the middle and upper reaches of the Yellow River,possibly implying potential covariation.However,the main finding in the work is the lack of fossil evidence,which is worthy of further investigation.关键词
磁性地层/莱州湾/渤海古湖/陆架演化/第四纪Key words
magnetostratigraphy/Laizhou Bay/Bohai paleolake/continental shelf evolution/Quaternary分类
地质学引用本文复制引用
易亮..莱州湾第四系初步框架及环境意义[J].沉积学报,2023,41(6):1739-1754,16.基金项目
国家自然科学基金项目(42177422,41888101)National Natural Science Foundation of China,No.42177422,41888101 （42177422,41888101）
