辽东湾LDD7孔晚更新世以来的沉积层序与古环境演化

Stratigraphic and Paleo-Environmental Evolution of Liaodong Bay Since Late Pleistocene:Evidence from Core LDD7

对取自渤海辽东湾中部LDD7孔的300个沉积物样品进行了微体古生物分析,对196个样品进行了粒度分析,并选取8个层位的底栖有孔虫混合种进行了AMS^14C测年,利用线形插值方法建立了该孔的年代地层框架。研究结果表明：自晚更新以来辽东湾中部保持了相对连续的沉积序列,LDD7孔记录了该区约60.85cal.kaBP以来的沉积环境演化过程。根据垂向上微体化石组合和岩性的变化,将全长50.1m的沉积物柱状样划分为9个沉积单元,分别代表晚更新世冰期旋回中随着海平面的变化,辽东湾中部区域在不同阶段分别处于海相、陆相或海陆过渡相沉积环境;LDD7孔中共识别出两次主要的海侵过程,分别对应着渤海中部Bc-1孔所记录的献县海侵与黄骅海侵;此次测年结果进一步明确了辽东湾中部两次海侵持续的确切时间,分别是45.84～27.66cal.kaBP和10.64～0cal.kaBP。此外,几个相关岩心的年代框架计算结果表明,献县海侵过程中辽东湾南部沉积速率低于中部,而献县海侵之后辽东湾南部的沉降总量和平均沉积速率都明显高于中部。

The benthic foraminifera and ostracoda faunas in 300 samples and the sediment grain sizes in 196 samples of a 50.1 m-long sediment core（LDD7）from the middle area of Liaodong bay areanalyzed to document the stratigraphy and reconstruct the environmental evolution during Late Pleistocene.In addition,^14 C dating of the benthic foraminifera from 8layers is analyzed using accelerator mass spectrometry to establish the accurate chronostratigraphic framework of the core.It is showed that the central area of Liaodong bay maintained a relatively continuous sedimentary sequence during Late Pleistocene.Core LDD7 recorded the sedimentary environment evolution of the last 60.85 cal.ka.Based on the result,9depositional units（U1to U9 in descending order）in core LDD7 are identified.These units are interpreted as marine facies,continental facies,or transitional facies in the different stages of the Late Pleistocene glacial cycles in the central region of Liaodong bay.By correlation with other wellstudied cores in the nearby area,two transgressive layers of Core LDD7 are in agreement with Xianxian transgression and Huanghua transgression,of which the durations of 45.84-27.66 cal.kaBP and 10.64-0cal.kaBP are detected.Besides,the average subsidence rate and deposition rate in the middle part of Liaodong bay show values significantly lower than those in the south area after Xianxian transgression based on this study;however,the deposition rate in the middle part was higher than that in the south area during Xianxian transgression process.