Sedimentology of cores from the shelf of Lazarev Sea, East Antarctica

Distinct facies types, classified in radiocarbon-dated sediments from the shelf of the Lazarev Sea, East Antarctica, reveal a detailed history of processes that have controlled sedimentation during the deglaciation over the last 10,000 yr. The ice retreat on this part of the Antarctic shelf started 9500 yr BP, marked by the deposition of laminated sediments, deposited from a floating ice shelf. These laminites, which occur on top of diamictons laid down from a grounded ice sheet, are the basal sediments of the postglacial sequence. The intensity of the Antarctic Coastal Current (ACC), directed by shelf morphology, controlled sedimentation of the postglacial facies. A residual glaciomarine sediment with the fine fraction winnowed by strong currents developed from 9000-8000 yr BP in the western part of the investigation area and from 9000-5000 yr BP in the eastern part, closer to the prominent 'Fenno Deep' trough. Current velocities apparently decreased between 8000 and 2000 yr BP due to a deflection of the ACC by advancing ice tongues to the east of the investigation area during the 'Hypsithermal'. This led to a deposition of fine-grained sediments, and clay mineralogy suggests a continental source, possibly near the grounding line of the Nivl Ice Shelf, rather than a winnowing of sediments near the shelf break or advection from deeper water. Current velocities intensified after 2000 yr BP, removed fine material from these sediments and led to a relict sediment, consisting of coarse bryozoan and molluscan debris.

基于东南极洲拉扎列夫海（Lazarev Sea）陆架经放射性碳定年的沉积物所划分出的独特沉积相类型，揭示了过去10000年冰消期内控制沉积作用的详细过程历史。该南极陆架区域的冰退作用始于距今9500年，其标志性特征为浮冰架沉积形成的纹层状沉积物的堆积。这类赋存于驻留冰盖沉积形成的混杂沉积物（diamictons）之上的纹层岩（laminites），是冰后期层序的基底沉积物。受陆架地貌调控的南极沿岸流（Antarctic Coastal Current, ACC）强度，控制了冰后期沉积相的沉积过程。在研究区西部，距今9000至8000年期间形成了经强流淘洗掉细粒组分的残留冰海沉积物；而在更靠近著名的芬诺海槽（Fenno Deep）的东部区域，该类残留沉积物的形成时期为距今9000至5000年。距今8000至2000年期间，受全新世大暖期（Hypsithermal）研究区东部推进的冰舌对南极沿岸流（ACC）的阻挡影响，海流流速明显降低，进而导致细粒沉积物的堆积；黏土矿物学分析显示其物源为大陆来源，可能位于尼夫冰架（Nivl Ice Shelf）的驻留线附近，而非陆架坡折带附近的沉积物淘蚀或深水平流带来的物质。距今2000年之后，海流流速再度增强，将这些沉积物中的细粒物质移除，最终形成了由粗粒苔藓虫和软体动物残骸组成的残留沉积物。