Miocene diatom biostratigraphy of the Atlantic sector of the Southern Ocean

Four ODP sites located between 64°S and 41°S in the eastern Atlantic sector ofthe Southern Ocean were investigated to refine the Miocene diatom biostratigraphic zonation tied to the geomagnetic chronology. The Miocene diatom stratigraphy from two sites located on Maud Rise (ODP Leg 113) is revised considering the progress in diatom biostratigraphic research, diatom taxonomy and magnetostratigraphic age assignment during the past 10 years. A new diatom zonation was erected for Site 1092 (ODP Leg 177) located on Meteor Rise integrating a magnetostratigraphic interpretation of the shipboard data. This zonation was also applied to Site 1088 (ODP Leg 177) located on Astrid Ridge. The study is focused to Middle and Upper Miocene sequences. It reveals latitudinal differentiations in stratigraphic species ranges and species occurrence pattern that are related to latitudinal differences in surface water masses reflecting the climatic development of the Antarctic cryosphere. Considering the latitudinal differences two stratigraphic zonations are proposed that are applicable to the northern and southern zone ofthe Southern Ocean, respectively. The southern Southern Ocean Miocene diatom biostratigraphic zonation consists of 16 zones in which 11 represent new or modified zones. The northern biostratigraphic zonation contains 10 diatom zones allowing a stratigraphic resolution in the range of 0.2-2 Myr. This paper also includes the taxonomic transfer of seven Miocene diatom taxa from genus Nitzschia Hassal to Fragilariopsis Hustedt.本研究对南大洋东大西洋海域内64°S至41°S之间的4个大洋钻探计划（Ocean Drilling Program, ODP）站位开展调查，旨在优化与地磁年代学相关联的中新世硅藻生物地层分带方案。针对位于毛德海隆（Maud Rise）的2个大洋钻探计划第113航次（ODP Leg 113）站位，结合过去十年间硅藻生物地层研究、硅藻分类学及地磁地层年代标定领域的研究进展，本研究对其产出的中新世硅藻地层序列进行了修订。针对位于梅特洛尔海隆（Meteor Rise）的1092站位（大洋钻探计划第177航次，ODP Leg 177），本研究结合船上实测数据的地磁地层解释结果，建立了全新的硅藻分带方案；该方案同时被应用于位于阿斯特丽德海岭（Astrid Ridge）的1088站位（大洋钻探计划第177航次，ODP Leg 177）。本研究聚焦于中新世中、晚期地层序列，揭示了地层物种分布范围与物种出现模式的纬度分异特征，该特征与表层水团的纬度差异相关，而后者反映了南极冰冻圈的气候演化进程。基于上述纬度差异，本研究分别提出了适用于南大洋北部与南部海域的两套地层分带方案：南大洋南部海域中新世硅藻生物地层分带共包含16个分带，其中11个为新建或经修订的分带；北部海域生物地层分带则包含10个硅藻分带，地层分辨率可达0.2~2百万年。此外，本研究还完成了7个中新世硅藻分类单元的分类学归属调整，将其从菱形藻属（Nitzschia Hassal）转移至脆杆藻属（Fragilariopsis Hustedt）。