Late Miocene to Holocene planktonic foraminifers from the subantarctic South Atlantic

Late Miocene to Holocene planktonic foraminifers from the subantarctic South Atlantic were investigated for their biostratigraphic and environmental significance. The calcareous planktonic microfauna are of low diversity and are very rare or absent at sites located below the CCD. The sediments recovered from Sites 703 and 704 on the Meteor Rise at about 47°S are useful for biostratigraphic and environmental studies. In the whole sequence 16 species or varieties of planktonic foraminifers were recognized. Two species occur in the uppermost Miocene. In the Pliocene the Globorotalia puncticulata population can be used to separate the early from the late Pliocene. The Pliocene/Quaternary boundary does not appear to be well distinguished in the foraminiferal assemblage. A faunal change noted at 2.5 Ma could correspond to the development of glaciation in the Northern Hemisphere and its Antarctic counterpart. At about 5.2 Ma the first increase in polar fauna near the Meteor Rise occurs. Two other cooling periods are indicated in these sequences at about 4 and 3 Ma. Moreover, the hydrologic environment became more productive at about 2.1 Ma and close to the Brunhes/Matuyama boundary.本研究针对南大西洋亚南极海域晚中新世至全新世的浮游有孔虫（planktonic foraminifers）展开调查，以明确其生物地层学与环境学研究意义。 钙质浮游微化石群（calcareous planktonic microfauna）多样性偏低，且在碳酸盐补偿深度（Carbonate Compensation Depth，CCD）以下的沉积站位中极为稀少甚至完全缺失。采自南纬约47°流星海隆（Meteor Rise）703、704站位的沉积物，可用于生物地层学与环境学相关研究。本完整沉积序列中共识别出16种浮游有孔虫（含变种）。 其中2个物种出现于晚中新世最顶部地层。 上新世地层中，斑点球室虫（Globorotalia puncticulata）种群可用于区分上新世早期与晚期。但在有孔虫组合中似乎难以清晰界定上新统/第四系界线。 约2.5 Ma（百万年前，million years ago）处记录到的动物群更替事件，可对应北半球冰川作用的发展及其南极地区的同类演化过程。 约5.2 Ma时，流星海隆附近首次出现极地动物群繁盛现象。该沉积序列中还记录到另外两次降温事件，分别发生于约4 Ma与3 Ma。此外，约2.1 Ma以及接近布容/松山极性反转界线（Brunhes/Matuyama boundary）时，区域水文环境的初级生产力显著提升。