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首页> 外文期刊>Paleoceanography >Late Oligocene to early Miocene geochronology and paleoceanography from the subantarctic South Atlantic
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Late Oligocene to early Miocene geochronology and paleoceanography from the subantarctic South Atlantic

机译：渐新世晚期到中新世早期的年代学和来自南极南大西洋的古海洋学

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At Ocean Drilling Program (ODP) Site 1090 on the Agulhas Ridge (subantarctic South Atlantic) benthic foraminiferal stable isotope records span the late Oligocene through the early Miocene (25-16 Ma) at a temporal resolution of ～10 kyr. In the same time interval a magnetic polarity stratigraphy can be unequivocally correlated to the geomagnetic polarity timescale (GPTS), thereby providing secure correlation of the isotope record to the GPTS. On the basis of the isotopemagnetostratigraphic correlation we provide refined age calibration of established oxygen isotope events Mil through Mi2 as well as several other distinctive isotope events. Our data suggest that the δ~(18)O maximum commonly associated with the Oligocene/Miocene (O/M) boundary falls within C6Cn.2r (23.86 Ma). The δ~(13)C maximum coincides, within the temporal resolution of our record, with C6Cn.2n/r boundary and hence to the O/M boundary. Comparison of the stable isotope record from Site 1090 to the orbitally tuned stable isotope record from ODP Site 929 across the O/M boundary shows that variability in the two records is very similar and can be correlated at and below the O/M boundary. Site 1090 stable isotope records also provide the first deep Southern Ocean end-member for reconstructions of circulation patterns and late Oligocene to early Miocene climate change. Comparison to previously published records suggests that basin to basin carbon isotope gradients were small or nonexistent and are inconclusive with respect to the direction of deep water flow. Oxygen isotope gradients between sites suggest that the deep Southern Ocean was cold in comparison to the North Atlantic, Indian, and the Pacific Oceans. Dominance of cold Southern Component Deep Water at Site 1090, at least until 17 Ma, suggests that relatively cold circumpolar climatic conditions prevailed during the late Oligocene and early Miocene. We believe that a relatively cold Southern Ocean reflects unrestricted circumpolar flow through the Drake Passage in agreement with bathymetric reconstructions.
机译：在Agulhas山脊（南亚次南大西洋）的海洋钻探计划（ODP）站点1090，底栖有孔虫的稳定同位素记录跨越渐新世晚期至中新世早期（25-16 Ma），时间分辨率约为10年。在相同的时间间隔中，磁极地层可以明确地与地磁极性时标（GPTS）相关，从而提供同位素记录与GPTS的安全相关性。在同位素同位素地层学相关性的基础上，我们为通过Mi2建立的氧同位素事件Mil和其他几个独特的同位素事件提供了精确的年龄校准。我们的数据表明，通常与渐新世/中新世（O / M）边界相关的最大δ〜（18）O落在C6Cn.2r（23.86 Ma）之内。在记录的时间分辨率内，δ〜（13）C最大值与C6Cn.2n / r边界重合，因此与O / M边界重合。跨越O / M边界对站点1090的稳定同位素记录与来自ODP站点929的轨道调谐稳定同位素记录进行比较，结果表明，这两个记录的变异性非常相似，并且可以在O / M边界处或以下进行关联。 1090站点的稳定同位素记录也为循环模式和渐新世晚期至中新世早期气候变化的重建提供了首个深海终端成员。与以前发表的记录的比较表明，盆地之间的碳同位素梯度很小或不存在，并且在深水流动方向上没有定论。站点之间的氧同位素梯度表明，与北大西洋，印度洋和太平洋相比，深海南部较冷。至少在17 Ma之前，南冷深部深水在1090号位居主导地位，这表明在渐新世晚期和中新世早期普遍存在相对寒冷的绕极气候条件。我们认为，相对寒冷的南部海洋反映出通过Drake通道不受限制的绕极流，并与水深重建一致。

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