Timing and nature of the deepening of the Tasmanian Gateway
Timing and nature of the deepening of the Tasmanian Gateway
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DOI：
10.1029/2004pa001022
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发表时间：
2004-12
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通讯作者：
C. Stickley;H. Brinkhuis;S. Schellenberg;A. Sluijs;U. Röhl;M. Fuller;M. Grauert;M. Huber;J. Warnaar;G. Williams
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作者：
C. Stickley;H. Brinkhuis;S. Schellenberg;A. Sluijs;U. Röhl;M. Fuller;M. Grauert;M. Huber;J. Warnaar;G. Williams
[1]在始新世/渐新世(∼34-33 Ma)的过渡时期，构造变化在澳大利亚和南极之间形成了一道深厚的塔斯马尼亚门，被广泛认为是南极冰冻圈增长和南极绕极流发展的主要机制。大洋钻探计划(ODP189)在塔斯马尼亚周围的四个地点发现了跨越E/O过渡区间的近乎连续的海洋沉积记录。这些记录基本上没有钙质微体化石，但包含了丰富的硅质和有机壁海洋微体化石的记录。在这项研究中，我们综合了1172站位(塔斯曼高原东部)的微古生物、沉积学、地球化学和古地磁资料，以确定与ODP189站位相关的E/O塔斯马尼亚门加深的四个不同的阶段(A-D)。A期，在∼35.5 Ma之前：轻微的初始加深，特征是具有初始凝聚幕的浅海前三角洲环境。B期，∼35.5-33.5 Ma：加深程度增加，以主要青绿石沉积和高能底水洋流开始为标志。C相，∼33.5-30.2 Ma：进一步加深到半深海深度，底流能量越来越大的幕式侵蚀。阶段D；30.2 Ma：建立以硅质碳酸盐软泥沉积为特征的稳定的、开阔的、暖温带的、少营养的环境。我们的综合证据表明，这一渐新世早期塔斯马尼亚门户的加深最初产生了一股相对温暖的表层水从南极湾向东流入西南太平洋。这种“Proto-Leeuwin”流从根本上不同于以往渐新世早期向东流动的冷水(例如“Proto-Acc”)的区域重建，因此为重建这一重大全球变化事件的区域到全球尺度的动力学提供了一个重要的新制约因素。
[1] Tectonic changes that produced a deep Tasmanian Gateway between Australia and Antarctica are widely invoked as the major mechanism for Antarctic cryosphere growth and Antarctic Circumpolar Current (ACC) development during the Eocene/Oligocene (E/O) transition (∼34–33 Ma). Ocean Drilling Program (ODP) Leg 189 recovered near-continuous marine sedimentary records across the E/O transition interval at four sites around Tasmania. These records are largely barren of calcareous microfossils but contain a rich record of siliceous- and organic-walled marine microfossils. In this study we integrate micropaleontological, sedimentological, geochemical, and paleomagnetic data from Site 1172 (East Tasman Plateau) to identify four distinct phases (A–D) in the E/O Tasmanian Gateway deepening that are correlative among ODP Leg 189 sites. Phase A, prior to ∼35.5 Ma: minor initial deepening characterized by a shallow marine prodeltaic setting with initial condensation episodes. Phase B, ∼35.5–33.5 Ma: increased deepening marked by the onset of major glauconitic deposition and inception of energetic bottom-water currents. Phase C, ∼33.5–30.2 Ma: further deepening to bathyal depths, with episodic erosion by increasingly energetic bottom-water currents. Phase D, <30.2 Ma: establishment of stable, open-ocean, warm-temperate, oligotrophic settings characterized by siliceous-carbonate ooze deposition. Our combined evidence indicates that this early Oligocene Tasmanian Gateway deepening initially produced an eastward flow of relatively warm surface waters from the Australo-Antarctic Gulf into the southwestern Pacific Ocean. This “proto-Leeuwin” current fundamentally differs from previous regional reconstructions of eastward flowing cool water (e.g., a “proto-ACC”) during the early Oligocene and thereby represents an important new constraint for reconstructing regional- to global-scale dynamics for this major global change event.