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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Expanded lacustrine sedimentation in the Qaidam Basin on the northern Tibetan Plateau: Manifestation of climatic wetting during the Oligocene icehouse
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Expanded lacustrine sedimentation in the Qaidam Basin on the northern Tibetan Plateau: Manifestation of climatic wetting during the Oligocene icehouse

机译：在北藏高原柴达木盆地扩大湖泊沉淀：少世冰屋期间气候润湿的表现

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The Qaidam Basin in the core area of arid Inner Asia has been considered undergoing continuous aridification over the Cenozoic. However, the Qaidam Basin is marked with expanded lacustrine sedimentation during the Oligocene, which contrasts with the fluvial or deltaic facies stratigraphically below (Eocene) and above (Miocene-present). The Oligocene lacustrine expansion challenges the idea of persistent aridification. To solve the conundrum, we reconstruct a long-term compound-specific hydrogen isotope (delta H-2) record from sedimentary leaf wax n-alkanes to evaluate the paleoclimatic context before, during, and after the Oligocene lacustrine expansion. The delta H-2 results reveal three shifts at ca. 40 Ma, 34 Ma, and 24 Ma. The leaf wax delta H-2 values range from -176.8 parts per thousand to -166.7 parts per thousand from 51 to 40 Ma, followed by an abrupt increase of 23.9 parts per thousand at 40 Ma. We interpret this rapid increase as enhanced aridification due to the coeval retreat of the Paratethys Sea from the region. At 34 Ma, the delta H-2 plunges across the Eocene-Oligocene transition (EOT). Post-EOT delta H-2 values are the lowest, vary with high amplitude from -187.1 parts per thousand to -153.2 parts per thousand, and are associated with the lacustrine facies expansion, indicating a wetter climate. By compiling the regional isotopic proxy studies, we observe the contrasting patterns in paleohydrology conditions since the EOT: the relaxation of aridity in the westerlies region versus the enhanced aridification in the East Asian summer monsoon region. We interpret that the west-east contrasting patterns represent the different climatic responses to global cooling: wetting in the west as a result of the enhanced moisture transport via westerlies replacing the subtropical high, and drying in the east due to the reduction in moisture content associated with weakening East Asian summer monsoon. Wetting in Inner Asia is synchronous with cooling in the ocean (North Atlantic) and on land (Xining Basin). Since 24 Ma, delta H-2 increases in response to warming during the latest Oligocene to the early Miocene when the subtropical high re-occupied Inner Asia, causing the aridity. This study reveals a dynamic climate in Inner Asia with different mechanisms responding to global change. (C) 2021 Elsevier B.V. All rights reserved.
机译：柴达木盆地位于干旱的亚洲内陆核心地区，被认为在新生代经历了持续的干旱化。然而，在渐新世期间，柴达木盆地以扩展的湖泊沉积为标志，这与以下（始新世）和以上（中新世）的河流或三角洲相地层形成对比。渐新世的湖泊扩张挑战了持续干旱化的观点。为了解决这个难题，我们从沉积叶蜡正构烷烃中重建了长期化合物特定氢同位素（δH-2）记录，以评估渐新世湖泊扩张之前、期间和之后的古气候背景。delta H-2结果显示，在约40毫安、34毫安和24毫安时发生了三次位移。叶蜡δH-2值在51-40mA范围内从-176.8份/千到-166.7份/千，然后在40mA突然增加23.9份/千。我们将这种快速增长解释为由于同时代的副塔提斯海从该地区撤退而导致的干旱化加剧。在34 Ma时，三角洲H-2穿过始新世-渐新世过渡期（EOT）。EOT后三角洲H-2值最低，变化幅度较大，从-187.1‰到-153.2‰，与湖相扩张有关，表明气候较湿润。通过编制区域同位素替代研究，我们观察了EOT以来古水文条件的对比模式：西风带地区干旱的缓解与东亚夏季风地区干旱的增强。我们认为，东西对比模式代表了对全球降温的不同气候响应：西风带代替副热带高压加强了水分输送，导致西部湿润；东亚夏季风减弱导致水分含量减少，导致东部干燥。亚洲内陆的湿润与海洋（北大西洋）和陆地（西宁盆地）的冷却是同步的。自24 Ma以来，在最近渐新世至早中新世期间，副热带高压重新占领亚洲内陆地区，delta H-2随着变暖而增加，导致干旱。这项研究揭示了亚洲内部的动态气候，以及应对全球变化的不同机制。（c）2021爱思唯尔B.V.保留所有权利。

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