Sedimentology and stable isotopes from a lacustrine-to-palustrine limestone deposited in an arid setting, climatic and tectonic factors: Miocene–Pliocene Opache Formation, Atacama Desert, Chile
Sedimentology and stable isotopes from a lacustrine-to-palustrine limestone deposited in an arid setting, climatic and tectonic factors: Miocene–Pliocene Opache Formation, Atacama Desert, Chile
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干旱环境下沉积的湖泊到沼泽石灰岩的沉积学和稳定同位素、气候和构造因素：智利阿塔卡马沙漠中新世-上新世奥帕奇组
DOI：
10.1016/j.palaeo.2015.02.039
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发表时间：
2015
期刊：
影响因子：
--
通讯作者：
A. D. Wet
中科院分区：
文献类型：
--
作者：
C. B. Wet;L. Godfrey;A. D. Wet
现场关系，岩相学，地理信息系统和地球化学的晚中新世-上新世石灰岩，奥帕奇形成，卡拉马盆地，阿塔卡马沙漠，智利表明，沉积相，成岩历史，和同位素从东部到西部的盆地。我们认识到两个相;以介形虫-硅藻泥岩和杂砂岩为特征的湖相和以浅水和成土特征为特征的沼泽相。对流域地形的地理信息系统分析显示，东部地区有一个流域内低压，西部水文梯度较大，“卡拉马收缩”限制了东西之间的流动。岩相学和地球化学结果证实，卡拉马收缩影响沉积参数，积水地下水的东部，形成一个浅水湖，并创造沼泽条件的西部。我们的分析表明，湖泊沃茨的13 C或18 O的富集比沼泽沃茨，即使岩石学研究表明，湖泊碳酸盐岩有一个复杂的成岩历史，来自地下水富含溶解矿物。如果西部碳酸盐岩的一个重要水源来自太平洋，而且演化程度较低，而东部石灰岩则是从东部输送过程中18 O耗尽的水中沉淀下来的，那么这种看似相反的观察结果就可以得到调和。今天，来自太平洋的湿气很少（如果有的话）到达内陆，远至卡拉马，这表明在晚中新世-上新世中期，由于寒冷的沿海太平洋洋流的上升流减弱或不存在，逆温区的破裂使太平洋的湿气到达内陆。这种不断变化的大气环流模式可能也影响了上层气流，今天阻止东部来源的水分穿越安第斯山脉，使其在晚中新世-上新世期间进一步向西进入阿塔卡马地区。总之，这些水分来源足以在卡拉马盆地产生富含碳酸盐的沼泽和湖泊环境。
Field relations, petrography, GIS, and geochemistry of a Late Miocene–Pliocene limestone, the Opache Formation, Calama Basin, Atacama Desert, Chile shows that depositional facies, diagenetic histories, and isotopes differ from eastern to western parts of the basin. We recognize two facies; lacustrine, characterized by ostracod-diatom mudstone and wackestone, and palustrine, characterized by both shallow water and pedogenic features. GIS analysis of the basin topography reveals an intrabasinal low in the eastern area and steeper hydrological gradients to the west, with the “Calama constriction”, restricting flow between east and west. Petrography and geochemical results confirm that the Calama constriction influenced depositional parameters, ponding groundwater to the east, forming a shallow lake and creating palustrine conditions to the west. Our analyses indicate that lake waters were less enriched in13C or18O than palustrine waters even though petrologic studies show that the lacustrine carbonates have a complex diagenetic history, derived from groundwater-rich in dissolved minerals. This seemingly contrary observation can be reconciled if an important source of water for the western carbonates was sourced from the Pacific Ocean and was less evolved, whereas eastern limestones precipitated from water which had become depleted in18O during transport from the east. Today, moisture from the Pacific very rarely, if ever, reaches inland as far as Calama, indicating that during the Late Miocene–Mid-Pliocene breakdown in the temperature inversion due to weakened or absent upwelling in the cold coastal Pacific current allowed moisture from the Pacific to reach inland. This changing atmospheric circulation pattern may have also affected upper level airflow that today blocks eastern sourced moisture from crossing the Andes, allowing it to reach farther westward into the Atacama region during the Late Miocene–Pliocene. Together, these moisture sources were sufficient to produce carbonate-rich palustrine and lacustrine environments in the Calama Basin.