Sedimentology of the mid-Carboniferous fill of the Olta paleovalley, eastern Paganzo Basin, Argentina: Implications for glaciation and controls on diachronous deglaciation in western Gondwana during the late Paleozoic Ice Age
Sedimentology of the mid-Carboniferous fill of the Olta paleovalley, eastern Paganzo Basin, Argentina: Implications for glaciation and controls on diachronous deglaciation in western Gondwana during the late Paleozoic Ice Age
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阿根廷帕甘佐盆地东部奥尔塔古谷中石炭纪充填物的沉积学：晚古生代冰期对冈瓦纳西部冰川作用和历时消冰作用的影响
DOI：
10.1016/j.jsames.2018.03.015
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发表时间：
2018
影响因子：
1.8
通讯作者：
Schencman, Jazmin
中科院分区：
文献类型：
--
作者：
Moxness, Levi D.;Isbell, John L.;Pauls, Kathryn N.;Limarino, Carlos O.;Schencman, Jazmin
在晚古生代冰期（LPIA），全球和区域气候驱动因素对冰川作用都有贡献。然而，从冰窖到温室的转变在冈瓦纳是不同步的，这表明，在某些情况下，区域控制在冰川消融中发挥了重要作用。对了解LPIA气候条件变化特别感兴趣的是东部帕甘佐盆地。该区域的两侧是位于阿根廷西部的Precordilleran和sierra Pampeanas地区的冰中心，以及位于东部的paran<s:1>、chaco - paran<e:1>和Sauce Grande盆地的主要冰原，所有这些冰原都位于南纬~ 40°至65°之间。关于帕甘佐盆地东部存在冰的假设是基于对狭窄、陡峭的Olta-Malanzán古山谷的解释，这些古山谷是由高山冰川雕刻的，或者是由东部冰盖的出口冰川雕刻的，冰川在古山谷内沉积了粗碎屑。然而，我们没有发现冰川作用的证据。相反，来自冲积扇/扇三角洲和岩石瀑布的砾石淤积了排水系统，导致了山谷东端的湖泊活动。奥尔塔古河谷西端由水下沉积或浅水下沉积的砂岩向海相泥岩过渡，表明存在海相海侵，而海相海侵又被推进的吉尔伯特型三角洲沉积覆盖。坠石是由从山谷壁上落下的岩石和漂流而来的湖冰形成的，而不是冰山。因此，我们得出结论，阿根廷西部的气候是由前科迪勒兰地区和Paganzo盆地西缘的隆起引起的冰川作用以及东部降水阴影的发生造成的。在中石炭世期间，西部冰川的消失先于同一古纬度其他地方的冰川消融，其原因是活动边缘的位置向西移动，冰川高地的崩塌，以及整个阿根廷西部降水阴影的扩大。
Both global and regional climate drivers contributed to glaciation during the late Paleozoic Ice Age (LPIA). However, the transition from icehouse to greenhouse conditions was asynchronous across Gondwana suggesting that, in some cases, regional controls played a significant role in deglaciation. Of particular interest to understanding changing LPIA climatic conditions, is the eastern Paganzo Basin. This region was flanked by ice centers in the Precordilleran and Sierras Pampeanas regions of Argentina on the west, and major ice sheets in the Paraná, Chaco-Paraná, and Sauce Grande basins to the east, all of which resided between ∼40 and 65° S latitude. Hypotheses on the occurrence of ice in the eastern Paganzo Basin are based on interpretations of the narrow, steep-walled, Olta-Malanzán paleovalley as carved by an alpine glacier or by an outlet glacier draining an eastern ice sheet, and that glaciers deposited coarse clastics within the paleovalley. However, we found no evidence for glaciation. Rather, gravel from prograding alluvial fans/fan deltas and rock falls ponded drainage resulting in lacustrine activity in the eastern end of the valley. A transition from either subaerially or shallow subaqueously deposited sandstones to marine mudstones in the western end of the Olta paleovalley suggest a marine transgression, which, in turn, was overlain by deposits of prograding Gilbert-type deltas. Dropstones were from rock falls off valley walls and rafting by lake ice rather than from icebergs. Therefore, we conclude that the climate in western Argentina resulted from uplift induced glaciation in the Precordilleran region and along the western margin of the Paganzo Basin, and the occurrence of a precipitation shadow to the east. The disappearance of the western glaciers during the mid-Carboniferous, prior to deglaciation elsewhere at the same paleolatitude, resulted from a westward shift in the position of the active margin, collapse of the glaciated upland(s), and an expansion of the precipitation shadow across the whole of western Argentina.
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