Provenance of late Paleozoic glacial/post-glacial deposits in the eastern Chaco-Paraná Basin, Uruguay and southernmost Paraná Basin, Brazil
Provenance of late Paleozoic glacial/post-glacial deposits in the eastern Chaco-Paraná Basin, Uruguay and southernmost Paraná Basin, Brazil
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乌拉圭查科-巴拉那盆地东部和巴西巴拉那盆地最南端晚古生代冰川/冰后沉积物的来源
DOI：
10.1016/j.jsames.2020.102989
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发表时间：
2021
影响因子：
1.8
通讯作者：
Mundil, Roland
中科院分区：
文献类型：
--
作者：
Fedorchuk, Nicholas D.;Griffis, Neil P.;Isbell, John L.;Goso, César;Rosa, Eduardo L.M.;Montañez, Isabel P.;Yin, Qing-Zhu;Huyskens, Magdalena H.;Sanborn, Matthew E.;Mundil, Roland
巴西巴拉那盆地和乌拉圭查科-巴拉那盆地都包含对重建冈瓦纳中部晚古生代冰中心至关重要的沉积记录。冰下地貌和冰川构造结构的方向表明，查科-巴拉那盆地东部和巴拉那盆地最南端的晚古生代冰川沉积物在遗传上是相关的，因为它们可能是由同一冰中心冰川作用的。然而，负责沉积这些沉积物的冰中心的位置和范围尚不清楚。此外，冈瓦纳大陆这一地区的冰期、间冰期和冰期后区间沉积物扩散模式的变化尚不清楚。因此，本研究利用 U-Pb 碎屑锆石年代学来评估查科-巴拉纳盆地东部（圣格雷戈里奥、塞罗佩拉多、特雷斯群岛地层）和最南端的巴拉那盆地（伊塔拉雷群）的冰川和冰后沉积物的来源。结果显示，查科-巴拉那盆地东部的所有样本的主要年龄峰值分别为~520–555 Ma、~625 Ma、750–780 Ma 和 900–1000 Ma。这些锆石被解释为来自乌拉圭东南部的库奇拉迪奥尼西奥地体和埃斯特角地体，也可能来自纳米比亚南部的纳马夸带。另一个重要来源可能是乌拉圭中/东部杜拉兹诺群的泥盆纪沉积岩。与此同时，来自巴拉那盆地最南端的冰川形成期伊塔拉雷群样本含有不同的碎屑锆石特征，峰值位于~580 Ma、~780 Ma、~2110 Ma 和~2500 Ma，与前寒武纪/寒武纪 Camaquã 盆地的底层沉积岩和变沉积岩非常相似。冰期和冰后沉积物中的碎屑锆石年龄表明，当地来源占主导地位。相比之下，查科-巴拉那盆地相对较远的冰洋层段的锆石年龄反映了东部和东南部更远的来源，这表明当冰川退缩和/或最大冰下侵蚀区转移时，更大的排水集水区打开。尽管查科-巴拉那盆地的大多数锆石年龄可归因于乌拉圭来源，但结果支持冰川从纳米比亚南部和乌拉圭东南部发散到查科-巴拉那盆地的假设。从那里，冰向西北流入巴拉那盆地，然后随着古气候变暖而退向非洲。我们研究区域的碎屑锆石库存与东部巴拉那盆地不同，这表明至少有两个独特的非洲冰川源区在巴拉那盆地和查科-巴拉那盆地沉积了沉积物。
The Paraná Basin, Brazil and the Chaco-Paraná Basin, Uruguay both contain sedimentary records that are critical to reconstructing late Paleozoic ice centers in central Gondwana. The orientations of subglacial landforms and glaciotectonic structures suggest that late Paleozoic glacial deposits in the eastern Chaco-Paraná Basin and the southernmost Paraná Basin are genetically related, as they were likely glaciated by the same ice center. However, the location and extent of the ice center responsible for depositing these sediments are unclear. Furthermore, changes in sediment dispersal patterns between glacial, inter-glacial, and post-glacial intervals are not understood for this region of Gondwana. Therefore, this study utilized U–Pb detrital zircon geochronology to assess the provenance of glacial and post-glacial sediments from the eastern Chaco-Paraná Basin (San Gregorio, Cerro Pelado, Tres Islas Formations) and the southernmost Paraná Basin (Itararé Group). Results show dominant age peaks at ~520–555 Ma, ~625 Ma, 750–780 Ma, and 900–1000 Ma in all samples from the eastern Chaco-Paraná Basin. These zircons are interpreted to have been derived from sources in the Cuchilla Dionisio Terrane and Punta del Este Terrane in southeastern Uruguay, and possibly the Namaqua Belt in southern Namibia. Another important source was likely Devonian sedimentary rocks of the Durazno Group in central/eastern Uruguay. Meanwhile, a sample of the glaciogenic Itararé Group from the southernmost Paraná Basin contains a different detrital zircon signature with peaks at ~580 Ma, ~780 Ma, ~2110 Ma, and ~2500 Ma that closely resembles underlying sedimentary and meta-sedimentary rocks of the Precambrian/Cambrian Camaquã Basin. Detrital zircon ages in the glacial and post-glacial sediments indicate that local sources were dominant. In contrast, zircon ages from relatively ice-distal glaciomarine intervals in the Chaco-Paraná Basin reflect more distal sources to the east and southeast, which indicates a larger drainage catchment opened when glaciers retreated and/or the zone of maximum subglacial erosion shifted. Although most zircon ages in the Chaco-Paraná Basin can be attributed to Uruguayan sources, results support the hypothesis that glaciers emanated from southern Namibia and southeast Uruguay into the Chaco-Paraná Basin. From there, ice flowed northwest into the Paraná Basin and then receded back towards Africa as the paleoclimate warmed. The detrital zircon inventory in our study region is distinct from the eastern Paraná Basin, suggesting at least two unique African source regions for glaciers that deposited sediments in the Paraná and Chaco-Paraná Basins.
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