Detrital zircon geochronology and provenance of Pleistocene loess and contributing glacial sources, midcontinental USA
Detrital zircon geochronology and provenance of Pleistocene loess and contributing glacial sources, midcontinental USA
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美国大陆中部更新世黄土和冰川来源的碎屑锆石年代学和物源
DOI：
10.1016/j.quascirev.2021.107201
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发表时间：
2021
影响因子：
4
通讯作者：
Counts, Ron C.
中科院分区：
文献类型：
--
作者：
Dendy, Sarah N.;Guenthner, William R.;Grimley, David A.;Conroy, Jessica L.;Counts, Ron C.
北美洲中部拥有广泛的黄土矿床，已经用地球化学、矿物学和地层学技术进行了研究，以探索冰川历史和沉积物来源。这些分析主要集中在最后一次冰盛期(LGM)期间积累的黄土沉积，部分原因是无处不在的未风化的皮奥里亚粉砂沉积。我们测试了碎屑锆石(DZ)U-Pb测年的实用性，它提供了一种抗风化的方法来确定黄土的来源，并且可以唯一地应用于LGM和更古老的(通常是更多的蚀变)前LGM黄土单元。我们测定了密西西比州和伊利诺伊河流域黄土沉积的DZ U-Pb年龄分布(n=1385 U-Pb年龄)：得梅因、上等、绿湾、密歇根湖和休伦-伊利。我们还测量了位于伊利诺伊河流域和密西西比河流域悬崖边的黄土遗址的DZ U-Pb年龄分布(n=4466 U-Pb年龄)。样本采集自皮奥里亚粉土(威斯康星事件；海洋同位素阶段(MIS2))、罗克萨纳粉土(威斯康星州事件；MIS3)、洛夫兰泥沙(伊利诺伊州事件；MIS6)和克劳利的山脊粉土(伊利诺伊州事件前)。LGM冰川碎屑提供了明显的DZ年龄特征，可用于识别冰川对黄土沉积的贡献。伊利诺伊河流域的Peoria粉土和密西西比河流域北部的Roxana粉土中的黄土DZ年龄特征随古密西西比河的堵塞和撕裂而在时间上发生变化，代表了DZ黄土起源方法在中大陆的概念验证。黄土DZ记录还提供了对末次盛冰期前的水系网络和冰叶范围的洞察。密西西比河谷MI3Roxana粉砂的DZ特征表明，得梅因小叶的沉积物输入很少，这表明该小叶是短暂的，存在于更靠北的地方，或者在此期间只向融水山谷提供了有限的沉积物。贯穿末次盛冰期前黄土单元的主要休伦-伊利叶特征表明，来自东部拉布拉多穹顶的冰流在早期冰川期间是一个持久的特征。最后，在密西西比河流域中下游前MIS2黄土中的一些来自西方的DZ年龄表明，遵循现代密苏里河水系的水系网络在末次盛冰期之前就已经存在，并与密西西比河水系整合。
Midcontinental North America contains extensive loess deposits that have been studied with geochemical, mineralogical, and stratigraphic techniques to explore glacial history and sediment provenance. Much of this analysis has focused on loess deposits that accumulated during the last glacial maximum (LGM), in part because of the ubiquity of unweathered Peoria Silt deposits. We test the utility of detrital zircon (DZ) U–Pb dating, which offers a weathering-resistant approach to the determination of loess provenance and can uniquely be applied to both LGM and older (commonly more altered) pre-LGM loess units. We determined DZ U–Pb age distributions (n = 1385 U–Pb ages) for the lobes that contributed sediment to Mississippi and Illinois River valley loess: Des Moines Lobe, Superior Lobe, Green Bay Lobe, Lake Michigan Lobe and Huron-Erie Lobe. We also measured DZ U–Pb age distributions (n = 4466 U–Pb ages) sampled from loess sites located along the bluffs of the Illinois River Valley and Mississippi River Valley. Samples were collected from Peoria Silt (Wisconsin Episode; Marine Isotope Stage (MIS 2)), Roxana Silt (Wisconsin Episode; MIS 3), Loveland Silt (Illinois Episode; MIS 6), and Crowley's Ridge Silt (pre-Illinois Episode).LGM glacial tills provide distinct DZ age signatures that can be used to identify glacial source contributions to loess deposits. Loess DZ age signatures in the Peoria Silt of the Illinois River Valley and the Roxana Silt of the northern lower Mississippi River Valley change temporally in a manner consistent with blockage and avulsion of the ancient Mississippi River, representing a proof-of-concept for the DZ loess provenance method in the midcontinent. The loess DZ record also provides insight into the pre-LGM drainage network and glacial lobe extents. DZ signatures for the MIS 3 Roxana Silt, along the Mississippi Valley, implies minimal sediment input from the Des Moines Lobe, suggesting this lobe was short-lived, existed further northward, or provided only limited sediment to meltwater valleys during this time. The dominant Huron-Erie Lobe signature throughout pre-LGM loess units shows that ice flow from the eastern Labrador Dome was a persistent feature during earlier glaciations. Finally, some western-derived DZ ages in pre-MIS 2 loess of the middle and lower Mississippi River Valley suggests that drainage networks that followed the modern Missouri River system were present prior to the LGM and integrated with the Mississippi River system.