Provenance of middle to late Pleistocene tills in Illinois, U.S.A.: evidence for long-distance (∼ 2000 km) ice transport during two successive glaciations

IF 2 4区 地球科学 Q1 GEOLOGY
D. Malone, D. Grimley, Jennifer N. Gifford, P. M. Colgan, J. Craddock, Andrew C. Phillips, Paul A. Meister, Theodor H. Lowe, Ellyn S. Rickels
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Abstract

Zircons extracted from 567 granitic cobbles, in middle to late Pleistocene tills of the Lake Michigan Lobe in Illinois, provide a remarkably consistent Archean age of ∼ 2.7 Ga, with 87% dating between 2.6 and 2.8 Ga. This finding suggests a persistent glacial flow path of the southern Laurentide ice sheet from the Superior Province into the Lake Michigan basin during Marine Isotope Stage 6 (Illinois Episode) and Marine Isotope Stage 2 (Wisconsin Episode). Based on published crystalline bedrock ages in the Canadian Shield, these cobbles are interpreted to have been transported as much as ∼ 2000 km southwestward from the Quebec–Labrador ice dome, east of Hudson Bay, to the ice-sheet terminus in central to southern Illinois, USA. Some of the glacial flow likely skirted eastern Hudson Bay (source of Omar erratics) and southern James Bay, and traversed outcrops of Huronian jasper conglomerate and diamictite along the north shore of Lake Huron. Transport across the Paleozoic strata may have been enhanced, in part, by an ice stream that advanced across relatively soft and water-saturated sediments that underlie the Lake Michigan basin. The Lake Michigan basin, although present earlier in some form, was likely significantly eroded and overdeepened by accelerated glacial flow and erosion during MIS-6, further constraining the southern Laurentide Ice Sheet (LIS) flow path and influencing its subsequent flow during the last glaciation. As the Lake Michigan Lobe thinned and radiated out from the Lake Michigan basin, topographic effects led to separation of sublobes during the LIS advance to its southernmost extent.
美国伊利诺斯州中晚更新世碛物的来源:两个连续冰期期间长距离(~ 2000公里)冰运输的证据
在美国伊利诺斯州密西根湖湖区的中晚更新世斜坡中,从567块花岗岩鹅卵石中提取的锆石提供了一个非常一致的太古宙年龄- 2.7 Ga, 87%的锆石年龄在2.6 - 2.8 Ga之间。这一发现表明,在海洋同位素阶段6(伊利诺伊期)和海洋同位素阶段2(威斯康星期)期间,南劳伦泰德冰盖从苏必利尔省进入密歇根湖盆地存在持续的冰川流动路径。根据加拿大地盾中已公布的结晶基岩年龄,这些鹅卵石被解释为从哈德逊湾以东的魁北克-拉布拉多冰穹向西南运输了约2000公里,到达美国伊利诺伊州中部至南部的冰盖终点。一些冰川流可能沿着哈德逊湾东部(奥马尔不稳定岩的来源)和詹姆斯湾南部,并沿着休伦湖北岸穿过休伦湖碧玉砾岩和辉晶岩的露头。在某种程度上,穿越古生代地层的运输可能是由于一条冰流穿过密歇根湖盆地下面相对较软且水饱和的沉积物而加强的。密歇根湖盆地虽然以某种形式较早出现,但在MIS-6期间可能受到加速的冰川流动和侵蚀的严重侵蚀和过度加深,进一步限制了南劳伦泰德冰盖(LIS)的流动路径,并影响了其在末次冰期期间的后续流动。随着密歇根湖裂片变薄并从密歇根湖盆地向外辐射,地形效应导致了在LIS向其最南端推进过程中亚裂片的分离。
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来源期刊
CiteScore
3.80
自引率
5.00%
发文量
50
审稿时长
3 months
期刊介绍: The journal is broad and international in scope and welcomes contributions that further the fundamental understanding of sedimentary processes, the origin of sedimentary deposits, the workings of sedimentary systems, and the records of earth history contained within sedimentary rocks.
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