Magnetic Susceptibility and Mineral Zonations Controlled by Provenance in Loess along the Illinois and Central Mississippi River Valleys
Magnetic Susceptibility and Mineral Zonations Controlled by Provenance in Loess along the Illinois and Central Mississippi River Valleys
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DOI：
10.1006/qres.1997.1947
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发表时间：
1998-01
影响因子：
2.3
通讯作者：
D. Grimley;L. Follmer;E. Mckay
中科院分区：
文献类型：
--
作者：
D. Grimley;L. Follmer;E. Mckay
磁化率（MS）模式已被证明对沿伊利诺斯州和中密西西比河流域超过350公里的厚层氧化皮奥里亚和罗克萨纳粉砂带的区域地层对比是有用的。C层黄土的MS变化受粉粒大小的磁铁矿含量控制，并被解释为反映沉积物来源的变化，这是由于苏必利尔湖和密歇根湖冰川裂片的波动以及密西西比河改道到现在的河道。粒度分布和扫描电镜观察表明，MS的地层变化分别不受风成分选和成岩溶蚀的显著影响。在皮奥里亚淤泥中划分了三个组成带（下、中、上），通常可以通过质谱、粘土层的发生、层间土壤和/或细微的颜色变化在野外进行追踪。这些带可以与先前研究的白云岩带（McKay, 1977）或粘土矿带（Frye et al.,1968）相关联，但通常比它们更有实际用途。然而，矿物学分析可以帮助确定有问题的带边界。MS和成分带可能间接记录气候信号，主要是通过全球变冷对密西西比河上游流域冰瓣波动的影响。
Magnetic susceptibility (MS) patterns have proven useful for regional stratigraphic correlations of zones within thick, oxidized Peoria and Roxana Silts along the Illinois and Central Mississippi River valleys for more than 350 km. Variations in MS of C horizon loess are controlled by silt-sized magnetite content and are interpreted to reflect changes in sediment provenance due to fluctuations of the Superior and Lake Michigan glacier lobes and the diversion of the Mississippi River to its present course. Grain size distributions and scanning electron microscopic observations indicate that stratigraphic changes in MS are not significantly influenced by eolian sorting or diagenetic dissolution, respectively. Three compositional zones (lower, middle, and upper) are delineated within Peoria Silt which usually can be traced in the field by MS, the occurrence of clay beds, interstadial soils, and/or subtle color changes. These zones can be correlated with, but are generally of more practical use than, previously studied dolomite zones (McKay, 1977) or clay mineral zones (Frye et al.,1968). However, mineralogical analyses can help to substantiate zone boundaries when in question. MS and compositional zones may indirectly record a climatic signal, primarily through the effect that global cooling has had on ice lobe fluctuations in the Upper Mississippi drainage basin.