A Holocene record of endogenic iron and manganese precipitation and vegetation history in a lake-fen complex in northwestern Minnesota
A Holocene record of endogenic iron and manganese precipitation and vegetation history in a lake-fen complex in northwestern Minnesota
复制标题
明尼苏达州西北部湖沼复合体内生铁和锰降水和植被历史的全新世记录
作者：
W. Dean;L. Doner
小新戈比湖和芬是明尼苏达州西北部新戈比河源头沃茨中广泛的湖泊和湿地网络的一部分，旨在研究地表和地下沃茨之间的相互作用。在11.2卡之前。ka，这些湖泊和湿地中的大多数相互连接，形成了冰川湖Willobee，这显然是当泥石流阻塞了Shingobee河时形成的。在11.2和8.5口径之间。卡，威洛比湖的水平下降，由于大坝的破坏，将深湖变成现有的湖泊和湿地。小Shingobee湖（LSL-B）的9米的核心和湖泊沉积物下的3.3米的泥炭在17米的核心小Shingobee芬（LSF-10）的分析表明，主要成分是外来的碎屑物质，内生碳酸钙和有机质。在这两个核心几乎所有的铁（Fe）和锰（Mn）被纳入内生矿物，被认为是X-射线无定形羟基氧化物矿物，发生在整个核心的显着数量;几乎没有铁和锰的贡献碎屑铝硅酸盐矿物。这表明，在全新世的大部分时间里，湖泊化学的外来流域贡献较小的溶解矿物负荷相比。此外，在3.5口径之前，ka，花粉带的边界相吻合的湖泊沉积物矿物学的大的变化，表明景观和气候过程与早，中全新世湖泊化学。花粉的时间序列，依次占主导地位的云杉，松树，山艾树橡树，桦树橡树，最后，白松是该地区的典型，反映了随着时间的推移，草原森林过渡区的位置变化。植被的这些变化对湖泊沃茨的地球化学产生了深远的影响。
Little Shingobee Lake and Fen are part of the extensive network of lakes and wetlands in the Shingobee River headwaters of northwestern Minnesota, designed to study the interactions between surface and ground waters. Prior to about 11.2 cal. ka, most of these lakes and wetlands were interconnected to form glacial Lake Willobee, which apparently formed when a debris flow dammed the Shingobee River. Between 11.2 and 8.5 cal. ka, the level of Lake Willobee fell as a result of breaching of the dam, transforming the deep lake into the existing lakes and wetlands. Analyses of a 9-m core from Little Shingobee Lake (LSL-B), and lacustrine sediments under 3.3 m of peat in a 17-m core from Little Shingobee Fen (LSF-10), show that the dominant components are allogenic clastic material, and endogenic CaCO3 and organic matter. In both cores almost all of the iron (Fe) and manganese (Mn) are incorporated in endogenic minerals, presumed to be X-ray amorphous oxyhydroxide minerals, that occur in significant quantities throughout the cores; almost no Fe and Mn are contributed from detrital aluminosilicate minerals. This suggests that, for most of the Holocene, the allogenic watershed contributions to lake chemistry were minor compared to the dissolved mineral load. In addition, prior to 3.5 cal. ka, pollen zone boundaries coincide with large changes in lake-sediment mineralogy, indicating that both landscape and climate processes were linked to early- and mid-Holocene lake chemistry. The pollen time series, with sequential domination by spruce, pine, sagebrush-oak, birch-oak and, finally, white pine is typical of the region and reflects the changing location of the prairie-forest transition zone over time. These changes in vegetation had some profound effects on the geochemistry of the lake waters.