Odom, J. Edgar
M.S. (Master of Science)
Department of Geology
Samples from five cores plus supplementary well logs were used to determine the lithology and mineralogy of Cambrian strata in eastern Iowa. In northeastern Iowa, the Cambrian consists primarily of sandstones lithologically similar to the type Cambrian in Wisconsin and Minnesota, while in southern Iowa the Cambrian strata above the basal Mt. Simon Sandstone contain primarily dolomite, shale, and siltstone as in the type Cambrian of the Ozark region. In central Iowa, the Cambrian strata above the Mt. Simon Sandstone and below the Momence Sandstone or the Eminence Dolomite consist predominantly of siltstone and dolomite. The Mt. Simon Sandstone throughout Iowa has a consistent lithologic character similar to the Mt. Simon in Wisconsin. In central Iowa, the sandstones typical of the Eau Claire Formation in Wisconsin and northeastern Iowa are restricted to the top and bottom portions of the formation, while siltstone and shale dominate the central portion. In southern Iowa, the Eau Claire elastics pass into carbonates and shales of the Bonneterre Formation. The superjacent Wonewoc Sandstone thins from north to south, and in central Iowa it passes into siltstones and very fine-grained, glauconitic sandstones which stratigraphically are assigned to the Lone Rock Formation. In northeastern Iowa, the Lone Rock Formation is lithologically similar to the type Lone Rock Formation of Wisconsin but in central Iowa this formation is predominantly siltstone with interbeds of shale and sandstone. This lithology is in turn replaced by siltstones, shales, and carbonates of the Davis Formation in southern Iowa. The St. Lawrence Formation is predominantly dolomite throughout Iowa although the Lodi Siltstone Member becomes more prevalent to the north. The Jordan Sandstone splits into a lower Momence Sandstone and an upper Gunter Sandstone separated by the sandy dolomites equivalent to the Eminence Formation. The Gunter is believed to be equivalent to the dolomitic sandstones at the base of the Ordovician Oneota Formation in Wisconsin and Minnesota. Quartz, K-feldspar, carbonate, glauconite, and clay minerals comprise the bulk of the Cambrian sediments in the study area. The percentage of feldspar is related to grain size, increasing with decreasing size through very fine sand then decreasing again in the silt size. Variations in the abundance of essential minerals are used to define seven mineralogical facies. Most of the Cambrian sediments in Iowa are thought to have been deposited in one of four marine environments: nearshore, inner shelf, outer shelf, or carbonate reef. The basal sands of the Mt. Simon Formation, however, were probably deposited in a fluvial environment. The geographic distribution of the sediments deposited in these different environments is related to transgression and regression of the Cambrian seas over the craton.
Flurkey, Andrew J., "The mineralogy and sedimentology of the Cambrian strata of eastern Iowa" (1976). Graduate Research Theses & Dissertations. 6008.
vi, 122 pages
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