West of Chamberlain travelers notice a “black streak” (informally the “Oacoma Zone”) running through the Pierre Shale, actually the DeGrey Member of the Pierre. The “black streak” is un-vegetated and many people assume the pasture and roadside has burned. However, this “streak” has a high abundance of manganese, especially in numerous nodules, and this element seems toxic to vegetation. These nodules were mined “by hand” in the 1930’s and shipped to Pittsburg, PA, by rail for processing and use in the steel industry (www.library.thinkquest.org). The federal government became interested in the resource and in 1930 geologists from U. S. Geological Survey estimated the resource contained 102,000,000 tons of metallic manganese (Hewett, 1930). In 1941, due to a need for hardened steel in World War II, the U. S. Bureau of Mines constructed a pilot plant (near mile marker 257 north side of highway) and began experimenting in mining and separation of the nodules from the shale (Cox and Beach, 1980). The mine closed in 1947 after the war. There have been periodic studies since that time, but no additional mining, as geologists, at present, do not believe a viable market exists for the manganese nodules (Cox and Beach, 1980). One may still observe remains of this interesting old mine.
|LARGE BURROW PARALLEL TO BEDDING PLANE, PERHAPS FROM A CRAB. THE KNOBBY SURFACE REPRESENTS VERTICAL BURROWS, PERHAPS FROM ACTIVITY BY WORMS.|
The Missouri River Trench is a major topographic and geologic structure trending mainly north-south in the center of South Dakota until the river abruptly turns east and then forms the boundary with Nebraska. The Cretaceous Pierre Shale is well exposed along the entire trench, and in many places the underlying Niobrara Formation crops out. In fact, the type section (where it was named) of the Niobrara is along the bluffs west of Yankton near the Niobrara River. In the central part of the state the Pierre Shale has a type section along the River near the capitol of Pierre. Many readers are familiar with these two formations if they have traveled along I-90 and crossed the river at Chamberlain. The view of the river and the rocks is spectacular, especially if traveling from east to west.
Many of the nodules are fossiliferous, including both body fossils and trace fossils. I recently stopped at a locality along the Missouri River and noticed a really nice burrow, perhaps a crab, well displayed on the bedding plane surface. In addition, numerous perpendicular structures represent activity by "worms".
Cox, L. J. and R. A., Beach 1980, Status of Mineral Resource Information for the Lower Brule Indian Reservation, South Dakota: Bureau of Indian Affairs Report 74.
Hewett, D. F., 1930, Manganese-iron Carbonate near Chamberlain, South Dakota: U. S. Geological Survey Memorandum for the Press, February 5, 1930 (noted in Cox and Beach, 1980).
|MANGANESE NODULES AND THE MANGANESE-RICH ZONE, PIERRE SHALE|