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Jordan Formation
The Jordan Formation (also classified as the Jordan Sandstone or the Jordan Member of the Trempealeau Formation) is a siliciclastic sedimentary rock unit identified in Illinois, Michigan, Wisconsin, Minnesota, and Iowa.〔(【引用サイトリンク】title= Jordan Sandstone )〕 Named for distinctive outcrops in the Minnesota River Valley near the town of Jordan it extends throughout the Iowa Shelf and eastward over the Wisconsin Arch and Lincoln anticline into the Michigan Basin.〔(【引用サイトリンク】title= Jordan Sandstone )〕
Stratigraphically, the Jordan Formation is the uppermost unit of the type St. Croixan Series (historically, the uppermost subdivision of the Cambrian in North America). It is predominantly composed of mature, poorly cemented quartz sandstone, though several distinct facies have been identified on the basis of grain size, feldspathic content, and sedimentary structures.
The Jordan is an important source of silica. Historically, the unit has been mined extensively for glass manufacturing, though recently it has been utilized as a source of frac sand. This porous, poorly cemented stratum is also an important aquifer and a major source of drinking water for people throughout the upper Midwest.
==Definition and History==
The earliest references to strata now referred to as Jordan were made by many of the pioneering geologists of the upper Midwest. In an 1852 report on the geology of Wisconsin, Iowa, and Minnesota, D. D. Owen assigned it to the uppermost part of his “Lower Sandstone” (the “Upper Sandstone” referring to what is now called the St. Peter). The term Jordan Sandstone was first applied in 1874 by N. H. Winchell, who based his description on exposures in a quarry near Jordan, Minnesota.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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