page_title: Jordan Formation
section_title: Overlying
hierarchical_section_title: Jordan Formation / Stratigraphy / Overlying
caption_attribution_description: English: An outcrop of late Cambrian and early Ordovician rocks in a roadcut at Miller's Curve, just to the west of Madison, Wisconsin. The Jordan sandstone is the light grey rock in the lower third of this outcrop, the Oneota (dolomitic carbonate) is the orange grey rock in the upper two thirds of the roadcut.
context_page_description: The Jordan Formation is a siliciclastic sedimentary rock unit identified in Illinois, Michigan, Wisconsin, Minnesota, and Iowa. 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.
  Stratigraphically, the Jordan Formation is the uppermost unit of the type St. Croixan Series. 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.
context_section_description: The Jordan is overlain by the Oneota Formation, a dolomitic carbonate unit of early Ordovician Age. The massive, well-cemented microbial carbonates of the Oneota Formation generally overlie several meters of sandy shale with calcareous interbeds referred to as Coon Valley or Stockton Hill Member. Although these beds have traditionally been allied with the Jordan Formation based on lithostratigraphic properties, but more recent sequence and biostratigraphic studies suggest it is more closely allied with the Oneota. The upper contact of the Jordan is interpreted to be a topographically complex, unconformable surface.
caption: An outcrop of late Cambrian and early Ordovician rocks in a road-cut at Miller's Curve, just to the west of Madison, Wisconsin. The Jordan sandstone is the light grey rock in the lower third of this outcrop, the Oneota (dolomitic carbonate) is the orange grey rock in the upper two thirds of the road-cut.
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