Stratigraphic range: Ordovician
|Overlies||St. Peter Sandstone|
|Paleozoic Stratigraphy of the Upper Midwest, USA|
Dates are approximate, and deposition occurred at slightly different times in different areas
It lies under the Platteville Limestone and above the Saint Peter Sandstone. Together, these three units represent a sequence of sea-level rise during Ordovician time. Because it is often very thin (~10 cm or less in the Twin Cities), it is often ignored in the general stratigraphy.
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