Glenwood Shale

Glenwood Shale
Stratigraphic range: Ordovician
Type	Formation
Underlies	Platteville Formation
Overlies	St. Peter Sandstone
Location
Country	United States
Extent	Minnesota

Paleozoic Stratigraphy of the Upper Midwest, USA
Dates approximate
Maquoketa Group (446–440 Ma)
Galena Group (454–446 Ma)
Dubuque Formation (447–446 Ma) Wise Lake Formation (449.4–447 Ma) Decorah Shale (454–452 Ma)
Platteville Limestone (455–454 Ma)
Glenwood Shale (~455 Ma)
St. Peter Sandstone (~459–~455 Ma)
Knox Unconformity (~470-~459 Ma)
Knox Supergroup (~497-~470 Ma)
Everton Dolomite Shakopee Dolomite Oneota Dolomite Jordan Sandstone Potosi Dolomite Potsdam Sandstone Munising Formation Davis Formation Franconia Formation Ironton Sandstone Galesville Sandstone Eau Claire Formation Mount Simon Sandstone
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The Glenwood shale cropping out in Minneapolis, Minnesota. In this photo, it is the thin, darker layer that lies between the Platteville Limestone (above: the less-eroded, layered unit that constitutes the majority of the photo) and the St. Peter Sandstone (below: a thin, white stripe of in-place rock followed by a slope of eroded St. Peter Sandstone material).

The Glenwood Shale is a thin Ordivician shale formation in the sedimentary sequence characteristic of the upper Midwestern United States.

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.