Glenwood Shale

Paleozoic Stratigraphy of the Upper Midwest, USA Dates are approximate, and deposition occurred at slightly different times in different areas This box:

Ordovician :Maquoketa Group (446–440 Ma) ::Neda Formation Brainard Formation Fort Atkinson Formation Scales Formation :Galena Group (454–446 Ma) ::Dubuque Formation (447–446 Ma) Wise Lake Formation (449.4–447 Ma) Dunleth Formation (452–449.4 Ma) Decorah Shale (454–452 Ma) Platteville Limestone / Group (455–454 Ma) Ancell Group (454–455 Ma) Glenwood Shale (~455 Ma) St. Peter Sandstone (~459–~455 Ma) --- Major Erosional Unconformity --- :Knox Supergroup ::--- Major Erosional Unconformity --- Everton Dolomite (only in S. Indiana) --- Major Erosional Unconformity --- Dunleth Formation Prairie du Chien Group * Shakopee Dolomite * New Richmond Sandstone (only in S. Indiana) * Oneota Dolomite * Dunleth Formation * Gunter Sandstone Cambrian :Knox Supergroup (ct'd) ::Jordan Sandstone Potosi Dolomite Potsdam Supergroup/Potsdam Sandstone Megagroup Munising Group Davis Formation Franconia Formation Ironton Sandstone Galesville Sandstone Eau Claire Formation Mount Simon Sandstone

Cambrian

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.

University of Minnesota: River Bluffs homepage

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