Ordovician - Maquoketa Formation

Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
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Ordovician - Maquoketa Formation

The Maquoketa Formation underlies the Door Peninsula and the Silurian rocks of eastern Wisconsin and also occurs as outliers in southwestern Wisconsin. It consists of three members:

• Brainerd: bluish shaly dolostone
• Fort Atkinson: buff massive dolostone
• Scales: bluish shaly dolostone

The bluish color is due to volcanic ash. The source of the ash was the Appalachians, which were undergoing an orogeny at this time. The ash was carried by wind and currents and deposited on the sea floor.

The Green Bay and Lake Winnebago lowlands are the result of ice scouring away the soft Maquoketa rocks.

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Created 11 Sep 1997, Last Update 17 July 2003

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