Updated Isopach Maps of Prairie du Chien, Trempealeau, and Munising of Michigan Basin

Robert V. Brady, Ronald J. Dehaas

As part of an ongoing project concerning the Lower Ordovician and Cambrian sections of the Michigan basin, consistent correlations from modern electrical logs have been used to develop structural and isopach maps of the Prairie du Chien, Trempealeau, and Munising of the Michigan basin.

The Prairie du Chien is subdivided into the upper Bruggers sandstone, the middle Foster formation, and the lower Umlor formation. The Bruggers is thickest in the area of the common boundary between Kalkaska, Crawford, Missaukee, and Roscommon Counties. The Foster and Umlor are thickest in Gladwin County.

The Trempealeau is thickest in the area of the common boundary between Bay, Midland, and Gladwin Counties. A secondary area of thickening also occurs in the extreme southwest, toward Berrien County.

The Munising Formation is thickest toward the southeast, despite the fact that it is entirely truncated by an erosional unconformity in extreme southeastern Michigan. An area of secondary thickening is present in the central basin, near Missaukee and Clare Counties.

AAPG Search and Discovery Article #91041©1987 AAPG Eastern Section Meeting, Columbus, Ohio, October 7-10, 1987.