RI-36 Paleozoic Lithostratigraphic Nomenclature for Minnesota

Abstract

Significant changes are made in stratigraphic nomenclature for the Paleozoic formations of Minnesota that reflect subsurface data acquired since 1969 and accord with changes in nomenclature in adjoining states. For the Cambrian section, dolostone that intertongues with the lower part of the Eau Claire Formation in the subsurface of south-central and southwestern Minnesota is interpreted to be a tongue of the Bonneterre Formation of northwestern Iowa. The Reno Member of the Franconia Formation, together with the Birkmose Member, is now interpreted to compose most of the formation, whereas the Tomah Member is now interpreted to have very restricted subsurface distribution; an additional dolostone member, here informally named the Davis, is recognized in the subsurface in south-central Minnesota. The uppermost member of the overlying Jordan Sandstone is here renamed the Coon Valley Member. For the Ordovician section, the Galena is now elevated to group status. The Cummingsville Formation, Prosser Limestone, and Stewartville Formation-formerly members of the Galena--now correspond in rank with their equivalents in adjoining states. In the Devonian sequence, formerly classified as entirely Cedar Valley Formation in Minnesota, the recently named Spillville Formation is recognized in the base of the sequence, and the Wapsipinicon Formation is now known to extend into Minnesota from Iowa. The name Cedar Valley is retained for the overlying Devonian rock unit.