The Pennsylvanian Pewamo Formation and associated Haybridge strata; toward the resolution of the Jurassic Ionia red bed problem in the Michigan Basin, U.S.A.

Two distinct and newly recognized, formation-scale stratigraphic units, predominantly red-bed sandstones and shales, are found on the surface and in the shallow subsurface of the central Michigan region. Here, we use core, field, and laboratory observations to document these strata, which we propose as one new formation, the Pewamo Formation. The Pewamo Formation consists of eolian quartz sandstones with red coloration due to iron-oxide diagenesis, and interbedded interdune lacustrine siliciclastic mudstones. We also describe for the first time the Haybridge strata, which contains red sandstones, red and gray shales, and coal, and has plant fossils and paleosol features. Macroscopic plant fossils and palynomorphs suggest a Pennsylvanian age for both units. These newly described continental deposits provide data about past environments, life, and climate for the late Carboniferous of Michigan. In addition, this study is an evaluation of Michigan's controversial "Jurassic red beds" and "Ionia sandstone."