A New Core of Shallow Red Beds from the Michigan Basin
The red beds of the Michigan Basin have been an enigma to sedimentologists and stratigraphers for decades. A core drilled in July 2008 in Lyons, Michigan has yielded 78 feet of shallow red sandstones that provide new data. Field work at abandoned, overgrown sandstone quarries supplements the core data. The core is composed primarily of very well-sorted quartz sandstone of variegated red, yellow, and orange coloration. This sandstone is characterized by highly spherical and frosted grains of bimodal grain size distribution. Larger sedimentary features include abundant high-angle cross-bedding, reactivation surfaces, and wind ripple lamina. Rare massive sandstones are coarser-grained. Thinner and less common units of black, gray, and red fine sand and silt contain laminations, mudcracks, burrows, and soft-sediment deformation. Our preliminary interpretation is that this core represents a semi-arid continental environment dominated by eolian processes. The sedimentologic characteristics are suggestive of dunes and interdune lakes. Extensive iron-oxide diagenesis is indicated by hematite cements, iron concretions, and Liesegang bands. To date, we have found no definitive age indicators in these rocks, although they seem to lie unconformably above the Pennsylvanian Saginaw Formation. We informally call this new rock the Pewamo sandstone. It may be associated with the Haybridge formation, a shallow unit elsewhere in the Michigan Basin composed of red sandstones, red shales with late Paleozoic plant fossils, and coal. These new findings support the need for a shallow drilling program to better characterize lithology, define aquifers, and interpret geologic history of Michigan.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009