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Mid-Jurassic Age “Red Beds” of the Michigan Basin

A. T. Cross
Michigan State University, E. Lansing, MI

A series of yellow-tan to purplish-red stained sandstones and gypsum beds intercalated in red and greenish-grey shales in the west central Lower Peninsula of Michigan, is clearly identified by palynology as mid-Jurassic in age.

Palynomorphs of late-Mesozoic age in the Michigan “Red Beds” were first reported by Cross and Shaffer, 1964. Later studies in Canada and Europe have made more precise age determination and correlation possible. Presence of pollen of Classopollis in profusion and a diverse mix of podocarp, tsugoid, laricoid, araucarian, cycadeoid, and ginkgoalean pollen indicate Bajocian-Bathonian age.

The “Red Beds” are closely correlated with the Mistuskwia beds of the Moose River Basin of the James Bay Lowland, Ontario, based on pollen from test cores. The palynoflora is similar to that of the Shaunavon and Gravelbourg Formations, Saskatchewan and Alberta, and to Sawtooth and Rierdon Formations, northwestern Montana.

Quarries, and oil, gas and water wells in the vicinity of lonia and Lyons indicate the lonia Sandstone is the basal member of this Jurassic sequence. The “Red Beds” appear to have accumulated in a large, inland playa with internal drainage on a broad, structurally controlled, intermittently reactivated, shallow depression. Absence of acritarchs and dinoflagellates suggest a non-marine origin. However, a brief transgression of an epeiric sea through a northerly channel, and development of a sabkha-like environment on a broad coastal plain of low-relief might be considered.

AAPG Search and Discovery Article #90900©2001 AAPG Eastern Section Meeting, Kalamazoo, Michigan