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Abstract: The Ionia Formation: New Designation for the Mid-Jurassic Age "Red Beds" of the Michigan Basin

Michigan State University, East Lansing, MI

A sequence of sandstones of yellowish-tan, purplish-red stained sandstones and gypsum beds intercalated in soft, reddish shales, long known as the "Michigan Red Beds", in the west-central Lower Peninsula of Michigan, is clearly identified by palynological analysis as mid-Jurassic (Bajocian-Bathonian) age. This stratigraphic sequence, about 0-60m thick, was rarely exposed in small quarries of Ionia Sandstone near low water level along the Grand River between Ionia and Lyons, Ionia County. It is penetrated by numerous water, oil and gas wells. It generally overlies the Pennsylvanian age Grand River or Saginaw Formations unconformably and is overlain by Pleistocene-Recent glacial deposits. This sequence of sandstone, red shales, and gypsum is here named the Ionia Formation. The Ionia Formation is correlated palynologically with the "Mistuskwia Beds" in two test cores, Moose River Basin, James Bay Lowland, Ontario. The palynoflora is similar to that of the Shaunavon and Gravelbourg Formations of western Saskatchewan, and to the Sawtooth and Rierdon Formations of northwestern Montana. Extensive study of the lithology, thickness and extent of the Ionia Formation has recently been completed by the U. S. Geological Survey.

AAPG Search and Discovery Article #90930©1998 AAPG Eastern Section, Columbus, Ohio