Devonian of Ontario and Michigan

Abstract Platform-type sediments which comprise the Devonian System in Ontario and Michigan have an areal extent of 85,000 square miles including offshore regions of the Great Lakes — Michigan, Huron, and Erie. Their maximum development (3,400 feet) is in the lower structural part of the Michigan basin where they lie beneath a Carboniferous cover. Devonian rocks rise to surface in the adjoining region of Ontario, where they are generally less than 1,000 feet thick. Rocks of earliest Devonian age are for the most part absent, except for thin sandstone remnants of Siegenian age (Oriskany, A fairly complete Middle Devonian sequence is represented in Michigan and adjacent areas of Ontario. A lower division, of Eifelian age, consists of a variety of limestone, dolomite, and saline facies (Amherstburg, Lucas, and Dundee Formations) that are coeval with the Onondaga limestones of western New York State and eastern Lake Erie. Succeeding late Middle Devonian (Givetian) rocks consist mainly of limestone (Rogers City, Traverse) in western and central Michigan, grading eastward through alternating limestones and shales to predominantly marine shale facies (Hamilton) in the Ontario peninsula. The Upper Devonian (Frasnian, Famennian) sequence is composed of minor sandstone, siltstone, normal-marine and black shale facies. The latter prevails in Ontario and adjacent areas of Michigan (Kettle Point-Antrim, Bedford, Berea, Sunbury) and grades to dominant normal-marine shale facies on the western margine of the basin (Antrim, Ellsworth). Graden Island) preserved locally on an irregular Upper Silurian surface. Sandy and siliceous limestones (Bois Blanc) of late Early Devonian (Emsian) age have wide distribution and form the oldest Devonian strata throughout most of the area. Devonian rocks in this area are economically important as a source of petroleum, and provide raw material for the manufacture of a wide variety of structural products.