Cambrian and Ordovician Rocks in Recent Wells in Southeastern Michigan

Abstract

All of the wells drilled to pre-Cambrian rocks in the Southern Peninsula of Michigan are located in five counties in the southeastern part of the state bordering the province of Ontario, Canada. The depth to pre-Cambrian in this area ranges from 3,300 feet in Lenawee County to 6,400 feet in Washtenaw County. The thickness of Middle Ordovician rocks penetrated in these wells varies from 660 feet in Lenawee County to 965 feet in St. Clair County and Upper Ordovician rocks from 585 feet in Washtenaw County to 750 feet in Lenawee County. Lower Ordovician rocks have not been found east of Livingston County. A well drilled on the Howell anticline, near the center of Livingston County, drilled 40 feet of St. Peter sandstone and was abandoned without penetrating the entire thickness of the sandstone. Small areas of commercial oil production occurring in the upper part of the dolomitized Trenton limestone of Middle Ordovician age have been found in Lenawee, Monroe, and Wayne counties, and oil is produced from Middle Orodvician rocks in Kent County, southwestern Ontario. Rocks of Upper Cambrian age underlie Middle Ordovician rocks and rest on pre-Cambrian rocks in a large part of southeastern Michigan. The thickness of Cambrian rocks varies from 1,160 feet in Washtenaw County to 140 feet in St. Clair County. This variation in thickness is due to the unconformity at the base of Middle Ordovician rocks which was brought about by uplift and erosion at the close of Lower Ordovician time. Cambrian rocks are missing in parts of Kent, Lambton, and other counties in southwestern Ontario, and in these places Middle Ordovician rocks overlie pre-Cambrian rocks. Showings of gas have been reported from the upper part of the Mount Simon sandstone, of Upper Cambrian age, in some of the wells in southeastern Michigan and showings of oil and gas have been found in Cam rian rocks in some wells in parts of southwestern Ontario where these rocks are present.