Detroit River Group (MIDdr;0)

State	Michigan
Name	Detroit River Group
Geologic age	Middle Devonian
Original map label	Ddr
Comments	Secondary unit description from USGS Geologic Names lexicon (ref. MI016): Named the Detroit River dolomite in southeastern MI, western Ontario, CAN, and northern OH for the Detroit River. Includes (ascending) Flat Rock dolomite (40 to 150 feet thick), Anderdon limestone (40 to 50 feet thick), Amherstburg dolomite (20 feet thick), and Lucas dolomite (200 feet thick) members. Disconformably overlies Sylvania sandstone. The Detroit River is of Devonian age. Revised the Detroit River to the Detroit River group. Includes the Sylvania sandstone at base. Maximum thickness is 1,000 feet in wells in central part of Southern Peninsula of MI; outcrop thickness commonly less than 200 feet.
Primary rock type	dolostone (dolomite)
Secondary rock type	limestone
Other rock types	sandstone
Lithologic constituents	Major Sedimentary > Carbonate > Dolostone (Bed) Minor Sedimentary > Carbonate > Limestone (Bed) Incidental Sedimentary > Clastic > Sandstone (Bed)Revised the Detroit River to the Detroit River group. Includes the Sylvania sandstone at base.
Map references	Milstein, Randall L. (compiler), 1987, Bedrock geology of southern Michigan: Geological Survey Division, Michigan Dept. of Natural Resources, scale= 1:500,000
Unit references	Milstein, Randall L. (compiler), 1987, Bedrock geology of southern Michigan: Geological Survey Division, Michigan Dept. of Natural Resources, scale= 1:500,000 USGS Geologic Names Lexicon (GEOLEX) [http://ngmdb.usgs.gov/Geolex/]
Geographic coverage	Charlevoix - Cheboygan - Emmet - Leelanau - Lenawee - Monroe - Presque Isle - Washtenaw - Wayne