|Geologic age||Late Devonian|
Sedimentary > Clastic > Mudstone > Shale
Sedimentary > Clastic > Sandstone
|Comments||Secondary unit description from USGS Geologic Names lexicon (ref. MI016): Bedford Shale and Berea Sandstone are not exposed in MI. They record, in the subsurface, a southwestward growth of a deltaic system into the Antrim sea during Kinderhookian time. The Bedford Shale is a bluish to light gray, silty shale that becomes sandy in its upper part and has a gradational contact with the overlying Berea Sandstone. It is commonly 15 to 30 m thick and thins and becomes fine grained to the west, where it intertongues with the Antrim. Reaches a maximum thickness of 76 m in the Michigan thumb area.|
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 found at: http://ngmdb.usgs.gov/Geolex/
|Counties||Alcona - Antrim - Lenawee - Livingston - Macomb - Montmorency - Oakland - Oscoda - Otsego - Saint Clair - Sanilac - Washtenaw - Wayne|