Ancell Group

Ancell Group, includes St. Peter Sandstone, Dutchtown Limestone, Joachim Dolomite, and Glenwood Formation; includes Prairie du Chien Group in Jo Daviess County of northwestern Illinois.
State Illinois
Name Ancell Group
Geologic age Middle Ordovician (Darriwillian) to Upper Ordovician (Stage 5)
Lithologic constituents
Sedimentary > Clastic > Sandstone (Bed)Sandstone can contain dunes, also can be shaly or argillaceous and conglomeratic at base.
Sedimentary > Carbonate > Dolostone (Bed)Dolomite can be cherty, sandy, or shaly or argillaceous.
Sedimentary > Carbonate > Limestone (Bed)Limestone can be cherty, sandy, or shaly or argillaceous.
Sedimentary > Chemical > Evaporite > Anhydrite (Bed)Gypsum or anhydrite.
Sedimentary > Chemical > Evaporite > Gypsum (Bed)Gypsum or anhydrite.
Comments Thickness from stratigraphic columns (from oldest to youngest): St. Peter Ss (75-350’), Dutchtown Ls (0-300’), and Joachim Dol (0-450’) in southern Illinois; St. Peter Ss (0-600’), Joachim Dol (0-50’), and Glenwood Fm (0-75’) in northern Illinois. St. Peter Ss is composed, from oldest to youngest, of the Kress Mbr, Tonti Mbr, and Starved Rock Mbr in northern Illinois (from strat. col.).
Stratigraphic units Kress Member, Tonti Member, and Starved Rock Member of the St. Peter Sandstone.

Kolata, D.R., comp., 2005, Bedrock Geology of Illinois: Champaign, Ill., Illinois State Geological Survey, Illinois Map Series 14, scale 1:500,000.

NGMDB product
Counties Boone - Calhoun - Carroll - DeKalb - Jo Daviess - Kendall - La Salle - Lee - Monroe - Ogle - Stephenson - Winnebago