Eau Claire Formation

Subcrops beneath Mississippi River alluvium in Allamakee County; surface exposures absent. Primary lithologies: sandstone, very fine to fine grained, part argillaceous; shale, silty, gray to green-gray, part glauconitic. Secondary lithology: siltstone, part argillaceous, part dolomitic. Minor: dolomite. Thicknesses: 120-145 ft (37-44 m).
State Iowa
Name Eau Claire Formation
Geologic age Middle Cambrian, upper Marjuman (formerly Dresbachian)
Lithologic constituents
Sedimentary > Clastic > Sandstone (Bed)very fine to fine grained, part argillaceous
Sedimentary > Clastic > Mudstone > Shale (Bed, Glauconitic)silty, gray to green-gray, part glauconitic
Sedimentary > Clastic > Siltstone (Bed)part argillaceous, part dolomitic
Sedimentary > Carbonate > Dolostone (Bed)

Witzke, Brian J., Anderson, Raymond R., and Pope, John P., 2010, Iowa Geological and Water Survey, DNR, Bedrock Geologic Map of Iowa, OFM-2010-1. Scale 1:500,000.

NGMDB product
Counties Allamakee