Cedar Valley Group (IADc;0)

Cedar Valley Group

Interval includes Little Cedar, Coralville, Lithograph City, and Shell Rock formations; Shell Rock Fm in northern Iowa only. Primary Lithologies: limestone, fossiliferous, variably argillaceous, part biostromal; dolomite, part fossil-moldic to vuggy, variably argillaceous. Secondary Lithologies: limestone, dense, “sublithographic”; dolomite/limestone breccia (evaporite collapse); limestone, sparse to unfossiliferous, argillaceous to shaly; shale, gray to green-gray, dolomitic. Minor: anhydrite/gypsum (outcrop belt only in Grundy, Tama, Poweshiek counties; extensive in subsurface of central and southern Iowa); chert; glauconite; sandy limestone/sandstone. Maximum thicknesses in outcrop belt: southeast Iowa, 80-135 ft (24-41 m); east-central Iowa 130-210 ft (40-64 m); northern Iowa 250-350 ft (76-107 m). Cedar Valley Group thins and is overstepped by Dl westward in Winnebago County.

State	Iowa
Name	Cedar Valley Group
Geologic age	Middle-Upper Devonian, middle Givetian-middle Frasnian
Lithologic constituents	Major Sedimentary > Carbonate > Dolostone (Bed)part fossil-moldic to vuggy, variably argillaceous Sedimentary > Carbonate > Limestone (Bed)fossiliferous, variably argillaceous, part biostromal; minor dense, “sublithographic”; minor sparse to unfossiliferous, argillaceous to shaly; incidental sandy limestone/sandstone Minor Sedimentary > Clastic > Mudstone > Shale (Bed)gray to green-gray, dolomitic Sedimentary > Clastic > Sedimentary-breccia (Bed, Calcareous)dolomite/limestone breccia (evaporite collapse) Incidental Sedimentary > Chemical > Chert (Bed) Sedimentary > Chemical > Evaporite > Anhydrite (Bed)anhydrite/gypsum (outcrop belt only in Grundy, Tama, Poweshiek counties; extensive in subsurface of central and southern Iowa)
References	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	NGMDB product page for 96753
Counties	Benton - Black Hawk - Bremer - Buchanan - Butler - Cedar - Cerro Gordo - Chickasaw - Delaware - Des Moines - Fayette - Floyd - Grundy - Hancock - Howard - Iowa - Jackson - Johnson - Jones - Linn - Louisa - Mitchell - Muscatine - Poweshiek - Scott - Tama - Washington - Winnebago - Winneshiek - Worth

Cedar Valley Group

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.