Douglas Group

Interval includes Stranger, Cass, Lawrence formations. Primary Lithologies: shale and mudstone, light to dark gray, part silt laminated. Secondary Lithologies: limestone, fossiliferous, part coated grain; siltstone to very fine sandstone; pedogenic mudstone, part red-brown, part calcareous/nodular. Minor: coal, carbonaceous shale; black shale. Maximum thicknesses 90-135 ft (27-41 m).
State Iowa
Name Douglas Group
Geologic age Upper Pennsylvanian, upper Missourian-lower Virgilian
Lithologic constituents
Major
Sedimentary > Clastic > Mudstone (Bed, Calcareous, Carbonaceous)light to dark gray, part silt laminated; minor pedogenic mudstone, part red-brown, part calcareous/nodular; incidental carbonaceous shale
Sedimentary > Clastic > Mudstone > Shale (Bed)light to dark gray, part silt laminated
Minor
Sedimentary > Clastic > Siltstone (Bed)siltstone to very fine sandstone
Sedimentary > Carbonate > Limestone (Bed)fossiliferous, part coated grain
Incidental
Sedimentary > Clastic > Mudstone > Shale > Black-shale (Bed)
Sedimentary > Coal (Bed)
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
Counties Adair - Adams - Cass - Fremont - Madison - Mills - Montgomery - Pottawattamie - Ringgold - Taylor - Union