Bronson Group

Interval includes Pleasanton, Hertha, Elm Branch, Swope, Galesburg, Dennis formations. Primary Lithologies: limestone, fossiliferous; shale/mudstone, light to dark gray. Secondary lithologies: mudstone to siltstone, gray to green-gray; limestone, coated grain. Minor: black shale, phosphatic; red/maroon mudstone; coal; chert. Maximum thicknesses 100-130 ft (30-40 m).
State Iowa
Name Bronson Group
Geologic age Middle to Upper Pennsylvanian, uppermost Desmoinesian-lower Missourian
Lithologic constituents
Major
Sedimentary > Carbonate > Limestone (Bed)fossiliferous; minor coated grain
Sedimentary > Clastic > Mudstone > Shale (Bed)shale/mudstone, light to dark gray; incidental red/maroon
Minor
Sedimentary > Clastic > Mixed-clastic > Siltstone-mudstone (Bed)mudstone to siltstone, gray to green-gray
Incidental
Sedimentary > Chemical > Chert (Bed)
Sedimentary > Clastic > Mudstone > Shale > Black-shale (Bed)phosphatic
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 - Appanoose - Audubon - Cass - Clarke - Dallas - Decatur - Guthrie - Harrison - Madison - Mills - Pottawattamie - Ringgold - Shelby - Union - Wayne