Dakota Formation widespread in western Iowa, lower sandstone-dominated Nishnabotna Member, upper mudstone/shale-dominated Woodbury Member. Correlative Windrow Formation found as erosional outliers in northeastern and north-central Iowa. Primary lithologies: sandstone, quartzose, very fine to medium grained; mudstone/shale, light to dark gray, variably silty-sandy, noncalcareous (Woodbury Mbr.). Secondary lithologies: sandstone, medium to very coarse grained, part pebbly to gravelly, locally cemented by iron oxides (Nishnabotna Mbr., Windrow Fm.), gravel, quartz and chert clasts; siltstone; mudstone, red, pink, yellow-brown, black (carbonaceous). Minor: lignite; siderite (concretions, pedogenic sphaerosiderite pellets, cemented siltstone); massive iron ore, silty to sandy (Windrow Fm.). Maximum thickness Dakota Fm. 500 ft (150 m), commonly 100-300 ft (30-90 m); Windrow Fm. 40 ft (12 m).
Interval includes Morgan School, Mouse Creek, Labette, Pawnee, Bandera, Altamont, Nowata, Lenapah, Memorial, Lost Branch formations. Primary Lithologies: shale/mudstone, light to dark gray; limestone, fossiliferous. Secondary Lithologies: mudstone, green-gray to red/maroon; shale, black, phosphatic; sandstone, very fine to medium grained. Minor: coal; siltstone, conglomerate. Maximum thicknesses: 125-175 ft (38-52 m).
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).
Interval includes Verdigris and Swede Hollow formations; base of map unit drawn at the widespread Whitebreast Coal. Primary Lithologies: shale/mudstone, light to dark gray, part silty to sandy; siltstone, gray. Secondary Lithologies: limestone, part fossiliferous, part sandy; sandstone, very fine to fine-grained. Minor: mudstone, red/maroon to brown; shale, black, phosphatic; carbonaceous shale; coal (beds locally > 2 ft); ironstone/siderite concretions; limestone concretions (may be septarian); pyrite. Average thickness 100 ft (30 m); maximum thicknesses to 130 ft (40 m).
Lower Cherokee Group in southern, central, and western Iowa includes Kilbourn, Kalo, Floris formations (primarily Atokan-lower Desmoinesian, locally Morrowan at base); Raccoon Creek Group in eastern Iowa includes “Caseyville” and Tradewater formations (primarily Morrowan at most localities; locally includes Atokan-lower Desmoinesian Tradewater Formation in upper part). Primary Lithologies: shale/mudstone, light to dark gray, part silty to sandy; sandstone, very fine to medium grained; siltstone, gray. Secondary Lithologies: carbonaceous shale/mudstone, gray to black; phosphatic black shale; limestone, dense, part fossiliferous, part sandy; coal (beds locally > 2 ft). Minor: sandstone, coarse-grained to granular, part conglomeratic; mudstone, red to pink; limestone concretions (may be septarian); cone-in-cone limestone; siderite/ironstone concretions and pellets; pyrite. Maximum thicknesses Raccoon Creek Group in Muscatine-Scott counties: 230-250 ft (70-75 m). Maximum thicknesses Lower Cherokee Group across outcrop belt: 200-370 ft (60-113 m). Maximum thickness in southwest Iowa subsurface: 650 ft (200 m).