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 “Graneros” Shale, Greenhorn Formation, Carlile Shale. Primary Lithologies: shale, medium to dark gray, variably silty, calcareous to very calcareous. Secondary lithologies: chalk, marl, argillaceous limestone, with skeletal (inoceramid) packstones; shale, gray, silty, noncalcareous. Minor: siltstone; calcite and siderite concretions. Maximum thickness 265 ft (80 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).
Interval includes lower “St. Louis” (Meramecian) Croton and Yenruogis members; upper “St. Louis” (lower Genevievian) Verdi and Waugh members (interval does not correlate with type St. Louis of Missouri); Pella Fm (upper Genevievian); base includes Sonora Fm (Meramecian) in parts of southeast Iowa (Lee, Van Buren, Henry, Des Moines, Jefferson counties). Primary Lithologies: dolomite, part silty/sandy, part fossiliferous; limestone, part sandy to fossiliferous; part “sublithographic,” part argillaceous. Secondary Lithologies: dolomite/limestone breccia; shale/marl, green-gray, calcareous; sandstone, fine to medium-grained; siltstone; gypsum/anhydrite (south-central Iowa). Minor: limestone, oolitic; shale, gray; shale, red to pink; chert/chalcedony. Croton Member contains gypsum-anhydrite in subsurface outside of outcrop belt. Interval is erosionally beveled to locally absent beneath Pcl; Pella Formation absent over broader areas. Maximum thicknesses for total interval 60-150 ft (18-45 m); maximum thickness Pella Formation 75 ft (23 m); maximum thickness “St. Louis” Formation 75 ft (23 m); maximum thickness Sonora Formation 35 ft (11 m).
Interval includes Burlington, Keokuk, and Warsaw formations. Upper Warsaw strata locally preserved at top of interval in extreme southeast Iowa are lower Meramecian age . Primary Lithologies: dolomite, part argillaceous to shaly; dolomitic limestone, fossiliferous; fossiliferous limestone (especially crinoidal packstone-grainstone). Secondary Lithologies: glauconitic limestone/dolomite; shale, gray to green-gray, part dolomitic, part silty; chert, nodular to bedded. Minor: quartz crystals, quartz geodes, chalcedony; phosphatic dolomite/limestone (“bone bed”); siltstone, dolomitic. Lithologies noted only in northern Iowa: oolitic limestone; “sublithographic” limestone; dolomite/chert breccia. Interval is erosionally beveled beneath sub-“St. Louis” and sub-Pennsylvanian unconformities. Maximum thicknesses in northern Iowa: 85-105 ft (26-32 m). Maximum thicknesses in southern Iowa: 155-240 ft (47-73 m).