Interval includes Pinicon Ridge, Otis, Spillville, and Bertram formations. Otis and Bertram formations restricted to east-central Iowa only; Spillville Formation in northeast Iowa only. Pinicon Ridge Formation oversteps Spillville and Otis edges in Fayette, Bremer, Black Hawk, Buchanan, southern Chickasaw counties to directly overlie Sh, Sw, or Om. Primary Lithologies: dolomite, part laminated, variably argillaceous, part fetid; limestone, dense, “sublithographic”, part laminated to intraclastic; dolomite, fossil-moldic to vuggy (Otis-Spillville fms). Secondary Lithologies: limestone/dolomite breccia (evaporite collapse); dolomitic shale and shaly dolomite, gray to green-gray, part silty-sandy; limestone, part peloidal to fossiliferous (Otis Fm). Minor: chert and chalcedony nodules (Pinicon Ridge Fm); sandstone; oolitic limestone (Otis Fm). Extensive anhydrite/gypsum in subsurface outside of outcrop belt. Maximum thicknesses in outcrop belt: east-central Iowa, 60-160 ft (18-49 m); northern Iowa, 10-130 ft (3-40 m), locally absent in Bremer County beneath Dc.
Formation includes Welton, Buck Creek Quarry, Waubeek, Palisades-Kepler, Johns Creek Quarry members; Palisades-Kepler and Johns Creek Quarry members contain carbonate mound facies. Erosionally beveled and truncated beneath Dw. Primarily Lithologies: dolomite, porous, fossil-moldic to vuggy, part very crinoidal (includes Welton Mbr); dolomite, cherty to very cherty, dense (Buck Creek Quarry Mbr). Secondary Lithologies: dolomite, sparsely fossil-moldic, dense, part vuggy (includes Waubeek Mbr); dolomite, coarsely crystalline, part very crinoidal (within Johns Creek Quarry, Palisades-Kepler mbrs); dolomite mudstone, dense. Minor: dolomite, slightly argillaceous; quartz druse, chalcedony, silicified fossils. Maximum thicknesses: 94-240 ft (29-73 m); may reach thicknesses to 300 ft (90 m); beveled and truncated beneath Dw.
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.
Formation includes Anamosa, Brady, LeClaire (Scott-Muscatine counties) members; Brady and LeClaire members are carbonate mound facies. Erosionally beveled and truncated beneath Dw. Primary Lithologies: laminated dolomite (Anamosa Mbr), part fetid/organic to east (Scott-Clinton counties); dolomite mudstone, dense, featureless. Secondary Lithologies: dolomite, fossiliferous to vuggy, moldic, part brachiopod-rich (Brady Member); dolomite, part coarsely crystalline, vuggy, fossiliferous to sparsely fossiliferous, part crinoidal (LeClaire Member). Minor: chert; intraclastic dolomite. Maximum thickness: 180 ft (55 m); beveled and truncated beneath Dw.
Mosalem Formation infills erosional paleovalleys incised into Maquoketa Shale; absent outside of paleovalleys. Lower Hopkinton Formation locally contains carbonate mound facies in Bremer County. Blanding Formation oversteps Tete des Morts-Mosalem edge in southern outcrop area. Primary Lithologies: dolomite, fossil-moldic to vuggy, fine to coarse crystalline; dolomite, dense to porous, cherty to very cherty, nodular to bedded chert (especially Blanding Fm). Secondary Lithologies: dolomite, dense, sparsely fossiliferous; dolomite, argillaceous, part laminated (Mosalem Fm). Minor: chalcedony, silicified fossils. Maximum thicknesses total interval: 160-330 ft (49-100 m), thickest in Dubuque, Jackson, Jones counties where Mosalem present; southern outcrop total thickness 65-130 ft (20-40 m). Formation thicknesses: Hopkinton, 65-160 ft (20-49 m); Blanding, 25-65 ft (8-20 m); Tete des Morts, 0-35 ft (11 m); Mosalem, 0-100 ft (30 m).
Interval includes Sweetland Creek Shale in southeast Iowa, and “Amana beds” of Iowa County. Lime Creek Fm onlaps eroded Ordovician surface in northwestern Iowa. Primary Lithologies: shale, gray to green-gray, dolomitic to calcareous; limestone, variably argillaceous, fossiliferous, part biostromal; dolomite, variably argillaceous, part fossiliferous. Secondary Lithologies: limestone, dense, “sublithographic” (upper part of carbonate-dominated facies in central and northwestern Iowa); shale, green-gray to brown, silty (Sweetland Creek Shale). Minor: siltstone; chert; oolitic limestone, carbonate breccia (central to northwestern Iowa). Thickness variations in outcrop belt: Sweetland Creek Shale of southeastern Iowa, 3-30 ft (1-9 m); Lime Creek Fm of southeastern to north-central Iowa, 40-200 ft (12-60 m); Lime Creek Fm of northwestern Iowa, 200-350 ft (60-105 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 is a northwestern limestone facies that correlates with dolomite strata (upper Hopkinton-lower Scotch Grove formations) to the south and east; locally interfingers with dolomite to south; it overlies progressively higher stratigraphic levels southward within the Hopkinton to Scotch Grove formations. Sl forms highest Silurian unit throughout its extent; unconformably overlain by Dw. Primary lithologies: limestone, dense, fossiliferous, part cherty to very cherty. Secondary lithologies: dolomitic limestone, dolomite. Minor: argillaceous to shaly chert residuum at top (may be basal Dw); shale, green-gray. Maximum thickness, 140 ft (43 m); average thicknesses: 20-60 ft (6-18 m).