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).