Named as the basal member (of 3) of the Lithograph City Formation (new) of Cedar Valley Group (rank raised) in north-central and central IA, Iowa shelf; named for Osage Springs County Park, 1 mi southwest of town of Osage, Mitchell Co. Type section designated in SE SE SE sec 35, T98N, R17W, in the Osage roadcut, Mitchell Co. Consists of vuggy fossiliferous dolomite and dolomitic limestone; locally contains coarsely crystalline calcite masses. Thickness varies from 16.1 to 20.5 ft across north-central IA and thins to 11 ft in central IA. Overlies "unit B" [age not stated]. Underlies Thunder Woman Shale Member (new) of Lithograph City Formation of Cedar Valley Group. Cross sections; graphic sections; measured section. Fossil list (diverse fauna of brachiopods; restricted conodont fauna; stromatoporoids). Forms the lower transgressive phase. Is equivalent to part of the Idlewild Member (new) of the Lithograph City Formation of east-central and southeast IA. Of Devonian age; Middle Devonian-Upper Devonian boundary lies somewhere in Lithograph City.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Named as the basal member of the Lithograph City Formation (named), one of four formations assigned to the Cedar Valley Group (revised). Term used in northern and central IA and adjacent MN on the Iowa shelf. Type locality is roadcut along County Road T38, SE SE SE sec 35, T98N, R17W, 3.9 km downstream from Osage Springs County Park, Mitchell Co, IA. Characterized by fossiliferous dolomite and dolomitic, in part slightly argillaceous, limestone. Calcite filled vugs and stylolites common. Becomes more limestone dominated southward. Varies from 3.4 to 7.5 m thick. Is 6 m thick at type. Overlies Iowa City Member (named) of Coralville Formation (rank raised) of Cedar Valley Group. Underlies laminated carbonates of Idlewild Member (named) of Lithograph City in northern outcrop belt, and underlies Thunder Woman Shale Member (named) of Lithograph City in southern outcrop belt and in subsurface of central IA. Conodont INSITA fauna (Middle Devonian, late Givetian) correlates with the Lowermost ASYMMETRICUS Zone (Late Devonian, Frasnian). Also has bryozoans, gastropods, corals, burrows locally. Shallow marine deposit in a restricted nearshore or mudflat environment. Nomenclature charts; graphic sections. Formerly part of unit C of Cedar Valley Group or part of Coralville Member of Cedar Valley Formation.

Source: GNU records (USGS DDS-6; Denver GNULEX).