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Mineral Resources > Online Spatial Data > Geology > by state > Iowa Geology

Geologic units in Webster county, Iowa

Cretaceous Undifferentiated (Phanerozoic | Mesozoic | Cretaceous-Early Cretaceous-Middle(?) Cretaceous-Late) at surface, covers 7 % of this area

Variably calcareous, serverely deformed shales, minor sandstone and carbonate rock; in Manson anomalous area only

Lithology: shale; sandstone; carbonate

Osage Series (Phanerozoic | Paleozoic | Carboniferous Mississippian-Early) at surface, covers 4 % of this area

Warsaw Formation- gray, dolomitic shale and argillaceous dolomite; chalcedonic chert. Locally contains many geodes.Approx thickness 85 ft. Keokuk Limestone- fossiliferous, gray or brown limestone and dolomite; gray and brown chert with white spicules, locally predominant in lower portion; minor brown or gray shale. Approx thickness 90 ft. Burlington Limestone- gray, fossiliferous limestone and darker gray dolomite; white and gray mottled fossiliferous chert, locally contains dolomite crystals; two widespread glauconite zones; basal sandstone locally in southeastern Iowa. Approx thickness 80 ft.

Lithology: dolostone (dolomite); limestone; shale; chert; sandstone

Ft. Dodge Beds (Phanerozoic | Mesozoic | Jurassic) at surface, covers 6 % of this area

Gypsum and red and green shale; in Webster CO only

Lithology: evaporite; shale; sandstone; mudstone

Meramec Series (Phanerozoic | Paleozoic | Carboniferous Mississippian-Late) at surface, covers 17 % of this area

Ste. Genevieve Limestone- fossiliferous limestone and red and green shale. Approx. thickness 50 ft. St. Louis Limestone- limestone and dolomite, sandstone locally perdominant; locally contains chert. Spergen Formation- sandy micaceous dolomite.

Lithology: limestone; dolostone (dolomite); shale; sandstone; chert

Cherokee Group (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian-Middle [Des Moines]) at surface, covers 61 % of this area

Cyclic deposits with carbonaceous shale, clay, siltstone, with lesser sandstone, and thick coal beds; minor but persistent limestone beds; may include parts of Atoka or Morrow Series.

Lithology: shale; claystone; siltstone; sandstone; coal; limestone

Colorado and Dakota Groups (Phanerozoic | Mesozoic | Cretaceous-Early Cretaceous-Middle(?) Cretaceous-Late) at surface, covers 3 % of this area

Sandstone and shale with minor limestone; includes Carlile, Greenhorn, Graneros, and Dakota FMs. Full section present in only the extreme NW part of Iowa; in southern and easternmost areas only Dakota is present.

Lithology: sandstone; shale; limestone

Kinderhook Series (Phanerozoic | Paleozoic | Carboniferous Mississippian-Early) at surface, covers 1 % of this area

Gilmore City Limestone- light gray fossiliferous limestone, commonly oolitic. Approx thickness 155 ft. Hampton Formation- limestone and dolomite; fossiliferous gray chert in lower portion. Approx. thickness 150 ft. Starrs Cave Formation- bio-fragmental limestone; oolitic in part. Approx thickness 15 ft. Prospect Hill Formation- greenish-gray siltstone. Approx thickness 90 ft. McCraney Limestone- very pale orange to pale yellowish-brown sublithographic limestone and brown dolomite. Approx thickness 65 ft.

Lithology: limestone; dolostone (dolomite); siltstone; chert