A field guide to the Cretaceous of Guthrie County

B.J. Witzke and G.A. Ludvigson

Iowa Department of Natural Resources, Geological Survey Bureau
Guidebook Series No. 17, 1996, 75 p.


Cretaceous exposures visited during this field trip are located within the historic region that encompasses western Iowa and eastern Nebraska where the original concepts and definition of the Dakota Formation were formulated. These rocks were first described in the written literature as exposures of "soft sandstone" along the bluffs of the Missouri River near the Omaha Indian's Blackbird burial grounds in the 1804 journal of Captain Clark, as recorded by the historic Lewis and Clark Expedition of the American West (see Tester, 1931). Meek and Hayden (1862) named the "Dakota Group" after exposures of sandstone alternating with shale and lignite in the "hills back of the town of Dakota [City]" in Dakota County, Nebraska. In Iowa, rock strata presently included in the Dakota Formation were subdivided by White (1870), into a lower "Nishnabotany [sic] sandstone," and upper "Woodbury sandstones and shales." White's (1870) early conception of the Dakota interval as being comprised of two distinctly different lithostratigraphic units was subsequently confirmed and revived by hydrogeologic research drilling studies in western Iowa (Ludvigson and Bunker, 1979; Whitley, 1980; Whitley and Brenner, 1981; Witzke and Ludvigson, 1982; Munter et al., 1983; Witzke et al., 1983; Witzke and Ludvigson, 1994). A comprehensive summary of the historical background of stratigraphic studies in the type Dakota region is presented by Witzke and Ludvigson (1994). The Nishnabotna Member of the Dakota Formation is the principal bedrock aquifer of western Iowa (Munter et al., 1983; Hunt and Runkle, 1985; Ludvigson and Witzke, 1992; Hansen et al., 1992). In many upland sites in the western part of the state, this confined aquifer is the only available large-capacity source of potable water supply. Chert and quartz-pebble conglomerate facies of the Nishnabotna are also developed as economic sand and gravel deposits where the unit crops out in southwest Iowa. Iron oxide-cemented ledges of Nishnabotna sandstone have been used as local building stones in southwest Iowa and southeast Nebraska, and massive ironstone deposits from similar coarse-grained facies of the Windrow Formation were once mined as economic iron ores in northeast Iowa and southeast Minnesota. Mudrock facies of the Dakota Formation are used for brick manufacturing, with operating clay pits located in Iowa, Minnesota, Nebraska, and Kansas.


Hansen, R.E., Thompson, C.A., and VanDorpe, P.E., 1992, Availability and quality of water from the alluvial, glacial-drift, and Dakota aquifers and water use in southwest Iowa: U.S. Geological Survey, Water-Resources Investigations Report 91-4156, 187 p.

Hunt, P.K.B., and Runkle, D.L., 1985, Ground-water data for the alluvial, buried channel, basal Pleistocene and Dakota aquifer in west-central Iowa: U.S. Geological Survey, Open-File Report 84-819, 168 p.

Ludvigson, G.A., and Bunker, B.J., 1979, Status of hydrogeologic studies in northwest Iowa: Iowa Geological Survey, Open-File Report 12-79, 37 p.

Ludvigson G.A., and Witzke, B.J., 1992, Cretaceous geology and the Dakota Aquifer of Iowa: Iowa Groundwater Association Newsletter, v. 2, no. 2, p. 12-13.

Meek, F.B., and Hayden, F.V., 1862, Descriptions of Lower Silurian (Primordial), Jurassic, Cretaceous, and Tertiary fossils, collected in Nebraska by the exploring expedition under the command of Capt. Wm. F. Reynolds, U.S. Topo. Engineers, with some remarks on the rocks from which they were obtained: Philadelphia Academy Natural Science Proceedings, v. 13, p. 415-447.

Munter, J.A., Ludvigson, G.A., and Bunker, B.J., 1983, Hydrogeology and Stratigraphy of the Dakota Formation in Northwest Iowa: Iowa Geol. Survey, Water Supply Bulletin No. 13, 55 p.

Tester, A.C., 1931, The Dakota Stage of the type locality: Iowa Geological Survey, Annual Report, v. 35, p. 197-332. White, C.A., 1870, Report on the Geological Survey of the State of Iowa,: Mills and Co., Des Moines, Iowa, v. 1, 391 p.; v. 2, 443 p.

Whitley, D.L., 1980, A Stratigraphic and Sedimentologic Analysis of Cretaceous Rocks in Northwest Iowa: Unpublished M.S. Thesis, University of Iowa, Iowa City, 81 p.

Whitley D.L., and Brenner, R.L., 1981, Subsurface stratigraphic and sedimentologic analyses of Cretaceous rocks in northwest Iowa: Iowa Geological Survey, Guidebook Series No. 4, p. 57-75.

Witzke, B.J., and Ludvigson, G.A., 1982, Cretaceous stratigraphy and depositional systems in Guthrie County, Iowa: Geological Society of Iowa, Guidebook No. 38, 46 p.

Witzke, B.J., and Ludvigson, G.A., 1994, The Dakota Formation in Iowa and the type area, in Shurr, G.W., Ludvigson, G.A., and Hammond, R.H., eds., Perspectives on the Eastern Margin of the Cretaceous Western Interior Basin: Geological Society of America, Special Paper 287, p. 43-78.

Witzke, B.J., Ludvigson, G.A., Poppe, J.R., and Ravn, R.L., 1983, Cretaceous paleogeography along the eastern margin of the Western Interior seaway, Iowa, southern Minnesota, and eastern Nebraska and South Dakota, in Reynolds, M.W., and E.D. Dolly, eds., Mesozoic Paleogeography of West-Central United States: Rocky Mountain Section, Society of Economic Paleontologists and Mineralogists, Denver, CO, p. 225-252.