Dakata and Windrow Formations

Dakota Formation widespread in western Iowa, lower sandstone-dominated Nishnabotna Member, upper mudstone/shale-dominated Woodbury Member. Correlative Windrow Formation found as erosional outliers in northeastern and north-central Iowa. Primary lithologies: sandstone, quartzose, very fine to medium grained; mudstone/shale, light to dark gray, variably silty-sandy, noncalcareous (Woodbury Mbr.). Secondary lithologies: sandstone, medium to very coarse grained, part pebbly to gravelly, locally cemented by iron oxides (Nishnabotna Mbr., Windrow Fm.), gravel, quartz and chert clasts; siltstone; mudstone, red, pink, yellow-brown, black (carbonaceous). Minor: lignite; siderite (concretions, pedogenic sphaerosiderite pellets, cemented siltstone); massive iron ore, silty to sandy (Windrow Fm.). Maximum thickness Dakota Fm. 500 ft (150 m), commonly 100-300 ft (30-90 m); Windrow Fm. 40 ft (12 m).
State Iowa
Name Dakata and Windrow Formations
Geologic age “Mid” Cretaceous; upper Albian-upper Cenomanian
Lithologic constituents
Major
Sedimentary > Clastic > Sandstone (Bed)quartzose, very fine to medium grained; medium to very coarse grained, part pebbly to gravelly, locally cemented by iron oxides (Nishnabotna Mbr., Windrow Fm.), gravel, quartz and chert clasts
Sedimentary > Clastic > Mudstone > Shale (Bed)mudstone/shale, light to dark gray, variably silty-sandy, noncalcareous (Woodbury Mbr.)
Minor
Sedimentary > Clastic > Mixed-clastic > Siltstone-mudstone (Bed, Carbonaceous)red, pink, yellow-brown, black
Incidental
Sedimentary > Chemical > Banded-iron-formation (Bed)massive iron ore, silty to sandy (Windrow Fm.)
Sedimentary > Clastic > Siltstone (Bed)siderite (concretions, pedogenic sphaerosiderite pellets, cemented siltstone)
Sedimentary > Coal > Lignite (Bed)
References

Witzke, Brian J., Anderson, Raymond R., and Pope, John P., 2010, Iowa Geological and Water Survey, DNR, Bedrock Geologic Map of Iowa, OFM-2010-1. Scale 1:500,000.

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