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Fort Dodge Formation

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Present only in Webster County. Primary lithologies: gypsum, mostly alabastrine (lower unit, Gypsum Creek Mbr.); redbeds including mudstone/claystone (red to green-gray), sandstone (very fine to medium and coarse grained) (upper unit, Soldier Creek Mbr.). Secondary lithologies: basal conglomerate and sandstone, carbonate clasts (Shady Oak Mbr.). Minor: quartz crystals. Maximum thicknesses: gypsum bed to 32 ft (10 m), upper redbeds to 52 ft (16 m).
State Iowa
Name Fort Dodge Formation
Geologic age Middle or Upper Jurassic, possibly Oxfordian
Lithologic constituents
Major
Sedimentary > Clastic > Mudstone > Claystone (Bed)redbeds including mudstone/claystone (red to green-gray)
Sedimentary > Clastic > Sandstone (Bed)very fine to medium and coarse grained, (upper unit, Soldier Creek Mbr.)
Sedimentary > Chemical > Evaporite > Gypsum (Bed)mostly alabastrine (lower unit, Gypsum Creek Mbr.)
Minor
Sedimentary > Carbonatecarbonate clasts (Shady Oak Mbr.)
Sedimentary > Clastic > Conglomerate (Bed)basal unit
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.
NGMDB product
Counties Webster