Mineral Resources On-Line Spatial Data
Mineral Resources > Online Spatial Data > Geology > by state > Iowa Geology
Geologic units in Black Hawk county, Iowa
- Maquoketa Formation (Phanerozoic | Paleozoic | Ordovician-Late [Cincinnatian]) at surface, covers 0.9 % of this area
Predominantly grayish-green shale in east-central area; predominantly brown dolomite and chert in the subsurface of north-central and western areas; red shale with limonite or hematite pellets (Neda) occurs locally at top.
- Cedar Valley Limestone (Phanerozoic | Paleozoic | Devonian-Middle) at surface, covers 74 % of this area
Finely crystalline and clastic limestone in upper part with coral and stromatoporoid-rich zones; brown, dolomitic limestone with biostromes of corals and stromatoporoids in middle part; gray argillaceous, fossiliferous limestone in lower part; dominantly dolomite with intervals of gypsum in the subsurface of central and southwestern Iowa.
- Wapsipinicon Formation (Phanerozoic | Paleozoic | Devonian-Middle) at surface, covers 15 % of this area
In descending order, finely crystalline limestone; brown dolomite with gypsum; gray, sandy shale and argillcceous limestone; and massive, finely crystalline, dolomitic limestone and pale-orange dolomite.
- LaPort City Chert (Phanerozoic | Paleozoic | Devonian-Early) at surface, covers 0.4 % of this area
Predominantly chert with limestone and dolomite; minor shale and sandstone. Found in subsurface only.
- Lime Creek Formation (Phanerozoic | Paleozoic | Devonian-Late) at surface, covers 2 % of this area
Fossiliferous limestone or dolomite in upper part with local stromatoporoid biostromes in north-central Iowa; extremely fossiliferous gray shale and argillaceous limestone in middle; gray shale in lower part with spore carps toward base.
- Niagaran Series (Phanerozoic | Paleozoic | Silurian) at surface, covers 7 % of this area
Gower Dolomite- LeClaire (reef phase) tough, greenish-blue dolomite; Anamosa (inner-reef) soft, yellowish-brown, thin-bedded dolomite. Hopkinton Dolomite- light colored dolomite with nodular chert.
- Alexandrian Series (Phanerozoic | Paleozoic | Silurian) at surface, covers 0.6 % of this area
Kankakee Formation- light colored dolomite; contains much interbedded chert. Approx thickness 155 ft. Englewood Dolomite- gray, sandy, silty, argillaceous dolomite. Approx thickness 55 ft