Mineral Resources On-Line Spatial Data
Mineral Resources > Online Spatial Data > Geology > by state > Nebraska Geology
Geologic units in Dawes county, Nebraska
- Niobrara Formation (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers < 0.1 % of this area
White to dark gray argillaceous chalk, marl, and shale. Weathers yellow to orange. Contains thin, laterally continuous bentonite beds, chalky carbonaceous shale, minor sand, and small concretions. Thickness 160-225 ft (49-69 m).
- Pierre Shale (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 29 % of this area
Mostly medium to dark-gray, brownish-gray, and black, fissle clay shale. Locally grades to thin beds of calcareous, silty shale or claystone, marl, shaly sandstone, and sandy shale. Locally contains thin seams of gypsum and sparse selenite crystals. Approx. max thickness 1970 ft.
- Terrace Deposits (Phanerozoic | Cenozoic | Quaternary) at surface, covers < 0.1 % of this area
Clay to boulder-size clasts deposited as pediments, paleochannels, and terrace fills of former flood plains. Thickness up to 75 ft (23m).
- Pierre Shale (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers < 0.1 % of this area
Blue-gray to dark-gray, fissile to blocky shale with persistent beds of bentonite, black organic shale, or light-brown chalky shale. Contains minor sandstone, conglomerate, and abundant carbonate and ferruginous concretions. Thickness 1,000-2,700 ft (305-823 m).
- Niobrara Formation (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 0.9 % of this area
Argillaceous chalk, limestone and shale. Chalk is medium gray to white, interbedded with thin layers of chalky shale; contains many fossil clams, oysters, and formanifera. Limestone is light gray to medium gray and yellowish gray, interbedded with medium-gray chalky shale; also contains fossil clams, oysters, and formanifera. Bedding plans commonly marked by thin layers of gypsum and locally a thin bed of red flint occurs at top of unit. Approx. max thickness 570 ft.
- Ogallala Group or Formation (Phanerozoic | Cenozoic | Tertiary | Miocene) at surface, covers 25 % of this area
Silt, sand, sandstone, gravel and conglomerate. Predominantly interfingered fine- to coarse grained, poorly sorted, arkosic, fluvial deposits of light-gray, light-olive-gray, and grayish-green calcareous silt and sand, and locally poorly consolidated conglomerate, sandstone, and siltstone.
- Carlile Shale (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 0.7 % of this area
Shale, limestone, and sandstone. At top, locally 5 feet of gray to pale-yellowish brown siltstone or very fine grained sandstone. Upper 200 feet of shale is drak gray to medium gray; locally contains ironstone concretions, and interbedded with thin siltstone. Lower 80 feet of shale is medium gray, calcareous, and contains many very thin bedded, fossiliferous, shaly limestone and calcareous shale layers. Approx. max thickness 300 ft.
- White River Group (Phanerozoic | Cenozoic | Tertiary | Oligocene) at surface, covers 22 % of this area
Clay, some claystone, silt and siltstone. Predominantly greenish gray and volcaniclastic. Other occurrences are greenish gray to white and bentonitic. Local channel sandstone at base. Aprox thickness 195 ft.
- Greenhorn Limestone and Graneros Shale (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers < 0.1 % of this area
Greenhorn Limestone- medium- to light-gray limestone interbedded with argillaceous limestone, marl and calcareous shale; contains Inoceramus fossils. Upper and lower contacts gradational. Approx. max thickness 30 ft. Graneros Shale- medium- to dark-gray, partly calcareous shale. Interbeds of siltstone, sandstone, and carbonaceous shale, and thin bentonite layers in upper part. Approx. max thickness 60 ft.
- Arikaree Group (Phanerozoic | Cenozoic | Tertiary | Oligocene Miocene) at surface, covers 22 % of this area
Consists mainly of gray, fine, loose to compact sand that has layers of hard, fine-grained dark-gray concretions which vary from few in to 15 in and often have tabular form. Includes a large amount of volcanic ash mixed in with the sand. Contains a number of channels filled with coarse conglomerate along ridge south of North Platte River. About 500 ft thick.