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Maquoketa Group

Maquoketa Group
State Illinois
Name Maquoketa Group
Geologic age Ordovician
Comments The upper Ordovician consists of the following formations : in the northern part of the state (Neda Formation, Brainard Shale, Fort Atkinson Limestone, Scales Shale,) and in the southern part of the state (Girardeau Limestone, Brainard Shale, Fort Atkinson Limestone, Scales Shale, Cape Limestone). Based on the stratigraphic column on the 1967 paper map, collectively this group of formations is about 20% limestone, 70% shale, and 10% sandy siltstone.
Primary rock type shale
Secondary rock type limestone
Other rock types siltstone
Lithologic constituents
Major
Sedimentary > Clastic > Mudstone > ShaleThe upper Ordovician consists of the following formations : in the northern part of the state (Neda Formation, Brainard Shale, Fort Atkinson Limestone, Scales Shale,) and in the southern part of the state (Girardeau Limestone, Brainard Shale, Fort Atkinson Limestone, Scales Shale, Cape Limestone). Based on the stratigraphic column on the 1967 paper map, collectively this group of formations is about 20% limestone, 70% shale, and 10% sandy siltstone.
Minor
Sedimentary > Carbonate > LimestoneThe upper Ordovician consists of the following formations : in the northern part of the state (Neda Formation, Brainard Shale, Fort Atkinson Limestone, Scales Shale,) and in the southern part of the state (Girardeau Limestone, Brainard Shale, Fort Atkinson Limestone, Scales Shale, Cape Limestone). Based on the stratigraphic column on the 1967 paper map, collectively this group of formations is about 20% limestone, 70% shale, and 10% sandy siltstone.
Sedimentary > Clastic > SiltstoneThe upper Ordovician consists of the following formations : in the northern part of the state (Neda Formation, Brainard Shale, Fort Atkinson Limestone, Scales Shale,) and in the southern part of the state (Girardeau Limestone, Brainard Shale, Fort Atkinson Limestone, Scales Shale, Cape Limestone). Based on the stratigraphic column on the 1967 paper map, collectively this group of formations is about 20% limestone, 70% shale, and 10% sandy siltstone.
Map references
Willman, H.B., and others, (compilers), 1967, Geologic Map of Illinois: Illinois State Geological Survey, scale= 1:500,000, paper.
Unit references
Willman, H.B., and others, (compilers), 1967, Geologic Map of Illinois: Illinois State Geological Survey, scale= 1:500,000, paper.
Counties Alexander - Boone - Bureau - Calhoun - Carroll - Cook - DeKalb - DuPage - Greene - Iroquois - Jersey - Jo Daviess - Kane - Kankakee - Kendall - Lake - La Salle - Lee - McHenry - Monroe - Ogle - Pike - Stephenson - Union - Whiteside - Will