Maquoketa Group (ILOm;0)

State	Illinois
Name	Maquoketa Group
Geologic age	Ordovician
Original map label	7390
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 > 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. 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.
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.
Geographic coverage	Alexander - Boone - Bureau - Calhoun - Carroll - Cook - DeKalb - DuPage - Greene - Grundy - Iroquois - Jersey - Jo Daviess - Kane - Kankakee - Kendall - Lake - La Salle - Lee - McHenry - Monroe - Ogle - Pike - Stephenson - Union - Whiteside - Will