| State | Illinois |
|---|---|
| Name | Tamms Group |
| Geologic age | Upper Silurian (Pridoli) to Lower Devonian (Emsian) |
| Lithologic constituents |
Major
Sedimentary > Carbonate > Limestone (Bed)Limestone can be cherty, dolomitic, silty, or shaly or argillaceous.
Minor
Sedimentary > Chemical > Chert (Bed)
|
| Comments | Thickness from stratigraphic column for southern Illinois (south of 40 degrees north latitude), from oldest to youngest: Bailey Ls (0-500’), Flat Gap Ls (0-100’), Grassy Knob Chert (0-300’), Backbone Ls (0-200’), and Clear Creek Fm (0-600’). [“Flat Gap Limestone" is oil well drillers' term.] Unit label in original GIS (Esri shapefile IL_Geologic_Units_500K_2005_Py) is 'Dt'; label on Legend of geologic map is 'DSt'. |
| References | Kolata, D.R., comp., 2005, Bedrock Geology of Illinois: Champaign, Ill., Illinois State Geological Survey, Illinois Map Series 14, scale 1:500,000. |
| NGMDB product | |
| Counties | Alexander - Jackson - Pulaski - Union |