Geologic units in Pulaski county, Illinois

Cretaceous undivided (Upper Cretaceous (Campanian to Maastrichtian)) at surface, covers 36 % of this area

Cretaceous undivided, includes Post Creek (Tuscaloosa), McNairy, and Owl Creek Formations (southern Illinois).

Clayton Formation, Porters Creek Formation, Claiborne Formation, Wilcox Formation (Tertiary (Paleocene) to Tertiary (Pliocene)) at surface, covers 33 % of this area

Clayton and Porters Creek Formations; Claiborne and Wilcox Formations.

Ullin and Salem Limestones (Mississippian (Visean)) at surface, covers 12 % of this area

Ullin and Salem Limestones in southern Illinois.

Tamms Group (Upper Silurian (Pridoli) to Lower Devonian (Emsian)) at surface, covers 9 % of this area

Tamms Group, includes Bailey Limestone, “Flat Gap Limestone”, Grassy Knob Chert, Backbone Limestone, and Clear Creek Formation.

St. Louis Limestone (Mississippian (Visean)) at surface, covers 6 % of this area

St. Louis Limestone.

Ste. Genevieve Limestone (Mississippian (Visean)) at surface, covers 2 % of this area

Ste. Genevieve Limestone.

Ft. Payne Formation (Mississippian (Tourniaisian to Visean)) at surface, covers 1.0 % of this area

Ft. Payne Formation, includes Springville Shale and Chouteau Limestone in southern Illinois.

Muscatatuck Group (Middle Devonian (Eifelian to Givetian)) at surface, covers 0.8 % of this area

Muscatatuck Group, includes Grand Tower Limestone and St. Laurent (Alto and Lingle) Formation in southern Illinois; includes Detroit River Formation, Wapsipinicon Limestone, and Cedar Valley Limestone in northern and western Illinois.

New Albany Shale, Blocher Shale, Sylamore Sandstone, Selmier Shale, Sweetland Creek Shale, Grassy Creek Shale, Saverton Shale, and Louisiana Limestone (Middle Devonian (Givetian) to Upper Devonian (Fammenian)) at surface, covers 0.5 % of this area

New Albany Shale, Blocher Shale, Sylamore Sandstone, Selmier Shale, Sweetland Creek Shale, Grassy Creek Shale, Saverton Shale, and Louisiana Limestone.