1. Geologic History of the Illinois Valley Mike Phillips Geology Professor Illinois Valley Community College

3. Illinois Rocks Igneous & Metamorphic: in the “Basement” Igneous & Metamorphic: in the “Basement” Sedimentary: bedrock Sedimentary: bedrock Unconsolidated material: on the surface Unconsolidated material: on the surface

5. Rocks of north- central Illinois Exposures in the upper Illinois Valley: Ordovician Ordovician Ottawa & Starved Rock Ottawa & Starved Rock Silurian Silurian Des Plaines R. Des Plaines R. Pennsylvanian Pennsylvanian remainder remainder

6. Rocks of the central Illinois Valley Ordovician (505 to 438 MYA) Ordovician (505 to 438 MYA) Shakopee Dolostone: shallow marine Shakopee Dolostone: shallow marine St. Peter Sandstone: beach St. Peter Sandstone: beach Galena-Platteville Dolostone: shallow marine Galena-Platteville Dolostone: shallow marine Silurian (438 to 417 MYA) Silurian (438 to 417 MYA) dolostone: shallow marine dolostone: shallow marine Silurian-Mississippian (417 to 320 MYA) Silurian-Mississippian (417 to 320 MYA) No rocks exposed: eroded or not deposited No rocks exposed: eroded or not deposited LaSalle Anticline: fold LaSalle Anticline: fold

7. Rocks of the central Illinois Valley Pennsylvanian (320 to 286 MYA) Pennsylvanian (320 to 286 MYA) Carbondale Carbondale Bond Bond Modesto Modesto

8. Rocks of the central Illinois Valley Pennsylvanian cyclothems Pennsylvanian cyclothems thin layers of varying type in repeated sequences thin layers of varying type in repeated sequences coal coal sandstone sandstone limestone limestone shale shale clay clay varying coastal env. varying coastal env. fluctuating sea level fluctuating sea level

10. Permian to Quaternary (286 to 1.8 MYA) erosion erosion

12. Pleistocene (1.8 MYA to 10,000 YA) Unconsolidated deposits Unconsolidated deposits diamicton diamicton sand and gravel sand and gravel sand dunes (near the river) sand dunes (near the river) loess loess laminated clay laminated clay

13. The ICE AGE

36. 10,000 YA to present

39. Thank You Mike Phillips Illinois Valley Community College www.ivcc.edu/phillipsmike_phillips@ivcc.edu(815)224-0394 “The Geologic History of The Illinois Valley” June 2006