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

2. Reading the Rocks Rock Type Rock Type Igneous Igneous Sedimentary Sedimentary Metamorphic Metamorphic Rock Cycle Rock Cycle

4. Reading the Rocks Igneous Igneous Metamorphic Metamorphic Sedimentary Rocks Sedimentary Rocks Form at the surface Form at the surface Environments of Deposition Environments of Deposition Sediment type Sediment type Sedimentary structures Sedimentary structures Fossils Fossils

7. 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

9. Rocks of north- central Illinois Exposures in the central Illinois Valley: Ordovician Ordovician Pennsylvanian Pennsylvanian

10. Rocks of the central Illinois Valley Ordovician (505 to 438 MYA) Ordovician (505 to 438 MYA) Shakopee Dolostone: shallow marine Shakopee Dolostone: shallow marine oolites oolites St. Peter Sandstone: beach St. Peter Sandstone: beach clean sand clean sand cross-beds cross-beds Galena-Platteville Dolostone: shallow marine Galena-Platteville Dolostone: shallow marine some fossils some fossils heavily bioturbated heavily bioturbated

12. Rocks of the central Illinois Valley Silurian-Mississippian (438 to 320 MYA) Silurian-Mississippian (438 to 320 MYA) No rocks exposed in Illinois Valley (present elsewhere) No rocks exposed in Illinois Valley (present elsewhere) eroded eroded not deposited not deposited buried buried LaSalle Anticline: fold LaSalle Anticline: fold

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

15. 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 fluctuating sea level fluctuating sea level

17. Permian to Quaternary (286 to 2 MYA) erosion erosion

19. Pleistocene (2 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

21. The ICE AGE

40. 10,000 YA to present

42. Thank You Mike Phillips Illinois Valley Community College www.ivcc.edu/phillipsmike_phillips@ivcc.edu(815)224-0394 “The Geology of LaSalle County” Saturday, March 19 (9:00-3:30)