Transcript PowerPoint file - Illinois Valley Community College

Geologic History of
the Illinois Valley
Mike Phillips
Geology Professor
Illinois Valley Community College
Reading the Rocks

Rock Type
Igneous
 Sedimentary
 Metamorphic


Rock Cycle
Reading the Rocks



Igneous
Metamorphic
Sedimentary Rocks
Form at the surface
 Environments of Deposition

Sediment type
 Sedimentary structures
 Fossils

Illinois Rocks



Igneous & Metamorphic: in the “Basement”
Sedimentary: bedrock
Unconsolidated material: on the surface
Rocks of northcentral Illinois
Exposures in the
central Illinois
Valley:
 Ordovician
 Pennsylvanian
Rocks of the central Illinois Valley

Ordovician (505 to 438 MYA)

Shakopee Dolostone: shallow marine


oolites
St. Peter Sandstone: beach
clean sand
 cross-beds


Galena-Platteville Dolostone: shallow marine
some fossils
 heavily bioturbated

Rocks of the central Illinois Valley

Silurian-Mississippian (438 to 320 MYA)

No rocks exposed in Illinois Valley (present
elsewhere)
eroded
 not deposited
 buried


LaSalle Anticline: fold
Rocks of the
central Illinois
Valley

Pennsylvanian
(320 to 286 MYA)
Carbondale
 Bond
 Modesto

Rocks of the central Illinois Valley

Pennsylvanian cyclothems

thin layers of varying type in repeated
sequences
coal
 sandstone
 limestone
 shale
 clay


fluctuating sea level
Permian to
Quaternary
(286 to 2 MYA)
 erosion
Pleistocene (2 MYA to 10,000 YA)

Unconsolidated deposits
diamicton
 sand and gravel
 sand dunes (near the river)
 loess
 laminated clay

The
ICE
AGE
10,000 YA to present
Thank You
Mike Phillips
Illinois Valley Community College
www.ivcc.edu/phillips
[email protected]
(815)224-0394
“The Geology of LaSalle County”
Saturday, March 19 (9:00-3:30)