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26 May 2016

Glaciotectonic thrust at Waubonsee Community College

Glaciers can cause thrust faults! Explore an example from a trench south of Chicago.

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20 September 2011

Giant City State Park, Illinois

Giant City State Park is a patch of protected forest south of Carbondale, Illinois, where there are some pretty cool exposures of Pennsylvanian-aged Makanda Sandstone. Here’s a typical look at one: Notice the deep chasm on the right. This leads, maze-like, to other flat-bottomed and vertically-walled canyons: The orthogonal joint sets produces some nice tall, cliff-like vertical exposures that reveal the history of these rocks in several stages: deposition by …

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15 July 2011

Friday fauxld: liesegang banding at Giant City

Today, the Friday fold is a fake! Looks like a nice set of asymmetric antiforms and synforms, right? But it ain’t! It’s naturally wiggly; primary not tectonic. The photo shows nothing more than differential erosion of hematite that was deposited by groundwater in permeable sandstone. It’s Liesegang banding! These hematite blobs are in the sandstone at Giant City State Park, south of Carbondale, Illinois. Several are cylindrical in form, presumably …

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