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Community Blog

Rock My World - Geology Field Trip

Authored by Russell W. Wilson
Posted on January 2, 2013
Filed under Community

Blog/Comm russ-n-rocks 1-2-13-2.jpgRuss Wilson is a member of a committee that is developing an outdoor geology exhibit for the Mead Wildlife Center that is owned and operated by the Wisconsin Department of Natural Resources in Wood County. The committee is gathering a variety of rock specimens from a 100-mile radius of the Mead in order to demonstrate the wide variety of geologic activity that has taken place in this neck of the woods over the past 2.8 billion years or so. Russ organized a field trip on April 14, which included retired geology professor Gene LaBerge, who mapped much of the bedrock in northern Wisconsin and who wrote the book on the geology of the Lake Superior region.

Community Blog RWW Geology Bob-with-small-Ripple-sample 1-2-13 2.jpg

The specimen shown in the pictures was formed from lava that erupted on the ocean floor in a rifting event. A rift occurs when tectonic plates diverge and basaltic lava flows out with the viscosity comparable to that of olive oil. The lava was very hot, but it cooled quickly when it hit the cold sea water. Much later, about 1.85 billion years ago, tectonic plates converged to form a mountain chain that geologists call the Penokee Range. That range has long since been eroded, buried by sedimentary rock deposited by rising sea levels, and then exhumed when the highland area of northern Wisconsin was raised up about 1.1 billion years ago when a rifting event took place that formed Lake Superior. A small remnant of the Penokee Range remains in Iron and Ashland counties.

When the most recent glaciation took place, it moved this rock from some-where in northern Wisconsin to its present location in the terminal moraine that runs east-west north of Highway 64. That glacier receded roughly 12,000 to 10,000 years ago just a blink of the eye in earth time  to reveal the rock.

Community Blog RWW Geology Strapping-it-up1 1-2-13-300x200.jpg