There is an optional all-day field trip to the Baraboo region on Saturday, April 26, 2003.

Be at Weeks Hall by 7:45 am.  We leave no later than 8:00 am, sun, rain, or snow.  Bring sturdy shoes for walking, warm clothes, a rain coat, and a bag lunch with drink.  We anticipate returning by about 4:30 pm.

Note: Click on the thumbnail images below for a full view.

Although this trip is optional, it gives you a chance to see rocks in the field and learn about Wisconsin geology.  In general, we will be investigating the Baraboo Quartzite, which has a depositional age of approximately 1650 to 1700 m.y.  The quartzite has been folded into a doubly-plunging syncline, and these resistant rocks form the Baraboo Range.

One of our early stops will be in Parfrey's Glen.  The images below show the Cambrian-age sandstone that was deposited in a shallow inland sea 530 m.y. ago, on top of the Proterozoic Baraboo Quartzite (which is not exposed in Parfrey's Glen).  Evidence for the proximity of the underlying Baraboo Quartzite can be seen in the frequency and size of cobbles of the Quartzite in the Cambrian sandstone.

We will also look at the Wisconsin-age glacial deposits (~10,000 yrs old), which include rocks scraped from the northern parts of the State.  Such glacial deposits allow us to reconstruct virtually the entire geologic history of the State by looking at the boulders contained in the glacial till.

The contact between the Baraboo Quartzite and Cambrian sandstone can be found along the East Bluff of Devil's Lake.  The unconformity lies high on East Bluff, but is buried beneath the center of Devil's Lake, indicating that the area occupied by the Lake once was a narrow seaway in the Cambrian.

The structural orientation of the southern limb of the syncline formed by the folded Baraboo Quartzite can be seen by looking at the bedding surfaces, which are recognized by the ripple marks preserved in the Quartzite.  It is quite remarkable that despite moderate degrees of metamorphism, the primary ripple marks created during deposition of the original quartz-rich sandstone are preserved (Photos below are from the Highway 12 road cut south of Baraboo).

Later in the day we will head to the NW side of the Baraboo Syncline, near the Upper Narrows/Ableman's Gorge region (see maps at top).  Here the Baraboo quartzite is standing on end (90o dip), and the Cambrian sandstone overlies the Quartzite in a marked angular unconformity.

A key feature of the Ableman's Gorge region is Van Hise Rock.  Named for U.W. Madison geologist Charles R. Van Hise, who became President of the University in 1903, this rock is a Historic Landmark that was saved from destruction by the Highway Department a number of years ago because of its key role in determining the geologic structure of the region.

The key to understanding Van Hise Rock is to look at the foliation preserved in the clay-rich layers, which re-crystallized to form micas that became oriented parallel to the fold axis during formation of the Baraboo syncline.

Additional relations between the Baraboo Quartzite and the Cambrian sandstone may be seen in the SW region of the Baraboo syncline, where we get a good feel for the paleogeography of this region over 500 million years ago.

The last image below is a geologic map of the State of Wisconsin, with an emphasis on the bedrock geology, which includes Archean, Proterozoic, and lower Paleozoic rocks.

Spring 2003 Semester