Abstract Cleavage refraction angles are used to estimate effective viscosity contrasts between interlayered quartzites and phyllites within the Baraboo Syncline, Wisconsin, USA. Both types of layers contain two major phases, quartz and pyrophyllite, with minor amounts of hematite. Quartz (with minor hematite) behaves as the strong phase and pyrophyllite acts as the weak phase. Cleavage refraction directly relates to mineralogy with a linear relationship between bedding/cleavage angle and strong-phase concentration. Mineralogy exerts first-order control over effective viscosity contrasts, which are generally small, in most cases <10. Effective viscosity contrasts are consistent across the fold, so are likely not to be highly strain dependent and indicate approximate linear viscous rheology. Microstructures suggest deformation was dominated by dislocation creep in layers with high quartz concentrations and diffusive mass transfer in layers with lower quartz concentrations, and that the transition of the deformation mechanism is gradual. Thus, the rheological flow laws at the small scale may not reflect the bulk flow law at the large scale over the span of the deformation. Effective viscosity contrasts allow an evaluation of samples compared to theoretical two-phase mixtures. The analysed samples most closely resemble the Reuss bound of two-phase mixtures, regardless of the mineralogy.

Abstract With its wide variety of geological features and phenomena packed into a small area, the Baraboo of south-central Wisconsin is among the most visited parts of the Midwest by geology students. This guidebook, the first comprehensive look at the area in decades, covers the spectrum of geological features present in the area, and it is useful as a teaching tool. An exceptional outdoor classroom, the Baraboo area contains a spectrum of geology, including excellent examples of geomorphology, glacial geology, structural geology, petrology, stratigraphy, and sedimentology. Ages of the strata range from 1.7-billion-year-old Precambrian to the Quaternary. The area has been studied for about a century, but it still holds surprises for professionals and students alike.

Abstract Cambrian strata in Wisconsin compose a sheet of mostly marine sandstone, with minor dolomite, deposited during the fluctuating advance of the North American epeiric sea. Sedimentary features and fossils indicate that deposition took place in both shallower, current-dominated regimes and deeper quiet-water settings swept by episodic storm surges. The sand sheet surrounds inliers of Precambrian rocks in the Baraboo area. The Baraboo inliers are remnants of an elliptical ring of islands in a subtropical shallow sea, which were gradually buried by Cambrian and Ordovician sediments. Spectacular conglomerates composed of red quartzite clasts accumulated around the islands, which were pounded repeatedly by waves that we presume to have been generated by tropical storms. Paleomagnetic evidence places Cambrian Wisconsin in the southern tropics. Boulders up to 1.5 m in diameter are well rounded whereas larger ones (up to 8 m) are not. This suggests the possibility of estimating the magnitude of the Cambrian storm waves using knowledge from modern oceanography and from wave trough experiments by coastal engineers. Such analysis suggests waves necessary to tumble quartzite boulders 1.5 m in diameter were of the order of 7–8 m high at their point of breaking. Such magnitudes are not uncommon today during storms on many modern rocky coasts.

Abstract The surficial geology of the Baraboo area is very important because it includes the transition from a glaciated region to the Driftless Area. The eastern portion of this area was glaciated as part of the Green Bay lobe of the ice sheet in this area. The terminal moraine is present and is characterized by sandy till. No valid information that substantiates glacial activity exists west of the city of Baraboo. The Driftless Area includes a site of the earliest Wisconsin habitation.

Abstract This road log is different than most in a variety of ways. It is similar in that the stops are numbered in a certain order. That is because each stop must have some identification and numbers are the simplest and easiest to follow. Mileage is provided between stops, not in a cumulative fashion. This makes it easy to arrange the stops to suit the specific leader(s) and students. Those who use this field guide can choose to visit the stops in any order that they wish. The complete trip is designed to take two full field days, but stops can be visited in any fashion that suits the wishes and schedule of the group. There are a few alternate stops that may be used in addition to or in lieu of some of the regular stops. The estimated time necessary to spend at each stop is indicated in the log to help in organizing your trip. The total estimated time of the combined stops is ~12–14 hours. This does not include any travel time or lunch stops so that leaders can develop their own plans. Unless indicated in the figure caption, all figures herein are those of the co-authors. The trip starts at the intersection of Wisconsin Highway 33 with Interstates I-90 and I-94 (Appendix Figure A1.) Enjoy!

ABSTRACT The Baraboo District includes an exceptional array of outcrops that have provided geological enlightenment to students and professionals, alike, for 150 years. In the late nineteenth century, several fundamental structural principles were developed here, such as criteria for determining stratigraphic facing and the significance of cleavage-bedding relations. More recent studies of deformational features in the folded Baraboo Quartzite, such as crenulation cleavage and quartz fabrics, have yielded insights into the kinematics of folding in the District and the significance of regional tectonics in the context of the Proterozoic assembly of North America. Additional petrologic, geochemical, and isotopic studies have established the age of the Baraboo Quartzite (≤1700 Ma), identified a Paleoproterozoic weathering profile, confirmed the supermature composition of the Baraboo Quartzite, established the presence of geon 14 hydrothermal alteration, and elucidated the Proterozoic tectonothermal evolution of the District, all of which bear importantly on Proterozoic tectonic, atmospheric, and climatic conditions in the southern Lake Superior region. By Late Cambrian time, the Baraboo Quartzite was a ring of islands, which was abutted by spectacular conglomerates deposited by tropical storms. These were surrounded by more distal sandstones and were eventually buried by Ordovician dolomite and sandstone. During the field trip, we will visit eleven localities, which have been selected to illustrate the key geological features of this North American classic.