Soils and Geology of Wisconsin Field Trip, October 2012
Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green
Bay
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Day 1: October 5, 2012
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The fall foliage was near its peak on Highway 29. |
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Beautiful fall view of Rib Mountain. |
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The pre-Pleistocene bedrock valley of the Wisconsin
River. |
Archean Gneiss
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This trip had one of the longest legs ever before the
first stop. All the stops were within a few miles of
Mellen. This outcrop is a few miles south on State Highway
13, tastefully decorated by primitive artists. |
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Archean-Proterozoic Contact
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A couple of miles east of Mellen off a side road are
outcrops of the Archean Ramsay Formation and Proterozoic
Palms Quartzite. |
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Close up of the Ramsay Formation, an amphibolite. |
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Looking at the Palms Quartzite. The outcrops of Ramsay
Formation are near the vehicles. The contact is concealed. |
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Left and below: some of the thicker beds have
spectacular plumose fracturing. Note how it splays into en
echelon fractures near the contacts. |
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Plumose fracturing originated at one point in this bed
and radiated in all directions. |
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Higher up (to the north) the rocks grade into iron
formation. |
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Left: nice en echelon quartz-filled cracks. Below: Yup, it's magnetic! |
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Red jasper in the iron formation. |
Mellen Gabbro
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A large outcrop of Mellen Gabbro is just north of town,
within sight. |
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Left: small basalt dike Below: the gabbro is essentially anorthosite with long plagioclase laths. |
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Mellen Intrusive Breccia
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Near the Mellen Gabbro is another intrusive unit, the
Mellen Granite, which fed rhyolite flows in the
Keeweenawan rift. |
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Not far north of the gabbro outcrop is a spectacular
outcrop of intrusive breccia, with gtabbro clasts enclosed
by granite. |
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Left: unusually shaped inclusion next to crystal-lined
cavity Below: Crystal-lined cavities are common, especially in areas with pegmatitic texture, indicating that the intrusion was very shallow, since open cavities cannot form under high pressures. |
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Left: some gabbro inclusions appear to exhibit
layering. |
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There are some areas of coarse pegmatite with graphic
texture. |
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Copper Falls
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| Below: views of the Bad River. |
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| Above: Copper Falls itself is not very dramatic. |
Below: Brownstone Falls is bigger and higher than
Copper Falls. |
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Vertical layers of Copper Harbor Conglomerate. |
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Keeweenawan sedimentary rocks |
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Staircase down to the river |
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Keeweenawan sedimentary rocks. |
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The prominent vertical rib on the right is Copper
Harbor Conglomerate. The recess to its left is Nonesuch
Shale, and the massive unit on the left is Freda
Sandstone. |
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Bridge over the Bad River |
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Climbing up to the top of the gorge |
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Freda Sandstone |
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Copper Harbor Conglomerate |
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Brownstone Falls is on the right. |
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Brownstone Falls. The rocks are lighter and pink
because they're rhyolite, probably erupted from the Mellen
Granite magma chamber. |
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Oh, deer! |
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Inclusions in flagstones of Tyler Formation. |
Dry Lodgings!
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Professor Luczaj ferreted out a ski lodge near
Ironwood. Wise move, as will shortly become apparent. |
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A roof looks good tonight. |
Day 2: October 6, 2012
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Not tenting was definitely a good plan. |
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Breakfast |
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Tyler Formation
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We are going to charge an Adventure Camping surcharge
plus a triple Character Building surcharge for this. |
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The Tyler Formation is a thick sequence of greywackes
and slates, a former continental slope deposit on the
Superior Craton. Below: the snow made for pretty scenery but poor rock visibility. |
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Graded bedding in a greywacke bed. Below: trying to see the rocks |
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Slickenside steps on a fracture surface. |
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Snowbow! There was enough light rain mixed with the
snow to give us this unusual sight. |
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Cleavage is obvious in the slates but absent in the
greywackes. |
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Archean Ramsay Pillow Lavas
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Snow on the trees was lovely. |
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Snow on the outcrops, not so much. Under good
conditions this outcrop has spectacular pillows but this
one was the only one visible. |
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Headed east to Bergland. |
Bergland Group
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Near Lake Gogebic there had been hardly any snow. |
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This stop features a variety of lithologies, including
this arkose. |
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Cross bedding in the arkose. Below: there was little snow at road level but some on the hilltops. |
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Lithic sandstone resting atop a basalt flow. Professor
Ryan Currier (right) ponders the outcrop. |
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| Above: columnar jointing in rhyolite. |
Below: A layer of lithic sandstone between rhyolite flows. |
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Rhyolite Outcrop
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A porphyritic rhyolite outcrop a couple of miles north
of Bergland had closely spaced lamellar joints. |
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Headed north |
Bonanza Falls
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Fall foliage. |
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If you can't get the concept of strike and dip here,
maybe you should re-think your major! The formation is
Freda Sandstone. The southeast dip is anomalous since most
Keeweenawan rocks in the region dip northwest. |
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Below: These may be algal mat structures. |
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Parting lineation on bedding surfaces indicates wave
direction. |
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there are numerous small but nice potholes here. |
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Panoramas of Bonanza Falls
Lake of the Clouds
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Views on the way to Lake of the Clouds |
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Views from the overlook, beginning in the north and moving around to west. |
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Epidote filled vesicles in a basalt flow. |
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Glacial polish and striations. Below: the group gathers for a picture. |
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View north to Lake Superior. |
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The circular patches of vesicles may be inclusions of vesicular
basalt or pipes where gases escaped. |
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Panoramas of Lake of the Clouds
Union Bay
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Union Bay features Lake Superior surf plus an
astounding array of sedimentary structures. Below: Mud cracks |
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The pretty day at Lake of the Clouds was a very
fortunate brief window. |
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Conglomerate layer in the sandstone. |
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Mud cracks on two scales. |
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Union Bay Beach
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A beach not far from Union Bay Campground is a good
place to observe dynamic beach processes. |
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Wave action was creating a lag deposit of pebbles in
the surf zone. It's also obvious how parting
lineation forms. |
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Red Pleistocene glacial lake clay. |
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Wave action leaves streaks of heavy minerals |
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A magnet confirms they're magnetite. |
Palms Quartzite at Wakefield
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A steep trail leads up Tower Hill on the outskirts of
town. Below: The Palms Quartzite is an attractive thin-bedded unit. |
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| Above: views of Wakefield. |
Below: the Palms grades into a darker facies to the north but there is no iron formation. It may be exposed further down the north slope of the hill. |
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After the beautiful weather at Lake of the Clouds, it
looked like a fine day from then on. But it was not to be.
Here a snow squall blows in. |
Panoramas of Wakefield
Potholes on Presque Isle River
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At the mouth of the Presque Isle River are some
wonderful potholes. |
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A suspension bridge crosses the river. |
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Looking north to Lake Superior. Note the joint control
on the channel. |
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The potholes here are among the most crisp and
perfectly round anywhere. |
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Looking downstream toward lake Superior. |
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Looking upstream. |
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Ball and pillow structures, load structures formed when coarse sediment is suddenly dumped on still wet sediments below. |
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The valley beyond the hill is a high water mouth of the
river. |
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Views of the Presque Isle River |
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Climbing out of the gorge |
Nadawaha Falls
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Left and Below: At high water this falls stretches
across the gorge but at low water the falls is pretty
modest. |
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Above, a small fall upstream Below: potholes |
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Two potholes straddling a fracture. Obviously the
potholes were initiated when rock spalled aoff along the
fracture. |
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Left and below: cross-bedding. |
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Day 3: October 7, 2012
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Sunday morning, there was still snow on the ground. |
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Mmmm, that feels goood! |
Big Cores
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The welcome center on US 51 in Hurley has several
gigantic cores, which may have been drilled
for starting a shaft, drainage, ventilation, or emergency access. |
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This could be Mellen intrusive breccia. The Wikipedia article
on Core drills links to an article in the December, 1943 issue of
Popular Science that describes a new drilling technique and says:
"today, 1000 feet below the earth's surface at Hurley, Wis., it is
cutting a mine shaft down toward the 3000 foot level of an operating
iron mine." In all likelihood, this is a piece of that core. That method could cut cores up to 16 feet long but is no longer used because it has been superseded by faster drilling methods. |
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Historical placard on Iron Mining. |
Powell Kyanite
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One of the few good outcrops of high grade metamorphic
rocks in Wisconsin. The significance of the cairns is
unknown. |
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Harrison Hills
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The hills on the horizon are the Harrison Hills, a
collection of kames and ice-walled lake plains. |
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The Harrison Hills are a maze of kames and kettles. |
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Even though soil scientists go around uttering
blasphemies like "soil outcrop," this is a Soils
and Geology field trip, meaning we gotta have a soils
stop. |
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Professor Luczaj fills in for Professor Fermaich, who
didn't come along this time. |
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Anyone who had spodosol, come up and collect your
prize. It's weakly developed but has the bright orange B
horizon and somewhat bleached A horizon. If that seems at
odds with the deciduous forest, bear in mind this is all
second or third growth and the original forest was pine. |
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Left and below: atop one of the ice-walled lake plains.
A small plateau of glacial and lake sediments. |
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Professor Luczaj explains how an ice-walled lake plain
forms. The drawing is now on sale at Sotheby's. |
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| Above: looking toward the eastern end of the plain. | Below: to the west, the topography drops off steeply. |
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The Harrison Hills are on the skyline. |
Irma Outlier
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Irma Hill is capped with indurated sandstone which scanty fossils indicate is Cambrian. This view looks west over the Wisconsin River valley. |
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One of the most interesting features here is an erratic of schist with big staurolite crystals. |
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Staurolite crystals stand out in relief on the boulder. |
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Left and below: autumn foliage from Irma Hill. |
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The big staurolite boulder is behind the yellow bushes
just right of the small pine. |
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Outcrops on Irma Hill. |
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The outcrop with orange leaves next to it has ripple marks. |