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


The fall foliage was near its peak on Highway 29.
Beautiful fall view of Rib Mountain.
The pre-Pleistocene bedrock valley of the Wisconsin River.

Archean Gneiss

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.

Archean-Proterozoic Contact

A couple of miles east of Mellen off a side road are outcrops of the Archean Ramsay Formation and Proterozoic Palms Quartzite.
Close up of the Ramsay Formation, an amphibolite.
Looking at the Palms Quartzite. The outcrops of Ramsay Formation are near the vehicles. The contact is concealed.
Left and below: some of the thicker beds have spectacular plumose fracturing. Note how it splays into en echelon fractures near the contacts.
Plumose fracturing originated at one point in this bed and radiated in all directions.
Higher up (to the north) the rocks grade into iron formation.
Left: nice en echelon quartz-filled cracks.

Below: Yup, it's magnetic!
Red jasper in the iron formation.

Mellen Gabbro

A large outcrop of Mellen Gabbro is just north of town, within sight.
Left: small basalt dike

Below: the gabbro is essentially anorthosite with long plagioclase laths.

Mellen Intrusive Breccia

Near the Mellen Gabbro is another intrusive unit, the Mellen Granite, which fed rhyolite flows in the Keeweenawan rift.
Not far north of the gabbro outcrop is a spectacular outcrop of intrusive breccia, with gtabbro clasts enclosed by granite.

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.
Left: some gabbro inclusions appear to exhibit layering.
There are some areas of coarse pegmatite with graphic texture.

Copper Falls

Below: views of the Bad River.

Above: Copper Falls itself is not very dramatic.
Below: Brownstone Falls is bigger and higher than Copper Falls.
Vertical layers of Copper Harbor Conglomerate.
Keeweenawan sedimentary rocks
Staircase down to the river
Keeweenawan sedimentary rocks.
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.
Bridge over the Bad River
Climbing up to the top of the gorge
Freda Sandstone
Copper Harbor Conglomerate

Brownstone Falls is on the right.
Brownstone Falls. The rocks are lighter and pink because they're rhyolite, probably erupted from the Mellen Granite magma chamber.


Oh, deer!
Inclusions in flagstones of Tyler Formation.

Dry Lodgings!

Professor Luczaj ferreted out a ski lodge near Ironwood. Wise move, as will shortly become apparent.

A roof looks good tonight.

Day 2: October 6, 2012


Not tenting was definitely a good plan.

Breakfast

Tyler Formation

We are going to charge an Adventure Camping surcharge plus a triple Character Building surcharge for this.
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.
Graded bedding in a greywacke bed.

Below: trying to see the rocks
Slickenside steps on a fracture surface.
Snowbow! There was enough light rain mixed with the snow to give us this unusual sight.
Cleavage is obvious in the slates but absent in the greywackes.

Archean Ramsay Pillow Lavas

Snow on the trees was lovely.

Snow on the outcrops, not so much. Under good conditions this outcrop has spectacular pillows but this one was the only one visible.
Headed east to Bergland.

Bergland Group

Near Lake Gogebic there had been hardly any snow.
This stop features a variety of lithologies, including this arkose.
Cross bedding in the arkose.

Below: there was little snow at road level but some on the hilltops.
Lithic sandstone resting atop a basalt flow. Professor Ryan Currier (right) ponders the outcrop.
Above: columnar jointing in rhyolite.
Below: A layer of lithic sandstone between rhyolite flows.

Rhyolite Outcrop

A porphyritic rhyolite outcrop a couple of miles north of Bergland had closely spaced lamellar joints.
Headed north

Bonanza Falls

Fall foliage.
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.

Below: These may be algal mat structures.

Parting lineation on bedding surfaces indicates wave direction.
there are numerous small but nice potholes here.

Panoramas of Bonanza Falls

Lake of the Clouds

Views on the way to Lake of the Clouds
Views from the overlook, beginning in the north and moving around to west.

Epidote filled vesicles in a basalt flow.
Glacial polish and striations.

Below: the group gathers for a picture.
View north to Lake Superior.

The circular patches of vesicles may be inclusions of vesicular basalt or pipes where gases escaped.

Panoramas of Lake of the Clouds

Union Bay

Union Bay features Lake Superior surf plus an astounding array of sedimentary structures.

Below: Mud cracks
 
The pretty day at Lake of the Clouds was a very fortunate brief window.
Conglomerate layer in the sandstone.
Mud cracks on two scales.

Union Bay Beach

A beach not far from Union Bay Campground is a good place to observe dynamic beach processes.
Wave action was creating a lag deposit of pebbles in the surf zone.  It's also obvious how parting lineation forms.
Red Pleistocene glacial lake clay.
Wave action leaves streaks of heavy minerals
A magnet confirms they're magnetite.

Palms Quartzite at Wakefield

A steep trail leads up Tower Hill on the outskirts of town.

Below: The Palms Quartzite is an attractive thin-bedded unit.
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.
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

At the mouth of the Presque Isle River are some wonderful potholes.
A suspension bridge crosses the river.
Looking north to Lake Superior. Note the joint control on the channel.
The potholes here are among the most crisp and perfectly round anywhere.
Looking downstream toward lake Superior.
Looking upstream.
Ball and pillow structures, load structures formed when coarse sediment is suddenly dumped on still wet sediments below.
The valley beyond the hill is a high water mouth of the river.
Views of the Presque Isle River
 
Climbing out of the gorge

Nadawaha Falls

Left and Below: At high water this falls stretches across the gorge but at low water the falls is pretty modest.
Above, a small fall upstream

Below: potholes
Two potholes straddling a fracture. Obviously the potholes were initiated when rock spalled aoff along the fracture.
Left and below: cross-bedding.

Day 3: October 7, 2012


Sunday morning, there was still snow on the ground.
Mmmm, that feels goood!

Big Cores

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.
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.
Historical placard on Iron Mining.

Powell Kyanite

One of the few good outcrops of high grade metamorphic rocks in Wisconsin. The significance of the cairns is unknown.

Harrison Hills

The hills on the horizon are the Harrison Hills, a collection of kames and ice-walled lake plains.
The Harrison Hills are a maze of kames and kettles.
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.
Professor Luczaj fills in for Professor Fermaich, who didn't come along this time.
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.
Left and below: atop one of the ice-walled lake plains. A small plateau of glacial and lake sediments.

Professor Luczaj explains how an ice-walled lake plain forms. The drawing is now on sale at Sotheby's.
Above: looking toward the eastern end of the plain. Below: to the west, the topography drops off steeply.
The Harrison Hills are on the skyline.

Irma Outlier

Irma Hill is capped with indurated sandstone which scanty fossils indicate is Cambrian. This view looks west over the Wisconsin River valley.

One of the most interesting features here is an erratic of schist with big staurolite crystals.

Staurolite crystals stand out in relief on the boulder.
Left and below: autumn foliage from Irma Hill.
 
The big staurolite boulder is behind the yellow bushes just right of the small pine.
Outcrops on Irma Hill.
The outcrop with orange leaves next to it has ripple marks.

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Created 11 October 2012,  Last Update 17 October 2012
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