Tri-State Field Conference 1980 Trip 1: Precambrian Basement Complex Of Northeastern Wisconsin

Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
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Steven Dutch And Donn P. Quigley, Leaders


The main purpose of this field trip is to examine the Precambrian rocks of the Mountain area, where rocks of a great lithological variety are exposed in a reasonably compact area. The route to and from the field area has also been selected to pass through a variety of interesting glacial landforms (Figure 1).

Route Description - Green Bay To Mountain

The field trip route heads west across the Fox River. Some shipping berths are north of the bridge on the west side of the river, others are upriver (south). in 1979 the port of Green Bay was visited by 293 ships, of which 260 were U.S. and Canadian lake freighters and 33 were ocean-going foreign flag ships. The port handled 2,800,000 tons of shipping. in the distance, is the Tower Drive Bridge, part of the I-43 system. The bridge (made of Japanese steel!) spans the mouth of the Fox River at a height great enough to clear the shipping channel. All other lower Fox River bridges are drawbridges. Waiting for trains and drawbridges is an integral part of life in Green Bay.

The fact that the Fox River flows northeast into a narrow, elongate bay sometimes poses environmental problems. When winds are strong from the northeast, or when spring runoff flows into Green Bay while it still has extensive ice cover, flooding may occur along the lower Fox River or the Green Bay shoreline. Northeast winds can also pile ice along the bay shoreline and cause damage to homes near the water.

There will be several gentle rises and falls in elevation as we head west across the city of Green Bay. Most of these steplike features are old shorelines which mark former high levels of Green Bay. The major recognized shorelines are the Nipissing (600-605 feet), Algonquin (also about 605 feet, but tilted), and higher stands at about 620 and 640 feet (Hough, 1976). The present bay elevation is 580 feet.

About 7 miles west of the center of Green Bay the route climbs through a hilly tract, formed by outwash terraces and some drumlins. The drumlins form a series of parallel ridges. The route climbs onto an elevated plain which was mapped by Thwaites (1943) as an outwash plain overlain by Gary lake beds. From here to about 2 miles north of Pulaski the terrain is mostly flat with occasional undulating patches of ground moraine.

The first town directly on the route is Pulaski, whose center is dominated by a large church and Franciscan Monastery. Northeastern Wisconsin is dotted with small ethnic settlements. Pulaski and nearby Krakow, of course, are of Polish origin. Many towns east of Green Bay were settled by Belgians. German and Scandinavian settlements are also common. North of Pulaski we begin to encounter hilly areas which are mostly outwash terraces. After passing the town of Gillett, some 19 miles beyond Pulaski, the landscape alternates regularly between hilly areas dominated by outwash terraces and flat lowlands which are mostly outwash and till plains. About 7 miles farther north, near the town of Suring, some of the lowlands are glacial lake floors. Suring lies 10 miles north of Gillett.

Just west of Suring is one of the few true moraines on this portion of the trip. A large gravel pit is being operated north of the road. The view at the top of the moraine is interesting, with typical swell-and-swale topography. in the distance to the north are hills of resistant Precambrian crystalline rock in the field trip area.

From here north the route lies mostly in thick outwash. Several kettle ponds lie on the route about 10 miles north of Suring. Shortly afterward, the first Precambrian outcrops appear, and the topography alternates between bedrock knobs and thick, sandy, pitted outwash.

Just north of the kettle ponds. Highway 64 joins from the right. About 4 miles beyond, watch carefully for a large bedrock bluff on the right. This bluff, of Belongia Granite, is an excellent example of stoss-lee topography. The up-ice (north) side is smoothly streamlined while the down-ice (south) side is steep and blocky because of plucking. This bluff is not visible until a few hundred feet away, so watch closely. From here to Mountain (1 1/2 miles) outcrops are numerous and highly varied in lithology. At Mountain we turn east onto County Highway W. This area was damaged by a tornado some years ago and fallen trees are still visible in the woods just east of town.

Stop 1: Baldwin conglomerate, Waupee Volcanics and Hagar Feldspar Porphyry

SE 1/4, NW 1/4, and NW 1/4, SW 1/4, Section 6, T31N, R17E, Oconto County, Wisconsin, Mountain 7.5-Minute Quadrangle.

This locality displays several Precambrian units within a short distance of the highway. in the woods about 100 m south of the highway are outcrops of the Waupee Volcanics. The rocks at this locality are thin-bedded meta-tuffs of the upper member of the Waupee Volcanics which strike ENE and dip steeply north. A few crenulations are visible.

Immediately north of the highway, the south side of the steep hill is made up of Baldwin Conglomerate, a quartzose grit or small-pebble conglomerate. A few of the clasts are similar to the Waupee Volcanics south of the highway, and are generally believed to indicate that the rocks here are younger to the north. Mancuso (1960) correlated this unit with the Thunder Mountain and McCaslin Quartzites and considered this area to lie on the southern limb of the McCaslin Syncline.

Higher up the hill, the Hagar Feldspar Porphyry is exposed. Caution the Hill can be very slippery in wet weather. This rock has a black groundmass with large pink feldspar and blue-gray quartz phenocrysts. The term "Rhyolite" was originally applied by Mancuso to most of the fine-grained igneous rocks in this area, but most have been remapped as intrusive rocks. Hagar Rhyolite is presently mapped north of the feldspar porphyry. it is lighter in color but otherwise similar in texture.

Stop 2: McAuley Granite Gneiss

NW 1/4, NW 1/4, Sec. 5, T31N, 417E, Oconto County, Wisconsin, Mountain 7.5-Mlnute Quadrangle.

Intrusive rocks associated with the Penokean orogeny (1600-1900 m.y.) are widespread in central Wisconsin but rare in this region. A possible example of such a rock is the McAuley Granite Gneiss. The McAuley Gneiss is a homogeneous pink or gray granitic gneiss composed of quartz, K-spar, plagloclase and biotite. There is no banding. The follation changes strike abruptly with no obvious pattern.

Two explanations for the contorted foliation have been advanced. One, the more conventional, is that the foliation is due to Penokean deformation of a small granitic intrusive. In this view the McAuley probably intruded the Waupee Volcanics and was then deformed later (or simultaneously) during the Penokean orogeny.

The other view, suggested by Read and Weis (1962), is that the McAuley Gneiss formed by metamorphism (granitization) of the tuffaceous member of the Waupee Volcanics, and that the irregular foliation is a relic of the original bedding, which was disturbed by post-depositional slumping. in support of this view, the McAuley Gneiss does lie along the strike of the Waupee Volcanics at Stop i, is about the same width as the upper tuffaceous and metasedimentary members, and is mapped as having a gradational contact by Medaris and others (1973, p. 53). The present author favors the more conventional interpretation, above, however.

Several types of late dikes occur in the gneiss. Near the road is a foliated greenstone dike which displays marked differential weathering. Also near the road is an aplite dike which cuts and offsets a thick quartz vein. At first glance this looks like a clear case of faulting before or during intrusion, but the geometry is also explained by simple dilation of the dike during intrusion (Figure 2). Several irregular masses of pink aplite occur higher up the hill.

Figure 2. Offset dike in the McAuley Gneiss. A. offset due to faulting, 6. offset due to dilation during intrusion.

Stop 3: Butler Rock

Deformed Waupee Volcanics. NW 1/4, SW 1/4, Section 5, T31N, RISE, Oconto County, Wisconsin, Shay Lake 7.5 minute Quadrangle.

We turn south from Highway W onto the West Butler Rock Road. Butler Rock is a large knob about 5 miles south of Highway W. The route passes first over a hilly area dominated by sand ridges (small eskers?), then across a short marshy stretch (glacial lake floor), then into a hilly area of pitted outwash. From the bus stop, proceed 0.4 miles down the jeep trail, then up a side track to the top of Butler Rock, about a 200-foot vertical ascent. This route is passable by field vehicle but not by bus! if the weather is fair and the foliage at its peak the view from the top should be spectacular. In the event of inclement weather this stop will be omitted because of the long walk it entails.

A detailed map of Butler Rock is presented in Figure 3. The overall geology of Butler Rock consists of E-W striking, roughly vertical rocks of the Waupee Volcanics, but with great small-scale structural complexity. Both thinly-laminated and massive units are present, the former possible representing tuffs or volcaniclastic rocks, the latter flows or dikes. Shear zones are very common, as are irregular patches of epidotization.


3. Structural sketch map of Butler Rock.

At Substop A is a fairly convincing example of a ventifact. The epidote patches are highly polished, and one contains a sharp-edged ridge very reminiscent of those which occur on dreikanters. Considering the high location and the amount of sand at the base of the hill, wind abrasion seems fairly plausible, especially during the late Pleistocene when periglacial conditions prevailed.

At Substop B, a small dike about 1m thick has been complexly folded and sheared. The axial plane of the folding is about parallel to bedding and strikes about 115 (Figure 4).

A small fold, one of the few which can be found on an outcrop scale in this area, occurs at Substop C. The fold is Z-shaped with an axial plane trace of 77. The core of one half of the fold has been crushed and sheared (Figure 5). The geometry of this fold is hard to reconcile with the geometry of the McCaslin Syncline. There does not seem to be any evidence for a west-closing fold between here and the McCaslin Syncline, such as classical structural geology would predict. it may be that this fold represents a. different deformation event than the one which formed the McCaslin Syncline.

Figure 4

Folded dike on Butler Rock (Substop B) Area shown is about 10 m across


Figure 5.

Z-fold on Butler Rock (Substop C) Area shown is about 5 m across.


Stop 4: Thunder Mountain Hatchery

Center of NW 1/4, Section 5, T32N, RISE, Marinette County, Wisconsin, Thunder Mountain 7.5-Mlnute Quadrangle.

Lunch Stop Water and rest: rooms available.

The first item of interest is a small knob in the middle of the south lawn. It consists of conglomerate sprinkled with attractive red euhedral garnets. No hammering, please. Read and Wels (1962) suggested this might be a slump breccia, but the texture could just as easily be that of a normal quartzitic conglomerate.

-31- The hill west of the hatchery buildings is made up of impure quartzite which strikes north-south and dips 40-50 W. A large sill of metadiorite occupies much of the top of the hill. Both contacts are visible. The metadiorite contains some quartzite xenoliths.

This locality lies at the eastern end of the McCaslin Syncline, and the attitude of the rocks here is consistent with the overall picture of a west- plunging syncline. The quartzite is conventionally mapped as the southern end of the Thunder Mountain Quartzite, but it is quite different from the main mass of quartzite. The quartzite at this locality is fine-grained and thin-bedded, whereas the main body of the Thunder Mountain Quartzite is massive, coarsely crystalline, and much purer. Thunder Mountain is visible as the high hill to the northwest. The best outcrops on Thunder Mountain Itself are on the west side in an area accessible by 4-wheel drive vehicles, The more accessible east side is thickly mantled with glacial deposits and has few outcrops. The map of Medaris and Anderson (1973) shows the rocks at this stop as being part of the Waupee Volcanics.

Stop 5: High Falls Reservoir

SE 1/4, NW 1/4, Section i, T32N, RISE, Marinette County, Wisconsin. High Falls Reservoir 7.5-Mlnute Quadrangle.

Several intrusive rock types are visible at this stop, as well as a variety of anomalous ice-flow indicators.

The igneous nomenclature at this stop has been quite confusing. The main rock types are a pinkish rock with large rounded quartz phenocrysts and a dark gray to black, medium-grained porphyry. Read and Wels (1962) called the pink rock Hagar Rhyollte and the dark unit Peshtigo River Porphyry.

Small granitic pods within the gray unit were called High Falls Granite. Medarls and others (1973a) correlated the pink unit with the Belongia Granite which occurs over a wide area south of Mountain, and called the dark unit Peshtigo Trachyandesite. The granitic veins and pods within the Peshtigo Trachyandesite were considered to be a syenitic border phase of the Belongia Granite.

The Belongia Granite at this stop is an attractive, distinctive rock which consists of a fine-grained pink goundmass that encloses 5-mm rounded phenocrysts of translucent gray quartz and pinkish K-spar. The quartz phenocrysts are far more conspicuous than the K-Spar. The porphyritic texture probably led to the early identification as rhyollte, but there are no signs of layering or flow banding, and an intrusive origin seems more likely.

The Peshtigo Trachyandesite is a dark, quartz-poor unit with small gray feldspar phenocrysts. its relations with the Belongia Granite are gradational, but Medarls and others (1973) felt that it predates the Belongia granite. Both of these units are considered part of the Wolf River Bathollth, an anorogenic granitic complex which has been dated between 1450 and 1500 m.y. old. The arrangement of the Belongia Granite and Peshtigo Granite and Peshtigo Trachyandesite, as well as several other units, is arcuate , and Medaris and others (1973b) suggested that this portion of the Wolf River Batholith may be a ring complex. A number of ring complexes occur in central Wisconsin on the western margin of the Wolf River Batholith.

Substop A (Figure 6) is a low rounded hill of Belongia Granite with incipient spheroidal weathering. Nearby, at B, is a small but perfect roche moutonee. Note that the ice flow, as indicated here, was from SE and NW. The same ice flow direction is indicated at C, where both chatter marks and very large crescentic gouges occur.

Ice flow indicators around High Falls Reservoir all show an anomalous ice- flow direction from SE to NW (Figure 7). A possible explanation might be that ice from the Green Bay Lobe to the east spilled into the Peshtigo River Valley and spread both up and down-valley.

Figure 7. ice-flow indicators in the High Falls area. Data collected by Tom Bader and Dave Comb under the supervision of Ronald Stieglitz and Joseph Moran. Arrows show directions of flow as inferred from stoss-lee features, chatter marks and crescentic fractures. Unornamented lines indicate striations. Dot in center of each symbol indicates location of data point.

The small peninsula D is made up mostly of Peshtigo Trachyandesite, with patches of granitic or syenitic material which is considered a border phase of the Belongia granite. A curious feature is the presence of deep grooves of roughly semicircular cross section. At the bottom of some of them is a joint with a narrow band of alteration on either side. Evidently some combination of deep weathering and mechanical erosion is responsible for these grooves.

High Falls Dam was built in the 1920's to provide power for the city of Green Bay. it now is used only for local power needs.

Route Description - High Falls Dam To Green Bay

From High Falls Dam to Crivitz the route passes through hilly terrain formed by pitted outwash and recessional moraines. South of Crivitz the terrain becomes gentler and is mostly ground moraine and thin outwash. Between Crivitz and Found is a historical marker which marks the halfway point between the equator and the North Pole. The latitude is not 45, as one might expect, but 45 8' 45.7". The distance to both the equator and the pole is 3107.47 miles. The discrepancy in the latitude is due to the way latitude is measured. Latitude is not defined by the angle between a location and the equator, measured from the center of the earth. Rather, it is defined by the angle a line normal to the earth's surface makes with the equatorial plane. Obviously, if you're going to measure position astronomically, it makes more sense to refer to the local vertical rather than some oblique line passing through the earth's center. The slightly ellipsoidal shape of the earth causes degrees of latitude to be slightly shorter at low latitudes than high (Figure 8).

Figure 8. Measurement of Latitude

Just north of Pound, about 10 miles south of Crivitz, the route passes between sand hills which are part of a large esker. The esker trends roughly E-W and can be traced for about 10 miles. Most of the conspicuous sand hills for the next 10 miles or so are eskers. Near Stiles, about 20 miles south of Crivitz, the terrain flattens out into a former floor of Green Bay (Thwaites, 1943). Much of the region between Stiles and Green Bay was devastated by the Peshtigo fire of 1871 (see following article). The few hills between Stiles and Green Bay are mostly sand dunes.

The Great Peshtigo Fire

The region north of Green Bay was devastated by the worst forest fire disaster in North American history on October 8. 1871, the same day as the much more famous Chicago fire. The following account is largely from Wells (1968).

After the depletion of the New England forests, lumbering activity in the U.S. shifted west to the Great Lakes. The original forest of northern Wisconsin was white pine, which furnished

lumber for the expanding settlements of the Midwest. Settlers in those days were extremely careless with fires, which usually tended to burn themselves out in the sparse understory of the then-virgin forests. In the warm, dry fall of 1876 there were many small brush fires in north eastern Wisconsin. it had only rained once since July.

On the evening of October 8, 1876, the weather changed. Strong winds caused the many small fires to coalesce into larger fires. The main fire started just northeast of Green Bay and burned much of the lower Door Peninsula. Many people believe the fire "jumped" across Green Bay, and in support of this idea, there are reports from ships in the bay of large burning branches falling far offshore. it is more likely, however, that the fires east and west of the bay originated independently.

Figure 9. Area destroyed by forest fires, October 8, 1871. Open circles show towns which were not destroyed, closed circles show towns which were destroyed.

Some settlers, aware of the fire danger, had plowed firebreaks around their homes. These helped if the fire was not too intense, but: in many areas the fire developed into a true firestorm and killed people who were in the middle of large clearings. Even previously burned-over ground was not always a safe refuge.

A number of villages were destroyed, most notably Williamsonville, near Brussels on the Door Peninsula, where 60 died. But by far the worst toll was taken at Peshtigo. When the fire danger became acute, the citizens of Peshtigo headed for the Peshtigo River, but many never made it. Of the 2500 people then living in Peshtigo, 600 died. including many Scandinavian immigrants who had arrived only a few days earlier. Some accounts say as little as ten minutes elapsed between the time the fire arrived at Peshtigo and the time the entire town was burning.

There are as many remarkable stories of the fire as there were people involved. One man. Reed Lovett, ran for a stream but was caught by the fire. He decided a quick death was preferable to a slow one, so he pulled out his knife and stabbed himself in the chest repeatedly. Meanwhile he kept running, eventually falling into the. stream. He survived. The parish priest at Peshtigo, Father Pernin, put his altar vessels in a cart and headed for the Peshtigo River. Despite the fire. being so intense that some people died only a few feet from safety in the river, the people in the river found their clothes catching fire, the altar vessels were undamaged, an event which many Catholic survivors, not surprisingly, considered miraculous. it finally rained on October 9, the day after the fire.

After the fire, it was found that in some areas even the stumps and roots of trees had been consumed. At least 1,150 people are known to have died. The last known survivor of the tire, Mrs. Augusta Wegner Bruce, who was two years old at the time, died in 1974 at the age of 104.

The governor of Wisconsin was out of the capitol directing relief efforts for victims of the Chicago fire when word arrived on October 10 of the disaster at Peshtigo. His wife, Many Fairchild, though she lacked legal authority to do so, ordered relief supplies bound for Chicago to be diverted north to Peshtigo, an action which won her praise for her decisiveness. Geology played a role in saving two other cities from a similar fate. Marinette, Wisconsin and Menominee, Michigan are only seven miles north of Peshtigo. Had the fire reached them with the same intensity, the disaster at Peshtigo would very likely have been repeated. However, north of Peshtigo there are many sand ridges, stabilized sand dunes formed during Pleistocene high stands of Lake Michigan. The vegetation is sparser on these ridges, and the fire was manageable when it reached Marinette and Menominee, so that these cities were largely spared.

There are few tangible traces of the fire today; little was left afterward. Perhaps the most poignant relic is in the Beyer Home Museum in Oconto: a charred dollar bill taken by his father from the pocket of a boy who died in the fire. A small museum in Peshtigo contains a few items, notably a dime and half dollar fused together by the heat. Next to the Peshtigo Museum is the cemetery where 300 victims are buried in a common grave. A few of the victims have individual grave markers, but these rarely mention the fire. Evidently the survivors felt that the date October 8, 1871 told the story by itself.

There are virtually no clear geologic or physiographic signs of the fire. The fire occurred late enough in the fall that little erosion occurred before the winter snow cover, and erosion the following spring was probably minimal as the area became revegetated. The ash layer has been obliterated by weathering and plowing. Probably the most lasting effect of the fire was the rapid (!) clearing of a large part of the lower Door Peninsula which hastened the opening of that area to farming.


Supplementary Stop S1: Cambrian Sandstones

In the event that severe weather forces the cancellation of Stop 3 (Butler Rock), we will visit the following two stops as time permits. They illustrate some of the lower Paleozolc stratigraphy of northeastern Wisconsin.

SE 1/4, SE 1/2, Sec. 33, T31N, R19E, Coleman, 15-Minute Quadrangle.

One of the few Cambrian outcrops in northeastern Wisconsin is located north of Highway 64 about 5 miles west of Pound. The friable nature of the Cambrian sandstones, and the coincidence of the recessional moraine belt with the Cambrian outcrop belt, combine to make outcrops very rare.

The sandstone exposed here is a fairly well-indurated, pure quartz sandstone with thin (10 cm) beds. The beds form low outcrops in the stream bank and ledges in the stream. No fossils have been found yet at this particular locality.

Supplementary Stop S2: Rouer Quarry

SE 1/4, NE 1/4, Sec. 6, T28N, R21E, Oconto West 7.5 minute Quadrangle, Wisconsin.

Contact between Platteville Dolomite and Saint Peter Sandstone (both Ordovician).

The low hill on which the quarry is situated is an outlier of Platteville Dolomite. in the quarry it is massive or thick-bedded and buff in color, grading into thin-bedded, blue-gray shaly dolomite near the base. Fossils are abundant: the massive dolomite contains abundant branching bryozoans, and the shaly material is rich in trilobite fragments. Recent reactivation of the quarry has exposed good trilobites, cephalopods, brachiopodss, and crinoids. Several complete crinoids and long crinoid stems have been found and are now in the UWGB study collection.

In the southern end of the quarry, the floor of the quarry is Saint Peter Sandstone, noted for its purity and good sorting. Here it is somewhat iron- stained but in other parts of the Midwest it is pure enough to quarry for glassmaking. it is generally weakly cemented, and at this locality it is very friable. The contact with the overlying Platteville Dolomite is somewhat gradatlonal over a meter or so.

This stop is labeled a Gravel Pit on the topographic map. Errors on U.S.G.S. maps are quite rare: the Survey tries to attain an accuracy of one error or less per 100,000 map symbols.

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