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OLLI Course on Geology and
Environmental Geology of the State College Area
Field Trip: From tropical shorelines to glacial ice fields, with orogeny mixed in, and all on Tussey Mountain: 400 million years of history
STOP ONE. Tussey Sink. Leave State College on 322 south. After passing a motorcycle place and the Shaner Baseball Complex, turn right on Taylor Hill Road. At the turn is Tussey Sink, a long, linear sinkhole. A small stream comes off the mountain and flows over the impermeable Reedsville Shale ("Or" on the geologic map), but when the limestone units (Ocn and Obl) are encountered, the stream goes into the sinkhole, and its water joins the groundwater system. That is a common occurrence along the mountain front. On the geologic map below, Tussey Sink is at the top of the map to the right of "Obl."
STOP TWO, Colyer Lake. Continue following Taylor
Hill Rd, then turn right on Lingle Road to the Colyer Lake Boat Access
Area.. Subcrop at the parking lot is shale and siltstone of the Reedsville
Formation ("Or"). The lake is underlain by Reedsville, which is impermeable.
Unfortunately, the same cannot be said for the dam. (The geologic map
above shows part of the lake underlain by limestone (an uncolored unit) but the
map probably is incorrect. Even if it were correct, a thin layer of
limestone would be underlain by Reedsville Shale, because the lake lies in the
The skyline ridge to the southwest is underlain by the Tuscarora Sandstone ("St"), whereas the lower ridge in front of it is underlain by the Bald Eagle Sandstone ("Obe"), and the intervening valley by the Juniata Formation ("Oj"). Colyer Lake lies in a short-wavelength anticline, with a syncline northwest of the anticline. The Bald Eagle wraps around the nose of that syncline, forming the hill (the end of "Tussey Mountain" on the geologic map above) to the west of the lake. Another short-wavelength syncline lies southeast of the Colyer Lake anticline, with Tuscarora and Juniata (at the "Oj") in its core. All those folds lie in a transition between the over-arching Nittany Valley anticlinorium and the Seven Mountains synclinorium.
STOP THREE, Bear Meadows Natural Area. Circle
around Colyer Lake, finding Lake Road west of the lake, and pass the western
boat access area. Then turn left on Treaster Kettle Road. This road winds up
through the Reedsville (through the "C" of "ROTHROCK" on the map above)
and up the axis of the Colyer Lake anticline, passing a nice exposure of rather
black Reedsville on the right. Just before the road deadends at Bear Meadows Road,
it passes into the Bald Eagle
(at the bottom left of the map above, at the top of the map below). Turn left on Bear
Meadows Road, stopping at a viewing area.
Bear Meadows Natural Area encompasses 890 acres
and was designated a Natural Area in 1966. The The bog is unique for several
reasons. In geologic terms it is a relict community that contains Pleistocene
fauna. Biogeographically it is a high altitude boreal sphagnum bog that was not
glaciated. Many bogs, like those in Canada, originated in glaciated terrain. At
1800 feet above sea level, Bear Meadows is higher than comparable bogs in North
America and is the only one surrounded by mountains. The mountains do not,
however, contribute very much sediment. Although the bog avoided glaciation, it
did receive the weather conditions of a glaciated region: cold and wet. The bog
sits in the Juniata Formation (look near the htop of the map above)..
Plants have prospered in this bog for over 10,000 years. Analyses of core samples from the bog have provided descriptors of previous climates. The bog is fed by several acidic springs, which together with tannic acid generated in the bog cause a low pH level, resulting in no fish life. A base layer of peat, up to eight feet thick, gives the water a brownish tint. As the water flows along Sinking Creek the pH level rises, and fish can be found downstream. The bog owes its continued existence to the low-pH water, resulting in dissolution of Al and killing off of many plant species, continued cool conditions, and continued influx of water.
STOP FOUR, Wampler Road. Continue on Bear Meadows Road to its intersection with Wampler Road. We will walk to a vista (a little northeast of the word "FOREST" in the southwest part of the map above). At the vista we look southeast to Broad Mountain, across the axes of several anticlines and synclines. The rocks in the vista are the Tuscarora Formation, forming ridges, and rocks younger than the Tuscarora and therefore younger than any in Nittany Valley. These sediments are sandstones, shales, and limestones, all marine ("Sc, Sbm, and Swc" on the map). They represent the tail end of the Taconian orogeny and the period of quiescence between the Taconian and Acadian orogenies. In that period the seaway over the continent was re-established, although periodic influxes of sediments continued to disturb it. The continent was then in tropical latitudes, and the water was warm (hence the title of this trip), the same conditions as for the limestone units that preceded the Taconian orogeny ("Ocn" and "Obl").
Along the roadside are blocks of Tuscarora sandstone that we can examine. It is light in color because it contains no clay, very hard because it consists of quartz grains cemented by quartz; it contains occasional larger-grained horizons, and has cross-bedding. These characteristics indicate that the mountainous source of its grains was some distance away and not particularly high (i.e., after the main phase of the Taconian Orogeny), and that the formation represents a beach or off-shore bar environment. On one slab, worm burrows are evident.
When we turn around from the vista, we see a
periglacial boulder field. The eastern and central US was invaded by
four periods of glaciation in the Quaternary period (last 2 my): Nebraskan at
1.8 my to 1.65 my, Kansan at 900,000 to 750,000 y, Illinoian at 400,000 to
250,000 y, and Wisconsin, a series of ice advances and retreats at 100,000 to
10,000 y. Pre-Wisconsin age ice advanced, from Canada, to about 40 km south of
Williamsport, and Wisconsin ice stopped about 50 km north of Williamsport. In
other words, ice did not invade the State College area. But during ice
advances, it was cold here, particularly on ridge tops, and average temperatures
were probably below freezing. Ice retreated about 15,000 y ago and covered a
large part of northern Canada until 8,000 y ago.
In many places atop the Seven Mountains, the Tuscarora sandstone was shaped by ice, frost, and freeze-thaw cycles. Large fields of angular boulders are found, particularly on south-facing slopes, from the tops of the ridges to the valley floors. Observable features include “patterned ground” – stone stripes and polygonal grouping of rocks. The breakup of bedrock and movement in fields occur by gelifluction: water released in the surface during a thaw cannot penetrate the frozen layer below. So the water is concentrated at the near-surface and produces a gel that lacks cohesion and can flow readily. These periglacial fields are moving very little today, as witnessed by the straight trees growing within them.
STOP FIVE, Whipple Dam. Continue on Bear Meadows
Road, around a hairpin turn, and then turn right on Beidelheimer Road.
Beidelheimer will intersect with Greenlee Road (south of "GREENLEE" on the map
above). Turn left on Greenlee and
follow it to a triangular intersection with Laurel Run Road, and follow Laurel
Run to Whipple Dam State Park (faintly visible on the map above to the right of
"Axemann Fm" at the left)..
At the dam we will see a small anticline defined by the Castanea Member of the Tuscarora Formation ("St"; the anticline is the yellow strip between "Sc" and "Sc"). The uppermost member of the Tuscarora, it is a fine-grained, dark-brown sandstone. Ripple marks are visible on one outcropping, testimony to its shallow-water origin. The Castanea is bounded on either side by Rose Hill Shale (part of the Clinton Group, "Sc") that supports a pine tree forest. To the south is a syncline and then another anticline, formed by Tuscarora ("St") in Greenlee Mountain. The ridge to the north is the unit stratigraphically above the Rose Hill, the Keefer Sandstone, part of the Clinton Group ("Sc"). Proceeding north from that ridge, we find a syncline exposing the Mifflinburg Formation ("Sbm"), then an anticline cored by the Keefer, a syncline with Mifflinburg bedrock, the Rudy Mountain anticline held up by the Tuscarora, a syncline with Clinton Group bedrock, then the top of the ridge held up by the Tuscarora, and finally the Nittany Valley anticlinorium. Those folds are also shown in a diagrammatic cross-section:
A schematic cross-section roughly along Route 26, with NW at the left and SE at the right.
STOP SIX, Whipple Dam area. We’ll stop and look at the evidence for a strike-slip fault that offsets the antcline we just saw. On the geologic map, that fault (the heavy line that IS NOT a road) offsets the yellow Tuscarora near the edge of the map. Some similar faults can be seen at the top of the map.
STOP SEVEN, time permitting, at Jo Hays Vista. From this vista we can see across the Nittany Valley to Bald Eagle Ridge, held up by the Tuscarora Sandstone, and beyond that the Allegheny Plateau. We are standing on Tuscarora atop Tussey Mountain, and below us we can see the much lower ridge formed by the Bald Eagle, with the Juniata forming the valley in between. In the Nittany Valley the Juniata Formation consists mostly of red shales and some red siltstones.