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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 syncline.)
     The skyline ridge to the southwest ("MOUNTAIN" at the bottom margin of the map above) 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 syncline, with an anticline east of the syncline.  The Bald Eagle wraps around the nose of that anticline, forming the hill ("Tussey Mountain" on the geologic map above) to the west of the lake.  Those folds, like many others, lie within the over-arching Nittany Valley anticlinorium.

 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), passing a nice exposure on the right, and just before it deadends at Bear Meadows Road, 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.

 STOP SEVEN, near Whipple Dam.  Keefer Sandstone (part of the Clinton Group, "Sc") forms the small ridge.  The sandstone contains quartz but also calcite and fossils, and so is about halfway between a sandstone and a limestone.  It also contains a 2-foot thick bed of oolitic hematite that was the iron source of all the furnaces in the 1800s except for those in the Nittany Valley.  There the iron source was a thick paleosoil that formed on the Gatesburg Formation.  At this location we can see pits where the iron ore was mined out.

 STOP EIGHT, 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.