This is 1 of 12 EarthCache sights in the SRWT. The first 100 to complete the trail will receive a geocoin commerating the SRWT, 60 of which are trackable. These will be available at the Mercer County Conservation District office Mon.- Fri. from 8 am to 4 pm after April 21st. We are located at 753 Greenville Road, Mercer, PA 16137. To learn more about this geoWatershed Trail, visit us by clicking here.
SHENANGO RIVER HISTORY (Mondok, 1990)
The Shenango River Basin is shared by the state of Ohio and the Commonwealth of Pennsylvania. The river and its tributaries drain 744 square miles of the Pennsylvania counties of Crawford, Lawrence, and Mercer and 285 square miles of the Ohio counties of Ashtabula, Mahoning, and Trumbull. The waters and its tributaries been used for transportation such as the Erie Extension Canal, watering livestock, and other household uses.
Prior to European settlement, the land area of the Shenango was inhabited by many indian tribes including the Seneca and the Delaware. The word Shenango itself comes from the Iroquoian word Shaningo meaning “beautiful one”.
The 75 mile long river begins in the marshes that are now part of Pymatuning Reservoir near Hartstown in Crawford County and eventually meets the Mahoning River near New Castle in Lawrence County.
ICE AGE INFLUENCES (Mondok, 1990)
The topography and soils in Pennsylvania and Ohio were shaped during the Ice Age that ended about 10, 000 years ago. Prior to this glacial epoch, the Shenango River flowed in a northerly direction to the Atlantic Ocean via the Great Lakes and St. Lawrence River. This dissected plateau was covered by glaciers; some were a mile thick in some places. Boulders, rocks, soil, sand, silt, and clay were carried with the glacial ice and deposited on glacial till, kame terraces, moraines, and eskers when the ice melts as the climate warmed. These deposits were so vast, that their ancient river valleys were filled, causing the flow from the Atlantic Ocean to the Gulf of Mexico.
SEDIMENTARY ROCK FORMATION
Sedimentary rocks are formed due to the forces of erosion by wind, water, and weathering. Over time, rocks erode and break down into pieces. These pieces travel down rivers and streams until they eventually settle on the bottom as sediment. Eventually, they are pressed together and form sedimentary rocks (ThinkQuest, 2000).
WHY ARE SEDIMENTARY ROCKS SO PROMINENT IN THIS AREA?
Sedimentary rocks are dominant in this region because this area was covered by an ocean for millions of years: first in the Cambrian period when the global sea level was high; during this time the ocean stretched far inland over most of the Northeast (Ansley, 2000).
The ocean also existed during the Taconic and Acadian mountain-building periods west of the new mountain ranges that were formed. The basin of the inland sea formed by the buckling of the crust from the compression of plates during the mountain-building stages(Ansley, 2000).
Conglomerates, sandstones, siltstones, shales, limestone, and dolostones are common rocks that were formed from these oceans and the bordering environments such as deltas, swamps, and tidal areas (Ansley, 2000).
SHENANGO RESERVOIR MISSISSIPPIAN ROCKS- SHARPSVILLE SANDSTONE
Sharpsville Sandstone was named due to the sequence of alternating layers of very fine-grained sandstone and shale. The Sharpsville Sandstone that is exposed along the Shenango Reservoir is a very fine-grained, planar-bedded sandstone. It is light to medium gray or yellowish gray in color and weathers to an almost grayish brown. You can see this formation across the Shenango River Lake along the streambank (Schiner and Kimmel, 1976).
A LOOK BACK AT THE MISSISSIPPIAN PERIOD
During the Mississippian period, the Inland Basin region was still an inland sea environment. Sediment was beginning to be shed into the basin from the Acadian highlands of the east. Gradually, the amount of incoming sediment into the basin declined. The shoreline of the sea moved back and forth across the basin as the sea level rose and fell. The changing water levels created alternating sequences of non-marine and marine sedimentary rocks. Limestones were beginning to form in areas of the sea that received little sediment and had high amounts of shell debris. This shell debris came from various mollusks and crustaceans that were alive during this period. (Ansley, 2000).
During this time period, the Northeast was still located along the equator, so the warm climate created lush vegetation. Large swamps covered the shorelines of the inland sea. Plant material in the swamps would die and accumulate into thick piles of peat. This peat became buried by sediment and more vegetation, eventually becoming compressed. Over time and continual burial, the peat was transformed into layers of coal. Thus, the Mississippian rocks of the Inland Basin region, are repeating sequences of alternating sedimentary rock and bands of coal due to the shifts in sea level that allowed lush vegetation to develop into swamps (Ansley, 2000).
SANDSTONE FORMATION
Sandstone is formed where sand is laid down and buried; this can occur anywhere that sand is prominent such as: river deltas, deserts, swamps, and ocean floors. As this sand becomes deeply buried, the pressure and slightly higher temperatures cause minerals to dissolve and become mobile. The sand grains become more tightly knit together, and the sediments are squeezed into smaller volumes. Cementing material moves into the sediment by the dissolved minerals. This forms the end product of sandstone (Alden, 2012).
The photo above depicts typical layering of sandstone.
COORDINATES TO PARKING AREA
You will park in a small plaza where a sub shop called “Lock, Stock, and Barrel” is located. Be sure to bring an empty stomach so that you can enjoy some delicious food to energize yourself before or after your expedition. The coordinates to the parking area are:
N41 15.922' W080 28.510'
To locate the beginning of the trailhead, go to the coordinates:
N 41 15.877', W 080 28.459'
The trail is known as Trout Island Trail. From the parking area, cross the street towards the Rite Aide. Head right up the hill and you will come to the trailhead rather quickly.
TO GET CREDIT FOR THIS CACHE:
Please be sure to send your answers to the following questions to jmccullough@mcc.co.mercer.pa.us in order to receive credit for this cache.
1. What type of rocks seem to be the majority of those exposed?
2. Find the culvert pipe that empties into the reservoir on the same side that you are standing. This is located along the creek upstream from the walkway; this creek is known as Pine Hollow Run. Locate the rocks that are exposed along Pine Hollow Run. Do they appear to be similar to those along the reservoir? Why or why not?
A special thank you to the Army Corps of Engineers for granting us permission to place this EarthCache.
References:
Alden, A. (2012). An Introduction to Sandstone. About. Com Geology. Retrieved from: http://geology.about.com/od/more_sedrocks/a/aboutsandstone.htm
Ansley, J. E. (2000). The Teacher-Friendly Guide to the Geology of the Northeastern U.S. Paleontological Research Institution, 32.
Mondok, J. (1990). The Shenango River. Shenango Riverscapes, 1-2.
Schiner, G.R. and G.E. Kimmel. (1976). Geology and Ground-Water Resources of Northern Mercer County, Pennsylvania. Water Resource Report, 33, 17.
ThinkQuest. 2000. Sedimentary Rocks. Retrieved from: http://library.thinkquest.org/J002289/sed.html