Site: WASHE 6-1:
Dunkard Group Section at Sam's Club, Washington, PA
Latitude: 40° 11' 01"N
Longitude: 80° 13' 07"W
Quadrangle: Pittsburgh West 7 1/2'
Formation(s): Dunkard Group, Middle of Washington Formation.
Purpose:This site includes a small sandstone channel, collecting of fine mudcrack specimens, and calcite samples. Section approximately 60 feet stratigraphically below WASHE 6-2.
Access and Parking:
Park adjacent to Sam's Club. Walk to parking lot level outcrop on hill side. Parking available for motor coach. Recommended for all age groups.
The above map does not include new roadways and development in the area.
Mass Transit Directions:
(Make sure you get an up-to-date PAT Transit schedule:
No PAT Transit service.
From the Cathedral of Learning, Drive 0.7 mi. west on Fifth Avenue. Make a Left on Craft Av. Go 0.1 mi., then make a right onto Blvd. of Allies, go 0.3 mi. then bear right onto entrance ramp to I-376. Stay on this highway through the Fort Pitt tunnels. Go a total of 8.0 mi. and exit onto I-79 south. Go 20.5 miles then exit onto I-70 east. Once on I-70 east, go 1.2 miles and exit on Beau Street. At end of exit ramp, make a right and go 800 feet. Turn left and follow road to shopping area. Turn right toward Sam's Club and park near hill in Sam's club parking lot.
See map and figures.
What you will see:
There are some very interesting features to examine at this site. A large sandstone channel is in the center and to the right of the outcrop. It cuts down, and into the underlying shale-siltstone interval. A much smaller channel is seen in just to the left of the center of the outcrop, at a level near the base of the larger channel. It is isolated within the shale/siltstone section. Below the large channel, near the base of the outcrop are several thin limestone layers. One layer, an approximately 10 to 15 cm thick laminated calcareous mudstone, contains excellent mudcracks. Interestingly, the surface of the bed also contain many small ostracode fossils. If you look closely, some of the ostracodes are found in the cracks themselves. Look closely on the surface of these mudstones for possible very rare amphibian tracks.
Look on the ground for pieces of white calcite that formed from groundwaters passing through these rocks long before this outcrop was formed.
Geologic History: Environment of Deposition:
During the early Permian, western Pennsylvania was located approximately 5 to 10 degrees south of the equator and had a tropical to subtropical environment. Some geologists suggest that the area was in a similar setting to that of modern-day New Guinea. Western Pennsylvania was the site of a deltaic system that bordered a large shallow sea coving much of the central North America. Sediments were fed into the delta region by large river systems originating in the growing Alleghanian mountains to the east. The mountains were growing because of the continuing convergent and collision of North America and the African portion of the Gondwana supercontinent.
Locally, large fresh to brackish water lakes would develop in the inter-distributary parts of the delta. According to Harper (1990), deposition in these large lakes involved carbonate precipitation by algae or other organisms. The conspicuous laminations (layering) that can be seen in many limestone layers is attributed to algal growth that occurred in extensive mats. Also found in these limestones are common breccia-conglomerates that may have formed by periodic drying of the lakebed and the formation of desiccation cracks. Long periods of exposure to weathering processes broke apart the lime beds forming breccias. These breccias were then covered with additional lake sediments as the lakes refilled (Berryhill and others, 1971)
The influx of silt and clay that did occur resulted in alteration of thicker carbonate and thinner non-carbonate muds that lithified into the limestones and shales that can be seen in this outcrop. A modern day analogue for these large lakes might be Lake Ponchartrain in the Mississippia delta region.
Below is a satellite image of the Lake Pontrarchain area.
The sandstone channel represents one of many in the Lower Waynesburg formation which represents the upper delta plain environment that extends into a regional basin that is being filled from the rising Appalachian mountains to the southeast (today's direction) and from highlands to the north (today's direction).
Here are the facies relationships in the Upper Pennsylvanian Uniontown Formation and the Permian Waynesburg Formation in southern Pennsylvanian and Northern West Virginia. This is from an untitled late 1970's guidebook by A. C. Donaldson (West Virginia University, retired).
The above two figures show the modern Ganges Delta. Compare with the paleogeographic map above.
Click on the thumbnails below for pictures of the outcrops:
Common ostracode fossils in the limestones, along with fish scales and fish teeth.
Berryhill, H. L., Jr., Schweinfurth, S. P., and Kent, B. H., 1971, Coal-bearing Upper Pennsylvanian and Lower Permian Rocks, Washington area, Pennsylvania: U. S. Geological Survey Professional Paper 621, 47p.
Edmunds, W. E., Skema, V. W., Flint, N. K., 1999, Pennsylvanian, in Shultz, C. H., ed, The Geology of Pennsylvania, Pennsylvania Geological Survey Special Publication 1, p. 149-169.
Harper, J. A., 1990, Fossil Collecting in the Pittsburgh Area, Pittsburgh Geological Society Guidebook. 50 pages.
Johnson, M. E., 1928, Geology and Mineral Resources of the Pittsburgh Quadrangle, Pennsylvania: Pennsylvania Geological Survey Bulletin A 27, 236 p.
Leighton, H. 1945, The Geology of Pittsburgh and its Environs: A Popular Account of the General Geological Features of the Region: Carnegie Institute Press, 2nd edition, Pittsburgh, PA , 80p.
Shaw, E. W., and Munn, M. J., 1911, Geologic Atlas of the United States: Burgettstown-Carnegie Folio, United States Geological Survey Folio 177 Field Edition, 123p.
Wagner, W. R., and others, 1970, Geology of the Pittsburgh Area: Pennsylvania Geological Survey General Geology Report G 59, 145p.
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