Site: NKENS 7-1:

Glenshaw Formation Sandstone Channel Rt. 28, Harmarville, PA (Hulton Bridge Locality)


Latitude:                             40 31' 50"N

Longitude:                          79 51' 01"W

Quadrangle:                        New Kensington 7 1/2'

Age:                                         Pennsylvanian

Formation(s):                     Conemaugh Group, Glenshaw Formation, channel sandstone below Bakerstown coal and cutting into Woods Run interval.

Purpose:                            This site offers a good example of a sandstone channel.

Access and Parking:

Outcrop is just above road level across ravine on opposite side of guard rail. Parking on side of road next to guard rail. Dangerous location, very high traffic area. No room for motor coach. Not recommended for children.



Mass Transit Directions:

(Make sure you get an up-to-date PAT Transit schedule:

No PAT Transit service.

Driving Directions:

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 1.6 mi. then bear right onto I-579. Stay on I-579 across the Allegheny River then get onto Rt. 28 East. Stay on Rt. 28 approximately 13.2 miles. Exit at the Harmarville exit. At the end of the exit ramp, make a left, go 0.5 miles and re-enter Rt. 28 in the westbound direction. Once on Rt. 28, go 1.1 miles and pull off next to the guardrail and park. Be very careful with high traffic. Outcrop is on cliff on other side of guardrail.

See map and figures.

What you will see:

This is one of the best exposures of rocks in the local Pittsburgh area. Unfortunately it is also one of the least accessible, being very steep and along a very busy highway. The entire section of the middle Conemaugh Group is exposed here, from the middle of the Glenshaw Formation to the middle of the Casselman Formation (see figure below). The best view of the outcrop can be seen from across the Allegheny River in Oakmont, at the Oakmont Yacht Club. However, up close, the best views are of a sandstone channel that cuts down though the Woods Run and Nadine limestone intervals.

    Plant fossils are common in the talus material found at the bottom of the outcrop. It is uncertain exactly where in the outcrop the shales have fallen from. In addition, there are abundant reddish brown nodules that may be found on  the talus slope. If broken open, the nodules occasionally contain some surprising fossils and shown below. Be very careful when splitting these nodules as they will shatter. Wear safety glasses. The nodules have grown around a geochemical anomaly caused by the presence of organic debris, such as a fish tooth, fish scale, or tree branch.

Geologic History: Environment of Deposition:

At road level, the channel sandstone is clearly visible, and shows a sharp erosional base that has cut through a significant part of the section. It is a distributary channel that formed during the regressive sequence overlying the marine facies of the Woods Run limestone. 

Stratigraphic section of the Hulton Bridge locality. From Donahue and Rollins (1974).

Paleogeographic map showing the region during Ames limestone time.

Paleogeographic map showing the region during Bakerstown shale time.

Paleogeographic map showing the region during Woods Run limestone time.

Paleogeographic map showing the region during Nadine limestone time.

Click on the thumbnails below for pictures of the outcrops:

A view of the whole channel.
A close-up of the south side of the channel.
A close-up of the north side of the channel
One of the many plant fossils that may be found in the talus slope. This is Mariopteris nervosa.
One of the many plant fossils that may be found in the talus slope. This is Calamites sp.
One of the many reddish concretions. This one is cored by pyritized pieces of Calamites. Note the barite mineralization in the fractures.
Another concretion. This one is cored by a fish tooth (center of right side).

Fossils:

Excellent plant fossils may be found in the shale talus at the bottom of the cliff and in the reddish nodules. Similarly, marine fossils may be found in the talus from the marine units.

References:

Donahue, J., and Rollins, H. B., 1974, Conemaugh (Glenshw) Marine Events: Field Guidebook, 3rd Annual Meeting, Eastern Section, American Association of Petroleum geologists, Pittsburgh Geological Society, 47 pages plus contributed papers.

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 p.

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.

Wagner, W. R., and others, 1970, Geology of the Pittsburgh Area: Pennsylvania Geological Survey General Geology Report G 59, 145p.

Click here for  an image of the County Geologic Map (1880)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

nd edition, Pittsburgh, PA , 80p.