Latitude:                         40° 35' 24"N

Longitude:                      80° 14' 25"W

Quadrangle:               Ambridge 7 1/2'

Age:                          Pennsylvanian

Formation(s):            Conemaugh Group, Glenshaw Formation, Mahoning shale, Mahoning sandstone, Brush Creek coal, Brush creek limestone.

Purpose:                   The Mahoning shale here is one of the best plant fossil collecting localities in the region. Also, there is fine collecting of marine fossils from the Brush Creek limestone.

Outcrop of Mahoning shale is above road level, up a steep 10-12 foot bank. No room for motor coach. The Brush Creek limestone occurs on an upper bench which is a more difficult climb. Park along wide berm along southbound PA 51 approximately 300 feet from the Abridge bridge (next to the third and furthest lamp post from the bridge). Climb up worn path along side of road. Recommended for all ages with strong caution as footing on very steep path is poor. Come in winter, autumn, or spring when there is little vegetation.

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

From Oakland, take any bus to downtown Pittsburgh. Then 16A to Ambridge. Get off at the nearest stop to the Ambridge-Woodlawn Bridge (11th Street at Merchant Street). Walk across bridge to outcrop area.

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. Go across Duquesne Bridge and follow exit to Rt. 65 (Ohio River Boulevard). Follow Rt. 65 into the town of Ambridge. Make a left onto the Ambridge-Woodlawn Bridge, then a left onto Constitution Boulevard (Rt. 51). Pull off at wide burn approximately 500 feet south of bridge near the last utility pole. Walk up steep slope to lower bench.

See map and figures.

This is the best plant fossil collecting locality in the Pittsburgh region. It has been documented by Burns (1991) and 'The Fossil Guy'  at http://www.fossilguy.com/sites/ambridge/. The Mahoning shales on the lower bench contain many layers of plant fossils that can be recovered by careful splitting of the shales with a hammer and fine chisel. The Brush Creek on the second and higher bench is a dark gray to black calcareous shale to argillaceous limestone that contains common marine fossils including brachiopods, pelecypods, gastropods, cephalopods, and corals. Occasionally, fossil fish teeth may also be found. The Brush Creek interval though is very difficult to reach.

Geologic History: Environment of Deposition:

The Brush Creek marine unit is regionally extensive and represents a quiet, poorly oxygenated environment close to shore. most likely a lagoon setting behind an offshore barrier island systems (Harper, 1990). It is at the climax of of of several marine transgressive sequences documented in southwestern Pennsylvania (Donahue and Rollins, 1974; Busch, and Rollins, 1984; Busch and Brezinski, 1984).

The Mahoning shale on the other hand is a delta plain deposit that formed at a point of maximum regression at the beginning of Conemaugh time.

Paleogeographic map showing the region during the during Mahoning Shale time.

Paleogeographic map showing the region during the during Brush Creek time.

Click on the thumbnails below for pictures of the outcrops:

A view of the Mahoning shales where the best plant fossils are found.

Some of the excellent plant fossils that can be found at this site. Note the 'fiddlehead' fern.

Some of the fossils found in the Mahoning include:

Calamites sp.

Neuropteris sp.

Pecopteris sp.

Some of the fossils found in the Brush Creek include:

Brachiopoda: Debyia sp., Chonetinella sp.

Cnideria: Stereostylus sp.

Gastropoda: Meekospira sp., Shansiella sp., Cymatospira sp.

Pelecepoda: Nucolopsis sp.

Fish teeth

Burns, J., 1991, Fossil  Collecting in the Mid-Atlantic States, Johns Hopkins Press, Baltimore, 201 p.

Busch, R. M., and Brezinski, D. K., 1984, Stratigraphic analysis of Carboniferous rocks in southwestern Pennsylvania using a hierarchy of transgressive-regressive units: Field Trip Guidebook for the Eastern Section Meeting of the American Association of Petroleum Geologists. 104 p.

Busch, R. M., and Rollins, H. B., 1984, Correlation of Carboniferous strata using a hierarchy of transgressive-regressive units: Geology, v. 12, p. 471-474.

Brezinski, D. K., 1983, Developmental Model for the Appalachian Basin marine Incursion: Northeastern Geology, v. 5, p. 92-99.

Donahue, J., and Rollins, H. B., 1974, Paleoecolgical anatomy of a Conemaugh (Pennsylvanian) marine events: in Briggs, G., ed., Carboniferous of the Southeastern United States, Geological Society of America Special Paper 148, p. 153-170.

Donahue, J., and Rollins, H. B., 1974, Conemaugh (Glenshaw) Marine Events: Field Guidebook for the third Annual Meeting of the American Association of Petroleum Geologists. 104 p.

Donahue, J., and Rollins, H. B., 1979, Coal Geology of the Northern Appalachians: Field Trip Guidebook for the Ninth International Congress of Carboniferous Stratigraphy and Geology. 45 p.

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.

Hoskins, D. M., 1973 third printing, Fossil Collecting in Pennsylvania: Pennsylvania Geological Survey Bulletin G 40, 126 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.

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)