Site: PGHBE 4-1:

Ames Limestone Outcrops and Saltsburg Interval Outcrop in Frick Park, Pittsburgh, PA


Latitude:                             40° 26' 05"N

Longitude:                          79° 54' 14"W

Quadrangle:                        Pittsburgh East 7 1/2'

Age:                                             Pennsylvanian

Formation(s):                      Conemaugh Group, Glenshaw Fm., Ames Limestone in two localities and the Saltsburg sandstone interval.

Purpose:                             This site provides an easily accessible outcrop of the marine Ames Limestone unit. A good fossil collecting locality. Also, the Saltsburg interval here.

Access and Parking:

Parking available for motor coach. Site is easy to access with a moderate walk along a trail. A second, but not as accessible site is a short walk up a hillside. Recommended for all age groups. Caution is advised on wet days as clay-rich soils and stream bed are very slippery.



Mass Transit Directions:

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

From Oakland, take a 61A or 61B bus to the corner of Forbes and Braddock avenues. Walk south on Braddock approx. 1000 feet until you come to a parking lot adjacent to the Frick tennis courts. Enter trail here. Return.

Driving Directions:

From the Cathedral of Learning, Drive east on Forbes Avenue. Make a right on Braddock Avenue. Go 0.1 mi., then make a right into the parking lot adjacent to the Frick Tennis courts. To get to the site, go south on the Braddock Trail approximately 1000 feet, passing an outcrop of the Pittsburgh redbeds along the way. When you reach the steps, go down into the valley where you will see a sign for the Falls Ravine Train. Follow the trail approximately 500 feet to outcrops of the redbeds. The continue another couple hundred feet to the outcrop of the Ames limestone in the stream.

Alternate Site: Alternatively, when in the parking lot, go north on the Braddock trail. As you get behind the tennis courts, head up the hill to Ames limestone ledges.

See map and figures.

What you will see:

The Ames outcrop here is one of the best in the region. It is in a streambed and along the adjacent hillside. The site corresponds to Saltsman’s (1986) section A. The Ames crops out as a distinctive limestone bench which consists of a gray to green-gray skeletal mudstone and wackestone. The total thickness of the limestone is approximately 1 meter. There are very large block of the Ames over a large part of the streambed indicating that differential erosion of the underlying weak redbeds caused the limestone to collapse into the stream. The pattern of the Ames beds here is somewhat irregular and may indicate that even the large limestone shelf in the stream may be part of the collapsed section. Below the Ames limestone are good exposures of the underlying section of tan to red shales of the Pittsburgh redbeds. Some shales and siltstones above the Ames limestone are exposed further up the trail.

As you return, be sure to examine the large outcrop just north of the base of the steps leading into the valley. Here you will see the a section that is stratigraphically 65 feet below the Ames limestone and is in the Saltsburg sandstone interval. However, only a thin (less than 20 inch) sandstone lens is present here and it rapidly pinches out to the north.

Geologic History: Environment of Deposition:

The environmental history represented at this site starts with the Pittsburgh redbeds that are exposed below the Ames limestone. These red shales have been interpreted as a paleosol horizon (ancient soil zone) on the Pennsylvanian delta by Donahue and Rollins (1974). They suggest that the red color and the claystone texture is similar to a laterite soil weathering profile. Lying above the redbeds is occasionally a thin (< 30 cm) coal referred to as the Harlem coal. This coal is very spotty in its distribution and does not occur here in Frick park. Instead, here we find the redbeds overlain by a very thin black carbonaceous shale which is in turn overlain by the Lower Ames shale, the first evidence that the delta is being flooded with seawater in a transgression. The shale is calcareous and commonly contains microfauna of gastropods, bivalves and brachiopods. The Ames limestone is one of several marine units within the Upper Pennsylvanian Conemaugh Group. The unit represents complete flooding of the delta during the maximum transgression (most extensive sea) of the Pennsylvanian period here in western Pennsylvania. The rocks were deposited in a shallow sea approximately 100 km northwest of the shoreline. The environment was relatively quiet subtidal with very little clastic (silt or clay) input from the land far to the east. The water depth was probably no more than 20 m. The limestone is divided into three parts: the Lower Ames limestone which is a micritic (fine-grained) fossiliferous limestone), the Middle Ames Shale which represents a brief regression, possibly associated with an influx of sediment from the delta plain to the east; and finally, the Upper Ames Limestone which is a micritic fossiliferous limestone indicating a return to quiet, clear water, marine conditions. Above the limestone is a little of the Upper Ames shale preserved. This shale marks the beginning of the retreat of the Ames sea and the influx of fine-grained sediments from the deltas to the east.

Paleogeographic map showing the region during the during Ames transgression. Modified from Al-Qayim (1983) and Busch and Brezinski (1984).

Click on the thumbnails below for pictures of the outcrops:

Ames limestone in stream. Many fossils can be seen in the pieces of Ames in the streambed.
Resistant Ames limestone in stream after collapse of underlying Pittsburgh redbeds.
Pittsburgh redbeds below Ames outcrop.
Close-up of the crurithyris-crinoidal limestone facies. Scale bar is 1 cm. Note the horn coral (stereostylus) and the crinoid columnal.
Strata above Ames limestone.
Saltsburg sandstone interval at the bottom of the valley.
Ames limestone outcrop behind the tennis courts.
Ames limestone outcrop behind the tennis courts.

Fossils:

The Ames is a very fossil-rich unit. All of the fossils are marine, and include brachiopods (crurithyris and neochonetes are most common), crinoids, horn corals, pelecepods, and gastropods. In addition fish teeth can be found in the Ames. The fossils are generally very small, but abundant. For a list of brachiopod and mollusc fossils, see Brezinski (1983). For pictures of the fossils see Hoskins (1973) or go to the fossils page.

References:

Al-Qayim, B. A., 1983, Facies analysis and depositional environments of the Ames marine member (Virgilian) of the Conemaugh Group (Pennsylvanian) in the Appalachian Basin [Ph.D. dissertation]: Pittsburgh, Pennsylvania, University of Pittsburgh, 306 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.

Saltsman, A. L., 1986, Paleoenvironment of the Upper Pennsylvanian Ames Limestone and associated rocks near Pittsburgh, Pennsylvania: Geological Society of America Bulletin, v. 97, p. 222-231.

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)