Latitude:

40° 39' 20"N

Longitude:

79° 58' 20"W

Quadrangle:

Valencia 7 1/2'

Age:

Pennsylvanian

Formation(s):

Conemaugh Group, Casselman Fm., Birmingham shale and Morgantown sandstone

Purpose:

This site is the most structurally complex site in Allegheny County offering spectacular views of syn-depositional faulting.

Parking for only one or two cars is available along the road adjacent to the railroad tracks. Site is difficult to access with a short walk down a relatively steep slope. Difficult walking along railroad tracks. NOT recommended for children. Caution is advised as one of the two tracks is still active. LOOK and LISTEN for TRAINS!

(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 1.6 mi. then bear right onto I-579. Stay on I-579 across the Allegheny River then get onto Rt. 28 East. Go approximately 6.6 miles and take the exit for Rt. 8 North (Etna). Stay on Rt. 8 for 11.9 miles and make a left in Bakerstown. Go 1.9 miles and make a left. Go 1200 feet and park along road. Walk to outcrop as described above.

See map and figures.

This is the most complex rock structure in the region. To see similar complexity you would need to travel to central Pennsylvania Valley and Ridge province. The diagram below is taken from Wagner and others (1970) and reflects the interpretation of R. Ross (Univ. Pittsburgh MS Thesis, 1933). It is generally quite accurate in the depiction of the larger-scale structures. Individual rock units are labeled from 1-9. Nine, the youngest would be the last deposited. The rock sequence in broken by a series of steep dip-slip faults. The rock units are tilted steeply, up to 45 degrees from their original horizontal orientation. The erosional base of the Morgantown sandstone serves as a marker horizon through the outcrop.

Geologic History: Why Faulting?:

The base of the Morgantown sandstone is an erosional feature that cuts pre-existing faulted and tilted sedimentary layers. In addition, most faults enter, then terminate within the overlying Morgantown sandstone. These two bits of information lead to the conclusion that faulting took place within the Birmingham - Wellersburg sequence prior to Morgantown time. The faulting may have occurred as a landslide (slump) into a large river channel as the river eroded into the adjacent slope. As the river eventually migrated over the slumped deposits, the sands of the Morgantown were deposited. Accommodation on the pre-existing faults continued with the addition of the weight of the overlying sand, and some of the faults propagated into the Morgantown sand.

This diagram and following explanation are from Hutchinson (1995).

    A) The Birmingham River meandering north of the locality carves a cut-bank into semi-consolidated sediments.

    B) A disaster, possibly an earthquake [associated with the developing Alleghanian orogeny to the east] triggers a massive landslide as blocks of the semi-consolidated land slide on               a decollement in the unstable clays at the base of the section.

    C) Later, as the Morgantown River system begins crossing the area, the blocks are eroded and filled with sand, logs, rip-up material, and plant mats or segments of semi-lithified peat (possibly Duquesne or Wellersburg)

    D) Continued loading causes slippage, this time involving semi-consolidated sandstone.

The stereonet diagram below shows that the faults are oriented roughly east-west and suggests that the maximum stress was sub vertical. However, if the beds are rotated to their originally horizontal position, the maximum stress would be vertical. This would certainly be the case if sediment loading and slumping was the cause of the deformation.

Lower hemisphere equal area projection of poles to faults in Bakerstown Station site.

This diagram and following explanation are from Hutchinson (1995). Sketches of the southeast wall of the Bakerstown Station railroad cut showing a) joints/faults and related soft-sediment deformation that developed in the basal Morgantown sandstone prior to reactivation of slide feature and b) the relationship of faults to a 6-8 in. (15-20 cm) thick cross-bedded sandstone layer in the Morgantown sandstone and c) section of a portion of the Bakerstown Station paleo-landslide illustrating the change in orientation of the maximum principal stress (σ1). Before sliding, σ1 is oriented vertically (gravity and overburden pressure) and after sliding, rotation of the Toreva block on the listric normal fault has been reoreinted σ1 a few degrees clockwise from vertical. The dashed line represents the future slip surface.

Click on the thumbnails below for pictures of the outcrops:

Beds of the Morgantown sandstone dipping to the south. North to right.

Wedge of Wellersburg coal caught between two fault blocks of the Morgantown sandstone. North to left.

Intense faulting and fracturing in the Morgantown sandstone, indicating that the sandstone was at least partially lithified prior to faulting. North to left.

The best-exposed normal fault in the outcrop. ~2m displacement of the hangingwall down to the north. Morgantown sandstone at the top, Birmingham shale below. North to right.

Intense cleavage developed in the Birmingham shale fault zone (shown in figure above). Cleavage orientation supports top to the north motion. North to right.

Another dip-slip fault. Birmingham shale to left and laminated siltstones to right. North to right.

No fossils found here.

Hutchinson, P. J., ed., 1995, Pittsburgh Geological Society Golden Anniversary (1945-1995) Field Guide Book. Pittsburgh Geological Society.

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.

Ross, R. B., 1933, Structures in the Conemaugh Formation near Bakerstown Station, Pennsylvania, unpublished Master's Thesis, University of Pittsburgh, Pittsburgh, PA.

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)