DESCRIPTION OF FIELD STOPS

The Catskill Clastic Wedge Of the Acadian Orogeny

The next series of formation represent the Catskill clastic wedge. Unlike the last series of thin formations, most of these formations run from hundreds to thousands of feet thick. The first formation we see (Needmore) represents the onset of basin subsidence corresponding to the collision of Avalon in the New York area. The Millboro was likely deposited as the basin bottomed out. The remaining formations successively fill the basin as the clastic wedge progrades into it.

Stop 9-Needmore Formation

Stop 9 is 0.5 mi (0.8 km) east of Stop 8 and 2.3 mi (3.8 km) west of Stop 10. It is a high, vertical road cut on the south side of U.S. 33. The rocks here are nearly horizontal, but large folds can be seen along the highway between Stops 8 and 9, which bring the Needmore into the same steeply dipping attitude as the Oak Flat section. The bottom half of the Needmore at this stop is made up of dark gray to black, laminate shales and silts.
Fossils are scattered through the section but tend to concentrate in richly fossiliferous zones of gastropods, cephalopods, brachiopods, and trilobites. Two black beds a few centimeters thick about a third the way up are especially rich in fossils. Bioturbated beds are also common. These characteristics indicate a quiet (shelf) environment with generally good circulation and oxygen levels. The black beds represent intervals of stagnation on the shelf, perhaps due to a sea level rise.
In the upper half of this outcrop a few fine sands a few cm thick appear. They have laminations and thicken and thin down the outcrop and may represent distal hummocky units.
The Needmore is an abrupt change from the underlying Oriskacy. The simplest interpretation is that the Oriskany to Needmore sequence was the result of a transgressive sea onto the craton. The Millboro Formation overlying the Needmore suggests a different hypothesis, however. At Stop 10 the fossils in the Millboro are dwarded, implying lower oxygen levels. To the north of Pendleton County there is a facies change and the Millboro name is dropped and replaced by the (older to younger) Marcellus. Mahantango, and Harrell formations, but at Stop 10 the Mrcellus is black and highly organic implying anoxic conditions. This trend to anoxic conditions from the Needmore to the Millboro and Marcellus implies a rapidly subsiding basin rather than a shelf in a simple transgressing sea. Support for the rapidly subsiding basin interpretation is in the overlying formations (Stop 10, 11 and 12). Therefore, the Needmore most likely marks the first clastic influx from the Acadian mountains rising to the east into a rapidly subsiding foreland basin to the west. Thus, in Figure 9 the Needmore lies under the Millboro, Brallier and, likely, Chemung and Hampshire, and was deposited before them at the earliest subsidence stage.

Stop 10-Millboro Formation

Stop 10 is 2.3 mi (3.8 km) east of Stop 9 and 2.0 mi (3.3 km) west of Stop 11; 1.5 mi (2.5 km) west of the U.S. 33 and West Virginia junction at Brandywine, West Virginia. The road cut is about 300 ft (77 m) long on both sides of the highway. Here, the Millboro dips a few degrees to the south.
The Millboro consists of dark gray to black, laminated to very thin bedded shales, siltstones, and fine grained sandstones. Small-scale cross laminations are sometimes seen in the rust weathering sands. In the east cut a 6 in (15 cm) thick zone is convolute bedded, produced by fluid escape and loss of grain-to-grain contact causing flowage. On some bedding planes the fauna are abundant, but consist mostly of dwarf brachiopods and clams which are current oriented. Occasional straight and coiled nautiliods can also be found but these are generally larger than the brachiopods and clams.
The Millboro reflects a deeper, more anoxic environment (the dwarf fauna) with periods of higher energy deposition (cross-laminated sand and current oriented fossils) than the Needmore at Stop 9. These two interpretations seem paradoxical since deeper environments are usually quieter. One major source of energy is a deep water environment is a turgidity current. Support for the idea that these deposits in the Millboro are the first, thin, distal deposits of a submarine fan prograding into the foreland basin can be found in the overlying Brallier formation at Stop 11.

Stop 11-Brallier Formation

Stop 11 is 2.0 mi (3.3 km) east of stop 10, 0.5 mi (0.8 km) east of U.S. 33 and West Virginia 23 junction at Brandywine, and 4.1 mi (6.8 km) west of stop 12. The cut is on the north side of the highway at a salt storage shed.
These rocks represent Bouma turbidite sequences of a mid-fan type (TCDE dominates, but other sequences including TABCDE are present). In some of the coarse silts between the sandstones abundant cross laminations may be the result of contour currents. These sequences are clearly visible and easily studied in the lower part of the cut. The upper portion of the cut is more weathered and illustrates the typical weathering pattern of the Brallier, which consists of jutting sand beds alternating with weathered shales. Various pieces of sandstone float have a variety of trace fossils and current marks such as shallow flutes and grooves.
By the time the Brallier Formation appears in the section the former deep water, nearly anoxic basin of the Millboro formation has begun to rapidly fill in with large submarine fans prograding from the east.

Stop 12-Chemung-Hampshire Transition

Stop 12 is 4.1 mi (6.8 km) east of Stop 11 and 2.6 mi (4.3 km) west of the crest of Shenandoah Mountain. The long road cut begins (traveling east) at a gentle "S" curve in the highway and extends up the hill for several hundred yards (meters).
The Chemung consists of gray, brownish-gray, green, and red shales, siltstones, red sandstones (becoming thicker upsection), occasional quartz pebbles or conglomerates, and scattered marine fossils and drifted plant fragments. It is one of the most variable formations in the region. Contacts with the underlying Brallier and overlying Hampshire are not lithologically distinct. The formation contacts are defined paleontologically, but for purposes of this field guide the base of the Hampshire is defined as the first appearance of distinctive point bar sequences.
The strip log in Figure 12 (two pages; location map on second page) summarizes some detailed environmental interpretations of the Chemung-Hampshire transition at Stop 12. The Chemung exhibits many shelf features, including well developed hummocky sequences seen in Facies II, III, and IV. Zones of nearshore facies with rod color, oscillation ripples, and/or root traces are also common, such as Facies I and VII. Facies IVB, VA, VB and VI include an unusually thick sequence of quartz pebble conglomerate. WE have interpreted this as a submarine fan feeder channel, but other interpretations are encouraged.
Some of the fining upward point sequences of the Hampshire (Facies XII) are close to the ideal model with scoured bases, mud-pebble lag gravels, and large-scale trough cross beds grading up into small-scale trough cross beds. Many variations of the point bar sequence are present, however. On the strip log point bar sequences come in at Facies XII, but continue for the next 2.5 mi (3.8 km) to the top of Shenandoah Mountain.
Allen and Friend (1968: p. 58) stated that the Hampshire (their Catskill) "was deposited in a vast coastal plain of alluviation" with the characteristics of a meandering river (point bar sequences). Thus, the plain of the Hampshire above. Beyond that, specific environmental interpretations of the Chemung are as widely different as it its color and lithology.

Stop 13-Pocono Formation

Stop 13 is 13.7 mi east of Stop 12 (11.1 mi east of the crest of Shenandoah Mountain). This outcrop is a large body (10-12 feet high) of large cross bedded sandstones on the north side of the road. There is a pull off directly opposite it on the south side of the road. If you get to Rawley Springs you are a mile or so past the stop.
Little or no recent work has been done on the Pocono in this region. There is a generalized description in Figure 9. In various places the Pocono contains evidence of nearshore marine as well as subareal delta deposits.
The sandstone body at this stop is interpreted as a tidal sand bar, although the evidence and arguments are indirect. Sand bodies with large cross bedding like this form in only a few environments, including tidal shelves and some river systems. If we could find a marine fossil in this outcrop it would help to narrow the interpretation down. At another cut east about half a mile a coal bed has been reported, indicating transitional or terrestrial environments there.
The significance of this formation is this. Below the Pocono is 2-3000 feet of meandering river deposits indicating terrestrial conditions were well established in this region during its deposition. The presence of the Pocono near shore and marine shelf deposits on top of the Hampshire indicates that the sea has begun to transgress back across the Hampshire terrestrial environments. The Pocono was deposited during the waning stages of the Acadian Orogeny as sediment supply decreased and sediment winnowing increased. To the west the carbonates of the Greenbrier formation overlying the Pocono (see Figure 1) indicate orogenic activity has finally ceased in this area.