Stop 1 – The Union Furnace Quarries
Leaders: David P. Gold and Arnold G. Doden
Pennsylvania State University
Most of the units defined in the roadcut at Stop 3 can be traced across the Little Juniata River to the east into the Union Furnace quarries. Our first stop will be to the two quarries operated by the New Enterprise Stone & Lime Co. The ”eastern” quarry represents the steep limb (general dip of 65o) of an inclined, open, asymmetric syncline, known as the Scotch Valley Syncline (Malik, 1999). A plunge of 13o/215o (Malik, 1999) is inferred from an S-pole plot of bedding orientation from the region (Figure 29A).
A down-plunge view of the axis on the B16 K-bentonite bed (Figure 30A) has been exposed in the stripped area on the remnant left between the two active Union Furnace quarries.
The “western” quarry is developed in the shallow limb, which has a general dip of 30o. The axial zone has recently been exposed in the northeast corner of the western quarry (Figure 30B). The orientation of the axial plane is 038o/76o (see Figure 29A). An annotated panoramic view of the highwall of the “western” quarry is shown in Plate 1.
A low angle thrust fault (Figure 31A) with a mesoscopic scale drag fold on the hanging-wall is exposed near the western side of the high-wall. This fault, oriented 065o/36o, designated the Scotch Valley Thrust by Malik (1999), places Loysburg strata over part of the Hatter Formation, and extends northward into a local thrust sheet. Despite an inferred movement of many hundreds of meters, the fault surface is sharp with a paucity of communited rock or gouge.
Many of the bedding planes contain slickensided surfaces, with steeply plunging slickenlines approximately perpendicular to the axial line of the major fold. These attest to a flexural slip mechanism, and an essentially concentric style for folding. Four major sets are apparent in the 31 faults plotted on orientation diagram (Figure 30B). The north-south set (highlighted in blue) represent antithetic strike-parallel faults exposed in the north wall of the west pit (Malik, 1999). A group of synthetic strike-parallel faults, associated with the Scotch Valley Thrust Fault are highlighted in pink. These dip shallowly to the southeast (~35o) and strike 065o to 070o (Malik, 1999). Cross-strike faults that trend 100o to 120o and dip steeply to the southwest (~60o) are highlighted in yellow. The remaining faults (not highlighted) are part of a complex system of mesoscopic scale faults (Figure 31B) exposed in a zone approximately 30.5 m (100 ft) wide in the southeast wall of the “east” quarry (now buried beneath an aggregate pile). The orientations of mesoscopic scale faults in this complex, transgressive, fracture zone are 070o/30o, 200o/60o, 180o/52o and 100o/65o (Malik, 1999), and represent a progression from a bedding fault to a wedge (ramp) fault to a strike fault (probably bedding) that juxtaposes upper Hatter beds under Loysburg strata. Complex drag folds, plunging steeply northwest are developed in the fault zone, and some of these may exhibit a cleavages in one or other of the following orientations, 220o/65o, or 270o /70o (Malik, 1999). This zone is interpreted as a “backward” ramp, and is inferred to have formed early during Alleghanian deformation, while the beds were still horizontal.
Without proper safety equipment we will not be able to examine the working face and high-wall, but we will be able to view (Plate 1) the 46-m (150-ft) face from a vantage point on the quarry floor, and safety of the vehicles. Unfortunately rubble from recent blasts has obscured much of the high-wall.
Reboard the bus and return to the quarry entrance.