Precambrian Highlands and Paleozoic Valley and Ridge
You are responsible for your own specimens and for obtaining locality information
and latitude and longitude for each site. Bring your specimens and notes to class.
On the way to the first stop we discussed Stable Isotope methods, including their use
for estimating continental glacier volume, and for determining the source rock for
various metamorphic rocks.
Stop 1. Along 206 north, just before Cranberry Lake you pass Adam Todd’s and
Frogmore restaurants, turn left at the little triangle, find the sign on the left, and
drive along the old track roadbed (now Sussex Trail) to the parking lot.
Ore Deposits in Precambrian Gneisses, Sussex Trail, Cranberry Lake, NJ. On the
walk in from the parking lot examine a meandering stream with a meander loop AND
a straight cutoff channel along the same section of river. Note the greater gradient in
the straight channel and its likely evolution, and the eventual fate of the meander
loop as an oxbow.
Right after the second small bridge and just before the Iron Mine sign is a small trail
on the right that runs toward Cranberry Lake. Leave the railroad and hike up to the
Bemco Mining District near Cranberry Lake's south shore. This complex was
originally called the Charlotte Mine and was an Iron producer. Look for exploration
drifts with black zircons in alkaline pegmatites; these are metamict from Uranium
and Thorium. Think of some origins for basaltic magmas (decompression melting in
divergent zones, melting point depression near dewatering ophiolites in a subduction
zone) and the genesis of felsic magmas and pegmatites through fractionation. Think
about Zircon structure, crystal damage during decay to a daughter isotope, Pb
daughter loss and Zircon self-repair, and consequences for zircon-based
geochronology.
The upper test drift
Do not collect here, the zircons are radioactive.
Closeup of the pegmatite
In this same area look for iron pits, exposed in cross section on the hillside.
Recall black smokers and their continental counterparts, consequent Iron ore
formation, and supergene enrichment.
On the way out examine rocks along the railroad bed. Discuss methods to distinguish
igneous and sedimentary sources for metamorphic rocks.
Stop 2. The Allentown Dolomite at Sparta, NJ., 15 southbound, under the Sparta
overpass. Compared the strikes and dips of rocks on either side of the fault. A check
of geologic maps revealed the proximity of complex structures in this area. Possible
models include faulted plunging folds with large throw along the fault and rotational
movement of blocks.
The block to the north of the fault. Unfortunately my photo of the fracture zone did not
come out.
Stop 3. Lake Hopatcong Intrusive Suite, Route 15 Park and Ride, exit mile 10.5,
Sparta Township, NJ. The underbelly of a Grenvillian volcanic arc.
The Grenvillian collision of Laurentia with Western South America and the assembly
of Rodinia formed these rocks. This area is called the Lake Hopatcong Igneous Suite,
and is a volcanic arc comprised of 1.3 by Orthogneiss and younger granites. Some
granites have gneiss xenoliths or schlieren. Pegmatites with large hornblende
crystals were also examined. Nearby along Rt 15 are Amphibolites and migmatites.
Orthogneisses south ramp
Gneiss xenolith, south ramp area
Granite Intrusion in Orthogneiss , south ramp
Surface Iron Oxide Staining, north ramp
Possible Schlieren, north ramp
Migmatite beyond north ramp,15 N
Next drive up 23 to the vicinity of High Point, NJ. On the way you drive by outcrops
of Franklin Marble, Hardyston Quartzite (the source of quartzite pebbles we saw last
time at Pebble Bluff), Leithsville Formation (limestone and dolomite, the source of
carbonates near the border fault at Holland), the Allentown again, the Martinsburg
Formation, the Shawangunk Formation, and the High Falls - Bloomsburg. We
stopped from lunch and maps at the Elias Cole Restaurant.
Stop 4. Blue Ridge Mountain, Rt. 84, Port Jervis, NY. Shawangunk\High Falls
transition, angular unconformity Omb\Ssg and the Taconic, the Shawangunk here as
a tidal flat, comparisons to modern tidal flats, Eurypterids as top level predators in
the Silurian, evolution of the Queenston clastic wedge, the Agnathans of the High
Falls.
Shawangunk High Falls-Bloomsburg transition
Delaware Water Gap (Another Trip)
Port Jervis, NY (Stop 4)
Angular Unconformity, Ordovician Martinsburg
folded by Taconic, Shawangunk above
Silurian Shawangunk Sandstones with dark
lenses of siltstone and shale
Mudcracks in High-Falls Bloomsburg
Stop 5, Tills along Rt. 6, Milford, Pa. Tills, Moraines and Drumlins
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