Passaic Fm. = " Brunswick"
Newark Basin Field Trip for Petrology
Stop 1 Orange Mountain Basalt, Chimney Rock, Bound Brook, New Jersey.
A peek through the fence reveals the flow heated red shales and siltstones of
the uppermost Triassic Passaic Formation. Along the stream, we'll examine
the interface between the two lowest of four flows.
Along Middle Brook we will examine successive layers of Basalt. The
contact with the underlying Passaic Fm. (old name “Brunswick Fm.) is
usually covered here, but we will see it easily in Flemington. where the dips
are greater.
Stop 2. Diabase Ring Dike at Round Valley Reservoir, Lebanon, New
Jersey.Along the North Shore of Round Valley Reservoir, a Diabase that
cooled from the early Jurassic magma is exposed.
Chris, Kari, Anna, Melissa, Ryan at the Diabase
"Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine
grained to aphanitic chilled margins which may contain tachylite (dark mafic
glass).Diabase normally has a fine, but visible texture of euhedral lath-shaped plagioclase
crystals (62%) set in a finer matrix of clinopyroxene, typically augite (20-29%), with
minor olivine (3% up to 12% in olivine diabase), magnetite (2%) and ilmenite (2%)." .
Such a texture is called Ophitic.
Travel via Rt. 31 to Flemington.
Discussion of Newark Basin using Roy Schliche's slides
Stop 3 Mine Creek Park and Morales Nature Trails, Capner St., Flemington,
NJ. Here is the Passaic Fm. under the Orange Mountain Basalt. The
Lockatong is exposed to the west across the Lockatong Fault. The beds here
dip steeply enough that we can see the alteration zone. Anna will discuss her
work on this important geo-cache.
Hornfels
Chris and Anna sample the Explosion Breccia
At the contact between the Orange Mountain Basalt and the Lockatong, the
Copper minerals Malachite and Azurite have formed. This area once had
small copper and silver mines.
Then Rt. 12 to 523 South (Sergeantsville Road) to Stockton, NJ near the
base of the Late Triassic.
Photo of roads to 29N heading up-section
Stop 4. Stockton Formation, Raven Rock, NJ.
The Stockton is the basal sediment in the Newark Basin. Usually interpreted
as fluvial, it doesn't show the cyclicity of younger Lockatong and Passaic
(formerly Brunswick) Formations. Sand-size particles of Proterozoic
gneisses and granites, plus Paleozoic sandstones and carbonates, washed into
the newly forming rift valley. We'll see the typical form, sandstone redbeds.
Stop 5. Lockatong Formation. The middle unit of the Late Triassic is the
Lockatong Formation. It can be black (organic-rich persistent lake with
Semionotus fish) or gray (very shallow lakes with frequent drying and
mudcracks) or red (the last stop, see below). It shows strong Milankovitch
cyclicity. N 40o 26.850' W75o 03.900'
Stop 6. Perkasie Member of the Passaic ( Brunswick) Formation, Milford,
NJ.
This is the Pebble Bluff locality. The Passaic is the uppermost Triassic
sedimentary deposit in New Jersey. It contains typical redbeds that range
from mudstones and fine sandstones that are usually interpreted as playas
and pediments , to coarse cobble and boulder conglomerates that coarsen as
we approach the border fault: fanglomerates. The obvious cyclic
sedimentation includes shorter and less widespread gray lake deposits.
Fanglomerate layer near the border fault
All sandstones and siltstones further away
The pebbles, cobbles and boulders are all quartzites, presumably from the
Cambrian Hardyston Quartz that is still exposed along the border fault. They
grow larger and more angular as we approach the fault.
Stop 7. Holland, NJ. Near the border fault, we will examine a small
exposure of breccia containing carbonate blocks. These probably were
derived from the Cambrian Leithsville Dolomite, which lies above the
Hardyston is also exposed along the fault.
Return to Campus.
Map for Stops 6 and 7, Milford and Holland, NJ.