WATCHUNG BASALTS in Triassic Redbeds
FIELD TRIP STOP – WATCHUNG BASALT FLOWS ON RED TRIASSIC BASIN SEDIMENTS OF THE NEWARK SERIES.
LOCATION: Proceed on I-80 in New Jersey till you get to Patterson. Travel two miles to the south near the intersection of Rifle Camp Road and US-46. More specific directions can be found in Schuberth (1968).
GEOLOGIC FEATURES: Triassic Watching Basalt Flow; Triassic redbeds of the Brunswick Formation; Vesicles in lava; Pillow Lava.
DESCRIPTION: At these exposures we see an impressive contact between the base of the first Watchung Basalt and the red sandstones of the Brunswick Formation. This is the stratigraphically lowest basalt flow in the Triassic Lowlands. Further west is found the Second Watchung Basalt. The presence of vesicles near the top individual lava flows as well as the fine-grained texture of the igneous rock suggest cooling near the surface. In places, elongate vertical vesicular tubes near the top of individual lava flows show a bending in one direction near the very top indicating the direction of flow shortly before hardening of the lava flow. The presence of the flows resting on non-marine red sediment as well as the presence of pillow lavas suggest emplacement of lava in shallow, nearshore water.
(1) Describe the formation of vesicles in a lava flow.
(2) Why are vesicles found near the top of the flow?
(3) How does a lava flow such as the Watchung Basalt differ fundamentally from a Sill such as the Palisades?
(4) Why are Pillow Lavas named as such?
(5) Are Pillow Lavas only found in shallow water? Explain why or why not.
(6) Why are redbeds red?
(7) Why are redbeds generally associated with non-marine deposition?
-Schuberth, Christopher J. 1968. The Geology of New York City and Environs. The Natural History Press, Garden City, New York. 304 pp.
Figure 1 - Contact between horizontally bedded red shales and sandstones of the Brunswick Formation and the overlying massive Watching Basalt. The Brunswick is the most prominent member of the Newark Series, thought to form nearly 10,000 feet of sediment derived from uplands to the west.
Figure 2 - Another view of the red sedimentary strata of the Brunswick Formation and the overlying Watchung Basalt.
Figure 3 - The Watchung Basalt has been quarried as traprock, rocks that are crushed into smaller pieces and used in the construction industry for roads and decorative purposes.
Figure 4 - The contact between two relatively thin flows separated by a more friable vescicular layer.
Figure 5 - Typical sandy beds of the Brunswick Formation. This rock has been quarried to be used in the "Brownstone" rock found in NYC construction.
Figure 6 - Christopher Schuberth points to a reptile footprint found in the Brunswick Fm.