Depositional
Setting and Taphonomy of Phytosaur-Bearing Beds, Triassic
Lockatong Formation near Collegeville, Pennsylvania
Nase, A.M.,
Rhoads, C.L., Rosenberger, J.E., Szajna, M.J., Hartline,
B.W., and Simpson,
E.L., 2004 [abs]: Depositional
Setting
and
Taphonomy
of
Phytosaur-Bearing
Beds, Triassic Lockatong Formation near Collegeville, Pennsylvania,
Northeastern Section (39th Annual) and Southeastern Section (53rd
Annual) Joint Meeting (March 25–27, 2004), Abstracts with Programs,
Vol. 36, No. 2, p. 96.
A
phytosaur cranium and post-cranial material along with various types
of isolated teeth were recovered from the Triassic Lockatong
Formation of the Newark Supergroup. This paper reports on the
fluvial and lacustrine depositional settings and taphonomy
associated with these newly discovered phytosaur materials.
Within the Lockatong Formation, Van Houten cycles are well developed
and subdivided into three divisions; 1- lake transgression, 2 –
high-stand, 3 – regression and lowstand facies (Olsen, 1980; 1986).
The phytosaur cranium and post cranium materials are found in
association with rooted-disrupted, red massive siltstone and
mudstone in division 1. Associated sedimentary features are
sandstones with upper plane beds and ripple cross stratification,
complex desiccation cracks, burrows, large root systems and
non-dinosaurian tracks. Based on these features, a fluvial overbank
is the most probable setting. Isolated teeth and bone fragments are
found in all the three divisions. Aside from isolated teeth in the
massive mudstones, the teeth elements are found in clast-supported
intraformational conglomerates and associated with lag concentration
represented as fish-scale conglomerates. Clast-supported
intraformational conglomerates are normally graded and consist of
mudstone and siltstone clasts. Some clasts display armoring by
silt-sized grains. The clast-supported intraformational lags are
best interpreted as fluvial flood deposits with hydrodynamic
concentration of ripped up clasts, bone and teeth. Fish-scale
conglomerates occur as lenticular graded beds mainly as isolated
scales and bone fragments, but some bone articulation is present
rarely. Associated oscillatory ripples indicate shallow-water
processes for the development of the fish-scale conglomerates.
Fish-scale conglomerates developed as a response to storms at the
fluvial-lacustrine interface.