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.
