DEPOSITIONAL SETTING AND TAPHONOMY OF PHYTOSAUR-BEARING BEDS, TRIASSIC LOCKATONG FORMATION NEAR COLLEGEVILLE, PENNSYLVANIA

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.