DEPOSITIONAL SETTING AND TAPHONOMY OF FISH-PART CONGLOMERATES, TRIASSIC LOCKATONG FORMATION, COLLEGEVILLE, PA

Fish-part conglomerates, associated with a partial phytosaur cranium and post-cranial material along with a variety of isolated teeth, were recovered from the Triassic Lockatong Formation of the Newark Supergroup. This paper interprets the depositional setting, a rarely reported lacustrine shoreface setting, and interprets the probable taphonomic history of the fish-part conglomerate that accumulated in the shoreface setting.

Within the Lockatong Formation, Van Houten cycles are subdivided into three divisions; 1- lake transgression, 2 - high-stand, 3 - regression and lowstand facies (Olsen, 1980; 1986). The fish-part conglomerates are composed of disarticulated redfieldiids. This facies occurs at the transition from division 1 to 2 and are found above an intraformational conglomerate composed of mudstone clasts. The phytosaur cranium and post cranium materials are found in division 1. Fish-part conglomerate are found as continuous beds or lenticular graded beds. Within the more continuous beds, some bone articulation is present. Associated oscillatory ripples indicate shallow water depths. Based on observations of fish kills in the Salton Sea, we propose that a mass kill of redfieldiids took place. Fish carcasses were driven shoreward by waves where they were disarticulated and reworked as lag concentrations in response to storm-generated waves. The intraformational conglomerate reflects the development of a shoreface retreat unconformity that eroded into the beach deposits.