INDEPENDENT CONFIRMATION OF FLUVIAL REWORKING AT A LANCE FORMATION (MAASTRICHTIAN) BONEBED BY TRADITIONAL AND CHEMICAL TAPHONOMIC ANALYSES

Abstract

ABSTRACT A dinosaur-bearing bonebed (Rose Quarry) from the uppermost Cretaceous (Maastrichtian) Lance Formation has yielded abundant, yet fragmentary, disarticulated, and disassociated bones and teeth of dinosaurs, turtles, crocodilians, and fish contained within a channelized sandstone unit along with large mud clasts. The vertebrate fossils of Rose Quarry possess varying abrasion states, tooth traces, and trampling marks, suggesting a complicated taphonomic history. To independently test hypotheses about the genesis of the assemblage, Rose Quarry bone samples were sent to members of our team who conducted “blind” analyses of their trace element signatures without knowledge of the physical taphonomic attributes of each specimen. The independent analyses of the chemical and physical taphonomic signatures both support a mixed, attritional bone concentration. Based on our cumulative data, we present a depositional model for the Rose Quarry bonebed in which a flooding event mixed bones already present in the channel or from an older bonebed with bones from the floodplain that had been scavenged, trampled, and broken. Our study demonstrates that striking variability is possible among fluvial bonebeds, and that such variability is influenced by pre-burial and post-burial factors, as well as depositional subenvironments and burial mechanisms. Additionally, we demonstrate that physical and chemical taphonomic analyses can independently confirm the taphonomic history of a bonebed.