TAPHONOMIC PUZZLES: USING RARE EARTH ELEMENT GEOCHEMISTRY TO UNRAVEL COMPLEX TAPHONOMY OF VERTEBRATE FOSSIL SITES IN THE YELLOW CAT MEMBER OF THE CEDAR MOUNTAIN FORMATION

Recognition of redefined Yellow Cat Member (YCM) strata (“lower” Yellow Cat Member) has revealed new vertebrate fossil sites. These sites are preserved in paleosols, spring-generated carbonates, lacustrine carbonates, clast-supported cobble conglomerates, matrix-supported pebble conglomerates, and overbank siltstone and sandstones. Sites include the Crystal Geyser Dinosaur Quarry (CGDQ), Dalton Wells Dinosaur Quarry (DWDQ), Suarez Site (SS), Don's Ridge South (DRS) and Don's Ridge North (DRN). The CGDQ, SS, DRS sites are all within 1.5 km of each other, while the DWGQ is about 40 km to the southeast.

REE are incorporated into fossil bone apatite during early diagenesis of bone. Since REE in fossil bone reflect pore-fluid geochemistry of the fossilization environment they can be used as a proxy to identify reworked and time-averaged material. REE patterns from YCM sites reveal lines of geochemical fractionation, mixing and paleo-redox trends during the time of fossilization. REE distribution can differentiate among sites as well as elucidate associations between sites. For example, the CGDQ is distinguished by its Ce anomaly, its unique spider diagram pattern, and its location on REE ternary and tetrahedral diagrams. In addition, two to three distinct geochemical signatures are present at the CGDQ. There are two geochemical signatures from the Suarez Site; bone from the lower part of the quarry, the “nodosaur layer,” is distinct from the predominately Falcarius sp. upper bone unit. The DRS sites which outcrop at various levels and in various lithologies along the southern side of Don's Ridge may represent multiple reworked bone layers fossilized along mixing lines. Bones from “cervical vertebrae layer” at the Don's Ridge Quarry have similar REE patterns as bones from the lower “nodosaur layer” of the SS, indicating possible relationships between the two. DWDQ (40 km southeast) has its own characteristic REE geochemistry and plots as a separate cluster from the bones in the CGDQ-Suarez Site-Don's Ridge area on ternary and tetrahedral diagrams. Higher sampling resolution and more detailed physical taphonomic data may reveal further associations and distinguishing characteristics of these sites.