BONE FRAGMENTS FROM THE MATRIX OF THE CLEVELAND-LLOYD DINOSAUR QUARRY (UPPER JURASSIC MORRISON FORMATION) AND THEIR BEARING ON DEPOSITIONAL RECONSTRUCTION

The Cleveland-Lloyd Dinosaur Quarry (CLDQ) represents the largest concentration of theropod dinosaur bones in the world and has produced nearly 10,000 bones since its initial excavations in the late 1920s. While the collection of macrovertebrate remains from the quarry has been the focus of much attention over the last 85 years, a detailed analysis of microfossils from the quarry assemblage has been largely under-investigated. Though identifiable microvertebrate fossils are rare at the quarry, the calcareous mudstone matrix is rich in small unidentifiable bone fragments (< 10 mm) that are likely autochthonous weathering products from larger bones and deposited syndepositionally to the main quarry assemblage. These fragments are readily-transportable sedimentary particles that can be used for detailed taphonomic comparisons between the CLDQ and neighboring localities for paleoenvironmental and depositional reconstructions. This study reports on the collection and characterization of small intramatrix bone fragments from the CLDQ and a stratigraphically lower site in the upper Morrison Formation (locality UWO-12-001, “Johnsonville”) which has yielded sauropod caudal vertebrae and microvertebrate fossils. Taphonomic characteristics of fossil fragments from each assemblage are compared for abrasion patterns and average hydraulic equivalences of the fossil fragments. The results indicate that the fragments at both localities have a higher hydraulic equivalence than the surrounding matrix, suggesting that the fragments represent a lag deposit. Furthermore, fragments recovered from the Johnsonville site show an elevated frequency of highly-abraded particles relative to the CLDQ, indicating a rather consistent depositional environment of moderate-energy flow. In contrast, the CLDQ shows a wide distribution of angular and rounded fragments, suggesting a depositional environment with variable periods of high- and low-energy flow and re-working. These findings support previous hypotheses that the CLDQ assemblage represents multiple depositional episodes rather than a single catastrophic event. These results provide insight into a complex depositional history of the Cleveland-Lloyd Dinosaur Quarry and regional Late Jurassic paleoenvironments.