Depositional Model of a Late Cretaceous Dinosaur Fossil Concentration, Lance Formation
A large Maastrichtian, nearly monospecific bonebed in the Lance Formation in eastern Wyoming has yielded 13,000 bones and fragments since 1996. Though excavation of the site continues, little is known of the circumstances and processes of deposition. This study aims to provide a depositional model for the bonebed. To accomplish this task we utilized 1D facies analysis of surrounding units and 3D analysis of the bonebed. The nature of the outcrop limited facies analysis to 1D. Four measured stratigraphic sections, each containing the bonebed unit, were taken and used in facies analysis. In addition, laterally continuous units were observed and mapped using real time kinematic (RTK) GPS equipment. For 3D analysis of the bonebed, we unitized a large GPS dataset collected over 20 years of excavation. Displaying and manipulating the points in ArcGIS allowed investigation of bone arrangement vertically and laterally within the bonebed. Facies analysis indicates that the local sediments of the Lance Formation were deposited on a relatively flat depositional plain as part of or near a delta. Facies assemblages are compatible with both a proximal to shore delta plain distributary and interdistributary environment and with a relatively low sinuosity meandering stream environment with periodic swampy conditions in the flood plain. The bonebed is proposed to be a result of a mass flow process resulting from the fluidization and mobilization of sediment due to seismic activity.
Earth Sciences, Geology, Paleontology, Paleontological excavations; Paleoecology; Facies - Geology - Wyoming; Sedimentology and deposition;, Lance Formation (Maastrichtian) -- Wyoming; Facies analysis; Bonebeds; Depositional plain;
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