NOVEL APPROACHES FOR INTERPRETING DEPOSITIONAL ENVIRONMENTS OF FOSSIL VERTEBRATES

Grain size distributions provide valuable information on sediment transport and mode of deposition, and reveal important insights into paleoenvironments when other tools may not be available. Laser diffraction granulometry (quantitative grain size analysis) is frequently used in Neogene sediment studies, however, this method is rarely used on samples of Mesozoic age or older, due to challenges of disaggregating material and removing diagenetic cements. Recent advances in chemical disaggregation and serial digestion have made it possible to use this method on older samples.

Here, we use laser diffraction granulometry to quantify the grain size distribution of rock matrix material surrounding several exemplar Mesozoic skeletons from the Gobi Desert. The majority of these specimens come from a single locality, Ukhaa Tolgod, which has produced many exquisite full skeletons of dinosaurs, mammals, and squamates. This method has the potential to reveal fine-scale variations in depositional environments, especially in distinguishing eolian from fluvial, or fluvially reworked aeolian. Application to Gobi fossils elucidates potential differences in burial modes for organisms of different taxonomic groups, such as ornithischian dinosaurs, theropod dinosaurs, squamates and mammals.