BIG TO SMALL: BIOGEOCHEMICAL SIGNALS OF DINOSAURS TO OSTRACODS AND EVERYTHING IN BETWEEN (Invited Presentation)

Detection of authigenic or biogenic isotope and elemental signals in ancient materials have been sought after for decades. The goal of such studies are to provide parameters such as seasonality trends, mean annual precipitation, paleotemperatures, and CO₂ concentrations or to provide specific biological or behavioral information such as migration routes. Although some work suggests ancient signals have been obliterated by diagenetic alteration, careful analysis via trace element, isotopic, microscopy, and spectroscopic work suggests original signals can be detected if careful analysis is taken. Detection of diagenesis can be determined via multi-proxy investigation or via pilot studies of multi-taxon assemblages. For example, petrographic, isotopic, and trace element analysis of fossil bone reveals a fossilization front in Pleistocene bone from Idaho Falls while a Cretaceous bone shows complete recrystallization of both phosphatic and carbonate isotopes to diagenetic equilibrium values. Multi-taxon assemblages from the Kaiparowits and Cedar Mountain formations of Utah and the Mooreville Chalk reveal discrete separation of taxa in C-O-isotope space and in the δ¹⁸O_p composition respectively based on ecology that suggest biogenic stable isotopic composition. Likewise, careful thin section work suggests that original meteoric calcite lines can be determined from pedogenic carbonate nodules as old as 201 million years and 100 million years. Finally, stable isotopic analysis of ostracods reveals both diagenetic and biogenic information when carefully analyzing internal steinkern molds versus valves. These examples suggest that careful screening of fossil samples or pilot studies can detect biogenic signals in material as old as 200 million years old and possibly older. With new instrumentation in the pipelines and new chemical systems being investigated, it is an exciting time for “paleobiogeochemists.”