Stable isotope geochemistry of the Upper Cretaceous sauropod nesting sites from La Rioja (NW Argentina): preliminary results

LÉA LEUZINGER; STEFANO BERNASCONI; TORSTEN VENNEMANN ; HECHENLEITNER, ESTEBAN MARTÍN; FIORELLI, LUCAS ERNESTO; ROCHER, SEBASTIÁN; PABLO HORACIO ALASINO

Congreso; 11º Congreso de la Asociación Paleontológica Argentina; 2016

The Upper Cretaceous sauropod nesting sites of Tama and Sanagasta (Los Llanos Formation, La Rioja) have been the subject of several palaeontological studies in recent years. While data on the sedimentology, taphonomy and morphology of eggs and egg clutches of these two nesting localities have already been published, no stable isotope analyses ? nonetheless very useful to complete, support and refine palaeoenvironmental and palaeoecological reconstructions ? have been carried out so far. Here we present preliminary results and interpretations of classical stable isotope analyses of oxygen (δ18O) and carbon (δ13C) on sauropod eggshells (Titanosauria), as well as on associated sediment and crystals. Stable isotope results were combined with physico-chemical (XRD, REE) and optical (SEM, CL, thin sections) analyses in order to assess the state of preservation of the fossils. While wellpreserved fossil material reveals aspects of dinosaur palaeoecology, diagenetically altered fossils provide important clues on the geological context. In addition to traditional stable isotope analyses, we used a recently developed method called clumped isotope thermometry that allows to directly measure the temperature of calcite precipitation. If the analyzed material consists of vertebrate fossils ? and provided that those are chemically pristine ? this temperature corresponds to the body temperature of the animal, and more precisely of the mother in the specific case of fossil eggs. In our context, the results indicate body temperatures similar to previously published data for Titanosauria, i.e., above 35°C.