An accumulation of dinosaur remains in fluvial deposits of Mulichinco Formation (lower Valanginian, Neuquén Basin), Patagonia, Argentina: Taphonomic and paleoenvironmental inferences

Abstract

Although the Neuqu´en Basin (Argentina) has an extensive record of fossil vertebrates for the Upper Cretaceous, little is known about the Early Cretaceous vertebrate faunas. The Mulichinco Formation (early Valanginian), where some dinosaur bone sites were found, provides important additional insights into the composition of continental fauna of that age. Although osteological studies of sauropod and theropod dinosaurs have been published for this unit, no taphonomic studies have been reported to date. Here, we describe the biostratinomic processes that took place on an accumulation of bones found in rocks of the Mulichinco Formation and discuss the relationships between those remains and the environment in which the bones were buried. Taphonomic alteration mechanisms were estimated, including articulation, weathering, abrasion, integrity, bioerosion, transport, and orientation. We described thoroughly a sedimentological section and micro-sections that indicate the stratigraphic location and spatial arrangement of the remains. Three sub-environments in the inferred braided fluvial system were determined and three levels with bones showing different taphonomic attributes were identified within the accumulation. The lag deposits contain indeterminate bone remains with signs of significant transport and probably from different origins. On the other hand, the channel infill contains an articulated carcass of a sauropod and associated remains, of para-autochthonous origin, with no significant transport.