Sedimentological and stratigraphically controlled preservation styles and distribution of fossil cetaceans from a new Early Miocene fossiliferous locality, Patagonia, Argentina

Prospecting fieldwork in a new fossiliferous locality of the marine Early Miocene Gaiman Formation (Patagonia, Argentina) results in the discovery of abundant fossil cetaceans (n = 29). We analyse stratigraphic, sedimentologic, palaeontologic, and taphonomic data with the aim of understanding the factors that control the preservation and distribution of these specimens. The cetacean sample is dominated by small odontocetes exhibiting five different preservation categories. Based on sedimentological features, three distinct facies were recognised in the stratigraphic section. Stratigraphically condensed deposits of facies C, related to a ravinement surface and subsequent transgressive deposits, enclose 52% of the specimens, grading from isolated postcranial elements to articulated and associated postcranial and cranial elements. In contrast, facies A and B exhibit predominantly isolated postcranial elements. Facies C shows higher degrees of corrosion, encrustation and fragmentation than those specimens from facies A and B, reflecting differences in preservation quality among the facies. The higher abundance and evidence of long exposure times recorded for facies C seems to be resulted mostly from physico-chemical factors after stratigraphic condensation. Finally, intrinsic biological features and ecological preferences of the specimens could explain the dominance of small-sized odontocetes in a restricted inner shelf to lower shoreface environmental setting.