Taphonomic modes on fluvial deposits of the Monte Hermoso Formation (early Pliocene), Buenos Aires province, Argentina

The sedimentary deposits of the Monte Hermoso Formation, outcropping at its type locality (Farola Monte Hermoso, Buenos Aires province, Argentina), accumulated through fluvial processes acting on highly sinuous rivers. The Monte Hermoso Formation comprises a rich vertebrate fauna corresponding to the Montehermosan Stage/Age (early Pliocene), which includes numerous and diverse vertebrate remains. Comparative taphonomic analysis indicated that the faunal assemblages coming from two different fossiliferous levels, FL 1 and FL 2, recognized in floodplain deposits and channel deposits respectively, are composed of remains affected by diverse taphonomic processes and therefore representing distinct taphonomic histories. The variations recorded between both fossiliferous levels, with respect to their taphonomic attributes and sedimentary context, allowed the recognition of two distinct taphonomic modes: floodplain in the FL 1 and channel-lag in the FL 2. These taphonomic modes represent different conditions within the range of taphonomic histories for the Monte Hermoso Formation assemblage formed by attritional accumulation of remains. At the moment, continental systems linked to fluvial environments have been poorly analyzed for the South American Neogene; this study contributes new information on taphonomic and paleoenvironmental characteristics of this type of deposit.