Floodplain taphonomic mode in a vertebrate assemblage from Salinas Grandes de Hidalgo, Cerro Azul Formation (Upper Miocene, central Argentina)

Abstract

Salinas Grandes de Hidalgo, a fossil locality in the east of La Pampa Province, Argentina, has yielded a rich assemblage of Late Miocene vertebrates, including Argentavis magnificens, the largest known flying bird, and a diverse mammalian fauna. Recent studies indicate that the intermediate section of Salinas Grandes de Hidalgo outcrop was dated to 5.9 ± 0.4 Ma, and describe the development of poorly confined flows interspersed with periods of surface stabilization associated with pedogenesis. In this contribution, we analyze the taphonomic attributes of the fossil remains from this site, using classical anatomical and taxonomic estimators. Clear taphonomic differences are observed between macro- and microvertebrate remains. Macrovertebrate skeletal elements are predominantly broken, disarticulated, and dispersed, showing varying degrees of weathering and limited evidence of bioerosion, corrosion, encrustations, or impregnation, suggesting a longer exposure prior to burial. Microvertebrate remains are also disarticulated and fragmented, withoutsigns of digestive corrosion, but exhibit a high degree of impregnation and minimal weathering. The development of soils during periods of stability likely favored the preservation of microvertebrate remains through burial by gradual but sustained sedimentation. The analysis allows interpreting that the assemblage resulted from the natural death of animals and gradual deposition in a floodplain environment. The anatomical representation, degree of articulation, and few evidences of abrasion suggest minimal transport in a low-energy, high-viscosity fluvial system over multiple events. Thetaphonomic characteristics are consistent with the floodplain taphonomic mode.