On the validity of the Macrochorobates scalabrinii Biozone (early Huayquerian Stage/Age, Late Miocene). Multi-proxy analysis of the enigmatic Arenas Blancas site (Buenos Aires Province, Argentina)

Abstract

Arenas Blancas is a poorly known fossiliferous site located in the lower reach of the Chasicó creek (Buenos Aires Province, Argentina), with great relevance from a biostratigraphic viewpoint. The Macrochorobates scalabrinii Biozone was defined in this site, proposed as the biostratigraphic basis of the early Huayquerian Stage/Age (Late Miocene); however, the geological context and faunal record of this site have never been studied in detail. In this work, we perform a multi-proxy analysis of the Arenas Blancas site, as well as a nearby site here called Curva de la Vaca, and provide new interpretations on their origin, age, and biostratigraphy. Sedimentological, stratigraphic, and geomorphological characteristics of both sites suggest that the sequences include fluvial/alluvial deposits that represent Quaternary terraces. The taxonomic analysis of the Arenas Blancas faunal assemblage evidences the presence of 14 mammal taxa, together with some fishes, reptiles, and birds; the assemblage is correlated with the assemblage from the Cerro Azul Formation assigned to the Chasicoan Stage/Age (Late Miocene), also recovered from the lower reach of the Chasicó creek. The use of the taxa proposed in previous works to characterize the Macrochorobates scalabrinii Biozone (including this species) is not supported due to their taxonomic status and/or temporal distribution. Taphonomic evaluation indicates that the assemblage is constituted by reworked specimens; in this frame, it is proposed that fluvio/alluvial events, occurred during the Late Pleistocene-Holocene, eroded the Upper Miocene substrate and reworked fossil remains. Based on the present evidence, the Macrochorobates scalabrinii Biozone is here rejected as a valid biostratigraphic unit.

Advances in the Understanding of Neogene Mammalian Fauna in the Pampean Region (Central Argentina) Through Revising “Biozone” Hypotheses Based on New Dates and Biochronological Analyses

“…The collection number and the exact locality where the specimen mentioned in Piñero et al (2021) was found are not provided; there is no basis for the correlation between the lithofacies association 3 of Zárate et al , (2007) and the Las Barrancas Member of Fidalgo et al , (1978, 1987) since the former study contradicts the lithostratigraphic schema of the latter. Finally, the provenance of other specimens of Chasichimys in the context of Zárate et al , (2007) schema was not discussed, and more recently, Tomassini et al (2023) stated that with a large sample of mammals with good stratigraphic provenance no faunisitic differences were found throughout the sequence of the Arroyo Chasicó Formation. Therefore, we consider it premature to accept as an observational fact the occurrence of superposed levels in the Arroyo Chasicó sequence containing Ch .…”

Redefining the Huayquerian Stage (Upper Miocene to Lower Pliocene) of the South American chronostratigraphic scale based on biostratigraphical analyses and geochronological dating

“…This agrees with Tomassini et al . (2023), who recently rejected the validity of this biozone based on taphonomical and taxonomical studies in the type locality.…”

Armadillo Osteoderms Altered by Digestion and How Taphonomy Can Help Taxonomy

“…Recently, taphonomic analyses have begun to be applied as a complementary tool to understand how osteoderms have been modified by taphonomic processes and, on this basis, to solve taxonomic issues involving Cenozoic representatives of this group. These studies have proposed that some taxa of glyptodonts (Urotherium antiquum, U. simplex, Paraglyptodon chapadmalensis, Trachycalyptus chapadmalensis, Lomaphorus chapalmalensis) were identified and characterized based on osteoderms affected by different processes (i.e., weathering, abrasion, soil corrosion) that modified the original ornamentation patterns and, therefore, resulted in taxonomic misidentifications (Zurita et al 2016(Zurita et al , 2017Barasoain et al 2022;Tomassini et al 2023).…”