MULTI-PROXY ANALYSIS OF THE ENIGMATIC SITE ARENAS BLANCAS (BUENOS AIRES PROVINCE, ARGENTINA) AND ITS REPERCUSSION ON THE PAMPEAN BIOSTRATIGRAPHY

TOMASSINI, R.L.; MONTALVO. C.I.; BEILINSON, E.; BARASOAIN, D.; SCHMIDT, G.; CERDEÑO, E.; ZURITA, A.E.; BONINI, R.; MIÑO BOILINI, A. R.; RASIA,L.; GASPARINI, G.M.

Jornada; XXXV Jornadas Argentinas de Paleontología de Vertebrados; 2022

Arenas Blancas is a poorly known 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 wasdefined from 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 were never studied in detail. Now, we perform amulti-proxy analysis of the Arenas Blancas site, as well as a nearby site so-called Curva de la Vaca (without fossils),and provide new interpretations on their origin, age, and biostratigraphy. Sedimentological, stratigraphic, andgeomorphological characteristics of both sites suggest that the sequences include fluvial/alluvial deposits thatrepresent Quaternary terraces; it is highlighted that, at the moment, no Quaternary fossils were founded in thesesites. The taxonomic analysis of the Arenas Blancas faunal assemblage reveals 14 mammal taxa, together withsome fishes, reptiles, and birds. This assemblage is correlated with the fauna from the Cerro Azul Formationassigned to the Chasicoan Stage/Age (late Miocene), also recovered from the lower reach of the Chasicó creek.Some mammals are abundant (e.g. Chasicotatus ameghinoi, Vetelia perforata, Typotheriopsis chasicoensis) and onetaxon (Cardiatherium chasicoense) is considered as typical of the Chasicoan Stage/Age in the Pampean region. Thetaphonomic evaluation indicates that the assemblage is constituted by reworked specimens. It is proposed thatfluvio/alluvial events, occurred during the late Pleistocene-Holocene, eroded the upper Miocene substrate andreworked fossil remains, which results in a significant temporal difference between the sedimentation of thedeposits and the fossil content of Arenas Blancas site. The updating data on the taxa used to characterize theMacrochorobates scalabrinii Biozone (including this species) show their low biostratigraphic value, considering theirtaxonomic status and/or temporal distribution. The available geological and paleontological evidence leads to rejectthis biozone as a valid biostratigraphic unit. This type of comprehensive study, involving multiple lines of evidence, isof great interest and necessary to make integral evaluations of the vertebrate assemblages preserved in fluvialenvironments. Particularly, the identification of reworking, a common process in different fluvial/alluvial systems, isessential when biochronological and/or biostratigraphic interpretations are proposed.