FORAMINIFERS FROM THE BARRANCA FINAL FORMATION (LATE MIOCENE): PALEOECOLOGICAL INFERENCES

ALLENDE, AYLÉN; NÁÑEZ, CAROLINA A.; LAPRIDA, CECILIA

Ciudad Autónoma de Buenos Aires

Congreso; XII Congreso de la Asociación Paleontológica Argentina; 2021

Asociación Paleontológica Argentina

The Barranca Final Formation was assigned to the Entrerriense or Paranense transgression, based on the foraminifera recovered from its type section, northern coast of the San Matías Gulf, Río Negro province. In this study, we conduct a paleoecological analysis of the foraminiferal assemblages from the type section, including quantitative approaches such as diversity indexes, porcellaneous/agglutinated/hyaline tests ratio, planktonic/benthic ratio and the proportion of infaunal and epifaunal morphotypes. Only five of the twelve samples analyzed were fertile, and only two of them yielded enough specimens to conduct quantitative analysis. The samples are stored at Servicio Geológico Minero Argentino (SEGEMAR) Micropaleontological Repository. Notwithstanding, forty-five species were recorded, and twenty-four of them are mentioned for the first time for the section. The assemblages are dominated entirely or in high proportion by hyaline species while agglutinated and porcellaneous species are scarce or absent. Porosononion granosum and Cribroelphidium discoidale are the dominant species. Quantitative analysis and paleoecological information of dominant species in the lower part of the section suggest shallow inner shelf to coastal conditions followed by a more restricted marine paleoenvironment. The dominance of infaunal morphotypes suggests soft bottom, high organic flux and/or some deficiency in oxygen. Upwards, an interval barren of foraminifera supports a regressive trend. At the middle part of the section, the reappearance of scarce foraminifera, mainly represented by Pseudoglandulina symmetrica and Porosononion granosum, together with glauconite record, suggests a new and minor transgressive pulse. The lack of foraminifera in the upper part of the section is consistent with the more proximal environments and upward continentalization proposed in previous studies.