Benthic foraminifera associations and their paleoenvironmental significance in the Hauterivian to Barremian marine beds of the Neuquén Basin, Argentina

CARATELLI, MARTINA; ARCHUBY, FERNANDO M

Salta

Congreso; Reunión de Comunicaciones de la Asociación Paleontológica Argentina; 2022

Asociación Paleontológica Argentina

The paleosynecological approach of the benthic fauna proved to be usefultools in the paleoecological and paleoenvironmental reconstructions of ancientmarine environments. In this work we present a case study of the benthicforaminifera of the Hauterivian to Barremian marine beds of the Agua de la MulaMember of the Agrio Formation (Neuquén Basin, Argentina). Bulk samples wereobtained across sedimentary successions at five localities spread from centralto northern Neuquén province. Samples were processed with standard procedures,specimens picked (up to n=300), identified and counted. Paleosynecologicalentities, i.e., fossil associations and assemblages, were created based oncluster analysis (complete linkage on Bray Curtis calculated on relativeabundances) and statistically evaluated with permutations (pvclust package of Rsoftware). Results were confirmed with principal coordinates analysis (PCoA)and permutational multivariate analysis of variance (PERMANOVA). Assemblagesand associations were characterized in terms of their alpha diversity. Therelationships between the paleosynecological entities and the explanatory variables,i.e., facies types, position into sequence stratigraphic schemes, biozone andgeographic location, were assessed with PCoA, redundancy analysis (RDA) andPERMANOVA. 44 out of 74 samples contained foraminifera and in 18 of them thesample size of 300 was reached. A total of 7,709 specimens of benthicforaminifera specimens distributed into 52 species, 31 genera, 15 families and5 suborders were included in the analysis. Eleven benthic associations wereidentified, eight of which are made of calcareous species (hyaline andaragonitic) and three of agglutinated species. Most of the associations arecharacterized by specific microhabitat distribution and abundance peaks ofcertain species, both related to paleoenvironment changes affecting theseafloor, thereby allowing the application of fossil associations in paleoenvironmentalinterpretations. No departure from normal salinity was detected. Also, lowlevels of oxygen are evident in relation to deepening following 3rd ordertransgressions, although no evidence of permanent anoxia was found in the Aguade la Mula Member. This study represents the first application of multivariate statisticalmethods to the evaluation of the benthic foraminifers, in order to assess the paleosynecologicalsignificance of these fossil associations recorded in the Agua de la Mula Memberof the Agrio Formation.