BENTHIC FORAMINIFERA ASSOCIATIONS AND THEIR PALEOENVIRONMENTAL SIGNIFICANCE IN THE HAUTERIVIAN TO BARREMIAN MARINE BEDS OF THE NEUQUÉN BASIN, ARGENTINA

CARATELLI MARTINA; ARCHUBY FERNANDO

Salta

Congreso; REUNIÓN DE COMUNICACIONES DE LA ASOCIACIÓN PALEONTOLÓGICA ARGENTINA; 2022

APA

The paleosynecological approach of the benthic fauna proved to be useful tools in thepaleoecological and paleoenvironmental reconstructions of ancient marine environments. In thiswork we present a case study of the benthic foraminifera of the Hauterivian to Barremian marinebeds of the Agua de la Mula Member of the Agrio Formation (Neuquén Basin, Argentina). Bulksamples were obtained across sedimentary successions at five localities spread from central tonorthern Neuquén province. Samples were processed with standard procedures, specimens picked(up to n=300), identified and counted. Paleosynecological entities, i.e., fossil associations andassemblages, were created based on cluster analysis (complete linkage on Bray Curtis calculated onrelative abundances) and statistically evaluated with permutations (pvclust package of R software).Results were confirmed with principal coordinates analysis (PCoA) and permutational multivariateanalysis of variance (PERMANOVA). Assemblages and associations were characterized in terms oftheir alpha diversity. The relationships between the paleosynecological entities and the explanatoryvariables, i.e., facies types, position into sequence stratigraphic schemes, biozone and geographiclocation, were assessed with PCoA, redundancy analysis (RDA) and PERMANOVA. 44 out of 74samples contained foraminifera and in 18 of them the sample size of 300 was reached. A total of7,709 specimens of benthic foraminifera specimens distributed into 52 species, 31 genera, 15families and 5 suborders were included in the analysis. Eleven benthic associations were identified,eight of which are made of calcareous species (hyaline and aragonitic) and three of agglutinatedspecies. Most of the associations are characterized by specific microhabitat distribution andabundance peaks of certain species, both related to paleoenvironment changes affecting the seafloor,thereby allowing the application of fossil associations in paleoenvironmental interpretations.No departure from normal salinity was detected. Also, low levels of oxygen are evident in relationto deepening following 3rd order transgressions, although no evidence of permanent anoxia wasfound in the Agua de la Mula Member. This study represents the first application of multivariatestatistical methods to the evaluation of the benthic foraminifers, in order to assess thepaleosynecological significance of these fossil associations recorded in the Agua de la MulaMember of the Agrio Formation.