Benthic foraminifera morphogroups as proxies for paleoecological analysis. An example from the Lower Cretaceous Agua de la Mula Member of the Agrio Formation (Patagonia, Argentina)

CARATELLI, MARTINA; ARCHUBY, FERNANDO M

Salta

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

Asociación Paleontológica Argentina

Foraminiferal morphogroups are widely used in paleoecological andpaleoenvironmental reconstructions of extant and ancient marine environments.Since morphological features of foraminiferal tests (i.e. chamber arrangement,mode of coiling, wall structure, type and number of apertures) are stronglyrelated to lifestyle and feeding strategies of foraminifera, test morphology canhypothetically be used for interpreting paleoenvironmental changes at thesea-floor. Here we present the first morphogroup analysis of benthicforaminiferal assemblages from the Agua de la Mula Member of the AgrioFormation in the Neuquén Basin (Northern Patagonia, Argentina), and provide astatistical comparison with a similar approach based on species’ abundances (see a companion abstract for the speciesanalysis). Bulk samples were obtained across sedimentary succession at fivelocalities spread from central to northern Neuquén province. Samples were processedwith standard procedures, specimens picked (up to n=300), assigned tomorphogroups and counted. Paleosynecological entities, i.e., fossilassociations and assemblages, were created based on cluster analysis (completelinkage on Bray Curtis calculated on relative abundances) and statisticallyevaluated with permutations (pvclust package of R software). Results wereconfirmed with principal coordinates analysis (PCoA) and permutationalmultivariate analysis of variance (PERMANOVA). Assemblages and associationswere characterized in terms of their alpha diversity. The relationships betweenthe paleosynecological entities and the explanatory variables, such as faciestypes, position into sequence stratigraphic schemes, biozone and geographiclocation, were assessed with PCoA, redundancy analysis (RDA), partial RDA andPERMANOVA. The amount of information shared by both species and morphogroupsmatrices, was calculated with a co-inertia analysis. The 7,709 specimensstudied were distributed into thirteen morphogroups, eight of them calcareous (hyalineand aragonitic), and five with agglutinated tests. Life positions and feedingstrategies of foraminifera were inferred from the literature. Seven benthicfossil associations based on morphogroups were identified, that in turn clusterinto two groups dominated by either infaunal or epifaunal morphotypes.Multivariate analyses showed significant values of localities in bothmorphogroup and species composition of samples, while facies and sedimentarysequences are weakly associated to both matrices. As expected, biozones showedsignificant influence in species distribution, and not in morphogroups. This isin agreement with species turnover, that is closely related to changes overgeological time, while morphogroups are expected to recur over time. Interestingly,the co-inertia coefficient showed a moderate value (RV=0.71) that implies thatboth matrices share a significant amount of information, but differ.