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

Salta

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

APA

Foraminiferal morphogroups are widely used in paleoecological and paleoenvironmentalreconstructions of extant and ancient marine environments. Since morphological features offoraminiferal tests (i.e. chamber arrangement, mode of coiling, wall structure, type and number ofapertures) are strongly related to lifestyle and feeding strategies of foraminifera, test morphologycan hypothetically be used for interpreting paleoenvironmental changes at the sea-floor. Here wepresent the first morphogroup analysis of benthic foraminiferal assemblages from the Agua de laMula Member of the Agrio Formation in the Neuquén Basin (Northern Patagonia, Argentina), andprovide a statistical comparison with a similar approach based on species’ abundances (see acompanion abstract for the species analysis). Bulk samples were obtained across sedimentarysuccession at five localities spread from central to northern Neuquén province. Samples wereprocessed with standard procedures, specimens picked (up to n=300), assigned to morphogroupsand counted. Paleosynecological entities, i.e., fossil associations and assemblages, were createdbased on cluster analysis (complete linkage on Bray Curtis calculated on relative abundances) andstatistically evaluated with permutations (pvclust package of R software). Results were confirmedwith principal coordinates analysis (PCoA) and permutational multivariate analysis of variance(PERMANOVA). Assemblages and associations were characterized in terms of their alphadiversity. The relationships between the paleosynecological entities and the explanatory variables,such as facies types, position into sequence stratigraphic schemes, biozone and geographic location,were assessed with PCoA, redundancy analysis (RDA), partial RDA and PERMANOVA. Theamount of information shared by both species and morphogroups matrices, was calculated with aco-inertia analysis. The 7,709 specimens studied were distributed into thirteen morphogroups, eightof them calcareous (hyaline and aragonitic), and five with agglutinated tests. Life positions andfeeding strategies of foraminifera were inferred from the literature. Seven benthic fossil associationsbased on morphogroups were identified, that in turn cluster into two groups dominated by eitherinfaunal or epifaunal morphotypes. Multivariate analyses showed significant values of localities inboth morphogroup and species composition of samples, while facies and sedimentary sequences areweakly associated to both matrices. As expected, biozones showed significant influence in speciesdistribution, and not in morphogroups. This is in agreement with species turnover, that is closelyrelated to changes over geological time, while morphogroups are expected to recur over time.Interestingly, the co-inertia coefficient showed a moderate value (RV=0.71) that implies that bothmatrices share a significant amount of information, but differ.