CONICET | Buscador de Institutos y Recursos Humanos

Despite being coeval faunas from the Levipustula levis biozone from the Late Paleozoic western central Argentinian basins, Levipustula and Aseptella-Tuberculatella/Rhipidomella-Micraphelia (AT/RM) associations show high compositional differences suggesting that their wide vs. restricted distribution is probably linked to a set of abiotic factors. We hypothesize that bathymetric preferences from dominant genera could partly explain some of their paleoecological differences. We describe and compare the faunas? structure at a regional scale using a proportional rank plot and estimated richness by rarefaction based on a generic occurrence data set. We also use an index for each genus? environmental preferences according to their occupancy along the bathymetric gradient. The Levipustula association is more diverse than AT/RM fauna. First, it is co-dominated by brachiopods (57%) and bivalves (43%), while the AT/RM fauna is brachiopod-dominated (>70%). Higher richness and evenness indicate that the Levipustula association would develop in more heterogeneous environments than the AT/RM association. Moreover, a higher dominance of brachiopods in the AT/RM association could be a paleoecological response to environments with low turbidity. So far, the bathymetric distribution assessment indicates that the AT/RM association exhibits preferences for deep waters while taxa with broader bathymetric affinities characterize the Levipustula association. Hence, the less diverse AT/RM association bearing deep-water specialists could have developed under greater glacial-influence in low turbiditic fjord-like environments, whereas the generalist Levipustula association could have occurred in open marine settings.