Palaeoecological analysis of marine benthic macroinvertebrate assemblages across a major stratigraphical discontinuity, Lower Cretaceous, Neuquén Basin, Argentina

Studying diversity patterns at the local scale can yield data on environmental fluctuations, habitat heterogeneity, etc. These local data can be integrated into regional and global perspectives, helping to reconstruct larger-scale processes. In the Berriasian–Valanginian of the Neuquén Basin (west-central Argentina), benthic invertebrate faunas are abundantly recorded in the Sierra de la Cara Cura (southern Mendoza Province) above and below a regional surface (the Intravalanginian Discontinuity) that marks a sea-level fall. The palaeoecology of these benthic faunas is analysed here. Five successive, non-recurrent assemblages were recognized and described along with their bearing facies. The lithological succession consists mostly of marlstones, wackestones, and floatstones: the discontinuity is represented by a bored surface with sandstone infilling. Across assemblages, richness decreases to a minimum at the Post-Discontinuity Assemblage and then rises again. Ecologically, in terms of motility, feeding, and tiering, the three pre-discontinuity assemblages are rather homogeneous, and the same is true for the two post-discontinuity ones. The assemblages are best described as following a redundancy model, with overall stable occupation of ecological niches. However, at the discontinuity surface, a moderate faunal turnover and a reconfiguration of ecospace usage take place, for example, deeper infaunals appear and motile taxa decrease. These features suggest changes in the oxygenation and consistency of the substrate. Thus, within a fully marine setting, in a short temporal window, the Intravalanginian Discontinuity caused a greater change in the functional ecology of benthic assemblages than those recorded among pre- and post-discontinuity assemblages.