Paleoenvironmental significance of benthic foraminiferal associations of the Hauterivian to Barremian marine beds of the Neuquén Basin, Patagonia, Argentina

Abstract

The upper Hauterivian-lower Barremian sedimentary sequences of the Agua de la Mula Member of the Agrio Formation (Neuquén Basin, Argentina) represent shallow marine environments characterized by mixed siliciclastic‑carbonate deposition. Ten benthic foraminiferal associations based on species composition were defined and evaluated in relation to explanatory variables such as facies, sequence stratigraphy, location and age. Variations in sedimentation rates, food and oxygen availability related to relative sea-level changes largely control distribution of the benthic foraminiferal associations. Four associations (Guttulina sp., Polymorphinids, Spiroplectammina sp.2-Haplophragmoides sp.1, and Planularia madagascariensis) are mostly composed by shallow infaunal, bacterial and detritivorous foraminiferal scavengers that largely occur in sandy facies within 3rd-order regressive systems tracts. These associations are thought to be indicative of well oxygenated and organic matter-rich sediments below the sediment-water interface. The remaining six associations consist of epifaunal, mainly opportunistic foraminifera with active herbivorous and detritivorous trophic strategies. Among them, Epistomina hechti - Epistomina australis and Reinholdella hofkeri associations occur in fine-grained, dark shales throughout 3rd-order transgressive systems tracts, and are considered related to oxygen and food stressed environment. An integrated approach, using benthic foraminifera (alpha diversity analysis, epifaunal/infaunal ratio) and multivariate statistical methods (cluster analysis, RDA, partial-RDA, PERMANOVA, PCoA), allowed to evaluate the paleosynecological significance of benthic associations, and to relate certain paleoenvironmental settings to relative sea-level changes recorded in the Agua de la Mula Member. The application of foraminiferal associations analysis in the paleoenvironmental interpretations led to recognize the influence of major relative sea-level changes in shaping higher-frequency sequences for this sector of the Neuquén Basin. Such approach can also be applied to other sectors of the basin and to high-frequency sedimentary sequences of comparable shallow marine settings.