Potential and limits of benthic foraminiferal ecological indices in paleoenvironmental reconstructions: a case from a Holocene succession of the Po Delta, Italy

Abstract

Classical (paleo-)ecological indices extracted from benthic foraminiferal assemblages are commonly applied to determine past environmental conditions.We tested the efficiency of selected indices (including wall type proportion, epifaunal/infaunal ratio and pooled diversity indices) on benthic foraminifera from a Holocene shallow marine succession of the Po Delta, in order to evaluate their advantages, limits and differences. The paleoenvironmental record was determined integrating species composition of assemblages. All indices clearly discriminated between low and high riverine influence, even though the boundary at three different core depths revealed their different sensitivity to the faunal response under hanging environmental conditions in terms of organic matter and sediment supply. Specifically, the lowest boundary was highlighted by wall structural types and epifaunal/infaunal ratio that were able to track the first inputs of organic matter provided by the prograding Po River mouths. Upward, low sand concentration and moderate foraminiferal abundance (expressed as Total Foraminiferal Number) indicated significant supplies of fine-grained sediments within a prodelta paleoenvironment. Lastly, diversity indices revealed stressful prodelta conditions with remarkable low diversity and high dominance values. We show that high paleoenvironmental resolution can be obtained through the integration of faunal indices, species composition and sediment grain size within deltaic successions, where many indices should be considered to comprehensively understand the onset of riverine influenced conditions.