How can stratigraphy contribute to conservation paleobiology? Insights from a mid-Holocene to present-day transitional system of the Po coastal plain (N Italy)

The definition of reference conditions has a major role for the understanding of the present-day and paleoecological quality status on transitional environments. The estuarine quality paradox and the paucity of unimpacted sites make the definition of reference conditions a challenging task. In this context, the integration of biological indicators with stratigraphic data is essential, as the vertical stacking pattern of facies composing the shallow subsurface of modern coastal plains reflects changes in physical-chemical parameters which, in turn, affect (paleo-)biotic communities.

In the Po coastal plain (N Italy), the mid to late Holocene back-barrier succession of the Mezzano Lowland and the adjacent present-day Bellocchio Lagoon offer a unique example of pristine paralic system for comparing reference conditions defined in fossil and modern settings, respectively. Benthic foraminifers and ostracods from the Mezzano succession allowed us to investigate vertical (i.e., temporal) and lateral (i.e., spatial) changes in (paleo-)environmental conditions, in analogy to the lateral variations recorded at the Bellocchio Lagoon.

Both sites present subtidal channel sands almost barren in autochthonous meiofauna and fine-grained lagoon sediments with abundant benthic foraminifers and ostracods mostly represented by euryhaline taxa recording the highest diversity. Intertidal muddy deposits are also recorded, including mud flat clays with abundant oligotypic assemblages dominated by highly-confined benthic foraminifers. In the present study, we demonstrate that changes in modern benthic foraminifer assemblages diversity and composition often interpreted as perturbations of ecological conditions in response to anthropogenic pressures also occur under natural state, as confirmed by paleoenvironmental conditions recorded by ostracods. This reflects the effects of authogenic processes at short time and geographic scales.