Integrated sedimentological and palaeoecological analysis of the Upper Pliocene Rio Stramonte section (Emilia-Romagna, Italy)

Understanding the complex interactions between organisms and their environment is fundamental for palaeoenvironmental and palaeoclimatic reconstructions. Biotic and abiotic components evolve through time and leave imprints in the biosedimentary record, which can be unravelled to trace how ecosystems respond to palaeoenvironmental changes. In this study, we apply an integrated approach combining sedimentological and palaeoecological analyses to reconstruct the palaeoenvironmental evolution of the Rio Stramonte section (Lugagnano Val D’Arda, Emilia Romagna, Italy) within a key climatic interval, the Piacenzian, which is the most recent example of prolonged global warming in the deep time record and a possible analogue for the future climate conditions. The Rio Stramonte section is 54 m thick and is assigned to the Late Pliocene (Piacenzian) based on preliminary biostratigraphic analyses (molluscs, foraminifera and nannofossils). Twenty-eight mollusc samples were collected for palaeoecological analysis, and a total of 3147 specimens belonging to more than 120 taxa of bivalves and gastropods were identified and studied. The palaeoecological analysis shows that mollusc assemblages are composed of both infaunal and epifaunal taxa of infralittoral and circalittoral settings. The sedimentological analysis indicates a vertical succession of lithofacies suggesting an overall regressive trend from the bottom to the top of the section, with variations in water depth (from approximately 40–50 m to 5–10 m) and sedimentation rates. In the lower part of the section sandy beds are rich in molluscs. Bivalve specimens mainly occur with disarticulated valves, however without evidence of corrasion, thus reflecting a short-distance transport. In the middle part of the section, composed of fine-grained sediments deposited in a shelf setting, specimens are preserved in life position indicating low-energy muddy bottoms. Finally, the upper part of the section is rich in bivalve and gastropod fragments due to transport processes. Indeed, in this part of the section sedimentological features, as hummocky cross stratification, probably related to storm waves, indicate a shallower environment compared to the lower and middle part of the section, possibly affected by density flows directly related to river floods. Based on sedimentological and palaeoecological analyses, the Rio Stramonte section deposited in a shallow-water marine environment (infralittoral to shallow circalittoral) affected by episodes of salinity reduction due to river discharge. These results contribute to a better understanding and characterisation of the mollusc faunas of the Palaeo-Adriatic Basin during the warm climatic interval of the Piacenzian.