Meta-analysis of a Holocene 14C database for the detection of paleohydrological crisis in the Venetian–Friulian Plain (NE Italy)

Abstract

The Venetian–Friulian Plain is the northernmost alluvial environment facing the Adriatic Sea and it represents the transition from the Mediterranean domain to the Alps and the temperate regions of central and eastern Europe. The investigated area consists of the alluvial systems of Brenta, Piave and Tagliamento rivers, forming distinct alluvial megafans fed by mountain basins of 1567, 3899 and 2580km2, respectively. The database of radiocarbon dates related to the Holocene alluvial evolution of the Venetian–Friulian Plain consists of 136 samples, 65 of them classified as change-after dates. We analyzed statistically the database with the aim of detecting periods of enhanced flooding activity. The individual calibration probability intervals of each radiocarbon age were summed, producing a cumulative probability density function (CPDF) plot for each alluvial system and for the whole database. Each change-after CPDF plot has been subtracted to its correspondent CPDF plot of the entire sub-dataset, obtaining a relative cumulative probability function (RCPF) curve.The analysis of these curves evidences that statistically significant information are available between about 8.5 and 0.8kacal BP. In particular, nine periods of enhanced flooding activity have been identified: 8.4–8.3, 7.5–7.2, 6.9–6.2, 5.5–5.3, 4.7–4.5, 2.3–2.1, 1.9–1.7, 1.6–1.4 and 1.3–0.8kacal BP. In the interval 8.5–0.8kacal BP, some sub-periods are not statistically significant because of the relatively few change-after dates available. Notably, between 4.5 and 2.3kacal BP no interval has been recognized, even if some important flooding deposits are documented in the stratigraphic and geomorphological record.Meta-analyses revealed quite a good correlation of several flooding periods occurred in the study area with the flooding record of the Lake Iseo (northern Italy), as well as with positive peaks in the Ice Rafted Debris (IRD) curve for the North Atlantic, namely Bond events 1, 3, 4 and 5. Comparison with other flood sequences obtained in Great Britain, Spain, Poland and Germany with the same statistical approach used in this work confirms the presence of some common intervals. In particular, synchronous periods of hydrological crisis are recorded in NE Italy and Great Britain at 7.5–7.3, 6.9–6.5, 6.3–6.2, 4.7–4.5, 2.3–2.1, 1.5–1.4, 1.3–1.1, 0.9–0.8kacal BP. Two of them, 4.7–4.5 and 0.9–0.8kacal BP, occurred also in the Iberian Peninsula. These results suggest that during the middle and late Holocene enhanced flooding activity in NE Italy is recurrently connected to events or phases of climatic deterioration at regional and continental scale, with minor influence of local forcings.