Late Quaternary incised and infilled landforms in the shelf of the northern Adriatic Sea (Italy)

The northern Adriatic shelf is punctuated by the presence of several incised and filled features that have been revealed by the offshore seismic and stratigraphic surveys carried out in the last decades. In this study we analyzed an area located in the northern Adriatic shelf, 30 km offshore of the Venice Lagoon and between 29 and 34 m below the mean sea level, where the most impressive examples were identified. By integrating the interpretation of about 3000 km of high-resolution seismic profiles (CHIRP) with sediment cores, paleontological analyses and radiocarbon dates, it was possible to distinguish between two generations of incised features. The older generation (Nadia) is represented by a fluvial incised valley that reaches a depth of up to 30 m and was formed and infilled during the LGM marine lowstand, probably between ca. 26 and 24 ka cal BP. The peculiar horizontal layering displayed by the infilling is characteristic of a low-energy environment. This suggest that, after its formation, the valley was first occupied by a swampy environment, which was then gradually filled-up with sediments received from nearby riverine systems. Differently, the younger generation (Attila) consists of a set of tidal inlets and channels with a maximum depth of 20 m, which are the legacy of a transgressive lagoon environment. The tidal nature of these features is confirmed by the geometry and paleontological content of their infilling and by their overall morphological and morphometric characteristics. The transgressive lagoon where these channels developed probably existed for just few centuries in the Early Holocene (ca. 10-9 ka cal BP). This period likely coincides with a temporary deceleration or stasis of the sea-level rise rate. This work presents new results for the paleogeographic and paleoenvironmental reconstruction of the northern Adriatic area, covering a period that spans from the middle LGM to the beginning of the Holocene.