A multidisciplinary environmental integrated approach to better understand the Tegnue Reefs formation, offshore Chioggia, Northern Adriatic Sea

Several hard substrata cover the northwestern Adriatic shelf around 20 m depth as patchy reefs called "Tegnue". These submerged reefs form many discrete sets from offshore Grado south to the Po river delta with a large field located off Chioggia. Even if the outer part of the reef is constituted by a thick biogenic formation the underlying structure, mainly buried, is made by cemented sand and this seems to be correlated with its origin not yet fully understood. Different genetic interpretations have been proposed thus far, contemplating among other cementation due to beach-rock like processes (e.g., Stefanon, 1969, Bonardi and Tosi, 2002, Bonardi et al., 2006) or the action of ascending fluids enriched in hydrocarbons (e.g., Gabbianelli et al., 1997, Casellato and Stefanon, 2008). An on-going project, mainly a multidisciplinary integrated approach, combining physical, biological, geological, geomorphological, hydrogeological and geochemical data, supported by a detailed bathymetric mapping, an overall general circulation modeling at high resolution, a robust geophysical evidence, and detailed underwater surveys performed by a team of scuba-diver scientists, aims to better understand the genetic processes backing the distribution, early genesis and evolution of such relevant habitats. Actually, using all the new available data, our plan is to verify which previous interpretations on the origin of the Tegnue core better match with the diagenetic processes that led to the cementation of the sand layers lying at the base of the organic reefs. Preliminary results suggest that the Tegnue reefs formed along paleochannels features related to the former alluvial plain and submerged by the Holocene transgression. Whatever their genesis, once exposed such rocky substrata are then quickly colonized by living organisms, which contribute to the growth and expansion of the reef. Calcareous algae and in general the organic concretion could have a role during the reef accretion, and benthic invertebrates like bryozoans, mollusks, serpulids and corals also contribute to the final building of the status of Tegnue's environment, but we want to demonstrate that the in first stage of consolidation abiotic phenomena could have played a major role. In order to prove our thesis a series of ground water sampling as well as rock sampling and sediment cores were carried out. The poster illustrates the overall ongoing program as well as some work in progress and first results from field cruise.