Clathritic microfabrics, fossilized giant bacteria, and tube worms provide new clues on radiometrically dated late Miocene seepage in the Romagna Apennines (Italy)

The late Miocene in the Mediterranean area was a period of drastic geological and climatic transformations that occurred in combination with widespread hydrocarbon emissions. This study aims to characterize seep carbonates from San Ver- nicio (Romagna, Italy), describing newly reported microfabrics using a combined petrographic-geochemical approach to get new insights on hydrocarbon seepage and its sedimentary products during the late Miocene in the studied area. Features herein reported include limpid spar-filled micro-domains (interpreted as a newly discovered gas hydrate-derived texture), spar-filled spheres representing giant sulphide-oxidising bacteria, dissolution cavities, botryoidal cements, and former organic-walled tube worms. In situ U-Pb dating of seep-related calcite cements within a former conduit yielded a lower intercept age of 6.8 ± 0.9 Ma (Tortonian – Messinian). This radiometric age, representing a late stage of seepage, postdates the deposition of the hosting sediments (< ca. 10.5 Ma, based on biostratigraphic proxies) by at least ca. 2.8 Ma. These findings add a useful piece to the complex puzzle picturing seepage activity in the Mediterranean area during the late Miocene