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 Vernicio (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.