Condotti carbonatici legati all'espulsione di fluidi ricchi in idrocarburi. Carbonate conduits linked to hydrocarbons enriched seepages.

Authigenic carbonate precipitation, mediated by microbial consortia, is one of the most relevant outcome, often accompanying hydrocarbon-rich fluid seepage. Fluids can move through conduits that, under special circumstances, could lead to authigenic mineralization forming carbonate chimneys from mm to plurimetric in size. The study aims to better define these structures which are still poorly known, with respect to other methane-derived carbonates and will be pursued by the three RU focusing on the definition of a complete scenario, leading to the formation of these features. We will address the analysis on carbonate samples, which are already at hand in our repository, from Cadiz, Northern-Central Adriatic Sea and Bari canyon, the Apennines, Tortonian of Calabria, Pliocene of Emilia. The duties of the RU of the ISMAR/CNR of Bologna will be mainly to analyze, in extreme detail, such samples with aliquots shared to be categorized for petrography, elemental geochemistry and stable isotopes, biomarkers and Sr dating. The carbonate conduits belong to those surface indicators of shallow or deep reservoirs that can be very useful for exploration purposes. In fact, the leakage of fluids up to the surface, previously needs the achievement of favourable condition leading to expulsion from source rocks, migration and accumulation within stratigraphic and structural traps. One of the duties of the research team of the University of Bologna is to provide the characterization of the reservoirs and to stress the occurrence of tectonic deformation and faulting as they can provide different migration pathways. The characterization of the reservoir rocks has to be integrated by that of the seal, which allows the leakage up to the surface, and to assess what are the main causes of seal efficiency loss as faults, non homogeneous permeability, or erosional events and consequent exposure of the reservoir. A previous geochemical study on the saline waters and on the associated hydrocarbons (gas and oil), occurring through the active seepages in the Northern Apennines, will be integrated by new analysis providing a unique opportunity to compare the isotopic signals recorded in modern seepages and in the recovered carbonate conduits which formed when the condition was marine, as the two groups belong to the same Apennine mountain front. The fluid migration pathways, developing through time within the reservoirs, must be related to the structural evolution, then we think that it is crucial to assess similarities or differences by the comparison between modern marine seepages and those presently emerged and included in the chain deformation, to fully characterize the depositional systems and the geologic evolution together with all those aspects concerning the geobiology, the biostratigraphy and the paleoecology. This purposes will be achieved also by means of the biostratigraphic support, provided by the RU of the University of Ancona, to reconstruct the chronology of the fossil bodies and to contribute to the description of the issue by analyzing paleo (ecological) communities in benthic foraminifera (both modern and fossil), in order to understand whether these associations may be characteristics of different types of emission, if they show comparable characters and if these characters can be recognized even in fossils condition. For biostratigraphic characterization will be applied quantitative standard methodologies, to frame the structure in a chronological succession; it will also be possible to examine from the point of view of content in calcareous nannofossils the infills of the conduits and the characteristics of muds accompanying emissions, in order to identify (by means of the age of calcareous nannofossil associations) from which layers deep emissions originate. It will be also characterized, by means of benthic foraminifers, the environment surrounding the conduits of fluid discharge.