Seep-carbonates are considered one of the most reliable indicators of fluid–expulsion processes along convergent margins.The majority of identified carbonate deposits containing fossil chemosynthetic assemblages (seep-carbonates) in the northern Apennines are concentrated in middle-late Miocene pelitic successions from two distint basin types: internal satellite Epiligurian basins, and external foredeep. The Epiligurian sediments consist of various depositional sequences; seep-carbonates are located in the middle-late Miocene outer shelf-slope deposits. In the foredeep, they occur in marly and clayey hemipelagites and fine-grained turbidites, located in slope-closure deposits (Langhian-early Messinian in age) passing laterally and capping huge arenaceous turbidites, or in slope deposits draping ephemeral topographic highs intercalated within the Langhian-early Serravallian basin plain turbidites (Mt Cervarola and Marnoso-arenacea Fms). In satellite basins, seep-carbonates occur in primary position and are associated with large debris flow deposits, whereas in the foredeep they are mainly hosted in thick pelitic intervals affected by an intense sediment instability such as slumps, intraformational breccias and extraformational slides.The great variability of the Apennine tectonic settings permitted different mechanisms of fluid expulsion: from diffuse discharge of pore fluids, related to mud diapir processes, to focussed or structurally aligned, fault-controlled pore fluid expulsion. Evidence of widespread discharge of fluids is commonly found in the chemoherms located in shallow-water deposits of the satellite basins and in foredeep slope pelites. Fault-controlled fluid expulsion characterizes venting within the thick pelitic intervals intercalated in the turbidite foredeep successions.These differences can be related to the degree of tectonic loading and rate of defluidization between the geometrically more elevated Epiligurian basins and the foredeep basins. Moreover, possible gas-hydrate contributions to fluid-expulsion processes are hypothesized in the foredeep, due to the more favorable conditions for gas hydrate dissociation in with respect to satellite basins
Fluid expulsion imprints in sedimentary chaotic intervals of the northern Apennines; seep-carbonates from the Miocene foredeep and satellite basins / Conti, Stefano; Fontana, Daniela; Gubertini, A.. - STAMPA. - Vol. 2:(2004), pp. 928-928. (Intervento presentato al convegno 32nd International Geological Congress., tenutosi a Firenze nel 20-28 Agosto 2004).