Sediment instability related to fluid venting in Miocene authigenic carbonate deposits of the northern Apennines (Italy)

Abstract

Chemosynthetic carbonates, identified by isotopic, palaeoecological and sedimentological features, are concentrated in middle-late Miocene satellite and foredeep deposits of the northern Apennines. Chemoherms in the foredeep are hosted in thick pelitic intervals, probably deposited in intrabasinal structural highs, which are entirely or partly involved in large slumps, in many cases associated with extrabasinal slides. Sediment textures in carbonates and in the enclosing foredeep pelitic sediments indicate a link between hydrocarbon-fluid venting, sediment deformation and mobilisation, and tectonics. The intensity and style of fluid release phases directly influenced chemoherm typology, and also determined overpressure conditions in low shear strength pelitic sediments, favouring sediment mobilisation and influencing slope instability, which widely affected the Apennine foredeep. Chemosynthetic carbonates are associated with sites of tectonically fractured and compressed sediments in the Apennine foredeep-thrust belt system, thus indicating a relation with the tectonic loading of the Apennine thrust-sheets, which favoured fluid expulsion along forerunner faults. Possible gas hydrate contributions to fluid expulsion processes are discussed, based on sediment textures compared with modern vent areas. Finally, sediment instability may have facilitated a large amount of fluid escape, thus stopping carbonate precipitation.

The Gela Basin pockmark field in the strait of Sicily (Mediterranean Sea): chemosymbiotic faunal and carbonate signatures of postglacial to modern cold seepage

“…Release of hydrocarbons has been invoked as a likely mechanism to trigger submarine slumps (Carpenter, 1981 and many others). On-land, similar causative scenarios have been suggested to account for localised Miocene chemosymbiotic faunal assemblages and/or authigenic carbonates associated with slumped bodies in the Apennine chain (Berti el al., 1994;Conti and Fontana, 2002;Lucente and Taviani, 2005).…”

Late Miocene seep-carbonates and fluid migration on top of the Montepetra intrabasinal high (Northern Apennines, Italy): Relations with synsedimentary folding

“…(1) in pelitic intervals included in Langhian-Serravallian basin-plain turbidites, or (2) in slope hemipelagites (Langhian-early Messinian) capping turbidites in proximity to the deformational fronts (Conti and Fontana, 2002).…”

Evidence of climatic control on hydrocarbon seepage in the Miocene of the northern Apennines: The case study of the Vicchio Marls

“…Cervarola and Marnoso-arenacea Formations (Conti et al, 2010a); -in slope deposits, such as the Vicchio Marls examined in this study, representing the closure stages of the migrating foredeep. Cold-seep carbonates can be associated with slumps, intraformational breccias and olistostromes due to intense sediment instability (Conti and Fontana, 2002;Lucente and Taviani, 2005). These units vary in size from a few to hundreds of meters, and derive from masses of foredeep and Ligurian-Epiligurian deposits which slid off submarine slopes.…”