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Silvia Ceramicola, Istituto Nazionale di Oceanografia e Geofisica Sperimentale - OGS (Italy)
Daniel Praeg, Istituto Nazionale di Oceanografia e Geofisica Sperimentale - OGS (Italy)
Andrea Cova, Istituto Nazionale di Oceanografia e Geofisica Sperimentale - OGS (Italy)
Daniela Accettella, Istituto Nazionale di Oceanografia e Geofisica Sperimentale - OGS (Italy)
Nigel Wardell, Istituto Nazionale di Oceanografia e Geofisica Sperimentale - OGS (Italy)
Roberto Barbieri, Università di Bologna (Italy)
Vikram Unnithan, Jacobs University Bremen (Germany)
Shipboard Scientific Parties, OGS Explora, Italy, Meteor, Germany & Pourquoi Pas? (France)
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The Calabrian Arc accretionary prism is being investigated in order to identify and characterize cold seep activity. Cold seeps were discovered on the Calabrian Arc in summer 2005 during a campaign of the Italian research vessel OGS Explora and have now been examined during two further oceanographic campaigns (of the r/v Meteor in 2006 and the r/v Pourquois Pas? in 2007), all in the framework of the EC-funded HERMES project. Here we present new information on the distribution of the cold seeps among the seabed tectonic features of the Arc and summaries ongoing investigations into their past and present activity from geophysical data, sediment cores and ROV seabed investigations.
Multibeam swath bathymetric and backscatter data were acquired in 2005 across an area of 160 x 220 km, from the Calabrian slope across water depths of 1000-4000 m. The morpho-bathymetric data reveal the main seabed tectonic features of the Arc and suggest a division into inner, central and outer zones. Integration of swath bathymetry with backscatter data allows the identification of mud volcanoes on the inner and central Arc, characterized by high backscatter and varying circular forms (mud cones, mud pies). The mud volcanoes have been investigated in detail at two locations, on the central and inner Arc, at features referred to respectively as the Pythagoras mounds and the OGS Explora mud volcanoes (better known as the Madonna dello Ionio). Multichannel seismic reflection profiles show the Pythagoras mud pie (c. 8 km in diameter) to form an inverted cone that extends up to 2 km below seabed, among the thrusts of the central Arc. On the inner Arc, seismic profiles show the three extrusive centres of the Madonna dello Ionio (two cones forming her breasts and a small mud pie forming her head, each up to 1.5 km wide) to lie within the Cenozoic succession of the Spartivento Basin. A 3D seismic volume constructed across the twin cones of the Madonna reveals buried cones interfingering with the upper part of the flanking Quaternary succession, indicating a long history of activity. Gravity cores from both features have proven grey mud breccias to lie at or near seabed, suggesting recent extrusive activity; gas was observed escaping from some cores. Microfossils in the mud breccias include foraminiferal species derived from strata as old as Cretaceous. ROV seabed investigations of the Pythagoras mud pie and the Madonna showed irregular relief attributed to mud volcanic flows, in most areas thinly mantled by pelagic muds. On the Madonna, ROV investigations revealed a few small centres of extrusion of warm, anoxic mud, indicating low levels of present-day activity following the prior widespread extrusion of mud breccias.
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