Book Description

The areas visited during the 10th Training-through-Research Programme were the Portuguese Margin, the Gulf of Cadiz, the Lucky Strike area of the Mid-Atlantic Ridge, the Rockall Trough, the Southern Faeroe margin, and the Varring Plateau (Norwegian margin). The investigations were aimed atstudying such geological processes as neotectonics, fluid migration and escape, sediment processes in canyons and sediment reworking and benthic biology in areas swept by deep-sea bottom currents as well as hydrothermal manifestations on mid-ocean ridges. A seismic and sidescan survey of the Marques de Pombal structure (Portuguese margin) allowed a better understanding of a fault system known here from previous studies such as the ARRIFAN0 and BIGSET projects. The fault pattern has been mapped and acoustic images have helped to evaluate the status of their activity. The Marques de Pombal structure showed little evidence of recent activity and is being covered by sediments. Shallow slides found in the vicinity of the structure may, however, indicate some occasional activity disturbing the overlying sedimentary cover. The Pereira de Sousa fault was found to be much more active. Six new mud volcanoes were discovered and studied in the Gulf of Cadiz. Most of them were proved to be recently active. The mud volcanism of the Gulf of Cadiz can be considered as two characteristic regions with different mud breccia lithological composition. Several types of lava sulphite ores sampled during the Azores campaign of Leg 2 allowed a better understanding of volcanic evolution and associated processes of this area. A short 3.5 kHz survey across the Porcupine Seabight mouth, combined with existing swath bathymetry data and a few cores from the area, confirmed the findings of the TTR-7 cruise that the Gollum channel system is currently inactive. The study of a canyon on the northeastern Rockall Trough margin showed that the system is inactive at the present time and the last pulse of active downslope sediment transport took place in immediate pre-Holocene time. Debris flows were found mostly on the flanks of the canyon while the axial zone showed numerous signs of erosion. Sand was not particularly common in the studied area. It is suggested that significant amounts of sand are trapped in the canyon head, possibly due to slumps blocking the narrower waist area. Abundant traces of seabed erosion found immediately beyond the canyon mouth indicate that this area is a bypass zone and sand deposition may occur further into the canyon mouth indicate that this area is a bypass zone and sand deposition may occur further into the basin plain. An extensive collection of TV-guided grab samples and seafloor video records, obtained from sites in the Northern Rockall Trough, Wyville-Thomson Ridge and Southern Faeroe Plateau, provided GOOd insight on the distribution of bottom fauna, including deep-water corals, and of coarse glaciagenie debris. New data on a BSR distribution pattern were obtained on the southeastern part of the Verring Plateau and they suggest that the formation of the Storegga Slide was not directly related to the dissolution of gas hydrates. The investigation also provided a new insight into gas hydrate formation and distribution in the area.