Transitional crust in the Newfoundland-Iberia rift and associated magnetic anomalies

International audienc

Iberian Atlantic Margins

The IAM project was part of an effort to study the deep geology of Europe. In particular the project aimed at exploring the nature of the deep continental and oceanic crust of the Earth in selected areas of the Atlantic margins of Iberia for a better understanding of the processes governing the formation of basins, outstanding structural features and the location of hydrocarbons and other natural resources. More information about the project at https://cordis.europa.eu/project/rcn/4817_en.html.The Iberian Atlantic Margins (1AM) project was a multinational research programme, coordinated by the Institute of Earth Sciences of Barcelona, CSIC (Spain) involving different academic institutions of Britain (University of Oxford and University of Durham), France (IFREMER), Portugal (University of Lisbon and Institute of Meteorology of Lisbon) and Spain (Institute of Earth Sciences of Barcelona, CSIC) and more than 40 associated scientists of European institutions attached to the main contractors. The project, financed by the European Community within its JOULE-Programme, aimed to explore the deep continental and oceanic Atlantic margins of Iberia for a better understanding of the formation and evolution of Atlantic type margins, outstanding structural features and potential location of hydrocarbons and other natural resources. The project was designed to acquire deep seismic multichannel data and onshore recording of wide angle and refraction data along the North Iberian margin; the West Iberia margin, including the Galicia margin, the Iberia and Tagus abyssal plain, and the continental shelf off Portugal; and the Gorringe Bank region and Gulf of Cadiz. The experimental part of the study consisted of the acquisition of over 3700 km of near vertical incidence deep seismic multichannel reflection data. This together with wide angle reflection and refraction data recorded by land stations and OBS (Ocean Bottom Seismometers) has resulted in a full coverage in terms of crustal structure and velocity information of the study region.Funded by European Commission FP3-JOULE 2, project ID JOU20177.Peer reviewe

Influence of seep emission on the non-symbiont-bearing fauna and vagrant species at an active giant pockmark in the Gulf of Guinea (Congo–Angola margin)

International audienceDetailed surveying with an ROV found that a dense and diverse cold-seep community colonises a giant pockmark located at 3200 m depth, 8 km north from the deep Congo channel. Several types of assemblages, either dominated by Mytilidae and Vesicomyidae bivalves or Siboglinidae polychaetes, are distributed on the 800-m diameter active area. The site is characterised by a most active central zone in a depression with abundant carbonate concretions and high methane fluxes where high-density clusters of mussels and siboglinids dominate. In contrast, the peripheral zones display large fields of dead and live vesicomyids on soft sediment, with a lower mean density and lower methane concentration in seawater. The associated megafauna includes Alvinocarididae shrimps, echinoids, holothurians of the family Synaptidae, several species of gastropods, two species of galatheids, and Zoarcidae and Ophidiidae fishes. Multivariate analyses of video transect data show that the distribution of these major megafauna species at the pockmark scale is influenced by the habitat heterogeneity due to fluid or gas emission, occurrence of hydrates, substratum variability and by the presence of large symbiont-bearing species. Several assemblages dominated either by mytilids, vesicomyids, or siboglinids have been sampled for megafauna densities and biomass estimations and stable isotope measurements (δ13C and δ15N) of dominant species and food sources. The highest estimates of megafauna densities have been obtained in mytilid beds. According to their stable isotopes values, non-symbiont-bearing species mainly rely on chemosynthesis-originated carbon, either as primary consumers of chemoautotrophic microorganisms, or at higher trophic level recycling organic matter, or relying on bivalve and tubeworm production. Most of them likely feed on different sources like shrimps, but differences according to habitat have been evidenced. Carbon and nitrogen isotope ratios of galatheids and benthic or benthopelagic fishes captured by trawls at increasing distances from the pockmark provide evidence of the high variability in the proportion of chemosynthesis-originated carbon in their diet, from 15% to 38%, according to the species captured as far as 4 km to the sit