HR: 1340h
AN: OS33C-1484    [Abstracts]
TI: Methane-derived authigenic carbonates in the Gulf of Cadiz: Cartography, distribution and controls
AU: * Magalhaes, V H
EM: vitor.magalhaes@ineti.pt
AF: Geosciences Department, University of Aveiro, Campus de Santiago, Aveiro, 3810-193 Portugal
AU: * Magalhaes, V H
EM: vitor.magalhaes@ineti.pt
AF: Marine Geology Department, National Institute of Engineering Technology and Innovation (INETI, EStrada da Portela, Apartado 7586, Alfragide, 2721-866 Portugal
AU: Pinheiro, L M
EM: lmp@geo.ua.pt
AF: Geosciences Department, University of Aveiro, Campus de Santiago, Aveiro, 3810-193 Portugal
AU: Pinheiro, L M
EM: lmp@geo.ua.pt
AF: Marine Geology Department, National Institute of Engineering Technology and Innovation (INETI, EStrada da Portela, Apartado 7586, Alfragide, 2721-866 Portugal
AU: Ivanov, M K
EM: FU@geol.msu.ru
AF: UNESCO Centre for Marine Geosciences, Moscow State University, Vorobjevy Gory, Moscow, 119899 Russian Federation
AB: Mineralogic, isotopic and biomarker analyses of authigenic carbonates (dolomite crusts, nodules, chimneys and aragonitic slabs or pavements) from the Gulf of Cadiz indicate their methane derived seepage origin. U/Th Dating of some samples indicates that they were formed during a long span of time (episodically during the last 250 ky), representing episodes of intense methane flux to the seafloor. The recent seep sites and the authigenic carbonate deposits were initially assumed as isolated occurrences but, with the increase of the detailed survey coverage acquired during the last 6 years, they have been encountered in several other locations (between 500 and 1400 m water depth), indicating that they can be far more common features in the Gulf of Cadiz Accretionary Complex than previously anticipated. This work describes a quantitative evaluation of the distribution of seafloor fluid seepage indicators observed on underwater video observations, during sample retrieval by video controlled grab, which are correlated with sediment samples and acoustic characteristics on the seismic profiles and on the side-scan sonar backscatter images. The site cartography, on bases of the interpretation of the underwater video observations allowed the identification and mapping of different seafloor facies. The main facies types represent (i) outcrops of bedrock, (ii) pelagic sediments, (iii) mud volcano mud breccia, (iv) methane derived authigenic carbonates, and (v) biological communities patches. A relationship between the occurrences of the authigenic carbonates with other fluid escape structures such as mud volcanoes, mud diapirs and probably deep fault systems is postulated. The occurrence of the seeping sites is in close relation with mud volcanoes and mud diapirs, indicating that those structures are preferential pathways for fluid escape. The Mediterranean Outflow Water (MOW) appears to have an effective control on the occurrence of the different types of authigenic carbonates, given that dolomite crusts, nodules and chimneys occur in places where the MOW have a strong erosive effect.
DE: 4820 Gases
DE: 4863 Sedimentation (1861)
SC: Ocean Sciences [OS]
MN: Fall Meeting 2005