During Leg 204 of the Ocean Drilling Program (ODP) in the accretionary complex of the Cascadia subduction zone, offshore the Oregon margin, more than 3600 meters of sediment cores were obtained. In order to complete the different analysis made during the Leg, the sedimentological, geochemical and magnetic study of more than 600 samples is being carried on. The sedimentological preliminary results show that the sediment of Hydrate Ridge consists in silty clay to sandy silt sediments, with some foraminifer-bearing zones and some gradded silt layers interpreted as turbiditic events. Volcanic glass horizons have been identificated also as turbidite layers. The magnetic results show that two main types of sediments can be distinguished in the Southern Hydrate Ridge: one characterized by high Isothermic Remanent Magnetization (IRM) 0.9 T/k values, corresponding to greigite dominated magnetic assemblages and another characterized by low I RM 0.9 T/k values typical for greigite-magnetite mixtures. The first one is located near the surface and below the Bottom Simulation Reflector (BSR), indicating the existence of a fossil Gas Hydrate Stability Zone (GHSZ). The comparison between sedimentological, mineralógicaI, magnetic and geochemical results will allow to better understand the gas hydrates formation, migration and location, and will help to identificate other fossil BSRs

VI Congreso Geológico de España, 12-15 julio 2004, Zaragoza.-- 4 pages, 2 figures

Peer reviewed