HR: 0830h
AN: OS51C-0869    [PDF]
TI: Rock Magnetic Signature of Gas Hydrates in Sediments from Southern Hydrate Ridge (Cascadia Margin)
AU: * Gracia, E
EM: egracia@utm.csic.es
AF: Unitat de Tecnologia Marina - CSIC, Pg. Maritim de la Barceloneta 37-49, Barcelona, 08003 Spain
AU: Larrasoana, J
EM: jcl1@soc.soton.ac.uk
AF: Institut Jaume Almera - CSIC, Lluis Sole i Sabaris s/n, Barcelona, 08028 Spain
AU: Martinez-Ruiz, F
EM: fmruiz@ugr.es
AF: Instituto Andaluz de Ciencias de la Tierra - CSIC, Campus Fuentenueva, Granada, 18002 Spain
AU: Ercilla, G
EM: gemma@icm.csic.es
AF: Institut de Ciencies del Mar - CSIC, Pg. Maritim de la Barceloneta 37-49, Barcelona, 08003 Spain
AU: Vizcaino, A
EM: alexis@utm.csic.es
AF: Unitat de Tecnologia Marina - CSIC, Pg. Maritim de la Barceloneta 37-49, Barcelona, 08003 Spain
AU: Garces, M
EM: mgarces@geo.ub.es
AF: Institut Jaume Almera - CSIC, Lluis Sole i Sabaris s/n, Barcelona, 08028 Spain
AB: Hydrate Ridge is a structural high located in the Cascadia accretionary wedge offshore Oregon, where gas hydrates were detected on the seafloor and an ubiquitous BSR suggested widespread distribution of hydrates. During ODP Leg 204 (July-September 2002), nine sites (1244 to 1252) were drilled along and across southern Hydrate Ridge. We took more than 600 samples (systematically 2/core) plus higher resolution (1/section) when crossing specific structural layers such as the BSR, and Horizons A, B, and B', defined on the 3D MCS. Sedimentological, mineralogical, geochemical and rock magnetic analyses are being carried out. We have completed measurements of magnetic susceptibility (k), Anhysteretic Remanent Magnetization (ARM), and Isothermic Remanent Magnetization (IRM) at 0.1, 0.4 and 0.9 T. Our data indicates two distinctive magnetic behaviours: 1) Low remanence intensities with low IRM/ARM and remanence to susceptibility ratios, and 2) Very high (and variable) remanence intensities with distinctively high IRM/ARM and remanence to susceptibility ratios. The first type mostly characterizes the first few meters of sediments and other intervals deeper in the cores, whereas the second one appears in discrete zones (e.g. around the BSR and other hydrate-rich intervals). We suspect that the first behaviour is dominated by magnetite and that the second one is linked to diagenetic formation of magnetic iron sulfides (mainly greigite), which frequently appear as cm-scale nodules. We will compare these results with sedimentological (grainsize), bulk/clay mineralogy and geochemical (major/trace-element and TOC) data from the same core intervals. This will allow us to examine the possible link between formation of gas hydrates and diagenetic growth of magnetic iron sulfides, which may have implications on the detection of gas hydrates and identification of fossil BSRs.
DE: 1615 Biogeochemical processes (4805)
DE: 1800 HYDROLOGY
DE: 3022 Marine sediments--processes and transport
DE: 5100 PHYSICAL PROPERTIES OF ROCKS
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting