Shallow Gas and High-resolution Studies in an Active Canyon: Cap de Creus, Gulf of Lions

HR: 1340h
AN: OS33C-1483 [Abstracts]
TI: Shallow Gas and High-resolution Studies in an Active Canyon: Cap de Creus, Gulf of Lions
AU: * Garcia-Garcia, A
EM: agarcia@es.ucsc.edu
AF: UCSC, 1156 High Street, Santa Cruz, CA 95064 United States
AU: * Garcia-Garcia, A
EM: agarcia@es.ucsc.edu
AF: AOA Geophysics Inc., 7532 Sandholdt Road, 2nd floor, Moss Landing, CA 95039 United States
AU: Orange, D L
EM: DaN_orange@AOAGeophysics.com
AF: UCSC, 1156 High Street, Santa Cruz, CA 95064 United States
AU: Orange, D L
EM: DaN_orange@AOAGeophysics.com
AF: AOA Geophysics Inc., 7532 Sandholdt Road, 2nd floor, Moss Landing, CA 95039 United States
AU: Lorenson, T
EM: tlorenson@usgs.gov
AF: USGS, 345 Middlefield Road MS-999, Menlo Park, CA 94025 United States
AU: Tesi, T
EM: tommaso.tesi@bo.ismar.cnr.it
AF: CNR-ISMAR, Via Mazzini 67, Bologna, 48100 Italy
AU: Miserocchi, S
EM: stefano.miserocchi@bo.ismar.cnr.it
AF: CNR-ISMAR, Via Mazzini 67, Bologna, 48100 Italy
AU: Schoolmeester, T
EM: tina_schoolmeester@ub.edu
AF: University of Barcelona, Campus de Pedralbes, Barcelona, 08071 Spain
AU: Levey, M D
EM: matt_levey@aoageophysics.com
AF: AOA Geophysics Inc., 7532 Sandholdt Road, 2nd floor, Moss Landing, CA 95039 United States
AU: Fabres, J
EM: joan@geo.ub.es
AF: University of Barcelona, Campus de Pedralbes, Barcelona, 08071 Spain
AU: Herbert, I M
EM: isabellE_herbert@aoageophysics.com
AF: AOA Geophysics Inc., 7532 Sandholdt Road, 2nd floor, Moss Landing, CA 95039 United States
AU: Sansoucy, M
EM: mylene.sansoucy.1@ulaval.ca
AF: Laval University, Pavillon Pouliot, local 4317, Quebec, G1K7P4 Canada
AB: The Cap de Creus canyon head off the northeast coast of Spain is a key feature in understanding the recent processes affecting the Gulf of Lions. During July 2004 Fugro Survey Ltd. and AOA Geophysics Inc., with the assistance of Barcelona University mapped the canyon head. Data were acquired with a hull-mounted Kongsberg Simrad EM300 30 kHz system. The resultant bathymetry was processed without interpolation or smoothing at grid spacings of three, five, or ten meters depending on bottom depth. Several EuroSTRATAFORM cruises run between 2004 and 2005 provided the groundtruthing of the acoustic and seismic data. Data on lithology, gas content and organic matter were obtained with box, piston, gravity and kasten cores. The analysis of the different echo characters in sub-bottom profiler data (distinct, indistinct, sharp, in step, chaotic, mounds and wavy echoes) provides a detailed understanding of the present seafloor and the recent processes that have shaped it. Backscatter data show significant variations throughout the field area and appear to be related to changes in seafloor sediment type. Laterally restricted high backscatter zones are related to seafloor outcrops of over- consolidated sediment and to possible gas seeps. The preliminary analyses show relatively little shallow gas in the core samples. Samples with anomalous gas (up to 715 ppm of methane) are limited to the northern flank of the canyon, where the samples also show higher amounts of organic matter and the seafloor suggests recent sediment drape. The southern flank and the canyon thalweg have no anomalous gas in any of the samples taken so far (all < 90 ppm of methane) although sediment accumulation rate studies indicate relatively high (but spatially variable) rates of accumulation in the canyon axis. Our working hypothesis is that away from the flood-related sediments off the Rh“ne delta (where methane content is up to 87440 ppm) the organic matter is being reworked and remineralized on its way along the western coast of the Gulf of Lions, so that the recent deposits in the canyon contain little reactive carbon. The anomalous samples on the northern flank may be related to methanogenesis of older sidewall canyon infill. Ongoing work includes analysis of samples acquired in 2005, and correlation of headspace gas analyses with CAT scans.
DE: 3004 Gas and hydrate systems
DE: 3022 Marine sediments: processes and transport
DE: 3025 Marine seismics (0935, 7294)
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 4820 Gases
SC: Ocean Sciences [OS]
MN: Fall Meeting 2005