HR: 1340h
AN: OS33C-1487    [Abstracts]
TI: Hydrocarbon prospect of the Tjornes Fracture Zone, north of Iceland
AU: * Richter, B
EM: br@isor.is
AF: Iceland Geosurvey, Grensasvegi 9, Reykjavik, 108 Iceland
AU: Brandsdottir, B
EM: bryndis@raunvis.hi.is
AF: Institute of Earth Science, University of Iceland, Sturlugata 7, Reykjavik, 101 Iceland
AU: Geptner, A
EM: geptner@geo.tv-sign.ru
AF: Geological Institute of Russian Academy of Science, 119017, Moscow, RUS 119017
AU: Driscoll, N
EM: ndriscoll@ucsd.edu
AF: Scripps Inst. of Oceanography, Univ. of California, La Jolla, San Diego, CA 92037 United States
AU: Boejesen-Koefoed, J
EM: jbk@geus.dk
AF: Geological Survey of Denmark and Greenland, Oster Voldgade 10, Copenhagen, DK-1350 Denmark
AB: The Tjornes Fracture Zone (TFZ) links the northern rift zone (NVZ) in Iceland with the Kolbeinsey Ridge north of Iceland. The TFZ was initiated during the Miocene (app. 7-9 Ma), following an eastward jump of the spreading axis in northern Iceland. A roughly 150 km long (EW) and 50 km wide (NS) deformation zone has since developed, incorporating both right-lateral movement along WNW-trending strike-slip faults and oblique extension within three major N-S trending grabens (from west to east the Eyjafjardarall, Skjalfandi and Oxarfjordur basins) with sediment thicknesses up to 4000 m. Newly made Ar/Ar age determinations on basement rock collected beneath the oldest sediments within these grabens (collected on the Tj”rnes horst), supports this (8 +/- 1 Ma). This indicates maximum age of the TFZ. Recently collected EM300 and RESON8101 multibeam bathymetric data, and CHIRP subbottom data combined with onshore mapping and data collection, have enhanced our understanding in this area. Areas of large, elongated and circular depressions (pockmarks) within Skjalfandi Bay and Oxarfjordur were mapped during a multibeam bathymetric surveys in 2002, 2003 and 2004. These pockmarks seem to be strongly connected to the underlying N-S tectonic lineament. Ocean floor photography indicate that seeps occur in some of them, as well as documenting changes in sediment color and hardness. Backscatter analyses, made on EM300 data within the Skjalfandi bay seem to document as well changes within the sediments supporting the existence of gas. CHIRP data show amplitude anomalies and acoustic wipe-out zones, indicative of gas accumulation within the sediments in several areas in Skjalfandi bay. Where present, acoustic wipe-out zones associated with the gas obscured all underlying reflectors as shallow as 5 meters below the ocean floor. These areas correlate remarkably with the backscatter data. An attempt was made to collect up to 3 m cores in areas where gascharged sediments were found, to apply hydrocarbon screening tests. Unfortunately only about one meter or less, long cores were collected, meaning that biodegradation could have seriously skewed the results (isotope signature). When screened, the samples turned out to be charged with very high methane values, mostly of biogenic origin. Only small hints of heavier hydrocarbons of questionable origin were found. Polycyclic Aromatic Hydrocarbons (PAH) indicate more strongly that some of the hydrocarbons in this area could be of thermogenic origin, the same way as in Oxarfjordur sands, slightly east of Skjalfandi Bay. There, natural gas is emitting from geothermal areas, containing high concentrations of evolved hydrocarbons. That gas probably originates from marine sediments and lignites, as isotopic analyses have indicated, similar to those observed on the Tjornes peninsula. It seems that gasforming processes are widespread within the eastern part of the TFZ but the origin of these gasses has not yet been confirmed. A possible source rock might be coal/lignite seams within the sediments, as simulation on the lignite has shown.
DE: 1055 Organic and biogenic geochemistry
DE: 3004 Gas and hydrate systems
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 4820 Gases
DE: 8169 Sedimentary basin processes
SC: Ocean Sciences [OS]
MN: Fall Meeting 2005