RV SONNE Fahrtbericht / Cruise Report SO227 TAIFLUX : Fluid and gas migration in the transition from a passive to an active continental margin off SW Taiwan, 02.04. - 02.05.2013, Kaohsiung - Kaohsiung (Taiwan)

Berndt, Christian, ed. (2013) RV SONNE Fahrtbericht / Cruise Report SO227 TAIFLUX : Fluid and gas migration in the transition from a passive to an active continental margin off SW Taiwan, 02.04. - 02.05.2013, Kaohsiung - Kaohsiung (Taiwan) . GEOMAR Report, N. Ser. 011 . GEOMAR Helmholtz-Zentrum für Ozeanforschung , Kiel, Germany, 104 pp. DOI 10.3289/GEOMAR_REP_NS_11_2013.

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Abstract

The underlying scientific motivation of SO227 was to constrain the geological processes
that control the distribution and saturation of hydrate in marine sediments. The most
important objective of the cruise was to observe the effect of additional fluid advection along
blind thrusts into the gas hydrate stability zone. With its clear distinction into a passive
margin and an active margin the area SW of Taiwan is particularly well suited for this kind of
research because it is very well studied and it is known where the tectonic structures of the
compression and subduction zone disturb the otherwise fairly homogeneous surface sediments
of the margin.
After a reconnaissance survey using multi beam echo sounder and side scan sonar we
selected two sites that are typical for the active and passive margin, respectively. At these two
sites we carried out comprehensive geophysical experiments including high-resolution 3D
seismic imaging with the P-Cable system, ocean bottom seismometer (OBS) deployments,
controlled source electromagnetic (CSEM) measurements, heat flow measurements, and
ground-truthing using HyBis and TV grab. While the P-Cable data allow us to determine the
internal structure of the study areas down to a depth of approximately 500 m below sea floor,
the OBS and CSEM data will constrain the hydrate and free gas saturation along twodimensional
transect through the 3D seismic cubes. The heat flow data will provide
information on the thermal conditions of the sediments.
The first site covers the Formosa Ridge on the passive margin of the South China Sea. The
ridge is the result of canyon erosion in the north, west, and east. The high-resolution threedimensional
seismic data show a continuous bottom simulating reflector (BSR) marking the
base of the hydrate stability zone. Particularly, underneath the canyon in the north the BSR is
much shallower than underneath the centre of the ridge. This may indicates that the canyon
incision has changed the hydrate stability field and that hydrate formation at depth has not
been able to adjust to the new pressure and temperature conditions.
The second site includes a roll over anticline called Four-Way-Closure Ridge which is the
surface expression of an underlying blind thrust. In this area numerous high amplitude
reflectors occur above the BSR. This unusual observation may suggest very high gas hydrate
saturations and coeval presence of free gas and gas hydrate in the sediments. Evaluation of the
OBS and CSEM data will allow to test this hypothesis. The 3D seismic data clearly show
fluid migration pathways through the gas hydrate stability to the sea floor.
Sea floor video footage and sampling confirmed the presence of on-going methane seepage
at the Formosa Ridge above the fluid migration pathway imaged in the 3D seismic data. They
also establish that there is at least one seep on the Four-Way-Closure Ridge at which methane
is released into the ocean above another seismically imaged fluid migration pathway. This is
the first active seep site with chemosynthetic ecosystems discovered on the active margin SW
off Taiwan.

Document Type: Report (Cruise Report)
Additional Information: Print-Ausg. in der GEOMAR-Bibliothek vorhanden
Keywords: SO227 ; TAIFLUX
Research affiliation: OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-GDY Marine Geodynamics
DOI etc.: 10.3289/GEOMAR_REP_NS_11_2013
ISSN: 2193-8113
Expeditions/Models/Experiments:
Date Deposited: 25 Sep 2013 11:03
Last Modified: 28 Oct 2016 09:34
URI: http://oceanrep.geomar.de/id/eprint/22017

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