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A new 3D seismic academic dataset across the west Galicia margin

Author(s): Gaël Lymer Geosystems Research Group, School of Geography, Earth and Environmental Science, University of Birmingham, UK, UK
D.J.F. Cresswell Geosystems Research Group, School of Geography, Earth and Environmental Science, University of Birmingham, UK
T.J. Reston Geosystems Research Group, School of Geography, Earth and Environmental Science, University of Birmingham, UK
C.T.E Stevenson Geosystems Research Group, School of Geography, Earth and Environmental Science, University of Birmingham, UK
J.M. Bull Ocean and Earth Science, National Oceanography Centre, University of Southampton, UK;
D. Sawyer Department of Earth Science, University of Rice, Texas
the Galicia 3D working group Lamont-Doherty Earth Observatory, Columbia University, New York/Institute of Marine Sciences, Barcelona, Spain

The west Galicia margin (western Spain) represents an ideal location to study the processes of continental extension and break-up. The margin is characterised by hyper-extended continental crust, thinning to less than 3 km, well defined rotated faults blocks with associated syn-kinematic sedimentary wedges, and exhumed serpentinized continental mantle. Faulted blocks are located above a strong reflector, the S reflector, generally interpreted as both a detachment and the crust-mantle boundary. In addition, the structures of the margin are well observed from seismic data due to limited post-rift sedimentary cover and poor volcanic activity.

During summer 2013, a new 3D high-resolution multi-channel seismic dataset has been acquired over the Galicia margin. It consists in 800 inlines (12.5m in spacing) and 5000 crosslines distributed on a ~680 km2 areal extent across the edge of the continental crust. This new 3D dataset is thus the largest academic one of its kind. These data capture the 3D nature of extension and break-up of the northern Atlantic continental margins, structured from the middle Jurassic to Early-Cretaceous.

Here we present some results from our interpretations of the 3D volume, focussing on the mapping of specific horizons: the seafloor, the base of the post-rift sedimentary cover, the top basement and the S reflector. Mapping these horizons provide 3D views of the margin structure, and the tight network of the data, as well as the quality of the seismic profiles reveal the texture of each horizon in 3D. The main crustal structures are roughly N-S oriented, in agreement with the direction of extension during the rifting. However the structures vary both along strike and cross strike, revealing the complex three-dimensional architecture of the margin. There is also a surprising NW-SE trend, observable at the scale of the margin in the organization of the crustal structures, but also at a smaller scale by corrugations at the top of the S reflector and on the top basement. This trend suggests more complex directions of extension and thinning mechanisms than expected. Furthermore, we focus on the internal structure of some of the faulted blocks through detailed interpretation of the crustal normal faults (see results in the poster session). We then show that the main faults are generally connected downward on the S reflector, revealing interactions between crustal thinning and the S. This demonstrates the important role of the S during the extension and the complex nature of the rifting processes.

Further works will lead to time-to-depth conversion of the seismic data, from our interpretations of the main horizons. It will allow for avoid local pull-up or velocity effects. This will enable to better define rifting processes and break-up mechanisms that led to the present-day architecture of the margin.


Title:
A new 3D seismic academic dataset across the west Galicia margin
Type:
Oral
Origin:
Academia
Day:
2
Session:
2
Daily sequence no.:
15
Lead author last name:
Lymer
Lead author first name:
Gaël
Affiliation(s):
Geosystems Research Group, School of Geography, Earth and Environmental Science, University of Birmingham, UK
Country:
UK
Abstract status:
ok
UID:
60