HR: 0800h
AN: T41E-1269    [Abstracts]
TI: Seismic Structure of the Continental Margin Offshore French Guiana and North-Eastern Brazil
AU: * Greenroyd, C
EM: christopher.greenroyd@durham.ac.uk
AF: Department of Earth Sciences, University of Durham, Durham, DH1 3LE United Kingdom
AU: Rodger, M
EM: Matthew.Rodger@earth.ox.ac.uk
AF: Department of Earth Sciences Department of Earth Sciences, University of Oxford, Oxford, OX1 3PR United Kingdom
AU: Peirce, C
EM: christine.peirce@durham.ac.uk
AF: Department of Earth Sciences, University of Durham, Durham, DH1 3LE United Kingdom
AU: Watts, A B
EM: tony@earth.ox.ac.uk
AF: Department of Earth Sciences Department of Earth Sciences, University of Oxford, Oxford, OX1 3PR United Kingdom
AU: Hobbs, R
EM: richard.hobbs@durham.ac.uk
AF: Department of Earth Sciences, University of Durham, Durham, DH1 3LE United Kingdom
AB: During November/December 2003 we carried out a marine geophysical survey of the continental margin offshore French Guiana and north-eastern Brazil onboard RRS Discovery. The survey comprised 1800 line km of coincident multi-channel seismic (MCS) reflection and wide-angle seismic refraction data which were acquired along 3 'transects' of the margin. In addition, more than 3000 line km of underway gravity and magnetic anomaly data were acquired. Preliminary processing of the MCS data has revealed the main stratigraphic units and the nature of the underlying basement at the margin. Up to 4 stratigraphic units have been identified, the uppermost of which is separated from lower units by an angular unconformity. We interpret the unconformity as of mid-Miocene age that corresponds to a major influx of sediment to the margin associated with uplift in the Bolivian Andes and the development of the Amazon deep-sea fan. The lower units beneath the fan offshore north-eastern Brazil comprise of gently landward-dipping reflectors that we interpret as post-rift sediments. Beneath the Demerara plateau offshore French Guinea, however, there is evidence of more steeply dipping reflectors that we attribute to Early Cretaceous and older syn-rift sediments. Basement has been imaged along each transect, most clearly beneath the middle and lower Amazon fan and the deep-water to the north of the Demerara plateau where we interpret it to be of oceanic-type. Preliminary processing of the wide-angle data recorded by ocean bottom instruments deployed at 10 km interval along each transect reveal high velocity arrivals at source-receiver offsets greater that 200 km. Ray-modelling indicate that primary intra-crustal first arrivals originate at major discontinuities within the stratigraphic column. Additional wide-angle land recording data contain arrivals at offsets greater than 400 km. We discuss here the results of the new seismic data, especially as they relate to the early opening history the Equatorial Atlantic and the structure and evolution of both its rift- and transform-type margins.
DE: 8105 Continental margins and sedimentary basins
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3025 Marine seismics (0935)
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting