FIG. 2 BASALTIC BRECCIA PRESENCE: SEISMIC LINE MD40-23
WE
1 cm
1 cm
Basalt above basement
MD84581
84DR03
84DR02
SU7702
SU7702MD84581
been eroded on parts of the structures is a limiting factor,
but the sands are also well defined by recent seismic. Several
other objectives exist on both flanks of the DFZ, with the
western side being the most attractive due to the increased
thickness of the sedimentary section.
Historical observation
The Davie Ridge, an exceptional structural feature of the
Mozambique channel, was identified in 1970 by the research vessel (R/V) Chain (CH99), and led geologists to suggest that it could represent a fault along which Madagascar
was displaced southwards in Late Jurassic. 1 Further seismic
and magnetic data collected in the late 1970s showed that
the breakup between Madagascar and Africa began 150 million years ago, that Madagascar moved southwards, and that
the Davie Ridge should correspond to the trace of the transform fault along which Madagascar drifted until the time of
anomaly MD ( 110 Ma). 2 3
Site 242, drilled by the Glomar Challenger Leg 25 in 1972,
did not reach the basement but the recovered sedimentary
column (676 m) is a complete hemipelagic sequence from Late
Eocene to Quaternary with a well-defined Eocene-Oligocene
boundary. 4 Piston cores recovered by R/V Suroit (SU2) in
1977 showed a basal, discontinuous, and thin pelagic sedimentary sequence of Late Cretaceous (Middle Coniacian) age
overlaying arkosic sandstones. 5 6 Dredging and coring from
the R/V Marion Dufresne cruise (MD 39) in 1984 confirmed
these results and demonstrated that the ridge is built on continental basement consisting of gneisses and meta-arkoses
which locally are covered by a deformed flysch, alkaline lavas,
tuffs and breccias, and by a thin succession of carbonate oozes
ranging from Cretaceous to present. 7 8
Seismic cruises MD 40 and MD 60 provided additional
information on the structural setting of the ridge. 9 The variety
of dredged and cored samples are described and projected for
selected seismic lines.
