Sedimentologial and stratigraphical aspects of the syn- to post-rift transition on fully separated conjugate margins
2014
The integration of several industry and scientific 2D seismic surveys with various
well data allowed for the first time a detailed analysis of the sedimentological,
stratigraphic and architectural changes recorded during syn- to post-rift transitions
on passive margins. The Northwest Iberia margin and its conjugate margin of
Newfoundland formed the basis for an interpretive model. Comparison with the
South Australia - East Antarctica conjugate margins enabled hypothesis testing and
premise refinement.
The breakup unconformity concept is revised and a more comprehensive term is
proposed for the stratigraphic surface recording the transition between syn- and
post-rift: the lithospheric breakup surface. This new term: a) discriminates between
continental crust breakup and complete lithospheric breakup as verified in several
magma-poor margins, and b) takes into account the different character this surface
can show according to its position on the margin. The concept of a breakup sequence
is proposed as a sedimentary sequence showing a distinct architecture to strata
deposited prior to the lithospheric breakup event. The breakup sequence records the
depositional changes occurring across the lithospheric breakup surface due to
lithospheric adjustments triggered by lithospheric breakup.
Contourites were identified for the first time as being associated with lithospheric
breakup, supposedly being triggered by the lithospheric plate in-plane stress release
occurring at the time of lithospheric breakup. Consequently, it is proposed that
contourites can be used as an indicator for established lithospheric breakup.
On the East Antarctica margin, a surface usually dated as mid Eocene to early
Oligocene by comparison with the conjugate South Australia margin, is dated as
latest Maastrichtian-earliest Palaeocene using data from IODP Site 1356. This new
date suggests that the surface is a lithospheric breakup surface, which can explain its
generation and the overlying strong contouritic deposition.
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