Sedimentologial and stratigraphical aspects of the syn- to post-rift transition on fully separated conjugate margins

• Main Author: Soares, Duarte
• Format: Thesis
• Language: English
• Published: 2014
• Subjects: QE Geology; East Antarctica; Antarc*; Antarctica; Newfoundland
• Online Access: https://orca.cardiff.ac.uk/id/eprint/68378/; https://orca.cardiff.ac.uk/id/eprint/68378/1/THESIS_Final%5B1%5D.pdf; https://orca.cardiff.ac.uk/id/eprint/68378/2/Electronic%20Theses%20and%20Dissertations%20Publication%20Form%20-%20Soares%202014.pdf

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.