SEMINÁRIOS DEPARTAMENTO DE GEOLOGIA MARINHA/ INETI
(Alfragide)
26 de Fevereiro de 2009 - 14.00 horas
(Alfragide)
26 de Fevereiro de 2009 - 14.00 horas
Doutor Tiago Cunha
(Departamento de Geologia Marinha do INETI)
(Departamento de Geologia Marinha do INETI)
TITLE:
Rifting along the west Iberia Margin: relationships between shallow and deep offshore observations and modelling results
Rifting along the west Iberia Margin: relationships between shallow and deep offshore observations and modelling results
ABSTRACT:
The West Iberia Margin (WIM) formed through a sequence of Mesozoic rift pulses, interspersed with periods of tectonic quiescence (or basin sagging), that culminated with continental break-up between Iberia and Newfoundland during the Early Cretaceous. From the latest Cretaceous onwards, the margin has been deformed under compression, associated with the Africa-Eurasia plate convergence. The sediments accumulated in the onshore and offshore rift basins along the margin provide a useful record of the margin’s subsidence and uplift history.
In this study, we apply 1-D “backstripping” techniques to 9 commercial wells located on the continental shelf off western Portugal, in order to recover the margin’s tectonic subsidence (i.e. that results from stretching and the thermal relaxation of the lithosphere) and put constrains on the amount of crustal thinning (β). Results show that during the early stages of rifting (Late Triassic-Early Jurassic) β varies between 1.16 and 1.32, which is up to 40% greater than previous estimates, and that from the Middle Jurassic onwards the main extensional episodes propagate northwards along strike the WIM.
In the offshore Northern Lusitanian Basin, between the Nazaré and the Aveiro faults, a long Early Cretaceous depositional hiatus maybe associated with the uplift and erosion of the continental shelf, when most of the extensional deformation focused to the west of the shelf break. Comparisons between calculated and theoretical tectonic subsidence curves suggest that up to 700 metres may have been removed from the shelf during this period. This is consistent with the deposition of thick Early Cretaceous sequences in fault delimited grabens and half-grabens along the continental slope. In the distal margin, over highly extended continental crust (β > 3) and/or transitional-type basement, a recently compiled sediment thickness dataset reveals several N-S to NNE-SSW trending depocentres, developed during the latest stages of rifting and continental break-up. We discuss how these stages may have affected the subsidence/uplift history of the proximal margin.
In this study, we apply 1-D “backstripping” techniques to 9 commercial wells located on the continental shelf off western Portugal, in order to recover the margin’s tectonic subsidence (i.e. that results from stretching and the thermal relaxation of the lithosphere) and put constrains on the amount of crustal thinning (β). Results show that during the early stages of rifting (Late Triassic-Early Jurassic) β varies between 1.16 and 1.32, which is up to 40% greater than previous estimates, and that from the Middle Jurassic onwards the main extensional episodes propagate northwards along strike the WIM.
In the offshore Northern Lusitanian Basin, between the Nazaré and the Aveiro faults, a long Early Cretaceous depositional hiatus maybe associated with the uplift and erosion of the continental shelf, when most of the extensional deformation focused to the west of the shelf break. Comparisons between calculated and theoretical tectonic subsidence curves suggest that up to 700 metres may have been removed from the shelf during this period. This is consistent with the deposition of thick Early Cretaceous sequences in fault delimited grabens and half-grabens along the continental slope. In the distal margin, over highly extended continental crust (β > 3) and/or transitional-type basement, a recently compiled sediment thickness dataset reveals several N-S to NNE-SSW trending depocentres, developed during the latest stages of rifting and continental break-up. We discuss how these stages may have affected the subsidence/uplift history of the proximal margin.
PARA ASSISTIR ÀS PALESTRAS, NÃO É NECESSÁRIO REALIZAR QUALQUER INSCRIÇÃO! BASTA DESLOCAREM-SE ATÉ ÀS INSTALAÇÕES DO INETI EM ALFRAGIDE (ESTRADA DA PORTELA - BAIRRO DO ZAMBUJAL).
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