Structural Evolution and Timing of Continental Rifting in the Northeast Atlantic, West Iberian Margin

Abstract

Regional (2D) seismic-reflection profiles, outcrop and borehole data are used to indicate that the bulk of Late Jurassic-earliest Cretaceous subsidence occurred in the present-day continental slope area. Five (5) principal regressive events (and their correlative basal unconformities) reflecting tectonic uplift and relative emersion in proximal basins are correlated with major rift-related tectonic events on the deeper margin. A significant portion of the west Iberian lower-plate margin was uplifted and eroded during the last stages of continental rifting. Such process was repeated at different times (and in different areas) as the locus of rifting and continental break-up migrated along the future passive margin. As a result, in west Iberia two distinct rift axes are recognised, a first axis extending from the Porto Basin to the Alentejo Basin and a second axis located on the outer proximal margin north of 380 30’N. We propose the late-rifting phases of tectonic quiescence, widespread erosion and sediment progradation on the inner proximal margin as marking the abandonment of extensional basins east of a major Slope Fault System (SFS), and the subsequent onset of syn-rift extension on the outer proximal margin. However, rift-related units of Triassic (and older?) to Middle Jurassic age are well represented on the outer proximal margin. This fact indicates that crustal extension on continental slope basins of west Iberia consisted of a prolonged process in which the last rifting episode is structurally imprinted over older – but not less important – rift episodes.