Rifting is commonly associated with vertical movements, whose stratigraphic record may be challenging to distinguish from that of independent dynamic topography. In this study, we propose a new approach to identify and date the necking phase of rifting and the peak of dynamic topography based on diagnostic stratigraphic fingerprints specific to each event. The necking phase is triggered by the yield of the strongest layer in the lithosphere and results in rift localization and possibly uplift over 100 km rift width. Necking is notably marked by: (1) the transition from syn- to post-tectonic deposits in the proximal domain; (2) a possible significant erosional unconformity; and (3) a rapid switch from shallow- to deeper-water settings in the necking and future distal domains. Conversely, the extent of dynamic topography is 500 km in diameter. Whereas dynamic topography uplift causes pervasive erosion of the continent and significant clastic deposits, its transition to subsidence induces a transgression expressed by a switch from clastic- to pelagic-dominated deposits in adjacent deep-water domains. By applying this approach to the southern North Atlantic margins, we highlight a northeastward younging of the necking phase from the Late Jurassic along the southern Iberian margin to the Early Cretaceous along the Biscay margin, whereas the peak of dynamic topography is of Aptian-Albian age along the entire Iberian-Biscay rift system. The approach described herein can be used to identify and date necking and/or dynamic topography worldwide.
Mathey et al. (Thu,) studied this question.