Syn- to post-rift transitions on passive margins: The case of the western Iberian margin (NE Atlantic)

A comprehensive set of 2D seismic reflection lines, borehole data from Industry wells, stratigraphic information from key outcrops, and published DSDP/ODP data, was used in the analysis of syn-to post-rift transitions offshore West Iberia, Northeast Atlantic. Continental break-up in Southwest Iberia resulted in the sudden influx of siliciclastic material in onshore and shallow-offshore basins, interpreted to represent a forced regression (FRST) which was accompanied by: a) westward tilting of the proximal margin, which sourced westward-prograding units; b) complete abandonment of syn-rift depocentres, which were blanketed by post-rift successions. However, differences between the southern and northern sectors of West Iberia are observed, most likely reflecting changes in the geological processes that led to continental break-up. Thus, regions where continental break-up occurred relatively close to the rift-shoulder areas show widespread regional hiatuses and an abrupt shallowing of sedimentary facies across the break-up unconformity. Also, areas where break-up occurred closer to the rift-shoulder should contain the larger thickness of syn- and post-rift reservoirs, a character reflecting shorter distances between sediment source areas and adjacent depocentres on the continental margin. In contrast, deep-offshore regions will have diachronous break-up unconformities and will materialise different sedimentary responses that will depend on relative accommodation space, sediment influx and sediment capture by topographic features inherited from the syn-rift stages