Comparative Stratigraphy and Subsidence History of Mesozoic Rift Basins of North Atlantic

Abstract

ABSTRACT Mesozoic rift basins around the North Atlantic all possess many of the following Upper Jurassic to Lower Cretaceous (Oxfordian to Albian) stratigraphic elements: (1) an early Oxfordian hiatus, (2) backfill deposits in Upper Jurassic paleovalleys, (3) multiple Tithonian transgressive-regressive sequences, (4) early Berriasian regressive sequences, (5) a sub-Valanginian unconformity overlain by coarse siliciclastic sandstones and conglomerates, (6) Valanginian to Hauterivian fining-upward sequences, (7) condensed Barremian sequences, and (8) prominent Aptian unconformities. More local features include abrupt Kimmeridgian deepening (Lusitanian basin, Portugal), Albian deepening (Cantabrian and Aquitaine basins, northern Spain and southern France), and late Albian-early Cenomanian source rejuvenation (Cantabrian basin, northern Iberia). Decompaction and backstripping of sediments from well and outcrop sections in six basins also reveal broad similarities in trends of rates of apparent basement subsidence. Relatively high rates (50–100 m/m.y.) characterize onset of rift phases in the Triassic and the Kimmeridgian. Locally, in the Lusitanian basin of Portugal, Kimmeridgian rates reach about 250 m/m.y. In the Cantabrian and Aquitaine basins, a third phase of rapid subsidence characterizes the Aptian-Albian interval after the main phase of continental breakup around Iberia. This phase may be due to transtensional stresses as Iberia continued to rotate relative to Europe, tensional intraplate stresses, or gravity driven partial collapse of the new continental margin. The North Atlantic Mesozoic basins share many features because they had a common origin controlled by intracontinental rifting and subsequent separation of Europe and North America. Pulses of extension generally are reflected in the stratigraphy of all of the basins. Superimposed on this record are the effects of eustatic sea level variations. The main difference between the Canadian Jeanne d’Arc basin and Iberian basins is the significantly greater Early and Middle Jurassic basement subsidence rate in the former (about 40 m/m.y. vs. 0–10 m/m.y.). This difference may result from prolonged extension on the Canadian side, perhaps due to northward transfer of shear stress from left-lateral transform motion between the Grand Banks and northwestern Africa.