Abstract
Seismic, outcrop and well data from West Iberia and Newfoundland are used to investigate sediment stacking patterns during continental breakup as a function of tectonic subsidence. In West Iberia, two breakup sequences are revealed on seismic data by marked strata offlap oceanwards from the present-day continental shelf. This character is similar to Newfoundland, where correlative strata comprise Lower Cretaceous–Cenomanian coarse-grained siliciclastics accumulated around local sediment-source areas. The interpreted data reveal that the two breakup sequences: 1) materialise sediment bypass onto continental-slope depocentres that experienced important tectonic subsidence during continental breakup, but without showing typical syn-rift growth packages; 2) generate specific forced-regressive stratigraphic intervals that relate to uplift and exhumation of the proximal margin. Subsidence and sediment stacking patterns in both West Iberia and Newfoundland reflect similar continental breakup processes as they evolved from the upper lithosphere- to their mantle-breakup stages. On both margins, coarse-grained siliciclastic units on the proximal margin give rise to thick shaley successions in deep-water basins. This work also confirms that in a setting dominated by a significant sediment influx, yet lacking the burial rates of continental slope basins in Newfoundland, West Iberia comprised accommodation-driven basins during continental breakup, not necessarily sediment starved. As a corollary of our analysis, we classify breakup sequences around the world based on the characteristic lithologies of their regressive–transgressive depositional cycles.
Highlights
Rift basins developed on future continental margins experience periods of enhanced subsidence that precede continental breakup by 10s of Ma (Peron-Pinvidic and Manatschal, 2009; Pérez-Gussinyé, 2012; Brune et al, 2014; Jeanniot et al, 2016)
We demonstrate that bypass units in continental-slope basins off West Iberia are composed of siliciclastic intervals that were deposited by gravitational processes in a tectonically active setting
This offlapping unit is associated with important tectonic subsidence in continental slope basins during continental breakup, and deposited a characteristic chaotic package that onlaps the continental slope to form an intermediate unit between drift and syn-rift strata
Summary
Rift basins developed on future continental margins experience periods of enhanced subsidence that precede continental breakup by 10s of Ma (Peron-Pinvidic and Manatschal, 2009; Pérez-Gussinyé, 2012; Brune et al, 2014; Jeanniot et al, 2016). Hinge-zone exhumation accompanies the continental breakup process per se (Braun and Beaumont, 1989), and reflects the characteristic two-stage plate breakup evolution of Huismans and Beaumont (2011) According to these authors, type I margins as West Iberia and Newfoundland experience crustal-necking breakup be-. We show that bypass units record a gradual transgression to form marked regressive–transgressive (R—T) depositional cycles These depositional cycles were generated as West Iberia and Newfoundland evolved from their upper lithosphere (crustal) breakup stage to mantle breakup and ocean spreading. C) Can breakup sequences be classified based on their key lithological character (and depositional facies) along the Atlantic Ocean and other rifted continental margins?
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