Abstract
The Orphan Basin is located in the deep offshore of the Newfoundland margin, and it is bounded by the continental shelf to the west, the Grand Banks to the south, and the continental blocks of Orphan Knoll and Flemish Cap to the east. The Orphan Basin formed in Mesozoic time during the opening of the North Atlantic Ocean between eastern Canada and western Iberia–Europe. This work, based on well data and regional seismic reflection profiles across the basin, indicates that the continental crust was affected by several extensional episodes between the Jurassic and the Early Cretaceous, separated by events of uplift and erosion. The preserved tectono-stratigraphic sequences in the basin reveal that deformation initiated in the eastern part of the Orphan Basin in the Jurassic and spread towards the west in the Early Cretaceous, resulting in numerous rift structures filled with a Jurassic–Lower Cretaceous syn-rift succession and overlain by thick Upper Cretaceous to Cenozoic post-rift sediments. The seismic data show an extremely thinned crust (4–16 km thick) underneath the eastern and western parts of the Orphan Basin, forming two sub-basins separated by a wide structural high with a relatively thick crust (17 km thick). Quantifying the crustal architecture in the basin highlights the large discrepancy between brittle extension localized in the upper crust and the overall crustal thinning. This suggests that continental deformation in the Orphan Basin involved, in addition to the documented Jurassic and Early Cretaceous rifting, an earlier brittle rift phase which is unidentifiable in seismic data and a depth-dependent thinning of the crust driven by localized lower crust ductile flow.
Highlights
The opening of the North Atlantic Ocean between eastern Newfoundland and western Iberia–Europe started with continental rifting in the Late Triassic to Early Jurassic which led to continental break-up and the initiation of ocean crust in the Aptian–Albian (e.g. Welsink et al 1989; Grant and McAlpine 1990; Bassi et al 1993; Enachescu et al 2005; Tucholke et al 2007; Alves et al 2009)
The Late Triassic–Early Cretaceous crustal extension resulted in several major rift basins like the Porcupine, Rockall, and Hatton basins off the Irish margin (Fig. 1) and
The Orphan Basin, which is the focus of this study, is a deep-water rift basin surrounded by the Newfoundland continental shelf in the west, the Grand Banks in the south, the Flemish Cap in the southeast, and the Orphan Knoll in the northeast (Fig. 2)
Summary
The opening of the North Atlantic Ocean between eastern Newfoundland and western Iberia–Europe started with continental rifting in the Late Triassic to Early Jurassic which led to continental break-up and the initiation of ocean crust in the Aptian–Albian (e.g. Welsink et al 1989; Grant and McAlpine 1990; Bassi et al 1993; Enachescu et al 2005; Tucholke et al 2007; Alves et al 2009). Its base shows reflections sub-parallel to the underlying Upper Cretaceous with no evidence of erosional or angular unconformity This succession is extremely thick above the edge of the continental shelf and thins considerably as we move to the east of the basin The eastern sub-basin is covered by a 2.5- to 4-km-thick post-rift succession, overlying the Jurassic–Lower Cretaceous syn-rift sediments (
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