Search

Interpretation of newly acquired modern broadband seismic reflection data and structural restoration of three regional, WNW-ESE oriented cross-sections across the Orphan Basin, Flemish Pass and Flemish Cap provide new insights into rift evolution and structural style in the area. Our results show that regional extension in the Orphan Basin and Flemish Pass area largely occurred between 170 Ma and 135 Ma, and later extension (135 Ma onwards) in the study area was accommodated east of Flemish Cap. Seismic stratigraphic mapping provides evidence for significant thicknesses of Jurassic strata throughout the Orphan Basin and Flemish Pass area, and structural interpretations highlight the importance of crustal-scale extensional detachment faults in controlling the geometry and position of Jurassic sub-basins at a range of scales. Stacked detachment surfaces and coincident extreme crustal attenuation (to ca. 3.1 km) are observed in eastern parts of the Orphan Basin in an area defined in this study as the Orphan Trough. Rifting style in the central, northern, and eastern parts of the Orphan Basin is dominated by low-angle detachment faulting with maximum extension perpendicular to the incipient rift axis. In contrast, structural geometries in the southwestern part of the basin are suggestive of transtensional deformation, and interplay of normal and strike-slip faulting. Results from map-based interpretation show that strike-slip faults within this transtensional zone are associated with displacement transfer between half-grabens of opposing polarity, rather than regional strike-slip displacement. These structures are interpreted as contemporaneous and kinematically linked to displacement along low-angle detachment surfaces elsewhere and are not attributed to distinct episodes of oblique extension. • Regional structural characterization of the Orphan Basin - Flemish Pass – Flemish Cap region. • Kinematic restoration and crustal area balancing of three laterally compatible, regional cross sections. • A single phase of protracted rifting from ca. 170 Ma to 135 Ma is interpreted in the Orphan Basin and Flemish Pass region. • Hyperextension, crustal-scale detachment surfaces and crustal attenuation associated with rift development. • Transtensional deformation in the southern part of the Orphan Basin compatible with rift-related extension. [ABSTRACT FROM AUTHOR]

The Orphan Basin and Flemish Pass region on the Newfoundland continental margin is a frontier area in terms of oil and gas exploration and remains poorly understood in terms of structural evolution and rift development. The area has few exploration wells and, until recently, sparse seismic data coverage. Existing gravity inversion and seismic refraction data from the area suggest that stretched continental crust in the Orphan Basin is highly attenuated (locally to < 5 km) but previously published structural restorations have been unable to fully restore the continental crust below the Orphan Basin to pre-deformed thicknesses (30–32 km). Here we perform a structural restoration of a regional, WNW-ESE oriented cross-section to investigate crustal structure, rifting style, and structural evolution of the Orphan Basin and Flemish Pass region. Interpretation is constrained by modern regional depth converted broadband 2D and 3D seismic reflection data, well data, and published gravity inversion results. Present-day crustal thicknesses are used as constraints for crustal area balancing and estimation of crustal thinning across the basin. We find that low-angle extensional detachments are widespread in the area, with offsets on individual structures of up to 42 km. Zones of attenuated continental crust are coincident with the presence of low-angle detachment surfaces displaying isostatic uplift of detachment footwalls. Comparison of total extension derived from crustal area balancing vs. structural restoration suggests approximately 39% of extension across the cross-section is unresolvable in seismic data. We attribute this to (i) ductile deformation prior to brittle faulting, (ii) subseismic-scale faulting, (iii) uncertainties in detachment breakaway positions, and (iv) unresolvable later offset of detachment surfaces. Widespread and relatively evenly distributed extension across the Orphan Basin and Flemish Pass region from Middle-Late Jurassic to Early Cretaceous influences sediment distribution across the region. Calibrated regional seismic mapping of the Orphan Basin suggests that significant thicknesses of Jurassic strata exist throughout the area, including in the northwestern part of the study area, where Kimmeridgian and Tithonian strata reach combined thicknesses of up to 4.9 km. • sSignificantthicknesses of Jurassic strataidentified throughout the Orphan Basin and Flemish Pass. • kinematic restoration and crustal area balancing used to constrain timing and amount of extension across the study area. • Structure dominated by low-angle extensional detachments with offsets on individual structures of up to 42 km. • Attenuated continental crust is coincident with low-angle detachment surfaces and isostatic uplift of detachment footwalls. [ABSTRACT FROM AUTHOR]