The Influence of Structural Inheritance and Multiphase Extension on Rift Development, the NorthernNorth Sea

Abstract

The northern North Sea rift evolved through multiple rift phases within a highly heterogeneous crystalline basement. The geometry and evolution of syn-rift depocenters during this multiphase evolution and the mechanisms and extent to which they were influenced by preexisting structural heterogeneities remain elusive, particularly at the regional scale. Using an extensive database of borehole-constrained 2D seismic reflection data, we examine how the physiography of the northern North Sea rift evolved throughout late Permian-Early Triassic (RP1) and Late Jurassic-Early Cretaceous (RP2) rift phases, and assess the influence of basement structures related to the Caledonian orogeny and subsequent Devonian extension. During RP1, the location of major depocenters, the Stord and East Shetland basins, was controlled by favorably oriented Devonian shear zones. RP2 shows a diminished influence from structural heterogeneities, activity localizes along the Viking-Sogn graben system and the East Shetland Basin, with negligible activity in the Stord Basin and Horda Platform. The Utsira High and the Devonian Lomre Shear Zone form the eastern barrier to rift activity during RP2. Toward the end of RP2, rift activity migrated northward as extension related to opening of the proto-North Atlantic becomes the dominant regional stress as rift activity in the northern North Sea decreases. Through documenting the evolving syn-rift depocenters of the northern North Sea rift, we show how structural heterogeneities and prior rift phases influence regional rift physiography and kinematics, controlling the segmentation of depocenters, as well as the locations, styles, and magnitude of fault activity and reactivation during subsequent events.

The influence of structural inheritance and multiphase extension on rift development, the northern North Sea

“…The generation of the accommodation for the upper postrift strata in the Late-syn-to Post-RP2 interval appears to be related to thermal subsidence following RP2 activity (Figure 11), as evidenced by the large thicknesses present in the South and Central Viking grabens (Figures 3b and 3c). The thickness of Latesyn-to Post-RP2 strata is locally accentuated by fault activity in the Sogn Graben and Marulk and Magnus Basins, and local westerly tilting in the north of the study area (Figures 11 and 12;Brekke & Riis, 1987). The increased thickness of Late-syn-to Post-RP2 strata in the north of the study area reflects a relative increase in activity related to proto-North Atlantic opening in the Møre Basin-Faroe-Shetland Basin-Rockall Trough axis to the north of the study area (Kristoffersen, 1978;Roberts et al, 1999), which is related to a decrease in rift activity in the northern North Sea.…”

“…Faults across the Northern Horda Platform are also reactivated during Late-syn-to Post-RP2, although this does not appear to be directly related to proto-North Atlantic extension in contrast to activity further north. Rather, Late-syn-to Post-RP2 reactivation of faults across the Northern Horda Platform is proposed to be related to flexural downbending occurring in response to the increase in tectonic activity to the north (Bell et al, 2014;Brekke & Riis, 1987). This suggests that activity across the Northern Horda Platform during Late-syn-to Post-RP2 was mainly related to local flexural stresses and that the eastern margin of the rift (east 10.1029/2019TC005756 Tectonics PHILLIPS ET AL.…”

“…Well data are typically collected at relatively shallow (2-3 km), more economic depths, with few wells penetrating deeper areas, particularly in the hanging walls of major faults. Previously, imaging of basement structures was confined to regional seismic sections, often limited to 2-D and at the expense of resolving shallow structure (BIRPS and ECORS, 1986;Fossen et al, 2014;Gabrielsen et al, 2015;Klemperer & Hobbs, 1991). However, more recently basement structures have been resolved beneath the northern North Sea rift, particularly where they are situated at relatively shallow depths on the rift margins (Bird et al, 2014;Fazlikhani et al, 2017;Lenhart et al, 2019;Patruno et al, 2019;Phillips et al, 2016;Reeve et al, 2013).…”

Pre-breakup extension in the northern North Sea defined by complex strain partitioning and heterogeneous extension rates

“…Early Cretaceous; post-145 Ma), we do not explicitly consider the detailed growth of fault systems most active at this time. We do, however, place our study within the more regional, late syn-rift-to-early post-rift tectono-stratigraphic framework erected by other authors (Bellingham & White, 2000;McLeod et al, 2000;Cowie et al, 2005;Phillips et al, 2019).…”

“…However, seismic-stratigraphic analysis of borehole-constrained 3D seismic reflection datasets indicate that extension and active faulting actually continued into the Early Cretaceous (140-145 Ma; Valanginian-Berriasian), with strain eventually focusing on fault systems bounding the eastern margin of the East Shetland Basin (Cowie et al, 2005; see also Faerseth et al, 1995;Bellingham & White, 2000;and McLeod et al, 2002). Strain localisation on these structures was associated with overall rift narrowing and ultimately abandonment of the East Shetland Basin (Cowie et al, 2005;Phillips et al, 2019).…”