Cretaceous revisited: exploring the syn-rift play of the Faroe–Shetland Basin

Abstract

Improved seismic imaging of the deep structures in the Faroe-Shetland Basin has revealed a complex Mesozoic rift system with shifting block polarity along the West Shetland Platform. Newly acquired seismic data has led to the focus of hydrocarbon exploration on structurally defined Mesozoic traps and has re-opened exploration in the deeper stratigraphic sections beyond the stratigraphic, Paleocene deep-water play. In the study area, rift geometry changes from symmetrical (south) to asymmetrical (north), the latter creating a large-scale seawarddipping flexure. The polarity shift may link up with deep-seated basement structures (rift-oblique lineaments) segmenting the rift zone. The initial rifting along the West Shetland Platform strongly influenced the depositional setting and lateral distribution of the Lower Cretaceous sediments. During rift initiation in the Early Cretaceous faulting took place along numerous small faults, which eventually linked up, creating a set of basin master faults in the main rift phase. Sand derived from rivers and longshore currents on the West Shetland Platform was transported down the axis of relay ramps and filled the juvenile rift basins. These sediments formed thick onlapping wedges, reflecting the continuous creation of accommodation space and the overall transgressive nature of the syn-rift and early post-rift succession. In this period, rift basins were elongated, which to some extent hindered cross-rift transport of coarse material except at relay ramps and rift-oblique lineaments. As fault movements ceased, the rift topography was levelled out and allowed gravity-driven systems to reach further into the basin, overstepping former cross-rift barriers. Lower Cretaceous syn-rift sediments are well exposed at several localities along the margins of the northern North Atlantic including onshore NE Greenland. The close analogy to the synrift structural setting imaged in the west of Shetland seismic succession may provide valuable information on structurally controlled depositional systems, reservoir architecture and properties.

An overview of the Upper Palaeozoic–Mesozoic stratigraphy of the NE Atlantic region

“…In the basins underlying the West Shetland Shelf, the Cromer Knoll Group was deposited in marginal-to shallow-marine and basinal marine environments that were subject to fluctuating aerobic/anaerobic bottom waters (Ritchie et al 1996;Harker 2002;Stoker & Ziska 2011). Common intraformational unconformities imply contemporary rifting, albeit localized and intermittent (Dean et al 1999;Harker 2002;Larsen et al 2010;Stoker 2016). An expansion of rift activity across the entire Faroe -Shetland -northern Rockall-Hebrides region probably occurred in the late Barremian/Aptian-Albian, with paralic to marine clastic deposition in all basins, including on the Hatton High.…”

“…14a). However, the increased subsidence of these basins was periodically interrupted by intermittent compression, uplift and erosion, which persisted throughout the Late Cretaceous (Dean et al 1999;Doré et al 1999;Larsen et al 2010;Stoker & Ziska 2011;Stoker 2016). In the northern Rockall Basin, the abundant Late Cretaceous -Paleocene sills throughout the Upper Cretaceous sequence, together with the intrusion of the axial volcanic seamounts, are probably associated with the crustal thinning.…”

Unravelling key controls on the rift climax to post‐rift fill of marine rift basins: insights from 3D seismic analysis of the Lower Cretaceous of the Hammerfest Basin, SW Barents Sea

“…Subsidence commonly outpaces sedimentation, resulting in the deposition of deep-marine mudstones with localized coarse clastic wedges deposited close to the footwall area (Leppard & Gawthorpe, 2006). Coarse-grained sediments have been described at the base of the fault scarp in slope aprons, slumps and slides, talus and coarse-grained aggradational or progradational fan deltas (Surlyk, 1978(Surlyk, , 1989Stow et al, 1996;Gawthorpe et al, 1997;Leppard & Gawthorpe, 2006;Larsen et al, 2010;Henstra et al, 2016;Elliott et al, 2017). Progradation tends to occur with low accommodation or high sediment supply or a combination of these factors (Gawthorpe & Leeder, 2000).…”

Depositional systems in multiphase rifts: seismic case study from the Lofoten margin, Norway

“…Progradational pulses of shelfal sands in the Barremian-Albian section have been documented along rift flanks across the northern North Atlantic rift system. For example, along the fringes of the North Sea Basin (Shanmugam et al, 1994;Brekke et al, 2001;Copestake et al, 2003); East Greenland (Kelly et al, 1998;Larsen et al, 1999); the Faroe-Shetland Basin (Grant et al, 1999; Larsen et al, 1999Larsen et al, , 2010; and near Spitsbergen (Midtkandal & Nystuen, 2009;Gjelberg & Steel, 2012). Such clastic wedges are also inferred to have existed along the eastern flank of the Norwegian margin (Martinsen et al, 2005), for example the clastic wedge of the M aløy terrace (Shanmugam et al, 1994;Vergara et al, 2001).…”