This paper presents an integrated seismic, petrophysical and core facies study of the Mey Sandstone Member of the Central North Sea Lista Formation. Seismic mapping and attribute analysis reveal that the Mey Sandstone Member is composed of distinct axial and lateral routing systems. In turn, the axial system can be divided into coeval western and eastern fairways defined by the underlying graben topography in a similar manner to the overlying Sele Formation (Forties) sandstones. These trends are confirmed by petrophysical analysis, which also reveals that the lateral systems are not as important as previously proposed and that the cycles of the Mey Sandstone Member prograded over time before a late stage of backstepping. These variations can be related directly to published sea-level curves. Core analysis reveals that mean grain size is the main control on sandstone quality and that similar proximal (channelized) to distal (sheet-like) changes in sedimentological facies occur to those described in the Sele Formation. It is argued that these deposits cannot be described as simple basin floor fans due to the impact of topography on turbidite flow routing and the existence of multiple entry points of sediment into the basin.

No abstract

Detrital garnet suites have been demonstrated to be reliable indicators of the mineralogical and lithological characteristics of sediment source areas. This study applies garnet analysis to the Paleocene to Eocene Sele Formation deep-water sandstone units of the central North Sea. These stratigraphic units are economically important as they represent one of the main hydrocarbon reservoir intervals in this mature basin. The routing of turbidity currents into the Central Graben has been demonstrated to be related to axial fans (ultimately sourced from Lewisian and Moine basement rocks and Triassic sandstones to the NW) and lateral fans (ultimately sourced from the Dalradian basement rocks to the west). Garnet analysis suggests the majority of samples can be attributed to the axial fan system and that the lateral system contributed little to sandstone deposition east of the Gannet Fields. This contradicts previous seismic mapping work, which suggested that the lateral fan system dominated sedimentation as far east as the Merganser Field. This reinterpretation is potentially important for our understanding of sediment routing and its impact on the distribution of reservoir quality, particularly as this is believed to relate directly to proximity to the shelf.

Behavior of sediment gravity flows can be influenced by seafloor topography associated with salt structures; this can modify the depositional architecture of deep-water sedimentary systems. Typically, salt-influenced deep-water successions are poorly imaged in seismic reflection data, and exhumed systems are rare, hence the detailed sedimentology and stratigraphic architecture of these systems remains poorly understood. The exhumed Triassic (Keuper) Bakio and Guernica salt bodies in the Basque–Cantabrian Basin, Spain, were active during deep-water sedimentation. The salt diapirs grew reactively, then passively, during the Aptian–Albian, and are flanked by deep-water carbonate (Aptian–earliest Albian Urgonian Group) and siliciclastic (middle Albian–Cenomanian Black Flysch Group) successions. The study compares the depositional systems in two salt-influenced minibasins, confined (Sollube basin) and partially confined (Jata basin) by actively growing salt diapirs, comparable to salt-influenced minibasins in the subsurface. The presence of a well-exposed halokinetic sequence, with progressive rotation of bedding, beds that pinch out towards topography, soft-sediment deformation, variable paleocurrents, and intercalated debrites indicate that salt grew during deposition. Overall, the Black Flysch Group coarsens and thickens upwards in response to regional axial progradation, which is modulated by laterally derived debrites from halokinetic slopes. The variation in type and number of debrites in the Sollube and Jata basins indicates that the basins had different tectonostratigraphic histories despite their proximity. In the Sollube basin, the routing systems were confined between the two salt structures, eventually depositing amalgamated sandstones in the basin axis. Different facies and architectures are observed in the Jata basin due to partial confinement. Exposed minibasins are individualized, and facies vary both spatially and temporally in agreement with observations from subsurface salt-influenced basins. Salt-related, active topography and the degree of confinement are shown to be important modifiers of depositional systems, resulting in facies variability, remobilization of deposits, and channelization of flows. The findings are directly applicable to the exploration and development of subsurface energy reservoirs in salt basins globally, enabling better prediction of depositional architecture in areas where seismic imaging is challenging.

Sediment gravity flow behaviour is influenced by seafloor topography associated with salt structures, which controls the depositional architecture of deep-water sedimentary systems. Typically, salt-influenced deep-water successions are poorly-imaged in seismic reflection data and exhumed systems are rare, hence the detailed sedimentology and stratigraphic architecture of these systems remains poorly understood. The exhumed Triassic (Keuper) Bakio and Guernica salt bodies in the Basque-Cantabrian Basin, Spain were active during deep-water sedimentation. The salt diapirs grew reactively, then passively, during the Aptian-Albian, and are flanked by deep-water carbonate (Aptian-earliest Albian Urgonian Group) and siliciclastic (middle Albian-Cenomanian Black Flysch Group) successions. The study compares the deposition in two salt-influenced confined (Sollube basin) and partially-confined (Jata basin) minibasins by actively growing salt diapirs, comparable to salt-influenced minibasins in the subsurface. The presence of a well-exposed halokinetic sequence, beds that pinch out towards topography, soft sediment deformation, variable paleocurrents and intercalated mass transport deposits (MTDs) indicate that salt grew during deposition. Overall, the Black Flysch Group coarsens- and thickens-upwards in response to regional axial progradation, which is modulated by laterally-derived MTDs from halokinetic slopes. The variation in type and number of MTDs within the Sollube and Jata basins indicate the basins had different tectono-stratigraphic histories despite their proximity. In the Sollube basin, the routeing systems were confined between the two salt structures eventually depositing amalgamated sandstones in the basin’s axis. Different facies and architectures are observed in the Jata basin due to partial confinement. The findings show exposed minibasins are individualised and that facies vary both spatially and temporally in agreement with subsurface salt-influenced basins. Salt-related, active topography and the degree of confinement are shown to be important modifiers of depositional systems, resulting in facies variability, remobilisation of deposits and ‘channelisation’ of flows. The findings are directly applicable to the exploration and development of subsurface energy reservoirs in salt basins globally, enabling better prediction of depositional architecture in areas where seismic imaging is challenging.