The dispersal and deposition of sediments in a rift basin are controlled by the sediment supply and the generation of accommodation space; hence, for the facies mosaic and depositional architecture of synrift sediments to be understood, both these variables must be constrained. Subsurface data sets, comprising three-dimensional (3-D) seismic and well data, provide the opportunity to quantify the rates of sediment supply and accommodation generation for the duration of the extensional event and over an area of regional extent.In this article, we address the controls on synrift sedimentation through detailed analysis of a high-resolution subsurface data set from the Late Jurassic northern North Sea rift basin. The sedimentation history in the study basin comprises four discrete stages intimately linked to the growth of the normal fault population. The earliest stage of rifting is characterized by a distributed fault population comprising a large number of faults with low slip rates. Sediment supply outpaced tectonic subsidence at this time, and rising eustatic sea level was the primary control on sedimentation. As rifting progressed, strain was localized onto a smaller number of active structures with higher displacement rates. The basin developed a grabenlike geometry, and the lateral propagation and linkage of fault strands controlled accommodation generation. Although the basin was flooded, the rate of sediment supply remained high and largely kept pace with the rate of tectonic subsidence. During the final two stages, the fully linked, half-graben bounding fault was the only active structure in the basin; the rate of sediment supply at this time was greatly exceeded by the rate of tectonic subsidence, and the basin became underfilled. Significantly, the final stage of the sedimentation history is characterized by large-scale fault interactions that changed the fault-controlled basin floor topography; hence, modified sediment dispersal and deposition.We conclude that sediment dynamics and facies distribution in a rift can only be understood in the context of the coevally active fault population. As the faults active at the close of a rift event are very different in location and character to those active during the initiation of rifting, this further emphasizes the need to integrate structural, sedimentary, and stratigraphic studies in rift basins.

ABSTRACT This study addresses the complex relationship between an evolving fault population and patterns of synrift sedimentation during the earliest stages of extension. We have used 3D seismic and well data to examine the early synrift Tarbert Formation from the Middle–Late Jurassic northern North Sea rift basin. The Tarbert Formation is of variable thickness across the study area, and thickness variations define a number of 1‐ to 5‐km‐wide depocentres bounded by normal faults. Seismic reflections diverge towards the bounding faults indicating that the faults were active contemporaneous with the deposition of the formation. Many of these faults became inactive during later Heather Formation times. The preservation of the Tarbert Formation in both footwall and hangingwall locations demonstrates that, during the earliest synrift, the rate of deposition balanced the rate of tectonic subsidence. Local space generated by hangingwall subsidence was superimposed upon accommodation generated due to a regional rise in relative sea‐level. In basal Tarbert Formation times, transgression across the prerift coastal plain produced lagoons and bays, which became increasingly marine. During continued transgression, barrier islands moved landward across the drowned bays. In the southern part of our study area, shallow marine sediments are erosionally truncated by fluvial deposition. These fluvial systems were constrained by fault growth monoclines, and flowed parallel to the main faults. We illustrate that stratal architecture and facies distribution of early sedimentation is strongly influenced by the active short‐lived faults. Local depocentres adjacent to fault displacement maxima focused channel stacking and allowed the aggradation of thick shoreface successions. These depocentres formed early in the rift phase are not necessarily related to Late Jurassic – Early Cretaceous depocentres developed along the major linked normal fault systems.

Through examination of the scaling relations of faults and the use of seismic stratigraphic techniques, we demonstrate how the temporal and spatial evolution of the fault population in a half‐graben basin can be accurately reconstructed. The basin bounded by the ≫62‐km‐long Strathspey–Brent–Statfjord fault array is located on the western flank of the Late Jurassic northern North Sea rift basin. Along‐strike displacement variations, transverse fault‐displacement folds and palaeo‐fault tips abandoned in the hangingwall all provide evidence that the fault system comprises a hierarchy of linked palaeo‐segments. The displacement variations developed while the fault was in a prelinkage, multisegment stage of its growth have not been equilibrated following fault linkage. Using the stratal architecture of synrift sediments, we date the main phase of segment linkage as latest Callovian – middle Oxfordian (10–14 Myr after rift initiation). A dense subpopulation of faults is mapped in the hangingwall to the Strathspey–Brent–Statfjord fault array. The majority of these faults are short, of low displacement and became inactive within 3–4 Myr of the beginning of the extensional event. Subsequently, only the segments of the proto‐Strathspey–Brent–Statfjord fault and a conjugate array of antithetic faults located 3.5 km basinward continued to grow to define a graben‐like basin geometry. Faults of the antithetic array became inactive ∼11.5 Myr into the rift event, concentrating strain on the linked Strathspey–Brent–Statfjord fault; hence, the basin evolved into a half‐graben. As the rift event progressed, strain was localized on a smaller number of active structures with increased rates of displacement. The results of this study suggest that a simple model for the linkage of 2–3 fault segments may not be applicable to a complex multisegment array.

Analysis of seismic, electrical log and core data from the northern part of the Brent Field enables the syn-tectonic fault scarp degradation complex which is mounted on the footwall scarp of the main block bounding fault to be characterized. The seismic geometry of this package of structurally degraded and sedimentologically reworked sediments describes a hierarchy of thickness variations that occur not only in a N–S orientation in response to changes in the underlying footwall geology, but also on a smaller, sub-km scale, where the complex is characterized by amalgamated cuspate-shaped forms. Within the complex, primary sedimentological integrity is generally preserved and displaced pre-rift formations remain stratigraphically the right-way-up. These observations support a model of translational–rotational sliding as the dominant mechanism for mass wastage from the scarp. Integrating these descriptions with biostratigraphical information from hanging wall Well 211/29–8, a nine stage model for the development and evolution of fault scarp degradation in the northern part of the Brent block is proposed. This describes the initiation of normal faulting and degradation in the Late Bajocian, followed by systematic failure of the scarp until the cessation of significant tectonic activity in the Volgian. The scarp continued to be denuded, probably by surface sediment reworking (e.g. slumps and flows), until complete burial was achieved in the Campanian. The mechanism of failure and the topography of the scarp are a function of the environment (submarine) and different relative strengths of the footwall rheologies. Although this study concludes that slide blocks have a potential to add significant volumes to the field hydrocarbon reserves, it also serves to illustrate the problems that are associated not only with accurate reservoir characterization but also in constraining the degree of compartmentalization within the complex.