Sediments of Kimmeridgian to Late Ryazanian age form a group of key hydrocarbon play fairways in the syn-rift Jurassic of the North Sea. The perceived yet-to-find reserves of these often subtle plays, lying at or below seismic resolution, have attracted considerable industry attention over the past few years. Reserves are currently estimated by BP Exploration at 1 to 5 billion barrels of oil equivalent, reservoired in three play systems: (1) apron fans (e.g. Brae type); (2) basin floor fans (e.g. Miller, Galley, Ettrick and Magnus types); (3) shallow marine shelf (e.g. Ula, Gyda, Fulmar, Piper, Clyde types).In order to assess the future exploration potential of this play fairway, a high resolution, predictive, sequence stratigraphy was erected for the North Sea Late Jurassic. The stratigraphic framework combines data from over 500 exploration wells with seismic and field data (Magnus, Brae, Miller, Ula, Gyda and Clyde).In the Late Oxfordian to Late Ryazanian, a total of 11 genetic stratigraphic sequences have been defined. They are bounded by maximum flooding surfaces which, within the limits of the biostratigraphy, represent basin-wide isochronous events across NW Europe and can be recognized in exploration wells and at outcrop from Greenland to the Wessex Basin. The maximum flooding surfaces have been biostratigraphically calibrated to provide a consistent and easily identifiable stratigraphic framework. Candidate sequence boundaries have been interpreted within this stratigraphic framework, from basin-ward shifts of facies belts, using sedimentological and wireline log data. The combination of these stratigraphic methods has produced a very powerful tool to predict the presence and distribution of potential reservoirs and play types across the entire North Sea Basin from outcrop in East Greenland to the offshore Netherlands.The model suggests that three major cycles of sand input into the basin can be recognized with an overall marked decrease in net sand content with time. Each cycle is bounded by tectonically enhanced maximum flooding surfaces representing major periods of basin floor reorganization. The intervening maximum flooding surfaces temporarily switch off sediment supply to the basin but do not offset depocentres. These events can form important, field-wide permeability barriers.It is proposed that the tectonically enhanced maximum flooding surfaces are a response to tectonic subsidence during maximum relative sea-level rise, whereas maximum clastic progradation occurs from basin margin uplift during relative sea-level fall. The model is considered to have application at regional and field-specific scales; for example, prediction of both basin floor fan distribution and potential intra-reservoir permeability barriers.

The early Palaeogene deposits of the Central North Sea have been divided by Stewart into ten depositional units, on the basis of seismic stratigraphy. These are interpreted as the products of variations in relative sea level. The units may be traced from the shelf into the basin using wireline log markers correlated within a biostratigraphic framework. These are interpreted as the signature of transgressive maxima when basinal clastic supply was at a minimum. The attitude of coal or lignite beds within the shelfal areas can be used to demonstrate a period of Palaeogene net uplift, followed by tilting and sinking of the shelf-edge and basinal areas during the later depositional episodes. Other than by a mechanism of load-induced differential compaction around buried or partially buried Mesozoic features no significiant rejuvenation of Mesozoic faults can be demonstrated. The area of uplift extended at least as far as the western limit of the Beauly Formation. The products of Stewart’s depositional episodes vary depending on the tectonic activity. During the uplift phase, thick massive basinal fans were deposited and little or no shelfal deposits are preserved. During the tilting/sinking phase thick progradational wedges were deposited, and basinal deposition was largely confined to shales with relatively small local sand systems.

T h e structural evolution of a basin cannot be reconstructed from sedimentary thicknesses alone without data on palaeobathymetry. T w o classes of geological horizons, are defined, profiles and traces. Profiles are time-lines and bound depositional units. Traces were formed at a known water depth and contain implicit palaeobathymetric data. such units are controlled directly by subsidence, while the thicknesses; of profile-bounded units may be unaffected by the subsidence or even the palaeotopography ofthe basin. prior knowledge of the palaeobathymetry, and it is impossible to distinguish between synsedimentary fault movement and onlap to a pre-existing fault scarp from thickness alone. Reconstruction of the basin history of the North Sea is difficult due to the lack of tracebounded units in the post-Jurassic. T h e validity of previously published studies depends largely on the quality and quantity of palaeobathymetric data included. An alternative basin history is proposed based on the few trace-bounded units in the North Viking Graben. This includes rifting episodes in the Triassic and Late Jurassic, and a period of uplift in the Palaeocene. Rock units bounded by traces are diachronous lithostratigraphic units, and the thicknesses of Dating fault movement from thickness variations in profile-bounded units is difficult without

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The tectonic history of the North Sea during the Middle and Upper Jurassic consists of initial basin-scale uplift, followed by subsidence. The subsidence is at least partly associated with a major rifting episode culminating in the Early–Mid-Kimmeridgian. Shallow marine depositional cycles of progradation and retrogradation are recognized throughout this time interval, with a periodicity of 1–5 million years.Twelve of these units, selected from data-constrained study areas, are described, and quantified data are presented on their geometry, duration, and the implied variations in accommodation volume.Sediment input rates into the basin decreased through the Middle and Upper Jurassic as hinterlands were drowned, and source/basin relief decreased. A corresponding evolution in the geometry of the units is seen, from wide tabular units in the Bajocian/Bathonian to narrow ribbon-geometry units in the Kimmeridgian.The continued decrease in sediment input resulted in an interval of basin-wide marine condensation. On seismic data this forms a prominent surface of marine onlap known as the Base Cretaceous (or Late Cimmerian) ‘Unconformity’.This pattern of decreasing depositional dimensions of shelf/shoreline systems is to be expected in marine rifts without access to continental drainage systems, where sediment supply decreases with syn-rift and post-rift subsidence of drainage basins. This decrease may happen throughout the late pre-rift to early post-rift, and the change from structure-independent to structure-dependent facies trends may not occur suddenly at the onset of rifting.