Although the ‘Mid-Cimmerian event’ or unconformity has been recognized over much of Europe, its exact stratigraphic relations and causal mechanism have remained unclear. Application of a genetic sequence stratigraphic approach (using 17 marine condensed sections and maximum flooding surfaces) to Jurassic sequences across NW Europe allows the stratigraphic succession to be subdivided into a series of time-slices (genetic stratigraphic sequences) and allows the true nature of the unconformity to be determined. They indicate that the main event’s correlative conformity falls in the Aalenian near the break between theopalinumandmurchisonaeammonite biochronozones. Further study of the associated spatial and temporal variation indicates that systematic truncation of stratigraphy occurred throughout the North Sea domain (the oldest stratigraphies subcrop in areas adjacent to the triple junction) with subsequent progressive onlap towards the same area. When integrated with igneous evidence, these observations are interpreted to confirm regional (Toarcian–Aalenian) domal uplift, resulting from the impingement of a broad-based (> 1250 km diameter), transient plume head or ‘blob’ at the base of the lithosphere. Progressive pre-rift, Aalenian–early Bathonian marine onlap records differential subsidence in response to the initial deflation of the dome while central regions may have continued to rise. Subsequent subsidence post-dated Bathonian–Callovian volcanism but still pre-dated the timing of most significant (Kimmeridgian–Volgian) rifting. Such temporal relations demonstrate that North Sea volcanism is inconsistent with a classic ‘passive’ rift model. Instead, it seems more appropriate to equate Mid–Late Jurassic North Sea development with an ‘active’ rift model following mantle-driven thermal doming.Integration of sedimentation patterns with basin development suggests that the early Toarcian–early Kimmeridgian succession records a long-term, second-order regressive–transgressive episode related to regional tectonism. Comparison with the current chart of coastal onlap and global sea-level change highlights the correlation of the Intra-Aalenian event with one of the most significant regressions (the 177 Ma event separating the Absaroka and Zuni first-order megacycles). The knowledge that this part of the curve appears to be based exclusively on sections from Dorset and Yorkshire, within and adjacent to the region affected by regional doming, suggests that there remains a need to test this part of the chart using sections from outside the uplifted area and emphasizes the impracticality of using just two relatively closely spaced sections in trying to define a truly global signal. Clearly, sections should be taken from several areas and preferably from different plates as tectonically uncoupled as possible. Until then, the worry will remain that regional tectonic events could overprint any global signal and be erroneously interpreted as abrupt changes in global eustasy. The fact that doubts such as these can be cast upon parts of the eustatic sea-level chart suggests that it is still someway off being a valid global standard with true predictive capabilities.

Thirty-three regionally correlatable marine condensed sections containing maximum flooding surfaces have been recognized in the area allowing the North Sea Jurassic succession to be subdivided into 32 genetic stratigraphic sequences (sensuGalloway). Each event is biostratigraphically calibrated using microfossils (dinoflagellate cysts, radiolaria, ostracoda and foraminifera). The new scheme provides the basis for a basin-wide stratigraphic framework for the Jurassic of the North Sea basin.

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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.

Application of sequence stratigraphic principles to the Hettangian–Oxfordian succession of the Inner Moray Firth basin has led to a new understanding of its sedimentary fill history at a greater resolution than has been previously possible. This interval was deposited in a variety of shallow marine to terrestrial environments, punctuated by a number of regionally correlatable transgressive events, during a phase of gentle thermal subsidence, prior to the renewal of major extensional rifting in Kimmeridgian times.Recognition of a significant regional stratigraphic break, the ‘Mid-Cimmerian Event’, allows this succession to be divided into two component depositional packages (Jla: Hettangian–Toarcian; J1b: Bathonian–Late Oxfordian). Identification of seven maximum flooding surfaces permits further subdivision into eight genetic stratigraphic sequences and enables the construction of a new basin-wide stratigraphic template. Erection of such a framework has important implications for our understanding of the basin’s sedimentary and tectonic evolution, and thus enables the Inner Moray Firth to be placed within its regional North Sea setting.Construction of palaeogeographic maps for a number of J1b genetic stratigraphic sequences allows accurate facies and, hence, reservoir prediction. Furthermore, stratigraphic data give important insights into the nature of the ‘Mid-Cimmerian Event’. The observed progressive increase in amount of truncation below this unconformity, together with the successive migration in the locus of sedimentary onlap above this unconformity, maximizes the stratigraphic separation towards the east. Similar temporal stratigraphic relations elsewhere in the North Sea suggest that this unconformity is related to the initiation and early subsidence of a regional ‘dome’ prior to its more significant collapse between Kimmeridgian and Early Cretaceous times.

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Exploration permits WA-299-P and WA-300-P lie west of the North West Cape in a frontier part of the Carnarvon Basin where the largely Mesozoic Exmouth Sub-basin abuts against shallow Palaeozoic strata of the Gascoyne Platform. The only exploration well, within the permits, Pendock–1, penetrated a thin Valanginian Birdrong Sandstone unconformably overlying Carboniferous to Silurian units, so the Mesozoic hydrocarbon potential of the area is effectively untested.The structure of the area comprises a complex mosaic of NNE–SSW trending Early Palaeozoic extensional, listric growth faults, dissected by NW–SE trending Permian extension relay zones. Subsequent phases of Callovian– Oxfordian and Valanginian uplift, together with Late Cretaceous and Miocene inversion along the main fault zone, further complicate the structure. Several seismic events, some of which correlate with magnetic anomalies, are discordant with the local stratigraphy indicating a probable igneous origin.The primary targets are the Birdrong Sandstone and underlying Wogatti Formation, both of which host onshore oil accumulations at Rough Range and Parrot Hill–1. The retrogradational clastic shoreline facies of the Birdrong Sandstone is well known along the eastern edge of the Dampier–Barrow–Exmouth Sub-basins. The Wogatti Formation was deposited as a more restricted alluvial/ fluvial sheet sand facies, so far identified only in the onshore Cape Range area. Where the Jurassic is preserved, fluvial/alluvial channel sand facies of the Middle Jurassic Learmonth Formation, known onshore at Sandy Point–1, and Callovian nearshore sands, as observed in Unknown Hill–l, are expected to be important secondary targets.The most promising play types within the Southern Carnarvon Basin are dip and fault-dip closures at Birdrong/Wogatti level associated with Late Cretaceous reactivation of the main NE–SW listric faults, and accentuated by later Miocene compression. The most significant exploration risks are charge and the high risk of biodegradation of reservoired liquid hydrocarbons (critically linked to reservoir temperature).

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