Multiple episodes of extensional tectonism dominated the formation of Mesozoic fault‐bounded basins on the Grand Banks of Newfoundland, the Irish Continental Shelf and the central North Sea. A range of structural and stratigraphic responses in the Jeanne d'Arc, Porcupine and Moray Firth basins support widespread synchronous tectonic controls on sedimentation during one of these episodes, the Late Cimmerian. Rifting was preceded by a phase of related tectonism during which subsidence rates began to vary across broad areas but without significant fault block rotation. This Late Cimmerian ‘onset warp’ pattern of subsidence is considered to have been essential in the establishment of restricted anoxic basins from latest Oxfordian through Kimmeridgian (sensu gallico) time and the development of one prolific layer of organic‐rich source rocks. The most prominent and widely recognized structural/lithostratigraphic response to Late Cimmerian rifting was the deposition of sediment wedges. Tithonian to early Valanginian strata generally thicken‐ into northerly trending faults in the Jeanne d'Arc and Porcupine basins, indicating that extensional stress was orientated WNW‐ESE across a very broad area. The misalignment of this regional Late Cimmerian extensional stress with local inherited structural fabric may be responsible for transpressional uplift of individual fault blocks in the Outer Moray Firth basin. Sedimentological responses to Late Cimmerian rifting were varied, though a common lithofacies stacking pattern is recognized. Variably thick conglomerates and/or sandstones were widely deposited at the start of rift deformation, while palaeoenvironments ranged from alluvial and braid plain to submarine fan even within individual basins. The relatively coarse basal sediments fine upwards into a second layer of commonly organic‐rich shales and mark The widest variations in palaeoenvironments and sediment thicknesses occurred during the last phase of Late Cimmerian rift tectonism, though all three basins show evidence of decreasing water depths, increasing oxygen levels and increasing grain size. This lithofacies stacking pattern of relatively coarse to fine to coarse (reservoir/source/reservoir) and the development of bounding unconformities are largely attributable to progressive changes in rift‐controlled subsidence. Rift basin subsidence rates are interpreted to increase from a low at initiation of faulting to a mid‐rift peak, followed by slowing subsidence to the end of extension. A number of counteracting crustal mechanisms that may account for progressive variations in rift‐induced subsidence are considered.

The Formation MicroScanner (FMS*) tool is an advanced dipmeter tool capable of producing high-resolution resistivity images of a borehole wall. When integrated with core and open hole logs, FMS images are of great utility in evaluating the thin bedded reservoir sequences of the Claymore and Scapa North Sea oil fields. Sedimentary features as small as 0.5 inches (1.2 cm) can be resolved on FMS images. Such detail is employed in the distinction of massive, parallel laminated, tipple cross-laminated, bioturbated and conglomeratic bedding types. The application of the FMS tool to reservoir description is not limited to bedding type identification. Bed boundaries, as well as small and large scale structural features, can be distinguished, including erosional contacts, slumps, fractures and faults. In the hydrocarbon-beating zone permeability distribution outwith cored intervals can inferred. This can be confirmed by relating resistivity changes to core measured permeability values. The proposed approach to FMS interpretation involves the integration of all available open hole logs with detailed local geological knowledge and core data. Aspect and image quality of the FMS log are important considerations. By imaging the borehole wall, the aspect of the FMS tool provides a direct method of relating features detected using open hole logs to those observed in cores. Image quality is largely dependent on resistivity contrast in the formation and correlation with cores is imperative to establish confidence limits for extrapolation into uncored intervals.

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Upper Jurassic sandstones are of great economic importance in the Moray Firth, where 22 known fields originally contained almost three billion barrels of oil reserves. Principles of genetic stratigraphy provide the basis for recognition, correlation and mapping of eight Moray Firth Humber Group units. Genetic unit boundaries, which are biostratigraphically constrained, represent marine flooding surfaces or unconformities that resulted principally from tectonic/erosional episodes. Tectonic evolution in the Late Jurassic consisted of pre-rift and syn-rift phases, with accompanying differences in facies associations and sandstone distribution. Pre-rift sandstones comprise regressive pulses within a predominant overall transgressive setting, a coal-bearing deltaic/paralic succession is commonly succeeded by shallow marine deposits. The transgression commenced in the Callovian in the west and shoreline facies migrated eastwards through into the Kimmeridgian ( sensu gallico ), toward the junction with the Central North Sea graben system. Syn-rift sandstones are mostly turbiditic in origin, deposited during episodic Late Cimmerian tectonism, that started in the late Kimmeridgian and continued through into the Early Cretaceous. Only isolated remnants of the shallow marine equivalents to these deep marine systems have been found to data, such as those of Volgian age in the Glamis field on the Fladen Ground Spur.