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The Jeanne d’Arc Basin offshore Newfoundland and the Porcupine Basin to the west of Ireland, developed under similar tectono-sedimentary conditions in pre-Late Cretaceous times. Rifting events in Permo-Triassic, Late Jurassic–Early Cretaceous and mid Cretaceous times were each followed by a phase of thermal subsidence. While a broadly common lithofacies pattern occurs within and between the basins, the detailed response of the basins differs in terms of style of structuring, reservoir architecture and quality of source rock development. The Late Jurassic–Early Cretaceous (Tithonian to Berriasian) rift episode is the most significant, with good reservoir sandstones and rich source rocks forming part of this rift sequence. A Late Oxfordian to Kimmeridgian onset warp phase resulted in the development of shallow marine limestones and deeper water organic-rich shales and marls in the Jeanne d’Arc Basin, with non-marine, shoreface and restricted marine sandstones and shales in the Porcupine Basin. The Late Jurassic–Early Cretaceous syn-rift episode resulted in the development of sandstone-prone successions which interfinger with good oil-prone source rocks in both basins. Reservoir architecture in both basins was influenced by this episode. Within the Porcupine Basin a range of lithofacies developed, ranging from fluvial channels and bars, to submarine fan turbidites. Within the Jeanne d’Arc Basin, periodic rejuvenation of fault footwalls produced conglomeratic pulses resulting in transverse alluvial fans which interfinger with axially-flowing braid channels and bars within the incised valley fills. Periods of increased subsidence resulted in the development of lacustrine facies and flood plain mudstones.

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.

Extensional tectonism is clearly a major factor in the formation of sedimentary basins. Tectonism influences many of the factors which control sediment deposition and preservation including: rates and styles of basin subsidence, accommodation space, drainage area size and topography, and rates of sediment input. These tectonically-influenced factors are interrelated and their local interplay determines, to a great extent, the formation, composition and structural style of sedimentary sequences.