Abstract This chapter describes Lower Jurassic second-order sequences J00 and J10, and their component third-order sequences J1–J6 and J12–J18. Two sequences (J1 and J3) are new, four sequences (J2, J4, J12 and J16) are amended and one sequence (J17) is renamed. A significant unconformity at the base of the J12 sequence (Upper Sinemurian) is present near the base of the Dunlin Group in the North Viking Graben–East Shetland Platform and in the Danish Central Graben, and correlates with an equivalent unconformity around the margins of the London Platform, onshore UK. A marked unconformity at the base of the J16 sequence is recognized in the North Viking Graben and onshore UK, where it is related to structural movements on the Market Weighton High, eastern England. Several levels of carbon enrichment (carbon isotope excursions (CIEs)) and associated geochemical changes tie to J sequences defining maximum flooding surfaces: the Upper Sinemurian CIE equates to the base J6 maximum flooding surface (MFS), the basal Pliensbachian CIE ties to the base J13 MFS, the basal Toarcian CIE relates to the base J17 MFS and the Toarcian Ocean Anoxic Event corresponds with the base J18 MFS.

Abstract This chapter describes Middle Jurassic second-order sequences J20 and J30, and their component third-order sequences, J22–J26 and J32–J36. The J22 sequence contains the major Intra-Aalenian Unconformity (‘Mid-Cimmerian’) across a wide area of the North Sea Basin and an equivalent event onshore UK. The base J24 (Lower Bajocian) is marked by the Rannoch Shale (Brent Group) and by the flooding of the Ollach Sandstone, Hebrides Basin. The base J26 (Upper Bajocian) ties to the Mid Ness Shale (Brent Group) and the base of the Upper Trigonia Grit Member, central England. The base J32 (Upper Bajocian) ties to the base of the Tarbert Formation, the base of the Great Oolite Group in central England and the base of the Great Estuarine Group, Hebrides Basin. The base J33 (Middle Bathonian) falls within the Tarbert Formation and the base of the Taynton Limestone, central England. The base J34 (uppermost Middle Bathonian) commonly falls at the top of the Brent Group. The base J36 (uppermost Bathonian) represents a major increase in marine influence, at the base of the Beatrice Formation, in the Inner Moray Firth and at the base of the Staffin Bay Formation, Hebrides Basin.

Abstract This chapter describes uppermost Middle Jurassic–lowermost Cretaceous second-order stratigraphic sequences J40, J50, J60 and J70, and their component third-order sequences J42–J46, J52–J56, J62–J66 and J71–J76. The latest Callovian–Berriasian was an interval of significant tectonism that led to the development of complex stratigraphy and highly variable successions, the elucidation of which is aided by the recognition of the correlation of the J sequences. Marine sedimentation dominated the Callovian–Berriasian interval, with the development of multiple sandstone members comprising reservoir units in many hydrocarbon fields, charged by marine source rocks (e.g. the Kimmeridge Clay Formation). Each of these units is subdivided and correlated by a succession of J sequences. Several sequences are renumbered (e.g. J54, J55, J65 and J66), some sequence definitions are amended or their basal boundaries recalibrated chronostratigraphically (J52, J54, J72, J73, J74 and J76) and new sequence subdivisions are recognized (J64a, J64b, J72a–J72c, J73a and J73b). Significant unconformities are recognized at the bases of the J54, J55, J62, J63, J64, J71 and J73 sequences. The top of J70 (J76) equates to the major ‘Base Cretaceous Unconformity’ seismic sequence boundary.

Abstract The most important North Sea Jurassic–lowermost Cretaceous lithostratigraphic units, as developed in the UK, Norway and Danish sectors, are summarized in this chapter (55 units from the UK, 25 from Norway and 10 from Denmark). Some significant issues remain with the use and application of lithostratigraphic terminology in the Jurassic of the North Sea Basin. In particular, there are inconsistencies in unit definition and nomenclature changes across country sector boundaries that obscure the recognition of regional stratigraphic patterns that exist across the region. To aid clarity and to overcome some issues of definition, some revisions are made to the existing lithostratigraphic schemes. Several informal lithostratigraphic units are described, a number of unit definitions are revised and various formerly informal units are formalized (Buzzard Sandstone Member, Ettrick Sandstone Member and Galley Sandstone Member). It is recommended that use of the Heno Formation in offshore Denmark is discontinued. In addition, four new lithostratigraphic member terms are introduced (Home Sandstone Member, North Ettrick Sandstone Member, Gyda Sandstone Member and Tambar Sandstone Member). All described units are placed into a sequence stratigraphic context. All significant lithostratigraphic boundaries conform with key sequence stratigraphic surfaces.

Abstract An updated, integrated biozonation scheme for the Jurassic (Hettangian)–lowermost Cretaceous (Upper Berriasian) of the North Sea Basin incorporates 49 palynology biozones plus subzones (based on dinocysts, spores and pollen) and 27 microfaunal zones plus subzones (based on foraminifera, radiolaria and ostracods) to provide the essential chronostratigraphic calibration of the defined sequences. The biozonation scheme is tied to standard ammonite zonal chronostratigraphy wherever possible. Parts of the biozonation scheme are also applicable to onshore UK (boreholes and outcrops), onshore Denmark (boreholes) and offshore Netherlands.

Abstract An updated sequence stratigraphic framework, comprising 39 third-order stratigraphic sequences, for the Jurassic–lowermost Cretaceous of the North Sea, is described by reference to key wells and seismic lines across the UK, Norway and Denmark sectors, and, where possible, to onshore UK outcrops. It appears evident that regional tectonics provided the main control on sequence development, particularly during the Late Jurassic. There is a close relationship between key sequence stratigraphic surfaces and many lithostratigraphic formation and member boundaries throughout the North Sea Jurassic. Four new sandstone members are defined. A biozonation scheme for the study interval is described that provides essential characterization of the defined sequences.

Abstract Detailed analysis of Jurassic stratigraphic relations in the North Sea highlights the occurrence of numerous, distinctive, and correlatable marine shale horizons. These horizons are often characterized by condensed sections in subbasin depocenters and shales marking the maximum extent of marine flooding into nonmarine environments on their margins. Biostratigraphic data indicate that these intervals are correlatable and isochronous within the level of resolution currently employed. Correlation of these maximum flooding surfaces allows the Jurassic stratigraphy to be subdivided into genetic stratigraphic sequences with chronostratigraphic significance. Mapping of stratigraphic relations using this approach from offshore areas of northwest Europe and onshore exposures in Britain, Greenland, and continental Europe allows the nature of Middle Jurassic ("mid-Cimmerian ") unconformities to be identified. The earliest and most significant of these unconformities occurs consistently in the Aalenian and is characterized by progressive truncation of stratigraphy throughout the North Sea area in a broadly concentric but asymmetric subcrop pattern over an area with a diameter greater than 1250 km. The oldest rocks subcrop immediately adjacent to the rift arm triple junction. Strata above the unconformity show that progressive marine onlap occurred from late Aalenian to early Kimmeridgian times with the central area covered by the youngest strata. These relations are interpreted to be consistent with widespread late Toarcian–Bathonian regional tectonic uplift (Central North Sea Dome) that was synchronous with crustal thinning in areas that later became the rift arms, followed by progressive onlap onto a gently dipping slope as the dome deflated during the Callovian–Kimmeridgian. Knowledge that igneous rocks of the Forties Province were emplaced after the development of the unconformity is consistent with ideal models of rifting consequent upon the impingement of a mantle plume head on the base of the lithosphere. However, since recent studies have demonstrated that the excess temperature in such a plume must have been minimal to be compatible with the limited melting observed, it cannot be considered to have been sufficiently hot to have caused widespread melting. This conclusion and the Callovian-Kimmeridgian deflation make it likely that the driving force was a transient plume head or "blob" rather than a focused, long-lasting "hot" jet. Simple comparison with the present global chart of coastal onlap and eustatic sea level change shows that the same intra-Aalenian "mid-Cimmerian unconformity" equates with the chart's most significant regressive changes in coastal onlap (the 177 Ma sequence boundary separating the Absaroka and Zuni first-order megacycles). However, this part of the curve appears to be based exclusively upon stratigraphical sections in Dorset and Yorkshire, associated with the geographically restricted region affected by regional, thermal-driven doming. Consequently, the study highlights the impracticality of using two relatively closely spaced sections to define a global eustatic signal for the Jurassic and suggests that there remains a need to test the global interpretation using sections drawn from outside the uplifted area. To the natural concern that local tectonic events have generated an apparent eustatic event must now also be added the possibility that asthenosphere-driven regional uplift may produce correlatable behavior over distances greater than 1000 km.