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 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 The most prolific reservoir package in the SW Barents Sea is currently the Upper Triassic–Middle Jurassic Realgrunnen Subgroup, comprising the main hydrocarbon accumulations in the Goliat, Snøhvit and Johan Castberg fields and the Wisting discovery. The interval continues to be the main target as hydrocarbon exploration ventures further into this region. However, the package varies considerably in thickness and reservoir quality throughout the basin, and it is therefore very important to understand how this package developed and what has affected it in the time since it was deposited. Here we review controls on the tectonostratigraphic evolution and facies distribution within the Realgrunnen Subgroup, and exemplify the variability in reservoir characteristics within the subgroup by comparing some key wells in relation to their depositional environment and provenance. New provenance data that record a turnover from reworked Triassic- to Caledonian-sourced mature sediment support facies observations which suggest temporal changes in the depositional environment from marine to fluvial. Much of the variability within the subgroup is attributed the tectonostratigraphic development of the basin that controlled accommodation, facies transitions and sediment distribution. This variability is reflected in subtle differences in reservoir quality important both for exploration and production in the remaining underexplored basin.

ABSTRACT Upper Triassic and Lower to Middle Jurassic strata in the Plomosas uplift of central Chihuahua accumulated in backarc and rift settings, respectively. The succession, as much as ~3250 m thick, consists of four stratigraphic units. The Cerro El Carrizalillo Formation (Carnian–Norian), a volcanic-lithic shallow-marine succession deposited in the (newly named) El Carrizalillo backarc basin, is characterized by predominantly Triassic detrital zircon ages. The overlying Plomosas Formation consists of three members: (1) the Cerro de Enmedio Member (Hettangian–Toarcian), a succession of conglomerate, siltstone, and shallow-marine carbonate strata deposited during the onset of extension in Chihuahua; (2) the Cerro Nevado Ignimbrite Member (176 ± 1 Ma; late Toarcian), a widespread ash-flow tuff; and (3) La Sofía Member (Aalenian–Callovian?), consisting of alluvial-fan conglomerate, fluvial sandstone, tidal sandstone and siltstone, and delta-plain red beds characterized by rapid facies changes, lithic compositions, and diverse Proterozoic, Paleozoic, and Triassic detrital zircon ages characteristic of a rift-basin setting. The extensional basin in which the Cerro de Enmedio and La Sofía members accumulated is termed the Plomosas basin. Improved age control provided by U-Pb maximum depositional ages from detrital zircon and U-Pb zircon analyses of the ignimbrite indicates that the Cerro El Carrizalillo Formation is partly correlative with the Chinle Formation of the Colorado Plateau, and the Plomosas Formation is equivalent to eolianites of the Glen Canyon and San Rafael Groups of the Colorado Plateau. Detrital zircon ages and sandstone textures are consistent with both proximal and distal sediment sources along the Laurentia-Gondwana suture and adjoining Grenville basement of Laurentia, including sources in northern Mexico and the composite Appalachian orogen. Although the depositional setting of the Cerro El Carrizalillo Formation was not connected to fluvial systems of the Chinle Formation, subsequent eolian transport of voluminous sediment to the overlying Cerro de Enmedio and La Sofía members from the Colorado Plateau ergs is suggested by the composition and texture of some sandstone, thick siltstone accumulations, and detrital zircon characteristics that broadly resemble those of the Colorado Plateau eolianites. Thick siltstone in the upper part of La Sofía Member is interpreted as deflated fine-grained sediment that was transported downwind from a time-equivalent erg to accumulate in shallow-marine and coastal-plain settings of the Plomosas basin.