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 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 Lower Mesozoic clastic rocks that unconformably overlie Paleozoic rocks within the Northern Sierra terrane provide clues regarding the evolution of the terrane during a 60 m.y. interval spanning the late Carnian through Bajocian. New detrital-zircon data provide fresh insights into the ages and provenance of these clastic rocks, together with new inferences about the Mesozoic tectonic evolution of the terrane. Previous studies have shown that from the late Carnian to the Sinemurian (~40 m.y.), a 1-km-thick section of subaerial to shallow-marine clastic arc-derived sediment accumulated and shallow-marine carbonate was deposited. At the base of this section, detrital-zircon results suggest the Northern Sierra terrane was located near a source area, possibly the El Paso terrane, containing Permian igneous rocks ranging in age from 270 to 254 Ma. By the earliest Jurassic, the detrital-zircon data suggest the Northern Sierra terrane was located near a source containing latest Triassic–earliest Jurassic igneous rocks spanning 209–186 Ma. The source of this material may have been the Happy Creek volcanic complex of the Black Rock terrane. A deep-marine, anoxic basin developed within the Northern Sierra terrane ca. 187–168 Ma. Approximately 3.5 km of distal turbidites were deposited in this basin. Previously reported geochemical characteristics of these turbidites link the Northern Sierra terrane with arc rock of the Black Rock terrane during this interval, except for a short time in the late Toarcian, when the terrane received an influx of quartz-rich sediment, likely derived from Mesozoic erg deposits now exposed on the Colorado Plateau. Clastic deposition within the Northern Sierra terrane ended in the Bajocian. Eruption of proximal-facies, mafic volcanic rocks and intrusion of hypabyssal rock and 168–163 Ma plutons reflect development of a magmatic arc within the terrane. These igneous rocks represent the first unequivocal evidence that the Northern Sierra terrane was located within a convergent-margin arc during the Triassic and Jurassic. Because detrital-zircon data from Lower Mesozoic strata within the Northern Sierra terrane indicate that it was depositionally linked with differing source areas through time early in the Mesozoic, the terrane may have been mobile along the western margin of Laurentia. There is little evidence from sediment within the Lower Mesozoic section of the terrane that can clearly be tied to the craton or the continental-margin Triassic arc prior to the late Toarcian. The absence of Upper Triassic or Lower Jurassic plutonic rocks within the terrane prior to the mid-Bajocian is also consistent with some form of isolation from the continental-margin arc system. While new detrital-zircon results place the Northern Sierra terrane proximal to the western margin of Laurentia in the late Toarcian, the current location of the terrane likely reflects Early Cretaceous offset along the Mojave–Snow Lake fault.

Abstract Carbonate platforms affected by salt tectonics form important hydrocarbon reservoirs. In an effort to gain new insights of the impact of diapirism on carbonate systems we have undertaken an integrated structural and sedimentological study of Jurassic carbonate platforms of the Moroccan High-Atlas basin. In this natural laboratory, the scale of outcrop exposure is similar in area to a large offshore seismic data set, and field observations provide high details on the geometries and facies distributions around diapiric structures. The Atlas intracontinental basin initiated during the Triassic, contemporaneously with Atlantic rifting. The Triassic synrift sequence includes thick shales and evaporite deposits accumulated in multiple tectonic sub-basins. A thick (>5000m) Jurassic sequence was deposited during an overall post-rift stage in a west-southwest/east-northeast shallow-marine basin open towards the NeoTethys. Since the Sinemurian, sedimentation was mainly carbonates. However, geodynamic events linked with the evolution of the Atlantic margin produced several phases of clastic influx leading to the development of mixed systems (Toarcian and Bathonian). During the Early Pliensbachian, an extensional tectonic event triggered synsedimentary diapiric movements which locally lasted until the Cretaceous. These movements were responsible for the development of narrow diapiric ridges of large extent (>100km), controlled by normal west-southwest/east-northeast relay faults. These ridges were separating several kilometers-wide elongated mini-basins, which subsidence was induced by salt/shale withdrawal. Regionally, diapiric movements have been discontinuous in time and space, leading to significant thickness variations within the different stratigraphic units. However, diapirism has not had any major influence on the nature and distribution of sedimentary systems at the basin scale. The impact of diapirs remains essentially localized in the immediate vicinity of these structures (km-scale), where they affected both stratigraphic geometries and facies distribution. This impact appears to be very different in oolitic and mixed ramp systems in which subtle differentiation of depositional profiles controlled progressive facies variations, or in bioconstructed carbonate systems in which diapiric movements had a major role on the location and morphology of platform margins and associated “micro-rim-basins.” In return, the geometry of the diapirs has been clearly influenced by the lithology of surrounding rocks.