The origin and genesis of major Jurassic unconformities within the triple junction area of the North Sea, UK

Abstract

Three Jurassic unconformities of intra-Aalenian, intra-Callovian and intra-middle Oxfordian age are consistently identified within the literature for the North Sea region but despite their common recognition these unconformities remain poorly understood and they are essentially spatially and temporally unconstrained. The recent development of a sequence stratigraphic framework for the Jurassic of the North Sea allows for a thorough investigation of the spatial and temporal characteristics of the intra-Callovian and intra-Oxfordian unconformities and these data have important implications for Middle and Late Jurassic rifting within the North Sea region.The intra-Aalenian unconformity is believed to have been generated as a result of an increase in geothermal gradient within the area and subsequent thermal uplift that preceded rifting. The stratigraphic gap associated with this unconformity increases towards the proposed location of a Middle Jurassic, triple junction centred dome. In contrast the stratigraphic break associated with the intra-Callovian and the intramiddle Oxfordian unconformities is found to increase onto what are now intra-rift highs and rift margin areas. These unconformities occur at the same time as distinct changes in the geometry of the fill of the triple junction and also occur at the same time as seismic scale extension. They do not appear to correlate to any supposed global fall in relative sea-level. Stratigraphic data indicate that three phases of extension occurred during the Callovian, middle and late Oxfordian and lastly during the Kimmeridgian and Volgian. Although the intra-Callovian and intra-middle Oxfordian unconformities can be confused with the effects of the Middle Jurassic North Sea dome unconformity, they are in fact the result of extension during the initial Callovian and Middle/late Oxfordian rift phases. The recognition of these regional unconformities suggests that the Middle and Late Jurassic rifting process was punctuated rather than being continuous.

Tectono-stratigraphic development of the southern part of UKCS Quadrant 15 (eastern Witch Ground Graben): implications for the Mesozoic–Tertiary evolution of the Central North Sea Basin

“…Subsequently, Thomas & Coward (1995), working in the Northern North Sea, have suggested that a Bathonian to Kimmeridgian phase of NW-SE oriented regional extension was superceeded by a separate phase of NE-SW extension in the latest Jurassic to Early Cretaceous, which placed older features, such as the Viking Graben, in sinistral shear. A similar model has been proposed for the Central North Sea area by Davies et al (1999) who proposed W-E extension in the end Bathonian/early Callovian, NW-SE extension in the Middle Oxfordian to Early Kimmeridgian and finally NE-SW extension in the Late Kimmeridgian and Volgian.…”

“…This was interrupted in the Toarcian-Aalenian, probably by the growth and subsequent deflation of a thermally-induced crustal dome centred in the east of the study area (Eynon 1981;Ziegler 1982;Underhill & Partington 1993;Davies et al 1999), which was associated with Bathonian-Callovian volcanism (Forties Volcanic Province; Smith & Ritchie 1993;White & Latin 1993). The age and dimensions (c. 1250 km radius) of this Mid North Sea dome (Ziegler 1982) have been documented by Underhill & Partington (1993) using sequence stratigraphy and analysis of the erosion pattern of the widespread 'Mid Cimmerian unconformity' associated with this event.…”

Altered basement rocks on the Utsira High and its surroundings, Norwegian North Sea

“…Together with a global regression, the consequence was that the seaway connecting the Boreal and Tethys seas was blocked causing deep erosion of Early Jurassic and older sediments (Vail et al, 1977;Ziegler, 1992). Hence, there is a marked unconformity (the midCimmerian or intra-Aalenian unconformity) separating the Lower Jurassic from the Middle and Upper Jurassic in the region (Davies et al, 1999) (Fig. 3).…”

North Sea hydrocarbon systems: some aspects of our evolving insights into a classic hydrocarbon province

“…They considered the amount of uplift associated with the transient mantle plume to have been in the region of 400 -500 m, somewhat less than earlier estimates. Davies et al (1999) highlighted the minimal impact of the deflating dome on the stratigraphic architecture of the succeeding Late Jurassic rift. Underhill and Partington's (1993) detailed stratigraphic correlations and analyses demonstrated the regional overstep of the Middle and Late Jurassic across the unconformity, truncation patterns to the north and west, facilitated by the well-constrained stratigraphies of the Viking Graben and Inner Moray Firth respectively.…”