Although the ‘Mid-Cimmerian event’ or unconformity has been recognized over much of Europe, its exact stratigraphic relations and causal mechanism have remained unclear. Application of a genetic sequence stratigraphic approach (using 17 marine condensed sections and maximum flooding surfaces) to Jurassic sequences across NW Europe allows the stratigraphic succession to be subdivided into a series of time-slices (genetic stratigraphic sequences) and allows the true nature of the unconformity to be determined. They indicate that the main event’s correlative conformity falls in the Aalenian near the break between theopalinumandmurchisonaeammonite biochronozones. Further study of the associated spatial and temporal variation indicates that systematic truncation of stratigraphy occurred throughout the North Sea domain (the oldest stratigraphies subcrop in areas adjacent to the triple junction) with subsequent progressive onlap towards the same area. When integrated with igneous evidence, these observations are interpreted to confirm regional (Toarcian–Aalenian) domal uplift, resulting from the impingement of a broad-based (> 1250 km diameter), transient plume head or ‘blob’ at the base of the lithosphere. Progressive pre-rift, Aalenian–early Bathonian marine onlap records differential subsidence in response to the initial deflation of the dome while central regions may have continued to rise. Subsequent subsidence post-dated Bathonian–Callovian volcanism but still pre-dated the timing of most significant (Kimmeridgian–Volgian) rifting. Such temporal relations demonstrate that North Sea volcanism is inconsistent with a classic ‘passive’ rift model. Instead, it seems more appropriate to equate Mid–Late Jurassic North Sea development with an ‘active’ rift model following mantle-driven thermal doming.Integration of sedimentation patterns with basin development suggests that the early Toarcian–early Kimmeridgian succession records a long-term, second-order regressive–transgressive episode related to regional tectonism. Comparison with the current chart of coastal onlap and global sea-level change highlights the correlation of the Intra-Aalenian event with one of the most significant regressions (the 177 Ma event separating the Absaroka and Zuni first-order megacycles). The knowledge that this part of the curve appears to be based exclusively on sections from Dorset and Yorkshire, within and adjacent to the region affected by regional doming, suggests that there remains a need to test this part of the chart using sections from outside the uplifted area and emphasizes the impracticality of using just two relatively closely spaced sections in trying to define a truly global signal. Clearly, sections should be taken from several areas and preferably from different plates as tectonically uncoupled as possible. Until then, the worry will remain that regional tectonic events could overprint any global signal and be erroneously interpreted as abrupt changes in global eustasy. The fact that doubts such as these can be cast upon parts of the eustatic sea-level chart suggests that it is still someway off being a valid global standard with true predictive capabilities.

No abstract

Thirty-three regionally correlatable marine condensed sections containing maximum flooding surfaces have been recognized in the area allowing the North Sea Jurassic succession to be subdivided into 32 genetic stratigraphic sequences (sensuGalloway). Each event is biostratigraphically calibrated using microfossils (dinoflagellate cysts, radiolaria, ostracoda and foraminifera). The new scheme provides the basis for a basin-wide stratigraphic framework for the Jurassic of the North Sea basin.

No abstract

We integrate observations of lithospheric extension over a wide range of spatial and temporal scales within the northern North Sea basin and critically review the extent to which existing theories of lithospheric deformation can account for these observations. Data obtained through a prolonged periodofhydrocarbon exploration and production has yielded a dense and diverse data set over the entire Viking Graben and its anking platform areas. These data show how syn-rift accommodation within the basin varied in space and time with sub-kilometer-scale spatial resolution and a temporal resolution of 2{3 Myr. Regional interpretations of 2D seismic re ection, refraction and gravity data for this area have also been published and provide an image of total basin wide stretching for the entire crust. These image data are combined with published strain rate inversion results obtained from tectonic subsidence patterns to constrain the spatio-temporal evolution of strain accumulation throughout the lithosphere during the 40 Myr (170{130 Ma) period of Late Jurassic extension across this basin. For the rst 25{30 Myr, strain localisation dominated basin development with strain rates at the eventual rift axis increasing while strain rates over the anking areas declined. As strain rates across the whole basin were consistently very low (< 3x10 ;16 s ;1 ), thermally induced strength loss can not explain this phenomenon. The strain localisation is manifest in the near-surface by a systematic migration of fault activity. The pattern and timing of this migration are inconsistent with exural bending stresses exerting an underlying control, especially when estimates of exural rigidity for this area are Preprint submitted to Elsevier Science 31 January 2005 considered. The best explanation for what is observed in this time period is a coupling between near-surface strain localisation, driven by brittle (or plastic) failure, and the evolving thermal structure of the lithosphere. We demonstrate this process using a continuum mechanics model for normal fault growth that incorporates the strain rate-dependence of frictional strength observed in laboratory studies. During the nal 10 Myr of basin formation, strain accumulation was focused within the axis and strain rates declined rapidly. Replacement of weak crust by stronger mantle material plus crustal buoyancy forces can adequately explain this decline.