Log-motif analysis of Paleogene oppositional systems tracts, Central and Northern North Sea: defined by sequence stratigraphic analysis

Abstract

Sequence stratigraphic analysis of North Sea Eocene and Paleocene seismic-reflection profiles and well data provides examples of lowstand, transgressive and highstand systems tracts, including the 'basin-floor thick', 'slope thick' and prograding-wedge facies of the lowstand systems tract. This study was initiated to evaluate the interpretation methodology, refine the biostratigraphic control and test the Vail-Exxon depositional model prior to undertaking a more regional study. The primary data consisted of 4200 km of multifold seismic reflection profiles distributed in a 20 km grid, calibrated using log suites from 45 wells including 37 with biostratigraphic data. Thirty-two micropalaeontologic bioevents from top Cretaceous to top Eocene were evaluated. Twenty-three bioevents were identified as useful chronostratigraphic markers and were used to constrain both well-log and seismic reflection profile correlations. In general, the mapped systems tracts are more spatially separated than suggested by the diagrammatic Vail-Exxon model and require biostratigraphic correlation to confirm temporal relationships. Many of the lowstand systems tracts appear to be line-sourced by several sediment-supply systems. Ten Paleocene and Eocene sequences were recognized in this study, compared to 22 on the Cenozoic cycle chart. The remaining 12 Cenozoic sequences are either absent or are coalescent and below the resolution of this study.

Architectural element analysis of turbidite systems, and selected topical problems for sand-prone deep-water systems

“…Relative lowstands in sea Ievel tend to be associated with lowstand turbidite currents as basin-floor and/or slope fans, for example, as has been demonstrated for the Paleogene of the Central and northern North Sea (Armentrout et al 1993;Den Hartog Jeger et al 1993;Galloway et al 1993;Vining et al 1993). This is because a fall in relative sea Ievel, which may be eustatically driven, Ieads to the effective narrowing of shallow-marine shelves and the propensity for fluvial/coastal systems to prograde towards, even reaching, the shelf-slope break.…”

Sequence and systems tract interpretation of the epicontinental Oligocene deposits in the Danish North Sea

“…Van Wagoner et al 1988). To distinguish between these two systems tracts, it is, among other things, important to examine whether a thick prograding deposit is located landwards or basinwards of the depositional shoreline break of the preceding sequence (Armentrout et al 1993). We have therefore arranged our log-profiles in Figs 5, 7, 8 and 9 in accordance with the palaeotopography interpreted from the seismic sections, assuming an even and gently southwestward dipping sea floor.…”

“…This systems tract tends to be a thin, mud-dominated interval, and the coeval basinal facies is sediment starved, forming part of the condensed section (Armentrout et al 1993).…”

“…According to Armentrout et al (1993), this systems tract includes log patterns of aggrading and prograding, upward coarsening parasequences.…”

Sequence stratigraphy in British geology

“…In studies using subsurface data, regional correlation of supposed maximum flooding surfaces within shallow marine strata is commonly based largely on correlation of gamma-ray maxima, thought to be generated by relatively argillaceous intervals within sandstones, organic-rich intervals within mudstones, or mineralized surfaces within a condensed section (see for discussion : Milton et al 1990;Partington et al 1993a, b;Creany & Passey 1993;Armentrout et al 1993;Hesselbo 1996). Two papers within this volume address different aspects of this topic.…”