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.