Sequence stratigraphic analysis is now carried out routinely on Mesozoic-Cenozoic sedimentary basins with a view to understanding their post-rift stratal geometries and predicting facies architecture. The conventional method embodies two concepts; the physical division of strata into unconformity-bounded units and their genetic interpretation on the assumption that hierarchical changes in sea-level represent the primary control on sedimentary architecture. The genetic model is reflected in a complex descriptive terminology and derives from the development of the method in shallow-water basins, where the results of analyses typically accord with geological data constraints. Applied to deep-water underfilled basins, however, the sea-level assumption yields results that are unsatisfactory and in many cases misleading, reflecting the influence of additional controls, including tectonic movements, deep-sea currents and climate (e.g. glaciation) on stratal geometries and facies architecture. This is illustrated by comparative analyses of examples from the deep-water Cenozoic basins of the NW European Atlantic passive margin, which contain a set of seismic megasequences, bounded by unconformable to conformable surfaces, correlative from shelf to slope to basinal settings. The deep-water successions contain regional, locally diachronous, submarine unconformities that were generated in response to changes in deep-water current circulation and slope processes, rather than subaerial erosion. These bound aggradational contourite drifts that include upslope accretion against basin margins. The deep-water successions interfinger at two levels with seaward-prograding shelf-slope wedges that reflect differential tectonic movements, involving coeval uplift and subsidence. The youngest wedges formed in the last 4 Ma and record seaward progradation of the margin by up to 100 km, overprinting high-amplitude variations in sea-level and coeval with changes in deep-ocean currents. Sediment supply by fluvial sources gave way in the Pleistocene to direct glacial sediment supply to the slope. In all these instances, the stratal geometries and facies architecture cannot be attributed to a simple lowering of regional sea-level, but instead reflect a complex interplay of controlling factors including tectonic movements, changes in sediment supply, deep-water current activity and climate, in addition to sea-level. Sequence stratigraphic analysis in such settings must recognise and evaluate alongslope, downslope and vertical components of sediment supply.
- Programområde 3: Energiressourcer