Sequence stratigraphic subdivision of the Humber Group in the Outer Moray Firth area (UKCS, North Sea)

Abstract

Abstract The Humber Group (Late Oxfordian-Ryazanian) in the Outer Moray Firth has been subdivided into 19 depositional sequences, which are firmly related to a newly defined, consistent biostratigraphic framework. Each sequence has been defined by core sedimentology (where possible), biostratigraphy and electric log patterns. In non-marine to shallow-marine environments (e.g. Piper Formation sensu lato ), well-defined transgressive and highstand (or regressive) systems tracts are recognized, which are extensively cored in the area due to their importance as reservoirs of major fields. In younger sections, sequence recognition is based on the presence of submarine fans and maximum flooding surfaces; sequences so defined are to some extent supported by the cyclicity of equivalent shallowmarine sand sequences near the basin margins. The sequence stratigraphy approach has clarified the lateral stratigraphic relationships of reservoir sand units within the Tartan Field, and the relationships between the reservoir sand units in the Tartan, Highlander and Petronella fields. The main causes of the observed cyclic sedimentation are interpreted as the complex interplay between sediment supply, subsidence rates and eustasy. Although the relative importance of the last two remains unclear, the sequence stratigraphic approach followed here has allowed rigorous description and consistent interpretation of vertical and lateral facies associations.