Review and computer modelling of the Brent Group stratigraphy

Summary The depositional history of the Brent Delta system can be analysed on three different levels: (i) the individual formations and their facies distribution, used for the interpretation of the depositional processes; (ii) the vertical succession of formations in each well, indicating the temporal changes in environment; (iii) the two- or three-dimensional array of sequences illustrating both the temporal and spatial variations within the delta system. The Brent Group is essentially one regressive-transgressive megacycle. The regressive part comprises the Rannoch and Etive Formations (delta front) and the lower Ness Formation (delta plain), and the transgressive system contains the Tarbert Formation (delta front) and the (upper) Ness Formation (delta plain). With the aid of a computer program, the succession geometry can be analysed in terms of the relative importance of sediment supply, eustasy and tectonics. The change from regressive to transgressive conditions was probably initiated by an increase in subsidence rates, whereas regressive pulses in the overall transgressive Tarbert Formation can be explained in part by eustatic sea-level falls.