Source‐to‐sink mass‐balance analysis of an ancient wave‐influenced sediment routing system: Middle Jurassic Brent Delta, Northern North Sea, offshore UK and Norway

Abstract

AbstractSediment mass‐balance analysis provides key constraints on stratigraphic architecture and its controls. We use the data‐rich Middle Jurassic Brent Delta sediment routing system in the proto‐Viking Graben, Northern North Sea, to estimate sediment budgets and mass‐balance between source areas and depositional sinks. Published studies are synthesised to provide an age‐constrained sequence stratigraphic framework, consisting of four previously defined genetic sequences (J22, J24, J26, J32). Genetic sequence J32 (3.9 Myr) records transverse progradation of basin‐margin deltas, sourced from the Shetland Platform to the west and Norwegian Landmass to the east. Genetic sequences J24 (1.1 Myr) and J26 (0.9 Myr) record the rapid progradation and subsequent aggradation of the Brent Delta along the basin axis, sourced from the uplifted Mid‐North Sea High to the south, and the western and eastern source regions. Genetic sequence J32 (2.2 Myr) records the retreat of the Brent Delta. Sediment budgets for the four genetic sequences are estimated using palaeogeographical reconstructions, isopach maps, and sedimentological analysis of core and well‐log data. The estimated net‐depositional sediment budget for the mapped Brent Delta system is 2.0–2.8 Mt/year. Temporal variations in net‐depositional sediment budget were driven by changes in tectonic boundary conditions, such as the onset of uplift before the deposition of genetic sequence J24. Over the same time period, the Shetland Platform, Norwegian Landmass and Mid‐North Sea High source regions are estimated to have supplied 2.3–5.6, 5.0–14.1, and 2.8–9.4 Mt/year of sediment, respectively, using the BQART sediment load model and independent geometrical reconstruction of eroded volumes, which are constrained by isostatic uplift estimates based on the geochemistry of syn‐depositional volcanic rocks. The net‐depositional sediment budget in the sink is an order‐of‐magnitude smaller than the total sediment budget supplied by the source regions (13.9–23 Mt/year). This discrepancy suggests that along‐shore transport by wave‐generated currents into the coeval Faroe‐Shetland Basin and/or down‐dip transport by gravity flows into the coeval western Møre Basin played a key role in redistributing sediments away from the Brent Delta system.