Quantitative analysis of net‐transgressive shoreline trajectories and stratigraphic architectures: mid‐to‐late Jurassic of the North Sea rift basin

Abstract

ABSTRACTThis paper outlines the use of the shoreline trajectory concept to understand the controls on net‐transgressive reservoir distribution and architecture in the highly productive Middle and Late Jurassic plays in the North Sea. Two broad groups of regressive–transgressive sandstone tongue are identified, with distinctive geometries, architectures and values of net‐transgressive shoreline trajectory defined by the stacking arrangement of multiple tongues. Shoreface tongues were supplied by longshore‐transported, marine‐reworked sediment and are associated with low‐to‐moderate transgressive trajectories (typically <0.2°). These tongues have variable dip extents that decrease weakly as the angle of shoreline trajectory increases, relatively small thicknesses that increase weakly with the angle of transgressive trajectory, and partial or no overlap with underlying and overlying tongues down depositional dip. Deltaic‐to‐estuarine tongues were supplied directly by fluvial sediment and are associated with moderate‐to‐very high transgressive trajectories (typically >0.1°). These tongues have small dip extents, variable thicknesses that increase weakly with the angle of transgressive trajectory, and partial to full overlap with underlying and overlying tongues down depositional dip, although vertically stacked tongues are separated by thin mudstones over much of their extents. There is some overlap in geometry and stacking arrangement of these two groups of sandstone tongues. The temporal and spatial distribution of shoreface and deltaic‐to‐estuarine sandstone tongues reflects linked variations in tectonic subsidence and sediment routing within the evolving rift basin. Deltaic‐to‐estuarine tongues with moderate‐to‐very high transgressive trajectories were developed in rapidly subsiding fault‐bounded depocentres supplied directly by fluvial sediment, whereas shoreface tongues with low‐to‐moderate transgressive trajectories characterised slowly subsiding fault terraces and platforms that were distant from fluvial sediment supply routes. Thus, the evolving structural template of the mid‐to‐late Jurassic North Sea rift can be used to predict reservoir distribution and architecture via analysis of shoreline trajectory.