Enigmatic Large-Scale Furrows of Miocene to Pliocene age from the Central North Sea: Current-Scoured Pockmarks?

This work presents seismic-stratigraphic, geometric and basinal descriptions for Middle and Late Miocene to Early Pliocene furrows from a deepwater intracratonic setting, based upon regional three-dimensional (3D) seismic data and supporting well information for the UK central North Sea. A range of erosional cross-sectional geometries, typically 1.5 km in width, display a continuum between V- and U-shapes with amalgamation producing complex geometries. Plan-view geometries show an evolution from circular to elongate teardrop and linked/complex structures, whilst seismic infill facies are planar, onlapping, divergent, transparent/opaque or complex. The circular structures (~1 km wide) resemble gas escape pockmarks, especially those in the Cainozoic of the adjacent Danish sector, whilst the linear furrows exhibit varying degrees of elongation and are often asymmetric in the direction of inferred bottom-current flow. A model is presented of initial pockmark crater formation, followed by bottom-current elongation and subsequent amalgamation of these structures to form furrows often over 25 km long. 3D seismic mapping of furrow asymmetry demonstrates a NW–SE trend in the west of the study area, rotating to SW–NE in the east, which supports the idea that an anticlockwise current system existed in the North Sea basin in the Neogene. Well data reveal that these structures contain a mixture of siltstone and carbonate stringers, associated with acoustic disturbance zones possibly indicative of palaeo-gas chimneys. These findings present an important update to the model governing furrow formational mechanisms in deepwater intracratonic settings with, in particular, an origin linked to down-slope pro-Skagerrak delta processes dismissed. This has implications for the velocity models used by the hydrocarbon industry and our understanding of regional pockmark activity during the Neogene in the central North Sea.