The Flamborough Tertiary outlier, UK southern North Sea

Abstract

A previously unrecorded outlier of Tertiary sediments is described from blocks 42/29 and 47/4b on the northeast corner of the East Midlands Shelf, southern North Sea, UK. Biostratigraphy in well 47/4b-6 indicates the presence of lateral time equivalents of the Horda, Balder-Sele and Lista Formations, the only occurrence of Tertiary sediments on the East Midlands Shelf. The outlier is 50 km from the Humberside coast, 30 km west of the nearest Tertiary sediments. The Tertiary strata subcrop thin Recent deposits over an area of 104 km 2 , and reach a maximum thickness of 700 m. Erosive truncation of these sediments shows that they are remnants of a more extensive Palaeogene cover on the East Midlands Shelf and they constrain the timing of inversion on the Dowsing Fault Zone and growth of the Sole Pit High. The outlier is compartmentalized in terms of structural style into an unfaulted westerly portion which is oval in outline, and an adjoining northwest-southeast trending graben. The contrasting geometries of these compartments reflect salt-controlled synclinal folding and thin-skinned extensional faulting detaching on Triassic salt respectively. Both mechanisms are effects of basinwards sliding of the Sole Pit High Mesozoic section upon Permian salt, triggered by Tertiary inversion on the Dowsing Fault Zone. Unconformities associated with the outlier indicate an initial, intra-Campanian phase of inversion, followed by two later episodes which may correlate with late Maastrichtian and intra-Miocene events recorded further south and east. The Palaeogene sediments within the outlier represent part of the eroded cover of the East Midlands Shelf predicted to have been present by sonic log-based studies of apparent exhumation.