Late Palaeozoic structural evolution of the Patch Bank Ridge and Utsira High, northern North Sea

This study focuses on the Late Palaeozoic development of the area east of Utsira High in the North Sea, where the stratigraphic section below the late Permian Rotliegend Group is undrilled. We use regional 3D seismic data to study structuring, sediment distribution and geomorphology across the Patch Bank Ridge and Utsira High in the North Sea. The results show that the Stord Basin and the bounding Utsira East fault initially developed during the Late Palaeozoic extension, probably during the Devonian, and that the Utsira Shear Zone controlled the location of Late Palaeozoic depocentres. The Patch Bank Ridge is an uplifted part of the Stord Basin where we identify Late Palaeozoic growth strata along the southern and northern flanks, indicating a similar timing of the structural evolution in this area. Two key wells, in the Sele High and Ling Depression, are used to relate a Late Palaeozoic isopach map with regional structuring, surface tilt and basement morphology to the enigmatic parts of the Late Palaeozoic basin system. Our results supplement regional models for the Late Palaeozoic basin development, we suggest that the deeply eroded Devonian half-grabens preserved on the Utsira High formed parts of an extensive basin system that show stratigraphic expansion towards their bounding faults. The Top Basement surface at these highs offers several distinct geomorphologies that evolved during three periods of exposure, expressed as (i) a tilted and rugose landscape, (ii) distinct drainage networks and (iii) peneplain surfaces. Cover sediments place these landscapes to the (i) Devonian, (ii) Carboniferous/Permian/Triassic and (iii) Late Triassic periods. The Top Basement surface of the Patch Bank Ridge and Utsira High is the result of diverse periods of erosion leading to various geomorphic expressions. (a) Utsira High Triassic peneplain (P in e) surface. The following three examples are from Patch Bank Ridge. (b) The southern flank has a rugose (R in e), mountainous appearance dipping steeply into the Ling Depression, (c) a mountainous appearance closer to its original orientation, and (d) cross-section the Patch Bank Ridge peneplain (P in e) surface with minor incisions. (e) The Top Basement depth structure map with distinct morphologies (P, R and DN). Location of close-up sections in (a-d) are indicated.image