Timing and mode of Paleogene deformation on the Southern North Sea Cleaver Bank High and its relation to uplift of the British Isles

Abstract

The aim of this project is to gain better constraints on the relative timing of uplift of the British Isles and Pyrenean shortening phase and to better understand the role of each in the Late Paleogene deformation on the Cleaver Bank High (CBH) and the southern North Sea in general. An exhaustive characterization of the stratigraphy and morphology of Late Paleogene deposits on the Cleaver Bank High area was carried out to make a differentiation between pre-, syn- and post-tectonic sedimentation. The analysis of seismic reflections geometry and seismic facies of regional 2D seismic lines of public access, along with well data, has allowed to identify and map a surface defining the onset of folding and estimate an age to it of Mid-Eocene, hence finding the probable time of salt tectonics initiation. Observations and evidence for gravity gliding as the driving force were used to conclude on the reigning type of deformation. The onset of folding was later used to guide a horizon flattening analysis to inquire for the first time in the southern North Sea into the plausible relationship of the southern British Isles uplift -and consequent basement tilt change- with the observed gravity gliding in the CBH area. The results showed a correspondence between the amount of exhumation of the southern British Isles with the stretching of Neogene deposits to the southwest and the basement dip change in some of the analyzed seismic lines. Given the close genetic relationship between the exhumation episodes and the tectonic phases from the Alpine collision, it is inferred that by the time the ‘onset of folding’ succession started to deposit the Laramide tectonic phase would have already acted and provided part of the total uplift, while the Pyrenean phase would have had a greater impact in providing the remaining amount of uplift necessary to finally reverse the basement dip from southwest to northeast and allow for imminent gravity gliding -and consequent folding- since Mid-Late Paleogene to present times.