The tectono-stratigraphic development and hydrocarbon habitat of the offshore southwestern British Isles and northwestern France
File(s)
Author(s)
Sheyh Husein, Sami
Type
Thesis
Abstract
Southwest Britain's sedimentary basins have been shaped by multiple superimposing tectonic events since the Variscan. Despite decades of hydrocarbon exploration and a significant subsurface database, the Western Approaches Trough and the South Celtic Sea region remain unprospective, with considerable knowledge gaps in their stratigraphy, tectonic processes, and petroleum systems. The results show that the Base Cretaceous Unconformity resulted from multiple erosional episodes during the Mid-Jurassic, Late Jurassic, Early Cretaceous and mid Cretaceous. These are linked to Variscan fault reactivation and the rift-to-drift transition of the Bay of Biscay. Importantly, the expanded mapping of Variscan structures in the Western Approaches and Brittany basins demonstrate how their reactivation potentially played a role in controlling denudation patterns during the Mid to Late Jurassic and Early Cretaceous. A novel finding is the discovery that the Upper Triassic salt as a more widespread, ductile regional seal that preserves hydrocarbon accumulations from breaches during the Jurassic and Cretaceous tectonism. Subsidence modelling reveals that simple syn-rift models underestimate observed subsidence magnitudes, suggesting denudation and a possibly tectonic component in the South Celtic Sea and Melville basins. Petroleum systems modelling identifies high risks associated with hydrocarbon charge timing and trap preservation, but highlights several viable pre-salt plays sourced by mid-Late Carboniferous source rocks. This study improves the geological understanding of Southwest Britain and Northwest France, contributing to a foundation for future exploration and resource assessment. It contributes to the wider understanding of post-Variscan basin evolution in Northwest Europe and offers explanations for how spatially and temporally distinct tectonic and denudation events can combine to generate large-scale composite unconformities.
Version
Open Access
Date Issued
2025-07-20
Date Awarded
2026-02-01
Copyright Statement
Attribution-NonCommercial 4.0 International Licence (CC BY-NC)
License URL
Advisor
Fraser, Alastair
Roberts, Gareth
Bell, Rebecca
Publisher Department
Department of Earth Science & Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)