3D seismic characterisation of igneous sill complexes in sedimentary basins: North-East Atlantic Margin
This thesis compiles the results of a 3D seismic-based study of the geometry and emplacement mechanics of igneous sills and sill complexes intruded into basins along the NE Atlantic Margin. Dolerite sills were intruded into the Upper Cretaceous and Paleocene mud-dominated sediments of these basins d...
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| Format: | Thesis |
| Language: | English |
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2004
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| Online Access: | https://orca.cardiff.ac.uk/id/eprint/55377/ https://orca.cardiff.ac.uk/id/eprint/55377/1/U200366.pdf |
| Summary: | This thesis compiles the results of a 3D seismic-based study of the geometry and emplacement mechanics of igneous sills and sill complexes intruded into basins along the NE Atlantic Margin. Dolerite sills were intruded into the Upper Cretaceous and Paleocene mud-dominated sediments of these basins during the Paleocene and Early Eocene, approximately synchronous with the onset of seafloor spreading between NW Europe and Greenland. Detailed interpretation of igneous intrusions in four case-study areas has revealed that sills adopt a wide range of geometries, ranging from near-concordant sheet-like forms to complex discordant forms. Detailed mapping illustrates that the traditional definition of a sill as 'a tabular igneous intrusion with concordant surfaces of contact' is inadequate when describing the fully three-dimensional geometry of sills. This has encouraged the development of a new classification scheme for igneous sills that considers their detailed three-dimensional geometry. Many sills have been found to adopt a saucer-shaped geometry and these are interpreted to form through a three-step model involving lateral propagation, inflation and overburden deformation, and intrusion along deformation-related peripheral fractures. 3D seismic mapping has allowed for igneous sill complexes to be imaged in three dimensions for the first time. These complexes are found to form highly interconnected networks that cover many kilometres of vertical section (∼8 km). Based on the interpretation a new model for the construction of sill complexes is proposed. In this model a sill complex builds up from deeper to shallower levels with sills intruded at one stratigraphic level acting as feeders for sills intruded at shallower levels. Interpretation of hydrothermal mounds and jack-up structures formed during sill intrusion has allowed for the timing of sill emplacement to be constrained in the four case-study areas. This has revealed that several discrete phases of intrusion took place during the Paleocene and earliest Eocene |
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