The mechanics of sill propagation and associated venting,
investigated using 3D seismic data from offshore Norway.
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This thesis reports on over 27 sills and 213 associated vents. The sills and vents were investigated using 3D seismic data, in a ~1000 km2 area, offshore Norway between the Møre and Vøring Basins (the Edvarda survey). A wide range of sill geometries are observed which are interpreted to be the result of five different processes acting on the sills. Three of these processes relate to how the host deforms. If sill intrusion causes deformation of the seafloor, creating folds, or the sills interact with folds created by neighbouring sills, sills are found to cross bedding (transgress) abruptly. Alternatively, if deformation is interpreted to be local, then continuously increasing Young’s Modulus with depth is interpreted to result in sills which transgress continuously upwards, akin to smooth ‘bowls’. At shallow depths the host is interpreted to fluidise, leading to limited transgression or in some cases multiple bowls. The seismic amplitude responses of shallow sills include flow related features such as channels and lobes. The other two processes interpreted to affect sill propagation stem from structures in the host: abrupt changes in lithology and pre-existing faults. Multiple sills are found to terminate, and in some cases form, at sand rich units in the otherwise mudstone dominated host. Additionally, some sills are interpreted to have intruded into a host with pre-existing polygonal faults, which led to angular sill geometries. Vents are found to occur directly above sills, often along the margins of sills, but in some cases over sill interiors, especially where the sills are locally shallower. Additionally, a cluster of 98, relatively small vents occur above the shallowest sill. Differential compaction and slumping are found to affect some larger vent morphologies. Overall, vent size is found to closely follow a power-law such that smaller vents are significantly more numerous than larger vents.
|Item Type:||Thesis (PhD)|
|Schools:||Earth and Ocean Sciences|
|Subjects:||Q Science > QE Geology|
|Last Modified:||19 Mar 2016 23:58|
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