Faults exert control over the formation of basins and are geometrically complex 3Dstructures. Several industries rely on characterisation of the subsurface and faults are an important component of subsurface models. Faults are poorly constrained in subsurface data sets and by necessity are approximated to planar membranes. To adequately characterise faults in 3D it is necessary to study exhumed faults in the field.The architecture of basin margin faults has received relatively little attention in the literature (Caine et al 2010 and Kristensen et al 2016 are notable exceptions). The North Solway fault is a basin margin fault exposed at the boundary of the Southern Uplands and the Solway-Northumberland trough. The fault offsets Lower Palaeozoic lithologies (basement) against Lower Carboniferous sediments. The North Solway fault is a rare example of an onshore fault with a basement footwall and sedimentary hanging wall. The fault is exposed in extensive along-strike and limited down-dip direction in a number of localities which are accessed at low tide.Field data is used to interpret the internal architecture and fault scale geometry of the North Solway fault. Sketches, descriptions and detailed mapping have been carried out and are complemented by quantitative data from scanlines, image analysis and orientation data.This study shows that the North Solway fault has a complex zig-zag plan-view geometry which has been offset by major cross faults. Simple segment linkage models are not adequate to describe the plan-view geometry of the fault. Fault throw can only be constrained to between 100m and 1500m, demonstrating the difficulty in characterising large faults. The internal architecture of the fault is shown to be a product of host lithology,deformation style, depth and fluid flow. The coupling of sedimentary processes and tectonic activity is demonstrated at the basin margin. Predictive algorithms which are used for faults within basins are not applicable in faults with a basement footwall. The textures within fault rocks such as gouge and breccias are shown to give an indication of the mechanical state of the fault at the time of deformation. Contrasting fault zone internal structures are observed where the fault is interpreted to be the result of either basement-basement faulting or basement-sedimentary faulting. The results of this study show that large basin bounding faults are highly variable in both down-dip and along-strike directions.
|Date of Award||20 May 2018|
- University Of Strathclyde
|Supervisor||Zoe Shipton (Supervisor) & Rebecca Lunn (Supervisor)|