OR/15/069 Model rules, use, limitations and uncertainty

Waters, C N, Terrington, R, Cooper, M R, Raine, R B, and Thorpe, S. 2015. The construction of a bedrock geology model for the UK: UK3D_v2015. British Geological Survey Internal Report, OR/15/069.

Model rules

• Wherever possible the 1:625 000 scale bedrock geology linework and stratigraphy were adopted in the section construction. In practice it was necessary to simplify some of the detail in terms of minor intrusions, minor faults and lithological facies variations within individual units. In the nearshore area, where 1:625 000 scale bedrock geology linework is not available, the 1:250 000 scale dataset was used. In Northern Ireland 1:10 000 scale bedrock linework was used locally to demonstrate the potential effects of faulting on the geometry of subsurface units.
• Significant faults are depicted as offsets of the stratigraphic units rather than as actual fault objects within the workspace.
• Superficial geology is excluded from the sections. This implies that where superficial deposits are present the bedrock unit floods up to the DTM (surface) in sections. In general the thickness of superficial deposits is insignificant at the intended model resolution.
• The depth cut off is variable depending on the nature of geology, it is generally 1.5–3 km but lies deeper where major aquifers and potential mineral or hydrocarbon sources are present within sedimentary basins.
• A false horizontal base at an arbitrary depth has been constructed for some units to provide a base for the section, these should not be interpreted as true bases for these units.
• Boreholes are hung from the given OD start height in most cases. Where a start height is not provided on the borehole log, the borehole was hung from the DTM.

Use of the model

Appropriate applications for the UK3D_v2015 dataset include the following:

• geoscience communication and education to illustrate national and regional British geology (from the available download);
• illustrating national or regional bedrock geology overviews for scientific publications for widespread and/or non-specialist use e.g. radwaste (Powell et al. 2010), shale gas (Mathers et al. 2012a) with an intended resolution of use in the 1:250 000–1:1 million range;
• catchment-basin scale first-order calculated volumes of structurally simple stratified geological units performed in GSI3D and exported. These have been mainly used to-date for hydrogeological modelling;
• regional GIS projects including the extents (x, y) of individual geological units (generated for use in GIS from GSI3D).

Limitations

Limitations inherent in the UK3D_v2015 dataset preclude such applications as:

• detailed geological assessments of any kind, e.g. borehole, site or linear route prognosis;
• resource-reserve estimation and exploration of any kind;
• any representation or use outside the intended regional to national (1:250 000–1:1 million) resolution range.