OR/15/074 Model assumptions, geological rules used etc
| Ambrose, K. 2015. GSI3D model metadata report for HS2 Area 8 (Drayton Bassett to Rugeley). British Geological Survey. (OR/15/074). |
First order river terrace deposits (RTD1-XSV) are modelled beneath alluvium where the two units are adjacent to each other. Figure 11 shows the distribution of these units, with a transparency applied to alluvium (pale yellow) to show the extent of RTD1-XSV (orange) modelled underneath.
Similarly, the extents of older glacigenic units are extended beneath younger Quaternary units. For example, Mid-Pliestocene glaciofluvial deposits (GFDMP-XSV) is extended beneath alluvium and second order river terrace deposits (RTD2-XSV).
In the glacial sediments an arbitrary line was used to determine the western limit of Anglian aged (Mid Pleistocene) superficial deposits, with all those to the west of northing 414 modelled as Devensian age. This necessitated the re-attribution of some of the superficial geology polygons.
An arbitrary decision made to define western limit of Anglian age (MP) superficial deposits, with all those west of around northing 414 attributed as Devensian age and modelled accordingly.
In some bedrock units the mapped subdivisions have been combined into single geological units. For example, all mapped units in the Keresley Member (KRS) are modelled as KRS-ARSC and all mapped subdivisions in the Whitacre Member have been combined into WIT-MDSD in the model.