OR/18/046 What geology do the GV Models show

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Whitbread, K, and Ritchie, C. 2018. Regional Geological Visualisation Models. Nottingham, UK, British geological Survey. (OR/18/046).

Within UK3D v2015 and DiGMapGB-625, the geology is characterised using combined lithostratigraphic and chronostratigraphic frameworks consistent with the BGS Lexicon at the times of their publication (2016 and 2007 respectively). The succession of strata is typically at Group level, however Formation level strata are included in UK3D v2015 sections in some areas, providing additional detail for parts of the succession — notably in the Chalk of southern and eastern England. Note that the formation-level detail in the UK3D sections is not reflected in the geological map at the ground surface.

The UK3D v2015 sections postdate DiGMapGB-625. The geological framework used in the construction of the UK3D v2015 sections includes recent stratigraphical revisions that are not reflected in DiGMapGB-625. In most cases, the effect of differences in lithostratigraphical attribution of units between the map and the model is minor at the scale of the GV Models. In a few cases, the stratigraphical revisions have involved changes to the attribution of the Group Level stratigraphy, for example to the Yoredale Group and Millstone Grit Group in parts of northern England, and the Warwickshire Group replacing part of the South Wales Upper Coal Measures Formation in South Wales, leading to apparent discrepancies between the UK3D v2015 and DiGMapGB-625 distributions of these units.

Some structurally complex zones, particularly those associated with minor igneous intrusions, may be represented in the surface geological map but not in the UK3D cross-sections. This is due to the relatively small scale of many of these features and limited constraint on the geometry of such structures at depth.

Superficial deposits which occur as a relatively thin layer of recent sediments overlying bedrock in many onshore and offshore areas are not shown within the models. Superficial deposits are typically thin (<10 m) in onshore areas, however thicker accumulations do occur locally. Sea bed sediments are also present in inshore areas, where they are typically considerably thicker than superficial deposits onshore. The absence of superficial deposits within the model represents a simplification of the geological system in the near-surface.

Selected boreholes were included within the UK3D v2015 sections, to help constrain the geological interpretation. The locations of these boreholes are shown as sticks within the GV Models (Figure 2). Original scanned logs and records for these boreholes, where available, can be accessed via hyperlinks in the model viewer. It should be noted that many additional boreholes were consulted by project geologists during UK3D v2015 construction to help constrain the model representation, this includes boreholes that are located off-section and therefore they are not shown explicitly in the GV Models.