OR/15/044 Modelled surfaces/volumes
Wakefield,O J W, and Barron, A J M. 2015. GSI3D Model metadata report for HS2 Area 6 (Cubbington to Hampton-in-Arden). British Geological Survey Internal Report, OR/15/044. |
The modelled bedrock, superficial and artificial deposits are listed in Table 1 in the relative stratigraphic order used in the model. Brief descriptions of the geological units are given here, but more detail can be found in the BGS Lexicon of Named Rock Units. The level of detail and extent of the natural geology in the model may differ from that shown in other BGS datasets. Artificial ground was modelled according to the corresponding 1:50 000 scale geological maps. Table 1 should be used as the legend for viewing images of the model in this report.
Name (LEX-RCS) | Lex Description | Lithology | Comment |
WMGR-ARTDP | Worked and Made Ground | Artificial Deposits | |
MGR-ARTDP | Made Ground | Artificial Deposits | |
WGR-VOID | Worked Ground | Void | |
ALV-XCZSV | Alluvium | Clay, silt, sand and gravel | |
HEAD-XCZSV | Head | Clay, silt, sand and gravel | |
PEAT-P | Peat | Peat | |
RTD1-XSV | River Terrace Deposits 1 | Sand and gravel | |
RTD2-XSV | River Terrace Deposits 2 | Sand and gravel | |
RTD3-XSV | River Terrace Deposits 3 | Sand and gravel | |
RTD4-XSV | River Terrace Deposits 4 | Sand and gravel | |
TILMP1-DMTN | Till Mid Pleistocene | Diamicton | Added for outlier on GFDMP at Balsall Common |
GFTMP-XSV | Glaciofluvial Terrace deposits Mid Pleistocene | Sand and gravel | In north only |
GFDMP-XSV | Glaciofluvial deposits Mid Pleistocene | Sand and gravel | |
DMG-XSV | Dunsmore Gravel Member, Wolston Glacigenic Formation | Sand and gravel | |
GLLMP1-XCZ | Glaciolacustrine deposits Mid Pleistocene | Clay and silt | [UPPER UNIT ADDED BY ILC] |
TILMP-DMTN | Till Mid Pleistocene | Diamicton | Includes much ODT |
GFDMP0-XSV | Glaciofluvial deposits Mid Pleistocene | Sand and gravel | Unit beneath TILMP added by ILC, restricted to north of area |
GLLMP-XCZ | Glaciolacustrine deposits Mid Pleistocene | Clay and silt | Very small outcrops only |
ODT-DMTN | Oadby Member, Wolston Glacigenic Formation | Diamicton | Now restricted to small outcrops in extreme south of area. Remainder to TILMP |
WOC1-XCZ | Wolston Clay Member, Wolston Glacigenic Formation | Clay and silt | Upper unit added by ILC, restricted to south-east of area |
WOSG-XSV | Wolston Sand and Gravel | Sand and gravel | restricted to south of area, now Wigston Sand and Gravel Member, Wolston Glacigenic Formation |
WOC-XCZ | Wolston Clay Member, Wolston Glacigenic Formation | Clay and silt | Restricted to south of area |
THT-DMTN | Thrussington Member, Wolston Glacigenic Formation | Diamicton | Now restricted to south of area. Remainder to TILMP |
BGSG-XSV | Baginton Sand and Gravel Formation | Sand and gravel | Restricted to south of area, one outcrop to GDU |
GDU-XCZS | Glacial deposits, undifferentiated | Clay, silt and sand | Includes indivisible BGSG, GLLMP and GFDMP beneath TILMP in west central part of Area 6 added by ILC |
SASH-MDST | Saltford Shale Member | Mudstone | Only present in down-faulted block in NW |
WCT-MDLM | Wilmcote Limestone Member | Mudstone and limestone, interbedded | Only present in down-faulted block in NW |
CTM-MDST | Cotham Formation | Mudstone | Only present in down-faulted block in NW |
WBY-SDST | Westbury Formation | Sandstone | Only present in down-faulted block in NW |
BAN-MDST | Blue Anchor Formation | Mudstone | Only present in down-faulted block in NW |
BCMU-MDST | Branscombe Mudstone Formation | Mudstone | See below |
AS-SDSM | Arden Sandstone Formation | Sandstone, siltstone and mudstone | See below. Important to note that in Area 6 this was originally modelled as AS-SISM, due to differences in lithology being mapped in Area 7. This was subsequently changed to AS-SDMS to match Area 7 (in Nov 2017) |
SIM-MDST | Sidmouth Mudstone Formation | Mudstone | See below |
TPSF-MDSA | Tarporley Siltstone Formation | Mudstone and sandstone, interbedded | See below |
BMS-SDST | Bromsgrove Sandstone Formation | Sandstone | Modelled unit includes locally mapped lenticular mudstone beds |
WRS-SDST | Wildmoor Sandstone Formation | Sandstone | Only present in faulted block in NE |
AW-MDSD | Ashow Formation | Mudstone and sandstone | Modelled unit includes locally mapped lenticular sandstone beds |
KHS-SDST | Kenilworth Sandstone Formation | Sandstone | Modelled unit includes locally mapped lenticular mudstone and conglomerate beds |
TLM-ARSD | Tile Hill Mudstone Formation | Argillaceous rocks and [subequal/subordinate] sandstone, interbedded | Modelled unit includes locally mapped lenticular sandstone beds |
ASY-ARSC | Allesley Member, Salop Formation | Argillaceous rocks and [subequal/subordinate] sandstone and conglomerate, interbedded | Modelled unit includes locally mapped lenticular sandstone beds |
KRS-ARSC | Keresley Member, Salop Formation | Argillaceous rocks and [subequal/subordinate] sandstone and conglomerate, interbedded | Modelled unit includes extensively mapped sandstone beds |
The strata of the Warwickshire Coalfield (central portion of model area: Figure 2) at rockhead and at depth to -30 m OD in the model all belong to the upper Carboniferous to Permian Warwickshire Group. Mapping and borehole data has enabled these to be fully subdivided in this model into four formations: in descending order the Ashow, Kenilworth Sandstone, Tile Hill Mudstone and Salop formations, the last divided into the Allesley and Keresley members (Table 1). However, within all these units beds of subordinate lithologies are widely mapped, but they are not distinguished within the model because of their significant lenticularity, the lack of information in boreholes, and the considerable additional work modelling these would impose. It is also likely that they would compromise successful and reasonably fast calculation of the model. See also Model limitations.
In the digital geological map data incorporated in the model (DiGMapGB-50; Figure 2) the Mercia Mudstone Group (MMG-MDST) was not subdivided, with the exception of the Arden Sandstone Formation (AS-SDSM), and locally thin siltstone beds or ‘skerries’ are not distinguished in the model. The presence of the Arden Sandstone where mapped at surface enables the distinction of the Branscombe Mudstone and Sidmouth Mudstone formations above and below, respectively. Inferred thicknesses of the constituent formations of the Mercia Mudstone Group, borehole data and field observations enabled the separation of the otherwise unmapped Tarporley Siltstone Formation at the base in the south-east of the model area (Figure 3). In addition, a fault-bounded outcrop of Bromsgrove Sandstone Formation in the north was reattributed as Tarporley Siltstone Formation. These changes were fed into the corporate 1:10 000 scale digital map data.
The area includes part of a highly complex Anglian glacigenic succession, which in places may be inadequately mapped for the purpose of constraining a 3D model (e.g. unclear superposition relationships, unlikely pinch-outs). Lenticular beds and repeated similar lithologies within this present further difficulties in modelling true/viable stratigraphical units. In addition, the correct identification of the Thrussington Member (THT) till and Oadby Member (ODT) till were doubtful in places and caused misfits. To address this, Oliver Wakefield reattributed some outcrops as Till, Mid Pleistocene (TILMP), although all Mid Pleistocene units are part of the Wolston Glacigenic Formation. After the model was submitted for technical check and QA, it was decided that in part of the area (west centre) it was necessary to combine the glaciofluvial (GFDMP-XSV) and glaciolacustrine (GLLMP-XCZ) deposits, plus a single outcrop of (dubious) Baginton Sand and Gravel Formation (BGSG-XSV), beneath the main till unit (TILMP) into one undifferentiated unit named Glacial deposits undifferentiated unit (GDU-XCZS, yellow in Figure 6 below) — see Model limitations.
Sections were named according to a wider HS2 project convention, with six longitudinal sections running southeast to northwest named HS2_Area6_NWSE_X_OLIVERW as appropriate including one to coincide with the proposed HS2 route (HS2_Area6_NWSE_line_OLIVERW), and thirteen northeast to southwest ‘rung’ sections named HS2_Area6_SWNE_X_OLIVERW. Eighteen additional sections were constructed to help constrain faulted areas and where issues were encountered with the model calculation.