OR/16/004 Modelled surfaces/volumes

From Earthwise
Jump to navigation Jump to search
Barron, A J M. 2016. GSI3D model metadata report for HS2 Area 3 (Newton Purcell to Thorpe Mandeville). British Geological Survey Internal Report, OR/16/004.

Table 1 is a list of the units modelled.

Table 1 Units modelled in Area 3.
Name in model LEXRCS Description Comments
NON-GEOLOGICAL MASS NONE-NONE For areas of woodland or buildings that mask the true DTM, especially in hollows
WMGR-ARTDP WMGR-ARTDP WORKED AND MADE GROUND
MGR-ARTDP MGR-ARTDP MADE GROUND
WGR-VOID WGR-VOID WORKED GROUND
LSGR-UKNOWN LSGR-UKNOWN LANDSCAPED GROUND
ALV-XCZSV ALV-XCZSV ALLUVIUM
HEAD-XCZSV HEAD-XCZSV HEAD
TUFA-CATUFA TUFA-CATUFA TUFA
GFDMP1-XSV GFDMP1-XSV GLACIOFLUVIAL DEPOSITS MID PLEISTOCENE, UPPER Upper GFDMP unit. Occurrence limited
TILMP1-DMTN TILMP1-DMTN TILL MID PLEISTOCENE, UPPER Upper Till unit. Includes parts of ODT of Towcester sheet
GFDMP-XSV GFDMP-XSV GLACIOFLUVIAL DEPOSITS MID PLEISTOCENE Median GFDMP unit. Occurrence widespread
TILMP-DMTN TILMP-DMTN TILL MID PLEISTOCENE, LOWER Main body of Till unit. Includes parts of ODT of Towcester sheet
GFDMP0-XSV GFDMP-XSV GLACIOFLUVIAL DEPOSITS MID PLEISTOCENE, BASAL Basal unit of glacigenic succession. Occurrence very limited
PET-MDST PET-MDST PETERBOROUGH MEMBER Uppermost bedrock unit, only present in overlap with Area 2 and Helper sections here
KLB-SDSM KLB-SDSM KELLAWAYS FORMATION
CB-LMST CB-LMST CORNBRASH FORMATION
FMB-LSMD FMB-LSMD FOREST MARBLE FORMATION Includes BWC-MDST of Towcester sheet
BLAD-MDLM BLAD-MDLM BLADON MEMBER
WHL-LMST WHL-LMST WHITE LIMESTONE FORMATION Includes BWL-LMST of Towcester sheet
RLD1-MDST RLD-MDST RUTLAND FORMATION Upper division of Rutland Formation
TY-LMOOL TY-LMOOL TAYNTON LIMESTONE FORMATION Lateral equivalent of WBRO
WBRO-LMST WBRO-LMST WELLINGBOROUGH LIMESTONE MEMBER Lateral equivalent of TY, present only in NE.
SHHB-ARSL SHHB-ARSL SHARP'S HILL FORMATION Lateral equivalent of RLD
RLD-MDST RLD-MDST RUTLAND FORMATION Lower division of Rutland Formation mudstone beds in area where WBRO is present above. Lateral equivalent of SHHB
STAM-SDSL STAM-SDSL STAMFORD MEMBER Lateral equivalent of HYSA, basal member of Rutland Formation in area where WBRO is present above
HYSA-SDST HYSA-SDST HORSEHAY SAND FORMATION Lateral equivalent of WBRO in area where TY and SHHB are present above
GOG-LMAS GOG-LMAS GREAT OOLITE GROUP In SE part of the model: includes WHL-LMST, RLD1-MDST, TY-LMOOL, SHHB-ARSL, HYSA-SDST
NS-SDLI NS-SDLI NORTHAMPTON SAND FORMATION
WHM-MDST WHM-MDST WHITBY MUDSTONE FORMATION
MRB-FLIR MRB-FLIR MARLSTONE ROCK FORMATION
DYS-SIMD DYS-SIMD DYRHAM FORMATION
CHAM-MDST CHAM-MDST CHARMOUTH MUDSTONE FORMATION In north of model probably includes RLS-MDLM**
WLI-LMST WLI-LMST WHITE LIAS FORMATION *
PNG-AROCLS PNG-AROCLS PENARTH GROUP *

*NB The White Lias Formation and Penarth Group appear in only a few cross-sections in the base of the model, very close to the cut-off depth of 30 m below OD, and therefore it is not possible to construct meaningful envelopes.

**The Rugby Limestone Member (RLS-MDLM) of the Blue Lias Formation is modelled beneath the Charmouth Mudstone Formation to the north-west in Area 4, adjoining Area 3. Its extent into Area 3 is very uncertain, and the location of its south-easterly pinch-out is unknown. Hence it is not modelled, creating a misfit with Area 4 model.

The units from the Cornbrash Formation (CB) to the Horsehay Sand Formation (HYSA) inclusive form the Great Oolite Group (GOG) and the Whitby Mudstone Formation (WHM) to the Charmouth Mudstone Formation (CHAM) form the Lias Group.

The Mid Pleistocene glacigenic succession (GFDMP1 to GFDMP0) was deposited at the extreme southern limit of the Anglian ice advance (Sumbler, 2002)[1] and is hence very complex. It was recommended against making any lenses (see Model development log 14/5/13) to aid calculation, resulting in the erection in the GVS of a sequence of three variants of GFDMP and two of TILMP, which were separated. This is nonetheless simplified from that as mapped (see especially grid square SP 66 33), necessitating changes to the respective geological units at outcrop (see Model development log).

Area 3 lies in the area where the East Midlands Great Oolite Group succession passes into that of the Cotswolds (Sumbler, 2002, pp8–13, fig. 5)[1], and for some units the BGS Sheet 202 (Towcester) and Sheet 219 (Buckingham) boundary (Figure 1) is taken as an arbitrary line where the passage takes place. Thus on DiGMapGB-50, there is a line between the Blisworth Clay Formation (Lex code BWC) in the north, and its approximate southern correlative the Forest Marble Formation (FMB), and likewise for the Blisworth Limestone Formation (BWL) and the White Limestone Formation (WHL). For the purposes of calculation, it proved necessary to merge these pairs (see Model development log). For the lower formations in the Great Oolite Group (GOG), where they are at depth in the south and east (no outcrop information), borehole data generally was inadequate to differentiate the formations and it was necessary to construct the ‘passage’ between them e.g. at W16290 in NWSE_3 (Figure 2).

Figure 2 Passage between GOG and component formations in section NWSE_3
Orange–GOG, lime green–RLD1, yellow–TY, pink HYSA.

In addition, in DiGMapGB-50, the Till in the Towcester district is coded as Oadby Member (ODT) whereas that in Buckingham is Till, Mid Pleistocene, which description includes the Oadby Member, so the former is subsumed in the latter — the join visible across the centre of Figure 9.

Reference

  1. 1.0 1.1 SUMBLER, M G. 2002. Geology of the Buckingham district — a brief explanation of the geological map. British Geological Survey Sheet Explanation, Sheet 219 (England and Wales).