OR/15/044 Supplementary work

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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.

Supplementary work on the model was conducted and the following section details additional changes to the model.

All fieldwork was undertaken 17-18/7/14. Office work on revised linework completed 1/8/14.

The Arden Sandstone Formation (AS) was previously mapped as discontinuous in places. More recent work (e.g. Warrington et al., 1980[1]) has shown that it is a continuous unit across much of the UK. Fieldwork was undertaken to correct this, together with office work looking at boreholes and the topography to extend parts of the outcrop beneath superficial deposits. This includes the area between HS2 areas 6 and 7 (Figure 12).

Some of the deep boreholes have not distinguished the Tarporley Siltstone Formation but it is inferred to be present everywhere at the base of the Mercia Mudstone Group in this region (Warrington et al., 1980[1]). Along the margin between Areas 5 and 6, Tarporley Siltstone Formation has been added with limited fieldwork and, in places, is constructed, based partly on an approximate thickness (Figure 13).

Problems were noted around the join between Area 6 and Area 7 where five outcrops of Bromsgrove Sandstone Formation had been mapped in two fault blocks but overlain by the Mercia Mudstone Group with no Tarporley Siltstone Formation delineated. This necessitated fieldwork to map in the Tarporley Siltstone. The whole area within the fault block was re-mapped as Tarporley Siltstone, apart from the middle one of the four outcrops of Bromsgrove Sandstone, on the south side of the village of Meriden, which was retained (compare Figure 2 and Figure 3). The outcrop of Bromsgrove Sandstone to the north east of Balsall Common has been changed to Tarporley Siltstone on the evidence of boreholes and a measured section in a railway cutting.

Within Area 6 the Tilehill Mudstone Formation is inferred to be present at depth in the Knowle Basin (western third of model area) beneath the Bromsgrove Sandstone Formation, in part based on cross-section on BGS Sheet 183 — Redditch. It is inferred to extend north in the fault block as drawn in cross-section Area6_NESW_Filler_14.

January–March 2015
New and amended linework on sheet 184 (Warwick) was compiled for adding to DiGMap 10 and 50. This includes the addition of Tarporley Siltstone Formation outcrop to the map face, amendments to the outcrop of the Arden Sandstone Formation (Figure 12) and superficial deposits, and some new faulting. This new linework was used to modify the geological model.

Figure 12    DiGMapGB-10 in north-west of Area 6 (SP18SE), with extended Arden Sandstone subcrop and additional fault.
Figure 13    Example of constructed top of Tarporley Siltstone Formation (grey).

References

  1. 1.0 1.1 Warrington, G, Audley-Charles, M G, Elliott, R E, Evans, W B, Ivimey-Cook, H C, Kent, P E, Robinson, P L, Shotton, F W, and Taylor, F M (editors). 1980. A correlation of Triassic rocks in the British Isles. Geological Society of London Special Report. No. 13.