OR/13/053 Boreholes

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Woods, M A, Haslam, R B, Mee, K, Newell, A J, and Terrington, R L. 2013. A guide to a new Geographical Information System for the Chalk of the Thames Basin: The Thames Chalk Information System (TCIS). (FutureThames cross-cutting Programme). British Geological Survey Internal Report, OR/13/053.

Formation tops were used as boundary indicators for defining the bases of immediately overlying formation surfaces. These data are shown as OD values listed under T_Depth_OD in the borehole attribute table. For example, the Base_SECK_Top_LECH_V2_0_Boreholes.shp records the Top LECH elevation relative to OD, and equates to the base Seaford Chalk Formation. A borehole dataset was generated for each Chalk formation (excluding combined formations) plus the Top and Base Chalk. An additional dataset was created showing the full borehole stratigraphy for each borehole used to construct the Top Chalk surface (Top_CK_All_Boreholes_V5ii.shp).

Thickness plots for use in GOCAD modelling were generated by identifying matches of boreholes between the different formational borehole datasets. A borehole match between datasets for adjacent formational units indicates that both the top and base of a formation are present in a given borehole, allowing its thickness to be calculated. For example, boreholes containing the Top SECK were matched against those containing Top LECH (equating with Base SECK). For each match in borehole ID, a relevant formational thickness was calculated for that borehole. These thickness values were then used to generate thickness plots for use in constructing formational surfaces.