OR/13/053 Data limitations

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.

• Some minor negative thickness values near the outcrop margin of the Chalk result from contrasts between the high-resolution survey data available for controlling the Top Chalk surface compared to the more generalised data used to generate formational surfaces. These negative values have been manually edited out as far as practicable. Negative thickness values are also generated by erroneous cross-over (i.e. intersection) of calculated formational surfaces close to the outcrop margin of formations; these have been reduced but not entirely eliminated (5.3, bullet 11, above).
• When gridding the formational surfaces, some detail has been lost where formation outcrops were constrained at a resolution of 50 m, but modelled at a mesh resolution of 500 m. Some cross-over of formational surfaces may occur in these areas.
• A number of borehole checks have been performed on the Top and Base Chalk datasets to remove duplicates, check start heights and query Top Chalk and Base Chalk levels. These procedures were not repeated at formation level.