OR/13/053 Structural data
| 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. |
The following shapefiles have been created and added to the Thames Chalk Information System:
- All Structural data
- Revised/synthesised fault network
The source data for the creation of these files are published papers and BGS reports, 3D models and maps. Much of these data are summarised by Haslam (in prep.), which also provides a list of reference sources for individual structures recognised in the project area.
The first layer (‘Filtered structures (V1)’) contains all the data available at the time of compilation including known structures in the deeper bedrock where no data is available for the Chalk. The lineaments represent either faults or the axial plane traces of folds. The category of each structure is revealed in the ‘Identify’ window when specific lineaments are interrogated in the GIS. No additional interpretation of the extent of lineaments is made in this layer.
The second layer (‘Filtered structures V10’) represents both a simplification and an interpretation of the first layer, focussing on the larger faults within in the Chalk; it comprises the known distribution of the larger faults seen in the first layer, and their inferred lateral extent based on further structural analysis. Simplification involved removal of duplicate faults, and faults smaller than approximately 2 km. Interpretation involved the linking and extension of the remaining larger fault structures. The methodology for analysing the behaviour of structures used colour- coded depth surfaces for the Top and Base Chalk, as well as borehole markers colour-coded for depth. Combining these data allowed correction for inconsistencies produced by incorrect or apparently incorrect borehole tops, and changes to lithostratigraphical surfaces that are not related to the constraining borehole data. Colour scales on the surfaces were varied to highlight as many changes within the surface as possible, especially in areas where the surface appears uniform due to censoring of the data by a particular colouring methodology. This is particularly important near surface boundaries and in deep sections. Modification of the depth-coded colour range for lithostratigraphical surfaces also allowed identification of structures in apparently uniform parts of surfaces, otherwise masked because the scale of the structures is below the threshold variation of the selected colour-scale.
Finally, to consolidate the lateral correlation of fault lineaments, the 1st vertical derived Bouguer anomaly gravity surface was modelled to the base of the Mesozoic succession. The Bouguer anomaly surface shows clear linear trends which match with published faults, allowing its use as a robust guide for projection of faults into areas with little to no data.