OR/13/053 Introduction

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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.

Geological data relating to the Chalk Group of the Thames Basin have expanded dramatically over the last 25 years, particularly since the initiation of new Chalk-focused BGS mapping programmes in the early 1990s. Underpinning the newly-acquired digital geological map data for the Chalk is a wealth of other information, particularly relating to detailed (sub-formation) stratigraphy and regional changes in thickness and facies. In recent years a range of digital 3D geological models have also been developed for the London Basin, leading to new interpretations of regional structure and Chalk basin architecture. Whilst most of these data are held in various corporate archives, there is a need to draw these diverse strands of information together into a single spatially referenced format, allowing easy data comparison and interrogation. This work addresses that need by displaying all these data in a newly developed Arc-GIS format, named Thames Chalk Information System (TCIS). Table 1 summarises the stratigraphy of the Chalk referred to in this report.

Table 1    The stratigraphy of the Chalk Group referred to in this report and used in the Thames Chalk Information System (TCIS) (not to scale).

In addition to standard topographical and geological map data, the TCIS contains:

  1. Depth to top Chalk, depth to base Chalk, and thickness of Chalk Group, displayed as shaded surfaces to emphasise regional trends.
  2. Chalk Group, Subgroup and formational thickness information, displayed as greyscale shaded surfaces to emphasise regional trends.
  3. Structural information (faults and folds).
  4. Chalk stratigraphy information including:
  • Chalk boreholes with stratigraphy interpretations based (predominantly) on geophysical logs and borehole core. Interpretations are held in the BGS Borehole Geology (BoGe) database.
  • Sections and boreholes in the Chalk Group that have been illustrated in publications and BGS reports.
  • Chalk sample localities for which information about detailed lithostratigraphy and biostratigraphy is available in publications and reports.
  • Distribution of key hardground surfaces developed in the Lewes Nodular Chalk Formation described by Bromley and Gale (1982)[1].
  1. Summary of existing 3D geological models of the Chalk of the Thames Basin, and the purpose(s) for which each is best suited.
  2. Summary of areas where lack of primary knowledge of the Chalk limits our understanding of its stratigraphy.
  3. Hydrogeological data (data delivered as part of a separate project and not discussed further herein).

Information about the assembly and construction of the TCIS is provided in 2 (below), and data relating to each of the above themes (with the exception of hydrogeological data) are briefly discussed in 3 (below), and in greater detail in 4–9 (below). Where themes show the distribution of data that require interrogation through secondary sources (e.g. reports, references, corporate databases), information about these is also summarised.

This account does not provide any commentary about the conclusions that may be drawn from analysis of these data.

References[edit]

  1. BROMLEY, R G, and GALE, A S. 1982. The Lithostratigraphy of the English Chalk Rock. Cretaceous Research, Vol. 3, 273–306.