A new physical property model for the Chalk Group of southern England

Chalk cliff
Map of boreholes
Chalk log

The Chalk Group forms the UK's most important aquifer, underlying densely populated parts of south east England. It is also vulnerable to pollution and prone to groundwater flooding, and is host to numerous major civil engineering projects including transport infrastructure and offshore wind farms. Understanding the lateral and vertical variation in the Chalk's physical properties will enable improvement to:

  • the management of water resources
  • the management of pollution risks
  • understanding of foundation conditions for major civil engineering projects
  • understanding of geological processes that controlled the formation of the Chalk, which in turn helps prediction about its likely character in areas where little is known

What is a physical property model of the Chalk?

Boreholes and outcropping successions are simulated as coloured cylinders in the model

As well as forming beautiful rolling landscapes that extend from western England to Lincolnshire and Yorkshire, the Chalk extends deep underground. Although the chalk appears relatively uniform, it actually shows significant vertical variation in key aspects, such as its clay content and hardness, and these also vary across county between different regions.

Our model is a 3D computer simulation of the surface and below ground distribution of the different types of chalk, based on combining information from mapping and outcrop descriptions with geological interpretations of borehole data, particularly geophysical logs. When complete, our model will show:

  • variation in the thickness of different units within the Chalk
  • distribution of hard chalks, and units of intensely hard chalk, called hardgrounds
  • distribution of clay rich units of the Chalk
  • occurrence of key structures that affect the Chalk
Modelling the internal structure of the undulating Chalk stratigraphy

For any borehole or outcrop point within the model, we have recorded the boundaries of the different Chalk formations, and produced separate logs of the types of chalk present. Statistical algorithms within the software used to construct the model extend the likely development of these different types of chalk into areas where we do not have data to constrain the interpretation. The model also contains records of key, widely developed marker beds within the Chalk, allowing high resolution correlation within the model.

Analysis of thickness patterns of different chalk units within the model.

A key scientific aim of the work is to better understand the geological processes controlling the distribution of the different types of chalk, so that we can make predictions about the nature of the Chalk succession in areas of the subsurface where little is currently known.

Hardground: intensely hard units of chalk that indicate periods of reduced rates of sedimentation, when the sea floor became highly cemented. These often form across structural highs, showing the importance of structure for understanding the physical properties of the Chalk.

Formation: named units into which the Chalk is classified on the basis of large scale variation. The physical property model also captures variation within these units.

Contact

For more information please contact Andrew Newell or Mark Woods.