3D Tomography in sediments: why mud matters.

Now my first year progression report has been handed in and my hangover has (nearly) disappeared I thought I’d copy Martin and give you a bit of insight into what my research is all about.

I’m currently studying at the Centre for Micromorphology, located at Queen Mary, University of London. This is the mecca for all those obsessed with the small-scale properties of sediments and other environmental materials.

The centre is currently using a combination of thin-section micromorphology, SEM (scanning electron microscopy) and a relatively new method, µCT (X-ray computed microtomography) to investigate sediments from a wide variety of sites all over the world.

I’m particularly interested in using µCT to examine the geotechnical and rheological properties of a range of sediments, with a focus on the subglacial environment.

 

What is µCT?

Anybody who’s ever broken a bone knows what an X-ray is: we use X-rays to visualise the structure of matter which is surrounded by something: bone surrounded by tissue for example. X-rays work because they detect variations in density instead of colour. Computed tomography (CT) uses thousands of X-rays, all taken from different angles, to produce a 3D volumetric model of a sample. µCT is essentially a micron resolution version of CT. The video below shows the interior of a core of basal ice taken during my MSc work at Aberystwyth University.

µCT is totally non-destructive – samples are not affected in any way by the process; this means 2 things. µCT is suitable for scanning precious samples like fossils, meteorites and cores, and samples can be scanned before, during & after modification (freezing a sample of sediment for example). This gives genuine time-dependent 3D data about environments which are notoriously hard to study.

 

What am I doing with it?

I’m trying to integrate µCT into sedimentology, a field that’s well established but which lacks true 3D data. Most of our knowledge about sediment behaviour, particularly deformation under stress, exists as a product of 2D or even dimensionless analysis. Data usually comes from characterising cliff exposures, a micromorphology thin section, or collecting bulk samples for particle size analysis or similar.

I’m trying to see how good µCT is at generating particle fabric data, mapping porosity and how useful this data is in the context of traditional sedimentology.

I’m off to Iceland for a month in August to collect some samples of pristine subglacial till for analysis in the hope that I can shed a bit more light on how these complex glaciers behave, and how they interact with the sediment underneath. 

 

Here are a few key references if you’re interested in the geoscientific applications of µCT:

Cnudde, V., & Boone, M. A. (2013). High-resolution X-ray computed tomography in geosciences: A review of the current technology and applications. Earth-Science Reviews, 123(C), 1–17.

Ketcham, R. A., & Carlson, W. D. (2001). Acquisition, optimization and interpretation of X-ray computed tomographic imagery: applications to the geosciences. Computers and Geosciences, 27(4), 381–400.

Kilfeather, A. A., & van der Meer, J. J. M. (2008). Pore size, shape and connectivity in tills and their relationship to deformation processes. Quaternary Science Reviews, 27(3-4), 250–266.

Taina, I. A., Heck, R. J., & Elliot, T. R. (2008). Application of X-ray computed tomography to soil science: A literature review. Canadian Journal of Soil Science, 88(1), 1–19.

 

Any questions or ideas please give me an email (j.w.e.groves@qmul.ac.uk), tweet me or check out my own website. Thanks for reading and have a good weekend!

 

John

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