Using dual-energy CT to discriminate sediment facies in a varved sequence

The attenuation of X-ray is influenced by the density (electron density, ρ_e) and the elemental composition (effective atomic number, Z_eff) of the object being imaged. The incident X-ray beams energy controls the relative importance of these two properties in the resulting X-ray attenuation. Yet, dual-energy X-ray computed tomography, or using two incident X-ray beams of different energy, has been used in medical sciences to distinguish the different compounds within a sample based on their density (electron density, ρ_e) and elemental composition (effective atomic number, Z_eff).

An innovative approach, i.e., the stoichiometric calibration for dual-energy X-ray computed tomography, was already successfully implemented to identify single and homogeneous minerals easily and non-destructively. It is here applied for the first time to a varved sequence with three distinct facies. The output of dual-energy X-ray computed tomography was compared against elemental geochemistry obtained at the same resolution using a micro-XRF core scanner. The three individual facies can be successfully differentiated using dual-energy X-ray computed tomography because their range of ρ_e and Z_eff values allow their discrimination. Correlations with elemental geochemistry are also discussed but are less conclusive, probably because of variations in grain size and porosity, and because these high-resolution analyses were not performed at the exact same location. We discuss the limitations when using dual-energy X-ray computed tomography on sediments but also demonstrates its potential to quantitatively study sediment cores in a non-destructive way.

This presentation is based on https://doi.org/10.1002/dep2.271