Application of micro-CT to resolve textural properties and assess primary sedimentary structures of deep-marine sandstones

Over the past decade, there has been growing interest in the sedimentological community to use micro X-ray computed tomography to analyse microfacies in sediment cores. However, little attention has been paid to the application of micro-computed tomography in lithified deposits, even though this can allow their texture to be characterised in three dimensions, providing key information about sedimentary structures. A novel application of micro-computed tomography in lithified sediment-gravity flow deposits is presented with the objective of characterising their internal 3D sedimentary structures. This technique is applied to three deep-marine sandstones showing different compositional properties: Cretaceous Gosau Group (Austria), Eocene Hecho Group (Spain) and the Oligocene Annot Formation (France). From micro-computed tomography data the size of particles and their distribution throughout the sample is reconstructed in 3D permitting a better visualisation of sedimentary textures. Particle distributions computed from micro-computed tomography are similar to those computed from thin section image analysis, corroborating the reliability of the micro-computed tomography to evaluate grain-size trends. Micro-computed tomography is complemented with micro-X-ray fluorescence and thin section petrographic analyses. In cases where mineral composition or grain size are homogeneous or matrix and grains have similar mineral composition, sedimentary structures do not appear visible from micro-X-ray fluorescence or thin section analyses. By separating particles based on their computed tomography density, it is possible to isolate the coarsest fraction, highlighting the sedimentary structures. This study demonstrates (i) the potential of micro-computed tomography in analyses of sedimentary structures from outcrop data and (ii) the importance of the mineralogical composition and degree of grain sorting in assessing the origin of structureless deposits. Considering the importance of visualising sedimentary structures when interpreting depositional processes, micro-computed tomography is a new and reliable tool to assess the physical properties of sandstones and to analyse their internal 3D sedimentary structures. A new application of micro-CT on consolidated sediment-gravity flow deposits is presented with the objectives to characterise its internal sedimentary three-dimensional structures. By separating particles based on their CT density, it is possible to isolate the coarsest fraction underlying the sedimentary structures from the fine-grained matrix. This study brings into light (i) the potential of micro-CT and particle-size distribution in the analyses of sedimentary structures from outcrop data and related interpreted processes (sediment transport) and (ii) the importance ofconsidering the mineralogical composition and the degree of grain sorting before reaching any interpretation of the processes generating structureless deposits.image

Automated summary

This study focuses on the application of micro-computed tomography in analysing sedimentary structures in lithified deposits. It demonstrates the potential of micro-CT in visualizing sedimentary structures and evaluating the physical properties of sandstones. By separating particles based on their CT density, the coarsest fraction underlying the sedimentary structures can be isolated. The study emphasizes the importance of considering mineralogical composition and grain sorting in interpreting structureless deposits.