Using computed tomography (CT) to reconstruct depositional processes and products in the subaqueous glaciogenic Champlain Sea basin, Ottawa, Canada

Al-Mufti, Omar N.; Arnott, R. W. C.; Hinton, M J; Alpay, S; Russell, H A J

doi:10.1016/j.geomorph.2022.108165

Cited by 5 publications

(1 citation statement)

References 48 publications

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“…At the centimeter-scale, samples were described based on the lithology, grain size, and sedimentary structures. Additionally, high-resolution (0.5 mm), nondestructive, X-ray computed tomography (CT) for imaging was used to characterize the fabric and structures in the representative core samples, with CT scans providing qualitative values to aid with centimeterscale descriptions [41,42]. Computer tomography scans rely on the variation of X-ray attenuation within the sediment cores which are expressed as Hounsfield units (HU; [43]).…”

Section: Dataset and Methodologymentioning

confidence: 99%

Quantifying Centimeter- to Microscale Heterogeneities in Sedimentary, Compositional, and Geomechanical Properties of Siltstone Deposits in the Lower Triassic Montney Formation, Northeastern British Columbia, Canada

2022

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Geological and geomechanical heterogeneities exist at multiple scales in fine-grained rocks; however, the complexity of characteristics at the centimeter- to microscale heterogeneities remains poorly understood. In this study, 10 representative samples composed of three centimeter-scale sedimentary fabrics (massive siltstone (F1), stratified siltstone (F2), and bioturbated siltstone (F3)) were analyzed from the Lower Triassic Montney Formation in the Western Canada Sedimentary Basin to describe sedimentological heterogeneity based on sedimentary fabric, compositional, and geomechanical properties. Sedimentary fabric was determined based on grainsize and the distribution of bedforms, which subdivide the facies into four μm- to mm-scale microfacies (massive siltstone (MF1), pinstriped laminated siltstone (MF2), planar- to cross-stratified siltstone (MF3), and bioturbated siltstone (MF4)). Microscale analysis using a scanning electron microscope was used to characterize microfacies and their respective mineralogical makeup (matrix, cement, and framework grains). To quantify heterogeneity, sedimentary fabric was assessed using a CT scan complemented by elemental composition (using X-ray fluorescence), and geomechanical hardness (using Equotip Piccolo Bambino handheld microhardness tool) was collected within a 1 cm by 1 cm grid within each sample. Datasets were compared using a discriminant analysis (DA) to recognize trends between multiple properties and suggest that sedimentary fabric with the highest centimeter-scale aluminum content from XRF (avg. 11%) comprises microfacies that are comparatively matrix-rich consisting of micas, negligible calcite cement, and exhibit the lowest handheld hardness values (<770). Alternatively, sedimentary fabric with a higher elemental calcium component (avg. 18%) comprises microfacies that are matrix-poor, cemented by carbonate (calcite and dolomite) and quartz, and overall exhibit a positive trend with hardness measurement (770–850). Furthermore, to relate the elemental and geomechanical proxies to controls on rock mechanics, natural calcite-filled fractures within the studied core intervals were characterized. Fractures were subdivided into three types—brecciated, bed-parallel, and vertical to subvertical fractures with each type being constrained to a specific sedimentary fabric. Based on centimeter gridding, microscale analysis and the degree of fabric interbedding play a primary role on the variability in mechanical hardness and the geometry and termination of natural fractures. Collectively, this dataset provides insight into the influence that sedimentary fabric and the distribution of elemental composition has on mechanical properties and natural fractures below well log resolution. These findings can be used to better model and predict fine-grained deposit characteristics before undergoing hydraulic stimulation.

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Section: Dataset and Methodologymentioning

confidence: 99%

Quantifying Centimeter- to Microscale Heterogeneities in Sedimentary, Compositional, and Geomechanical Properties of Siltstone Deposits in the Lower Triassic Montney Formation, Northeastern British Columbia, Canada

2022

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The origin of planar lamination in fine‐grained sediment deposited by subaqueous sediment gravity flows

Al‐Mufti,

Arnott

2023

The Depositional Record

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Planar lamination is a ubiquitous component of modern and ancient fine‐grained sediments deposited by subaqueous sediment gravity flows. These sediments commonly exhibit alternating sub‐millimetre‐thick, sharply bounded silt‐rich and clay‐rich layers that change little in thickness or sediment texture over lateral distances that range up to at least several tens of metres. Silt‐rich layers are moderately to well‐sorted and a few tens to hundreds of microns to a single silt‐grain thick. In contrast, clay‐rich layers are more poorly sorted, and a few tens to hundreds of microns thick. The thickness and regular alternation of these texturally differentiated interlayers, in addition to the absence of features suggesting transport bypass or deposition by migrating rugged bed forms, suggest alternating physical processes and related modes of deposition in the near‐bed region immediately above the bed. Previous interpretations have focussed on clay flocculation, which is difficult to reconcile with the high fluid shear conditions in the near‐bed region. Here it is suggested that in the millimetre to sub‐millimetre‐thick viscous sublayer at the base of a hydraulically smooth turbulent flow, a combination of high fluid shear and sediment concentration initially leads to shear thinning and enhanced mobility in the lower part of the flow, and for silt to continue settling to the bed forming a well‐sorted silt lamina. As silt settles and clay‐size sediment increases in concentration, hydrodynamic lubrication forces strengthen and reduce mobility of the near‐bed part of the flow. This condition is then perturbed by a bedward‐directed outer flow disturbance that dramatically increases frictional stresses and effective fluid viscosity and ultimately shear jamming that causes gelling and deposition of a poorly sorted clay‐rich layer. This process is then repeated multiple times to build up a deposit composed of alternating silt‐rich and clay‐rich laminae overlain by structureless mud deposited directly from suspension.

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

Cornard,

Degenhart,

Tropper

et al. 2023

The Depositional Record

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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.

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Using computed tomography (CT) to reconstruct depositional processes and products in the subaqueous glaciogenic Champlain Sea basin, Ottawa, Canada

Cited by 5 publications

References 48 publications

Quantifying Centimeter- to Microscale Heterogeneities in Sedimentary, Compositional, and Geomechanical Properties of Siltstone Deposits in the Lower Triassic Montney Formation, Northeastern British Columbia, Canada

Quantifying Centimeter- to Microscale Heterogeneities in Sedimentary, Compositional, and Geomechanical Properties of Siltstone Deposits in the Lower Triassic Montney Formation, Northeastern British Columbia, Canada

The origin of planar lamination in fine‐grained sediment deposited by subaqueous sediment gravity flows

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

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