Shortwave infrared hyperspectral imaging as a novel method to elucidate multi-phase dolomitization, recrystallization, and cementation in carbonate sedimentary rocks

Abstract

Carbonate rocks undergo low-temperature, post-depositional changes, including mineral precipitation, dissolution, or recrystallisation (diagenesis). Unravelling the sequence of these events is time-consuming, expensive, and relies on destructive analytical techniques, yet such characterization is essential to understand their post-depositional history for mineral and energy exploitation and carbon storage. Conversely, hyperspectral imaging offers a rapid, non-destructive method to determine mineralogy, while also providing compositional and textural information. It is commonly employed to differentiate lithology, but it has never been used to discern complex diagenetic phases in a largely monomineralic succession. Using spatial-spectral endmember extraction, we explore the efficacy and limitations of hyperspectral imaging to elucidate multi-phase dolomitization and cementation in the Cathedral Formation (Western Canadian Sedimentary Basin). Spectral endmembers include limestone, two replacement dolomite phases, and three saddle dolomite phases. Endmember distributions were mapped using Spectral Angle Mapper, then sampled and analyzed to investigate the controls on their spectral signatures. The absorption-band position of each phase reveals changes in %Ca (molar Ca/(Ca + Mg)) and trace element substitution, whereas the spectral contrast correlates with texture. The ensuing mineral distribution maps provide meter-scale spatial information on the diagenetic history of the succession that can be used independently and to design a rigorous sampling protocol.

Mechanisms controlling the localisation of fault‐controlled hydrothermal dolomitisation, Derbyshire Platform, UK

“…It is not until later phases of dolomitisation, along N-S faults, that these more characteristic textures are observed and there is a change from replacement of wall rock to cementation of fractures. In this case, a backstepping of the reaction front is less evident that in other studies (McCormick et al, 2021;Stacey et al, 2021), but instead high pressure fluids were focussed along narrow fault splays that appear to derive from the main NW-SE trending crustal lineament. However, the process is somewhat similar; fluid pressures built because matrix permeability had been reduced, forcing fluids to rupture the rock at high pressure, forming saddle dolomite cemented breccias and zebra textures.…”

“…It has become clear that there is unlikely to be a common model for all fault‐controlled hydrothermal dolomite bodies, but that fault‐plane convection of sea‐water, fluid convection along basal aquifers and fluid mixing are all likely to be important controls on the localisation of dolomite bodies (Benjakul et al, 2020; Hollis et al, 2017; Koeshiydayatullah et al, 2020; Stacey et al, 2020, 2021). It has also become evident that in many bodies, progressive occlusion of porosity results in the back‐stepping of reaction fronts in time so that fluid flux is constrained to fault planes, where fluid pressures can build (Koeshiydayatullah et al, 2021; McCormick et al, 2021; Stacey et al, 2021). This can lead to the formation of the most characteristic features of HTD; saddle dolomite cemented breccias and zebra dolomite textures.…”

Basin scale evolution of zebra textures in fault‐controlled, hydrothermal dolomite bodies: Insights from the Western Canadian Sedimentary Basin

“…Such recrystallization occludes porosity and results in the core of the HTD body being younger than its margins. This phenomenon can be recognized by the spatial distribution of each paragenetic stage in the strata (McCormick et al, 2021), alongside a systematic increase in the dolomitization temperature and δ 18 O fluid values towards the core of the HTD body (Koeshidayatullah et al, 2020). Recrystallization coincides with the shift from zoned, planar‐e dolomite (distal to the fluid source) to unzoned, planar‐s to nonplanar dolomite (proximal to the fluid source).…”

“…Recrystallization coincides with the shift from zoned, planar‐e dolomite (distal to the fluid source) to unzoned, planar‐s to nonplanar dolomite (proximal to the fluid source). Such relationships have been established at the outcrop scale (Koeshidayatullah et al, 2020; Koeshidayatullah et al, 2021; McCormick et al, 2021; Stacey et al, 2021), but whether they hold true at the basin scale is equivocal. Likewise, the relationship between these dolomitization patterns and the formation of zebra textures, boxwork textures and dolomite breccias has not been investigated.…”

“…Evidence in support of recrystallization includes (i) the increased crystal size from RD1 to RD2 and (ii) the shift from oscillatory‐zoned, planar‐e dolomite to an unzoned mosaic of planar‐s dolomite (Koeshidayatullah et al, 2020; Stacey et al, 2021). There is a spatial relationship between presence of RD2 and SD within the HTD bodies, which strongly suggests that the fluid flow event(s) that formed SD1 also gave rise to recrystallization of pre‐existing dolomite in the strata (McCormick et al, 2021).…”