Papers by Cole A . McCormick
Hydrothermal Dolomitization: New Techniques Shed Light on an Old Paradigm
Abstracts with programs, Dec 31, 2022
Eustatic and Tectonic Controls on the Development of the Stratigraphic Architecture of the Cayman Islands, British West Indies
Properties of dolomitizing fluids indicated by rare earth elements: A case study of the Upper Miocene to Pliocene dolostone on the Xisha Islands, South China Sea
Sedimentary Geology
Basin scale evolution of zebra textures in fault‐controlled, hydrothermal dolomite bodies: Insights from the Western Canadian Sedimentary Basin
Basin Research
Structurally controlled dolomitization typically involves the interaction of high‐pressure (P), h... more Structurally controlled dolomitization typically involves the interaction of high‐pressure (P), high‐temperature (T) fluids with the surrounding host rock. Such reactions are often accompanied by cementation and recrystallization, with the resulting hydrothermal dolomite (HTD) bodies including several ‘diagnostic’ rock textures. Zebra textures, associated with boxwork textures and dolomite breccias, are widely considered to reflect these elevated P/T conditions. Although a range of conceptual models have been proposed to explain the genesis of these rock textures, the processes that control their spatial and temporal evolution are still poorly understood. Through the detailed petrographical and geochemical analysis of HTD bodies, hosted in the Middle Cambrian strata in the Western Canadian Sedimentary Basin, this study demonstrates that a single genetic model cannot be applied to all the characteristics of these rock textures. Instead, a wide array of sedimentological, tectonic and ...
An experimental study of the transition from tensile failure to shear failure in Carrara marble and Solnhofen limestone: Does “hybrid failure” exist?
Tectonophysics
Failure of brittle rocks under axisymmetric extensional loading, when the minimum principal stres... more Failure of brittle rocks under axisymmetric extensional loading, when the minimum principal stress is tensile, results in the formation of one or more opening-mode cracks that are oriented normal to the extension axis. When all the principal stresses are compressive, failure occurs through the formation of numerous grain-scale tensile cracks, which coalesce into a shear-mode fault that is inclined at >20 • to the maximum principal stress. There have been few attempts to study the transition between these failure modes, particularly those that incorporate microstructural analyses. A transitional mode of failure, termed "hybrid failure", is often proposed to describe the orientation of faults between these end-member loading conditions, but this concept has traditionally been based on a parabolic, "Griffith-type" failure envelope that describes the growth of the single most criticallyoriented crack. By integrating axisymmetric rock deformation experiments with microstructural analyses, it can be shown that failure under these transitional conditions involves the formation of several transgranular tensile cracks, which coalesce into a shear-mode fault that is inclined at <10 • to the maximum principal stress. The stress intensity at the tip of each crack interacts with adjacent cracks to produce a stair-step geometry along the failure surface. These are what may be appropriately considered "hybrid faults", the angle of which systematically increase as the maximum principal stress, and thus the differential stress increases. There is, however, no evidence of a distinct "hybrid failure" mode, which involves the in-plane propagation of a single crack that is subject to a combined shear stress and tensile normal stress. The results of this experimental study provide novel insights into the mechanical behaviour of carbonate rocks and into the interpretation of meso-scale natural examples of failure under mixed stress-states.
Replication Data for: "Shortwave infrared hyperspectral imaging as a novel method to elucidate multi-phase dolomitization, recrystallization, and cementation in carbonate sedimentary rocks
Replication Data for: "Shortwave infrared hyperspectral imaging as a novel method to elucida... more Replication Data for: "Shortwave infrared hyperspectral imaging as a novel method to elucidate multi-phase dolomitization, recrystallization, and cementation in carbonate sedimentary rocks".
Replication Data for "On the efficacy and limitations of isolated carbonate platforms as "oceanic dipsticks" to reconstruct subsidence histories, a case study from the Paleogene to Neogene strata on Grand Cayman and Cayman Brac, B.W.I
Figures, tables, and appendix to accompany manuscript.
Eustatic and Tectonic Controls on the Development of the Stratigraphic Architecture of the Cayman Islands, British West Indies
On the efficacy and limitations of isolated carbonate platforms as “oceanic dipsticks” to reconstruct subsidence histories, a case study from the Paleogene to Neogene strata on Grand Cayman and Cayman Brac, B.W.I
Marine Geology, 2021
Abstract Carbonate sedimentary successions that developed on isolated oceanic islands typically c... more Abstract Carbonate sedimentary successions that developed on isolated oceanic islands typically comprise a series of unconformity-bounded packages of strata that reflect eustatic sea level changes superimposed on local tectonic movements. Resolving the subsidence and/or uplift of these islands, which are often assumed to have simple tectonic histories, is challenging because the tectonic movements are commonly of similar magnitudes to the eustatic oscillations. The uncertainty associated with each of the components involved in the construction of subsidence diagrams (e.g., age constraints, decompaction, eustatic sea level curves, paleobathymetry), therefore, introduces significant error margins when assessing the tectonic histories of isolated carbonate platforms. By using two end-member subsidence diagrams for the Paleogene to Neogene successions on Grand Cayman and Cayman Brac, it can be shown that their subsidence rates were heterogeneous over time and that the evolution of these islands vary significantly even though they are situated in the same basin. Although these islands, located 150 km apart, were subject to uniform changes in eustatic sea level, they have different stratigraphic architectures owing to their independent tectonic histories. From the Oligocene to the late Pliocene, the tectonic histories of Grand Cayman and Cayman Brac were analogous, and they subsided at a rate of 5.6 to 9.9 m/Myr. From the late Pliocene to ~400 ka, however, northeast Cayman Brac was uplifted by 165 m and tilted with a rotational axis offshore from the southwest end of the island, whereas Grand Cayman was uplifted by ~10 m with no rotational component. The results of this study challenge the assumption that isolated carbonate platforms have simple tectonic histories, while exploring and highlighting the common problems that are encountered with the construction of subsidence diagrams.
Scientific Reports, 2021
Carbonate rocks undergo low-temperature, post-depositional changes, including mineral precipitati... more 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...
U-Pb geochronology reveals that hydrothermal dolomitization was coeval to the deposition of the Burgess Shale lagerstätte
Communications earth & environment, Jun 13, 2024
Fault-controlled, hydrothermal dolomitization often occurs at margins between shallow-water carbo... more Fault-controlled, hydrothermal dolomitization often occurs at margins between shallow-water carbonate platforms and deep-water sedimentary basins. In western Canada, for example, the platform margin between the Cathedral Formation and the Burgess Shale Formation has been dolomitized at temperatures up to~200°C, with local magnesite, talc, and clinochlore mineralization. At the same time, the Burgess Shale Formation includes exceptional fossils that provide key evidence of the radiation of the animal phyla during the Cambrian Period (541 to 485.4 Ma). This lagerstätte and Mg-rich minerals within the adjacent and underlying strata, however, have been critically understudied. Here we show, using carbonate U-Pb geochronology, that western Canada was tectonically active and subject to hydrothermal dolomitization during the Middle Cambrian (Miaolingian Epoch) to Middle Ordovician (488.1 ± 18.8 Ma). These results extend the latest stages of rifting along the western margin of Laurentia into the Paleozoic, while also suggesting that the dolomitization of the Cathedral Formation occurred at the same time as the deposition of the Burgess Shale lagerstätte.
Communications Earth & Environment, 2024
Fault-controlled, hydrothermal dolomitization often occurs at margins between shallow-water carbo... more Fault-controlled, hydrothermal dolomitization often occurs at margins between shallow-water carbonate platforms and deep-water sedimentary basins. In western Canada, for example, the platform margin between the Cathedral Formation and the Burgess Shale Formation has been dolomitized at temperatures up to~200°C, with local magnesite, talc, and clinochlore mineralization. At the same time, the Burgess Shale Formation includes exceptional fossils that provide key evidence of the radiation of the animal phyla during the Cambrian Period (541 to 485.4 Ma). This lagerstätte and Mg-rich minerals within the adjacent and underlying strata, however, have been critically understudied. Here we show, using carbonate U-Pb geochronology, that western Canada was tectonically active and subject to hydrothermal dolomitization during the Middle Cambrian (Miaolingian Epoch) to Middle Ordovician (488.1 ± 18.8 Ma). These results extend the latest stages of rifting along the western margin of Laurentia into the Paleozoic, while also suggesting that the dolomitization of the Cathedral Formation occurred at the same time as the deposition of the Burgess Shale lagerstätte.
Basin Research, 2023
This is an open access article under the terms of the Creative Commons Attribution-NonCommercial ... more This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.
Tectonophysics, 2022
Failure of brittle rocks under axisymmetric extensional loading, when the minimum principal stres... more Failure of brittle rocks under axisymmetric extensional loading, when the minimum principal stress is tensile, results in the formation of one or more opening-mode cracks that are oriented normal to the extension axis. When all the principal stresses are compressive, failure occurs through the formation of numerous grain-scale tensile cracks, which coalesce into a shear-mode fault that is inclined at >20 • to the maximum principal stress. There have been few attempts to study the transition between these failure modes, particularly those that incorporate microstructural analyses. A transitional mode of failure, termed "hybrid failure", is often proposed to describe the orientation of faults between these end-member loading conditions, but this concept has traditionally been based on a parabolic, "Griffith-type" failure envelope that describes the growth of the single most criticallyoriented crack. By integrating axisymmetric rock deformation experiments with microstructural analyses, it can be shown that failure under these transitional conditions involves the formation of several transgranular tensile cracks, which coalesce into a shear-mode fault that is inclined at <10 • to the maximum principal stress. The stress intensity at the tip of each crack interacts with adjacent cracks to produce a stair-step geometry along the failure surface. These are what may be appropriately considered "hybrid faults", the angle of which systematically increase as the maximum principal stress, and thus the differential stress increases. There is, however, no evidence of a distinct "hybrid failure" mode, which involves the in-plane propagation of a single crack that is subject to a combined shear stress and tensile normal stress. The results of this experimental study provide novel insights into the mechanical behaviour of carbonate rocks and into the interpretation of meso-scale natural examples of failure under mixed stress-states.
Scientific Reports, 2021
Carbonate rocks undergo low-temperature, post-depositional changes, including mineral precipitati... more 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.
Marine Geology, 2021
Carbonate sedimentary successions that developed on isolated oceanic islands typically comprise a... more Carbonate sedimentary successions that developed on isolated oceanic islands typically comprise a series of unconformity-bounded packages of strata that reflect eustatic sea level changes superimposed on local tectonic movements. Resolving the subsidence and/or uplift of these islands, which are often assumed to have simple tectonic histories, is challenging because the tectonic movements are commonly of similar magnitudes to the eustatic oscillations. The uncertainty associated with each of the components involved in the construction of subsidence diagrams (e.g., age constraints, decompaction, eustatic sea level curves, paleobathymetry), therefore, introduces significant error margins when assessing the tectonic histories of isolated carbonate platforms. By using two end-member subsidence diagrams for the Paleogene to Neogene successions on Grand Cayman and Cayman Brac, it can be shown that their subsidence rates were heterogeneous over time and that the evolution of these islands vary significantly even though they are situated in the same basin. Although these islands, located 150 km apart, were subject to uniform changes in eustatic sea level, they have different stratigraphic architectures owing to their independent tectonic histories. From the Oligocene to the late Pliocene, the tectonic histories of Grand Cayman and Cayman Brac were analogous, and they subsided at a rate of 5.6 to 9.9 m/Myr. From the late Pliocene to ~400 ka, however, northeast Cayman Brac was uplifted by 165 m and tilted with a rotational axis offshore from the southwest end of the island, whereas Grand Cayman was uplifted by ~10 m with no rotational component. The results of this study challenge the assumption that isolated carbonate platforms have simple tectonic histories, while exploring and highlighting the common problems that are encountered with the construction of subsidence diagrams.
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Papers by Cole A . McCormick