| Titre | Bioturbation, heavy mineral concentration, and high gamma-ray activity in the Lower Cretaceous McMurray Formation, Canada |
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| Auteur | Fustic, M ; Nair,
R; Wetzel, A; Siddiqui, R; Mathews, W; Wust, R; Bringue, M;
Radovic, J |
| Source | Palaeogeography, Palaeoclimatology, Palaeoecology vol. 564, 110187, 2020 p. 1-17, https://doi.org/10.1016/j.palaeo.2020.110187  Accès ouvert |
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| Année | 2020 |
| Séries alt. | Ressources naturelles Canada, Contribution externe 20200671 |
| Éditeur | Elsevier |
| Document | publication en série |
| Lang. | anglais |
| DOI | https://doi.org/10.1016/j.palaeo.2020.110187 |
| Media | papier; en ligne; numérique |
| Formats | pdf; html |
| Province | Alberta |
| SNRC | 83I; 83P; 73L; 73M; 84A; 84H; 74D; 74E |
| Lat/Long OENS | -114.0000 -110.0000 58.0000 54.0000 |
| Sujets | échantillons carrotés; ichnologie; bioturbation; zircon; origine; bancs arqués; diagraphie géophysique; diagraphie par rayons gamma; analyses de faciès; faciès sédimentaires; datation radiométrique;
datation au uranium-plomb; analyses par diffraction des rayons x; méthodes de fluorescence aux rayons x; microscopie des lames minces; analyses pétrographiques; analyses minéralogiques; radioactivité; analyses des minéraux lourds; concentration;
enrichissement des minéraux; Formation de Mcmurray ; sédimentologie; paléontologie; géophysique; géochronologie; minéralogie; géologie économique; Sciences et technologie; Nature et environnement; Phanérozoïque; Mésozoïque; Crétacé |
| Illustrations | cartes de localisation; diagraphies; diagrammes; diagrammes; photographies; tableaux |
| Programme | GEM2 : La géocartographie de l'énergie et des minéraux L'ouest de l'Arctique-Beaufort-nord du Yukon |
| Diffusé | 2020 12 29 |
| Résumé | (disponible en anglais seulement)
In the Lower Cretaceous McMurray Formation (Alberta, Canada), many intervals of intensely bioturbated (Bioturbation Index = 5-6) fine-grained sediments are
characterized by high gamma-ray (GR) readings. Several methods, including sedimentary facies analysis, thin-section petrography, handheld spectral gamma-ray, portable X-ray fluorescence, X-ray diffraction, inductively coupled plasma-mass
spectrometry, microprobe of K-feldspar, energy dispersive spectroscopy, and detrital zircon geochronology by laser ablation-inductively coupled plasma-mass spectrometry, were used to investigate the interval of interest in core samples. The
mineralogical analysis shows that these intervals are enriched in heavy mineral grains, and particularly in zircons. The content of radioactive elements is variable. Thorium is commonly elevated up to three times, uranium nil to two times, and
potassium content usually remains normal. The studied intervals consist of interbedded, bitumen-saturated crossbedded and/or ripple cross-laminated sandstone (high-energy deposits) and light-gray bioturbated mudstone (low-energy deposits), commonly
addressed as inclined heterolithic strata (IHS). IHS represent tidally influenced, brackish-water, upper point-bar deposits. The zircon grains become concentrated while hydraulic processes interact with bioturbation: the burrowing animals cause
significant sediment mixing that allows the lightest sediment particles to go back into the suspension. Additionally, bioturbation increases the surface roughness along the sediment-water interface and, causes more turbulent flow, allowing for quartz
and other light grains to be removed by traction and/or saltation, while dispersed heavier zircon grains become trapped and concentrated in open burrows. So far, this study is the first to demonstrate the importance of bioturbation in the enrichment
of zircon grains in IHS. The interaction of bioturbation and hydraulic processes explains the apparently counter-intuitive enrichment of heavy minerals in a low-energy depositional setting. This scenario likely applies to numerous intervals
characterized by similar GR and/or zirconium spikes across the McMurray Formation. Furthermore, it can be expected that in other sedimentary basins and stratigraphic units, similar studies will demonstrate that the proposed mechanism is
universal. |
| Sommaire | (Résumé en langage clair et simple, non publié)
Cet article propose un mécanisme permettant d'expliquer les relevés de rayons gamma exceptionnellement élevés dans les sédiments fins de la
formation de McMurray du Crétacé inférieur (Alberta, Canada). Les analyses montrent que ces intervalles sont enrichis en grains de minéraux lourds, en particulier en zircons dans ces dépôts influencés par les marées. Les grains de zircon se
concentrent lorsque les animaux fouisseurs mélangent les sédiments, permettant aux particules les plus légères de retourner en suspension. La bioturbation augmente également la rugosité de surface à l'interface eau-sédiments, ce qui permet d'éliminer
les grains plus légers tandis que les grains de zircon se concentrent dans les terriers. La compréhension de ce processus facilitera l'interprétation des diagraphies de puits, couramment utilisées dans l'exploration des ressources
énergétiques. |
| GEOSCAN ID | 327954 |
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