GEOSCAN, résultats de la recherche


TitreIn situ Modelling of conodonts using x-ray micro-tomography
AuteurGadd, M G; Peter, J M; Gaidies, F; Gouwy, S
SourceExplore no. 174, 2017 p. 22
Séries alt.Secteur des sciences de la Terre, Contribution externe 20160424
ÉditeurAssociation of Applied Geochemists
Documentpublication en série
Mediapapier; en ligne; numérique
Sujetsconodontes; biostratigraphie; minéralisation; distribution stratigraphique des fossiles; morphologie des fossiles; descriptions des fossiles; minéraux métalliques; paléontologie
ProgrammeÉtude des gîtes de sulfures massifs volcaniques, Initiative géoscientifique ciblée (IGC-4)
LiensOnline - En ligne
Résumé(disponible en anglais seulement)
The understanding of whether or not the multiple Ni-Mo-Zn-PGE mineralized showings and prospects that are exposed over several hundred kilometers in the Yukon, Canada are part of a single time-stratigraphic layer would have major exploration implications for this style of mineralization. A new method for imaging condont elements reported here may provide age constraints for these mineralized shales. Conodont elements are feeding apparatuses of eel-like marine vertebrates comprised of the mineral hydroxylapatite (but commonly altered to fluorapatite during diagenesis). They are widespread throughout Paleozoic strata and are commonly used as index fossils for Paleozoic epochs. We have identified, during optical microscopic examination of polished thin sections, the presence of abundant conodont elements within Devonian-aged hyper-enriched black shale (HEBS) Ni-Mo-Zn-PGE deposits in the Yukon Territory, Canada, that were previously overlooked. These conodont elements may provide key information on regional biostratigraphic correlation of the geographically widespread mineralized layer. Correct identification of conodont subspecies requires documentation of 3D morphology, but extraction of conodont elements from indurated shales is typically problematic and requires the use of harmful, environmentally deleterious reagents (e.g., hydrofluoric acid). The conodont elements are very delicate and physical and chemical extraction methods may fracture or destroy ornamentation. Our previous attempts at extraction using electric pulse disaggregation resulted in the destruction of these microfossils. However, recent advances in high-energy x-ray micro-computed tomography allow detailed, ultra-high-resolution (5 micron), 3D models of the conodont elements inside intact rock samples (Fig. 1) to be constructed. Such models could potentially be used to identify key conodont subspecies, which are typically confined to narrow zones within Paleozoic epochs and thus provide age constraints for the HEBS layer that are currently lacking. High-energy x-ray micro-computed tomography has other important use application to support mineral exploration. For example, these methods can be used to image indicator minerals to characterize surface textures and determine distance of transport from source.
Résumé(Résumé en langage clair et simple, non publié)
Cette courte note technique décrit une méthode utilisée pour obtenir des images de microfossiles in situ. Ces images peuvent être utilisées pour placer des contraintes d'âge sur les roches.