Using volcaniclastic rocks to constrain sedimentation ages: To what extent are volcanism and sedimentation synchronous?

Autor: Pierre Pellenard, Marc Poujol, Marie-Pierre Dabard, Céline Ducassou, Sylvie Bourquin, Thierry Nalpas, Gloria Heilbronn, Marc Jolivet, Erwan Hallot, Jianxin Yu, Camille Rossignol
Přispěvatelé: Géosciences Rennes (GR), Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR), Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Centre National de la Recherche Scientifique (CNRS), Biogéosciences [UMR 6282] (BGS), Université de Bourgogne (UB)-Centre National de la Recherche Scientifique (CNRS), Cambridge Arctic Shelf Programme (CASP), University of Cambridge [UK] (CAM), Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences [Wuhan] (CUG), 41572005, National Natural Science Foundation of China, 2018/02645-2, Fundação de Amparo à Pesquisa do Estado de São Paulo, Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES), Biogéosciences [UMR 6282] [Dijon] (BGS), Université de Bourgogne (UB)-AgroSup Dijon - Institut National Supérieur des Sciences Agronomiques, de l'Alimentation et de l'Environnement-Centre National de la Recherche Scientifique (CNRS)
Jazyk: angličtina
Rok vydání: 2019
Předmět:
Zdroj: Sedimentary Geology
Sedimentary Geology, 2019, 381, pp.46-64. ⟨10.1016/j.sedgeo.2018.12.010⟩
Sedimentary Geology, Elsevier, 2019, 381, pp.46-64. ⟨10.1016/j.sedgeo.2018.12.010⟩
ISSN: 0037-0738
Popis: International audience; Volcaniclastic rocks are commonly used to date sedimentary series since absolute ages are routinely obtained from several geochronological methods. In this work, we present five selected geochronological studies (UPb on zircon) on late Paleozoic to Mesozoic volcaniclastic series from Asia, with the aim of discussing if absolute ages obtained on volcaniclastic rocks can be used directly to date sedimentation. For all these volcaniclastic series, volcanism and sedimentation are reputedly coeval and zircon grains have been dated to obtained depositional ages. Nevertheless, among the five volcaniclastic series, only two provide U-Pb/zircon ages that are demonstrably representative of the sedimentation ages (Guandao Section, south China, and Luang Prabang Basin, Laos). In the three other series (Wusu Section, northwest China, Chahe and Daxiahiou sections, south China), U-Pb/zircon ages are not suitable to constrain depositional ages. Perhaps more troubling, all the zircon grains collected from a volcanic layer in the Wusu Section are shown to exhibit ages that are much older than the sedimentation age of the deposits in which the volcanic layer is interbedded.These five examples highlight two prerequisites that must be fulfilled in order to date the deposition of volcaniclastic sediments using geochronological methods: (i) at least some of the dated minerals must have crystallized during or just before one of the last eruptions that provided the volcaniclasts, and (ii) volcanic activity and sedimentation must have been coeval. Accurate sedimentation ages from radiometric dates can only be assessed if these prerequisites are fully demonstrated. A reliable method to verify this consists in systematically comparing the maximum depositional ages obtained from a set of samples along a section with their relative position in the section. Indeed, maximum depositional ages getting younger upwards in a section likely demonstrate that the volcaniclasts were produced during sedimentation and contain grains that crystallized immediately before each eruption. In such conditions, orders of magnitude for time scales of reworking can be estimated. They relate to the episodic and different rates of development of the volcanic edifices and fields, competing with the time necessary for erosion, transport and sedimentation.
Databáze: OpenAIRE
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