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

Abstract

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Sedimentology and U-Pb dating of Carboniferous to Permian continental series of the northern Massif Central (France): Local palaeogeographic evolution and larger scale correlations

“…X-ray Diffraction (XRD) for the bulk rock and the clay-size fraction (< 2 µm) were performed at the Biogéosciences Laboratory (Université de Bourgogne) to determine the mineralogical content of 33 clay layers that potentially correspond to tonsteins, and 3 samples of the enclosing detrital sediments (Table 1). By comparison, the mineralogical contents of the layers distinguish tonsteins that are directly derived from volcanic ashes from volcanic-sedimentary rocks, containing a mixture of ashes and detrital particles (Pellenard et al 2017;Rossignol et al, 2019).…”

“…Their close association with tonstein layers and the fact that these volcaniclastic deposits are only found as debris flows suggest that they correspond to catastrophic events that were deposited during periods of volcanic activity. However, in the absence of geochronological constraints for the volcaniclasts, it cannot be excluded that at least part of the volcaniclasts could have been reworked from older volcanic deposits (e.g., Rossignol et al, 2019). Lake deposits (L1 and L2) or playa-lake (PL1 and PL2 facies associations) are either located laterally from the delta, where detrital input is weaker, or in the more distal part of the lake.…”

“…Determination of depositional ages of volcaniclastic rocks from radiometric dating is not always straightforward, as recently highlighted by Rossignol et al (2019). In order to make sure that the age obtained from radiometric dating corresponds to the deposition age, two conditions must be verified: (i) the magmatic eruption must be coeval with sedimentation (i.e., the volcanic ashes were not reworked), and (ii) the dated minerals must have crystallised shortly before the magmatic eruption.…”

“…xenocrysts, antecrysts, e.g. Rossignol et al 2019, and references therein), and thus may yield dates that are older than the actual depositional ages. Conversely, older dates obtained from apatite crystals exotic to the magma are not expected to be preserved because of the low closure temperatures of this mineral (450-550°C, Schoene and Bowring, 2007).…”

Tectonic controls on the Maastrichtian-Danian transgression in the Magallanes-Austral foreland basin (Chile): Implications for the growth of the Southern Patagonian Andes

“…Therefore, there is a good representation of all populations to interpret provenance. Likewise, when we considered the number of grains analysed per sample (to calculate a maximum depositional age), there was a 95% chance of finding at least three grains from every population that makes up ≥ 7% of the total zircon content (Rossignol et al, 2019). A detailed description of the separation, analytical and statistical technique, as well as raw histograms and Concordia plots for detrital zircon analyses, can be found in Appendix C. The detrital zircon U-Pb geochronological analyses are shown in Appendix D.…”