Preprints
https://doi.org/10.5194/gchron-2021-45
https://doi.org/10.5194/gchron-2021-45

  12 Jan 2022

12 Jan 2022

Review status: this preprint is currently under review for the journal GChron.

Cyclostratigraphy of the Middle to Upper Ordovician successions of the Armorican Massif (western France) using portable X-ray fluorescence

Matthias Sinnesael1,2,3, Alfredo Loi4, Marie-Pierre Dabard5,, Thijs R. A. Vandenbroucke2, and Philippe Claeys1 Matthias Sinnesael et al.
  • 1Analytical, Environmental and Geo-Chemistry, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
  • 2Department of Geology, Ghent University, Krijgslaan 281/S9, 9000 Ghent, Belgium
  • 3IMCCE, CNRS, Observatoire de Paris, PSL University, Sorbonne Université, 77 Avenue Denfert-Rochereau, 75014, Paris, France
  • 4University of Cagliari Department of Chemical and Geological Sciences, Cittadella Universitaria, Blocco A – 09042, Monserrato, Italy
  • 5Géosciences UMR6118 CNRS/Université Rennes1, Campus de Beaulieu, 35042 Rennes, Cédex, France
  • deceased

Abstract. To expand traditional cyclostratigraphic numerical methods beyond their common technical limitations and apply them to truly deep-time archives we need to reflect on the development of new approaches to sedimentary archives that traditionally are not targeted for cyclostratigraphic analysis, but that frequently occur in the impoverished deep-time record. Siliciclastic storm-dominated shelf environments are a good example of such records. Our case study focusses on the Middle to Upper Ordovician siliciclastic successions of the Armorican Massif (western France), which are well-studied in terms of sedimentology and sequence stratigraphy. In addition, these sections are protected geological heritage due to the extraordinary quality of the outcrops. We therefore tested the performance of non-destructive high-resolution (cm-scale) portable X-ray fluorescence and natural gamma-ray analyses on outcrop to obtain major and trace element compositions. Despite the challenging outcrop conditions in the tidal beach zone, our geochemical analyses provide useful information regarding general lithology and several specific sedimentary features such as the detection of paleoplacers, or the discrimination between different types of diagenetic concretions such as nodules. Secondly, these new high-resolution data are used to experiment the application of commonly used numerical cyclostratigraphic techniques on this siliciclastic storm-dominated shelf environment, a non-traditional sedimentological setting for cyclostratigraphic analysis. In the lithological relatively homogenous parts of the section spectral power analyses and bandpass filtering hint towards a potential astronomical imprint of some sedimentary cycles, but this needs further confirmation in the absence of more robust independent age constraints.

Matthias Sinnesael et al.

Status: open (until 24 Feb 2022)

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Matthias Sinnesael et al.

Matthias Sinnesael et al.

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Short summary
We used new geochemical measurements to study the expression of astronomical climate cycles recorded in the Ordovician (~460 million years ago) geological sections of the Crozon Peninsula (France). This type of geological archives is not often studied in this way, but as they become more important going back in time, a better understanding of their potential astronomical cycles is crucial to advance our knowledge on deep-time climate dynamics and construct high-resolution timescales.