Preprints
https://doi.org/10.5194/gchron-2022-26
https://doi.org/10.5194/gchron-2022-26
 
14 Nov 2022
14 Nov 2022
Status: this preprint is currently under review for the journal GChron.

Multiple Early Holocene eruptions of Katla produced tephra layers with similar composition to the Vedde Ash

David Harning1, Thor Thordarson2, Áslaug Geirsdóttir2, Gifford Miller1,3, and Christopher Florian4 David Harning et al.
  • 1Institute of Arctic and Alpine Research, University of Colorado, Boulder, USA
  • 2Faculty of Earth Sciences, University of Iceland, Reykjavík, Iceland
  • 3Department of Geological Sciences, University of Colorado, Boulder, USA
  • 4National Ecological Observatory Network, Boulder, USA

Abstract. The Vedde Ash, first described in Norway and dated to ~12000 cal a BP, has been taken to represent tephra derived from a large eruption of the Katla volcano in Iceland and dispersed across the North Atlantic and Europe. However, evidence for tephra layers with similar composition to the Vedde Ash, but of different ages, questions the utility of isolated Vedde-like tephra layers as reliable and independent age control. Here, we report three stratigraphically separated Early Holocene Katla tephra layers from the lake Torfdalsvatn, in north Iceland, that have bimodal chemical composition similar to the Vedde Ash. By using previously published conventional 14C ages and revised calibration curves, we provide new ages for these tephra layers of ~11375, 11360, and 11200 cal a BP – all substantially younger than the Vedde Ash. Torfdalsvatn’s record stands as an important reminder that repeated explosive eruptions of Iceland’s major volcanos during the deglacial cycle have produced multiple tephra plumes with similar geochemistry that may span 1000s of years. As a result, we urge caution when using isolated Icelandic tephra layers in distant regions as precise geochronometers without supporting age control.

David Harning et al.

Status: open (until 26 Dec 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on gchron-2022-26', Jan Mangerud, 17 Nov 2022 reply
    • AC1: 'Reply on CC1', David Harning, 28 Nov 2022 reply
  • RC1: 'Comment on gchron-2022-26', Anonymous Referee #1, 22 Nov 2022 reply
    • AC3: 'Reply on RC1', David Harning, 28 Nov 2022 reply
  • CC2: 'Comment on gchron-2022-26', Simon Larsson, 23 Nov 2022 reply
    • AC2: 'Reply on CC2', David Harning, 28 Nov 2022 reply

David Harning et al.

David Harning et al.

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Short summary
Volcanic ash layers are a common tool to synchronize records of past climate, and their estimated age relies on external dating methods. Here, we show that the chemical composition of the well-known, 12000 year-old Vedde Ash is indistinguishable with several other ash layers in Iceland that are ~1000 years younger. Therefore, chemical composition alone cannot be used to identify the Vedde Ash in sedimentary records.