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Sökning: WFRF:(Sigmarsson Olgeir)

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  • Jonsson, Daniel Freyr, et al. (författare)
  • The multi-component Hekla Ö Tephra, Iceland : a complex widespread mid-Holocene tephra layer
  • 2020
  • Ingår i: Journal of Quaternary Science. - : WILEY. - 0267-8179 .- 1099-1417. ; 35:3, s. 410-421
  • Tidskriftsartikel (refereegranskat)abstract
    • Large Plinian eruptions from Hekla volcano, Iceland, produce compositionally zoned tephra used as key markers in tephrochronology. However, spatial variations in chemical composition of a tephra layer may complicate its identification. An example is the 5950-6180 bp cal a bp Hekla o tephra layer, which shows compositional spread from rhyolite, dacite and andesite to basalt. In soil sections north of Hekla, the SiO2 content of the tephra glass reaches 76 wt% in the lowest unit of the Hekla o deposit and decreases to 62-63 wt% in the uppermost unit. Intermingled within the whole deposit are basalt tephra grains having 46-47 wt% SiO2. The composition of the basalt glass includes primitive basalt and a more evolved basalt (MgO >6 and <6 wt%, respectively). Together with literature data, the Hekla o tephra and the so-called T-Tephra/Hekla-T are most likely from contemporaneous eruptions of different vents on the Hekla volcanic system, forming a single important marker tephra (Hekla oT) deposited over 80% of Iceland. Identification is complicated by its spatial compositional heterogeneity, such as systematic decrease in SiO2 content from the east to the west of Hekla volcano. Consequently, an individual tephra layer from a large explosive eruption can have different composition at different locations.
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