New Early Holocene tephra horizons from the Faroe Islands

• The early Holocene climate in the North Atlantic region was rather unstable and three cold events superimposed upon a general warming took place during the earliest part of the Holocene: the Preboreal oscillation (11.3-11.1 ka BP), the Erdalen event (10.3-10.2 ka BP) and the 9.3 ka BP event (e.g. Dahl et al., 2002; Rasmussen et al. 2007). There is relatively little known about early Holocene tephrochronology in comparison to the Last Glacial/Interglacial transition and the mid to late Holocene, although there is no reason to believe that Icelandic eruptions were less frequent during the early Holocene. The main focus of the present study is improve the dating and geochemical identification of early Holocene tephras on the Faroe Islands, using wiggle-match or Bayesian techniques for age-depth modelling and EMPA analyses for geochemical fingerprinting of tephras. Identification of tephras is also aided by XRF core scanning. While this method is still in its infancy, some promising results have been reported recently regarding the identification of cryptotephra in marine and lacustrine sediments. The Faroe Islands is an ideal area to test the method, since tephras ranging from basaltic to rhyolitic are abundant but usually not visible to the naked eye (Wastegård, 2002). We have investigated new cores taken in 2009 from previously studied sites and new sites with high sediment accumulation rates during the early Holocene. Results from the first analyzed peat and lake sediment cores from the Faroe Islands show that several previously unreported tephra horizons occur below the visible Saksunarvatn tephra dated to c. 10 300 cal. yr BP (Rasmussen et al. 2007). Two layers are rhyolitic, one dacitic and one basaltic. The XRF core-scanner data has been especially useful for identifying basaltic cryptotephra horizons.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences (hsv//eng)

Nyckelord

Earth sciences

Geovetenskap

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