Holocene tephrostratigraphy in Vestfirðir, NW Iceland

Abstract

We present a tephra stratigraphical and tephrochronological record from eight lakes in Vestfirðir, NW Iceland. About 50 tephra units have been identified, representing nearly 30 eruptive events originating from five volcanic systems: Hekla, Katla, Snæfellsjökull, Grímsvötn and Veiðivötn‐Bárðarbunga. Most of the tephra layers originate from Grímsvötn, although there is a prominent presence of andesitic to basaltic tephra layers from Hekla in the record. We propose that the previously described Brattihjalli tephra is actually the 6060‐year‐old Hekla Ö tephra marker layer, recording a more north‐westerly dispersal than before and providing new correlation possibilities across Iceland. Thus, the Hekla Ö tephra covers as large an area in Iceland as the Hekla 5, Hekla 4, Hekla 3 and Hekla 1104 tephra layers, emphasizing its importance as a chronological marker. The tephra markers Hekla 1693, V877/Settlement layer, Sn‐1, Hekla 3 and Hekla 4 have been found and, additionally, our study identifies four potential tephra markers, the Katla D1 ∼2750 cal a BP, Katla D2 ∼3700 cal a BP, Reykjarfjörður tephra ∼8800 cal a BP and Dagverðardalur tephra ∼9300–9500 cal a BP. Our data reveal several new tephra layers in Vestfirðir, including chronological markers important for dating and correlation.

The multi‐component Hekla Ö Tephra, Iceland: a complex widespread mid‐Holocene tephra layer

“…A relatively primitive basalt composition has previously been observed in tephra layers in soil sections from central and south‐east Iceland (Óladóttir, , ) and in lake sediments in east, west and north‐west Iceland (Hardardóttir et al , ; Jóhannsdóttir, ; Gudmundsdóttir et al , , ; Gunnarsson, ; Harning et al , ). Furthermore, a more evolved basalt composition is seen in at least three tephra layers in central and west Iceland (Jóhannsdóttir, ; Óladóttir, ; Gunnarsson, ).…”

“…The size fraction is expected to cover all glass compositions in each sample, but does not reflect their relative proportions in the whole deposit. The results were compared with analyses of glasses from Hekla Ö in both distal and proximal areas (Gudmundsdóttir et al , , , ; Óladóttir et al , ; Sigurgeirsson and Hjartarson, ; Eddudóttir et al , ; and new data from selected soil sections; see Fig. ) along with X‐ray fluorescence (XRF) analyses of crystal‐poor pumice clasts from another section of Tagl, analysed at the Geochemical Laboratories at McGill University in Montreal.…”

“…The presence of the Hekla Ö tephra in soil sections in central and SE Iceland has been known for decades (Larsen and Vilmundardóttir, ; Gudmundsson, ). More recently, several studies have confirmed the widespread dispersal of the Hekla Ö tephra over Iceland (Gudmundsdóttir et al , ; Óladóttir et al , ; Sigurgeirsson and Hjartarson, ; Eddudóttir et al , ; Gudmundsdóttir et al , , ; Jónsson, ), as well as in offshore sediments north of the island (Gudmundsdóttir et al , ). North and north‐east of Hekla, the Hekla Ö tephra is frequently found in association with two other layers, the Hekla Mó tephra (ca.…”

“…Gudmundsdóttir et al, 2011Gudmundsdóttir et al, , 2016Óladóttir et al, 2011;Eddudóttir et al, 2016). Recently, considerations as to whether a tephra layer called Brattihjalli tephra is a part of the Hekla Ö tephra have been discussed by Gudmundsdóttir et al (2018) who suggested that thẽ 6060-6615 cal a BP Brattihjalli tephra in NW Iceland (Schomacker et al, 2016) represents the western part of the Hekla Ö, indicating an even more westerly distribution.…”

“…Changes in the silicic component and the basaltic component of the Hekla Ö tephra as observed in distal deposits from east to west across Iceland. LÖG (Gudmundsdóttir et al , ), KAR, SNÆ, SAU, HRE, NÚP (Óladóttir et al , ), KVÍ (Gudmundsson, ), SVA, HER (this study), LGA, MD99‐2275 (Gudmundsdóttir et al , ), BAR, KAG (Eddudóttir, ; Eddudóttir et al , ; this study), SKR/SKO, (Gudmundsdóttir et al , ; Harning et al , ), BAE, TRK (Harning et al , ), NHV, DAG, REY, BRA (Gudmundsdóttir et al , ), HST (Hardardóttir et al , ; Jóhannsdóttir, ), HAK, HVÍ (Jóhannsdóttir, ), ARN (Gunnarsson, ), TAGL (Jónsson, ; this study), and MOS, ELL (Sigurgeirsson and Hjartarson, ). See Fig.…”