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| Titel |
Tephra in marine sediment cores offshore southern Iceland: A 68,000 year record of explosive volcanism |
| VerfasserIn |
Christina Bonanati, Heidi Wehrmann, Maxim Portnyagin, Kaj Hoernle, Maryam Mirzaloo, Dirk Nürnberg |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250135815
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| Publikation (Nr.) |
 EGU/EGU2016-16724.pdf |
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| Zusammenfassung |
| Explosive volcanic eruptions on Iceland, even of intermediate magnitude have far-reaching
impacts. Their far-distal deposits have been found up to Northern Continental Europe and
Greenland. On Iceland, the harsh environment and strongly erosive conditions limit the
preservation of volcanic deposits and their accessibility on land. The area offshore southern
Iceland preserves information about the depositional fans at medial distance from the
volcanic source. Here we use this sedimentary archive to reconstruct the Icelandic eruption
record in greater detail. This high resolution geological record allows us to infer eruption
frequencies and explosiveness in great detail and contributes to the assessment of Icelandic
volcanic hazards, volcano-climate interaction, stratigraphy and palaeoceanographic
reconstructions.
Eight gravity cores were obtained during RV Poseidon Cruise 457, at 260 to 1,600 m water
depths and distances of 130 to 400 km west to southeast of Iceland. The ∼4 to 10 m long
sediment cores reach back to the Late Pleistocene (∼68 ka BP; dated by 14C and
sedimentation rates), mostly excluding the Holocene. Potential tephra layers were identified
by visual inspection and color scans. Volcanic glass shards were analyzed for their
major element composition by electron microprobe and assigned to their eruptive
source by geochemical fingerprinting. More than 50 primary tephra layers and
nearly as many reworked layers were identified, several of which were correlated
across the cores. The mostly basaltic tephra shards are derived from the Katla,
Grímsvötn-Lakagígar, Bárðarbunga-Veiðivötn, and Hekla volcanic systems. Primary and
mixed layers with particles of unique bimodal composition identical to the ∼12 ka BP
Vedde-Tephra from the Katla Volcanic System, including rhyolitic particles, were identified
in nearly all cores and used as time marker and for inter-core correlation. Tephra
layers of unique unknown composition were also identified and stratigraphically
assigned across some of the cores. Intercalated dropstones from Heinrich events
provide additional age constraints. The core and tephra correlations are supported
by color scans, of which the *b-values tie in with the δ18O Greenland Ice-core
record.
The marine tephrostratigraphy offshore southern Iceland extends the eruption record
further back in time than currently inferred from terrestrial Iceland and in more
detail than far-distant deposits. It provides depositional evidence for previously
unrecognized eruptions and demonstrates that Icelandic volcanoes erupted more
often than previously thought. The depositional time frame of the tephra layers in
the cores facilitates to integrate climatically-induced variations in sedimentation
rates and conditions at the different sites around Iceland with changes in eruption
frequency. |
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