Distribution, sediment magnetism and geochemistry of the Saksunarvatn (10 180 ± 60 cal. yr BP) tephra in marine, lake, and terrestrial sediments, northwest Iceland
✍ Scribed by Prof. John T. Andrews; Aslaug Geirsdóttir; Jórunn Hardardóttir; Sarah Principato; Karl Grönvold; Gréta B. Kristjansdóttir; Gudrún Helgadóttir; John Drexler; Arny Sveinbjörnsdóttir
- Publisher
- John Wiley and Sons
- Year
- 2002
- Tongue
- English
- Weight
- 568 KB
- Volume
- 17
- Category
- Article
- ISSN
- 0267-8179
- DOI
- 10.1002/jqs.727
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✦ Synopsis
Abstract
In 1997, seismic surveys in the troughs off northwest and north Iceland indicated the presence of a major, regional sub‐bottom reflector that can be traced over large areas of the shelf. Cores taken in 1997, and later in 1999 on the IMAGES V cruise, penetrated through the reflector. In core MD99‐2269 in Húnaflóaáll, this reflector is shown to be represented by a basaltic tephra with a geochemical signature and radiocarbon age correlative with the North Atlantic‐wide Saksunarvatn tephra. We trace this tephra throughout northwest Iceland in a series of marine and lake cores, as well as in terrestrial sediments; it forms a layer 1 to 25 cm thick of fine‐ to medium‐grained basaltic volcanic shards. The base of the tephra unit is always sharp but visual inspection and other measurements (carbonate and total organic carbon weight %) indicate a more diffuse upper boundary associated with bioturbation and with sediment reworking. Off northwest Iceland the Saksunarvatn tephra has distinct sediment magnetic properties. This is evident as a dramatic reduction in magnetic susceptibility, an increase in the frequency dependant magnetic susceptibility and ‘hard’ magnetisation in a −0.1T IRM backfield. Geochemical analyses from 11 sites indicate a tholeiitic basalt composition, similar to the geochemistry of a tephra found in the Greenland ice‐core that dates to 10 180 ± 60 cal. yr BP, and which was correlated with the 9000 ^14^C yr BP Saksunarvatn tephra. We present accelerator mass spectrometry ^14^C dates from the marine sites, which indicate that the ocean reservoir correction is close to ca. 400 yr at 9000 ^14^C yr BP off northwest Iceland. Copyright © 2002 John Wiley & Sons, Ltd.