A quantitative x-ray diffraction inventory of volcaniclastic inputs into the marine sediment archives off Iceland: a contribution to the Volcanoes in the Arctic System programme
|Author(s)||Andrews John T.1, Kristjansdottir Greta B.1, 2, Eberl Dennis D.3, Jennings Anne E.1|
|Affiliation(s)||1 : Univ Colorado, Dept Geol Sci, Inst Arctic & Alpine Res, Boulder, CO 80309 USA.
2 : Univ Iceland, Sch Engn & Nat Sci, VR II, IS-107 Reykjavik, Iceland.
3 : US Geol Survey, Boulder, CO 80303 USA.
|Source||Polar Research (0800-0395) (Co-action Publishing), 2013 , Vol. 32 , N. 11130 , P. 1-15|
|WOS© Times Cited||4|
|Note||Supplementary files : http://www.polarresearch.net/index.php/polar/rt/suppFiles/11130/0|
|Keyword(s)||X-ray diffraction, tephras, Iceland Holocene|
|Abstract||This paper re-evaluates how well quantitative x-ray diffraction (qXRD) can be used as an exploratory method of the weight percentage (wt%) of volcaniclastic sediment, and to identify tephra events in marine cores. In the widely used RockJock v6 software programme, qXRD tephra and glass standards include the rhyodacite White River tephra (Alaska), a rhyolitic tephra (Hekla-4) and the basaltic Saksunarvatn tephra. Experiments of adding known wt% of tephra to felsic bedrock samples indicated that additions >= 10 wt% are accurately detected, but reliable estimates of lesser amounts are masked by amorphous material produced by milling. Volcaniclastic inputs range between 20 and 50 wt%. Primary tephra events are identified as peaks in residual qXRD glass wt% from fourth-order polynomial fits. In cores where tephras have been identified by shard counts in the >150 mu m fraction, there is a positive correlation (validation) with peaks in the wt% glass estimated by qXRD. Geochemistry of tephra shards confirms the presence of several Hekla-sourced tephras in cores B997-317PC1 and -319PC2 on the northern Iceland shelf. In core B997-338 (north-west Iceland), there are two rhyolitic tephras separated by ca. 100 cm with uncorrected radiocarbon dates on articulated shells of around 13 000 yr B. P. These tephras may be correlatives of the Borrobol and Penifiler tephras found in Scotland. The number of Holocene tephra events per 1000 yr was estimated from qXRD on 16 cores and showed a bimodal distribution with an increased number of events in both the late and early Holocene.|