No abstract

Northern Europe has been affected by fallout of tephra from volcanic eruptions in Iceland throughout at least the Late-glacial and Holocene. Microscopic volcanic ash horizons found in the British Isles, northern Germany and Scandinavia (e.g. Hekla 4) now provide important regional isochrons. Over recent years analytical techniques such as electron probe microanalysis (EPMA) have helped identify these distal tephra layers by glass geochemistry. Early tephra work in Sweden used refractive indices and bracketing radiocarbon dates for identification, resulting in tentative correlation. This paper presents geochemical data for Icelandic Holocene tephra in Sweden. Several sites in central Sweden have four distinct mid-Holocene tephra layers. Correlation with the Icelandic record indicates that the following tephra layers are present: Hekla 4 (ca. 3830 yr BP), Kebister tephra (ca. 3600 yr BP), Hekla 3 (ca. 2880 yr BP) and Askja AD 1875. Preliminary analyses suggest that more, previously unidentified, tephra layers are present in low concentrations in the region, indicating potential for expanding the Swedish tephrochronology for palaeoecological and palaeoenvironmental work in northern Europe.

This pilper reports the presence of a volcanic ash layer in western Sweden which is geochemically identiticd as the Kebister tephra. This tephrdpresenceof (dated c. 3600 14C BP) was discovered at Kebister, Shetland and thc rcsults presented here indicate that the deposit may have a greater geographical distribution than previously thought. The geochemistry of the volcanic glass was analysed by using discrete grain electron probe microanalysis (EPMA). Thc SiO2 content of the glass ranges from 66.19 to 71.96%, FeO content 2.73 to 6.07% and MgO content 0.15 to 0.57%˜ The tephra can he distinguished from the more widespread Hekla 4 tephra (c. 3800 14C BP) on the basis of calcium and magnesium contents.

Varve chronologies are regarded as one of the most accurate dating techniques of the Quaternary. Most work currently focuses on the process of varve formation and the environmental histories revealed in the sediments. This review aims to examine the latest investigations in relation to the recent linking of the Swedish Varve Chronology to the present (Cato, 1986). It is concluded that the Chronology would benefit from a more detailed study of the processes of formation, and that this may be achieved by using volcanic ash (tephra) as an environmental tracer.

Sigurdur Thorarinsson has inspired generations of tephrochronologists. In his thesis in 1944 he outlined the prospect of finding ash from some of the major Icelandic eruptions in peat bogs in Scandinavia. Since Christer Persson’s pioneering work in the 1960s, more than 15 tephra horizons have been identified in distal peat and sediment sequences in Sweden. The most widespread tephra from the Last Glacial-Interglacial transition (LGIT, ca. 15–9 ka BP) is the rhyolitic phase of the Vedde Ash (ca. 12.1 ka BP) which has been found in several sites with lacustrine sediments and uplifted marine clays south of the Younger Dryas moraines. Two significant new additions to the LGIT tephrochronological frameworks of NW Europe are the Hässeldalen (ca. 11.3 ka BP) and Askja-S tephras (ca. 10.4 ka BP). The most significant mid to late Holocene isochrones in Sweden are Hekla-4 (ca. 4260 BP), Hekla-S/Kebister (ca. 3720 BP), Hekla-3 (ca. 3000 BP) and Askja-1875. Other layers have been identified in single sites and are so far less valuable as marker horizons, but are potentially important for the future.