A Lateglacial–early Holocene tephrochronology for SW Sweden

Abstract

Four cores from southwestern Sweden are presented together with their tephra geochemistry. Two cryptotephra horizons were confirmed geochemically in the cores, the Vedde Ash and the Hässeldalen Tephra. The Lateglacial Hässeldalen Tephra (11 360–11 300 cal. a BP) offers great potential as a regional isochrone to add a new degree of certainty to the deglaciation chronology of southern Sweden, including the extent of glacial Lake Bolmen. In addition, the geographical distribution of the Hässeldalen Tephra has recently been extended outside of Sweden, making it an important time‐marker horizon in northern Europe. There are potential difficulties, however. Proper identification of the actual isochrone is complicated by the vertical pattern of shard distribution, which could be the result of several eruptive events, as well as by the fact that shards from the 10‐ka Askja horizon (10 500–10 350 cal. a BP) were found in close stratigraphical proximity. The geochemical data presented are the result of improved EPMA methodology, which significantly reduces sodium mobilization. The results therefore have slightly altered values, which has consequences for classifying new finds when they are compared with previous data for geochemically similar tephras. Finally, potential indications of the Borrobol/Penifiler horizon are presented, although the existence of the horizon could not be confirmed geochemically. This highlights the need to retrieve cores from different locations within a basin based on an analysis of basin morphology if horizons are to be located.

Lateglacial cryptotephra detected within clay varves in Östergötland, south‐east Sweden

“…The Lateglacial Laacher See Tephra (ca. 12 880 cal a BP) has been reported (but not confirmed) to be present in a Baltic Sea core (Påhlsson and Bergh Alm, ) and the Early Holocene Hässeldalen and Askja‐S tephras (11 360–11 300 cal a BP and 10 350–10 500 cal a BP, respectively; Davies et al ., ; Lind and Wastegård, ; Lilja et al ., ) are known to occur across the southern Baltic area and might also be used to synchronize varved records with other palaeoclimate records.…”

Revisiting the Borrobol Tephra

“…Lilja et al . ). These small but persistent differences in alkalis and SiO 2 probably reflect improved analytical conditions.…”

“…While the Vedde Ash often presents a clear-cut horizon, even at low concentrations (e.g. Lilja et al 2012), the BT and PT remain ambiguous.…”

“…Recent studies have indicated the possibility that different horizons may still be identical in terms of their major elements (Davies et al 2004;Pyne-O'Donnell 2007;Lind et al 2013;Jennings et al 2014), leading to difficulties in identification. Studies have also indicated that the identification of the isochron, the point of initial deposition of the tephra that defines its eruption age, may not be as straightforward as first thought (Davies et al 2007;Lilja et al 2012;Payne & Gehrels 2010).…”

STOP 2: Late-glacial and postglacial environmental changes, Lake Āraiši, Vidzeme Upland

“…The Hässeldalen tephra (11,300 cal yr BP) is the possible source for this tephra. Lilja et al (2013) point out that, due to several eruptive events and stratigraphical proximity, the 10-ka Askja could be another possible source. Even though there are two possible sources, this discovery offers great potential as a regional isochrone, which could be used to synchronize the chronology and sediment records of the central and northern European deglaciation.…”