First discovery of cryptotephra in Holocene peat deposits of Estonia, eastern Baltic

摘要

This article reports the first discovery of middle Holocene cryptotephra from a peat sequence in Estonia, eastern Baltic. Two sequences, Mustjarve and Parika (located 110 km apart), were chosen for a pilot study aimed at finding traces of tephra fallout during the middle Holocene. Peat accumulation at both sites started in the early Holocene (c. 9500 - 9000 C-14 yr BP; c. 11 000 - 10 000 cal. yr BP) and continued throughout the whole Holocene. The radiocarbon-dated intervals between c. 2000 and 5000 C-14 yr BP (c. 2000 - 5500 cal. yr BP) were chosen from both sites for the study. Colourless tephra shards were identified at 312 - 316 cm below the peat surface in the Mustjarve peat sequence, while no tephra was found in peat of the same age at Parika. Electron microprobe analyses suggest a correlation with the initial phase of the Hekla-4 eruption (c. 4260 cal. yr BP), although the age - depth model indicated an age around 4900 cal. yr BP. Small concentrations of colourless to light brown tephra shards at 266 - 270 cm in the Mustjarve sequence indicate that the Kebister tephra (c. 3750 cal. yr BP) might also be present, but geochemical analyses were not possible. The low concentration and small size of the tephra particles indicate that Estonian bogs are probably on the verge of where tephrochronology is possible in northwestern Europe. Further studies of full Holocene sequences are required in order to discover traces of other ash plumes reaching as far east as the eastern Baltic area.