Widespread tephra layers in the Bering Sea sediments: distal clues to large explosive eruptions from the Aleutian volcanic arc

• Published in: Bulletin of Volcanology
• Main Authors: Derkachev, A. N., Ponomareva, V. V., Portnyagin, Maxim V., Gorbarenko, S. A., Nikolaeva, N. A., Malakhov, M. I., Zelenin, E. A., Nürnberg, Dirk, Liu, Yanguang
• Format: Article in Journal/Newspaper
• Language: English
• Published: Springer 2018
• Subjects: Bering Sea; Pacific; Semisopochnoi Island; Alaska
• Online Access: https://oceanrep.geomar.de/id/eprint/44601/; https://oceanrep.geomar.de/id/eprint/44601/1/Derkachev.pdf; https://doi.org/10.1007/s00445-018-1254-9

Tephra layers within marine sediments provide information on past explosive eruptions, which is especially important in the case of remote island arcs where data on proximal pyroclastic deposits can be scarce. Three Alaska-Aleutian tephras (labeled Br2, SR2, and SR4) were found in the late Pleistocene-Holocene sediments of the Bering Sea (north Pacific). We fingerprint glass from these tephras with the help of single-shard electron microprobe and LA-ICP-MS analyses and provide microprobe data on minerals from two of these tephras. The large compositional variability of the Alaska-Aleutian volcanoes permits the use of ratios of highly incompatible trace elements (Ba/Nb, Th/Nb, Th/La, La/Nb) for identification of distal tephra sources by comparison of these ratios in tephra glass and proximal bulk rock analyses. This method, along with mapped tephra dispersal, has allowed us to link tephras under study to Aniakchak, Semisopochnoi, and Okmok volcanoes, respectively. Our results indicate that tephra Br2 was derived from the ~ 3.6 ka Aniakchak II caldera-forming eruption (Alaska, USA). This is the first ever finding of the Aniakchak II tephra in Bering Sea sediments, which permits enlargement of its tephra volume and eruption magnitude to ~ 100 km3 and 6.8, respectively. Tephra SR2, dated at ~ 12.2 ka, is likely associated with a post-glacial caldera on the Semisopochnoi Island, Aleutians (USA). Tephra SR4 (dated at ~ 64.5 ka), likely was derived from an earlier undocumented eruption from Okmok volcano (Aleutians). All three regionally spread tephra layers are valuable isochrones, which can be used for correlating and dating of Bering Sea sediments.