1:45 PM - 3:15 PM
[HQR03-P02] Tephrostratigraphy during the past 100,000 years in the Yanohara Bog, Aizu Area, Northeast Japan
Keywords:tephrochronology, Yanohara Bog, Aizu Area, cryptotephra, Tt-E tephra
Tephrochronology is a unique method for Quaternary chronology that can synchronize terrestrial, lacustrine, and marine sediment records using tephra layers. Precise tephrostratigraphic frameworks are important for reconstructing volcanic eruptive histories and providing crucial time-markers for geological and geomorphological studies. Recent tephrostratigraphic studies of lake sediments, such as those from Lake Suigetsu in Japan, have provided precise ages for tephras detected in these lake sediments. These tephras can improve dating information for proximal stratigraphy and other volcanic areas based on tephrostratigraphic frameworks. In the northern Kanto to southern Tohoku region of northeast Japan, there are many Quaternary volcanoes that have repeatedly erupted explosively, but there are no suitable lakes as repositories of tephrostratigraphy from Late Pleistocene to Holocene. This study focuses on the Yanohara Bog formed by a landslide in the Aizu area, southern Tohoku region and aims to construct a precise tephrostratigraphy and estimate eruption ages.
We conducted coring excavation at Yanohara South Bog (YNH-P1) and Yanohara North Bog (YNH-P2) using a portable percussion coring system (PPCS: Kaneda et al., 2018). Cryptotephras were detected based on grain size distribution, and glass shards concentration. We analyzed heavy mineral composition, refractive index of volcanic glass shards using RIMS2000, and major element composition of volcanic glass shards using SEM-EDS. We also obtained radiocarbon ages.
The YNH-P1 core length is 667 cm. YNH-P1 core consists of almost peat and peaty silt. We detected five visible tephra layers and two cryptotephras. The source volcanoes of these tephras are Asama, Aira, Daisen, Akagi, Tateyama, and Ontake. Tephra of 641.0 cm depth has not been correlated. The YNH-P2 core length is 400 cm. YNH-P1 core consists of peat and peaty silt (upper half) and light brown silt to sand (lower half). We detected two visible tephra layers and five cryptotephras. The source volcanoes of these tephras are Asama, Aira, Haruna, and Towada. Radiocarbon dating results of YNH-P2 core are consistent with the tephrostratigraphy. In this study, we obtained key tephrochronological frameworks in Aizu area.
We conducted coring excavation at Yanohara South Bog (YNH-P1) and Yanohara North Bog (YNH-P2) using a portable percussion coring system (PPCS: Kaneda et al., 2018). Cryptotephras were detected based on grain size distribution, and glass shards concentration. We analyzed heavy mineral composition, refractive index of volcanic glass shards using RIMS2000, and major element composition of volcanic glass shards using SEM-EDS. We also obtained radiocarbon ages.
The YNH-P1 core length is 667 cm. YNH-P1 core consists of almost peat and peaty silt. We detected five visible tephra layers and two cryptotephras. The source volcanoes of these tephras are Asama, Aira, Daisen, Akagi, Tateyama, and Ontake. Tephra of 641.0 cm depth has not been correlated. The YNH-P2 core length is 400 cm. YNH-P1 core consists of peat and peaty silt (upper half) and light brown silt to sand (lower half). We detected two visible tephra layers and five cryptotephras. The source volcanoes of these tephras are Asama, Aira, Haruna, and Towada. Radiocarbon dating results of YNH-P2 core are consistent with the tephrostratigraphy. In this study, we obtained key tephrochronological frameworks in Aizu area.