Quaternary stratigraphy of the Osaka sedimentary basin, central Japan

Yoshikawa, Shusaku

doi:10.4116/jaqua.51.1

Cited by 1 publication

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“…This age was determined via both the subsurface stratigraphy along the coast of the Osaka Bay (Yoshikawa and Miyakawa, 1997), and sequence stratigraphy in the Kazusa Group (Ito, 1994 (2000), in the Osaka Group, K1-223 is correlated with Hgw-Ks5, which is interbedded between the marine clay layers referred to as Ma 9 and Ma 8 (MIS 12; Yoshikawa and Mitamura, 1999). In addition, Yoshikawa (2012) showed that the eruptive age of Minatojima I, which is correlated with Ks5, is 430 ka (MIS 12). The age of Ks5 corresponds to a time of low sea level associated with MIS 12 (434-458 ka), as determined from the stratigraphic position of Ks5 in deep-sea sediments of the C9001C core from the east continental slope off Shimokita Peninsula (Domitsu et al, 2011;Matsu'ura et al, 2017).…”

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confidence: 99%

Characterization and correlation of the Hegawa‐Kasamori 5 tephra, a widespread tephra aged c. 450 ka associated with large‐scale pyroclastic flows from southern Kyushu, SW Japan

Nishizawa

Suzuki

2019

J Quaternary Science

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A Middle Pleistocene widespread tephra, defined here as Hegawa‐Kasamori 5 tephra (Hgw‐Ks5), has been newly recognized over a broad area of Japan. Large‐scale pyroclastic flow deposits associated with co‐ignimbrite ash fall deposits (CAFDs) of Hgw‐Ks5 have been identified in the proximal southern Kyushu area, south‐west Japan. Hgw‐Ks5 possibly originated from the Aira caldera in southern Kyushu, and it is widely spread and intercalated with deposits of the Kasamori Formation, Honshu Island, more than 1000 km away from the source. In the north‐west area of the Aira Caldera, the tephra is sparsely distributed in the form of non‐welded ignimbrites, and is exposed stratigraphically above the well‐known Kobayashi‐Kasamori tephra. Hgw‐Ks5 is characterized through petrographic features, major element geochemistry of glass shards, and refractive indices of orthopyroxene. The results of previous stratigraphic isotope studies indicate that the eruptive age of Hgw‐Ks5 is 434–458 ka (Marine Isotope Stage 12). Assuming that the CAFDs originating from the Aira Caldera are distributed concentrically, the apparent volume of Hgw‐Ks5, estimated from the area of distribution and CAFD thickness, is ~100 km3. Therefore, a volcanic explosivity index of 7 is assigned to the Hgw‐Ks5 eruption.

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