Late Pleistocene tephrostratigraphy of the sediment core MD01-2421 collected off the Kashima coast, Japan

An IMAGES core MD01-2421 (45.83 m) from the northwest Pacific Ocean off central Japan yielded twenty-three tephra beds. Descriptions of the twenty-three tephra beds have been made using the major-element composition of glass shards and refractive indices (RI) of glass shards and phenocrysts. As a result, at least seven on-land maker tephra layers have been identified. Two tephras come from Kyushu : Aira and Aso calderas. Four tephras come from central Honshu : Mt. Akagi, Hakone caldera, Mt. Ontake, and Mt. Tateyama. One tephra, the lowest layer of all, comes from northeast Honshu : Numasawa caldera. During the process of identifying the tephra beds, it became clear that the RI of Ontake No.1 Pumice (On-Pm1) at Suruga-Oyama (type locality), derived from Mt. Ontake, changed gradually during its eruption, and the RI of glass shards (1.503-1.506) in the middle to the top portion of the fall units was higher than the RI (1.501-1.503) in the lower unit, known as its type value. Furthermore, an age model for MD01-2421 was constructed by means of the oxygen isotopic stratigraphy of the benthic foraminifera (SPECMAP age : Martinson et al., 1987), using 12 calendar ages of foraminiferal fossils calculated from the accelerator mass spectrometry (AMS) 14C ages (younger than 44 ka) and AT tephra (Oba et al., 2006). This sedimentary core covers the last 144,000 years. The eruptive age of each tephra bed in this core and its error included in each SPECMAP age can be estimated from this age model. Akagi-Kanuma tephra (Ag-KP) is one of the marker tephra beds in the north Kanto Plain, and is 44.2±4.5 ka. Hakone-Tokyo (Hk-TP) tephra covers the south Kanto Plain, and is 66.0±5.5ka. Aso-4 tephra is 87.1±6.7 ka. We estimate the eruptive age of Ontake No.1 Pumice (On-Pm1), which lies just above the marine terrace surface and is regarded as having formed during MIS 5.3 in the south Kanto Plain, as 95.7±5.3 ka. The stratigraphic position of On-Pm1 in the oxygen isotopic stratigraphy agrees with geomorphologic evidence. Tateyama D tephra (Tt-D) derived from Mt. Tateyama in the Hida Mountains, central Japan, is 98.9±3.5 ka. Numazawa-Tagashira tephra (Nm-Tg) is described in the north Kanto Plain, and its stratigraphic evidence, estimated from shoreline sediments, matches the eruptive age of 129±3.0 ka of this study. This is the first time the stratigraphic relationship among these several tephra beds has been documented in a single section with a continuous and precise oxygen isotopi