Fig. 7

a, b Grain size distributions of selected fusion residues of a MR14-E01 PC11 and b KR13-02 PC05. Data are offset according to their depth, and the depth of each sample is indicated on the right. c, d Depth variation of median grain size from c MR14-E02 PC11 and d KR13-02 PC05. Samples with bimodal grain size distributions were not plotted. The paleomagnetic polarity zones of Usui and Yamazaki (2021) are shown on the right of c. Black indicates normal polarity, white indicates reversed polarity, and gray indicates a zone with an uncertain polarity pattern. e Temporal variation of median grain size from LL44-GPC3 (Janecek and Rea 1983) and DSDP Site 576 (Janecek 1985). The geomagnetic polarity timescale (GPTS) between 40 and 25 Ma (Ogg 2020) is shown on the right. The chemostratigraphic units (Tanaka et al. 2020a) are shown on the right of c and d. For a color cord, see Fig. 1