Abstract
Central Tokyo is underlain by the Pleistocene Tokyo Formation, which is considered to have been deposited during Marine Isotope Stage (MIS) 5e based on stratigraphic examination of the core type section (Yoyogi Park core). In this study, we investigated the Kita-ku Central Park core from the eastern Musahino Upland to re-examine the stratigraphy of the Tokyo Formation in this area. Two depositional cycles, each of which is composed of a basal gravel bed and overlying shallow marine sandy and muddy sediments, are observed at depths shallower than 33 m in the core, based on sedimentary facies and diatom analyses. Tephrostratigraphy indicated that the upper cycle was deposited during MIS 7e, and the lower depositional cycle may have accumulated during MIS 9 or during an earlier stage. The upper depositional cycle is considered to represent the Tokyo Formation. These results suggest that the Tokyo Formation includes a number of sedimentary cycles that not only formed during MIS 5e but also during earlier MIS periods. The distribution of the Tokyo Formation across central Tokyo should be re-examined from a stratigraphic perspective in the future.
