We investigated a late Quaternary terrestrial sedimentary sequence (Uwa Formation) in core IC2, from a site adjacent to that of the reported core IC on NW Shikoku Island, SW Japan, and developed its tephra and pollen stratigraphy to refine the age model of the formation. First, we identified 19 horizons with high glass shard concentrations in the IC2 core sediments as possible tephras or cryptotephras, and correlated them with reported tephras on the basis of the major- and trace-element compositions of their glass shards. All correlated widespread tephras and cryptotephras were products of volcanoes in the Kyushu volcanic zone (Aso, Kakuto, Aira, Ata, and Kikai calderas). Second, we confirmed the presence in core IC2 of two pollen zones dominated by Quercus subgen. Cyclobalanopsis, which is an indicator of very warm interglacial vegetation. In the Japanese Islands, these two vegetation zones have usually been considered to characterize marine isotopic stages (MISs) 1 and 11. A previous study of the Uwa Formation correlated the upper pollen zone to MIS 1, but the lower zone was not correlated to MIS 11; rather, it was inferred to be older than MIS 12 because it was stratigraphically below the “Oda” tephra (equivalent to a distal Kasamori 5 [Ks5] tephra [MIS 12]). In this study, however, noting that the Naruohama-IV tephra (Nh-IV; MIS 10d) and Ks5 cannot be distinguished by their shard chemistries, we inferred that the suggested “Oda” tephra actually correlates to Nh-IV, rather than to the Ks5 tephra. By re-assigning the “Oda” tephra to Nh-IV, we could correlate the underlying Quercus subgen. Cyclobalanopsis-abundant zone to MIS 11 and, consequently, a pair of pollen zones indicating cool and warm conditions below the MIS 11 pollen zone to MISs 12 and 13, respectively. The resulting age model whereby tephra and pollen constraints are integrated showed a roughly constant sedimentation rate from MIS 13, without any long-term gaps; further, our MIS 13 horizon in core IC2 corresponds to the reported 1 Ma tephra horizon in core IC. Therefore, these findings represent a dramatic change in the Uwa Formation age model and validate the Uwa Formation as one of the most useful terrestrial archives of Quaternary tephrostratigraphy and paleoclimatic fluctuation in SW Japan.

我们调查了核心 IC2 中的第四纪晚期陆地沉积序列（Uwa 组），该地点与日本西南部四国岛 NW 报告的核心 IC 相邻的地点，并开发了其火山灰和花粉地层学以完善地层的年龄模型. 首先，我们将 IC2 核心沉积物中玻璃碎片浓度高的 19 个层位确定为可能的 tephras 或 cryptotephras，并根据其玻璃碎片的主要和微量元素组成将它们与报告的 tephras 相关联。所有相关的广泛分布的tephras和cryptotephras都是九州火山带（Aso，Kakuto，Aira，Ata和Kikai破火山口）火山的产物。其次，我们证实了核心 IC2 中存在以Quercus subgen 为主的两个花粉区。青冈，这是非常温暖的间冰期植被的指标。在日本群岛，这两个植被带通常被认为是海洋同位素阶段 (MIS) 1 和 11 的特征。先前对 Uwa 组的研究将上部花粉带与 MIS 1 相关联，但下部带与 MIS 无关11; 相反，它被推断为比 MIS 12 更老，因为它在地层上低于“Oda”火山灰（相当于远端 Kasamori 5 [Ks5] 火山灰 [MIS 12]）。然而，在这项研究中，注意到 Naruohama-IV tephra (Nh-IV; MIS 10d) 和 Ks5 无法通过它们的碎片化学来区分，我们推断建议的“Oda”tephra 实际上与 Nh-IV 相关，而不是与Ks5 tephra。通过将“Oda”tephra 重新分配给 Nh-IV，我们可以关联底层的Quercus亚根。Cyclobalanopsis - MIS 11 的丰富区，因此，一对花粉区分别指示 MIS 11 花粉区下方的凉爽和温暖条件到 MIS 12 和 13。由此产生的年龄模型，其中整合了火山灰和花粉约束，显示 MIS 13 的沉降速率大致恒定，没有任何长期差距；此外，我们在核心 IC2 中的 MIS 13 层位对应于报告的核心 IC 中的 1 Ma tephra 层位。因此，这些发现代表了宇和组年龄模型的巨大变化，并证实宇和组是日本西南部第四纪陆地地层学和古气候波动最有用的陆地档案之一。