The beginning and the formation process of Kurotaki Unconformity base of the Kazusa Group, related to the origin of Kanto plain

黑泷不整合面是渤索半岛上新世—更新世喀苏群底部的一个明显的地质缺口。关于不整合的成因有构造运动、海底滑坡等多种说法，但没有一个明确的答案。本研究通过对覆盖不整合的Kazusa群中广泛穿插的层序年龄的识别和确认，明确了博索半岛各地覆盖Kurotaki不整合地层的年龄。结果表明，博索半岛上覆盖黑泷不整合的Kazusa群基底层沉积年龄为3.2 ~ 1.9 Ma，而三浦半岛上更新世Kazusa群与上新世三浦群之间不存在沉积间隙。据此，笔者认为黑泷不整合是2.3 ~ 1.9Ma连续发生的几次局部海底滑坡的结果。

The Kurotaki Unconformity is a conspicuous geologic gap recognized at the base of Plio-Pleistocene Kazusa Group in Boso Peninsula. Various opinions such as structural movement or submarine landslide on the origin of the unconformity have been examined, but the clear answer is not provided. This study clarified the age of the strata covering the Kurotaki Unconformity at various places in Boso Peninsula through the identification and confirmation of chronological age of the wide spreded tephras intercalated in the Kazusa Group covering the unconformity. As a result, the author found that the sedimentation age of the base layer of Kazusa Group covering the Kurotaki Unconformity ranged from 3.2 to 1.9 Ma in Boso Peninsula, but there was no sedimentary gap between the Plio-Pleistocene Kazusa Group and Pliocen Miura Group in Miura Peninsula. From these facts, author regarded the Kurotaki Unconformity as the result of several local submarine landslides occurred sequentially in 2.3 - 1.9Ma.