Stratigraphy of the Late Pleistocene and the Holocene and Sedimental Environment in the Yawatahama and the Kawanoishi Lowlands,Ehime Prefecture,southewest Japan

摘要

In the Yawatahama and the Kawanoishi Lowlands,locate in the western part of the Shikoku Island,the late Pleistocene and the Holocene sediments are divided into the Uwa Kai and the Yawatahama-ko Formations.The volcanic ash found in the middle part of the Uwa Kai Formation and Honai Volcanic Ash in the middle part of the Yawatahama-ko Formation can be correlated with Kuju-daiichi Pumice and Kikai-Akahoya Volcanic Ash respectively.The middle part of the Uwa Kai Formation deposited since 80-70ka and before 51ka of the late Pleistocene as marine sediment. The upper part of the Formation was deposited since 51ka the late Pleistocene as non-marine sediment. The Yawatahama-ko Formation was formed during the Holocene. At first,the formation began to deposit in drowned valley and next,the inner-bay prodelta and delta-front deposits followed during the early to middle Holocene. Finally,interdistributary bar sediments in the Kawanoishi Lowland and inner-bay sediments in the Yawatahama Lowland have been deposited since the middle Holocene.