Beach-Ridge Ranges and Their Formative Periods on Three Holocene Coastal Plains in the Southeastern Part of Fukushia Prefecture, Northeastern Japan

This paper describes forms and formative periods of beach ridge ranges on three Holocene coastal plains in the southeastern part of northeastern Japan.In the first place, numbers and morphological features of beach-ridge ranges have been examined through aerial photographic interpretation, fieldwork and topographic profiles produced from 1:2, 500 national large scale maps. Secondly, based on 14C ages of backmarsh deposits behind each beach-ridge range and nearshore deposits including shell fossils, formative period of each beach-ridge range was estimated. These facts mentioned above were used in correlation of beach-ridge ranges on the coastal plains.Results are summarized as follows.1) Beach-ridge ranges on these coastal plains are divided into three on the basis of morphological evidence and formative periods, although some differences are recognizable among the three coastal plains. From comparison of geomorphological and geologic settings, it is inferred that these differences result from effect of wave action and morphological variation in basement overlain by alluvium.2) Each beach-ridge range, in order from inland most, started forming before 4, 000y. B. P., at 3, 000y. B. P. and 1, 700-1, 600y. B. P., respectively.