The Formation of Late Pleistocene and Holocene Sand Dunes on Kikaijima Island, Nansei Islands

Abstract

― 683 ― Abstract Coastal sand dunes dating to the latter part of the late Pleistocene were constructed at sub-stantially lower sea levels on Kikaijima Island. They are preserved because of large-magnitude uplifts ascertained from occurrences of outstanding late Pleistocene and Holocene coral terraces. In addition, because Holocene sand dunes occur close to those of Marine Oxygen Isotope Stage 3 （ MIS 3 ） , the island is ideal for examining the environments of the formation of sand dunes, which were constructed under different climatic and sea-level conditions. Distributional and depositional features of sand dunes are clarified, and their chronology is constructed on the basis of tephrochronology, 14 C dating, and chronological relationships of the sand dunes with marine terraces of known age. The environments of sand-dune formation on Kikaijima are examined in relation to climatic and sea-level records within regional and global contexts. Nine tephra layers are recognized. These include two widespread tephras, Kikai-Akahoya tephra （ K-Ah ） and Aira-Tn tephra （ AT ） . The other seven tephras, consisting of fine ash layers, are newly recognized and named Kikaijima-1 tephra （ Kj-1 ） to Kikaijima-7 tephra （ Kj-7 ） , of which the upper six, lying between K-Ah and AT, are aged from 13,000 to 30,000 cal BP. Holocene sand dunes began to form at c . 8,000 cal BP before the culmination Island is mainly related to the occurrence of coastal sandy beaches during sea-level high stands. Although Holocene sand dunes are related to Holocene high stand, those of MIS 3 are related to high stands during cycles of sea-level fluctuations in MIS 3. The longitudinal landform of the sand dunes recognized in the late MIS 3 suggests that the prevailing winds in MIS 3 were stronger than in the Holocene. This study provides critical data for constructing a chronological framework that integrates various aspects of palaeoenvironments, as well as human interactions and responses in southern Kyushu.