Sedimentary Facies and Chronology of Core Samples from the Naka-Ikemi Moor, Fukui Prefecture, Central Japan

Sedimentary environment for the past 50 ka

Abstract

A continuous long core of peaty sediments bored from the Naka-Ikemi Moor Central Japan (lat. 35°39' N., long. 136°5' E.), contains records of paleoenvironmental changes during the Last Glacial and Holocene periods. The Naka-Ikemi Moor stretches about 1.3 km from the west to east. This peculiar shapes and crustal movements had been pointed out by purely from a topographical point of view. And this moor is regarded as a waste-filled valley created by sort of tectonic depression at the eastern part of the Tsuruga Plain. From the stratigraphical examination, some volcanic ashes were detected as follows : Kikai-Akahoya Tephra (K-Ah : 6.3 ka), Aira-Tn Tephra (AT : 24 ka), Daisen Kurayoshi Tephra (DKP : ca. 50 ka). Values of bulk density measurements and radiocarbon dates of core samples indicate that the Naka-Ikemi core samples contain continuous records for the past 50 ka. The average sedimentation rate of Naka-Ikemi Moor was increased after the fall of AT volcanic ash had occurred. The sedimen tation process of Naka-Ikemi Moor has also been clarified by sedimentary facies and value of loss on ignition of core samples. Value of loss on ignition began to increase since the end of Last Glacial, suggesting the increase of organic material caused by environmental changes.