Quaternary Research
Volume 56, Issue 2 , September 2001, Pages 231-241
doi:10.1006/qres.2001.2258
Copyright (c) 2001 University of
Episodic emergence in the past 3000 years at the Akkeshi estuary, Hokkaido, northern Japan
Yuki Sawai
International Research Center for Japanese Studies, 3-2 Oeyama-cho, Goryo, Nishikyo-ku, Kyoto City 610-1192, Japan
*present address; Active Fault Research Center, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, Site C7 1-1-1 Higashi, Tsukuba 305-8567, Japan
Received
Abstract
At the Akkeshi estuary, rapid emergence interrupted Holocene submergence at least four times in the past 3000 years. Each emergence event produced an upward change from estuarine mud to freshwater peat. While the estuarine mud abounds in brackish and marine diatoms, freshwater taxa dominate the peat. Emergence events occurred from 1700 to 2300, 1000 to 1300, and 500 to 700 cal yr B.P. An additional emergence event predated by several decades a volcanic ash that erupted in A.D. 1694. At least three of the events produced contacts abrupt enough to represent uplift during earthquakes. Such uplift may reconcile seemingly conflicting records of vertical crustal movement in eastern Hokkaido. This tectonically active area, which is being subducted by the Pacific plate at 8 cm/yr, contains marine terraces that imply 0.1-0.5 mm/yr of net uplift in the late Quaternary. However, these terraces adjoin tide gages that recorded 8-9 mm/yr of steady submergence in the 20th century. The terrace uplift need not conflict with the gaged submergence if the region is subject to occasional coseismic uplift, as during the emergence events implied by Holocene geology near Akkeshi.
Author Keywords: sea level: Holocene: diatoms: earthquakes: