Late Holocene geomorphological development of beach ridges in western Hamamatsu strand plain, central Japan

• Sato Yoshiki

  Institute of Geology and Geoinformation, National Institute of Advanced Industrial Science and Technology

• Fujiwara Osamu

  Research Planning Office for Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology

• Ono Eisuke

  Faculty of Education, Niigata University

Bibliographic Information

Other Title

• 浜松平野西部における完新世後期の浜堤列の地形発達過程
• ハママツ ヘイヤ セイブ ニ オケル カンシン セイ コウキ ノ ハマテイレツ ノ チケイ ハッタツ カテイ

Abstract

The Hamamatsu strand plain of the eastern Nankai Trough region is typical of the strand plains in Japan. In the western part of the plain, six series of beach ridges (BRs I to VI) have developed from land to sea in the past 7,000 years. The formation processes of BRs I to IV were reconstructed mainly from salinity changes in the back marshes, which indicate enhanced or reduced seawater invasion, which in turn reflects the degree to which the beach ridges were developed and thereby protected the back marshes from the sea. Salinity changes were estimated from analyses of fossil diatom assemblages in sediment cores. The ages of the deposits were estimated based on AMS ¹⁴C ages and tephrochronology of the core samples.<BR>In the Higashi-Kandagawa lowland, an inner bay environment developed at ca. 8,000-7,000 calBP. Water salinity in the lowland showed repeated fluctuations before finally arriving at stable freshwater marsh conditions at ca. 3,200 calBP. The inter-ridge marsh between BR I and II was a brackish lagoon environment after 7,000 calBP. The lowland showed an increase in water salinity at ca. 3,200 cal BP and thereafter was a fresh-water marsh. The inter-ridge marsh between BR III and IV was a brackish lagoon at ca. 4,000calBP. Following an increase in water salinity, the lowland became a fresh-water environment at ca. 2,000calBP.<BR>A reconstruction of environmental changes in the lowlands indicates that the formation of BRs I to IV started at ca. 8,000-7,000, ca. 7,000, ca. 7,000-4,000, and ca. 4,000calBP, respectively. The BRs were fully developed by ca. 3,400-3,000calBP (BRs I to III) or ca. 2,000 cal BP (BR IV).<BR>In the study area, BR I is a primary barrier that formed during a period of sea level rise, and BRs II to IV are secondary barriers that formed after the Holocene high stand. It is a unique and important feature of the geomorphological development of the study area that the closure of each back marsh by beach ridges did not occur via a simple development. Instead, the salinity-increase events in the back marshes indicate the repeated rise and fall of the beach ridges. Breaching of the beach ridges was probably in response to erosion by storm and tsunami waves or seismic-related coastal subsidence.

Journal

• The Quaternary Research (Daiyonki-Kenkyu)

  The Quaternary Research (Daiyonki-Kenkyu) 55 (1), 17-35, 2016

  Japan Association for Quaternary Research

Keywords

• beach ridge
• Hamamatsu strand plain
• diatom fossil assemblage
• Amagi-Kawagodaira pumice
• Holocene

Details

• CRID: 1390001206497660416
• NII Article ID: 130005137556
• NII Book ID: AN0034136X
• DOI: 10.4116/jaqua.55.17
• ISSN: 18818129
• ISSN: 04182642
• NDL BIB ID: 027086720
• Web Site: https://ndlsearch.ndl.go.jp/books/R000000004-I027086720
• Web Site: https://www.jstage.jst.go.jp/article/jaqua/55/1/55_17/_pdf
• Text Lang: ja
• Data Source:
  • JaLC
  • NDL
  • Crossref
  • CiNii Articles
  • KAKEN
• Abstract License Flag: Disallowed