Strontium and neodymium isotopic signatures indicate the provenance and depositional process of loams intercalated in coastal dune sand, western Japan

Yu Saitoh, Toru Tamura, Yoshinori Kodama, Takanori Nakano

Research output: Contribution to journalArticle

Abstract

Isotopic analyses of strontium and neodymium suggest that layers of loam intercalated in dune sand on the Japan Sea coast at Tottori, western Japan, consist of a mixture of Asian dust from China and locally derived sediment. An outcrop exposure shows a succession of late Pleistocene dune sand, a lower loam layer, Daisen-Kurayoshi Pumice (DKP; 50-55ka or older), an upper loam, Aira-Tn tuff (ca. 30ka), and Holocene dune sand, in ascending order. Bulk samples of the loam layers show an upward increase in 87Sr/86Sr, suggesting that the contribution of Asian dust increases upward. The Sr isotopic values also suggest a greater contribution of Asian dust in the silt fraction than in the bulk sample. Asian dust transported by westerly jet from the Taklamakan or Gobi desert is the main constituent of the upper part of the lower loam, of which isotopic values of silicate portion is isotopically identical to those of desert sand in China (87Sr/86Sr, 0.717-0.719; -Nd, -9.5 to -9.4). In contrast, the Sr and Nd isotopic values of DKP (87Sr/86Sr, 0.705; -Nd, -2.6 to 0.6) are close to those of the volcanic rocks of Mt. Daisen, which is regarded as the source of the tephra. The isotopic signature suggests that Asian dust also have contributed to the upper part of the upper loam layer. The upward increase of 87Sr/86Sr within each of the loam layers suggests that the contribution of Asian dust increased as the proportion of reworked deposits from the underlying layer (dune sand or DKP) decreased by burial. In contrast, 87Sr/86Sr in DKP shows little vertical change, suggesting very rapid deposition without entrainment of the underlying lower loam layer.

Original languageEnglish
Pages (from-to)272-278
Number of pages7
JournalSedimentary Geology
Volume236
Issue number3-4
DOIs
Publication statusPublished - 2011 May 1
Externally publishedYes

Keywords

  • Coastal dune
  • Eolian dust
  • Loess
  • MIS 3
  • Strontium and neodymium isotopes

ASJC Scopus subject areas

  • Geology
  • Stratigraphy

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