Geology and radiolarian biostratigraphy of the Miocene and Pliocene Series exposed along the Koitogawa River, Boso Peninsula, Japan

DOI Web Site Web Site 6 Citations 31 References
  • Sawada Taiki
    Graduate School of Life and Environmental Sciences, University of Tsukuba. Present address; Japan Petroleum Exploration Co., Ltd.
  • Shindo Ryota
    Nihon Tennen Gas Co., Ltd.
  • Motoyama Isao
    Graduate School of Life and Environmental Sciences, University of Tsukuba.
  • Kameo Koji
    Department of Earth Sciences, Chiba University

Bibliographic Information

Other Title
  • 房総半島，小糸川流域の中新・鮮新統の地質と放散虫化石層序
  • ボウソウ ハントウ コイトガワ リュウイキ ノ チュウ シン センシントウ ノ チシツ ト ホウサンチュウ カセキソウ ジョ

Search this article

Abstract

Neogene marine sedimentary rocks exposed around the upper course of the Koitogawa River are subdivided into the Amatsu, Kiyosumi, and Anno formations. The Amatsu Formation is dominated by hemipelagic mudstone, the Kiyosumi Formation consists mainly of thick sandstone layers and thin mudstone layers, and the lower part of the Anno Formation consists of interbedded sandstone and mudstone. These formations contain many sets of key tuff layers that are useful in correlating geologic sections exposed along rivers and roads.<br>Radiolarian assemblages from the Amatsu and Kiyosumi formations are characterized by low-latitude species, including Diartus petterssoni, Diartus hughesi, and Didymocyrtis penultima, which are associated with mid- to high-latitude species including Lychnocanoma magnacornuta and Spongurus pylomaticus. Based on the stratigraphic distribution of radiolarian species, the sedimentary sequence extending from the Amatsu Formation to the upper part of the Kiyosumi Formation is correlated with low-latitude Zones RN5 to RN10-RN11 and the North Pacific Eucyrtidium inflatum Zone to Spongurus pylomaticus-Cycladophora sakaii Zone.<br>There exist some discrepancies in numerical age estimates provided by the present and previous studies of planktonic foraminiferal and radiometric ages, although the radiolarian biostratigraphy is in good agreement with that based on calcareous nannofossils. Based on these biostratigraphic and radiometric age data, we propose an age-depth model and estimated sedimentation rates. The sedimentation rate is moderate (about 20 cm/k.y. on average), but shows an abrupt decrease at the middle-upper part of the Amatsu Formation (to 2.8 cm/k.y.). This slow sedimentation occurs in an interval of relatively coarse sedimentary facies devoid of signs of tectonic movement, suggesting that fine fractions were winnowed away by water currents.

Journal

Citations (6)*help

See more

References(31)*help

See more

Related Projects

See more

Keywords

Details 詳細情報について

Report a problem

Back to top