Recognition of a Floodplain within Braid Delta Deposits of the Oligocene Minato Formation, North-East Japan: Fine Deposits Correlated with Transgression

  1. Michael D. Blum3,
  2. Susan B. Marriott4 and
  3. Suzanne F. Leclair5
  1. Koji Yagishita1 and
  2. Osamu Takano2

Published Online: 17 MAR 2009

DOI: 10.1002/9781444304350.ch29

Fluvial Sedimentology VII

Fluvial Sedimentology VII

How to Cite

Yagishita, K. and Takano, O. (2005) Recognition of a Floodplain within Braid Delta Deposits of the Oligocene Minato Formation, North-East Japan: Fine Deposits Correlated with Transgression, in Fluvial Sedimentology VII (eds M. D. Blum, S. B. Marriott and S. F. Leclair), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304350.ch29

Editor Information

  1. 3

    Baton Rouge, Louisiana, USA

  2. 4

    School of Geography and Environmental Management, University of the West of England, Bristol BS16 1QY, UK

  3. 5

    Department of Earth and Environmental Sciences, Tulane University, Dimwiddie Hall, New Orleans, LA 70118, USA

Author Information

  1. 1

    Department of Geology, Iwate University, Morioka-City, Iwate, Japan 020-8550

  2. 2

    Japan National Oil Corporation, Mihama-ku, Chiba-City, Chiba, Japan 261-0025

Publication History

  1. Published Online: 17 MAR 2009
  2. Published Print: 15 FEB 2005

Book Series:

  1. Special Publication Number 35 of the International Association of Sedimentologists

Book Series Editors:

  1. Ian Jarvis

Series Editor Information

  1. School of Earth Sciences and Geography, Centre for Earth and Environmental Science Research, Kingston University, Penrhyn Road, Kingston-upon-Thames KT1 2EE, UK

ISBN Information

Print ISBN: 9781405126519

Online ISBN: 9781444304350



  • fluvial Oligocene Minato formation, north-east Japan;
  • fluvial Oligocene Minato Formation, north-east Japan - mostly of clast-supported conglomerate beds;
  • geological setting, lithofacies and palaeocurrent analysis;
  • marine sediments at southern basin margin;
  • inland floodplain environment;
  • palaeocurrent pattern of Minato formation;
  • transgressive (TST) or highstand systems tracts (HST);
  • Minato formation lithofacies


The fluvial Oligocene Minato Formation, north-east Japan, consists mostly of clast-supported conglomerate beds interpreted to represent deposition by a braided river system. Tuffaceous sandstone beds, a facies interpreted to indicate a nearshore sedimentary environment, however, are interbedded with conglomerates at the southern basin margin, suggesting that the distal Minato Formation represents a coalescing braid delta. Moreover, laterally extensive fine-grained sediments that include in situ lignite beds were recently exposed at a large quarry in the northern part of the basin, and are interpreted to be of floodplain origin. The recognition of fine-grained sediments within thick conglomerates enables the correlation of alluvial plain and marine strata, and provides an excellent chronostratigraphical basis for interpreting the two different depositional facies in terms of sequence stratigraphy.

The Minato Formation is interpreted to represent part of a transgressive systems tract, and correlations suggest that base-level rise can have a profound effect on inland alluvial sedimentation in a coarse-grained braided system. As a result of sea-level rise, widespread but thin shallow-marine sediments may extend a few tens of kilometres inland over fluvial deposits. The generally high gradient of braided rivers, however, means that shallow-marine sediments are unable to spread over gravelly braided systems. Instead, in the case of the Minato Formation, a slight change of stream gradient produced by the sea-level rise caused fining of the river gravels, resulting in floodplain formation.