The Hunghae Formation, SE Korea: Miocene Debris Aprons in a Back-Arc Intraslope Basin

  1. Dorrik A. V. Stow
  1. Moon Young Choe and
  2. Sung Kwun Chough

Published Online: 29 APR 2009

DOI: 10.1002/9781444304473.ch44

Deep-Water Turbidite Systems

Deep-Water Turbidite Systems

How to Cite

Choe, M. Y. and Chough, S. K. (2009) The Hunghae Formation, SE Korea: Miocene Debris Aprons in a Back-Arc Intraslope Basin, in Deep-Water Turbidite Systems (ed D. A. V. Stow), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304473.ch44

Editor Information

  1. Department of Geology, University of Southampton, UK

Author Information

  1. Department of Oceanography, Seoul National University, Seoul 151, Korea

Publication History

  1. Published Online: 29 APR 2009
  2. Published Print: 11 NOV 1991

ISBN Information

Print ISBN: 9780632032624

Online ISBN: 9781444304473

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Keywords:

  • Ulleung (Tsushima) back-arc basin;
  • intraslope basins;
  • Hunghae Formation;
  • parallel-laminated sand beds;
  • low-concentration turbidity currents

Summary

During early to middle Miocene times a sudden opening of the Ulleung (Tsushima) back-arc basin in the East Sea (Sea of Japan) led to the development of intraslope basins along the rifted southwestern margin (southeast Korea). Abrupt subsidence resulted in the deposition of the 200 m thick Hunghae Formation (middle Miocene), a sand/mudstone sequence that can be divided into five facies. Facies I (sand and mudstone couplet) and II (coarse sand) are turbiditic in origin, as evidenced by massive, graded, crudely-layered and parallel-laminated sand beds. Facies III (homogeneous mudstone) is characterized by various lignite and plant fragments, clastic and biogenic grains that are randomly oriented, suggestive of hemipelagic deposition. Facies IV (chaotic deposit) is characterized by the disruption of beds, the presence of isolated siltstone blocks (or balls) and large clasts in the muddy matrix, indicative of retrogressive rockfall and slide/slump. Facies V (conglomerate) is of debris flow origin, as evidenced by clast- and matrix-supported features, floating large clasts and absence of traction structures.

Individual facies are organized into two types of facies association: (1) homogeneous mudstone (facies III) associated randomly with the rest (facies I, II, IV and V), indicative of hemipelagic and episodic sediment-gravity flow processes, respectively; (2) conglomerate (facies V), coarse sand (facies II) and sand/mudstone couplet (facies I), representing the flow transformation from debris flow to high- and low-concentration turbidity currents. These facies associations are similar in many respects to modern and ancient debris (or slope) aprons found elsewhere. Numerous isolated slide/slump blocks, wedged conglomerates with armoured mudstone balls, discontinuous lignite-containing sand/mudstone beds, chaotic structure and growth faults suggest that the deposition occurred on a steep slope (intraslope basin) off coalescing fan-deltas, mainly by unchannellized sediment-gravity flows. Ancient deposits with irregular facies sequences can be viewed as debris-apron systems, which provide alternatives to submarine-fan models in many clastic basins with a line rather than point source.