--> Abstract: Recognition of Intertidal Storm Deposits and Stratigraphic Reconstruction Using Wavelength of Hummocky Cross-Stratification: Observations and Deductions from Korean Tidal Flats, by Byong Cheon Yang, Robert W. Dalrymple, and Seung Soo Chun; #90039 (2005)

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Recognition of Intertidal Storm Deposits and Stratigraphic Reconstruction Using Wavelength of Hummocky Cross-Stratification: Observations and Deductions from Korean Tidal Flats

Byong Cheon Yang1, Robert W. Dalrymple1, and Seung Soo Chun2
1 Queen's University, Kingston, ON
2 Chonnam National University, Kwangju, South Korea

Non-barred, open-coast tidal flats (up to 6 km wide) are extensively developed along the west/southwestern coast of Korea where tidal ranges are upper mesotidal to lower macrotidal. The surface sediment, showing a slightly seaward-fining trend, consists predominantly of fine to very fine sand, except for ephemeral mud deposits during the summer. Because of the absence of barrier islands, these tidal flats are subject to intense storm waves during the winter when significant wave heights offshore average 2-3 m. Intertidal deposits consist predominantly of storm beds in which HCS and planar lamination are abundant. These deposits superficially resemble those considered typical of shorefaces. However, the shallow water depth and tidal modulation of water depths produce diagnostic features. Because of the depth-limited maximum wave size on the tidal flats, the wavelength of the HCS is relatively small (< 2 m) and the maximum wavelength decreases systematically in a landward direction. These observations reveal that HCS is formed by an orbital ripple, such that the HCS wavelength (L) is proportional to bottom-orbital diameter (do): L = 0.75 do. Because most storms typically last 3-4 tidal cycles, tidally modulated water-depth and wave-size changes produce repeated changes in the wavelength of the HCS within a single storm bed: gradational upward decreases and increases in bedform wavelength are interpreted as falling-tide and rising-tide successions, respectively. These findings open the possibility of using HCS wavelength to reconstruct changes in paleo-water depth independently of the sand:mud ratio, which may be controlled by sediment supply.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005