Up-Estuary Variation of Sedimentary Facies and Ichnocoenoses in the Mixed-Energy Gomso-Bay Estuary, Korea

ByongCheon Yang¹, Bob Dalrymple², Murray Gingras¹, and SeungSoo Chun^3
1Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB, Canada
²Geol. Sci. and Geol. Eng., Queen's University, Kingston, ON, Canada
³Faculty of Earth Systems and Environmental Sciences, Chonnam National University, Kwangju, South Korea

Estuaries are commonly associated with transgressive to early highstand coastlines, and since the development of sequence stratigraphy, many estuarine deposits have been recognized in the ancient record. The existing estuarine facies models have been very useful in the interpretation of such deposits, but these models focus on wave- and tide-dominated end members of the spectrum of estuary types and do not represent mixed-energy estuaries effectively. This is a serious shortcoming because such estuaries are common.

The Gomso-Bay estuary is a funnel-shaped, coastal embayment, which opens westward to the Yellow Sea. Tides are semidiurnal with a mean range of 4.33 m. Winds are seasonally intense and waves are able to enter the estuary because the tidal flux prevents the development of a protective barrier. Surface sediments, cancores and topographic profiles reveal that the physical and biological facies within the Gomso-Bay estuary are influenced by both tides and waves. Because of the up-estuary decrease in wave energy, physical structures pass from wave-dominated planar lamination and hummocky cross-stratification at the estuary mouth to tide-dominated heterolithic stratification in the inner estuary. The infaunal distribution is sensitive to physiological stresses, and traces increase in size from the inner bay to the outer bay. The mappable trends in sedimentary facies and ichnofacies (i.e., facies belts) are oblique to the estuarine margin in the outer and middle bays because of wave refraction, whereas facies belts in the inner bay are parallel to the estuary margin, reflecting tide-dominated conditions. The findings provide improved criteria to assist in the recognition of the deposits of mixed-energy estuaries, and can be used to make interpretations of the geometry of coastlines and clastic reservoirs in ancient examples.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas