UP-estuary variation of sedimentary facies and ichnocoenoses in an open-mouthed, macrotidal, mixed-energy estuary, Gomso Bay, Korea

Integrated sedimentologic and ichnologic studies from the open-mouthed, Gomso Bay estuary on the western Korean coast have revealed that both tides and waves play an important role in estuarine sedimentation. Because of up-estuary decrease in wave energy, physical structures pass up-estuary from wave-dominated planar lamination and hummocky cross-stratification to tide-dominated heterolithic stratification. 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 appear to be 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. Although useful estuarine facies models have been constructed from a growing number of modern and ancient studies, the estuarine classification schemes based on tidal range and geomorphic elements are apparently in conflict. Modern examples from Willapa Bay and this study confirm that the facies-belt model should be considered to be the most useful in applying the estuarine classification, and estuary morphology is related directly to the tidal prism rather than tidal range. In this context, the study results can be used to make interpretations of the geometry of coastlines and clastic reservoirs in ancient examples.