근소만 퇴적환경의 계절적인 변화

Abstract

INTRODUCTIONThe western tidal flats of Korean Peninsula are directly influenced by monsoons. Affected by waves in winter and tidal currents in summer, the seasonal change of sediment characteristics comprises deposition and/or erosion. Geunso Bay in the mid-west of Korea is a semi-enclosed bay with a mean tidal range of about 6 m. The tidal flats are largely developed all along the side of the bay. In this study, we attempted to understand the seasonal variations of sediment characteristics caused by sedimentary processes, through monitoring sedimentation rates on Geunso tidal flat and comparing with other tidal flats of the semi-enclosed bay type.METHODSThe sedimentation rate at two transects was determined for a year by periodically measuring the changes in depth between the surface and plate. The surface sediments for sedimentary analysis were sampled at 45 stations in February and August 2009. The grain-sized distributions were determined by using standard sieving and Sedigraph 5100. The inclusive graphic method was used to determine sediment type, mean, sorting, skewness and kurtosis.RESULTS The surface sediments in Geunso Bay were classified into five sedimentary facies. In winter, surface sediments on tidal flat were mainly composed of poorly-sorted muddy and silty sand. The tidal flat near the shoreline was consisted of sandy mud. The sub-tidal flat was dominated by the silty sand sediments. In comparison sedimentary facies in summer with those in winter, muddy sand sediments on tidal flat extended to sub-tidal area and sandy mud sediments in the western part extended to southward tidal flat. The annual sediment accumulation rate was encountered up to 51.7 mm/year in Line W. In Line E, the sediments were deposited within 800 m from shoreline and were eroded 800 ; 1800 m from shoreline. The seasonal variations of sedimentation showed that the accumulation was dominated during spring and winter at Line W, whereas the deposition was occurred