반 폐쇄성 가막만의 현생퇴적층 발달특성

Abstract

Distribution pattern and sediment environment of recent sediments in Gamak Bay of the South Sea of Korea are studied using the high-resolution seismic profiles coupled with sediment sampling. The Gamak Bay is a semi-enclosed bay bounded by the Yeosu Peninsula and Dolsan Island. The bay is connected to the Namhae and Yeoja Bay through numerous tidal inlets in the south. Also there is a narrow passage to the Yeosu Bay in the northeast. The mean grain size of surficial sediment lies around 6∼9Φ. Sediments in the bay consist of silt and clay with progressive decrease toward the inner bay. Total Organic Carbon (TOC) content of the surface sediments vary between 0.40% and 3.12%, and CaCO3 content ranges from 0.21 to 60%. The northwest side of the bay is characterized by high TOC content and low CaCO3 content. The low C/N ratios implies that the organic matters are mainly derived from marine organism. The seismic sedimentary sequence overlying acoustic basement can be divided into two depositional units (Unit Ⅰ and Ⅱ) bounded by a prominent mid-reflector. The acoustic basement is characterized by irregular topography. Generally it occurs at the depth between 20 m and 40 m below the mean sea level and deepens gradually to southward. The Unit Ⅰ mostly occupying the channel-fill facies can be interpreted as tidal environment deposits during transgression. Mid-reflector appears within the sedimentary sequence at the depth of about 15∼28 m below the sea level. The upper layer Unit Ⅱ shows the progradational pattern towards southward. Unit Ⅱ was deposited during the last 6,000 yrs when sea level was close to the present level. Origin of the Unit Ⅱ sediment is speculated as a result of accumulating suspended sediments derived from the Seomjin River.