This study tries to establish the classification system of marine terrace by investigating marine terraces in the Gangdong area, Ulsan in the East Coast, the Boryeong area in the West Coast and the Seopo area in the South Coast. The marine terrace in ...
This study tries to establish the classification system of marine terrace by investigating marine terraces in the Gangdong area, Ulsan in the East Coast, the Boryeong area in the West Coast and the Seopo area in the South Coast. The marine terrace in the Gangdong Coast is classified into the Holocene Surface (elevation of ancient shoreline of 5~6 m), Lower I Surface (elevation of ancient shoreline of 20~25 m), Middle Surface (elevation of ancient shoreline of 50 m), High II Surface (elevation of ancient shoreline of 75 m), High I Surface (elevation of ancient shoreline of 95 m), Higher High II Surface (elevation of ancient shoreline of 120 m), Higher High I Surface (elevation of ancient shoreline of 145 m) and Higher High Gangdong Surface (elevation of ancient shoreline of 160 m). The marine terrace was dated with assumptions that uplift rate is 0.227㎜/y and the Lower I Surface corresponds to MIS 5e. After formation of the Lower Surface in the East Coast, the East Coast was uplifted, while the West Coast was subsided. After formation of the Middle Surface in the East Coast, however, both the East and West Coasts was uplifted, while the uplift rate in the East Coast was higher than in the West Coast. On the other hand, some authors have argued that marine terrace systems in the East and West Coasts are similar to each other and the elevation of ancient shoreline in the Lower Surface in the West Coast corresponding to the Last Interglacial agrees with the East Coast. Because this study reveals that formative period of marine terrace with an elevation of ancient shoreline of 20~23 m in the Nampo area, Boryeong, is MIS 9 corresponding to the High Surface with an elevation of 70 m in the East Coast, it can be suggested that the uplift rate in the West Coast was much lower than in the East Coast. In the respect of spatial difference in uplift rates in the northern and southern parts of the East Coast, this study concludes that there is no spatial difference in uplift rates since the middle Pleistocene, because marine terrace systems in the Samcheok and Jeongdongjin areas in the middle East Coast and in the Eupcheon and Jigyeong areas, Gyeongju and Gangdong area, Ulsan in the southern East Coast are similar to each other with an comparison of elevation of ancient shoreline in the Higher High Surface in the Gangdong area and in the East Coast. On the other hand, it is possible that recent movement of active fault is more active in the Southeastern Coast than in the middle East Coast. 5 groups in geomorphic surfaces of marine terrace with elevations of ancient shoreline of 15~17 m, 20~23 m, 25~30 m, 35~40 m and 42~45 m are found in the Nampo area, Boryeong, Chungnam Province in the West Coast. The surfaces older and higher than the surface with an elevation of 20~23 m fragmentarily distribute and are small due to high dissection. These distributional pattern is similar to the High or Higher High Surfaces in the East Coast. Based on stratigraphy of loess-paleosol sequence and OSL age dating results, the geomorphic surface with an elevation of ancient shoreline of 20~23 m corresponding to MIS 9 was used as a key bed. In other words, the Lower Surface in the West Coast corresponds to the High Surface with an elevation of ancient shoreline of 70 m in the East Coast, suggesting that uplift rate in the West Coast is much lower than in the East Coast. Remain of the Higher High Gangdong Surface in the Gangdong area and marine terrace with the highest elevation of 54 m in the Seopo area result in highly resistant bedrock to erosion process. In the South Coast, marine terraces in Jahye-ri, Seopo-myeon, Sancheon-si, distribute along ridges and show small areas, due to the bedrock with high joint density, the weathered hill and the high energy wave affecting wave-cut platform formation. Distributional patterns of marine terraces with elevations of ancient shoreline of 10~12 m, 15~18 m, 20~24 m, 25~28 m, 30~33 m, 35~38 m, 40~45 m and 45~50 m (54 m) are similar to the Boryeong area in the West Coast rather than to the East Coast.