Coastal landscape evolution tracked from late Holocene wave-cut benches in the Sinan Archipelago, Southwest Korea

Abstract

Glacio-isostatic adjustment (GIA) and tectonic activity are important factors in the formation of marine terraces. Late Holocene wave-cut benches in the eastern part of the West Sea of Korea, also called the Yellow Sea, can be divided into two steps: 531 cm above sea level (ASL) for the upper bench (T2) and 464–481 cm ASL for the lower bench (T1). Sediments on the benches are classified into four units, and are interpreted to be beach deposits according to gravel shape, texture, and seaward inclination. The overlying sediment indicates that T2 was formed at approximately 530 cm ASL before 2900 yr BP, and T1 at approximately 460–480 cm ASL before 1520 yr BP. Late Holocene (4000–2000 yr BP) relative sea level (RSL) curves based on GIA models are inconsistent with the wave-cut bench elevations. Comparing T1 and T2 benches to the RSL curves of the West Sea, the upper and the lower benches were uplifted by approximately 5–8 m and 4–7 m, respectively. Although the area is several hundred kilometers away from plate boundaries, the high frequency of earthquakes in the West Sea may have induced the uplift of wave-cut benches during the last 2000 years. These indicate that the west coast of the Korean Peninsula (KP) should no longer be considered an area of subsidence, but be assigned to a regime of uplift during the late Holocene.