Mid-Holocene sea-level fluctuation inferred from diatom analysis from sediments on the west coast of Korea

Diatoms from the KS2009 core sediment on the coast of the West Sea, Kunsan-si and the KR07 trench sediment collected from the neighboring Sabsi island, Korea, were analyzed for Holocene sea-level fluctuations. In KS2009 core sediment, results of AMS 14C dating identified five stratigraphic horizons ranging from 2200 to 9100 BP. The results obtained by measuring the radiocarbon dating from the KR07 were as follows: −0.34 m.a.s.l: 6108 BP, −0.74 m: 6488 BP, −1.46 m: 6838 BP, and −1.58 m: 7208 BP. Diatom assemblages from KS2009 indicated: Facies A (barren zone: KS2009 (−23.5 to −20.3 m)) → Facies B (high tidal flat: KS2009 (−20.3 to −14.6 m)): Holocene marine transgression → Facies C (mid tidal flat: KS2009 (−14.6 to −2.0 m)): falling sea-level − rising sea-level → Facies D (high tidal flat: KS2009 (−2 to 2 m)): rising sea-level. Thus, after seawater influx started at 8300 BP, seawater rose with fluctuations (rising and falling). The KR-07 trench deposit of Sabsi island showed: Facies A' (barren zone: KR07 (−1.58 to −1.18 m)) → Facies B' (bog: KR07 (−1.18 to −0.76 m)) → Facies C' (tidal marsh: KR07 (−0.76 to −0.52 m)) → Facies D' (tidal flat: KR07 (−0.52 to −0.28 m)) → Facies E' (tidal marsh: KR07 (−0.28 to −0.08 m))→ Facies F' (tidal flat: KR07 (−0.08 to 0.06 m)). Transgression occurred first about 8,300 BP at the west coast of Korea: around 6300–6000 BP, there was a drop in the sea-level and around 6000–4000 BP, there was a rapid rise. Also, Repetition of falling and rising occurred since 4500 BP.