Holocene transgressive stratigraphy of a macrotidal flat in the southeastern Yellow Sea; Gomso Bay, Korea

Gomso Bay, located on the western coast of Korea, has a mean tidal range of 4.3 m and is directly open to the Yellow Sea. Analysis of eighteen vibracores (in two transects) from extensive tidal flats on the south side of the bay shows that the Holocene tidal-flat deposits consist of three depositional units: (1) a basal Unit I (intensely bioturbated silt with occasional remnant subparallel lamination), (2) an intermediate Unit II (highly bioturbated, faintly laminated sandy silt or silty sand), and (3) an upper Unit III (slightly to moderately bioturbated very fine to fine sand with abundant parallel lamination and cross-lamination). Units I, II, and III can be interpreted as a result of subtidal to intertidal sedimentation on the mud flats, mixed flats, and sand flats, respectively. Tidal-channel deposits are partly preserved, occurring in Units II and III. Storm deposits, preserved predominantly in Units II and III, generally have sharp erosional bases and consist of thick approximately 10 cm) massive shelly sand (often graded) that is overlain by thin, waning-stage, parallel-laminated and cross-laminated sand and mud. These intertidal deposits show a coarsening-upward succession underlain unconformably by pre-Holocene semiconsolidated, oxidized mud (Unit O). The coarsening-upward Holocene Gomso deposits represent a transgressive, retrograding phase within a parasequence, associated with low accumulation rates. The unconformable boundary between pre-Holocene Unit O and Unit I is a transgressive surface of erosion (TSE) formed during the Holocene transgression.