EARLY HOLOCENE SEA LEVEL RISE AND GEOMORPHOLOGICAL DEVELOPMENT OF THE YEONGSAN RIVER, KOREA

A notable environmental change in the early Holocene was the sea level rise over most of the Earth. This has attracted a great deal of scientific attention because the sea level rise is critical in understanding the isostatic responses, sediment flux and compaction, paleo-climate change, landscape evolution, and prehistoric human occupation. Sea level rise during the early Holocene would significantly alter sedimentation and erosion patterns as well as the topography of coastal areas. The sedimentary environments could have been unstable at the non-marine and marine boundary in the early Holocene as well.

The sea level positions in Korea during the Holocene still remain unclear. A complicated coastline of the west coast of Korea is bordered by numerous coastal embayment, estuaries, and islands formed by the inundation during the last postglacial sea level rise. These coastal embayments are major depocenters for the fine-grained sediments, resulting in the development of long stretch of broad, extensive Holocene marine tidal flats along the west coast of Korea. A marine influence can be observed at 10400 yrBP (-21 m) and 8600 yrBP (-14 to -12 m) around the Yeongsan River Estuary. In macro-tidal regions having tides greater than 4 m like the study area, however, seawater can intrude upstream along the river channel bottom for more than several kilometers due to tidal forcing in the form of a salt wedge, resulting in a marine signal in an inland area located higher than the mean sea level position.

The boundaries between Holocene and underlying pre-Holocne deposits in the lower reaches of the Yeongsan River are largely classified into two groups: paleosol - marine deposit, and fluvial sand & gravel - marine deposit. Occasionally, peats or lacustrine deposits are also observed. Paleosol represents the subaerially exposed earth surface just before the sea water inundation, and fluvial the channel deposit of the Yeongsan River. Information on the distrubution of these deposits along the Yeongsan River would help to delineate the channel path and size of the Yeongsan River and to reconstruct the timing and elevation of the sea level at that time. Here we provide a compilation of 80 drilling core data along the lower reach of the Yeongsan River, with particular emphasis on the Holocene and pre-Holocene boundary.