Jeong-Heon Choi

Reconstruction of Holocene coastal progradation on the east coast of Korea based on OSL dating and GPR surveys of beach-foredune ridges

Coastal dunefields along the east coast of Korea have long been thought to have originated from beach ridges that prograded during the Holocene, but there has been little chronological evidence based on absolute dating. In this paper, we use optically stimulated luminescence (OSL) dating and ground-penetrating radar (GPR) surveys to reconstruct the coastal progradation of Anin dunefield in the Gangneung area on the east coast of Korea. GPR profiles and sedimentological analyses of four beach-foredune ridges reveal that the ridges are composed mainly of beach deposits showing seaward-dipping and horizontal laminae, capped by eolian sands with landward-dipping laminae. The beach deposits are, in places, underlain by fluvial sands with gravels. Coupled with data from OSL dating, we interpret these results to mean that the fluvial sands and rounded cobbles were deposited in the study area, during the last glacial period. Between the mid-Holocene (~6.5 kyr) and c. 3.5–3.0 kyr, the transgression rate of the sea decreased and coastal progradation occurred. Between c. 3.5 and 3.0 kyr, foreshore sediments, including granules and pebbles, accumulated over the older beach deposits, indicating erosional events. Progradation resumed at ~3.0 kyr and continues to the present. During the past 3 kyr, there has been an average rate of progradation of ~0.14 m/yr. The beach-foredune ridges in the Gangneung area represent the evolution of coastal progradation on the east coast of Korea during the Holocene.

Application of newly developed NCF-SAR protocol to Quaternary sediments from Suncheon and Jeongok, South Korea

Present study is an attempt to test the applicability of recently developed natural sensitivity corrected single aliquot regeneration (NCF-SAR) protocol for samples from archaeological sites of South Korea. The protocol monitors the sensitivity change during measurement of natural OSL (Optically Stimulated Luminescence) signal and provides a methodology to correct for it. The natural OSL signals in the quartz samples from Suncheon (fluvial) and Jeongok (aeolian) sites were either in dose saturation region or lying well above the luminescence dose response curve, suggesting the possibility of sensitivity changes during natural OSL signal measurements. These samples thus provide opportunity to test the NCF-SAR protocol. The results suggest that, for the samples examined in this study, there are significant sensitivity changes during the natural OSL signal measurements. The ratio of TL (Thermoluminescence) peaks before and after natural OSL measurement was used to correct for the sensitivity changes. The dose distribution obtained using NCF had less scatter. However, in some cases, even the NCF correction could not resolve the issue of natural signal lying above saturation dose, indicating some other unidentified factors are also responsible for this oversaturation of quartz OSL signal.

Reevaluation of Th and U concentrations in marine sediment reference materials using isotope dilution MC-ICP-MS: towards the analytical improvements in dose rate estimation for luminescence dating

The thorium and uranium concentrations of four marine sediment reference materials (CRMs NIST 1646a, NRCC HISS-1, MESS-3 and PACS-2) were determined using isotope dilution-multiple collector-inductively coupled plasmas-mass spectrometry (ID-MC-ICP-MS), aiming at helping the assessment of reliability in dose rate estimation for luminescence dating. Quintuplicate analyses of the CRMs revealed their intrinsic heterogeneity in the concentration of both elements (up to 23% and 8% for thorium and uranium, respectively, in 2σ standard error level) for individual sub-samples of about 100 mg. The thorium and uranium concentrations of all CRMs determined in this study were significantly lower (up to 45%) than the provided or reported informative values, requiring reevaluation of their reference concentrations. The use of informative thorium and uranium concentrations in these CRMs as standard values for elemental analysis of unknown samples will result in overestimated dose rates, and thus age underestimation when applied to luminescence dating techniques.

Geochronology and sedimentary environment at the Udu-dong archeological site, Chuncheon, South Korea

The Udu-dong archeological site in Chuncheon, South Korea, dates back to the Proto–Three Kingdoms Period (approximately 100 BC to AD 350). Many artifacts, including some earthenware, have been excavated in these ancient dwelling sites. We applied three geochronological dating methods (radiocarbon, optically stimulated luminescence (OSL), and archeomagnetic dating) to the archeological remains of this large-scale human settlement and reconstructed the history of depositional processes prior to human settlement. The timing of the ancient community’s settlement was investigated by radiocarbon dating of the charcoal fragments collected from old furnaces. Archeomagnetic dating allowed us to constrain the time period of the settlement’s abandonment by dating the last use of fire. The timing and development of fluvial deposits underlying the settlement site were reconstructed by OSL dating combined with sedimentary facies analysis. Our results show that, following the deposition of coarse sediments starting 10,000 years ago, the region formed a stable floodplain environment starting around 3000 years ago; people began to form clustered settlements approximately 50 years later. For the subsequent 150 years or so, the area was heavily used as a settlement site, with people evenly distributed across it, before eventual abandonment of the site around AD 200–250. Because the sedimentary deposits do not show any significant facies change during this period, we conclude that any catastrophic events were not the main reason for settlement abandonment. This study suggests that combining scientific and archeological analyses have significant benefits for studies of such archeological sites. Therefore, continuous collection of such data can provide important information for the excavation and protection of prehistoric or historic sites.