Luminescence dating of coastal deposits from the Chanthaburi Plain, Thailand

The ongoing global sea‐level rise urges us to better understand the dynamics of coastal processes for predicting future changes. Sedimentary deposits reflect past coastal environments but require precise chronological data to place evidence into a temporal context. While radiocarbon dating is widely employed, it is associated with several methodological challenges and frequently there is an absence of datable material in coastal deposits. Luminescence dating provides an important advantage over radiocarbon by directly determining the time of sediment deposition. However, this method is affected by problematic issues such as partial bleaching, bioturbation and dose rate assessment, which can lead to inaccurate age determinations. As a case study demonstrating good scientific practice in luminescence dating, we investigated deposits from the Chanthaburi Plain, Thailand, for reconstructing past coastal dynamics. Luminescence screening is used to identify potential signal disturbances and select appropriate sample positions in the drill cores. Luminescence dating was performed on 13 samples accompanied by detailed analysis regarding dose rate with a focus on water content and radioactive disequilibrium. The dated samples indicate depositional ages ranging between 7.2 and 4.6 ka. Comparison with radiocarbon ages (18 samples) reveals that plant material often represents modern roots and that molluscs tend to systematically underestimate the sedimentation age, likely due to partial recrystallisation. Our data suggest at c . 6.5 ka, a location of the coastline ~8.1 km inland from the present position. At around 4.6 ka, the coastline was about 7.2 km from the present shore. Together with previously published data, this indicates a sea‐level regression from the Middle Holocene highstand towards the Late Holocene.