Site formation processes and environmental change during the Late Pleistocene–Holocene in Long Long Rak Cave, Mae Hong Son, Thailand

ABSTRACT

Cave sediments are key archives of past environmental and climatic change, and yet, detailed terrestrial records from tropical south‐east Asia remain scarce, particularly from archaeologically relevant sites. This study analyses 29 sediment samples from Long Long Rak Cave, an archaeologically significant site with evidence of human burial and occupation dating to ~2 ka, Thailand, using X‐ray fluorescence (XRF), X‐ray diffraction (XRD), particle‐size analysis and thermoluminescence (TL) dating (six age estimates) to investigate environmental change and sedimentary processes. Sedimentation patterns vary between chambers, reflecting differences in cave morphology and microclimate. Higher‐energy depositional conditions during ~13.4–11.3 ka, as evidenced by coarse sediments, erosional surfaces and Fe/Mn nodules formed under fluctuating redox conditions, indicate variable hydrological conditions with episodic higher‐energy flow events and enhanced sediment transport, broadly corresponding to terminal Pleistocene climatic instability, including the Younger Dryas. This was followed by a transitional phase of reduced and variable water input prior to a stratigraphic discontinuity at ~10.3 ka, which marks a shift to lower‐energy slackwater deposition and reduced sediment supply, marking Early Holocene hydrological adjustment. Evidence for post‐depositional modification includes clay translocation, Fe/Mn oxide and phosphate mobilisation, secondary calcite precipitation and bioturbation by termites and humans. Human activity is restricted to upper deposits dated to ~2 ka, indicating that most natural sediment accumulation predates cultural use of the cave.