Micromorphology, mineralogy, and geochemistry of sediments at the tham lod rock shelter archaeological site in Mae Hong Son, Thailand: Suggestions of a late pleistocene climate

Abstract

Sediments from an archaeological pit at the Tham Lod rock shelter in Mae Hong Son, Thailand, reveal sparse palaeo-environment and palaeoclimate information in the north-western region of Thailand and Southeast Asia. This study is a pioneering work for the site. Micromorphological, mineralogical, and geochemical methods were applied for analyses. The sediment profile was divided into two zones: the upper 0–338 cm depth and the lower 338–450 cm depth. Intense chemical weathering occurred in the lower zone, indicated by low quantities of kaolinite and high chemical index of alteration (CIA, 64.55–73.36%), reflecting greater humidity. The upper zone yielded mild CIA (<47.21%) and contained ubiquitous smectite, indicating drier conditions. Overall sediments (along the profile, 0–450 cm depth) were affected by leaching and thin section analyses suggested a wet/dry cycle during diagenesis under humid tropical conditions. Micromorphological and geochemical analyses indicated that mudstone, sandstone, and limestone were major parent materials of sediments deposited mainly in a fluvial environment in the lower zone, which changed to a colluvial environment in the upper zone. The palaeoclimate during 12,770–33,340 yr BP was in the Last Glacial Maximum Period, characterized by drier and cooler than the present climate. The period ≥33,340 yr BP was wet and cool. Evidence of prehistoric human occupation, including bone and charcoal fragments, appeared in sediments in the upper zone, sug-gesting animal hunting for survival.