Phytolith analysis and reconstruction of palaeoenvironment at the Nabokri valley plain, Buyeo, Korea

Abstract

The soil profile between 12.0 and 14.0 m.a.s.l. was deposited at the Nabokri Valley Plain, Buyeo, Korea from approximately 6000 BP to the present. Through phytolith analysis of 20 samples collected at 10 cm intervals, five Phytolith Assemblage Zones (PAZs) are identified. Based on the number of various types of phytoliths and occurrence of specific families adapting to the particular climates, this study yields the climatic indices, reconstructs the paleoclimates, and estimates the human activities during the reconstructed period. The five PAZs are well correlated to the chronology of sedimentary layers and construction periods of the artifacts at the archaeological excavation. The Buyeo area was temperate and wet during the Neolithic Age (PAZ-I) and there is no phytolith evidence of vegetation change by humans. The climate can be characterized as temperate and wet during the early Bronze Age (PAZ-II), but then cooling later. During this period, agricultural activities began with the Panicoideae including Oryza sativa. In the early Iron Age, the climate became warmer. The climate during the Proto-Three States Age (PAZ-III) since 2000 BP was variable, and species such as O. sativa and Panicoideae were actively cultivated. The Three States Age can be characterized by variable climates similar to the Proto-Three States Age. The Ic (Climate index) and Iph (Humidity-aridity index) values indicate that the climates were first wet and then became drier. Agricultural activities are identified from the Bronze Age (PAZ-II) through Three States Age and Joseon Dynasty (PAZ-IV) based on the presence of cultivation layers as well as specific phytolithic indicators of agriculture. The uppermost layer (PAZ-V) shows no evidence of agricultural activities due to the significant decrease in the number of phytoliths, perhaps from recent abandonment.