Paleovegetation and paleoclimate changes based on terrestrial n-alkanes and their carbon isotopes in sediment from the Jeongok-ri Paleolithic Site, Korea

Abstract

Carbon isotope of total organic carbon (δ¹³C_org) and long-chain n-alkanes, which are terrestrial plant biomarkers, and their compound-specific carbon isotope ratios (δ¹³CALK) were investigated in the sediment of the Jeongok-ri Paleolithic Site in central Korea to interpret changes in paleovegetation and paleoclimate. The δ¹³C_org ranged between approximately -24‰ and -27‰, suggesting different organic matter sources. Relatively lighter δ¹³C_org occurred in lower part and the occurrence of heavier δ¹³C_org in upper part may indicate terrestrial C₃ plant dominance and/or a mixture of C₃ and C₄ plants, respectively. The patterns of n-alkane distribution were characterized by a continuous predominance of oddnumbered n-alkanes, particularly nC₂₉ and nC₃₁, and by variation in the distribution of evennumbered n-alkanes. Total concentration of n-alkanes and distributions of each number of n-alkanes are quite different over time, suggesting paleovegetation changes. The average chain length (ACL) and carbon preferences index (CPI) showed gradual variations with distinctive switching points at about 160 ka. This variation reflecting changes in paleovegetation type, is coincident with those of the δ¹³C_org. Individual n-alkane isotopes, δ¹³CALK, ranged between 18.64‰ and 38.09‰, suggesting different sources of n-alkanes. Although some petrogenic sources of n-alkanes were possible, the distribution of nalkanes and their δ¹³C_ALK support paleovegetation and paleoclimatic variations in Jeongok-ri Paleolithic site, Korea for the last 300 ka.