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 (δ13Corg) 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 δ13Corg ranged between approximately −24‰ and −27‰, suggesting different organic matter sources. Relatively lighter δ13Corg occurred in lower part and the occurrence of heavier δ13Corg 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 odd-numbered n-alkanes, particularly nC29 and nC31, and by variation in the distribution of even-numbered 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 δ13Corg. 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 n-alkanes and their δ13CALK support paleovegetation and paleoclimatic variations in Jeongok-ri Paleolithic site, Korea for the last 300 ka.