The paleoclimate significance of hydrogen isotopic composition of individual hydrocarbon compounds in the Early Cretaceous Yixian Formation sediments from western Liaoning
Hydrogen isotope composition of n-alkanes and isoprenoid alkenes were carried out on lacustrine sediments collected from an excavated profile of the Early Cretaceous Yixian Formation in Sihetun,western Liaoning.The aim was to provide hydrogen isotope composition information on regional paleoclimatic conditions during Jehol Biota booming in the Early Cretaceous.The hydrogen isotope composition of n-alkanes has a large variation,ranging from -232.1 to -93.6.The correlation results of hydrogen isotope composition between dominated n-alkanes suggest that n-C_(29) and n-C_(31) mainly originated from terrestrial higher plants,while n-C_(23) are primarily attributed to aquatic plants.The calculated DeltadeltaD_(mid-long) composition changes from -28.8 to 85.0,suggesting that the climate fluctuated periodically during Jehol Biota booming,but gradually changed from warm and dry to warm and humid then returned to warm and dry.Particularly pristane and phytane are significantly depleted in deuterium relative to n-alkanes,and phytane depleted in deuterium relative to pristane,combining with their carbon isotope composition,the different hydrogen isotope composition between the two isoprenoids may be caused by different pathways associated with their derivation from a common phytol precursor during geological diagenetic evolution.