辽西下白垩统义县组烃类化合物氢同位素组成及古气候环境意义

The paleoclimate significance of hydrogen isotopic composition of individual hydrocarbon compounds in the Early Cretaceous Yixian Formation sediments from western Liaoning

以四合屯剖面下白垩统义县组三段湖相沉积为研究对象,对抽提物中正构烷烃和无环类异戊二烯烃的氢同位素组成进行了测定,以期为热河生物群繁盛时期的古气候和古环境变化提供氢同位素组成的证据。结果显示,正构烷烃的氢同位素组成介于-232.1‰^-93.6‰,在剖面上变化明显;主峰碳数正构烷烃氢同位素组成的相关性分析显示,n-C29与n-C31主要来自陆生高等植物,而n-C23则主要来自水生植物。中碳数正构烷烃与高碳数正构烷烃氢同位素组成差值(ΔδDmid-long)的剖面变化在-28.8‰~85.0‰,指示热河生物群繁盛时期的气候波动显著,呈现由干旱逐渐变为温湿,再回归干旱的阶段性循环特征。特别是姥鲛烷和植烷的氢同位素组成较正构烷烃明显偏轻,而姥鲛烷较植烷的氢同位素组成相对轻微偏重,结合它们的碳同位素组成证据,这一差异很可能是由于成岩演化过程中植醇形成姥鲛烷和植烷的途径不同而引起。

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-C29 and n-C31 mainly originated from terrestrial higher plants, while n-C31 are primarily attributed to aquatic plants. The calculated Dmid-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 he caused by different pathways associated with their derivation from a common phytol precursor during geological diagenetic evolution.