临夏盆地13.0~4.3 Ma湖相沉积物中正构脂肪酮记录的古气候演化

本文主要采用气相色谱-质谱分析技术对临夏盆地13.0~4.3 Ma沉积地层剖面样品进行检测，根据样品中正构烷烃、正构脂肪酮-2和正构脂肪酮-3的分布特征，揭示了正构脂肪酮对环境气候的指示意义。正构脂肪酮-2、正构脂肪酮-3与正构烷烃具有相同的有机质来源。其中正构脂肪酮-2的C₂₁^-/C₂₂⁺及正构脂肪-3-酮的C₂₁^-/C₂₃⁺比值变化与地质历史时期的气候与环境条件具有较好的相关性，对环境温度及湿度等变化有一定的指示意义。正构脂肪酮-2、正构脂肪酮-3的高、低碳数优势的转化指示研究区在13.0~4.3 Ma间的古气候具有四个较为明显的变化阶段，其中10.77~9.42 Ma、7.17~6.92 Ma气候由干冷变为暖湿，9.42~7.17 Ma、6.92~6.45 Ma气候由暖湿变为干冷，临夏盆地的干旱化事件指示了我国西北内陆现代干旱气候可能从8 Ma左右开始。

Paleoclimate of Past 13.0-4.3 Ma Recorded by n-alkan-ones in Lacustrine Sediments in Linxia Basin

In order to reveal the climatic significance of n-alkan-ones, a series of biomarkers, mainly including n-alkan-2-ones and n-alkan-3-ones, were identified from lacustrine deposit samples collected from the Maogou profile, Linxia Basin, by using the conventional gas chromatography-mass spectrometry (GC-MS) method. The organic matter source of n-alkan-ones was consistent with n-alkanes. The C₂₁^-/C₂₂⁺ value of n-alkan-2-ones and the C₂₁^-/C₂₃⁺ value of n-alkan-3-ones had good correlation with the paleoclimate and paleoenvironment, these provided indicative significance of the change of environmental temperature and humidity. Four climate shifts occurred from 13 Ma to 4.3 Ma are revealed by the switch of high carbon number predominance and low carbon number predominance of the n-alkan-2-ones and n-alkan-3-ones. The climate turned from dry-cold to warm-humid from 10.77 Ma to 9.42 Ma and 7.17 Ma to 6.92 Ma, respectively, and turned from warm-humid to dry-cold from 9.42 Ma to 7.17 Ma, 6.92 Ma to 6.45 Ma. The drought events in Linxia Basin indicated that the beginning of inland dry climatic conditions in Northwest China was started from about 8 Ma before present.