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甘肃秦安的新近纪风成红土堆积是东亚大陆古环境演化的重要载体之一,但相对第四纪黄土而言,对其记录的古环境信息仍缺乏生物标志化合物方面的研究.本文对秦安QA-I剖面早-中中新世代表性黄土和古土壤层样品开展了初步的正构烷烃分析,并与前人发表的不同时期的风成沉积和水成沉积代表性样品进行对比.结果显示:(1)QA-I剖面中的正构烷烃碳数分布范围为C_(14)~C_(35),其中来源于微生物的低碳数部分(C_(14)~C_(20))的含量明显高于来自高等植物叶蜡的高碳数部分(C_(26)~C_(35)),主峰碳处于C_(16)~C_(18),中碳数部分(C21~C_(25))的相对含量最低,这些特征与第四纪黄土及晚中新世-上新世三趾马红土中一些强发育的古土壤层类似,但与弱风化的黄土和三趾马红土及水成沉积明显不同;(2)QA-I剖面样品的高碳数部分虽具有一定的奇偶优势,但碳优势指数(CPI)明显较各类风化较弱的样品低.上述结果显示,秦安中新世风尘红土堆积经历了较强烈的风化成壤和微生物作用,导致其中的长链正构烷烃较显著的氧化和降解,并以微生物贡献的短链正构烷烃为主.微生物对全岩有机质(TOC)的贡献以及对TOC碳同位素的影响需在古环境重建中予以充分考虑.
The paleoclimate lateritic accumulation in Qinan, Gansu, is one of the important carriers of paleoenvironment evolution in the East Asian continent. However, compared with the Quaternary loess, the paleoenvironmental information recorded in this area still lacks the research on biomarker compounds.In this paper, QA-I The preliminary n-alkane analysis of the early-middle Miocene representative loess and palaeosol samples was carried out and compared with the representative samples of aeolian sedimentation and sedimentation from different periods previously published. The results show that: 1) The carbon number distribution of n-alkanes in QA-I profile ranged from C_ (14) to C_ (35), and the content of C_ (14) ~ C_ (20) The main peak carbon in the higher carbon fraction (C_ (26) ~ C_ (35)) of leaf wax of higher plants was in the range of C 16 C 18 and C 21 C 25, These features are similar to those of the Quaternary loess and late Miocene-Pliocene horseshoe loam, but they are obviously different from weak-weathered loess and three-toed horseshoe and water sediments ; (2) Although the high carbon number of the QA-I profile has some parity advantages, the carbon index (CPI) is obviously weaker than that of various weathered The above results show that the accumulation of Aeolian dust and dust in the Qin’an area underwent intensive weathered pedogenesis and microbial action leading to significant oxidation and degradation of the long-chain n-alkanes in them, Alkanes.The contribution of microorganisms to total organic matter (TOC) and its influence on TOC carbon isotopes should be fully considered in paleoenvironment reconstruction.