松辽盆地湖相烃源岩中生物标志物的单体烃碳同位素组成特征及其意义  

The carbon isotopic composition of individual biomarkers in lacustrine source rocks from Songliao Basin and its biogeochemical implication

作　　者：王丽[1] 曹新星[1,2] 李艳[1,2] 尹琴[3] 宋之光[1] 

机构地区：[1]中国科学院广州地球化学研究所有机地球化学国家重点实验室,广东广州510640 [2]中国科学院大学,北京100049 [3]中国石油化工股份有限公司河南油田分公司勘探开发研究院,河南郑州450018

出　　处：《地球化学》2015年第4期337-347,共11页Geochimica

基　　金：国家自然科学基金(41321002)

摘　　要：本研究对松科一井嫩江组一和二段（K2n^1和K2n^2）岩芯样品进行了有机碳稳定同位素和单体烃分子碳同位素分析，结合其他地球化学参数探讨了沉积环境与母质生物之间的关系。正构烷烃碳同位素在-35．7‰～-28．7‰之间变化，显示了各链长正构烷烃具有不同的母质生源。其中，中链正构烷烃（MCA）碳同位素明显贫^13C，偏轻达5‰，可能与其先体母质部分地利用了有机质降解的贫^13C的CO2有关。嫩江组藿烷碳同位素（δ^13Chopane）处于-32．00‰～-68．65‰之间，在嫩一段下部的δ^13Chopane）偏轻达到-68．65‰，表明该时期存在甲烷营养菌。在嫩一段δ^13CGa较重、δ^13Chopane显著偏轻的层段与水体分层、间歇性透光带缺氧相对应，反映了该时期的化跃层界面较浅，缺氧层上升到了透光带，这种极端的水体环境有利于沉积有机质的保存，造成了该层段高TOC、高HI的富有机质烃源岩的形成；而在嫩二段伽马蜡烷缺失、δ^13Chopane较重时，则反映了水体的化跃层界面较深，环境相对较为氧化，有机质保存条件变差，导致了该段TOC和HI相对较低。由此可见，水体化跃层界面的深浅不仅控制了湖泊沉积有机质的丰度，还影响了水体中微生物的发育，在化跃层较浅的层段，嗜甲烷菌、化学自养菌发育，而在化跃层较深的层段，水体中以化学自养菌为主。另外，δ^13CGa和δ^13C4-甲基甾烷与水体盐度呈正相关关系，水体盐度越高，其碳同位素值越重。Stable carbon isotopic compositions （δ^13C） of organic matter and molecular hydrocarbon biomarkers in the first and second members of Nenjiang Formation （K2n^1 and K2n^2） from the SK-1 drilling well are studies, and combined with other geochemical parameters, aimed to investigate the relationship between depositional paleoenvironment and initial organisms of organic matter. The n-alkanes show a wide range of carbon isotopic values, varying from -35.7‰ to -28.7‰, indicating that the n-alkanes with different carbon chain lengths may have different sources. For example, the medium-chain n-alkanes are significantly depleted in ^13C and more negative （ca. 5‰） than short-chain and long-chain n-alkanes, which are probably due to its original organism partly utilized the ^13C-depleted CO2 from degradation of organic matter. The δ^13C values of hopanes vary from -32.00‰ to -68.65‰, with the lightest value （ca. -68.65‰） in the lower part of K2n^1, suggesting a predominant origin of methanotrophic bacteria. Isotopically heavier gammacerance and significantly lighter hopanes in K2n^1, coincide with water stratification and intermittently anoxic photic zone, which represent a shallow chemocline. The extreme water environment, anoxia spreading upward to euphoric zone, is conducive to the preservation oforganic matter, resulting in high values of TOC and HI in this section. By contrast, absence of gammacerane and isotopically heavier hopanes in K2na reflect the deeper chemocline, corresponding to a relatively oxic environment and low values of TOC and HI. Thus, the depth of water chemocline can not only control the abundance of organic matter in lacustrine sediments, but also affect the growth of microbial community. Chemoautotrophic bacteria are dominant in the water body with a deeper chemocline while chemoautotrophic bacteria and methanetrophic bacteria develop in the shallower chemocline. Moreover, δ^13C values of gammacerance and 4-methylsteranes are related to water salinity, i.e., the highe

关 键 词：分子碳同位素 化跃层 古水体环境 松科一井 

分 类 号：P593[天文地球—地球化学]