本研究对松科一井嫩江组一和二段(K2n1和 K2n2)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(δ13Chopane)处于–32.00‰~–68.65‰之间,在嫩一段下部的δ13Chopane偏轻达到–68.65‰,表明该时期存在甲烷营养菌。在嫩一段δ13CGa较重、δ13Chopane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、δ13Chopane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,δ13CGa和δ13C4-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 (δ13C) of organic matter and molecular hydrocarbon biomarkers in the first and second members of Nenjiang Formation (K2n1 and K2n2) 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. Then-alkanes show a wide range of carbon isotopic values, varying from–35.7‰ to–28.7‰, indicating that then-alkanes with different carbon chain lengths may have different sources. For example, the medium-chainn-alkanesare significantly depleted in13C and more negative (ca. 5‰) than short-chain and long-chainn-alkanes, whichareprobably due to its original organism partly utilized the13C-depleted CO2 from degradation of organic matter. Theδ13C values of hopanes varyfrom–32.00‰ to–68.65‰, with the lightest value (ca.–68.65‰) in the lower part of K2n1, suggesting a predominant origin of methanotrophic bacteria. Isotopically heaviergammacerance and significantly lighterhopanes inK2n1, coincide with water stratification and intermittently anoxicphotic zone, whichrepresentashallow chemocline. The extreme water environment,anoxiaspreading upward toeuphotic zone,isconducive to the preservation of organic matter, resulting in high values of TOC and HI in this section.By contrast, absence of gammacerane and isotopicallyheavierhopanes inK2n1reflect the deeper chemocline, corresponding toarelatively oxicenvironment 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,butalso affect the growth of microbial community.Chemoautotrophic bacteriaare dominantinthe water body with a deeper chemocline whilechemoautotrophic bacteria and methanetrophic bacteriadevelopintheshallower chemocline.Moreover,δ13C values of gammacerance and 4-methylsteranesare related to water salinity, i.e., the higher the water salinity is, the isotopically heavier gammacerance and 4-methylsterane would be produced.
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