黔北地区下志留统龙马溪组烃源岩生物标志物

应用气相色谱和色谱-质谱分析技术,对黔北地区下志留统龙马溪组烃源岩的甾烷和萜烷进行测试分析。结果表明,正构烷烃为后单峰型,主峰碳为C22～C30,Pr/Ph值为0.48～0.64,Pr/nC17为1.35～4.22,Ph/nC18为0.92～0.97。甾烷中,具孕烷系列的异常高值,C27、C28和C29呈规则甾烷"V"字型分布(C27C28C29),具明显的C27优势,甾烷/藿烷比值为0.57～0.71。萜烷类中具三环萜烷高值,低升藿烷,高伽马蜡烷指数特征。成熟度方面,OPE1,Ts/(Ts+Tm)分布在0.42～0.48之间,C3122S/(S+R)值为0.6～0.66,C29ββ/(ββ+αα)在0.56～0.58之间,反映出龙马溪期具明显的水体分层和高还原环境。有机质主要来源于浮游水生生物和藻类,并经历了一定的生物降解过程。烃源岩的热演化已进入高成熟-过成熟阶段。

The biomarkers in the source rocks from the Lower Silurian Longmaxi Formation in northern Guizhou

The steranes and terpanes in the source rocks from the Lower Silurian Longmaxi Formation in northern Guizhou are determined with the aid of gas chromatography and chromatography-mass spectrographic analysis.The analytical results suggest that the n-alkanes in the source rocks display a back single-peak pattern,with the main peak carbon values ranging from C22 to C30.The Pr/Ph ratios vary from 0.48 to 0.64;Pr/nC17 ratios vary from 1.35 to 4.22,and Ph/nC18 ratios vary from 0.92 to 0.97.The pregnane and homopregnane are very rich in steranes.C27,C28 and C29 display a regular V-type distribution pattern（C27 C28 C29）,with a C27 dominance.The sterane/aromadendrane ratios range between 0.57 and 0.71.The terpanes are characterized by high tricycloterpane values,low aromadendrane values and high gammacerane indexes.All the values for the maturity such as OPE1,Ts/（Ts ＋ Tm） ratios ranging between 0.42 and 0.48,C3122S/（S ＋ R） ratios ranging between 0.6 and 0.66,and C29 ββ/（ββ ＋αα） ratios ranging between 0.56 and 0.58 indicate the stratified water bodies and highly reduced conditions during the Longmaxian.The organic matter dominantly came from planktons and algae,and has been subjected to a certain degree of biodegradation.The thermal evolution of the source rocks has reached up to the stages of high maturation and overmaturation.