黔北地区下志留统龙马溪组烃源岩生物标志物

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

关键词:  黔北地区  龙马溪组  烃源岩  生物标志物

Key words:  northern Guizhou  Longmaxi Formation  source rock  biomarker

摘要:

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(C₂₇ > C₂₈ < C₂₉),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,OPE<1,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。

Abstract:

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 OPE<1,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.