黔北务川-正安-道真地区铝土矿系中生物标志物及其地质意义

Biomarkers of bauxite-bearing strata and its geological significance in Wuchuan-Zheng’an-Daozhen area,northern Guizhou Province

黔北务川-正安-道真地区铝土矿位于石炭系黄龙组和二叠系梁山组之间,主要属于沉积型铝土矿。通过气相色谱(GC)与气相色谱-质谱(GC-MS)手段分析铝土矿系钻孔岩心中的生物标志物,发现了含量丰富的正构烷烃、类异戊二烯烷烃、萜类化合物与甾类化合物。对10个样品饱和烃组分GC分析表明,正构烷烃主要呈双峰式分布特征,碳数分布n-C14～n-C35,CPI值范围为0.90～3.45,表现出奇偶优势。姥鲛烷/植烷(Pr/Ph)值为0.38～077,表现出明显植烷优势。对3个样品饱和烃组分GC-MS分析表明,萜烷类化合物以C30藿烷占优势,相对丰度由大到小依次为五环三萜烷、三环萜烷、四环萜烷,并检测出少量的γ-蜡烷。规则甾烷C27-C28-C29呈近L型或V型分布,并含少量4-甲基甾烷。根据生物标志物特征参数,结合岩心样品岩相学特征,确定了铝土矿系中有机质的陆上植物与低等菌藻类双重来源,铝土质沉积时为偏酸性较还原环境,明确了铝土矿系的形成过程受到来自陆上与沉积水体内两个古生态系统的双重作用。

The bauxite deposits between the Carboniferous Huanglong Formation and Permian Liangs- han Formation in Wuchuan-Zheng＇an-Daozhen area, northern Guizhou Province mostly belong to sedi- mentary bauxite. Abundant biomarkers including n-alkanes, isoprenoid, terpenoids and steroids in drill- ing core samples are detected by GC and GC-MS. The results of GC reveal that most of n-alkane in ten samples are composed of n-C14 ~ n-C35 and characteristic of double-peak distribution. CPI ranges from 0.90 to 3.45, indicates obvious odd-even carbon number predominance. Pristane to phytane ratios （Pr/Ph） vary from 0.38 to 0.77. According to the results of GC-MS, the relative abundance from higher to lower is pentacyclic triterpanoids, tricyclic terpane, tetracyclic terpane, and C30 hopane is most abun- dant in the terpanes, meanwhile, small quantities of gammacerane are detected. Regular steroids distrib- uted in ＂L＂ or ＂V＂ shape includes a small amount of 4-methyl sterane. Combined with petrographical characters of samples, the biomarker parameters indicate a reductive sedimentary environment which shows slant acidity, the organic matter in bauxite deposit originate from both terrestrial plant and bacteria/ algae. It clearly shows double influences from terrestrial and aquatic palaeoecosystems during bauxite forming process.