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传统观点认为由于奥陶系没有陆生高等植物出现，故而不会出现腐殖型有机质。首次在塔里木盆地塔中北斜坡中、上奥陶统泥灰质烃源中发现了类似于腐殖型有机质的海相偏腐殖型烃源岩。生物学、有机岩石学及核磁共振分析表明，奥陶系偏腐殖型烃源岩以宏观藻为主要生烃母质，其产物主要为凝析油和天然气。该类烃源岩主要是发育在灰泥丘沉积模式的丘间洼地和层状生物灰泥丘沉积亚相中的泥质灰岩类。该类烃源岩及其产物具有独特的生物标志化合物特征：较高的姥植比值、三环萜烷中低碳数部分含量较高及丰富的重排甾烷等。由该类烃源岩所生成的天然气的地化特征也较为特殊：较高的氮气含量、偏轻的甲烷碳同位素值和较高的干燥系数等。由于具较高的有机质丰度和生烃潜力，故该类烃源岩是塔中地区重要的气源岩。

DISCOVERY OF THE BIAS HUMIC TYPE HYDROCARBON SOURCE ROCKS IN ORDOVICIAN IN TALIMU BASIN

??According to traditional viewpoint it is thought that the humic type organic matter can't be found in the Ordovician because of lacking higher terrestrial plants.The marine bias humic type,which is similar to the humic type organic matter,hydrocarbon source rocks have been firstly found in the Upper-Middle Ordovician marly source rocks at the North Slope of the Cantral Talimu in Talimu Basin.Through the analyses of biology,organic petrology and nuclear magnetic resonance,it is shown that by taking the macro-algae as the major kerogen,the products of the Ordovician bias humic type hydrocarbon source rocks were mainly the condensate and natural gas.These hydrocarbon source rocks are mainly the marls which were developed in the cross-mound sag and bedded biological limemud mound sedimentary subfacies of the limemud mound sedimention model.These hydrocarbon source and their products are of distinctive biomarker characteristics,i.e.higher pristane to phytane ratio,higher low-molecular-weight compound content in tricyclic terpane and abundant rearranged sterane,etc.Relatively special geochemical properties were found in the natural gas generated from these hydrocarbon source rocks,i.e.higher nitrogen content,mathane carbon isotopic value's being on the light side and higher drying coefficient,etc.Owing to the fact that the hydrocarbon source rocks are of higher organic matter abundance and source potential,they are the important gas source rocks in the Central Talimu region.