鄂尔多斯盆地北缘固阳县北中元古界长城系烃源岩地质特征及意义

是否发育有效烃源岩是鄂尔多斯地区中元古界成藏的关键。综合利用野外地质考察、显微薄片鉴定和地球化学分析等研究方法对固阳县北中元古界渣尔泰山群阿古鲁沟组烃源岩地质特征开展研究。研究表明，中元古界烃源岩岩性为低级区域变质作用形成的炭质板岩及片岩，其矿物成分以石英为主，其次为斜长石、钾长石及白云母，还有少量菱铁矿。烃源岩有机碳含量高，变化在0.17%～21.62%之间，平均值为5.53%；有机质类型以Ⅰ型为主，其次为Ⅱ型；Ro变化范围为4.32%～5.09%，T_max值介于556 ℃～564 ℃，处于过成熟阶段。稀土元素体现出LREE富集和轻、重稀土分异明显的特点，δEu介于0.43～0.49之间，表现出Eu的明显负异常；微量元素含量及比值指示阿古鲁沟组烃源岩形成时的沉积环境为水体深度大、水动力条件弱的并且与外海沟通受到限制的贫氧—缺氧的闭塞环境，沉积相类型为温暖潮湿气候条件下淡化泻湖相。

Geological characteristics and significance of source rocks of Mesoproterozoic Changchengian System in north of Guyang County of the northern margin of Ordos Basin

The development of effective source rocks is the key to Mesoproterozoic hydrocarbonaccumulation in Ordos area. In this paper, the geological characteristics of source rocks in theAgulugou Formation of the Zhaertaishan Group of Mesoproterozoic Changchengian System in northof Guyang County were studied by means of field geological investigation, microscopic sectionidentification and geochemical analysis. Researches show that the source rock is carbonaceous slateand a small amount of schist with quartz as the main mineral composition, followed by plagioclase, potassium feldspar and muscovite, and a small amount of siderite. The contents of organic carbonin the source rocks are high, and the value ranges from 0.17% to 21.62%, with an average of 5.53%.The type of organic matter is Ⅰ kerogen, and the second is Ⅱ kerogen. The value of Ro ranges from 4.32% to 5.09%, and the T_max value is from 556 ℃ to 564 ℃. These results show that the thermal evolution of source rocks is high, and is in the over-mature stage. Their NASC normalized REE patterns of the source rocks are characterized by LREE enrichment with obvious different valuebetween LREE and HREE with distinctive negative Eu anomalies（δEu: 0.43～0.49）. The content and ratio of trace elements indicate that the sedimentary environment of the source rocks of Agulugou Formation is an oxygen-deficient-anoxic closed environment with large water depth, weakhydrodynamic conditions and limited communication with the open sea and the sedimentary faciesare desalinated lagoon facies in warm and humid climate.