苏北地区早寒武世黑色页岩地球化学特征与有机质富集模式

Geochemical features and organic matter enrichment in the Early Cambrian black shale, northern Jiangsu area

张玉玺 陈建文 周江羽

Yuxi Zhang Jianwen Chen Jiangyu Zhou

早寒武世期间沉积的一套富有机质页岩，沉积厚度大，有机质含量高，是目前华南地区海相页岩气勘探重要目标层系之一。以苏北地区XYZ-1为例，利用钻井岩心资料和地球化学测试分析数据，探讨早寒武世幕府山组黑色页岩的沉积环境及有机质富集模式研究。结果表明，XYZ-1井幕府山组为一套黑色、深灰色炭质页岩夹薄层状碳酸盐岩的沉积层序，顶部和底部发育有石煤层。幕府山组V/（Ni+V）平均值为0.74，Ni/Co的平均值为6.78，U/Th的平均值为1.46，V/Sc的平均值为65.43，氧化还原指标表明幕府山组整体为缺氧的沉积环境，在底部和顶部存在两次较为强烈的硫化事件。幕府山组炭质页岩的平均值为5.62%，其中72.2%的样品大于2%，与相关系数高达0.89。因此，缺氧的沉积条件为有机质的富集和保存提供了保障，硫化的沉积环境是有机质富集的关键因素，苏北地区幕府山组具备了发育良好烃源岩和储层的条件。

A set of black shale deposited in the Early Cambrian and characterized by a large thickness and high organic matter content is one of the important exploration target strata for marine shale gas in South China.The sedimentary environment and enrichment mechanism of organic matters in the black shale are discussed based on the core and geochemical data from Well XYZ-1 drilled through the Early Cambrian Mufushan Formation in northern Jiansu area.The Mufushan Formation in Well XYZ-1 is a set of depositional sequence of black and dark gray carbonaceous shale with stone coal layers on top and at bottom and interbeds of thin-layered carbonate rocks.The average values of V/(Ni+V), Ni/Co, U/Th, and V/Sc are 0.74, 6.78, 1.46, and 65.43, respectively.These ratios as indicators of redox environment suggest that the sediments were under anoxic conditions and two strong sulfidation events once occurred at the bottom and top.The average total organic carbon () content of the Mufushan carbonaceous shale is 5.62%, with the value of 72.2% of the samples collected greater than 2%.The - correlation coefficient is as high as 0.89.The hypoxic environment with sulfidation events provided favorable conditions for the enrichment and preservation of organic matters, thus laid down foundation for the development of high-quality source rocks and reservoirs in the Mufushan Formation of northern Jiansu.

10.11743/ogg20200416