塔中地区志留系柯坪塔格组内不整合的微观证据

在前人研究的基础上, 通过钻井资料、地震资料和岩心资料分析相结合的方法, 识别出了塔中地区志留系柯坪塔格组上二亚段与上一亚段之间可能存在一不整合面; 又通过薄片和地球化学等微观手段证实了这一不整合面存在的合理性.研究结果表明: 1)塔中地区志留系柯坪塔格组上三亚段和上二亚段中的黄铁矿发生了褐铁矿化作用, 并且这种氧化作用在横向上具有可追踪性; 2)上三亚段中具有收缩缝的沥青是早期生成的成熟度较低的油气在运移至构造高部位过程中遭受氧化作用而形成的; 3)上三亚段和上二亚段中的碳酸盐胶结物主要是在淡水或混合水环境中形成的; 上一亚段和石炭系中的碳酸盐胶结物主要是在海水环境中形成的.这些微观证据相互印证了该区在上二亚段与上一亚段之间存在一不整合面.这对该区层序的划分及后期油气勘探具有重要意义.

Microscopic evidence of stratigraphic unconformity within the Silurian Kepingtage Formation in Tazhong area

On the basis of previous research, an uncomformable surface between the 1st sub-member of upper member of Kepingtage Formation in Tazhong area and the 2nd was discerned by the log information, the drilling core and the seismic profile. Then the rationality of the existence of the uncomformable surface was confirmed by some microscopic means, such as the thin section, the data of geochemistry, and so on, which could play a part in dividing the sequence of strata and the late oil and gas exploration in the area. There are several results as follows: 1)The ferritization of pyrite in the 1st and 2nd sub-member of upper member of Kepingtage Formation in Tazhong area is widthwise traceable. 2)The asphalt with shrink fractures in the 3rd sub-member of upper member of Kepingtage Formation formed because of the oxidation of the low maturity hydrocarbon during the migration of the oil and gas from the low tectonic position to the high. 3)Carbonate cement in the 3rd and 2nd sub-member of upper member of Kepingtage Formation mainly formed in fresh water or admixing water, and carbonate cement in the 1st and carboniferous mainly formed in sea water. These microscopic evidence confirms there is a phenomenon of the stratigraphic unconformity at the top boundary of the 2nd sub-member of upper member of Kepingtage Formation