黄骅坳陷千米桥地区奥陶系碳酸盐胶结物的形成序次

PRECIPITATION SEQUENCE OF CARBONATE CEMENT OF THE ORDOVICIAN IN QIANMIQIAO AREA,HUANGHUA DEPRESSION

在不同时期,由于埋藏深度不同,成岩环境的氧化还原性不同,形成的胶结物的特征也就不同。有些情况下,胶结物期次之间是连续的,即呈“整合接触”。而有些情况下,两个期次之间是不连续的,曾发生过溶蚀,形成“不整合接触”。有些孔隙和裂缝形成早,其内胶结物的期次齐全,而有些孔隙和裂缝形成晚,就会缺失一些期次。因此,胶结物可以像地层一样进行划分和对比。据此可以分析成岩环境的变化,判断孔隙和裂缝形成的时期等。由于成岩环境的变化常与构造运动有关,因此胶结物地层学的研究可以间接地分析构造运动发生的时期。黄骅坳陷千米桥地区奥陶系碳酸盐岩的裂缝和孔隙中,充填了5期胶结物,每期胶结物阴极发光的特征不同,其中第二期与第三期胶结物之间存在溶蚀不整合。根据胶结物的特征,可划分出5期裂缝,形成于三叠纪、中-晚白垩世、古近纪末、新近纪末等。

In different ages, owing to differences in burial depth and in oxidation-reduction conditions of diagenetic environments, the cements precipitated are different in character. In some cases, the precipitation of cements of different generations is continuous, and the contact between two generations of cements is conformable. But in other cases, the precipitation process is once interrupted by dissolution, and the contact between two generations of cements is unconformable. Some pores and fissures form early, and generations of cements in them are complete. But some pores and fissures form late, and some generations of cements are missing. Thus, cements can also be divided and correlated like strata. Thereby, the change of diagenetic environments can be analyzed, and the time of pore and fissure formation can be inferred. As change of diagenetic environments is commonly related with structural movements, time of structural movement can also be inferred through the study of cement stratigraphy. In Ordovician carbonate rocks of the Qianmiqiao area of the Huanghua Depression,pores and fissures are filled with 5 generations of cements. Each generation shows different colors of cathodoluminescence. Between the second and third generations of cements there exists a dissolution unconformity. Based on characteristics of cements,5 times of fracturing can be recognized,which occurred in the Triassic, the Middle-Late Cretaceous, the end of Paleogene and end of Neogene.