泥岩成岩矿物演化特征与成岩体系划分:以东营凹陷古近系为例

成岩过程中泥岩的成岩矿物会随成岩体系的改变而发生变化，因此有效地识别成岩矿物组合与划分成岩体系，对深刻 理解有机质生烃的差异性具有重要的意义。文章选取东营凹陷古近系不同层段埋深在1200~4500 m的泥岩，通过岩石薄片、 扫描电镜和X射线衍射等检测，有效地区分了外源输入的矿物（如石英）与成岩矿物（亮晶方解石和白云石）等显微特征的差 异，据此建立了定量估算泥岩中成岩转化的黏土矿物含量的方法：C陆源=（C/Q）沙一×Q样品和C成岩=CXRD-C陆源，其中C为黏土矿物含 量，Q为石英含量，更好地反映了泥岩成岩过程中黏土矿物的演化特征。在埋藏演化过程中泥岩中的成岩矿物和组合呈现出 两段性，3000 m以上黏土矿物和白云石的成岩转化较慢，形成了以伊蒙间层+高岭石的成岩矿物组合，推断其经历了酸性成岩 环境和开放成岩体系；3000 m以下黏土矿物和白云石的成岩转化过程加快，形成了以伊利石+绿泥石+白云石的成岩矿物组 合，推断其经历了碱性成岩环境和封闭成岩体系，充分展现了泥岩在深浅层成岩环境和体系的差异性。与前人研究东营凹陷 泥岩中由有机质生烃产生异常压力造成的开放/封闭体系界限基本吻合，表明泥岩中矿物埋藏演化经历的成岩体系与有机质 生烃形成的压力体系具有较好的响应关系，这对认识不同成岩体系下有机质的生烃过程和生烃机理的差异性具有重要的 意义。

Evolution of Diagenetic Minerals and Classification of Diagenetic Systems in Mudstones: A Case in the Paleogene of the Dongying Sag

The diagenetic minerals in mudstones generally change with diagenetic systems during diagenesis. Therefore, in order to deeply understand the difference of hydrocarbon generation in mudstones, effectively identifying the diagenetic mineral associations and dividing diagenetic systems are essential. The Paleogene mudstone samples from the Dongying Sag, China, buried at a depth of 1200-4500 m were selected and evaluated by rock thin section, scanning electron microscopy and X-ray diffraction, to distinguish the differences in microscopic features between exogenously input minerals (e.g., quartz) and diagenetic minerals (e.g., sparry calcite and dolomite). Based on the results, a method on quantitatively estimating the diagenetic transformation content of clay minerals is established: (CTerrestrial=(C/Q)Es1 ×Qsample and Cdiagenetic=CXRD-CTerrestrial (C: clay mineral content, Q: quartz content)). This method can better reflect the diagenetic evolution of clay minerals. During the burial process, the diagenetic minerals and associations in mudstones display a two-stage feature. Above 3000 m, the diagenetic transformation of clay minerals and dolomite is slow, forming a smectite+ kaolinite association, which is inferred to have experienced an acidic diagenetic environment and open diagenetic system. The diagenetic transformation is accelerated below 3000 m, forming an illite+chlorite+dolomite association, which is inferred to have experienced an alkaline diagenetic environment and closed diagenetic system. This fully demonstrates the differences between deep and shallow diagenetic environments and systems. This understanding is consistent with the previous results that the boundary of open and closed systems is caused by the abnormal pressure which is generated by hydrocarbon generation in the mudstones. This implies that the diagenetic systems revealed by diagenetic minerals have a good response to the pressure system generated by hydrocarbon generation. Thus, dividing diagenetic systems is significant for understanding the heterogeneities in hydrocarbon generation processes and mechanisms under different diagenetic systems.