摘要
Compaction and silicon cementation are the dominant processes reducing porosity and permeability in quartzose sandstones during diagenesis. Despite the wealth of information about quartz cementation, there are still unanswered questions related to mechanisms of growth of quartz cement and the diagenesis processes. In this study we present an electron backscatter diffraction （EBSD） analysis, combined with optics and cathodoluminescence （CL） information, for the quartz sandstones from the Upper Triassic Xujiahe Formation of Sichuan Basin, in order to reveal the microstructural and crystallographic features of the silica cementation and detrital grain during the compaction. The EBSD is a crucial technique to provide essential crystallographic data on the quartz grain and its cement. Quartz cement is shown to be syntaxial to its host quartz grain. EBSD data-based orientation maps show dauphin6 twinning and low angle boundary to be common in the host grains and quartz cement of the samples. The dauphin6 twins occurred in grain-grain contacts and in cement-crystal boundaries, and commonly crossed grain cement boundaries. These features indicate that there may be two types of dauphin6 twins, one inherited twins from the source area and the other developed by compaction-induced grain boundary deformation. These investigations suggest that strong mechanical compaction may occur after and/or during quartz cement growth in the later diagenesis of the Xujiahe sandstones. EBSD has a capability of revealing microstructural information and regarding mechanisms of diagenesis crystal growth in quartzose sandstones.
Compaction and silicon cementation are the dominant processes reducing porosity and permeability in quartzose sandstones during diagenesis.Despite the wealth of information about quartz cementation,there are still unanswered questions related to mechanisms of growth of quartz cement and the diagenesis processes.In this study we present an electron backscatter diffraction(EBSD)analysis,combined with optics and cathodoluminescence(CL)information,for the quartz sandstones from the Upper Triassic Xujiahe Formation of Sichuan Basin,in order to reveal the microstructural and crystallographic features of the silica cementation and detrital grain during the compaction.The EBSD is a crucial technique to provide essential crystallographic data on the quartz grain and its cement.Quartz cement is shown to be syntaxial to its host quartz grain.EBSD data-based orientation maps show dauphiné twinning and low angle boundary to be common in the host grains and quartz cement of the samples.The dauphiné twins occurred in grain-grain contacts and in cement-crystal boundaries,and commonly crossed grain cement boundaries.These features indicate that there may be two types of dauphiné twins,one inherited twins from the source area and the other developed by compaction-induced grain boundary deformation.These investigations suggest that strong mechanical compaction may occur after and/or during quartz cement growth in the later diagenesis of the Xujiahe sandstones.EBSD has a capability of revealing microstructural information and regarding mechanisms of diagenesis crystal growth in quartzose sandstones.
基金
supported by National Natural Science Foundation of China(Grant Nos. 40802050,40872149)
China Postdoctoral Science Foundation (Grant No. 20070420065)
