APPLICATION OF THE SCANNING ELECTRON MICROSCOPE (SEM) IN CLASTIC DIAGENESIS

The development of the Scanning Electron Microscope (SEM) has been a tremendous technological advancement in the study of clastic diagenesis. With possible magnifications in the thousands, the SEM has allowed petrographers the opportunity to explore the internal depths of clastic sedimentary rocks. This exploration has led to a better understanding of cement and pore distribution and morphology, their interrelationships, their timing of formation, and dissolution and compaction processes. The addition of an energy dispersive spectrometer and cathodoluminescence imaging system further advances the capabilities of the SEM in the study of clastic sedimentary rocks.

The SEM has been essential for this researchers past studies in sandstones of the Frio Formation (diagenesis in volcanic glass-rich intervals), the Vicksburg Formation (chlorite formation and distribution), and Wilcox Group (illite morphology and distribution). Recently, research on the petrology and geochemistry of the Oligocene-Early Miocene Panjgur Formation and Paleocene Ispikan Formation and Wakai mélange in the Makran accretionary belt of southwest Pakistan, has led to the recognition of a very interesting chlorite morphology and associated carbonate dissolution event. The chlorite appears to have undergone a period of dissolution followed by recrystallization into a form not common for sedimentary chlorite. At the same time the carbonate has undergone dissolution and replacement by the newly crystallized chlorite. Initial reaction is that this event is recording the transition to low-grade metamorphism, as would be expected in this tectonically active region. Further research is needed, but the SEM will play a significant role in understanding the mystery held within these rocks.