SEM-CL investigation of sedimentary organic matter samples

High-resolution scanning electron microscopy (SEM) visualization of sedimentary organic matter (SOM) is widely utilized in the geosciences for evaluation of microscale rock properties relevant to depositional environment, diagenesis, and the processes of fluid generation, transport, and storage. However, despite thousands of studies which have incorporated SEM approaches, the inability of SEM to differentiate SOM types has hampered the pace of scientific advancement. In this study, we show that SEM-cathodoluminescence (CL) properties can be used to identify and characterize SOM at low thermal maturity conditions. Eleven varied mudstone samples with a broad array of SOM types, ranging from the Paleoproterozoic to Eocene in age, were investigated. SOM fluorescence intensity and CL intensity showed an almost one-to-one correspondence, with certain exceptions in three samples potentially related to radiolytic alteration. Therefore, because CL emission can be used as a proxy for fluorescence emission from SOM, CL emission during SEM visualization can be used to differentiate fluorescent from non-fluorescent SOM. This result will allow CL to be used in SEM-based studies as a visual means to quickly differentiate SOM types without employing correlative optical microscopy and could be widely and rapidly adapted for SEM-based studies in the geosciences.