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- Title
Cathodoluminescence differentiates sedimentary organic matter types.
- Authors
Hackley, Paul C.; McAleer, Ryan J.; Jubb, Aaron M.; Valentine, Brett J.; Birdwell, Justin E.
- Abstract
High-resolution scanning electron microscopy (SEM) visualization of sedimentary organic matter (SOM) is a widely utilized petrographic approach for better understanding of fluid generation, transport, and storage processes in mudrock. However, despite thousands of studies incorporating SEM approaches, the inability of SEM to differentiate SOM types (e.g., primary versus secondary SOM), has hampered the pace of discovery and scientific advancement. In this study, we show that SEM-cathodoluminescence (CL, electron-induced photon emission) properties can be used to identify and characterize SOM types from immature to peak-oil window thermal conditions. Shale and mudrock samples (n=ll) representing a broad array of sedimentological character (clastic versus carbonate), depositional environment (lacustrine versus marine), geologic age (Paleoproterozoic to Eocene), kerogen type (Types I, II), and petrographic organic matter assemblage (vitrinite, inertinite, liptinite, and solid bitumen) were investigated. Fluorescence (photon-induced photon emission) intensity of SOM and CL intensity showed an almost one-to-one correspondence, with certain exceptions which are potentially related to radiolytic alteration. Fluorescence and CL intensity also displayed an inverse correlation against reflectance and Raman spectral properties, i.e., as fluorescence and CL intensity decreased, the reflectance and Raman carbon peaks of SOM types systematically increased in the same sample. 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 SOM (liptinite maceral group, some solid bitumen) from nonfluorescent SOM (vitrinite and inertinite maceral groups, high maturity solid bitumen). That is, CL emission can be used in SEM-based petrographic studies as a visual means to quickly differentiate SOM types without employing correlative optical microscopy. Use of SEM-CL represents a potential breakthrough improvement over prior schemes for SEM-based identification of SOM types using petrographic textures, and could be widely and rapidly adapted for SEM petrographers with access to a CL detector.
- Subjects
CATHODOLUMINESCENCE; SEDIMENTATION &; deposition; ORGANIC compounds; SCANNING electron microscopy; GEOLOGY
- Publication
Bulletin of the Geological Society of Greece, 2023, p21
- ISSN
0438-9557
- Publication type
Article