A common tool in provenance studies of clastic sedimentary rocks is the geochemical composition for identification and differentiation of potential catchment areas. However, not only source rock lithologies but also for instance sorting, alteration, leaching or new mineral formation influenced by the climate during erosion, transport and deposition or by diagenesis during burial influence the geochemical provenance signal (Augustsson et al., 2023). Therefore, the consideration of the genetic and diagenetic changes of the deposits, i.e. their development over time, plays an important role for a meaningful interpretation of geochemical data for provenance studies.
To test this, we investigate Permo-Carboniferous terrestrial sandstone and conglomerate. The units represent changing palaeogeographic and climatic conditions. In addition, the deposits underwent diagenetic changes during deep burial and partial uplift to present-day borehole depths of 1500-2500 m. We use polarization, cathodoluminescence, and scanning electron microscopy, microprobe analyses, XRD, XRF, and ICP analyzes. Initial results indicate correlations of the Chemical Index of Alteration and K2O/Na2O with the preservation state of detrital feldspar and the diagenetic clay minerals kaolinite and illite. Th/Sc and Y/Zr correlate with lithoclast composition (felsic versus mafic igneous and metamorphic) and the intergranular components (matrix versus cement). This allows the separation of Carboniferous and Permian samples. It is a result of changing climatic and diagenetic conditions.
Reference: Augustsson, C., Aehnelt, M., Olivarius, M., Voigt, T., Gaupp, R., & Hilse, U. (2023). Provenance from the geochemical composition of terrestrial clastic deposits-a review with case study from the intracontinental Permo-Triassic of European Pangea. Sedimentary Geology, 106496.