An integrated sedimentological, PXRD, and PXRF approach to resolve facies ambiguity in peritidal carbonates: a case study from the Upper Ordovician Saluda Formation

ABSTRACT The inherent subjectivity and limited reproducibility of facies descriptions are widely recognized. These challenges are exemplified in variably dolomitized, peritidal mixed carbonate–siliciclastic deposits where traditional sedimentological facies analyses rely heavily on qualitative observations to distinguish lithologic variability. This study introduces an integrative workflow in the Upper Ordovician (Katian) Saluda Formation that combines qualitative lithological descriptions and detailed petrographic observations with quantitative powder X-ray diffraction (PXRD) and portable X-ray fluorescence (PXRF) data to provide a more objective and robust basis for facies characterization. Six distinct lithofacies were identified in the Saluda Formation. Based on their elemental composition, these can be subdivided into two broad compositional groups: carbonate-dominated lithofacies (Facies 2, 5, and 6) characterized by elevated Ca and Sr, and siliciclastic-influenced lithofacies (Facies 1, 3, and 4) characterized by higher concentrations of terrigenous proxies (Al, K, Ti, Zr, and Rb), reflecting a mixed carbonate–siliciclastic mineralogy. Principal component analysis (PCA) of the PXRF dataset shows that samples from the same lithofacies generally cluster together in PCA space, supporting a relationship between quantitatively derived geochemical variability and qualitatively derived sedimentological attributes. Collectively, these data provide new insights into the processes controlling deposition of the Saluda Formation as an accommodation-limited, shallow-marine, peritidal mixed carbonate–siliciclastic system with significant spatial and temporal variability, which was likely influenced by Late Ordovician tectonic and climatic conditions near the Cincinnati Arch. More importantly, this study demonstrates the value of integrating qualitative sedimentological and petrographic observations with quantitative geochemical and mineralogical data to refine facies delineation, increase facies reproducibility, and improve recognition of compositional variability in mixed depositional systems, particularly in fine-grained peritidal facies.