Principal component analysis reveals the relationship between carbonate facies, geochemical properties, and diagenetic overprint

Marine carbonate archives in transitional coastal-to-basin settings are susceptible to syn- and post-depositional alteration, a feature that complicates the interpretation of primary environmental signals encoded in the sedimentary archive at the time of deposition. This study utilises Principal Component Analysis (PCA) to elucidate the intricate relationships between facies types, environmental controls, and the sediments' respective diagenetic susceptibilities to geochemical resetting within lower Aptian carbonates of the Kazhdumi Intrashelf Basin (Zagros Basin, Iran). The focus is on proximal mid-ramp to intrashelf-basin carbonates. Integrating facies analysis, petrography, geochemistry, and PCA, the following outcomes result: (i) Proximal facies exhibit higher Mn/Ca and lower Sr/Ca ratios linked to enhanced fluid-rock interactions and terrigenous input. Marine δ¹³C values and elevated Sr/Ca ratios are more pronounced in distal facies. (ii) Bulk isotope values from distal carbonates are characterised by enriched δ¹³C and depleted δ¹⁸O values. This suggests increased marine productivity in cooler waters and intermittently anoxic-suboxic conditions. (iii) In shallower, warmer, and well‑oxygenated proximal mid-ramp waters, reduced organic carbon burial, isotopically light carbon from terrestrial sources and the oxidation of organic matter result in lowered δ¹³C and higher δ¹⁸O values. The study demonstrates that despite complex diagenetic overprint, marine proxy signals remain discernible. Supported by microfacies data, PCA reveals a multi-faceted system that drives geochemical variability within a facies/bathymetric context. This outcome emphasises the critical importance of detailed facies analysis and geochemical profiling in reconstructing palaeoenvironmental conditions.