Multi-element Signatures of Precipitation and Diagenetic Processes in Sedimentary Carbonates Revealed by 30-µm-Scale Laser-Ablation Mapping

The bulk concentrations of major, minor, and trace elements within the primary and diagenetic phases of sedimentary carbonates have been frequently used to reconstruct the ambient chemistry, temperature, and primary productivity of past oceans. However, the geochemical signals in carbonate rocks reflect a complex mixture of primary precipitation processes that produce sedimentary grains, fluid-rock exchange that alters chemistry of existing carbonate phases (e.g., skeletal grains, micrite, peloids), and the precipitation of new phases below the sediment-water interface (i.e., pore filling cements) that introduce geochemically distinct components into the bulk rock. Because these phases are often mixed at scales of centimeters, millimeters, and even microns, bulk measurements can convolve primary seawater signals with later diagenetic contributions, adding challenge to interpretations of past ocean conditions. Here we present micron-scale (30-μm spot size) multi-elemental maps of multiple carbonate microfacies using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to investigate how mineralogical components and diagenetic processes partition trace metals within carbonate fabrics. Eight representative microfacies including skeletal grains, microbial fabrics, micrite, peloids, and pore-filling cements were mapped for U, Mo, Mn, Fe, Sr, Mg, Ce, and Ba concentrations. Elemental distributions show large within-microfacies variability and strong spatial clustering that corresponds to distinct primary components (skeletal grains, peloids, micrite) and diagenetic phases (early and late cements). Skeletal grains and cements preserve high-contrast geochemical gradients and multimodal distributions reflecting mineralogical partitioning and localized diagenetic alteration. In contrast, micrite matrix displays smaller spatial clusters and more homogeneous elemental distributions consistent with greater pore-fluid buffering and chemical homogenization. Multivariate and spatial statistical analyses further reveal coupled Fe–Mn (and locally Mo and Ba) enrichment domains consistent with suboxic to anoxic pore-water conditions, whereas Sr–Mg enrichments track mineralogical controls and recrystallization pathways. These results demonstrate that bulk carbonate geochemistry integrates multiple micron-scale signals produced by biomineralization, cementation, and diagenetic fluid interactions. Spatially resolved geochemical mapping can reveal previously unresolved diagenetic domains, diagnose diagenetic processes in conjunction with petrographic analysis, and improve the fidelity of deep-time carbonate geochemical reconstructions through identification of the best-preserved primary phases.