Clay-driven dolomitization at moderate to high temperatures: Evidence from hydrothermal experiments

Dolomite formation remains a debated topic in sedimentary geology, particularly concerning the mechanisms driving its precipitation under natural conditions. While microbial processes have been well studied, the influence of abiotic factors, such as clay minerals, is less understood. This study uses hydrothermal reactor experiments at 80–250 °C to examine the role of clay minerals in post-compactional dolomitization. Results show that smectite and illite effectively promote dolomitization by providing nucleation sites and aiding Mg²⁺ dehydration through their highly negative surface charges. In contrast, kaolinite and dickite were less effective due to their charge neutrality. In calcite-kaolinite mixtures, dolomite formed at 200 °C when kaolinite partially converted to smectite but was inhibited at 250 °C due to dickite formation. Samples containing only calcite showed little to no dolomite formation, highlighting the role of reactive clays. Dolomitization occurred through two mechanisms: (1) complete calcite dissolution followed by dolomite nucleation, and (2) recrystallization with progressive Mg incorporation. These findings support clay-catalyzed dolomitization as a significant abiotic pathway in ancient muddy carbonates and mixed clastic-carbonate systems.