Decarbonation generates considerable CO2 in sedimentary basin environments: Implications for the formation of secondary pores

Carbon dioxide (CO 2 ) is a crucial acidic component in sedimentary basins , significantly influencing the formation and evolution of dissolution-type reservoirs. While carbonate decarbonation is a primary source of CO 2 , its occurrence under basin conditions remains debated. To address this, we conducted high-temperature, high-pressure in situ and ex situ experiments on the CaCO 3 -SiO 2 -H 2 O, CaMg(CO 3 ) 2 -SiO 2 -H 2 O, and CaCO 3 -SiO 2 -H 2 O-MgCl 2 systems to investigate decarbonation conditions and mechanisms. The results indicate that temperature is the dominant controlling factor: calcite decarbonation occurs above 275 °C, while magnesium-rich diagenetic systems react at temperatures as low as 100 °C. Pressure inhibits decarbonation, and system openness determines the solid-phases products. In nearly closed systems, kerolite forms and dehydrates into talc, while calcite undergoes dolomitization in the presence of Mg-rich fluids. In open systems, talc dominates, with less dolomitization, and the release of CO 2 promotes decarbonation. Based on these results and previous case studies of silica- and magnesium-rich hydrothermal fluids interacting with carbonate strata, we propose that carbonate decarbonation is a significant source of CO 2 in sedimentary basins, contributing to the development of dissolution-type reservoirs. Further research should explore the implications of these mechanisms for hydrocarbon reservoir formation. • Decarbonation in sedimentary basins produces significant CO 2 . • High temperatures (>100 °C) and Mg-rich environments enhance decarbonation. • Open systems favor silicate formation, while closed systems promote dolomitization. • Decarbonation-derived CO 2 enables secondary pore formation and preservation in deep reservoirs.