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Caves deliver freshwater from coastal carbonate landscapes to estuaries but how these caves form and grow remains poorly understood. Models suggest fresh and salt water mixing drives dissolution in eogenetic limestone, but have rarely been validated through sampling of mixing waters. Here we assess controls on carbonate mineral saturation states using new and legacy geochemical data that were collected in vertical profiles through three cenotes and one borehole in the Yucatan Peninsula. Results suggest saturation states are primarily controlled by carbon fluxes rather than mixing. Undersaturation predicted by mixing models that rely on idealized end members is diminished or eliminated when end members are collected from above and below actual mixing zones. Undersaturation due to mixing is limited by CO2 degassing from fresh water in karst windows, which results in calcite supersaturation. With respect to saline groundwater, controls on capacity for mixing dissolution were more varied. Oxidation of organic carbon increased pCO2 of saline groundwater in caves (pCO2 = 10-2.06 to 10-0.96 atm) relative to matrix porosity (10-2.39 atm) and local seawater (10-3.12 atm). The impact of increased pCO2 on saturation state, however, depended on the geochemical composition of the saline water and the magnitude of organic carbon oxidation. Carbonate undersaturation due to mixing was limited where gypsum dissolution (Cenote Angelita) or sulfate reduction (Cenote Calica) increased concentrations of common ions (Ca2+ or HCO3−, respectively). Maximum undersaturation was found to occur in mixtures including saline water that had ion concentrations and ratios similar to seawater, but with moderately elevated pCO2 (Cenote Eden). Undersaturation, however, was dominated by the initial undersaturation of the saline end member, mixing was irrelevant. Our results add to a growing body of literature that suggests oxidation of organic carbon, and not mixing dissolution, is the dominant control on cave formation and enlargement in coastal eogenetic karst aquifers. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

• Dissolution mechanisms for multi-genesis of paleokarst have been clarified. • The formation mechanism of karst collapse columns (KCCs) has been revealed. • Three main factors controlling paleokarst and KCCs have been illustrated. • The evolution model of paleokarst and KCCs have been established. • Spatial distribution of paleokarst and KCCs has been predicted. Karst water in the Middle Cambrian-Lower Ordovician carbonates is the ecological resources and domestic water in the Huainan coalfield (Anhui Province, China), but it also directly threatens the safe production of coal mines due to the development of paleokarst and karst collapse columns (KCCs). Most of the Middle Cambrian-Lower Ordovician carbonates in Northern China experienced multistage tectonic movements and were affected by multi-type corrosive fluids, but very few studies focused on the effect of multistage fluid-rock reaction on the formation of paleokarst and KCCs. To investigate the formation mechanisms and characteristics of paleokarst and KCCs, this study integrated petrographic studies, isotope geochemistry (C and O) and minor elements (Ba, Mn, and Sr), and clarified the sources and types of corrosive fluids. Through this study, meteoric water, formation water, hydrothermal fluids, and mixing fluids were determined as the four main types of corrosive fluids that formed pores, vugs, fractures, caves, and KCCs in the Middle Cambrian-Lower Ordovician carbonates. The meteoric dissolution is controlled by carbonic acid solution recharge conditions which affect the karst development in the Cambrian and Ordovician paleoweathering crusts and local carbonate outcrops. Hydrothermal fluids with high-temperature, high-pressure and high-corrosivity can develop a strong hydrothermal pore-fracture system in the Cambrian carbonate, which is the reason that KCCs can develop in the Cambrian strata in the Huainan coalfield. The mixing dissolution is controlled by sulfuric acid dissolution and usually occurs in the water tables and the fault and fracture zones, which are conducive to the development of caves and KCCs. In addition to the above four corrosive fluids, the development of paleokarst and KCCs in the Huainan area is also controlled by stratigraphic lithology and geological structures, especially for faults and fractures, which are the main migration channels of corrosive fluids. An evolution model of paleokarst and KCCs was established, providing a plausible interpretation for better understanding of the spatial distribution of paleokarst and KCCs. In practice, this study provides critical references for predicting the spatial distribution of paleokarst and KCCs in Northern China coalfields, as well as the exploration and development of karst water around the world. [ABSTRACT FROM AUTHOR]