DISSOLUTIONAL MICRO-TEXTURES ON CARBONATES: CURRENT WORK AND FUTURE OPPORTUNITIES

Large scale karst features are readily observable; however, the micro-textures that develop on these rocks and the preferential dissolution of their constituent allochems has only started to be fully explored. In a controlled laboratory setting, so far six carbonate rocks have been dissolved: dolostone (two), limestone (two), and marble (two). Polished samples were placed in a beaker of deionized water on a stir plate and had CO₂ continuously injected over several days. The conductivity of the water was monitored and acted as a proxy for the dissolution rate. Discrete samples were collected from the beaker for [Ca²⁺] analysis via atomic emission spectroscopy allowing dissolution rates to be calculated. Each rock type, both pre- and post- dissolution were analyzed under a SEM to investigate the textures that were developed by dissolution; all samples were sonicated in ethanol for cleaning and held in a desiccation chamber prior to analysis. Early processed samples were run without a coating and analyzed under a low energy electron beam, later samples were coated in Au-Pd and analyzed under a higher energy electron beam.

Only some of the rock types had their dissolution rates calculated; the oolitic limestone dissolved at a rate of 1,579 cm yr^-1 and the pentamerous limestone at 799 cm yr^-1. Other rock types were not analyzed due to observed inconsistencies over the experiment length due to HVAC issues, which appears to have been addressed now. In all rock types under SEM it appeared that the allochems dissolved preferential to the cements. In rocks with no discernible allochems (i.e. marble and mud) dissolution appeared to occur along cleavage planes or evenly across the samples’ surface.

In the future additional petrographic analysis, XRD analysis, and additional carbonate rock types will be investigated, especially those with a wider variety of allochems and mineralogy’s to determine and investigate dissolutional micro-textures more fully. Evaporite rocks may also be considered in the future. As increased atmospheric CO₂ continues to modify the climate, so too will it impact karst processes. Understanding what dissolves from carbonate rocks will improve our understanding of karst and carbon sequestration.