DISSOLUTIONAL MICRO-TEXTURES ON CARBONATE ROCKS IN A LABORATORY SETTING

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 not been fully investigated. In a controlled laboratory setting, six carbonate rocks were dissolved: dolostone (gray and pentamerous), limestone (gray and oolitic), and marble (coarse and fine). 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 in conductivity over the experiment length. These issues appear to have been remedied by adding a temperature probe to the experimental setup to hold temperature constant; changes in HVAC controls resulted in a loss of steady climate control in the lab. In all rock types it appeared that the allochems dissolved preferential to the cements under SEM. 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, XRD analysis, additional petrographic analysis, and additional rock types will be investigated, especially those with a wider variety of allochems to more fully determine and investigate dissolutional micro-textures. As increased atmospheric CO₂ continues to modify the climate, so to will it impact karst processes. Understanding what dissolves from carbonate rocks will improve our understanding of landscapes and carbon sequestration.