EVALUATING CARBONATE DISSOLUTION AND PRECIPITATION IN A SHORT TIME-FRAME USING SEM: TECHNIQUES AND PRELIMINARY RESULTS FROM POSTOJNA CAVE, SLOVENIA

Abstract

Carbonate dissolution and precipitation are important geologi-cal processes whose rates often require quantification. In natu-ral settings, these processes may be taking place at a slow rate, and thus, it may not be easily visible which of these processes is occurring. Alternatively, if the effects of precipitation/dissolu-tion are visible, it may not be clear if they are still underway or an artefact of past conditions. Moreover, these two oppos-ing processes may flip states depending on the environmental conditions, such as, on a seasonal basis. Here, we present the technical details and preliminary results of a method using carbonate tablets and Scanning Electron Microscopy (SEM) to evaluate which process (carbonate dissolution or precipitation) is occurring, using as an example, a cave environment. Our method involves making tablets by encasing blocks of carbonate rock into resin and polishing these to form a completely flat and smooth “zero surface”. These tablets are observed under SEM in exactly the same points both before and after exposure to the field environment, using a system of marking lines at spe-cific locations on the resin. Our results show significant differ-ences in the before and after images of the tablet surface after just six weeks in the cave. Furthermore, the use of the insoluble resin zero surface permits a comparison of the starting height with the new dissolved/precipitated surface that can be used to quantitatively estimate the rate of dissolution/precipitation happening at a field location in a relatively short time-frame (weeks/months). This method could be used in numerous nat-ural and industrial settings to identify these processes that can be caused purely geochemically, but also through microbial-mediation and physical weathering.