AN UNUSUAL CLAY-RICH KARST FILL IN THE SOUTHEASTERN YUCATAN REVEALS UNRECOGNIZED GEOLOGIC COMPLEXITIES AND POTENTIAL RESOURCES IN THE REGION

Clay mineral deposits can be important economic resources and provide important geologic records for understanding the environment. Although sedimentary palygorskite and palygorskite-montmorillonite deposits are known in the central Yucatan and more rarely from the southeastern Yucatan (Krekeler and Kearns, 2009), sedimentary deposits of discrete smectite minerals are comparatively rare in the geologic record. Previous work in the Reforma region has identified only one small sedimentary deposit of montmorillonite (Krekeler et al., 2007), however potential exists for other similar sedimentary deposits to exist. The present investigation is the first evaluation of the mineralogy of an unusual paleokarst fill of mixed magenta and white clay in the Reforma region, a type of deposit previously unobserved in the Yucatan. Preliminary X-ray diffraction data confirm smectite as the dominant phase with trace amounts of kaolinite. The magenta color of the clay was originally thought to be from cobalt solid solution based on limited SEM data; however, recent TEM data indicate the presence of iron oxide nanoparticles which may be the primary cause of color and reflective spectra broadly support this interpretation. The deposit is interpreted to be a gravity fill of a small cave where an overlying montmorillonite bed mechanically failed into the underlying cavity; subsequently, an Fe-oxide-rich material interacted with the clays, yielding the magenta color. The occurrence of another montmorillonite-rich deposit in the Reforma region potentially indicates a regional trend of increasing smectite content in sedimentary rocks from the central Yucatan towards the southeastern Yucatan and may indicate smectite beds are more extensive in the region than previously understood. Smectite clays are an ideal liner to prevent contamination of groundwater from wastewater reservoirs. The Yucatan has prevalent karst features and is highly susceptible to groundwater pollution and would benefit from larger resources of this clay. Additionally, the deposit may be of geoarcheological significance - further investigation of this deposit may help to source clays used for pigments and pottery in Mayan artifacts.