HYPOGENE SPELEOGENESIS IN THE GRAND CANYON; MINERALOGICAL, STRUCTURAL, AND GEOSPATIAL INVESTIGATIONS FROM THE BOPPER CAVE SYSTEM

New insights into the development of the Bopper Cave System (BCS) at Grand Canyon National Park suggest that the BCS is a hypogene cave system and a relict feature of the ancient Redwall (R) aquifer. Formed in the Mississippian Redwall Limestone, the BCS is greater than 64 km and contains countless rare and colorful unidentified formations The spatial patterns of these cave passages, geomorphological features, faults, and speleothems suggest the BCS formed from deeply seeded fluids rising along basement faults intersecting the ancient R aquifer. X-ray diffraction results of 24 secondary mineral samples show the presence of clays, silica, iron and manganese oxides and hydroxides, variations of sulfates, and possible organic compounds. The mineralogy of these speleothems in the BCS reflects fluctuations in the geochemistry of the paleo-aquifer. The presence of clay and silica bearing corrosion residue powder suggest a strongly corrosive environment with sulfuric acid corrosion of bedrock. Accumulations of low-density colorful secondary mineral formations are enriched in iron and manganese oxides and hydroxides. Simple dissolution of carbonate bedrock leaves trace amounts of Fe and Mn residues, whereas the deposits in the BCS are highly enriched, suggesting a hypogenic origin. The large quantities and spatial distribution of sulfate minerals, including numerous gypsum formations and Na-, Fe-, Zn-, and Mg-sulfates, are indicative of a highly sulfidic groundwater system. These minerals were deposited in an evaporative environment after a lowering of the paleo-water table. Organic compounds including carbon chains and nitrogen compounds are also identified and may suggest microbial activity and biotic precipitation of speleothems. The mineralogies found in the BCS are atypical of epigenic cave development and more closely reflect sulfuric acid speleogenesis. The presence of hypogene speleogenesis in the Grand Canyon suggests that past speleogenetic processes, which enlarged the porosity and permeability of the system, increased the capacity for storage and rapid hydrologic response. These characteristics define the behavior of the modern groundwater system. Hypogene speleogenesis also holds implications for identifying regional neotectonic-speleogenetic processes on the Colorado Plateau.