RECONNAISSANCE GEOMICROBIOLOGY SURVEY OF LEHMAN CAVE, GREAT BASIN NATIONAL PARK

Some of the world’s largest and most spectacular limestone caves, including Carlsbad Cavern and Lechuguilla Cave, formed by sulfuric acid speleogenesis. These caves form where hydrogen sulfide (H₂S)-rich ground waters interact with oxygen in recent surface recharge or cave air. Although “active” sulfidic caves are rare and are limited to a handful of sites worldwide, “fossil” sulfidic caves that contain morphological and mineralogical evidence for past sulfidic acid speleogenesis are more common. Lehman Cave in Great Basin National Park, NV, is a fossil sulfidic cave that has some passages that preserve features of its sulfidic past (Hose, 2018). Until recently, however, little was known about the geological history and evolution of the cave system, and the geomicrobiological processes that affect the modern cave have not yet been explored. We used microbiological and geochemical analyses to characterize multiple floor and wall deposits in the cave, including clastic sediments, ferromanganeses wall crusts, and white floor and wall deposits from the Gypsum Annex region. Mineralogical characterization of the white deposits using X-ray diffraction and electron microscopy shows they are composed of microcrystalline calcite, dolomite, quartz, and gypsum. Microbial biomass in most of these and other cave sediments is very low, but enrichment cultures indicate that organoheterotrophic populations are present, including members of the Actinobacteria and Alphaproteobacteria. We will present results from ongoing work using rRNA methods and additional geochemical characterization to compare how the microbiology and mineralogy of these deposits compare to similar deposits from well-studied ancient sulfidic caves like Lechuguilla and Spider Caves.

Hose, L.D., 2018, Hypogenic Karst in the Snake Range, Eastern Nevada. Geological Society of America Abstracts with Programs. Vol. 50, No. 5 doi: 10.1130/abs/2018RM-313838