LAVA TUBE SPELEOTHEMS AS PUTATIVE ANALOG EXTRATERRESTRIAL BIOMARKER TARGETS

Our NASA PSTAR project, BRAILLE (Biologic and Resource Analog Investigations in Low Light Environments), includes a study of basaltic lava tubes as analogs for cave environments on Mars and other planetary bodies. To date, we have sampled in 9 caves (Valentine, Hopkins-Chocolate, Golden Dome, L300, L460, V460 and 3 others) in Lava Beds National Monument (N. CA, USA): 3 with significant public visitation and 6 with limited access.

One of BRAILLE’s goals is to characterize biologically mediated secondary mineral structures (speleothems) on the basis of mineralogical, hydrogeochemical, and microbiological analyses. Here we report on the first two of these parameters. The caves are biologically active, with conspicuous microbial films and coatings and ubiquitous secondary mineral structures ranging in stature from mm to several cm. Speleothems exhibit structural diversity including marked cryptocrystalline features such as thin encrustations, coralloidal growths and overhangs, gours, altered basalt polyps, and hollow “soda straws”. X-ray diffraction and fluorescence analyses revealed mineralogic compositions dominated by plagioclase feldspars (andesine, albite), pyroxene (augite, enstatite) and olivine (forsterite), while hematite, magnetite, Ca-Be phosphates, periclase, Fe-oxides and hydrates were also common. Silica was prevalent throughout the caves, in crystalline (quartz) and cryptocrystalline (opal) forms. In a few encrustation samples, cryptocrystalline silica co-occurred with calcite. Deriving from either in situ mineral dissolution or surface water infiltration, dissolved constituents of floor puddle and ceiling drip water were characterized for major cations (Si²⁺ > Na⁺, > Ca²⁺ > Mg²⁺ > K⁺) and anions (NO₃^- > Cl^-, > SO₄^2- > PO₄^3-). Both dissolved organic carbon (DOC) and nitrogen (as NO₃^-) were high, at 6–32 mg/L and 6–7 mg/L, respectively. Such levels of DOC and TN may indicate active biogeochemical processes with all available essential light elements such as COHSPN. Our investigations provide ground truth data for BRAILLE analog robotic science and mapping mission activities at Lava Beds and may offer valuable constraints for future planetary mission instrumentation development and science return.