COMPREHENSIVE QUANTIFICATION OF DIAGENETIC ALTERATION, TESTING ROBUSTNESS POTENTIAL OF ROSICKYTE AS POTENTIAL MARS ANALOG AT THE MINERAL-MICROBIAL INTERFACE

Microbial mat samples from Bad Water, CA were tested in an extreme transient stress environment, due to high altitude exposure as part of a student balloon launch project. Previous investigation by other workers (Douglas and Yang, 2002) utilizing Mars analog evaporitic microbial mats from Bad Water, CA have suggested the presence of microbially moderated biosignatures, such as rosickyte, and are found in microstratigraphic layering of a coupled microbial mat corresponding to diverse minerology along an oxidative/reductive gradient. Our examination of the coupled microbial mat by XRD, RF, SEM and pH, confirms the presence of microstratigraphic minerological assemblages associated with distinct microbial communities; however, mineralogical results determined an absence of rosickyte and a different mineralogy from prior studies. Visible microscopy substantiates existence of both filamentous and cocci form cyanobacteria consistent with possible nitrogen fixers and desiccation resistant cryptoendolithic bacterium, tentatively identified as Mars relevant Chroococcidiopsis sp. (Cockrell et al., 2005). Hypersaline, evaporitic, microbial assemblages from Bad Water are extremely adaptive on both spatial and temporal scales and remain extant and viable throughout the sedimentary column, despite dramatic environmental variability, especially in conditions of UV attentuation (Seyferman et al., 2015). It should be noted that our sample recovered from this region experienced climatic reorganization since the original sample study in 2002 (California Drought Index %12; 2002 to California Drought Index %100; 2015). Studying the pH, δ¹⁵N as well as δ¹³C suggest N-fixation vertical partitioning consistent with G⁰ along an oxidative/reductive gradient where the microbial community diversity appears tightly spatially coupled to minerological composition. The sample could show a switch between an oxidative nitrogen fixing metabolism to a reductive dark metabolism thus incurring rapid diagenesis at the microbe-mineral interface. We therefore examine to what extent does dark metabolism diagenesis alter potential biosignatures such as rosickyte, which may not be stable over geological timescales, either on Earth or on Mars.