MINERALOGICAL AND GEOCHEMICAL TRENDS IN MINI-CORES FROM CARBONATE SEEP DEPOSITS IN A MARS ANALOG SERPENTINIZING SYSTEM

Serpentinization-driven subsurface habitats, such as those found within the mafic-ultramafic Coast Range Ophiolite, experience through-going Ca²⁺ - OH^- type waters (Barnes et al., 1967, 1972) of extremely high pH (up to 12); excess Ca²⁺ in these fluids react with Earth’s CO₂-rich atmosphere in soils and at springs to produce travertines. This unique suite of precipitated and subsequently weathered materials includes carbonate cements (travertines) of varying chemistry deposited by seeping alkaline (current surface pH ~8) fluids. Ongoing studies suggest that alkaline springs and their associated minerals are surface expressions of presently occurring serpentinization reactions in the subsurface. As such, the springs can potentially shed light on the microbial diversity in the subsurface biosphere as well (Brazelton et al., 2011). This report includes a compilation of mineralogical and geochemical analyses of miniature rock cores (1” x 10”), taken within such seeps, with inferences into the nature of the depositional environment and subsurface conditions. The site locality is the UC Davis McLaughlin Natural Reserve, Lower Lake, CA, and surrounding areas within the Coast Range Ophiolite. X-ray diffraction, scanning electron microscopy, and petrographic evaluations were effective analyses of the cores. The travertine had undergone meteoric diagenesis due to heterogenous mixings of alkaline seep fluids and percolating waters at or near the surface. These alkaline springs and their carbonate deposits are an important analog for potentially biologic systems, and we speculate that the carbonates in particular may preserve mineral-sealed biosignatures that may prove useful in searching for evidence for early life and life on Mars.