NanoSIMS analysis of organic carbon from the Tissint Martian meteorite: Evidence for the past existence of subsurface organic-bearing fluids on Mars

Two petrographic settings of carbonaceous components, mainly filling open fractures and occasionally enclosed in shock-melt veins, were found in the recently fallen Tissint Martian meteorite. The presence in shock-melt veins and the deuterium enrichments (delta D up to +1183 parts per thousand) of these components clearly indicate a pristine Martian origin. The carbonaceous components are kerogen-like, based on micro-Raman spectra and multielemental ratios, and were probably deposited from fluids in shock-induced fractures in the parent rock of Tissint. After precipitation of the organic matter, the rock experienced another severe shock event, producing the melt veins that encapsulated a part of the organic matter. The C isotopic compositions of the organic matter (delta C-13 = -12.8 to -33.1 parts per thousand) are significantly lighter than Martian atmospheric CO2 and carbonate, providing a tantalizing hint for a possible biotic process. Alternatively, the organic matter could be derived from carbonaceous chondrites, as insoluble organic matter from the latter has similar chemical and isotopic compositions. The presence of organic-rich fluids that infiltrated rocks near the surface of Mars has significant implications for the study of Martian paleoenvironment and perhaps to search for possible ancient biological activities on Mars.