Identification and analysis of carbon-bearing phases in the Martian meteorite Nakhla

Indigenous reduced carbon has been observed in the Martian meteorite Nakhla. For the first time we have analyzed the in situ carbon by a suite of micro-analytical techniques in order to identify and characterize the reduced carbonaceous matter. Optical analysis of the Nakhla petrographic thin-section revealed the existence of a dark brown/red vein-filling material appearing as a series of bifurcating intrusions into a fine (<300 nm width) crack / fissure system within an olivine/augite groundmass. Micro-analytical analyses utilizing Focus Ion Beam (FIB) extraction techniques, FESEM/EDX, STEM/EDX, NanoSIMS Ion Microprobe, Laser Raman Spectroscopy, Stepped-Combustion Isotopic Mass Spectrometry have been utilized. The structure of the carbonaceous phase in Nakhla indicates it could not have been introduced allochthonously in its current physical form. The close association to a region of secondary mineralization (i.e., iddingsite) implies, although certainly does not confirm, a connection with the period of Martian aqueous alteration experienced by the rock. This carbonaceous material has similarities to macromolecular carbonaceous matter and yet possesses a complex structural and textural morphology that is not observed in carbonaceous or ordinary chondrite meteoritic kerogen. One of the possible origins for the carbonaceous matter is from biogenic processes operating on Mars.