PRESERVATION OF MICROBIAL BIOSIGNATURES IN SILICEOUS HOT SPRING DEPOSITS, WITH APPLICATIONS TO MARS EXPLORATION - BUILDING ON JACK FARMER'S LEGACY

The deposits of silica-precipitating hot springs have been found in rocks on Earth as old as Archean and are considered high priority targets in the search for a Martian fossil record. The discovery of silica-rich deposits by the rover Spirit in Gusev Crater and at other locations on Mars with the CRISM instrument on the Mars Reconnaissance Orbiter (MRO), provides evidence of potential past hydrothermal systems on Mars that may have been favorable for microbial life. Therefore, understanding biosignature capture and preservation in these deposits is important for better focusing future exploration strategies of similar deposits on Mars, and for developing effective instruments for future missions to explore for a fossil record of past Martian life.

Miocene-aged siliceous sinter deposits from the Coromandel Peninsula, New Zealand and the Devonian Drummond Basin in NE Australia, with comparisons to modern silica hot spring deposits in Yellowstone National Park and the Taupo Volcanic Zone, New Zealand were investigated to better understand processes of biosignature capture and preservation, and how post-depositional changes (i.e. diagenesis) affect microtexture, composition and biosignature retention.

The Miocene and Devonian sinters have experienced significant overprinting of primary textures by diagenetic cementation of the originally porous sinter framework and recrystallization of opaline silica to quartz. Despite extensive recrystallization, primary depositional textures and other bioindicators (e.g., biofrabrics, plant remains, microbial filaments, and organics) are preserved, especially in cooler distal apron microfacies. Analyses using visible/near-infrared (VNIR) spectroscopy and Raman spectroscopy were consistent with organic signatures of disordered carbonaceous material – i.e. kerogen.

These results reveal the utility of paired, non-destructive techniques, such as VNIR spectroscopy and Raman spectroscopy, while microscale mapping of primary and secondary phases reveals paragenetic relationships and links mineralogy to the microtextural framework of the rock. This enables more precise petrogenetic interpretations, provides a context for inferring microscale variability and habitability, and focuses the search for fossil biosignatures in similar deposits on Mars.