143-7 Searching for Biosignatures Within Fluid Inclusions in Bedded and Displacive Halite From the Mars-Analog Permo-Triassic Spearfish Formation of North Dakota

Abstract:

Ancient acid brine systems are essential for interpreting past environments on Earth and understanding ancient Martian environments. Evaporite minerals from hypersaline lakes, such as halite (NaCl), have recently captured the attention of astrobiologists because of their ability to rapidly trap and preserve surface water, air, microorganisms, and organic compounds during precipitation. Here, we investigated biosignatures preserved within fluid inclusions in halite from the Permo-Triassic Spearfish Formation in the Halite #1 core from McKenzie County of western North Dakota. The Spearfish Formation contains both bedded halite, which precipitated from lake waters, and displacive halite, which grew syndepositionally within shallow acid-brine groundwater. Samples were examined using transmitted and UV-vis light microscopy at magnifications ranging from 6.3× to 2000×. Bedded halite hosted abundant primary fluid inclusions containing water, vapor, accidental daughter crystals, suspect cells, and organic compounds, as well as secondary fluid inclusions, many of which were filled with liquid hydrocarbons. In contrast, displacive halite contained only rare, isolated fluid inclusions. Primary fluid inclusions were examined for suspect cells, which appeared as single or clustered orange, yellow, and clear spheroids that fluoresced pale to bright yellow under UV-vis light. Some vapor bubbles fluoresced blue or yellow under UV-vis light, suggesting the presence of organic compounds coating the vapor phase. Fluorescent responses of organic material and the vapor phase were documented, and images were compiled for digital analysis to automate hue co-variation sorting.

Disparities in the distribution of inclusions and organic material between bedded and displacive halite were observed. This preliminary petrographic comparison of fluid inclusions in bedded and displacive halite demonstrates that bedded halite is a more promising target for preserving cells and organic compounds than displacive halite. Therefore, bedded halite on Mars should be an important exploratory target in the search for evidence of past life.

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