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Investigating the incorporation of organic matter into evaporite minerals as a tool to search for the record of life on Earth and elsewhere

Session: New Voices in Geobiology

Presenting Author:

Melonie D. Nguyen

Authors:

Nguyen, Melonie D.¹, Celestian, Aaron², Corsetti, Frank³

(1) Earth Sciences, University of Southern California, Los Angeles, CA, USA, (2) Natural History Musuem Of Los Angeles, Los Angeles, CA, USA, (3) Earth Sciences, University of Southern California, Los Angeles, CA, USA,

Abstract:

Evaporites (minerals that precipitate from fluids during evaporation, e.g., gypsum, halite, carbonates, and other salts) are a target for exobiologic study because, on Earth, organic material can become incorporated as the minerals precipitate from the fluid and potentially preserved over geologic time. However, it is not as well understood exactly how the organic matter/microbes are incorporated or where they might reside (e.g., intracrystalline areas, fluid inclusions, etc.) when evaporites form. In order to have the best search image when prospecting for life elsewhere, it is important to know the relationship between organic matter in the environment and how and where the organics might reside within the evaporite minerals. Fluid inclusions in evaporites also have the potential to inform about the chemistry of the environment during evaporite formation. Evaporite minerals, like gypsum, are found on Mars are potential hosts for microbial life or contain organic matter that can support life.

We aim to understand how and where organic matter is incorporated into minerals and to recreate the starting geochemical and biological conditions of the precipitating environment. Key questions include: How does organic matter incorporate into evaporites/what is the relationship between the starting concentrations of organics and what ends up in the evaporite crystal? Are fluid inclusions representative of the precipitating environment? Is it possible to recreate starting geochemical conditions of a precipitating environment from a salt? While natural evaporative systems are abundant and straightforward to access on Earth, studying such deposits can be complicated by the uncontrolled variables (sediment reworking, secondary crystallization). Great Salt Lake and Searles Lake saline lakes were chosen as field sites to collect brine and evaporites. These sites, Searles Lake and Great Salt Lake, are notable in their comparability to Mars. Our approach will include laboratory experiments on composed brines where experimental conditions (introduction of known quantities of organics/microbes) can be controlled as well as natural samples to compare to the experimental results