Primary fluid inclusions in bedded halite from the 830-million-year-old Browne Formation in central Australia contain organic solids and liquids, as documented by transmitted light and UV-petrography. screw. These objects are consistent in size, shape, and fluorescent response to prokaryotic and algal cells, and to aggregates of organic compounds. This finding shows that microorganisms from saline depositional environments can remain well preserved in halite for hundreds of millions of years and can be detected in situ with optical methods alone. This study has implications for the search for life in terrestrial and extraterrestrial chemical sedimentary rocks.
As halite crystals grow in saline surface waters, they trap mother water in primary fluid inclusions. In addition to trapping the mother waters, they can trap any solids that were in the water near/on the crystal face. These solids include tiny crystals of evaporated minerals or organic materials. Previous studies of modern to Permian halites have documented the presence of prokaryotic and eukaryotic organisms and organic compounds, including beta-carotene.
This study uses non-destructive optical techniques to identify and document organic matter in primary fluid inclusions in 830 million year old halite. Sara Schreder-Gomes, Kathleen Benison and Jeremiah Bernau had access to core samples from the Neoproterozoic Browne Formation through the Geological Survey of Western Australia.
The halite was well preserved and allowed them to examine halite crystals from 10 halite beds at different depths. They used transmitted light petrography and UV-visible light petrography to identify primary fluid inclusions and their contents. The team found that the solids trapped in the fluid inclusions were compatible with prokaryotic and eukaryotic cells, and with organic compounds, based on their size, shape, and fluorescent response to UV-visible light.
This study reinforces the utility of nondestructive optical methods as a first step in examining chemical sediments for biosignatures. The petrographic context of the fluid inclusions is essential to ensure that the contents of the fluid inclusions represent the original mother liquors and are therefore of the same age as the halite. This study also shows that microorganisms can be preserved in fluid inclusions in halite for millions of years and suggests that similar biosignatures could be detected in chemical sediments from Mars.
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