IT’S A TRAP! THE PRESERVATION POTENTIAL OF ANCIENT HALITE

Chemical sediments, such as bedded halite (NaCl), are strongly influenced by environmental conditions during deposition and, if unaltered, may preserve microfossils and microorganisms for hundreds of millions of years. Recent studies show that halite can be an excellent repository for biosignatures and other environmental data. However, the preservation potential of halite remains relatively untested. Halite is the perfect trap. As halite grows, “step-like” cleavage-controlled irregularities rapidly enclose the surface brine and any other matter from the environment as fluid or solid inclusions. These inclusions function as “snapshot” repositories of surface water, air, solids, and microorganisms. Here, we showcase a non-destructive approach of petrographic examination for recognizing the potential range of organic materials in situ in halite. We used Permian bedded halite of western equatorial Pangaea, as a case study. Halite from the Nippewalla Group of Kansas (Amoco Rebecca K. Bounds, Andarko Davis, and AEC 5 cores) and the Opeche Shale of North Dakota (Gulf Romanysyn core) reveals chevron and cumulate crystals with primary fluid inclusions, many containing microbes and tiny accidental daughter crystals. Solid inclusions along growth bands, mainly comprised of tiny crystals and organic material, were also trapped as the halite precipitated. Biological material in the halite includes representatives from the five domains of life. Besides archaea, bacteria, fungi, and green algae, there are also abundant fragments of coniferous cuticle, some of which bear stomata, alongside bisaccate pollen grains, charophyte algae, and fibers of an organic nature. Whole insects and insect segments have also been recognized as sold inclusions. Organic compounds, including beta-carotene, are also present. Life and taphonomic processes in continental environments of dry climates are relatively poorly understood. Bedded halite may represent the most important sink of terrestrial organic matter in arid environments, as it traps both organisms living in parent lake waters, as well as materials blown into the lake. Detailed study of fossils in halite has implications for the better understanding of life in extreme terrestrial environments, as well as aid in the search for life on Mars.