PETROGRAPHY AND LASER RAMAN SPECTROSCOPY OF ACCIDENTAL DAUGHTER CRYSTALS IN FLUID INCLUSIONS IN MARS-ANALOG HALITE

Halite formed in acid saline lakes from Permian time contain micron-scale features that provide evidence for past environmental conditions. This study uses petrography and laser Raman spectroscopy to study accidental daughter crystals in fluid inclusions in the Opeche Shale of North Dakota, and the Cedar Hills Sandstone and Blaine Formation of Kansas. These micron-scale features were trapped inside halite at time of deposition, providing clues about parent water chemistry. Besides daughter crystals in fluid inclusions, organic material, solid crystal inclusions, and any other features trapped in halite are also documented. Petrography was used to distinguish accidental daughter crystals that precipitated from lakes water from eolian grains. The importance of a one-micron diameter laser is also noted, because it allows for focusing of daughter crystals as small as 3 µm in diameter. Five hydrated sulfate minerals have been found, along with carbonate grains that may represent eolian grains. Results of this research may develop specific minerals as diagnostic indicators of low pH brines for acid saline lake deposits. This project also has application to the analysis of solid and fluid inclusions found in other ancient acid saline halite forming systems on Earth and Mars. Finally, this work shows the importance of petrography and laser Raman spectroscopy for the study of salts brought back by the Mars Sample Return mission.