GYPSUM IS AN OVERLOOKED REPOSITORY FOR MICROFOSSILS

Evaporite minerals have long been, generally, considered absent of any fossils. However, cells of microorganisms, pollen, and organic compounds such as beta-carotene and glycerin have all been documented in both modern and ancient halite. Gypsum forms by similar processes in many of the same environments as halite, but few attempts have been made to investigate this salt mineral for organic materials. Here, we summarize the microfossils we’ve found to date in modern and ancient gypsum with known sedimentological context. In particular, we present here data from bottom-growth gypsum that grew in modern neutral and acid saline lakes and modern gypsum reworked as associated eolian grains from Western Australia, northern Chile, and White Sands National Park of New Mexico, as well as from Triassic eolian gypsum from the Red Peak Formation (Chugwater Group) of Wyoming. We also investigate gypsum vein cements for biosignatures. Our results demonstrate that various organic materials are trapped in gypsum crystal interiors, both within fluid inclusions and as solid inclusions. Methods used include optical petrography, using transmitted and UV-vis light, laser Raman spectroscopy, and palynological processing using dissolution of host gypsum. We have documented cells of suspect bacteria and/or Archea, algae, fungi, pollen, plant cuticles, and arthropod parts. Organic compounds found include beta-carotene and long-chain waxes. Based on these findings, we propose attention be paid to gypsum and other sulfate minerals in the search for biosignatures on Earth and Mars.