A COMPARISON OF THE BASIC OPTICAL DATING PROPERTIES OF TWO NATURAL GYPSUM SAMPLES AS ANALOGS FOR COMPONENT MINERALS IN MARS SURFACE SEDIMENTS

Gypsum is a calcium sulfate typically found within sedimentary evaporite environments. Optical dating is a chronometric technique used to determine the depositional age of sediments by determining when they were last exposed to light. The method is based on solid-state dosimetric properties of mineral grains. Optical dating has been proposed as a robotic in-situ geochronology tool for understanding and interpreting the geomorphic and climatic history of Mars. Sulfate minerals have been identified as important participants in Mars surface processes. In this project basic optical dating properties including radiation dose response, measurement induced sensitivity change, and fading were documented and compared for two different natural gypsum samples from White Sands National Monument and from an outcrop of the Pierre Shale in North Dakota. White Sands gypsum was formed as a surface evaporite, then eroded and transported by wind into sand dunes. The Pierre Shale gypsum was a single crystal formed from ground water precipitation. Our results indicated very few differences in the optical dating properties of the two samples that could be considered characteristic or diagnostic. However, differences in the normalized signal intensity and saturation doses were observed between the two samples. Further work is warranted to better understand the significance of the observed differences and their implications for optical dating on Mars.