Unraveling the sedimentary history of gypsum sand in the northern polar sand seas of Mars

Grant #: NNX13AC80G
Senior Scientist: Lori Fenton

In 2005, a large quantity of the mineral gypsum was unexpectedly identified in the high latitude dune sands of Olympia Undae. Because gypsum is formed in the presence of liquid water, the discovery of this extensive deposit has important implications for the climatic and sedimentary history of the currently cold and dry north polar region of Mars. Indeed, the presence of this mineral within Amazonian strata (< ~3.5 Ga) could have global implications, because it contradicts the current view that sulfate minerals only formed in abundance on Mars much earlier in the planet's history, during the Hesperian (or Theiikian) Epoch (> ~3.5 Ga). Images from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) indicate that gypsum sand grains appear to concentrate at dune crests, but it is not known whether aeolian processes alone could be responsible for this effect, nor what the significance of this pattern may be. Despite its potential importance in unraveling Mars' geological history, the origin of the gypsum and its role in sedimentary and polar processes is disputed and poorly constrained. 

What is lacking from current studies, and what would address the question of sulfate origin and transport history, are two investigations: 1) an examination of how aeolian processes distribute gypsum grains across active dunes, and 2) a comprehensive high-spatial resolution study of the correlation between aeolian morphology and hydrated mineral concentration in the north polar sand seas. We propose to address these issues with the following two objectives: 

Objective #1: Perform field and lab analyses of mineral abundance and grain size using a terrestrial analog: dunes containing both gypsum and more resistant terrigenous (e.g., quartz) grains at White Sands National Monument in New Mexico. Using both a visible/near-infrared (VNIR) spectrometer and an X-ray Diffraction (XRD) system, this work will determine how aeolian processes influence the transport and grain size distribution of gypsum sand relative to harder sand grains. 

Objective #2: Investigate CRISM spectra, as well as High Resolution Imaging Science Experiment (HiRISE) and Context Camera (CTX) images spanning Olympia Undae, to determine how the concentration of gypsum and other hydrated minerals varies with the sedimentary history of the sand sea. 

The goal of these objectives is to constrain the origin and history of gypsum in the sand sea. The expected significance of the proposed work is to explain the presence of young (Amazonian) hydrated minerals on a planet where most other such minerals are much older (Hesperian). In addition, the work will determine the transport history of gypsum grains within Olympia Undae, which may have implications for climate-driven shifts in wind regime. Finally, coordinating VNIR reflectance data and XRD data in the field will provide background in an aeolian environment bearing hydrated sulfates, providing "ground truth" for the Chemistry and Mineralogy instrument (CheMin) on the Mars Science Laboratory, and preparing for associations between CRISM data from orbit and XRD data on the surface.