Date of Graduation


Document Type


Degree Type



Eberly College of Arts and Sciences


Geology and Geography

Committee Chair

Kathleen C Benison

Committee Co-Chair

Helen M Lang

Committee Member

Dorothy J Vesper


Salar Ignorado is situated at high elevation in the Andes Mountains of northern Chile in an extremely arid, small, intervolcanic basin and contains pools of acid (pH 3.3 -- 4.1) saline (5 -- 30 ppth) water that are precipitating gypsum crystals. Gypsum crystals trap acid saline water from the pools as fluid inclusions. Little research has been conducted on fluid inclusions in gypsum. At Salar Ignorado two types of bottom-growth gypsum form from the surface pools: large bladed and tiny needle-like crystals. Salar Ignorado gypsum contains primary fluid inclusions of three distinct morphologies, oriented parallel to crystal face. Petrography and microthermometry were performed on 27 gypsum crystals from Salar Ignorado. Most primary fluid inclusions are all liquid, however some primary inclusions are composed of liquid and a gas phase. One large gypsum crystal, hosting primary fluid inclusions along 28 successive growth bands, was the focus for fluid inclusion studies. Microthermometric results in geochemical trends. This crystal shows a change in parent fluids, during growth, from low salinity to high salinity to low salinity. At the bottom of the crystal, the lowest six fluid inclusion assemblages have salinities of 1.7 to 5.1 eq. wt. % NaCl. The next nine fluid inclusion assemblages have significantly higher salinity (18.6 and 25.5 eq. wt. % NaCl) inclusions. The twelve fluid inclusion assemblages near the top of the crystal have low salinity (1.6 to 7.9 eq. wt. % NaCl) like those at the bottom of the crystal. The high salinity fluid inclusions in the middle of this gypsum crystal are interpreted as the migration of hydrothermal fluids to the surface, which are intimately linked to the local active magmatism. Secondary evidence of hydrothermal pulses are high molecular weight hydrocarbons and hydrogen sulfide odors upon crushing.;A variety of microorganisms are trapped both as solid inclusions and as potentially viable halophilic and acidophilic prokaryotes and eukaryotes within fluid inclusions in this Mars-analog gypsum. Pennate diatoms, green algae, and prokaryotes have been documented in gypsum precipitated from acid (pH 1.8--4.6) saline (5%--28% total dissolved solids) waters at Salar Ignorado and its larger neighbor, Salar Gorbea. Evaluation of Salar Ignorado gypsum indicates that primary fluid inclusions record hydrochemistry and microbiology of various intervals of waters. This study has implications for detailed interpretations of past environments from ancient gypsum in the rock record, as well as clues for the search for life on Mars.;This thesis has shown for the first time that primary fluid inclusions in gypsum can serve as proxies for various environmental conditions. Detailed study of Salar Ignorado gypsum has identified trends in surface water salinity, degassing of hydrogen sulfide and hydrocarbons, and fossilization of microorganisms.