New Mexico Geological Society Annual Spring Meeting — Abstracts

Travertine deposits from the Soda Dam springs in the Jemez Mountains, northern New Mexico, provide a record of the paleohydrology, paleoclimatology and geothermal history of the area. Travertine deposits occur along the Soda Dam fault just upstream of the village of Jemez Springs along the Jemez River. Travertine deposits here are predominately calcium carbonate precipitates from the Soda Dam hot springs and its precursors. Carbonates are a powerful tool because of the wide variety of information that can be received from slight changes its mineralogy and mineral chemistry. We employed X-ray diffraction to examine a suite of samples from the Soda Dam area. We used the Rietveld method to obtain calcite lattice parameters, magnesium occupancies, and to quantify concentrations of accessory minerals such as quartz, aragonite and dolomite. A goal is to test whether travertine age or stable isotope composition correlates with lattice parameters or mineralogy, and to evaluate whether perhaps temperature is recorded by mineralogic variation such as aragonite (hot) versus calcite (cooler). The calcite deposits also range from spars to micrites, suggesting possible differences in precipitation conditions. The samples analyzed ranged in age from modern deposits to deposits of > 500ka. Modern travertines were collected from deposits associated with waters that ranged from 20-40 C. We also examined laminated samples with alternating textures (e.g., spar and micrite). Preliminary analyses on the textural differences show encouraging results. All samples are composed of calicite. Using lattice parameters, we estimate magnesium content in the calcite ranging up to 5%. Site occupancy information shows a possibility of higher Mg contents. The micrites and spars of different ages also had measurable variations in magnesium content. These results are refined by a rietveld analysis, to take out the error involved with preferred orientation to make the results as accurate as possible. Additional analysis will determine if there is a correlation between trace element concentrations (Mn, Fe, Sr, Ba) and the magnesium content or lattice parameters. We anticipate that systematic examination of stable isotope composition and composition via xrd will allow greater understanding of the relative importance of factors such as fluid mixing and temperature variations in the travertine-depositing system.