Water-Rock Interactions in Sediments Below Modern Evaporites

Dylan Childs, “Water-Rock Interactions in Sediments Below Modern Evaporites”
Mentor: Lindsay McHenry, Geosciences

The use of remote sensing spectrometers allows us to determine the composition and mineralogy of surface sediment from a distance without the need to physically collect samples. One limitation of this however is that the data we collect only represents the very surface and not further in depth. Our objectives in this research are to compare mineral assemblages from the surface and shallow subsurface to assess and identify any patterns present that could allow us to better infer overall composition. If relations between surface composition and that at depth can be related, then remotely sensed mineralogical data would be more useful. This could lead to better understanding of planetary surfaces to which we don’t have direct access, providing more insight into past environmental conditions and why certain regions look the way they do today. In this experiment I used a one-meter long core sample collected from a modern evaporite crust near Lake Tecopa, California. The core was then divided into 2 cm intervals and I analyzed the mineralogy and geochemistry of each sample. I used X-ray powder diffraction and X-ray fluorescence to identify the minerals present in each sample, their compositions, and how their concentrations changed over time. Prominent changes in abundance with depth were only observed for the evaporite mineral, halite. It was abundant at the surface, and rare from 1-6 cm decreasing in abundance with depth. Halite was absent from samples deeper than 6 cm. Additional analysis will help determine the elemental composition of these samples, and assess how representative the surface composition can be of the whole.

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