Earth and Planetary Sciences ETDs

Publication Date

7-1-2016

Abstract

The Valle Grande Paleo-lake in the southeastern portion of Valles Caldera, NM, U.S.A. provides a useful location to study short distance source-to-sink variation in geochemistry and mineralogy. In this study, lithium is the primary focus in order to test its effectiveness at recording past environmental change. This is possible due to the ~75 m of lake sediment that has been drilled and cored in this region and the extensive paleo-climate work that has been completed with this material; this has provided a strong understanding of past environmental change throughout the lifespan of the lake. Chemical and mineralogical analyses were conducted in the lake sediment and from source rock material surrounding Valle Grande to understand such changes during the weathering, erosion, and deposition of this material. Finally, as this is a depositional basin dominated by a single type of igneous rock in an arid region, it provides a useful analog to Martian lacustrine settings, such as Gale Crater which also is characterized by a closed depositional basin dominated by an igneous rock type, basalt rather than rhyolite. In the drill core lithium was minimally enriched in the interglacial sediment compared to the glacial; in addition, the trend for lithium with depth was somewhat similar to established climate proxies. However, these changes were not as distinct as the trends seen with the other proxies and the mean values for the two periods investigated were within one standard deviation of each other. The ChemCam instrument on the Mars Science Laboratory rover analyzed the rock surface, drill hole walls, tailings, and unprocessed and sieved dump piles to investigate chemical variations with depth in the first two Martian drill holes and possible fractionation or segregation effects of the drilling and sample processing. The drill sites are both in Sheepbed Mudstone, the lowest exposed member of the Yellowknife Bay formation. Yellowknife Bay is composed of detrital basaltic materials in addition to clay minerals and an amorphous component. The drill tailings are a mixture of basaltic sediments and diagenetic material, such as calcium sulfate veins, while the shots on the drill site surface and walls of the drill holes are closer to those pure end members. The sediment dumped from the Sample Acquisition, Processing, and Handling Subsystem is of similar composition to the tailings; however, due to the specifics of the drilling process, the tailings and dump piles come from different depths within the hole. This allows the ChemCam instrument to analyze samples representing the bulk composition from different depths. On the pre-drill surfaces, the Cumberland site has a greater amount of CaO and evidence for calcium sulfate veins, than the John Klein site. However, John Klein has a greater amount of calcium sulfate veins below the surface, as seen in mapping, drill hole wall analysis, and observations in the drill tailings and dump pile. In addition, the Cumberland site does not have any evidence of variations in bulk composition with depth down the drill hole, while the John Klein site has evidence for a greater amount of CaO (calcium sulfates) in the top portion of the hole compared to the middle section of the hole, where the drill sample was collected.

Degree Name

Earth and Planetary Sciences

Level of Degree

Masters

Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Crossey, Laura

Second Committee Member

Fawcett, Peter

Third Committee Member

Wiens, Roger

Language

English

Keywords

Mars, MSL, Lithium, Valles Caldera

Document Type

Thesis

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