New Mexico Geological Society Annual Spring Meeting — Abstracts

The objective of this project is the interpretation of geochemical and mineralogic indicators of climate change present in an 80- meter core recovered from the Valle Grande located in the Valles Caldera, New Mexico. The core being examined here represents a climate record for the mid-Pleistocene. Due to the limited source terrain of the basin, this sediment core becomes valuable as an indicator of regional changes in climatic variations. The results of this geochemical analysis will be correlated with sediment mineralogy, sedimentology, and an array of other data compiled by the research team. Ultimately, the results will be combined to generate a model of regional climate for the mid-Pleistocene over the time interval sampled by the core.

The study of redox processes in lakes reveals an interesting explanation of numerous, interdependent chemical reactions that occur at the lake bottom. Preliminary geochemical data from the Valle Grande sediment core has been collected and analyzed using ICP-OES. Data sampling is on the scale of every 20 cm. Eight major elements and 13 trace elements are being analyzed for further consideration. The presence of Fe and Mn oxides in the sediment core can be used as an indicator of oxygenation of anoxic bottom waters. Oxygenation of bottom waters can be related back to lake depth and stratification. Correlations between the relative concentration of Fe and Mn values collected implies that there were periods of oxygenated bottom waters followed by reducing conditions. Additionally, a rise in Fe/Mn may be indicate the onset of reducing conditions.