APPLICATION OF HIGH-RESOLUTION, IN-SITU MAJOR ELEMENT ANALYSIS OF SEDIMENTARY STRATA IN THE CENTRAL ANDES TO RECONSTRUCT CLIMOFUNCTIONS

Laser-Induced Breakdown Spectroscopy (LIBS) is a novel handheld analytical technology that presents the possibility for a major advance in in-situ geochemical measurements for a variety of applications in the Earth Sciences. A handheld LIBS analyzer is easily transported to remote field locations and can be used to take elemental concentration measurements of geological materials in outcrop. The analyzer works by pulsing a high-powered laser to convert a small amount of target material into a plasma, and an onboard Optical-Emission Spectrometer (OES) measures the emitted optical spectrum. Calibration is based on relationships between the concentrations from samples of known elemental composition and their spectral responses. The built-in computer uses pre-made calibrations to calculate the elemental compositions of unknown samples. Here, we present results obtained using preliminary calibrations for bulk-rock geochemical analysis of fine grained sedimentary rocks (clay to medium sand). We test the efficacy of these calibrations by taking high-resolution in-situ LIBS analyses from exposures of Upper Cretaceous through Pliocene stratigraphy in the Altiplano Plateau of Western Bolivia. We test the ability of LIBS to identify changes in degree of weathering, total carbon content, and major element geochemistry through several stratigraphic sections. Ongoing and future research is focused on improving calibrations by collecting samples that were identified as difficult to analyze in the field and using traditional high precision laboratory methods (XRF, ICP-MS) to measure true elemental compositions. One of the greatest strengths of the LIBS analyzer is that new calibration matrices can be retroactively applied to previously obtained spectra, allowing a scientist to collect a an extremely high-resolution dataset in the field, take a small amount of key physical samples for laboratory analyses and greatly improve the accuracy of the high-resolution LIBS data.