Light Absorption Spectroscopy as a Paleoclimate and Correlation Technique for the CRP and CIROS-1 Drill Cores, McMurdo Sound, Antarctica

Coring at CIROS-1 and at the three drillsites of the Cape Roberts Project (CRP) provided a record of glacial influence in McMurdo Sound, Antarctica, during the Late Eocene and Oligocene. All four sites have well established sequence stratigraphies. Prior analyses of one CRP site, CRP-2, suggested a correlation between sequence stratigraphy and provenance, attributed to a link between local sea level and climate. However, sampling density was low. We have used light absorption spectroscopy (LAS) for high-resolution (0.5-1.0 m spacing) determination of downcore mineralogic variations at the four sites. LAS is a rapid, nondestructive mineral identification technique that measures the absorption spectrum, in visible and near-infrared bands (350-2500 nm), of light reflected from any surface. At these drillsites, relative abundance of smectite and illite is thought to reflect warm/humid (smectite-rich) versus cold/dry (illite-rich) paleoclimates. The 3300 LAS-based measurements of smectite/illite variations, confirmed by widely spaced XRD determinations, exhibit a pattern of generally higher smectite contents within highstand system tracts, suggesting that warmer climates correspond to higher local sea levels. Conversion of these high-resolution records from core depth to age is hampered by correlation uncertainties between the CIROS-1 and CRP cores. The smectite/illite curves, as well as other spectral characteristics, are very useful in correlating these Antarctic drill cores.