Mineralogy of Pleistocene Sediments Under the McMurdo Ice-Shelf (ANDRILL-MIS Project)

The criosphere in the McMurdo Sound region has undergone significant modifications during the last 1 Ma. Consequently, the sedimentary sequences under the McMurdo ice-shelf provide geological data to reconstruct variations in transport and depositional mechanisms of terrigenous material due to variations in ice sheet extension, grounding line position, main ice-stream flows and sea-ice coverage during glacial and interglacial periods. Our study aims to characterize the Pleistocene glacimarine sediments recovered during the ANDRILL-McMurdo Ice Shelf Project in Windless Bight (South of Ross Island) from a mineralogical point of view. Clay an heavy mineral from the clay and sand fractions, respectively, have been semiquantitatively determined using X-ray diffraction and SEM-EDS techniques. Illite, chlorite, and smectite comprise the clay mineral assemblage, being illite and smectite the principal components; olivine, titanoaugite and glass dominate the heavy mineral assemblage; diopside, orthopyroxene, amphibole, garnet and apatite are present in minor amount. The sets of analyses show that the sediments are a mix of local McMurdo Volcanic Group (MVG) rocks and Transantarctic Mountains (TAM) source rocks from the south and west. The down core variations of the two sets of data are not correlated. Clay mineral assemblage present a strong variation between 30 and 50 mbsf. Differently, variations in heavy mineral assemblage are linked to variation in sedimentological facies, as revealed by canonical discriminant function analyses.