Detrital mineral composition and provenance of the Camp Century basal ice sediments

The Camp Century Ice core, NW Greenland, recovered a 4.5 m basal section consisting of frozen sediments and debris-rich ice. This material was recently re-discovered in Danish ice core storage and visually logged. As part of a multi-disciplinary effort to unlock the climatic and paleo-environmental signal of this unique record, we have analysed detrital mineral composition and metamorphic ages. Bulk mineral analyses were performed at the Geological Survey of Denmark and Greenland on grain mounts from 2 core intervals using a SEM automated quantitative mineralogy (AQM) approach coupled to laser ablation ICP-MS analyses. This setup allows us to gain a full mineral description together with single-grain U-Pb dates for a large population of metamorphic components, e.g. apatite, rutile, titanite and zircon. In addition, amphibole grains were picked for ⁴⁰Ar-³⁹Ar dating performed at the LDEO Argon Isotope Lab. Mineralogical characterization was completed by X-Ray diffraction analysis of the fine fraction to determine the presence and nature of potential clay weathering products, and single-crystal X-ray diffraction was utilized to characterize the atomic arrangements of minerals that occur in solid solutions. The AQM results indicate that metamorphic minerals are present in sufficient amounts (100’s) for gaining statistically valid provenance data. Preliminary results show ages in the 1900 – 1700 Ma range (amphibole, rutile) and around 2700 Ma (zircon). This, along with the presence of swelling clays in the sediments, is consistent with weathering of the local bedrock, and/or sediments transported from the Inglefield orogenic belt north of the site. To gain information on the youngest thermal events of sediment sources, potentially revealing deep glacial incision, (U-Th-Sm)/He dating of single apatite grains is underway. Preliminary work on the 125-250 µm size fraction yield abundant subhedral-to-subrounded, euhedral apatite suitable for thermochronology. Here we report the results from the different methods and discuss the implications for understanding erosional processes and potential transport pathways of the Camp Century basal ice sediments.