Holocene variations in mineral and grain-size composition along the East Greenland glaciated margin (ca 67°-70°N): Local versus long-distance sediment transport

摘要

Quantitative X-Ray Diffraction (qXRD) analysis of the <2 mm sediment fraction from surface (sea floor) samples, and marine sediment cores that span the last 10-12 cal ka BP, are used to describe spatial and temporal variations in non-clay mineral compositions for an area between Kangerlussuaq Trough and Scoresby Sund (～67°-70°N), East Greenland. Bedrock consists primarily of an early Tertiary alkaline complex with high weight% of pyroxene and plagioclase. Farther inland and to the north, the bedrock is dominantly felsic with a high fraction of quartz and potassium feldspars. Principal Component (PC) analysis of the non-clay sediment compositions indicates the importance of quartz and pyroxene as compositional end members, with an abrupt shift from quartz and k-feldspar dominated sediments north of Scoresby Sund to sediments rich in pyroxene and plagioclase feldspars offshore from the early Tertiary basaltic outcrop. Coarse (<2 mm or <1 mm) ice-rafted sediments are largely absent from the trough sediments between ～8 and 5 cal ka BP, but then increase in the last 4 cal ka BP. Compositional unmixing of the sediments in Grivel Basin and Kangerlussuaq Trough indicate the dominance of local over long distance sediment sources, with pulses of sediment from tidewater glaciers in Kangerlussuaq and Nansen fjords reaching the inner shelf during the Neoglaciation. The change in IRD is more dramatic in the sediment grain-size proxies than in the quartz wt%. Forty to seventy percent of the variance in the quartz records from either side of Denmark Strait is explained by low frequency trends, but the data from the Grivel Basin, East Greenland, are distinctly different, with an approximate 2500 yr periodicity.