XRD mineralogy of sediments from the Greenland east coast

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.

本研究采用定量X射线衍射（qXRD）分析，针对覆盖过去10~12校正千年距今（cal ka BP）的海底表层样品与海洋沉积物岩芯，提取其中<2毫米的沉积物级分，对东格陵兰康格路苏槽（Kangerlussuaq Trough）与斯科斯比松（Scoresby Sund，约67°~70°N）之间海域的非黏土矿物组成时空变化特征进行刻画。基底岩系整体以早第三纪碱性杂岩为主，其辉石（pyroxene）与斜长石（plagioclase）质量分数较高；往内陆更深处及北部，基底岩系以长英质为主，富含石英（quartz）与钾长石（potassium feldspars）。对非黏土沉积物组成开展的主成分分析（PC）表明，石英与辉石是关键的组成端元组分：斯科斯比松以北的沉积物以石英和钾长石为主，而毗邻早第三纪玄武岩露头的近海海域沉积物则以辉石和斜长石为主，二者存在显著的突变转换。粗粒（<2 mm或<1 mm）冰筏沉积物在约8~5 cal ka BP的槽谷沉积物中基本缺失，但在过去4 cal ka BP以来含量显著升高。对格里维尔盆地（Grivel Basin）与康格路苏槽的沉积物开展组成解混分析后发现，本地物源贡献占优，优于长距离搬运的外源物源；新冰期（Neoglaciation）期间，来自康格路苏峡湾与南森峡湾的潮汐冰川沉积物脉冲可抵达内陆架区域。冰筏碎屑（IRD）的含量变化在沉积物粒度代用指标中比石英质量分数更为显著。丹麦海峡两侧的石英记录中，40%~70%的方差可由低频趋势解释，但东格陵兰格里维尔盆地的观测数据特征显著不同，呈现约2500年的周期性变化。