Mineralogical Analysis of Primary and Secondary Source Sediments to Linnévatnet, Spitsbergen, Svalbard, 2006

Linnévatnet, Spitsbergen, Svalbard is a high Arctic lake containing a sediment record that extends through most of the Holocene. Laminated lake sediments such as those found in Linnévatnet can serve as high resolution proxies for long term climate change. This study utilizes detailed mineralogical analysis to identify changes in the source of sediments to Linnévatnet during the late Holocene. These climatically sensitive sediment sources include a major proglacial river; alluvial fans, solifluction lobes and the meltwater stream from a small cirque are secondary sources. Distinct bedrock lithologies (phyllite, sandstone, carbonate and dolerite) in the valley strike north-south parallel to the lake, making provenance work possible. Pebble counts, conducted in the field at each sediment source, reveal a strong correlation between cobble and boulder lithology and underlying bedrock source. Laboratory identification of the gravel fraction of surficial sediment samples indicates increased break down of phyllite and carbonate in comparison to the sandstone. Grain size analysis of source sediments implicates differences in the mechanism of sediment transport and deposition at different sources. Unique mineral compositions were identified for each sediment source studied using paired x-ray diffractometer (XRD) and quantitative analysis of the sand, silt and clay sized fractions. West shore solifluction sources are recognized by the abundance and presence of sheet silicates (muscovite, chlorite, kaolinite) in all size fractions. The cirque outwash stream is distinguished by higher amounts of chlorite in all size fractions and the abundance of albite in the silt fraction. East shore sources are characterized by higher amounts of carbonate minerals and the presence of accessory minerals (rutile, pyroxene). Linnéelva sediments contain relatively less carbonate, albite and chlorite/kaolinite than the west and east shore sources. Continuous grain size analysis of four surface cores from different locations in the lake show variations in grain size through time, indicating changes in sediment transport. Paired XRD and quantitative analysis of the silt and clay fractions from core subsamples indicate changes in mineralogical composition down core at all locations but are limited in scope. Higher amounts of silt, paired with an increase in chlorite/kaolinite and a distinct stratigraphy, indicate increased glacier activity in the core proximal to the cirque. Higher amounts of sand, decoupled from silt trends and paired with the presence of local mineralogy (orthopyroxene, calcite) in the two deep basin cores indicate increased east slope activity. Differences in grain size distribution of the two deep basin cores implicate solifluction lobes as a contributor to sedimentation in the north end of the deep basin.

斯瓦尔巴群岛（Svalbard）斯匹次卑尔根岛（Spitsbergen）的林讷湖（Linnévatnet）是一座北极高纬度湖泊，其沉积记录覆盖了全新世（Holocene）的大部分时段。像林讷湖这类具纹层结构的湖泊沉积物，可作为长期气候变化的高分辨率代用指标（proxy）。本研究通过详细的矿物学分析，识别全新世晚期林讷湖沉积物物源的变化。对该湖沉积物具有气候敏感性的物源包括：一条主要的冰缘河流，以及冲积扇、泥流舌（solifluction lobes）和小型冰斗融水溪流这三类次级物源。流域内独特的基岩岩性（千枚岩phyllite、砂岩sandstone、碳酸盐岩carbonate和辉绿岩dolerite）呈南北走向，与湖泊走向平行，这为物源溯源研究提供了可行性。野外针对各沉积物物源开展的砾石计数结果显示，砾石和漂砾的岩性与下伏基岩物源之间存在显著相关性。对表层沉积物样品的砾石组分进行实验室鉴定后发现，相较于砂岩，千枚岩和碳酸盐岩的破碎程度更高。对各物源沉积物的粒度分析表明，不同物源的沉积物搬运与沉积机制存在差异。通过X射线衍射仪（X-ray diffractometer, XRD）配对分析与砂、粉砂、黏土级组分的定量分析，本研究为各研究沉积物物源确定了独特的矿物组成特征：西岸的泥流舌物源在所有粒级组分中均富含层状硅酸盐矿物（白云母muscovite、绿泥石chlorite、高岭石kaolinite）；冰斗融水溪流的特征为所有粒级组分中绿泥石含量更高，且粉砂级组分中富含钠长石（albite）；东岸物源则以更高含量的碳酸盐矿物及伴生矿物（金红石rutile、辉石pyroxene）为特征。林讷河（Linnéelva）沉积物的碳酸盐、钠长石及绿泥石/高岭石含量相对东西两岸物源更低。对取自湖内不同位置的4根表层岩芯开展连续粒度分析，结果显示不同时段的粒度存在变化，表明沉积物搬运机制发生改变。对岩芯亚样的粉砂与黏土级组分开展X射线衍射仪配对分析与定量研究，结果显示所有站位的岩芯矿物组成均随深度发生变化，但研究范围有限。在靠近冰斗的岩芯中，粉砂含量升高，伴随绿泥石/高岭石含量增加与清晰的地层结构，这指示冰川活动增强。在两个深盆地岩芯中，砂含量升高且与粉砂变化趋势解耦，同时伴生有本地矿物（斜方辉石orthopyroxene、方解石calcite），这表明东坡的侵蚀活动增强。两个深盆地岩芯的粒度分布存在差异，这说明泥流舌是深盆地北端沉积物沉积的贡献源之一。