【摘要】 湖泊碎屑沉积物的粒度分布可以提供与区域气候变化相关的湖泊水文变化信息。然而,由于湖泊沉积物多峰分布固有的复杂性,其粒度组分成因的解释仍存在很大的不确定性。本文利用对数正态分布函数对内蒙古达里湖36个表层沉积物样品的粒度组分进行了分离,并探讨了各组分特性与特定沉积环境(包括每个采样点位的离岸距离和水深)之间的关系。结果表明,达里湖现代碎屑沉积物包含5个截然不同的单峰粒度分布,分别代表5个不同的粒度组分。虽然其相对百分含量随湖泊水动力条件而变化,但每个组分均保留着各自的众数粒径、搬运方式、沉积环境等特性。这些组分自细而粗可分为:长期悬移粘土组分、离岸带悬移细粉砂组分、离岸带悬移中粗粉砂组分、近岸带悬移细砂组分、近岸带跃移中砂组分。近岸带环境两个组分的百分含量与现今湖泊水深呈负相关,揭示出沉积岩芯近岸带组分与地质历史时期湖面状况相关联的数值模型。该模型在达里湖沉积岩芯中的应用显示,近岸带组分百分含量增加与同岩芯孢粉序列重建的区域降水减少相对应。两种独立的代用指标在时间上的一致性,不仅展示了对数正态分布函数分离多峰沉积物的有效性,而且揭示出利用粒度组分-湖面状况模型重建湖泊古水文的潜力。更多还原

【Abstract】 The grain-size distribution of clastic sediments in lakes may provide an important source of information on changes in the hydrology of lakes associated with regional climatic variations.For lake sediments,however,there is still great uncertainty in explaining the genesis of grain-size components due to the inherent complexity of polymodal grain-size distributions.In this study,the grain-size components of 36 surface sediments of Dali Lake(43°13’ ~43°23’N,116°29’~ 116°45’E),Inner Mongolia,were partitioned using a lognormal distribution function and the relationship between the identity of each component and the specific sedimentary environment(including the offshore distance and water depth of each sampling site) was investigated.The data indicate that the modern clastic sediments of Dali Lake contain five distinct unimodal grain-size distributions representing five grain-size components.Each of the components retains its identity including modal size,manner of transportation and environment of deposition although the relative percentage varies with the hydraulic condition throughout the lake.,These components are specified from fine to coarse modes as long-term suspension clay,offshore-suspension fine silt and medium-to-coarse silt,and nearshore-suspension fine sand and saltation medium sand.The percentage of the nearshore components displays a negative correlation with water depth across the modern lakebed,suggesting a model for linking the nearshore components in sediment cores to the lake level status in the geological past.The model was applied to a sediment core from Dali Lake where high percentages of the nearshore components in the core sediments were correlated with low regional precipitations reconstructed on the pollen profile of the same core.The coincidences between two independent proxies do not only demonstrate the validity of lognormal distribution function in partitioning polymodal sediments but also reveals the potential of the grain-size component-lake level status model for lake’s paleohydrological reconstruction.更多还原