长白山西麓泥炭灰分粒度特征及其环境意义

本文提取长白山西麓哈尼、孤山屯沼泽地晚更新世以来泥炭沉积中所含的高分辨率无机矿物颗粒信息,追索泥炭灰分的物质来源、粒度组成特征及规律,进一步揭示本区泥炭灰分粒度的古环境意义。粒度分析结果表明,长白山西麓泥炭灰分颗粒粒径集中在1~350 μm,灰分组成以各类粉砂为主;本区泥炭灰分粒度分布概率累积曲线以二段式占多数,频率分布曲线呈现单峰（10~100 μm）、双峰型（10~100 μm,100~1 000 μm）特征,搬运方式以悬移和跃移为主。由于本区沼泽地地处湿润区,泥炭灰分的粒度组成主要受到流水动力变化的影响,沼泽地水文状况的变化引起了泥炭灰分粗细的变化。因而,长白山区沼泽地泥炭灰分的粗细主要指示夏季风强弱,可用于反演古降水的变化。晚更新世以来泥炭灰分粒度的变化曲线显示本区全新世9.2 ka,8 ka和5 ka存在干旱事件,古降水历史具有“干-湿-干”旋回。由于这些干旱事件与全新世几次著名的冷事件几乎同时出现,故推测本区古气候模式为冷干和暖湿组合。

Grain-size Characteristics and Environmental Significance of Peat Ash in the West Foothill of Changbai Mountain

In order to recognize the provenances, granularity characteristics of peat ash, and further reveal the paleo-enviromental significance of peat ash. Two peat cores in Hani and Gushantun Peat-land in the west foothill of Changbai Mountain are collected. The results of grain size analysis show that the dominant size of peat ash is 1~350 μm. Which means peat ash is mainly composed of different kinds of silt. What is more, the majority probability cumulative curves for particle size distribution are with two sections. At the same time, frequency distribution curves show unimodal type (10~100 μm), bimodal type (10~100 μm, 100~1 000 μm). These show that the transportation ways of peat ash is suspension and saltation. And the grain sizes changed with the hydrologic condition in the peat land. In the dry season, the water power is weak and the peat ash content is relatively fine. But in the wet season, surface runoff carries the coarse particle into the swamp and deposits. Therefore, the peat ash can be used for rebuilding the evolution of paleo-precipitation and it can be a proxy for the summer monsoon. In addition, 9.2 ka, 8ka and 5ka drought events in Holocene are recognized from the grain size changing curve and the curve also reveals a "dry-wet-dry" cycle in the precipitation history. Because these events correspond to the famous cold events, so we may draw the conclusion that dry and cold, warm and wet may be matched in the process of climate change.