Fly ash consists of mainly silt-size spherules that form during high-temperature coal combustion, such as in steam locomotives and coal-burning power plants. In the eastern USA, fly ash was distributed across the landscape atmospherically beginning in the late 19th century, peaking in the mid-20th century, and decreasing sharply with implementation of late 20th century particulate pollution controls. Although atmospheric deposition is limited today, fly ash particles continue to be resedimented into alluvial and lacustrine deposits from upland soil erosion and failure of fly ash storage ponds. Magnetic fly ash is easily extracted and identified microscopically, allowing for a simple and reproducible method for identifying post-1850 CE (Common Era) alluvium and lacustrine sediment. In the North Carolina Piedmont, magnetic fly ash was identified within the upper 50 cm at each of eight alluvial sites and one former milldam site. Extracted fly ash spherules have a magnetite or maghemite composition, with substitutions of Al, Si, Ca, and Ti, and range from 3–125 µm in diameter (mainly 10–45 µm). Based on the presence of fly ash, post-1850 alluvial deposits are 15–45 cm thick in central North Carolina river valleys (<0.5 km wide), ~60% thinner than in central Illinois valleys of similar width. Slower sedimentation rates in North Carolina watersheds are likely a result of a less agricultural land and less erodible (more clayey) soils. Artificial reservoirs (Lake Decatur, IL) and milldams (Betty’s Mill, NC), provide chronological tests for the fly ash method and high-resolution records of anthropogenic change. In cores of Lake Decatur sediments, changes in fly ash content appear related to decadal-scale variations in annual rainfall (and runoff), calcite precipitation, land-use changes, and/or lake history, superimposed on longer-term trends in particulate pollution.

中文翻译：

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磁性飞灰作为沉降后冲积和湖泊沉积物中的年代记号：来自北卡罗来纳州和伊利诺伊州的示例

粉煤灰主要由高温煤燃烧过程中形成的粉粒状小球组成，例如在蒸汽机车和燃煤发电厂中。在美国东部，粉煤灰从19世纪末开始分布在整个大气中，在20世纪中叶达到顶峰，并随着20世纪末的颗粒物污染控制而急剧减少。尽管今天大气沉积受到限制，但由于山地土壤侵蚀和粉煤灰储藏池的破坏，粉煤灰颗粒仍被重新沉积到冲积物和湖相沉积物中。磁性粉煤灰易于提取并在显微镜下进行鉴定，从而为鉴定1850 CE（共同时代）后的冲积层和湖相沉积物提供了一种简单且可重复的方法。在北卡罗莱纳州皮埃蒙特，在八个冲积场和一个以前的米尔达姆场均在上部50厘米以内发现了磁性粉煤灰。提取的粉煤灰小球具有磁铁矿或磁赤铁矿成分，替代了Al，Si，Ca和Ti，直径范围为3–125 µm（主要为10–45 µm）。根据飞灰的存在，北卡罗来纳州中部河谷（宽<0.5 km）的1850年后冲积物厚15–45 cm，比伊利诺伊州中部类似宽度的谷地薄约60％。北卡罗莱纳州流域的沉积速度较慢，可能是由于耕地面积减少和土壤易蚀性（黏土性）降低的结果。人工水库（伊利诺伊州迪凯特湖）和密尔达姆斯（北卡罗来纳州贝蒂米尔斯）为粉煤灰方法提供了时间顺序测试，并提供了人为变化的高分辨率记录。在迪凯特湖沉积物中，