Collaborative Research: Resolving the Enigma of Late Quaternary Loess on the Great Plains

黄土本质上是大气尘埃的堆积，厚的黄土沉积物提供了尘埃输送和沉积的长期记录。 这一记录在研究过去、现在和未来的环境变化方面越来越重要。 沙尘的产生受气候变化的强烈影响，但也对气候产生反馈效应。 大平原中部的黄土记录了过去25，000年来异常快速的灰尘沉积，大大超过了世界其他地方主要沙漠灰尘来源顺风的沉积速率。 这些大平原黄土堆积的高速率挑战了我们目前对主要自然粉尘来源及其过去活动的理解。 这个项目将测试两个假设，可能有助于解释快速黄土沉积在大平原。 有一种假说认为，黄土的快速沉积发生在大面积沙丘形成时，这些沙丘是由先前在中原地区积累的河流和湖泊沉积物形成的。 如果这些沉积物在过去的25,000年里被风改造，它们将被分类为沙丘砂和细粒灰尘。这一假设将通过使用光学测年来比较沙丘区形成和快速灰尘沉积的时间，并通过比较黄土的成分与拟议的源材料进行测试。 第二种假设认为，大平原的尘埃沉积集中在源区附近，导致非常高的沉积率，比其他干旱地区要高得多。 如此高的近源沉积率是由于异常粗糙的尘埃以及尘埃源和尘埃汇之间非常稳定的边界造成的。 通过比较大平原和北方黄土高原下风向黄土沉积速率和粒径的变化趋势，对这一假说进行了验证。 该项目的这一部分将加强在大平原和中国工作的研究人员之间的思想和技术交流，这两个地区都有厚厚的，广泛的黄土沉积物，提供了长期环境变化的宝贵记录。

Loess is essentially an accumulation of atmospheric dust, and thick loess deposits provide a long-term record of dust transport and deposition. This record is of growing importance in research on past, present, and future environmental change. Dust production is strongly influenced by climatic change, but also has feedback effects on climate. Loess in the central Great Plains records episodes of extraordinarily rapid dust deposition over the past 25,000 years, greatly exceeding deposition rates downwind of major desert dust sources elsewhere in the world. These high rates of Great Plains loess accumulation challenge our current understanding of major natural dust sources and their past activity. This project will test two hypotheses that may help explain rapid loess deposition on the Great Plains. One hypothesis states that episodes of rapid loess deposition occurred when large dune fields formed from stream and lake sediments that had previously accumulated in the central Plains. If those deposits were reworked by the wind during the past 25,000 years, they would have been sorted into dune sand and fine-grained dust. This hypothesis will be tested by using optical dating to compare the timing of dune field formation and rapid dust deposition, and by comparing the composition of the loess to the proposed source materials. The second hypothesis proposes that dust deposition in the Great Plains was concentrated near source areas, leading to very high deposition rates, to a much greater degree than in other dry regions. Such high near-source deposition rates would result from unusually coarse dust and a very stable boundary between dust sources and sinks. This hypothesis will be tested by comparing downwind trends of loess deposition rate and particle size in the Great Plains and the Loess Plateau of northern China. This part of the project will enhance interchange of ideas and techniques between researchers working in the Great Plains and China, both regions with thick, extensive loess deposits that provide valuable records of long-term environmental change.