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

点击翻译按钮获取中文摘要

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.