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Crescentic dune migration and stabilization： Implications for interpreting paleo-dune deposits as paleoenvironmental records

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Journal of Geographical Sciences 2017年第11期27卷 1341-1358页

作者： XU Zhiwei Joseph A. MASON LU Huayu YI Shuangwen ZHOU Yali WU Jiang HAN Zhiyong School of Geographic and Oceanographic Sciences Nanjing University Nanjing 210023 China Department of Geography University of Wisconsin Madison Wl 53706 USA School of Geography and Tourism Shaanxi Normal University Xi'an 710062 China

Paleo-dune deposits have been widely used as a proxy indicator of past dune ac- tivity, which is further used to reconstruct paleoclimates. However, recent studies have criti- cally examined the reproducibility of dune chronologies and the complexity of paleo-dune deposits as paleoenvironmental records. This paper addresses questions on the paleoenvi- ronmental implications of dune chronostratigraphies that have been raised by those reviews, in the specific case of crescentic dunes, using a case study from the Mu Us dune field, north-central China. The processes of turn-over and stabilization of relatively small crescentic dunes are first investigated by observational evidence. In combination with the analysis of a simplified sand preservation model and stratigraphic records, the effect of dune morphody- namics on sand preservation is demonstrated. It is especially evident that thick, nearly in- stantaneously deposited sand units record dune stabilization near the very end of a dune activity episode, while thin sand units may signal the preservation of sand deposited earlier in episodes of activity. Interpreting the distribution of luminescence ages that indicate sand deposition over time is not as simple as assumed in some previous work. Low frequency of sand ages could indicate an interval of either dune field stabilization or extensive dune activity but poor sand preservation. A peak of sand age frequency likely represents a shift in dune field activity towards stabilization, not a peak of active dune extent, especially if it partially overlaps with an independently identified interval of stabilization （e.g. one recorded by pa- leosols）. The nature and magnitude of these biases in the distribution of sand ages over time are strongly affected by the magnitude of net sand accumulation, which is in turn related to sand supply, transport capacity and sand availability, and ultimately climate change. Rela- tively short dune stabilization and turn-over time （101 to 102

关键词： dune activity dune chronologies dune morphodynamics dune turn-over time OSL dating paleoen- vironmental interpretation

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