Magnetic and geochemical characteristics of Gobi Desert surface sediments: Implications for provenance of the Chinese Loess Plateau

摘要

Controversy exists regarding the sources of the eolian dust for the immense Loess Plateau of north-central China, the largest accumulation of windblown loess in the world. Because the loess accumulation rate, unit thickness, and particle size all decrease from northwest to southeast, it has long been thought that the northern deserts, especially the Mongolian Gobi, are the major loess source, a view supported by newly applied mineralogical provenance techniques (electron spin resonance, ESR). Here, we examine surface samples from the Gobi Desert and compare their magnetic and geochemical properties with those of last glacial loess samples from across the Loess Plateau region. The mineralogy, geochemistry, and magnetic properties of Gobi Desert samples are variable (most likely reflecting local lithological complexity), distinctive, and, critically, nonoverlapping with the notably homogenous characteristics of the last glacial loesses spanning the Loess Plateau. It is likely that the source areas for the plateau encompass a much larger area than any one proximal desert region, in order to account for (1) the extreme degree of mixing, (2) the volume of loess generated and transported, and (3) the mineralogical and magnetic mismatch evident here between the Mongolian Gobi samples and the last glacial loess.