Regional lithofacies and pedofacies variations along a north to south climatic gradient during the Last Glacial period in the central Loess Plateau, China

Five lateral sand–loess–palaeosol continua occur within the last glacial sediments of the central Loess Plateau of China along a 500 km north to south climatic gradient. The continua shift southward or northward in concert with desert expansion or contraction, respectively. Lateral lithofacies (desert sand to loess) variations are evident at the north end of the gradient and follow Walther's Law of the correlation of facies. Lateral pedofacies (loess to palaeosol) variations are present near the south end of the gradient, where the climate was warmer and wetter. The lateral stratigraphic changes from sand to loess or loess to soil are driven by variations in the rate of sedimentation along a climatic gradient. Vertical stratigraphic profiles at the north end of the gradient reveal alternating sand and loess beds. In contrast, alternating loess and palaeosols occur within the same stratigraphic interval in the southern Loess Plateau, where dust accretion rates were lower. However, in high resolution studies of climate change vertical profiles of alternating loess and palaeosols (especially weak palaeosols) may not reflect regional or global climate change. Alternating loess and weak palaeosols may reflect local variations in the balance between the rates of dust accretion and pedogenesis. Local fluctuations in either of these rates could result in the presence of time equivalent loess and palaeosols at high resolutions. Thus, some of the high resolution loess-palaeosol alternations may reflect local climatic variation rather than global or hemispherical climate change.