Is a Middle Pleistocene climatic optimum recorded in the loess-palaeosol sequences of Eurasia?

Abstract

An attempted correlation of selected Brunhes and uppermost Matuyama silt sequences in Eurasia and a comparison of the successive pedogenic features raises the question of climatic evolution during the Middle Pleistocene interglacial stages. In the Italian piedmont of the Alps, the strongly developed palaeosols found on the superposed loessic silts show an upward change, particularly clear during Stages 11 and 9, in the characteristics of their Bt horizons. This expresses a progressive shift, during the Brunhes chron, from warm and humid to relatively cooler and drier interglacial conditions. A simultaneous progressive change in palaeosol features is found in the loess sequences of different climatic regions in western and central Europe and in central Asia. This is in marked contrast to the Loess Plateau of central China where the best developed palaeosol (S5-1) correlates with Stage 13. The existence of S5 has recently been referred to Penck and Brückner's Great Interglacial of the Alps, a classic concept which is, however, clearly contradicted by the loess-palaeosol record in this region. Apart from the Loess Plateau, which may have experienced some regional irregularities in the strength and extent of the summer monsoon, there is no evidence from the loess-palaeosol record to support the occurrence of a Middle Pleistocene climatic optimum in Eurasia.