Holocene dust accumulation and the formation of polycyclic cinnamon soils (luvisols) in the Chinese Loess Plateau

Abstract

Chinese loess-palaeosol sequences are well known for their records of monsoonal climatic variations. However, the modern processes of dust accumulation and soil formation remain poorly understood. A high-resolution investigation on modern soils, including the measurement of magnetic susceptibility, particle-size distribution, total Fe, total organic carbon, CaCO 3 content, and optical stimulated luminescence (OSL) dating was carried out on the Zhouyuan loess tableland in the southern Loess Plateau. The results indicate that modern cinnamon soils (luvisols) have developed on contemporarily accumulated aeolian dust during the Holocene. The aeolian loess accumulated during the Younger Dryas was identified in the top part of the Malan Loess that underlay the modern soil by OSL dating and proxy climatic data. It indicates that the Malan Loess accumulated during the last glaciation (marine isotope stages 2-4) does not serve as the parent material for the modern soils. Pedogenesis of the soils started with the increased precipitation and soil moisture that have occurred on the loess tableland since the early Holocene. Precipitation-driven pedogenesis and organic activities are responsible for the leaching of CaCO 3 , decomposition of mineral dust and the production of clay and ferromagnetic minerals. Drier intervals have interrupted soil formation several times, and therefore profiles with multiple soils have been developed at many sites on the loess tableland. At places where soil erosion was relatively strong, either a single soil or welded soils are preserved in the Holocene profiles. This does not necessarily mean, however, that modern soils over the plateau have been developed without interruption under a constantly warmer, moister climate. This is significant for understanding the surface processes and climatic variation during the formation of the numerous palaeosols over the Loess Plateau in the Quaternary.

Chronology of the Holocene loess-paleosol section and its deposition and pedogenesis on the south of Chinese Loess Plateau

“…It is noticed that this continuous aeolian loess accumulation rate is mainly determined by the upper part of the S 01 unit, formed at the end of the Holocene Climatic Optimum. During that period, the East Asian summer monsoon did not show obviously weakening, confirmed by proxy records of Li/Ba ratio, Rb/Sr ratio and MS (Figure 4), but the East Asian winter monsoon had already intensified as shown by the decreased fine sand in this stratum in the section (Figure 5), and as also supported by the other studies (An, 2000;Huang et al, 2003;Mayewski et al, 2004). This further indicates that, firstly, there exist asynchronous changes on millennial to sub-millennial timescales between the East Asian winter monsoon and summer monsoon, showing the winter monsoon change occurs slightly prior to the summer monsoon change (Xiong et al, 1996;Yuan et al, 2004;Stevens et al, 2007); secondly, the loess accumulation rate is mainly controlled by the winter monsoon, which determines the total aeolian-dust input.…”

“…But by detailed analysis of MS, Rb/Sr ratio and Li/Ba ratio in the early Holocene, it is shown that these proxy values are still low (Figure 3), indicating a relatively weak pedogenesis during that period. Many studies suggested that ecologic condition had not still recovered during the period that climate was shifting from the onset of the Holocene to the Holocene Climatic Optimum in loess depositional area (Huang et al, 2003;Kohfeld and Harrison, 2003;Mayewski et al, 2004), thereby the pedogenic intensity of loess deposit, mainly controlled by climatic and ecologic conditions, was still weak. This suggests that influencing factor on loess deposition is mainly controlled by winter monsoon intensity, but as to pedogenesis it is related to various factors, such as local climate, geomorphology, ecology, and even deposition rate.…”

“…(An et al, 1991;Kalm et al, 1996;Zhao, 2002;Ding et al, 2002;Chen et al, 2003;Jia et al, 2005), providing the essential information for the paleoclimate reconstruction; the second one is chronology of the reconstructed paleoclimate change (Guo et al, 2002;Lu et al, 2004;Steven et al, 2006), which offers a possibility to correctly understand deposition and pedogenesis of aeolian loess deposit. By using various proxy records within loess deposit, the essential climate change information has already been obtained over the Latest Pleistocene and the Holocene in the Guanzhong Basin (Shi et al, 1994;Lu et al, 1997;Huang et al, 2001Huang et al, , 2002Huang et al, , 2003Huang et al, , 2004Pang and Huang, 2006), south of the Chinese Loess Plateau. But unfortunately, chronologies of loess-paleosol sequences, especially dated using absolute methods are extremely sketch.…”

Holocene colluviation and its implications for tracing human-induced soil erosion and redeposition on the piedmont loess lands of the Qinling Mountains, northern China

“…The chronology was based on optical simulated luminescence (OSL) dating and archeological identification of the pottery shards collected from the profiles, representing different cultures for which 14 C ages are available (Institute of Archaeology, CASS, 1991). The chronology was checked with pedostratigraphic correlation with other dated Holocene loess-soil profiles in the Weihe River valley (Huang et al, 2003). OSL dating was carried out on a Risø-TL/OSL-DA15 Dating System using the fine-grain single-aliquot regenerative-dose protocol (Murray and Wintle, 2000) under the supervision of professor Huhou Li in the TL/OSL dating laboratory of Shaanxi Normal University.…”

Holocene loess and its deposition dynamics in the upper reaches of the Huaihe River

“…It has been proved that the dust of the Loess Plateau mainly comes from the northwestern inland gobi and desert, transported by the East Asian monsoon systems and westerlies (Liu, 1988;An et al, 1991a;Zhang et al, 1994Zhang et al, , 1997Zhang et al, , 2001Lu et al, 2000;Huang, 2001;Huang et al, 2003;Sun, 2002Sun, , 2004Mayewskia et al, 2004). Along the dominant wind directions from northwest to southeast, the grain size decreases downwind by sediment sorting, so that the sediment represented zonal distribution, consisting of aeolian sand, sandy loess, loess and clayey loess in turn (Liu, 1988).…”