The Ustic Isohumisol (Chernozem) distributed over the Chinese Loess Plateau: Modern soil or palaeosol?

Abstract

The Ustic Isohumisol (Chernozem), widely distributed over the Chinese Loess Plateau, is classified as a modern soil by agricultural pedologists and as a palaeosol by geoscientists. High-resolution investigations into this soil, including field observations, element analysis, optically simulated luminescence dating and measurements of magnetic susceptibility and particle-size distribution, were carried out over the plateau uplands. The results show that the formation of physico–chemical properties and development of the soil profiles has kept pace with the land surface growth because of incessant dust accumulation during the Holocene. The continuously intensified weathering of accumulated dust from 11,500 a B.P. had resulted in an increased chemical differentiation through time during the early Holocene. The development of the Ustic Isohumisol occurred over the uplands between 8500 and 3100 a B.P., when the chemical differentiation reached its maximum because of increased precipitation and ample soil moisture in response to the mid-Holocene Climatic Optimum. The soil formation had sustained for ca. 5400 years and ceased at 3100 a B.P. A major pedogenic regression occurred from 3100 a B.P. because of climatic aridity and intensified dust accumulation over the Loess Plateau. The newly accumulated loess and topsoil has the Ustic Isohumisol buried at a depth of ca. 50–80 cm in general. The pedogenic regression has been intensified by incorporation of the reworked components by increased runoff and erosion–redeposition. Large-scale land reclamation extended to the uplands at ca. 2170 a B.P. An agricultural landscape of dry farming has formed since ca. 1500 a B.P. Thereafter, the present topsoil has accumulated and has been affected by the intensified cultivation and addition of barnyard manure in history. The solubles are retained in the topsoil because of dry climate and scant soil moisture.