Paleosols in the Luochuan Loess Section

Abstract

There are many paleosols embedded in the loess in northern China, which were formed during the warm humid periods occurring during the Pleistocene. These paleosols vary in their degree of both pedogenesis and weathering, reflecting the intensity of warm humid climate and duration of the period with such climate. Thus, it is considered that paleosols could give a clue to the analysis of paleoenvironments. The present study aims at presenting some supporting evidences to the stratigraphy and chronology of the Chinese loess based on pedoJogical investigations on paleosols.

Paleosols and loess beds from the present land surface through the first “powdery sand” loess were described and sampled in the Luochuan area, Shaanxi Province. The field investigation revealed that S5 has the most highly developed clay ilIuviation horizon and can be classified as a burozem according to the Chinese soil classification system. SI and S4 are next to SS in their degree of development in soil morphology. S2, S3, S6, and S8 are thought to correspond to luvic drab soil, while S7 to drab soil. Modern soil (MS) at the present land surface and SO, which is called locally hei-lu-to and thought to have been formed during the early warm period of the Holocene, are least developed and are classified as dark loessial soils, on account of the dark coloration of their A horizons.

Clay content of 25% demarcated best paleosols and loess samples, the former having all LiC texture, while the latter CL texture. The layer between S6 and S7 is regarded by some researchers as a weathered loess bed and by others as a paleosol. Using textural criteria we considered it as a paleosol and designated it as S6'. Moisture content of air-dried samples served as another criterion. Free carbonate and free iron oxide contents were found to be less reliable as criteria for distinguishing paleosols from loess.

Key Words:

• paleosol
• Chinese loess
• paleoclimate