Micromorphology and genesis of paleosols in the Luochuan loess section, China: Pedostratigraphic and environmental implications

Abstract

The loess-paleosol sequence in the well known Potou section near Luochuan covers the entire Pleistocene back to 2.5 Ma in a much more complete sequence than any known from Europe or North America. To deduce a record of the Pleistocene climatic history an understanding of the genesis of the paleosols is important. Main diagnostic features normally observable in surface soils have disappeared in the case of fossil soils; therefore micromorphology is of outstanding importance because it enables the reconstruction of original properties and polygenetic soil development, especially in pedocomplexes. The upper part of the loess-paleosol sequence can well be compared with the δ 18 O-record shown in the SPECMAP curve of the Brunhes epoch although the sequence of paleosols shows partly an even more detailed record of cold and warm stages and allows more specific informations regarding the paleoclimate of the interglacial periods (cf. Fig. 2). The last four paleosols, represented by the S1-pedocomplex, the upper part of the S2 and the S3 are genetically well comparable with the natural Holocene soil, indicating a similar climate with a tall grass steppe vegetation. The S6 is a steppe soil also, whereas the five soils of the S4, the S5-complex and the S7 are forest soils, indicating more moist and partly warmer interglaciations than the Holocene. The loess-paleosol sequence of the Matuyama epoch seems to give more paleoclimatic informations than the deep-sea cores known so far. The Lishi loess below the B/M-boundary down to 84 m in the section contains two more soils (S11 and S13) which are developed under steppe vegetation in interglaciations similar to the present one and four forest soils (the S8-complex, the upper soil of the S9 and the S10) indicating again more moist interglaciations than the Holocene. Most of the numerous soils in the Wusheng loess are probably formed synsedimentarily as alternation of soil formation and addition of loess. The “Red Clay” at the basis consists of four intensively developed but truncated paleosols; the parent material of at least the lower part must be regarded as Pliocene loess.