Luochuan Loess Section Research Articles

A STUDY ON 10 Be IN QUARTZ FROM LOESS OF CHINA (I)——In situ COSMOGENIC ~(10)Be AND EROSION RATES OF SOURCE REGIONS OF LOESS

In situ cosmogenic ~(10)Be in quartz from loess deposited in the last 2,000,000 a is considered to have been derived mainly from initial ~(10)Be in source regions and it bears abundant information about changes in erosion rates of source regions. As [have been estimated, the concentrations of "in situ cosmogenic ~(10)Be" in quartz from samples GL47(L1) andGL83 (L2) collected from the Luochuan loess section are 5×10~5 atom/g and 2.2×10~6 atom/g, respectively. As calculated on the basis of the above estimates, the erosion rates of the source regions are: eBeL1=1.5×10~(-3) cm/a for the L1 period (10,000—90,000 a) and eBeL2=3.8×10~(-4) cm/a for the L2 period (130,000—190,000 a). Studies of "in situ cosmogeuic ~(10)Be" in quartz from loess at deeper levels are expected to be applied to ~(10)Be dating of loess strata.

The magnetic properties of particle-sized samples from the Luo Chuan loess section: evidence for pedogenesis

Measurements of magnetic susceptibility and of laboratory remanences have been carried out on particle size fractions of loess and palaeosol samples from Luo Chuan, China. They show that the sub-micron clay fraction of the palaeosol is greatly enriched in fine-grained (< 0.03 μm) ferrimagnetic minerals and thus confirm the importance of secondary pedogenic components in the magnetic record from the section. The assemblages of magnetic minerals in both the loess and the palaeosol are interpreted as strongly bimodal with inferred detrital and pedogenic contributions to both. Climatically modulated magnetic variations between palaeosols and intervening loess layers arise from fluctuations in the absolute and relative importance of these two components. Of the two, the pedogenic component appears to exercise the stronger control on susceptibility variations in these Luochuan samples.

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

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.

Paleosols in the Luochuan Loess Section

Paleosols in the Luochuan Loess Section

Paleosols in the Luochuan Loess Section

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...

Rare-earth elements in Luochuan loess section, Shaanxi province

TheΣ REE in loesses of different ages in the Luochuan section shows a narrow range of variation, indicating the homogeneity of loessic materials in chemical composition. The REEs in loess are concentrated mainly in silt-sized detrital minerals.Loesses and paleosols of different ages all are relatively enriched in rare-earth elements of the Ce family, and show similar REE distribution patterns. The fractionation among various REEs in the loess is different from that in morainic, marine and lacustrine sediments, but is similar to that in sand samples from deserts in Northwest China.The ratios of Ce/Ce* and Eu/Eu* reflect that the provenance of loessic materials and their accumulating area are all in an oxidation environment with weakly basic mediums under arid or semi-arid climate.