| 其他摘要 | Soil erosion on the Loess Plateau is one of the hotspots of recent research in
geosciences. The available studies mainly focused on soil erosion and sediment yield
models，soil and water conservation effect of plant community, physical mechanism
of erosion and sediment yield, temporal and spatial distribution of soil erosion, while
only a few studies for soil erosion in geological time. To understand the erosion
history of geological period, distinguishing the role of natural erosion and artificial
acceleration erosion, providing basis for the respective control measures.
It is one of the main issues that how human activities affected the global climate,
and currently, we could not judge the impact of human activities on long-scale
climatic fluctuation. Global climate change still should obey its own regularity, which
is regulated by earth orbital parameters, solar cycle and so on; it is independent of the
human will. Now, the climate is experiencing a transition from warm-wet to cool-dry
weather. This study selected Pleistocene as the studying time range, in order to
neglect the impact of human activities on the Loess Plateau, and discuss the erosion
periods by pure natural evolve. The central south part of the Loess Plateau is sensitive
to the climate change, and has typical loess layers, soil erosion is very conspicuous,
and the loess layer records the intensity change of summer and winter monsoon
completely, all these show that this area is good for ancient climate and ancient
erosion study.
Through field survey on the study area and sampling analysis in laboratory, we
made clear that climatic change period and fragile ecological environment is the
background for intensive soil erosion; tectonic uplifting is unsuitable for taking as
erosion period, for it lasts for such a long period but could not lead to severe soil
erosion. Determining erosion surface is excellent geological record for erosion event or erosion period, and defining erosion surface as unconformity surface between loess
and paleosol layers, the erosion surface generally formed in the upcoming period of
paleosol. The occurrence time of erosion event is the formation time of the bottom
layer of overlying strata over the erosion surface. River terrace might not indicate
erosion period; the absent of genetic horizon is normal phenomenon during the
formation of loess-paleosol layers; it could not be taken as erosion surface and to
obtain erosion period, too.
For inversing ancient climate change, Chinese loess records were terrestrial
sediments that could compared to those records in ice core and deep-sea. We
compared magnetic susceptibility curve which shows the intensity change of summer
monsoon, ODP677δ18Ocurve and SPECMAP, got 13 climatic change period which
could be regarded as erosion periods, the occurrence time and corresponding loess
layer is: 2.580MaB.P（N/Q）; 2.190MaB.P(S29 top); 1.870MaB.P(S26 bottom);
1.240MaB.P(S14 bottom)；1.120MaB.P(S12 bottom); 0.964MaB.P(S9-1 bottom);
0.865MaB.P(S8 bottom) ； 0.760/0.780MaB.P(S7 bottom and top); 0.621~0.531
MaB.P(S5); 0.412MaB.P(S4 bottom); 0.336MaB.P(S3 bottom); 0.245MaB.P(S2
bottom); 0.128MaB.P(S1 bottom)。
We found 7 erosion surfaces in Luochuan, which record 6 erosion periods, they
are 2.580MaB.P; 1.240MaB.P; 1.120MaB.P; 0.964MaB.P; 0.128MaB.P;
0.073MaB.P(L1bottom)。
In Weinan, we mainly studied Yangguo loess-paleosol layer, but only found 1
erosion surface, which indicate two erosion periods: 0.412MaB.P and 0.128MaB.P。
In Tongchuan, we found 4 erosion surfaces, among which 0.531MaB.P is
Tongchuan erosion period. The other erosion periods occurred at 0.412MaB.P and
0.128MaB.P.
Caijiapo, Wuzhangyuan, Jiangzhang and Fufeng Town in Baoji, we found
9erosion surfaces, record 6erosion periods, they are 0.760MaB.P; 0.621~0.531MaB.P;
0.412MaB.P; 0.336MaB.P; 0.245MaB.P; 0.128MaB.P. Among them, the erosion
event happened at 0.128MaB.P. is more severe than the others, many erosion surfaces
were found here.
In Chunhua, we found 3 erosion surfaces, represent 0.710MaB.P, 0.412MaB.P. and 0.128MaB.P. erosion events. While in Yangling, only one erosion surface was
found, indicate at 0.128MaB.P, there was severe soil erosion.
But we found no erosion surface to correspond these 3 erosion periods:
2.190MaB.P; 1.870MaB.P and 0.865MaB.P.
Key Words: Pleistocene; the Chinese Loess Plateau; Soil Erosion; Erosion
Surface; Erosion Period |
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