Soil Erosion During Pleistocene On The Central South Part Of The Loess Plateau

Soil erosion on the Loess Plateau is one of the hotspots of recent research ingeosciences. The available studies mainly focused on soil erosion and sediment yieldmodels,soil and water conservation effect of plant community, physical mechanismof erosion and sediment yield, temporal and spatial distribution of soil erosion, whileonly a few studies for soil erosion in geological time. To understand the erosionhistory of geological period, distinguishing the role of natural erosion and artificialacceleration 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-scaleclimatic fluctuation. Global climate change still should obey its own regularity, whichis regulated by earth orbital parameters, solar cycle and so on; it is independent of thehuman will. Now, the climate is experiencing a transition from warm-wet to cool-dryweather. This study selected Pleistocene as the studying time range, in order toneglect the impact of human activities on the Loess Plateau, and discuss the erosionperiods by pure natural evolve. The central south part of the Loess Plateau is sensitiveto 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 monsooncompletely, all these show that this area is good for ancient climate and ancienterosion study.Through field survey on the study area and sampling analysis in laboratory, wemade clear that climatic change period and fragile ecological environment is thebackground for intensive soil erosion; tectonic uplifting is unsuitable for taking aserosion period, for it lasts for such a long period but could not lead to severe soilerosion. Determining erosion surface is excellent geological record for erosion event or erosion period, and defining erosion surface as unconformity surface between loessand paleosol layers, the erosion surface generally formed in the upcoming period ofpaleosol. The occurrence time of erosion event is the formation time of the bottomlayer of overlying strata over the erosion surface. River terrace might not indicateerosion period; the absent of genetic horizon is normal phenomenon during theformation of loess-paleosol layers; it could not be taken as erosion surface and toobtain erosion period, too.For inversing ancient climate change, Chinese loess records were terrestrialsediments that could compared to those records in ice core and deep-sea. Wecompared magnetic susceptibility curve which shows the intensity change of summermonsoon, ODP677δ18Ocurve and SPECMAP, got 13 climatic change period whichcould be regarded as erosion periods, the occurrence time and corresponding loesslayer 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); 0.621~0.531MaB.P(S5); 0.412MaB.P(S4 bottom); 0.336MaB.P(S3 bottom); 0.245MaB.P(S2bottom); 0.128MaB.P(S1 bottom)。We found 7 erosion surfaces in Luochuan, which record 6 erosion periods, theyare 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 1erosion surface, which indicate two erosion periods: 0.412MaB.Pand 0.128MaB.P。In Tongchuan, we found 4 erosion surfaces, among which 0.531MaB.P isTongchuan erosion period. The other erosion periods occurred at 0.412MaB.P and0.128MaB.P.Caijiapo, Wuzhangyuan, Jiangzhang and Fufeng Town in Baoji, we found9erosion 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 erosionevent happened at 0.128MaB.P. is more severe than the others, many erosion surfaceswere 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 wasfound, 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.Pand 0.865MaB.P.