【作者】 伍铁牛；

【导师】 雷廷武；

【作者基本信息】 中国科学院研究生院（教育部水土保持与生态环境研究中心） ， 土壤学， 2010， 博士

【摘要】 黄土高原土壤侵蚀在近几十年一直是地学界研究的热点内容之一。现有的目标和成果多集中于侵蚀产沙模型、各种植被的水土保持效应、降雨侵蚀产沙的物理机制、土壤侵蚀的时空分布等方面,而对地质时期的土壤侵蚀问题研究较少。了解黄土高原在地质时期的侵蚀历史,以区分自然与人为侵蚀各自的作用,为相应的防治对策提供依据。人类活动影响全球气候为当前世界关注的焦点,但对于长时间尺度的气候冷暖旋回的影响程度现在尚不能做出判断。全球气候变化依然要服从其固有的规律,是地球轨道参数、太阳活动周期等因素共同作用的结果,不会以人类的意志转移。当前正处于气候由暖湿转冷干的过渡时期。本文选取更新世作为研究的时间范围,以忽略人类活动对黄土高原土壤侵蚀的影响,而从纯自然环境演变来探讨黄土高原中南部的土壤侵蚀期;黄土高原中南部为气候变迁敏感地区,黄土地层典型,土壤侵蚀问题较为突出,对冬夏季风强弱变化记录完整,有利于开展古气候与古侵蚀研究。通过对研究区的野外考察和采样分析,明确了更新世黄土高原发生强烈侵蚀的环境条件是气候过渡期及脆弱的生态环境;认为构造抬升期由于其持续时间过长、引起的土壤侵蚀强度与范围有限而不作为侵蚀期加以研究;确定侵蚀面是土壤侵蚀事件或侵蚀期良好的地质记录,将黄土高原的侵蚀面定义为黄土-古土壤地层中由于侵蚀而形成的不整合面,这些不整合面一般形成于古土壤发育期即将开始的时期;以侵蚀面上覆地层底部的形成时间近似为侵蚀期的发生时间;认为河流阶地不一定都能指示侵蚀期;古土壤发生层次的缺失是黄土-古土壤地层形成过程中正常的地质现象,也不能作为侵蚀面来推求侵蚀期。中国黄土沉积是与冰芯、深海记录相媲美的反演古气候变迁的载体之一。通过对洛川与杨凌第四层古土壤的采样分析,得出MIS11时期研究区气候稳定、极端气候事件少见,以此认为此期不应成为强烈侵蚀期。将反映夏季风强度变化磁化率曲线与ODP677δ18O曲线、SPECMAP相比照,得出了13个可能是侵蚀期的气候过渡期,其发生时间和对应的黄土地层层位分别是:2.580MaB.P(N/Q);2.190MaB.P(S29上部);1.870MaB.P(S26下部);1.240MaB.P(S14底部);1.120MaB.P(S12底部);0.964MaB.P(S9-1底部);0.865MaB.P(S8底部);0.760/0.780MaB.P(S7底部和上部);0.621~0.531MaB.P(S5);0.412MaB.P(S4底部);0.336MaB.P(S3底部);0.245MaB.P(S2底部);0.128MaB.P(S1底部)。在洛川找到了7处侵蚀面,分别记录了2.580MaB.P;1.240MaB.P(S14底部);1.120MaB.P;0.964MaB.P(S9-1底部);0.128MaB.P(S1底部)和0.073MaB.P.共计6个侵蚀期。在渭南重点考察了阳郭镇的黄土-古土壤地层,仅发现了一处典型的侵蚀面,指示0.412MaB.P和0.128MaB.P两个侵蚀期。在铜川市王益区和印台区找到了4个侵蚀面,其中S5-3与下伏地层的不整合面是铜川期侵蚀留下的侵蚀面,记录了0.531MaB.P的侵蚀期。其余地层记录了0.412MaB.P,0.128MaB.P两个侵蚀期。在宝鸡市岐山县蔡家坡、五丈原和扶风县县城、绛帐等地的考察一共找到了10处侵蚀面,记录了0.760MaB.P,0.621~0.531MaB.P,0.412MaB.P,0.336MaB.P,0.245MaB.P和0.128MaB.P共计6个侵蚀期。其中0.128MaB.P发生的侵蚀事件普遍而强烈,有多处侵蚀面发现。在淳化找到了3个侵蚀面,代表0.710MaB.P,0.412MaB.P和0.128MaB.P三个侵蚀期。杨凌黄土地层记录了0.128MaB.P发生的强烈侵蚀事件。而2.190MaB.P;1.870MaB.P和0.865MaB.P这3个理论气候侵蚀期没有发现对应的侵蚀面。更多还原

【Abstract】 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.更多还原