| Soil erosion rule for nearly500years is of great significance for the establishment of the Loess Plateau Soil Erosion management. Through the Loess Plateau Zizhou extensive fieldwork, I Select a small beach sediments are flood ditch after Zizhou Pang Small Watershed in Loess depression as the main object of study. Loess-lying southern Zizhou is the oldest whole red all-natural poly marsh sediment type in China which has been dated to440a BP. It is an excellent source to study its physical and chemical properties of the sludge. In this way, not only the reason of soil erosion in the Loess Plateau and the sedimentary environment at that time can be revealed but also some basic data and scientific basis for soil erosion can be provided for governing the Loess Plateau Soil Erosion.This study is supported by the National Natural Science Foundation (41071012) Based on the sedimentary characteristics during our fieldwork and data analysis in laboratory, macro sedimentological characteristics, particle size distribution and geochemical elements characteristics of small beaches ditch cross-section can be summed up. Besides, the sediment provenance, sedimentary environment, the relationship between the formation of loess deposition profile and regional rainstorm is discussed in this paper. The main ideas are as follows:1) After the depression of small watershed in loess small beach warping dam ditch, the sedimentary cycle shows obviously " coarse-fine-coarse-fine". This sedimentary cycles recorded59times relatively great flood depositions in small beach, thus indicates59times great storm events. Sedimentary cycles in the particle size shows gradually thicken from the very end to the top, Exhibit poly marsh sedimentary features:and the dividing line between the sedimentary cycles is extremely clear.2) Small beach lying ditch cross-section loess silt dam-composed mainly by clay sediment grain size (<5μm), fine sand (5～10μm), coarse silt (10～50μm), very fine sand (50～100μm), fine sand (100～250μm) and a small sample particles>250μm. Characteristics of sectional sediment grain size parameters are as follows:the median diameter between5.3～48.2μm, the average particle size between6.1～50.1μm; standard deviation (Φ values) between1.2to1.92, skewness between0.13to0.48, kurtosis between0.84to1.68, sorting coefficient between0.62to1.41.3) In the Small beach lying ditch cross-section loess silt dam sediments, the most highest average abundance of major elements is Si whose abundance is46.81%, Al and Ca elements followed respectively by9.8%and6.51%. Distribution of major elements can clearly indicate the presence of sedimentary cycles. The performance is each major element values alternating from high to low in the vertical direction:The cross-section of major elements such as Al, Fe, Mg, Ca, K was negatively correlated with the average particle size:show less coarse alluvium in content, and the content of fine particles in the silt layer is more. The average particle size is negatively correlated, Na Si elements have a positive correlation with the average particle size, which is relatively rich in fine-grained silt layer and less coarse silt content in the layer. From the distribution of Si in the profile view, its distribution in the cross section is consistent with the change in the average particle size profile. Distribution of trace elements found can also be a clear indication of the presence of sedimentary cycles. Such as:changes in trace elements Cu, Mn, Rb, Ni, Pb content and the average particle size was a strong negative correlation. The average particle size increases with the content of these five elements show a clear decreasing trend. More relevant than the five elements Sr between elements and the average particle size and the average particle size of less relevance, also show a negative correlation, Pelements and the average particle size shows a weak positive correlation with silt particles that increases.4) The area of loess depression small beach after the watershed which is typical of check dam sedimentary environment is approximately0.1km2. The flood water power formed by hydrodynamic storm is the main driving force in transport and deposition. Although the flood hydrodynamic conditions (moving force) are not the same of the interannual or within the year, changes in the particle size of each deposition cycle is stable instructions depositional environment (deposition power) more stable. Interannual climate change the structure of the sediments which mainly concentrated at the top end of the flood sediments that fine particle component parts. |
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