泾阳泾河段全新世剖面元素地球化学特征与洪水变化

Element Geochemical Characteristics and the Flood Changes at the Holocene Profiles in Jinghe Valley of Jingyang

根据泾阳泾河一级阶地前缘沉积剖面(JYc)中285个样品的元素、化合物含量和粒度分析,对泾阳泾河段全新世剖面元素地球化学特征与洪水变化进行研究,结果表明,元素Mn、Ni、Cu、Zn、Ga、Pb、Sc、Ti、Nb、Th、U、Rb、V、Ba、Co和化合物Al2O3、Fe2O3、K2O含量在剖面各层中变化明显,分辨率高,能够清晰地指示洪水以及降水量的变化;JYc剖面分为41个沉积层,指示了41次大小不同的洪水和41个降水较多的年份;沉积物粒度细,元素Mn、Ni、Cu、Zn、Ga、Pb、Sc、Ti、Nb、Th、U、Rb、V和化合物Al2O3、Fe2O3、K2O含量高,元素Ba、Co含量低,指示沉积时洪水强度小,洪水位低,降雨量少;沉积物粒度粗,元素Mn、Ni、Cu、Zn、Ga、Pb、Sc、Ti、Nb、Th、U、Rb、V和化合物Al2O3、Fe2O3、K2O含量低,元素Ba、Co含量高,指示沉积时洪水强度大,洪水水位高,降雨量多。泾河泾阳段洪水代表的是黄土高原泾河流域的洪水,特大洪水与大洪水,来自整个泾河流域或泾河流域大部分地区,较小的洪水来自泾河流域小部分地区。泾河流域发生洪水的原因有3种:1.年降水量明显增加造成;2.年降水量没有增加,而是由短时暴雨造成;3.年降水量没有增加,而是由于降水集中、持续时间长造成的洪水。泾河泾阳段JYc剖面的洪水沉积主要是由中度涝灾、大涝灾、特大涝灾形成的,轻度涝灾一般不会造成洪水灾害。

Based on the grain size and geochemical element from the 285 samples taken in the front of the first ter- race at the Jinghe vally of Jingyang, the relationship between the element geochemical characteristics and the flood changes at the Holocene was studied. The results show that the content of Mn, Ni, Cu, Zn, Ga, Pb, Sc, Ti, Nb, Th, U, Rb, V, Ba, Co, A1203 , Fe203 and K20 change obviously in the profile. Each component changes obviously in the entire profile, which can clearly reflect the variations of flood and precipitation with high resolving power. The pro- file may be divided into 41 sediment layers, indicating 41 flood events at different scales and 41 years with much precipitation. The finer grain size is, the higher contents of Mn, Ni, Cu, Zn, Ga, Pb, Sc, Ti, Nb, Th, U, Rb, V, A1203, Fe203 and K20 are and the lower content of Ba, Co are, which indicates small flood intensity, low flood level, and less precipitation in deposition. In contrast, the coarser grain size is, the lower contents of Mn, Ni, Cu, Zn, Ga, Pb, Sc, Ti, Nb, Th, U, Rb, V, A1203 , Fe203 and K20 are and the higher content of Ba, Co are, which indicates high flood intensity, high flood level, and more precipitation at deposition. The floods of Jingyang reach at Jing River represent the floods of Jing River basin in Loess Plateau. Catastrophic floods and big floods came from the whole drainage ba- sin of the Jing River or the large parts of the basin. Moderate floods came from the small parts of the basin. There are three causes to cause flooding in Jing River, i. e drastic increase in annual precipitation, episodic rainstorm without increase in annual precipitation and concentrative and long-time rainfall without increase in annual precipita- tion. The flood sediments in the section of JYc were supposed to be resulted from the moderate flooding disaster, big flooding disaster and catastrophic disaster.