郧西县庹家湾黄土剖面色度参数特征及其古气候重建

通过对湖北省郧西县庹家湾黄土剖面的色度参数分析,并结合磁化率、粒度、铷锶比(Rb/Sr)指标揭示汉江上游地区风成黄土的色度特征及其与气候变化的关系。应用X-rite VS450型分光测色仪对庹家湾黄土剖面色度参数进行了测量。结果表明:庹家湾黄土剖面红度a*的变化与沉积物氧化铁含量呈显著正相关,平均值由高到低依次为S_0(6.34)MS(5.52)L_t(5.18)L_0(4.98)L_1(4.82)T_(1-al_2)(3.66);亮度L*的变化与氧化铁含量和有机质含量均呈负相关,其中氧化铁含量对L*的影响更大,L*在黄土层出现了峰值;色调角h*在古土壤层呈现低值(68.64°),黄土层呈现高值,a*/b*与h*特征相反,在古土壤呈现高值(0.39),黄土层呈现低值;其中在马兰黄土L_1中存在两层弱古土壤层L_1-S_2、L_1-S_1,其色度参数特征较L_1具有较高的a*值和a*/b*值及较低的L*值和h*。黄度b*指示该区域气候变化有一定的局限性,h*、a*/b*、L*和a*均可作为良好的气候替代指标,a*值和a*/b*值越大指示气候越暖湿,成壤作用越强,L*值和h*越大指示气候越冷干,成壤作用越弱。h*、a*/b*、L*和a*共同记录了该地区晚更新世以来气候经历了晚更新世末期的干冷、全新世早期逐渐回暖、全新世中期的温暖湿润、全新世晚期气候逐渐干冷,在马兰黄土形成时期,气候出现了短暂的温暖湿润期(27.5~21.5ka B.P.)。

Chroma Characteristics and Paleoclimetic Reconstruction of the Loess-paleosol Profile at Tuojiawan in Yunxi County, Hubei Province

Through integrated analysis of the chroma parameters,magnetic susceptibility,grain size and Rb/ Sr ratio of the Tuojiawan loess-paleosol profile in Yunxi County,the correlation between the features of chroma parameters and palaeoclimatic change in the upper reaches of Hanjiang River was revealed.The results showed that:a* was strongly positively correlated with the content of iron oxide,and the average value of a* was significantly different between loess and paleosol layers,andfollowed the order of S0 (6.34) ＞MS (5.52)＞L(5.18)＞L0 (4.98)＞L1 (4.82)＞T1-al2 (3.66).L* was negatively correlated with the content of iron oxide and organic matter,with iron oxide having a greater effect on L*,which reached the peak in the loess layers.h* was the lowest (68.64°)in the paleosol layers,but was high in the loess layers.In contrast,a*/b* was high in the paleosol layers (0.39),but was low in the loess layers.In Malan Loess,there were two weak paleosol layers,i.e.L1-S2 and L1-S1,which showed higher a* and a*/b*,but lower L* and h* than Malan Loess.h *,a*/b*,L* and a* could be used as good indicators of climatic change.A high a* and a */b*,or a low L* and h * indicated that the climate was warm and wet,and the pedogenesis was strong.In conclusion,h *,a*/b*,L* and a * together recorded the climatic evolution since the late Pleistocene:the climatic was cold and dry during the late Pleistocene,but a short warm and wet period happened in the glacial period (27.3-21.6 ka B.P.),then the climatic gradually became warm and humid during the early-mid Holocene.However,cold and dry climate appeared again since the late Holocene in the region.