郧县前坊村剖面黄土-古土壤序列风化成壤及古气候研究

秦岭作为我国南方和北方地理、气候、自然环境的天然分界线，并当作是黄土高原的南屏障。汉江上游谷地地区位于秦岭南侧，属于北亚热带气候区域，受季风气候活动影响强烈。为了探讨该地区在亚热带气候背景下，风成黄土成壤改造对气候变化的响应机制，通过对汉江上游谷地前坊村（QFC）剖面磁化率、烧失量、粒度、Rb/Sr等理化性质进行研究。结果表明:①末次冰期以来沙尘暴很有可能越过秦岭在其南侧堆积，黄土-古土壤剖面地层序列从上到下依次为:MS-L₀-S₀-Lt-L₁-AD；这些沉积物完整记录了一级阶地上晚更新世气候变化信息，地层单元受到各个时期不同程度成壤强度的改造。②前坊村剖面中，理化性质在不同地层单元有显著差异。例如磁化率、烧失量、Rb/Sr指标平均含量的高值出现在古土壤层中，低值出现在黄土层；而Zr/Rb含量变化正好相反；这些理化性质表明，在古土壤发育期，水热条件进入最适宜期，沉积物的风化成壤作用显著；在黄土堆积期，气候寒冷干燥，主要以粉尘堆积为主，沉积物的风化成壤作用较弱。③秦岭南侧北亚热带汉江上游前坊村一级阶地剖面化学风化强度变化揭示了黄土-古土壤环境气候变化的规律:末次冰期以来（大约18.0～11.5 ka B.P.），气候干冷，沙尘暴频繁出现，沉积物以黄土堆积为主，成壤作用微弱，形成马兰黄土（L₁）；全新世早期（约11.5～8.5 ka B.P.），气候由干冷向暖湿方向转变，但主要以干冷为主，形成过渡层（Lt）；在全新世大暖期（8.5～3.1 ka B.P.），气候条件达到最优阶段，水热配合较好，生物活动活跃，成壤作用十分显著，发育了古土壤S₀；到了全新世晚期以来（3.1 ka B.P.）气候又由暖湿向干冷方向转变，成壤作用明显减弱，沙尘暴出现较为频繁，形成了以黄土堆积为主的全新世黄土（L₀）。现代表土层（MS）是在（1.5 ka B.P.）以来气候转暖，加之人类长期农业耕作扰动，在全新世黄土L₀顶部叠加而形成的。

Study on Loess-Weathering Paleosol Sequence and Paleoclmate Evolution in QFC Profile in Yunxian,China

Qinling Mountains as a natural boundary of South-North of China geography, climate, natural environment, and as the Loess Plateau of South barrier. The upper reaches of Hanjiang River valley area is located in the south of Qinling Mountains, belonging to the northern tropical climate. Through the upper reaches of Hanjiang QFC profile susceptibility, loss on the ignition, particle size, Rb/Sr and other physicochemical properties were studied. The results showed that: (1) since the last glacial dust storms may well crossed the Qinling Mountains in the south of accumulation, Loess-Paleosol sequence stratigraphic sequence from top to bottom: MS-L₀-S₀-Lt-L₁-AD; these sediments records recorded a complete terraces of the late Pleistocene climate change information, stratigraphic units by various periods of different periods of different degree of intensity of soil information. (2) Physical and chemical properties were significantly at different stratigraphic units of QFC profile. Such as magnetic susceptibility, LOI, high value of Rb/Sr index average content appear in paleosols, the lower value in the loess layer, and the change of the content of Zr/Rb is just the opposite; these physicochemical properties suggest that the development of paleosol period, hydrothermal conditions into the most suitable period, sediment weathering pedogenesis significantly; in the stage of loess accumulation,cold and dry climate, mainly by the dust deposition, sediment weathering pedogenesis weaker. (3) Qinling Mountains South North Asia tropical upper reaches of Hanjiang River Front terrace profile of chemical weathering intensity change reveals the loess paleosol climate changes: since the last glacial period (about 18～11.5 ka B.P.), climate is dry, frequent sandstorms, sediment in the loess accumulation, pedogenesis weak, forming a typical loess (L₁); the early Holocene (about 11.5 ~8.5 ka B.P.), climate change from dry and cold to warm and humid direction, but mainly in the dry and cold, to form a transition layer (Lt); in the Holocene warm period (8.5 ~3.1 Ka B.P.), climate conditions to achieve the optimal stage, with good heat water, biological activity active, pedogenesis is very significant, development of ancient soil S₀; Since the late Holocene (3.1 Ka B.P.), climate change from warm humid to cold direction, pedogenesis significantly weakened, sand storms appear more frequently, formed in loess deposits of Holocene loess based (L₀). Modern surface layer (MS) in(1.5 Ka B.P.), since the climate warming, and our long-term agricultural tillage disturbance, formed in the Holocene Loess L₀ top stack.