湖北郧西县庹家湾剖面粒度组成特征及其环境意义

对湖北省郧西县庹家湾(TJW)剖面的地层序列、年代、磁化率及粒度组成进行研究。结果表明:TJW剖面具有表土(MS)→全新世黄土(L0)→古土壤(S0)→过渡层(Lt)→马兰黄土(L1)→黄土与砂互层(T1-al2)→砾石层(T1-al1)的地层序列;在马兰黄土层上部的黏粒含量、黏粒/粉砂值以及磁化率值明显高于典型马兰黄土,而接近古土壤(S0),其成壤作用明显,属于较典型的弱古土壤层(L1-S1和L1-S2),其年龄在27.3~21.6 ka B.P.之间。此现象反映了在汉江上游地区,晚更新世时期的冰期气候并不是持续稳定的,在27.3~21.6 ka B.P.期间存在相对短暂的温暖湿润阶段,这次气候事件可与黄土高原地区进行良好对比。

GRAIN SIZE DISTRIBUTION AND ITS SIGNIFICATION IN TUOJIAWAN PROFILE,HUBEI PROVINCE

The Loess-palaeosol profile was surveyed in detail and sampled systematically at the Tuojiawan site on the first river terrace in the upper Hanjiang valley. The stratigraphic and sedimentological characteristics, pedogenic modification characteristics and the profile structure were observed in the field. Magnetic susceptibility, particle-size distribution and optical luminescence dating(OSL) were analyzed in laboratory. The results showed that TJW profile recorded the environment features and evolution with the stratigraphic series on the first terrace from the bottom to the top was listed as fluvial gravel(T_1-al1)→eolian loess and alluvial sand inter-beds(T_1-al2)→Malan loess(L₁)→transitional loess(L_t)→palaeosol(S₀)→recent loess(L₀)→modern soil(MS). Different degree of weathering intensity in different stratigraphic. The content of clay, clay/coarse silt ratio, magnetic susceptibility in the top of Malan loess were higher than those in the typical Malan loess. It was showed that the weathering intensity on the top of Malan loess (228~260 cm and 294~370 cm) was obviously higher than that on malan loess, close to the palaeosol(S₀), belongs to the weak palaeosol(L₁-S₁ and L₁-S₂). The OSL age results showed that the two layers of weak palaeosol (L₁-S₁ and L₁-S₂) were deposited between 27.3 and 21.6 ka BP. TJW loess-palaeosol sequence recorded monsoonal climate change since Pleistocene. Including the cold and arid glacial and a short time the climate was warm and wet in the glacial period(27.3~21.6 ka BP), the gradually intensified southeast monsoon during the early Holocene periods, the strongest monsoon in the mid-Holocene, and the monsoon recession and the climate drying during the late Holocene.