会宁地区全新世黄土沉积粒度特征及其古气候意义

Grain Size Characteristics in the Loess-paleosol at Huining Section and Its Signification to Paleoclimate during Holocene

以会宁陈塬剖面全新世段的粒度变化作为主要研究对象,辅以磁化率曲线变化,对该区全新世时期的气候变化进行了初步分析。研究认为,会宁地区全新世时期黄土—古土壤沉积以粗粉砂（16~63μm）为主,占47.99%~55.78%,其次为细粉砂（4~16μm）、砂粒（〉63μm）和黏粒（〈4μm）,对粒度参数的计算显示,该时期粒度组成较单一,分选较差,粒度频率分布曲线较宽平且呈微弱正偏。将气候变化分为4个阶段：16~11.3 ka BP,晚更新世向全新世过渡时期;11.3~8.5 ka BP,波动时期;8.5~4.5 ka BP,变暖时期;4.5 ka BP至今,现代气候时期。粒度指标对气候变化尤其是具有显著影响的气候事件反映更加敏感,对全球性气候变化和东亚季风边缘区区域性的气候变化均有良好记录。

The grain size of Holocene loess in the Huining area was taken as the main subject,and a preliminary discussion was conducted on climate changes during the whole Holocene. Study showed that coarse silt（ 16- 63μm） was a major component of size fraction in the course of Loess-paleosol deposition,accounting for 47. 99%-55. 78%,followed by fine silt（ 4- 16 μm）,sand（ 〉63 μm） and clay（ 〈4 μm）. Through calculating the parameters of grain size,it suggested that the composition was simplex,the sorting was poor,and the curve of grain size frequency distribution was flat and showed a slight positive bias in Holocene. The eolian sediments in Huining were typical,climate changes could be divided into 4 stages： 16- 11. 3 ka BP,late Pleistocene to Holocene transition period; 11. 3- 8. 5 ka BP,change period; 8. 5- 4. 5 ka BP,warming period; and 4. 5 ka BP. Up to now,the modern climate period. Grain sizes were much more sensitive to climate changes,especially to the climate events with significant effects,also they had a good record to climate change for the global and regional edge area of east Asia monsoon.