金衢盆地加积红土多指标记录的环境变化

Environmental Changes in Jinhua-Quzhou Basin: A Study Based on the Recording of Aggradation Red Earth's Multi-index

金衢盆地连片、集中分布有较厚的第四纪古红土。选择汤溪(TX)加积型红土剖面进行了磁学、色度和粒度的测量,研究结果表明:1)剖面上段的表土层和均质红土层磁化率高,磁性矿物以亚铁磁性矿物为主;剖面中段的网纹红土层磁化率低,磁性矿物以不完整反铁磁性矿物(如赤铁矿)含量为主;剖面底部的黄色网纹化砾石层磁化率低,磁性矿物以不完整反铁磁性矿物为主。2)色度指标值(a*、b*、L*)偏高说明东部季风区湿热的气候条件,不同层位的差异说明不同层位具有不同的成土环境。3)粒度组成显示有一定的风成沉积特征,比较一致,以粉砂为主,但不同土壤层之间存在差异。剖面底部黄色网纹化砾石层可能为干冷的早期河流沉积环境;中部网纹红土层反映的是暖湿多水而且干湿交替变化频繁的沉积环境;上部均质红土层则反映了与现代区域气候相似的沉积环境。

Jinhua-Quzhou basin has a concentrated distribution of the thick Quaternary red earth. In this study,we investigated TX aggradation red earth profile with the method of magnetism,chromaticity parameters and grain size. The results suggest： 1） The surface earth and typical red earth of the upper section have a high magnetic susceptibility and high concentration of magnetic minerals. The magnetic minerals is mainly ferromagnetic minerals. The plinthitic red earth in the middle part of the profile has a low magnetic susceptibility and concentration of magnetic minerals. The magnetic minerals is mainly antiferromagneric minerals（ such as hematite） The yellow plinthitic gravel earth in the bottom of the profile has a low magnetic susceptibility and concentration of magnetic minerals,The magnetic minerals is mainly antiferromagneric minerals. 2） The value of chromaticity parameters（ a＊、b＊、L＊） is high,which suggests their different forming environments. 3） Grain size distribution shows some aeolian deposition characteristics,it is mainly silt fraction and relatively unanimous,but there＇re differences between different earth. The yellow plinthitic gravel earth in the bottom of the profile may form in early river sedimentary and dry-cold environment. Aggradation red earth in the middle of the profile reflects the sedi-mentary environment was warm-wet and dry-wet alternation of frequent changes. The typical red earth of the upper profile reflects that sedimentary environment was similar to the modern regional climate.