南方风尘堆积中网纹红土风化成壤特征时空变化和古环境研究

Vermiculated red clay(VRC) is a kind of terrestrial sediments which wide spreads in south China, also is a kind of key records which can be used to study environmental evolution in tropical and subtropical China. Up to date, because of complexities of its soil parent materials, weathering foctors and pedogenesis process, some scientific problems are not still clear such as causes of VRC with climatic signals, temporal-spatial regulations of VRC weathering intensity, and so on. Obviously, it is urgently required to study temporal-spatial variations of vermiculated process based on same soil parent materials. Our study will try to set up a comparable lithostratigraphic sequences of aeolian-dust VRC in mid-subtropics of China by paleomagnetism and optical stimulated luminescence dating. Based on some evidences from geochemistry, pedology, mineralogy, we can reveal the temporal-spatial regulations of VRC, seek some proxy indexes with palaeoclimatic significance, explore palaeoenvironmental features during VRC development. Especially, we can understand paleoclimatic charaterstics during unusually strengthened East Asian monsoon and provide a scientific basis for regional response of global change.

网纹红土是我国长江以南地区大范围分布的陆相沉积，是研究热带亚热带地区环境演化的关键记录。但其母质类型多样，网纹化作用的因素和过程比较复杂，具有气候意义的网纹红土成因，风化程度的时空规律等尚不明晰，迫切需要开展母质相同红土的网纹化过程时空变化研究。项目拟以风尘沉积网纹红土为载体，古地磁和释光测年相结合，建立中亚热带地区网纹红土岩性地层序列对比框架，在此基础上利用地球化学、土壤学、矿物学证据揭示网纹红土成壤特征的时空规律，探索该类网纹红土的网纹化机理与成壤模式，寻求具有气候意义的环境指标，解析网纹发育期古环境特征。本项目的实施，有望进一步理解网纹红土记录的极端暖湿期的古气候变化特征，为全球变化区域响应研究提供科学依据。

网纹红土是中国南方地区古环境研究的重要陆相沉积载体。调查表明，风成加积型网纹红土主要分布于25°N至31°N之间的中亚热带地区。项目以中亚热带皖、浙、赣、湘境内12个典型风成加积型红土剖面为基础，将ESR、OSL和古地磁测年技术相结合，开展典型剖面年代学研究，在此基础上辅以20余处对比采样点，基于土壤学、矿物学、地球化学等多元指标探讨网纹红土风化特征及其时空变化，网纹红土的物源来源和网纹化机制，进而揭示红土区更新世以来古环境演化的特征以及亚热带季风环流的行为特征。项目弥补了金衢盆地红土年代资料缺失的状况，并建立了典型剖面年代学框架，在此基础揭示中更新世以来红土的风化趋势、风化突降事件及气候转型事件，成果与黄土高原西峰剖面长尺度风化记录及湖北三宝洞石笋初始234U/238U值记录的冰量周期有较好的可比性。同时，在充分讨论红基质与白网纹粒度组成、化学组成、风化特征、粘土矿物组成、磁学性质的基础上，关注红基质与白网纹之间铁含量及铁形态特征的差异，构建网纹红土铁迁移模型，理解网纹化机制及其形成环境。尝试探讨加积型红土粉砂粒级地球化学特征的物源意义，为物源示踪提供新的思路。