中国南方红土古环境重建中存在的几个问题

随着黄土-古土壤系列在中国北方第四纪古环境演变的成功恢复，对中国南方红土所记录的古环境和全球变化信息的研究也逐渐成为热点。然而，纵观最近10多年来对中国南方红土古环境变化的研究现状，还存在不少问题，一些结论尚难以令人满意，从成因机理上未能给予有力的理论支持。对在风化壳形成机理的认识、风化壳剖面记载环境变化的历史、红土-沉积旋回所反映的古气候变迁、红土和黄土的古环境记录的对比等方面的研究中暴露出的一些问题，本文进行了剖析和讨论。

Problems in the Paleoenvironmental Reconstruction of Laterite in South China

With Successful recovery of loess-paleosol sequence on Quaternary paleoenvironmental change in North China, lateritic research on paleoenvironment and global change has been gradually becoming a hotspot in South China. Despite surveying research results over the last ten years, there are still a few questions. Some conclusions are not satisfactory and provide no forceful theoretic supports from the genetic mechanism,such as follows: First, There is a difference about understanding of weathering crust formation mechanism. The basis of the paleoenvironmental reconstruction of weathering crust is to correctly catch on the forming processes and the focus is the role and status of groundwater, i.e., whether groundwater should be considered as a weathering factor, which bears on the debate. We think that groundwater shouldn't become a factor of weathering action. Especially, from the angle of weathering crust's being the information carrier of environmental change, groundwater can neither record the environmental information,nor modify and destroy environmental records. Second, whether red weathering crust can record the history of environmental change . As the information carrier of paleoenvironmental change, red weathering section may record environmental evolution history, namely, the oldest weathering section top carries the environmental information at the beginning of forming weathering crust , and the interface between bedrock and weathering crust represents weathering characteristics under modern weathering condition. But, owing to superposition of different weathering stages on the same section, migration of elements or minerals within profile during weathering process, weathering action making equilibrium with micro-environment inside profile not local atmospheric environment, and also appearance of 'pedogenic inertia' phenomenon during weathering, to abstract environmental information from different layers in red weathering crust and further deduce Quaternary paleoenvironmental change, is very difficult and challenging. Third, whether laterite-deposition cycles can reflect evolution of paleoclimate. Being different from that loess-paleosol sequence is the direct result in the condition of paleo-monsoon alternative change per se, the weathering intensity of deposit on which red weathering section is developed is more weak than laterite, but this can't make out that deposit was formed in cold stage. Because deposit is formed in aqueous condition and laterite or red wearhering section in aerial condition, laterite-deposit sequence was formed in two kinds of different genetic backgrounds and difference in weathering indices between laterite and deposit has no unambiguous climate indicative meaning. In addition, whether laterite makes equilibrium with environment before new deposit overlying, up to now, can't be identified and saperated effectively. Last, whether paleoenvironmental records between laterite and loess is comparable. Accurate dating is the basis of profile correlation. Because dating of weathering section hasn't been resolved all the while, we can't make a affirmative answer about comparability between red weathering section including laterite-deposition cycles and loess-paleosol sequence at what scale of time and space. In conclusion, Quaternary paleoenvironmental research in South China is full of difficulty, but extensive laterite bears sufficient paleoenvironmental information. Our aim to put forward previous questions is to well resolve them in future, and lateritic paleoenvironmental research in South China will be shoulder heavy responsibilities.