甘肃白银晚泥盆世古土壤发生学特征及其古环境重建研究

Exploring “Deep-time” paleoclimatic changes and paleoenvironmental events is an essential part of the past global change researches. As an important material for paleoclimate and paleoenvironment reconstruction, paleosol of different ages has been widely studied all over the world. However, there is few report of Sinic Devonian paleosol, and systematical paleoenvironmental reconstruction by Sinic Devonian paleosol is especially scarce..This project will research on the red sediments of the Late Devonian Shaliushui Formation in Baiyin, Gansu province. During field trip we have observed many characteristic macroscopic and microscopic features of paleosol in the red sediments, which were stated as mudstone deposits in previous studies. Based on this prelimilary finding, the project plans to conduct a systematical research of these paleosol-like red sediments, and to prove they are buried paleosol by their pedogenetic and micro-morphological features according to the theory of Quarternary paleosol and modern soil as well. After analyzing pedogenetic features of the paleosol profile, and the relationship between the pedogenesis intensity.and paleoclimate changes, we are going to ascertain reliable parameters reflecting pedogenesis intensity and paleoclimate changes, deduce the temperature and precipitation, and reconstruct the paleoenvironment during the Late Devonian in the study area..This project will provide not only important scientific facts helping to recognize the Late Devonian stratigraphy in the studied area, useful experiences for identifying Deep-time paleosol, but also more comprehensive understandings about the Devonian environment and climate changes.

探索"深时"地球古气候变化及古环境事件是全球变化研究的重要议题。古土壤是恢复古气候环境的重要材料，而国内目前对泥盆纪古土壤的研究匮乏，利用古土壤系统开展晚泥盆世古环境重建方面的研究更是缺乏。本项目选取甘肃白银晚泥盆世沙流水组红色沉积为研究对象，前期考察发现该套地层从宏观和微观方面均表现出古土壤具有的特征，与过去认为的“水成”泥岩具有显著差异。在此基础上，本项目拟基于第四纪古土壤和现代土壤学理论，对白银晚泥盆世红色沉积开展系统研究，从发生学、微形态学等方面提出依据，确证该红色沉积为古土壤。同时通过详细分析研究区古土壤剖面的成壤特征，深入探讨古土壤成壤程度与成土环境的关系，遴选出能够反映古土壤风化成壤强度和古气候变化的可靠指标，恢复研究区古温度和古降水量，重建晚泥盆世古土壤形成时期的古环境。开展本项研究，对重新认识研究区地层、鉴别深时古土壤及理解泥盆纪古气候与古环境变化提供重要的科学依据。

古土壤是恢复古气候环境的重要材料，被埋藏的泥盆纪古土壤经历了复杂的地质环境变化，一般难以辨识。对泥盆纪古土壤的辨识是本项目研究的重点。本项研究通过对甘肃白银晚泥盆世沙流水组地层野外详细观察、描述、分析获取了重要的第一手材料。采样剖面包括磁窑剖面（100个样品）、大红沟剖面（60个样品）、沙流水剖面（30个样品），共采集样品190个。根据土壤层次、结构、根迹、钙结核、黏土胶膜、铁锰胶膜等主要鉴定标志从宏观和微观方面对沙流水组红层沉积进行分析，证实该套红色沉积为古土壤。同时根据肺鱼洞穴、古土壤成壤特征， Rb/Sr、Ba/Sr比率及磁化率等在剖面上的变化，得出研究区晚泥盆时期为半干旱-半湿润季节性气候，植被类型主要为林地和灌木丛。沙流水组地层中古土壤的发现对研究中国西北泥盆纪气候变化有着重要的意义。