准噶尔盆地边缘黄土记录的西风区古环境演化特征

Westerly circulation, as a main part of Asia climate system, has deeply influence to the environment of the arid and semi-arid region of China. The Junggar Basin in Xinjiang is an ideal area to explore the evolution of westerlies; Loess on the edge of the basin is the ideal object for regional environment evolution research. However, there are many problems remain to be solved in the study of the Xinjiang loess, such as stratigraphic age, provenance and environmental proxies. .This project selects the loess in the Junggar Basin as the research object, explore difference of loess source characteristics through geochemical means, and collect typical loess sections in different distributed regions, whose time scale will be established by paleomagnetic, OSL, and 14C dating methods. In this research, we will systematic research on environmental proxies, focus on the ecological environmental proxies such as organic carbon isotope and sporopollen, link with particle size, magnetic susceptibility, carbonate and other conventional index. On the base of reliable chronology research, this project is aiming to reconstruction paleoenvironment evolution sequence, then obtain its temporal and spacial variation characteristics, and to explore the law and driving mechanism of westerlies environmental evolution by comparing with the paleoenvironment records from monsoon region, polar, marine and so on. The project has important academic and practical significance for understanding the evolutionary process and driving mechanism of the westerlies and the change of ecological environment in the arid semi-arid area.

西风环流作为亚洲气候系统的重要组成部分，深刻影响着我国干旱半干旱区的环境演变过程。新疆准噶尔盆地地处西风区，其边缘广泛堆积的厚层黄土是研究西风演化的理想材料，但在物源、时代、环境指标意义等方面尚待深入研究。本项目拟在查明黄土分布特征的基础上，采用元素分析和碎屑锆石示踪方法，探讨不同分布区黄土物源特征；选取不同区域典型黄土剖面，运用古地磁、光释光和14C等多重方法建立精确的年代标尺；以有机碳同位素、孢粉等生态环境指标为重点，结合粒度、磁化率、碳酸盐含量等常规指标，建立适用于西风区黄土的环境代用指标体系；结合年代标尺重建古环境演化序列，获取时空变化特征；进而与季风区、极地、海洋等古环境记录对比，探讨西风区环境演化规律及机制。项目研究对认识干旱半干旱区生态环境变化、西风演化过程及驱动机制有重要的理论和现实意义。

本项目在查明新疆准噶尔盆地边缘黄土分布特征基础上，采用元素分析和碎屑锆石示踪方法，系统采集和和分析了黄土样品及可能源区表土样品，探讨了天山北麓黄土物源特征及其与伊犁黄土的物源差异，明确了天山北麓的黄土主要来源于中亚干旱区及准噶尔盆地，且沙漠贡献在黄土分布带内存在东西向变化，其西段与伊犁河谷黄土的物源相近；选取了典型黄土剖面，通过古地磁、光释光测年分析，结合与黄土高原的对比，确定了SW剖面黄土沉积开始于约400ka B.P.。.剖面磁组构分析所指示的主风向随深度存在变化，由下部的东北向逐渐变为西北向，至150ka B.P.逐渐转为西风为主导。结合色度及磁化率等环境指标分析，黄土沉积过程可分为三个阶段，约400~320ka B.P.以相对稳定的西北风为主要搬运动力，沙漠为重要物源；320~150ka B.P.西北风逐渐减弱，西风携带的粉尘比重增加；在150ka B.P.左右出现了搬运动力的明显转变，西风逐渐增强至以西风为主导，气候也由冷干向相较暖湿过渡。.项目研究中的物源分析，为新疆地区风成沉积的物源研究提供了新的地球化学数据，提出了准噶尔盆地边缘黄土在物源上存在东西向分异，且与伊犁黄土有明显相关性；通过黄土剖面研究，明确了天山北麓黄土沉积的起始时间约为400ka B.P.，为西风区黄土及古环境研究提供了新的年代参考，所记录的古环境转变特征，为理解区域构造及西风演化过程具有重要的科学意义。