柴达木盆地西部盐湖沉积岩相特征记录的亚洲内陆干旱化

In the past several decades, the history and forcing mechanism of Asian interior aridification has attracted considerable interest and has been extensively studied. However, due to absence of paleoclimatic record driectly obtained from Asian inland, there are still many unsolved problems related to Asian aridification. The Qaidam basin in the northeastern part of Tibetan Plateau is directly situated in the arid Asian inland, with a thickness of more than 10,000 meters sediments which provide a good opportunity for investigating history and forcing mechanism of aridity in Asian inland. This proposal will carry out a systematic lithofacies analysis on saline deposits exposed by two new deep cores, namely SG-1b (723m，7.3-1.6Ma) and SG-3 (600m，3.1-0.01Ma) in western Qaidam basin. Analysis techniques such as detailed core-section description, thin section, mineral components, grain size, and elements, aiming to recognize lithofacies types and related paleoclimatic information. On the basis of lithofacies variation and previous paleoclimatic results retrieved from SG-1 core (938.56m，2.8-0.1Ma), we will reconstruct a high-resolution arid paleoclimatic record in Qaidam basin since 7.3Ma , and hence reveal arid events in Asian inland during this time interval. Based on correlation of regional climatic changes with uplift of Tibetan Plateau and global ice volume, we will discuss the forcing mechanism of aridification.

亚洲内陆干旱区是地球环境系统的重要组成部分。长期以来，有关亚洲内陆干旱化的起始时间、演化过程和驱动机制存在许多争议，根本原因在于缺少直接来自亚洲内陆干旱区的地质记录。青藏高原东北部的柴达木盆地位于亚洲内陆干旱区，独特的地理位置使其成为研究亚洲内陆干旱化过程和机制的极佳场所。本项目拟对柴达木盆地西部新获取的SG-1b（723m，7.3-1.6Ma）和SG-3（600m，3.1-0.01Ma）深钻所揭示的盐湖沉积进行系统的岩相学研究，通过精细的岩芯观察、薄片分析、矿物鉴定、粒度和元素分析等方法识别岩相类型并判定其古气候意义，根据岩相组合的变化规律结合前期中德千米科学深钻SG-1孔（938.56m，2.8-0.1Ma）的已有成果，首次从沉积岩相学角度定量-半定量的建立柴达木盆地7.3Ma以来高分辨率的内陆干旱气候记录，厘定这一期间亚洲内陆干旱区的干旱事件，探讨盆地晚中新世以来干旱历史的驱动因素。

通过详细的岩芯手标本观察描述、薄片分析、X射线衍射和扫描电镜等手段，对柴达木盆地西部7.3 Ma以来的盐湖沉积进行精细的岩相学和古气候环境研究。主要取得了三方面的研究成果：（1）通过研究柴达木盆地西部地表盐湖和千米深钻SG-1、SG-1b孔的古代盐湖沉积特征，建立了识别不同盐湖沉积亚环境的岩相标志。包括盐泥坪（含盐/膏泥岩）、盐盘/暂时性盐湖（溶蚀石盐）、常年性盐湖（人字形石盐）、常年性分层深盐湖（底部生长石盐）等4种盐湖沉积亚环境；（2）恢复了柴达木盆地西部7.3 Ma以来的盐湖沉积序列与干旱化的演化过程。精细的岩相学分析和古沉积亚环境解译确定出3.6 Ma、3.3 Ma、2.48 Ma、2.26 Ma、1.69 Ma、1.26 Ma、0.13 Ma和0.08 Ma等8次干旱化事件，认为这些事件所代表的亚洲内陆干旱化过程主要受晚中新世以来北半球冰量旋回影响，密切受控于全球变冷的过程；（3）在显微镜下对SG-1孔的原生石盐流体包裹体进行观察，在我国首次发现了2.26 Ma以来的大量古嗜盐菌，包括古原核生物和盐湖杜氏藻及其分泌的类胡萝卜素等有机质。通过统计5100个石盐流体包裹体中的古原核生物个数、大小、分布比例等参数，建立古嗜盐菌2.26-0.08 Ma的丰度变化曲线。从中识别出0.35 Ma的极端干旱事件，并证明了古嗜盐菌的演化与亚洲内陆干旱化的强化密切相关。