六盘山盆地六盘山群李洼峡组-马东山组湖相沉积物记录的早白垩世碳同位素偏移事件

The Oceanic anoxic events (OAEs) reflect the perturbations of global carbon cycle associated to the paleoclimatic and paleoceanographic change. However, its respondence on the land system and the relationships with the global carbon cycle and climate change as well as the interaction along the ocean - land - atomsphere is unclear. In particlar, it is substantial to discover the more records from terrestrial sediments. In our preliminary research, we found that one of two bedds of the black shales and grayblack mudstones in the Liupanshan group,characters of the signifcant carbon isotope excursion for the organic matter and bulk rock,indicating that they are possibly the OAEs record in the continental sediments. Thus, this proposal attempt to extend this research in order to obtain the complete record of the carbon isotope excursion during 125-110 Ma on the Huoshizhai section, based on the sampling and measurement for the carbon isotope of the organic matter in the rocks, and carbon and oxygen isotope of the bulk rock,coupled with the analysis on the sedimentary facies and palynology data. We believe that the data obtained will contribute to our understanding to the comparison between land and marine records and the intheraction along the ocean - land - atomsphere system.

大洋缺氧事件是大洋短期的碳埋藏事件，它与全球碳循环、古气候和古海洋变化关系密切，但对这一事件在陆地系统中的响应、全球碳循环与气候变化在海-陆-气圈层的相互作用等问题还需进一步研究，特别是需要发现更多来自陆地沉积物的直接记录。本项目拟在六盘山地区发现的早白垩世缺氧事件（碳同位素偏移事件）初步研究结果基础上，通过对有古地磁年代控制的六盘山群李洼峡组和马东山组湖相沉积物系统的有机质碳同位素和全岩碳、氧同位素采样测定，结合详细的地层沉积环境和孢粉分析，获取125-110 Ma间陆相沉积物记录的碳同位素偏移事件，为开展白垩纪大洋缺氧事件的海陆记录对比、全球碳循环及气候变化在海-陆-气圈层的相互作用提供基础资料。

项目组通过野外观察、采样和实验室测试分析，获得了六盘山群李洼峡组和马东山组湖相沉积物的有机质碳同位素和全岩碳、氧同位素数据，查明了该段地层的沉积环境为浅-半深湖相，发育三个特征的页岩层段，页岩层段沉积环境为缺氧-还原环境，明确了该段沉积物记录了二个比较明显的碳同位素偏移段。结合全球海洋记录及陆相湖盆地球化学特征，确认两个碳同位素偏移段分别对应于白垩纪中期2个缺氧事件，即OAE1a和OAE1b，代表陆地系统对大洋缺氧事件的响应。第二个碳同位素偏移事件由4个小事件组成，与特提斯北部法国vocontine盆地缺氧事件OAE1b小事件序列Jacob、Kilian、Paquier和Leenhardt相当，指示白垩纪中期六盘山地区气候变化受全球变化控制。研究成果为开展碳同位素偏移事件在陆地和海洋沉积物的记录对比、探讨大洋缺氧事件在陆地系统的响应、全球碳循环及气候变化、海-陆-气圈层相互作用研究提供了基础资料。. 此外，为了更全面的理解白垩纪气候变化及六盘山地区白垩纪中期碳循环机制，在项目计划任务之外，增加了研究时间段的气候变化及环境效益方面的研究。项目取得了白垩纪中期陆地系统对大洋缺氧事件的响应、我国西北地区中新生代构造-气候演变、早白垩世气候状态、被子植物在东亚地区的早期出现、白垩纪超静磁带组成等5项成果，研究成果是当前地球科学领域亟待解决的难点和热点问题。其中前4项成果对认识全球气候变化及岩石圈-水圈-大气圈-生物圈在碳循环过程中的耦合作用具有重要的意义。