湖北习家店古新世河湖相沉积记录的高热事件研究

In recent years, several hyperthermal events in Paleocene have been identified mainly from marine sediments and their corresponding terrestrial records remain scarce, which limits further understanding of the characteristics of these hyperthermal events. In order to place these events in a continuous, well-dated, high-resolution terrestrial sequence, magnetostratigraphic investigation will be conducted on the Paleocene fluviolacustrine sediments at Xijiadian in the Hubei Province. According to occurrence time of the Paleocene hyperthermal events provided by previous studies, some layers of Paleocene hyperthermal events will be identified. Then high-resolution pollen, carbon and oxygen isotope of carbonates, susceptibility, color measurements and conventional geochemical analyses will be performed on the event layers of the Xijiadian section and various climatic records with high-resolution will be established. Combined with changes in the lithology and sedimentologic texture, some Paleocene hyperthermal events in the study area will be compared with other Paleocene hyperthermal events to explore the triggering factors of these events and the possible dynamic linkage with the global climate and environment shift during this period.

近年来，不同地区的海相沉积钻孔识别出一系列古新世高热事件而缺乏相应的陆相记录，在很大程度上限制了对这些事件特征的理解。为了将这些事件放到一个年代制约好的高分辨率的连续陆相沉积剖面中进而很好的了解它们的具体特征，本课题以湖北李官桥盆地习家店剖面古新世河湖相沉积为研究对象，通过磁性地层研究建立可靠年代地层框架。参考前人研究提供的古新世高热事件发生年龄，通过高分辨率孢粉、碳酸盐碳氧同位素、红度、磁化率以及地球化学等常规手段，提取该剖面古新世高热事件发生期间的高分辨率气候变化信息，建立各种气候-环境指标演变序列。在此基础上，结合沉积物岩性和沉积构造特征，将研究区古新世高热事件与其它全球和区域高热事件进行对比，分析我国乃至东亚古新世高热事件的促发原因及其与全球气候变化的动力学联系。

本项目对湖北习家店剖面1609 m厚的地层开展了包括磁性地层、粒度、地化、粘土矿物等在内的系统研究。结果显示，习家店剖面从65.6 Ma连续沉积到37.6 Ma，跨越28 Ma。各指标综合分析显示，在沉积期间，两个构造控制期与3个气候控制期相互交替发生。构造活动在65.6-59 Ma期间发生在东秦岭的研究区周围，主要表现为来自附近的粗颗粒粉尘显著增加；在55-54 Ma期间，构造活动扩大到亚洲范围内并显著增强，表现为东-中亚各地出现相变、沉积速率加快等显著的沉积变化，可能响应印度-亚洲碰撞。59-55 Ma见证了东亚风化逐渐增强，可能归因于全球增温。54-50.5 Ma全球继续增温导致东亚干旱化增强。50.5-37.6 Ma期间全球降温减弱蒸发蒸腾作用，增加有效水汽，增强了东亚的化学风化。这些研究成果诠释了构造作用与气候变化如何交替影响古近纪亚洲环境演化。