始新世晚期-渐新世早期气候过渡事件（EOT）的陆相沉积有机质响应

The rapid climate transition from greenhouse climate toward glacial-interglacial climate occurred during the late Eocene to the Early Oligocene (so called EOT event) of Cenozoic Paleogene period， was an important event that has important impact on the contemporary and future global climate change．The cause of this climate transition is less understanding as the climate responses to the EOT event vary greatly at different terrestrial region of latitude, for example, the degree of cooling in the high latitude regions during the EOT varies; but there is a general lack of research on the low latitude regions. Maoming oil shales, are lacustrine organic rich sediments in the low latitude region that deposited in the late Eocene to the Early Oligocene of Paleogene. The research on hydrocarbon composition, source and environmental specific biomarkers and the carbon and hydrogen isotopic composition of individual compounds in the Maoming oil shales and their climate significance are scientific and practical important for a comprehensive understanding of the global climate responses and the cause of the EOT events and the future climate change prediction. This project proposed to analyses the organic matter composition and carbon and hydrogen isotopic composition of individual hydrocarbon compounds in a manner of high-resolution associated with the studies of the strata dating, pollen analysis, aiming to reveal the paleoclimatic and environmental information that recorded in the Maoming oil shales, and therefore to build a reliable paleoclimatic change profile in the low latitude region corresponding to the marine sourced EOT event.

古近系始新世晚期-渐新世早期发生的由“温室气候”向“冰期-间冰期”转变的气候过渡事件（EOT）是影响现今和未来全球气候变化的重要事件。引发这一变化的原因机制尚不清楚，且EOT事件在不同陆地区域的响应不同，中高纬度地区的降温幅度差异很大，但缺乏低纬度地区的研究资料。茂名油页岩是形成于始新世-渐新世过渡期的低纬度陆相富有机质沉积，深入详细地研究其沉积有机质蕴含的古环境及剖面变化信息，对认识EOT气候过渡事件在全球各地的响应及发生原因、预测未来气候变化等有重要的科学价值。本项目拟通过对茂名油页岩沉积有机质烃类、生物标志物组成及其碳氢同位素组成的高分辨剖面变化分析，并结合地层定年、孢粉分析等研究，详细研究茂名油页岩保存记录的古气候环境信息，建立油页岩沉积时期的古气候变化曲线及其与EOT气候过渡事件的相关性，为研究全球气候变化状态下区域性低纬度地区的古气候响应提供科学依据。

茂名油页岩的有机质类型以I型为主, 有机质丰度极高, TOC在9.0%~28.9%之间, 热解参数Tmax在427 oC-437 oC之间, 处于低成属演化阶段，而测年数据显示茂名油页岩为41个百万以后的沉积产物。油页岩中检出了丰富的甾烷和藿烷化合物，其中甾烷化合物主要为规则甾烷、重排甾烯、4-甲基甾烷、4-甲基重排甾烯同系物，单体碳同位素组成显示高丰度的4-甲基甾烷来自于沟鞭藻类。在油页岩沉积剖面顶部间断性检测到高丰度的具生源专属性的丛粒藻烷, 显示油页岩上部沉积时期的水体环境快速改变并引起丛粒藻间歇性繁盛。所有样品中均检出了具有指示水体盐度和水体还原分层意义的MTTC和芳基类异戊二烯系列化合物, 显示油页岩沉积时期主要为淡水-半咸水的水体环境, 没有出现明显的水体盐度分层。正构烷烃碳同位素组成变化范围为-31.8‰ ~ -16.2‰；不同碳数正构烷烃碳同位素组成之间的相关性均很好, 指示母质来源具有均一性。油页岩中正构烷烃碳同位素组成在剖面上波动应主要与大气CO2分压的变化有关。油页岩正构烷烃氢同位素组成在剖面上的存在阶段性变化并呈现显著负偏 (为-206.5‰）, 显示沉积时期出现间歇性大气强降水引起湖泊水体氢同位素组成变轻, 导致水生生物体合成的有机质氢同位素组成出现异常负偏。最后，茂名油页岩沉积剖面上正构烷烃碳、氢同位素组成在中段所呈现的异常剧烈变化应与全球性EOT气候过渡期在时间上密切相关, 可能反映了低纬度陆相沉积有机质对全球性EOT气候过渡期的响应。