白垩纪湖泊细粒沉积中有机碳埋藏效率与机制：来自缺氧背景下矿物表面保存的研究

Organic-mineral interactions in fine-grained sediments challenge the traditional view of anoxia preservation of organic matter (OM). By contrast, anoxia and mineral surface protection combined may produce a high-rate organic carbon (OC) burial in some high-resolution continental margin marine records. However, there is little study regarding OM preservation by anoxic and mineral surface constraints in lacustrine settings because of more complex terrestrial processes. This project studies lacustrine organic-rich deposits formed during the Cretaceous anoxic setting in Qingshankou and Nenjiang formations of the Songliao Basin. We aim to reveal the efficiency and mechanism of OC burial, based on anoxic and mineral surface constraints. We will analyze the OC burial efficiency under different oxygen conditions in different lacustrine facies. OM occurrences and their preservation effect in microscopic pores will be discussed in detail based on evidence from organic-mineral interactions, which will contribute to reveal the OC preservation mechanism by the mineral surface constraint. This comprehensive research of anoxia and mineral surface protection will provide insight into the relative contributions to OC burial efficiency. This project will establish the model of OC preservation mechanism under different oxygen conditions. Thus, it will become critical for understanding the OC preservation and accumulation in lacustrine fine-grained sediments. Our findings will also provide new knowledge about the occurrence, accumulation and exploration of shale oil and gas.

缺氧条件一直被作为细粒沉积中有机质保存的主控因素，但普遍存在的有机质-矿物相互作用对此提出挑战。大陆边缘高分辨率海相沉积表明，缺氧与矿物表面保存的共同作用使有机碳埋藏效率大幅提高。然而，湖泊沉积比海洋受更复杂的陆源影响，使缺氧背景下有机质的矿物保存机制能否适应陆相仍存在质疑。本项目以松辽盆地白垩纪缺氧背景下青山口组和嫩江组发育的富有机质细粒沉积为研究对象，揭示缺氧条件和矿物表面共同作用下有机碳的埋藏效率与保存机制。首先，通过不同湖泊相带中高分辨率缺氧记录对比研究，探讨不同含氧条件下有机碳埋藏效率；其次，通过有机质赋存状态及其微观孔隙保存作用研究，揭示矿物表面作用下有机碳的保存机制。最后，综合研究缺氧与矿物表面保存共同作用下有机碳埋藏效率及相对贡献，建立不同含氧条件下有机碳保存机制模型。本研究将深化对湖泊沉积中有机碳保存与富集机制的理解，对低熟页岩油气赋存状态、富集机理和勘探具有重要意义。

缺氧条件一直被作为细粒沉积中有机质保存的主控因素，但普遍存在的有机质-矿物相互作用对此提出挑战。大陆边缘海相环境下缺氧与矿物表面保存共同作用使有机碳埋藏效率大幅提高，而湖泊沉积比海洋受更复杂的陆源影响，使缺氧背景下有机质的矿物保存机制能否适应陆相仍存在质疑。本项目以松辽盆地白垩纪缺氧背景下发育的富有机质细粒沉积为研究对象，开展不同含氧条件下有机碳埋藏效率、矿物表面作用下有机碳保存机制、缺氧与矿物协同作用下有机碳高效埋藏机制研究，揭示缺氧条件和矿物表面共同作用下有机碳的埋藏效率与保存机制。本项研究主要取得以下成果与认识：（1）查明了陆相湖泊沉积时期缺氧环境与有机碳保存的关系：青一段TST晚期至HST早期温暖-湿润气候条件下湖泊富营养化促进母质生源繁盛，稳定的水体底部盐度分层加强了水体缺氧程度，浅水到深水湖泊水体的盐度分层与缺氧程度逐渐增强，从而使深湖-半深湖具有更好的水介质保存条件；（2）探讨了陆相富有机质泥页岩矿物比表面作用与有机碳保存的关系：黏土结合有机质是有机质的主要赋存方式，高矿物比表面促进水体中分解微小有机质的矿物吸附作用，青一段TST晚期至HST早期发育的矿物比表面使有机碳高度富集，半深湖区高矿物比表面与黏土矿物组合类型有关；（3）揭示了有机碳高效埋藏是矿物表面保存与缺氧条件共同作用的结果：青一段TST晚期和HST早期有机碳的高埋藏效率与缺氧背景下高矿物比表面有关，HST晚期缺氧背景下矿物表面作用减弱使有机碳保存效率降低。本研究将深化对陆相湖泊沉积中有机碳保存与富集机制的理解，对低熟页岩油气赋存状态、富集机理和勘探具有重要意义。