埋藏成岩过程中生物成因原白云石演化的模拟研究

The origin of sedimentary dolomite is still a long-existing enigma in earth sciences, frequently referred to as the “dolomite problem”. The microbial or organogenic dolomite model has been recently proposed to offer one explanation for the occurrence of dolomites throughout the earth history. However, growing evidence showed that microorganisms could only precipitate proto-dolomite (disordered dolomite) rather than ordered dolomite (ideal dolomite). According to the field observations, it suggested that proto-dolomite could undergo maturation and recrystallization, and finally convert to the more stable phase, fully ordered dolomite. However, to test such hypothesis, more observations such as the one based on lavatory simulation are still necessary. Additionally, the question on whether the biosignatures of biogenic proto-dolomite could somehow preserve upon diagenesis is still unclear. The objective of this project is therefore to probe the alteration of biogenic proto-dolomite under experimentally diagenetic conditions. By using multiple approaches, such as bacterial cultivation, geochemistry and mineral analysis, a set of experiments will be conducted to address the role of elevated temperature and pressure on the transformation of biogenic proto-dolomite, aiming at the establishment of biosignature of ordered dolomite. This project would be of great significance for optimizing the microbial or organogenic dolomite model, improving our understanding of “dolomite problem” and seeking for microbial biomarkers in rock records.

白云石的成因机制一直是地质学领域备受关注的研究热点，常被称为“白云石问题”。近些年来提出的“微生物（有机）白云岩模式”为解答白云石问题提供了新思路。然而，最新的研究陆续表明微生物只能诱导原白云石的形成，而不能沉淀有序白云石。沉积学证据推测历经埋藏成岩作用，原白云石可转化为结构更稳定有序白云石，但这一假说亟需室内模拟研究佐以支撑。在成岩反应中，生物成因的原白云石向有序白云石转变，其生物作用信号的保存状况也值得研究和关注。本项目以模拟埋藏成岩过程中生物成因原白云石的演化历程为研究主旨，通过微生物学、地球化学和矿物学等多学科交叉手段，解析温度和压力对生物成因原白云石的矿物学及地球化学标记的影响，最终尝试建立一套区别生物成因和非生物成因白云石的标志。这一研究对于弥补“微生物（有机）白云岩模式”的缺失环节、促进“白云石问题”的深入研究、寻求地质记录中的微生物作用痕迹等方面具有重要的理论意义。

白云岩是全球良好的油气储集体，具有重要的经济研究价值。然而，其主体矿物——白云石的成因机制却是困扰学者的百年难题，至今仍是沉积学乃至整个地球科学领域的研究热点。根据野外调查和室内模拟实验，地质微生物学家提出“微生物白云石模式”。该模式认为微生物活动可以在常温常压条件下催化白云石的形成。“微生物白云石模式”一经提出，便广受关注并被视作解答“白云石问题”的一把钥匙。近年来学者逐渐认识到微生物只能促进原白云石的生成，而不能沉淀有序白云石。随着时间的推移和埋藏成岩作用，原白云石晶体不断调整，直至形成有序白云石。然而，目前人们对成岩环境中生物成因原白云石的演化行为尚不清晰，亟需模拟实验给予解答。基于此，项目负责人和合作者利用不同微生物功能群及其代谢产物成功合成低温原白云石，并查明封闭成岩体系中原白云石如何向有序白云石转化历程。研究结果表明：浮游微生物、微生物胞外结合型聚合物、小分子有机酸以及黏土矿物具备催化原白云石沉淀结晶的能力，并且这些催化效应与其表面负电荷密度正相关。黏土矿物催化形成的原白云石形貌与微生物成因原白云石一致，表明形貌不能作为辨识原白云石来源的标志。低温合成的原白云石含有丰富的晶包有机质和结构水分子，其中结构水分子可以充当内源流体促进原白云石向有序白云石转化。项目执行期间，共发表学术论文8篇，其中3篇刊登于Earth and Planetary Science Letters和Geochimica et Cosmochimica Acta这些自然指数期刊上。