Nanoscale Investigation of Microbial Role in Promoting the Smectite to Illite Transformation

蒙脱石-伊利石间层粘土矿物在沉积盆地中普遍存在。蒙皂石向伊利石的转化与烃类的成熟、运移和圈闭、孔隙压力的发展、岩石胶结作用和孔隙度降低以及孔隙水化学有关。尽管反应的重要性，存在相当大的模糊性如何蒙皂石转化为伊利石作为一个功能的地质变量。在沉积物成岩过程中，蒙脱石向伊利石的转化与石油的成熟过程基本一致，但有机质与粘土矿物反应之间的关系尚不明确。我们假设，联系是在微生物发挥的作用，在有机物氧化耦合金属还原，在蒙脱石伊利石转化。泥质岩中存在着丰富的微生物（~106个/g）和活跃的微生物与粘土矿物。金属还原微生物已被发现在埋藏深度约3000米，并在高达100摄氏度。这些条件涵盖了粘土成岩作用期间常见的条件。在富含有机质的页岩中也存在活的微生物（104-105个细胞/g），并且它们的丰度在粘土成岩作用开始时或在超压下的那些页岩中可能更高。条件现场和实验室证据都表明微生物在粘土矿物反应中的重要作用，但微生物活动和粘土矿物转化之间的功能联系知之甚少。我们最近的研究表明，微生物可以在室温下一个月内将绿脱石（蒙皂石的一种）转化为伊利石。该反应通常需要在不存在微生物活性的情况下在延长的时间段内高得多的温度。我们建议使用独特而强大的分析工具，包括环境细胞透射电子显微镜（EC-TEM）和电子能量损失谱（EELS），研究微生物对蒙脱石向伊利石转化的影响。具体来说，这个为期三年的提案的目标是：1）调查地下细菌对成岩条件下蒙皂石向伊利石转化的程度和速率的影响; 2）确定转化过程的机制; 3）探索微生物如何影响转化的动力学。我们假设微生物通过1）还原蒙皂石中的结构Fe（III）; 2）产生有机酸来促进蒙皂石向伊利石转化。含Fe（III）的蒙皂石（0.5-4.2 mmol Fe 3 +/g）在自然环境中很常见。为了模拟蒙皂石-伊利石成岩作用，将在三种不同温度（30 ℃、61 ℃和90 ℃）下使用嗜中温、嗜热和超嗜热的Fe（III）还原菌（S.腐霉G.金属还原菌、芽孢杆菌、铁还原地热杆菌）。将使用各种天然蒙皂石样品。还原实验将在良好控制的条件下设计，以模拟成岩作用。还原产物将通过各种技术进行分析，包括化学萃取、XRD、EC-TEM、EELS、穆斯堡尔谱和氧同位素。将尝试将微生物的影响整合到蒙皂石到伊利石的转化模型中，这将对有机质成熟和石油运移产生重大影响。在本课题结束时，我们将回答以下问题：1）在成岩条件下，微生物是否加速了蒙皂石向伊利石的转化？2)他们是如何实现这种加速的？3)在细菌存在的情况下，蒙脱石转化为伊利石的反应机理是什么？更广泛的影响。拟议的工作将与国家实验室和大学之间的合作进行，并将涉及三名PI和他们的三名学生三年。学生将在学术机构和政府实验室工作，以获得独特的研究经验。将开发讲习班、网页、课程材料、通讯和博物馆展览，以有效和广泛地传播研究成果。将作出重大努力，为那些没有博士课程和代表性不足的机构以及K-12学校提供讲座。

Smectite-illite interstratified clay minerals are ubiquitous in sedimentary basins. The smectite to illite transformation is linked to the maturation, migration and trapping of hydrocarbons, the development of pore pressures, rock cementation and porosity reduction, and pore water chemistry. Despite the importance of the reaction, considerable ambiguity exists as to how smectite is converted to illite as a function of geological variables. It is well known that the smectite to illite transformation is approximately concomitant with maturation of petroleum during sediment diagenesis, but the relationship between organic matter and clay mineral reactions has yet to be rigorously established. We hypothesize that the linkage is in the role that microorganisms play, in regards to organic matter oxidation coupled to metal reduction, in the smectite to illite transformation. Sufficient evidence has accumulated that abundant (~106 cells/g) and active microbes and clay minerals co-exist in argillaceous rocks. Metal-reducing microbes have been discovered at burial depths of ~3000 meters, and at up to 100oC. These conditions bracket those commonly found during clay diagenesis. Viable microbes (104-105 cells/g) also exist in organic-rich shales, and their abundance may be higher at the onset of clay diagenesis or in those shales under the .overpressure. condition. Both field and laboratory evidence suggest the important role of microbes in clay mineral reactions, but the functional linkage between microbial activity and clay mineral transformations is poorly understood. Our recent investigations have shown that microbes can transform nontronite (a smectite variety) to illite at room temperature in one month. This reaction typically requires much higher temperatures over extended time periods in absence of microbial activity. We propose to investigate the effects of microbes on the smectite to illite transformation, using unique and powerful analytical tools including environmental cell transmission electron microscopy (EC-TEM) and electron energy loss spectroscopy (EELS). Specifically, the goals of this three-year proposal are to 1) investigate the effects of subsurface bacteria on the extent and rate of the smectite to illite transformation under diagenetic conditions; 2) determine mechanisms of the transformation process; 3) explore how microbes affect kinetics of the transformation. We hypothesize that microorganisms promote the smectite to illite transformation via 1) reduction of structural Fe(III) in smectite; 2) production of organic acids. Fe(III)-containing smectite (0.5-4.2 mmol Fe3+/g) is common in natural environments. To simulate smectite-illite diagenesis, the effects of bacterial Fe(III)-reduction will be studied at three different temperatures (30oC, 61oC, and 90oC) using mesophilic, thermophilic and hyperthermophilic, Fe(III) reducing bacteria (S. putrefaciens, G. metallireducens, Bacillus infernus, Geothermobacterium ferrireducens). A variety of natural smectite samples will be used. Reduction experiments will be designed under well-controlled conditions to mimic diagenesis. Reduction products will be analyzed by a variety of techniques, including chemical extraction, XRD, EC-TEM, EELS, Mossbauer spectroscopy and oxygen isotopes. Attempts will be made to integrate microbial effects into smectite to illite transformation models, which will have major implications for organic matter maturation and petroleum migration. By the end of this project, we will have answered the following questions: 1) do microbes accelerate the smectite to illite transformation under diagenetic conditions? 2) how do they achieve this acceleration? 3) what are mechanisms for the smectite to illite reaction in presence of bacteria? Broader impacts. The proposed work will be carried out with collaborations between national labs and university, and will involve three PI.s and their 3 students for three years. Students will work in both academic institution and governmental labs to gain unique research experiences. Workshops, web pages, course materials, newsletters and museum exhibits will be developed to efficiently and broadly disseminate research results. Major efforts will be made to deliver lectures to those institutions without PhD program and underrepresented, as well as K-12 schools.