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

蒙脱石-伊利石层间粘土矿物在沉积盆地中普遍存在。蒙脱石向伊利石的转变与油气的成熟、运移和圈闭、孔隙压力的发展、岩石胶结和孔隙度的降低以及孔隙水化学有关。尽管该反应很重要，但作为地质变量的函数，蒙脱石是如何转化为伊利石的，存在相当大的模糊性。众所周知，蒙脱石到伊利石的转变与沉积成岩过程中石油的成熟大致同时发生，但有机质与粘土矿物反应之间的关系尚未得到严格的建立。我们假设这种联系是微生物在有机物氧化和金属还原中所起的作用，在蒙脱石到伊利石的转化中。已有充分证据表明，在泥质岩石中存在着丰富的（~106个/g）活性微生物和粘土矿物。金属还原微生物已经在3000米深的地下，高达100摄氏度的环境中被发现。这些条件是粘土成岩作用中常见的条件。富有机质页岩中也存在活菌（104 ~ 105个细胞/g），其丰度可能在粘土成岩初期或超压下页岩中较高。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，但微生物活动与粘土矿物转化之间的功能联系尚不清楚。我们最近的研究表明，在室温下，微生物可以在一个月内将非沸石（一种蒙脱石品种）转化为伊利石。在没有微生物活动的情况下，这种反应通常需要更长时间的高温。我们建议利用独特而强大的分析工具，包括环境细胞透射电镜（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，这项为期三年的提案的目标是：1)研究地下细菌对成岩条件下蒙脱石向伊利石转化的程度和速度的影响；2)确定转化过程的机制；3)探索微生物如何影响转化动力学。我们假设微生物通过以下途径促进蒙脱石向伊利石的转化：1)还原蒙脱石中的结构铁（III）；2)有机酸的生产。含铁（III）的蒙脱石（0.5-4.2 mmol Fe3+/g）在自然环境中很常见。为了模拟蒙脱石成岩作用，研究了在三种不同温度下（30℃、61℃和90℃）细菌对铁（III）还原的影响，使用了中温、嗜热和超嗜热的铁（III）还原细菌（S. putrefaciens、G. metallireducens、Bacillus infernus、gethermobacterium ferrireducens）。将使用各种天然蒙脱石样品。还原实验将在良好的控制条件下设计，以模拟成岩作用。还原产物将通过多种技术进行分析，包括化学萃取，XRD, EC-TEM， EELS，穆斯堡尔光谱和氧同位素。将尝试将微生物效应整合到蒙脱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。到本项目结束时，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脱石向伊利石的转化？他们是如何实现这种加速的？3)细菌存在下蒙脱石与伊利石反应的机制是什么？更广泛的影响。拟议的工作将在国家实验室和大学之间合作进行，并将涉及三个PI。S和他的三个学生在一起三年。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。将发展讲习班、网页、课程材料、通讯和博物馆展览，以便有效和广泛地传播研究成果。在没有博士课程和代表性不足的机构以及K-12学校，将大力开展讲座。

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.