富含微生物体系内温压条件对自生碳酸盐岩和铁硫化物形成的影响

Eeffect of the Temperature and Pressure Conditions on the Formation of Authigene Carbonate Minerals and Iron Sulfide in a Microorganisms System

甲烷渗漏区沉积层中存在的大量自生碳酸盐岩和铁硫化物,是指示天然气水合物存在的标志。但对其形成条件的实验研究还不多见。利用自主研发的模拟装置,首次在富含甲烷氧化菌和硫酸盐还原菌的微生物系统内,通过水化学分析方法,探讨不同温度和压力下水化学组分的变化;通过扫描电镜和能谱分析方法,确定自生碳酸盐和铁硫化物的形态和种类,研究它们在不同温压条件下的形成规律。结果表明:5℃,8℃和10℃实验中,p H保持在6.5~7.4之间,ORP稳定在-100.0 m V附近,HCO-3浓度为202.55~639.93 mg/L。2.5 MPa,5.0 MPa和7.5 MPa实验中,p H在6.1~7.2之间,ORP稳定在-100.0^-50.0 m V之间,HCO-3浓度为324.08~789.95 mg/L。温度和压力通过影响微生物代谢产生S2-和HCO-3、离子结合两个过程,最终控制矿物的形成。碳酸钙、菱铁矿和铁硫化物在各实验中都有生成。温度升高:HCO-3浓度变化范围变小,S2-浓度增加,氧化还原电位减小;碳酸钙形成较少;菱铁矿随温度升高而增加,铁硫化物形成随S2-浓度增加而变广,表明温度升高促进铁硫化物和菱铁矿的形成。压力增加:S2-生成量增加,ORP(氧化还原电位)变得更小;形成的铁硫化物颗粒越大且形态更好;生成的碳酸钙变少,可能受到S2-浓度的影响。这些实验结果对于研究全球海洋中碳和硫的存储及循环、自生矿物的形成机理等都具有重要意义。

Aboundant authigene carbonate minerals and iron sulfide in sea-bed methane cold seeps are important geologic markers to prospect natural gas hydrate（ NGH）. However,there are very limited experimental researches on their formation conditions. The aquantic chemical changes of water systems with sulfate reducing bacteria and anaerobic methanotrophic archaea under various temperatures and pressures were simulated and investigated as the first time by using a home-made sealed bioreactor system. Minerals morphology,carbonate species and iron sulfide under different temperatures and pressures were checked using scanning electron microscope（ SEM） and X-ray diffraction（ XRD） to study on their precipitation regulation. For the experiments under 5 ℃,8 ℃ and 10 ℃,the p H values and concentrations of HCO3^- were in ranges of 6. 5-7. 4 and 202. 55-639. 93 mg/L,respectively. The oxidation-reduction potential（ORP） stayed near-100.0 mV. For the experiments under 2.5 MPa,5.0 MPa and 7.5 MPa,the p H values and concentrations of HCO3^- were in range of 6.1-7.2 and 324.08-789.95 mg/L,respectively. The oxidation-reduction potential（ ORP） was remained from-100 mV to-50.0 mV. These experimental results demonstrated that temperature and pressure might control authigene carbonate minerals formation by influence of microbial metabolism to provide the source for S^2- and HCO3^-,which were able to form the minerals combined with cations. Calcite,siderite and iron sulfide were precipitated in all experiments whereas the HCO3^- concentration was diminishing,the S^2-concentration was rised and ORP decreased when the temperature was increased. The distribution of siderite and iron sulfide was increasing with temperature and S^2-concentration,probably indicating that increasing temperature could facilitate the formation of iron sulfide and siderite. The S^2-produced by microbes metabolism and negative values of ORP（ below 0） were decreasing along with increasing pressure. Simultaneously,carbonate formation was increased and the distribution range of iron sulfide became wider and also better in morphology. The decrease of calcium carbonate precipitation might be controlled by the concentration of S^2-. These results could be significant to provide insights into the storage and cycle of carbon and sulfur,and the formation mechanism of authigene minerals in global ocean.