摘要
新疆乌鲁木齐地区养牛场剖面中二叠统芦草沟组以发育浅湖至半深湖背景下的中层深灰色、灰色碳酸盐岩、粉砂岩、细砂岩与中、厚层灰黑色泥岩、油页岩的互层沉积为特点。湖相碳酸盐岩以微晶白云岩为主体，其次为微晶灰岩。微晶白云岩主要由白云石、铁白云石及少量方解石等组成，常混有泥质组分且富含有机质。镜下观察白云石主要为微晶（〈4μm）／Z微亮晶（4—10μm），极少数为亮晶（〉10μm）。扫描电镜分析发现微晶白云岩中存在微球状（直径约9μm）、微棒状（长度约0．3-1．2μm）及微米级它形（〈5μm）等3种微形貌的白云石，其中微米级它形白云石在白云岩中占绝大多数。在微晶灰岩中还发现了直径约70-150nm。形态与球菌相似的纳米微粒。具有微生物矿化的特征。研究区白云岩Sr丰度及Sr／Ca比总体持平或略高于微晶灰岩，Mn丰度远高于微晶灰岩，C、0同位素均高于微晶灰岩。暗示了白云岩可能形成于比微晶灰岩更深及盐度更大的水下还原环境，二者之间缺乏明显的交代关系。芦草沟组白云岩的δ13CmB介于9．2％-15．6％，强烈正偏的δ13CPDB可能是产甲烷古茵的代谢活动引起有机质碳同住素分馏的结果。以上特征表明，研究区芦草沟组白云石的沉淀可能与产烷带厌氧微生物的代谢活动引起的甲烷生成作用有关。
Middle Permian Lucaogou Formation is characterized as lacustrine dark gray or gray carbonate rocks, interbeded with sand- stone, thick balck mudstone and oil shale in Yangniuchang section, Urumchi, Xinjiang Province. The carbonate rocks were mainly composed of dark gray dolomicrite, then gray micrite. The dolomicrite comprised micro-crystalline dolomite, ankerite and calcite with mixture of clay-sized quartz and enrichment of organic matter. Three micromorphologies of dolomite were found under SEM, /11- cluding microspheroids （9ttm in diameter）, micro-rods （2m） and micron-sized （〈5m） anhedral dolomite, and the micro-anhedral dolomite held the majority in dolomicrite. There were also found large amount ofnanoparticles （70-150nm in diameter） in the micrite with shape very similar to micrococcus. Compared with the micrite, dolomicrite has higher Sr value, St/Ca ratio, Mn value, and δ13sO value, which indicate that the dolomicrite is formed in deeper anoxic water with higher salinity than micrite, and the dolomicrite lacks of replacement textures from micrite. The δ13 of dolomicrite ranged from 9.2 %0 to 15.6%0. The higher δ13 value may be the re- suit of isotope fractionation led by methanogens. Such characteristics indicate that the dolomite precipitation had close relationship with the bacterial methanogenesis in methane-producing zone.
出处
《地质通报》
CAS
CSCD
北大核心
2013年第4期661-670,共10页
Geological Bulletin of China
基金
国家自然科学基金项目《北疆地区二叠系湖相白云岩成因研究》(批准号:40802024)
《中国中西部地质历史时期湖相白云岩类比研究与实验模拟》(批准号:41272115)
《新疆北东部三塘湖地区二叠纪地幔热液喷流沉积及其形成机理》(批准号:41272116)
大陆动力学国家重点实验室自主研究课题《新疆三塘湖盆地中二叠统芦草沟组湖相热水沉积岩地球化学特征及同位素示踪》(编号:BJ11054)
关键词
湖相
白云石
微球
微棒
纳米微粒
微生物甲烷生成作用
中二叠统
lacustrine
dolomite
micro-spheroid
micro-rod
nanoparticles
bacterial methanogenesis
Middle Permian
