中文摘要：

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。

英文摘要：

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.