中文摘要：

陕西镇安西口地区构造上属于南秦岭微板块，二叠纪时该地区与华南板块被勉略洋（东古特提斯洋的一个分支）分隔，而成为南秦岭微板块上的一个孤立台地。由于其二叠纪时处于华北和华南板块的汇聚带，同时又位于沟通古特提斯和泛大洋的重要通道上，其特殊的古地理位置使其具备与华南乃至全球其它地区二叠系对比的重要古地理和古环境意义，具有成为二叠系经典剖面的潜力。本次研究共分析60件样品，从中发现具有地层划分对比意义的平台型牙形刺分子4属18种。这些化石分布于上石炭统至上二叠统的地层中，且主要产于中二叠统水峡口组和上二叠统的西口组、熨斗滩组及龙洞川组。根据牙形刺的产出情况将研究区二叠系划分出13个带，自上而下为：长兴阶（changhsingian）的Clarkina subcarinata带和C．changxingensis带；吴家坪阶（Wuchaipingian）的C．postbitteri带，C．dukouensis带，C．liangshanensis带和C．orientalis带；卡匹敦阶（Capitanian）的Mesogondolella posterserrata带，Mshannoni带，M.altudaensis带和M．granti带；罗德阶（Roadian）的M.nanjingensis带；亚丁斯克阶（Artinskian）的Sweetognathus whitei带；阿瑟尔阶（Asselian）-萨克马尔阶（Sakmarian）的S．inornatus带。最后，主要依据牙形刺带对陕西镇安西口二叠系剖面的生物地层进行重新划分，确立了3统9阶，从而能够更好地进行洲际对比。

英文摘要：

Xikou area of Zhen＇ an, Shaanxi Province, NW China belonging to the South Qinling micro-continental block （SQL）, was separated by Mianlue Ocean from South China Block （SCB） during Permian. It was surrounded by deep-water basin and became an isolated platform in SQL. It was located in the convergent zone between North China Block （NCB） and SCB, and was situated on the passage linking Paleo-Tethys Ocean and Panthalassa at the same time. The special location destined this profile of great palaeogeographic and paleoenvironmental significant for the correlation with other Permian profiles in South China and other places in the world, which also provides a potential for this profile to become a classical Permian profile. This study analyzes 60 microfossil samples, and from which 4 genus and 18 species of conodonts are identified. These conodonts distribute from the Upper Carboniferous to the Upper Permian, and mainly occur in the Middle Permian Shuixiakou Formation, the Upper Permian Xikou Formation, Yundoutan Formation and Longdongchuan Formation. According to the occurrence of conodonts, 13 conodont zones can be recognized on the profile, including Clarkina subcarinata zone and C. changxingensis zone of the Changhsing- Jan stage, C. postbitteri zone, C. dukouensis zone, C. liangshanensis zone and C. orientalis zone of the Wuchaipingian stage, Mesogondolella posterserrata zone, M. shannoni zone, M. altudaensis zone and M. granti zone of the Capitanian stage, M. nanjingensis zone of Roadian stage, Sweetognathus whitei zone of the Artinskian stage, S. inornatus zone of the Asselian-Sakmarian stage. Based on the conodont zones, we establish a new scheme of biostratigraphic classification including 3 series and 9 stages, which can compare well with global standard.