【作者】 杨浩；

【导师】 王永标；

【作者基本信息】 中国地质大学 ， 古生物学与地层学， 2006， 硕士

【摘要】 华南地区晚二叠世末碳酸盐台地上广泛发育一套钙质微生物岩，这些钙质微生物岩以发育“花斑状”构造为特征，部分微生物岩伴生有叠层石层、鲕粒灰岩层。通过仔细的野外和室内工作，初步揭示微生物岩产出的古地理环境、时代、微生物岩内化石的组成、岩石特征以及岩石地球化学特征。 通过野外观察，微生物岩出露的古地理位置大致可以分为三类：(1)南盘江盆地内孤立碳酸盐台地上；(2)上扬子地区台内生物礁顶上；(3)中下扬子碳酸盐台地边缘生物礁顶上。微生物岩和上下地层之间为一种整合的接触关系。厚度从几米到十几米不等，并向台地周围深水区逐渐尖灭。 通过对微生物岩中已发现的牙形石化石的综合分析，发现所研究的6条剖面中均产有牙形石化石H．parvus。据现有的发现，H．parvus均出现在微生物岩的内部，距微生物岩底部(绝灭界线)有一定的距离。通过与浙江煤山标准剖面的对比，将微生物岩的时代确定为晚二叠世末到早三叠世早期。 微生物岩中的化石主要以钙质微生物为主，同时伴生有小型的腹足、双壳、有孔虫和介形虫，在一些微生物岩中还发现有分类不明的棒状化石。微生物岩所代表的这种特殊的古代生态系可称之为菌藻生态系。微生物岩中钙质微生物化石主要以两种形态出现，即“束囊状”和球状。“束囊状”化石经初步鉴定为肾形藻(Renalcis)或Epiphyton。微生物岩中菌藻类化石的发现为了解大绝灭后礁顶上残存下来的古生物群落的组成及当时的古海洋环境提供了重要的化石材料。 从岩石特征上看，微生物岩主要以发育“花斑状”构造为特征，但不同地区表现形式有所不同。在南盘江盆地南边的广西地区，微生物岩以斑状和丘状构造为主要特征；在北边的贵州边阳地区，则表现为纹带构造，同时可见大型的藻叠层；而川东地区钙质微生物岩以发育穹隆状构造、纹带状构造及指状构造为主要特征；鄂东南地区表现为纹带状构造和丘状构造，局部出现柱状叠层构造。引起微生物岩的这种岩性差异的原因可能是其沉积水深的不同，同属于浅海相沉积的微生物岩，水深细微的不同，就可能造成不同的岩石特征。但微生物岩在岩石结构上基本一致，即由微晶基质和中、粗晶方解石指状体或斑点所组成。 通过对微生物岩的岩石地球化学分析，认为微生物岩形成于一个盐度相对较高的水化学环境中。另外，地球化学分析显示微生物岩受后期成岩变化的影响较小，基本保持了成岩时的特征。微生物岩中常量元素Mg的变化和微量元素Sr的高含量可以用来解释当时古海洋的高盐度。稀土元素分配曲线结果显示，在作登微生物岩上的泥岩层的沉积物来源应该与台地沉积物无关，可能是由于海水翻转将深海沉积物涌起，而在台地上形成。稀土元素Ce在“花斑状”微生物岩中的负异常揭示了这类微生物岩形成于一个相对氧化的水环境中，但Ce在其他灰岩中的分布特征仍显示了火绝灭后海洋为一种普遍的缺氧水体。 碳氧同位素分析显示，碳稳定同位素的负偏主要出现在微生物岩与晚二叠世生物碎屑灰更多还原

【Abstract】 The microbialites occur widely above the mass extinction line in the Late Permian carbonate platform in South China. The microbialites are characterized by the peculiar structure of "graniphyic fabric", as well as stromatolite and oolites at some locations. After carefully observe and study, we make clear the paleogeography position and age of the microbialites. The fossil composition, lithology and geochemistry characters have been studied too.The microbialites’ paleogeography position can be divided into three types: (1) on the top of the isolated carbonate platform within the Nanpanjiang Basin; (2) on the top of reefs which were developed within the Upper Yangtze platform; (3) on the top of reefs which were built up along the margin of Middle-Lower Yangtze platform. The microbialites had a conformity relationship with the overlying and underlying strata. The thickness of the microbialites was from several meters to tens meters, and gradually disappeared from shallow water to deep water.According to the study of conodonts, H.parvus fossils have been found in the microbialites from six sections. All the conodont fossils found so far are produced within the microbialites and have a distance to the bottom of the microbialites. By correlation with the GSSP at Meishan, it is proposed that the microlialites spanned the latest Permian and Earliest Triassic.Calcified microbe are the main fossils discovered in the microbialites, and some micro-gasteropods, bivalves, foraminifer, ostracods, micro-problematical fossils can also be found. This special ecological system represented by the microbialites may be called bacterium-alga system. Globular cynobacteria and chambered fossils are the main types of calcified microbe. The chambered fossils had been identified as Renalcis or Epiphyton. The calcified microbe found in the microlialites provides important material for study of ancient biotic community on the top of the reefs and the conditions of the ancient marine environment after mass extinction.Generally, the microbialites displays the structure of "graniphyic fabric". However, there are some other different lithological characteristics in different places. The microbialites in the South of Nanpanjiang Basin have characteristics of spot and mound structure. The microbialites in the north of the basin have veins or big stromatolite. In East Sichuan, the microbialites characteristics were arched, veins and digitate structure. Microbialites in South-east Hubei have veins, mound structure and stromatolites. This different maybe explain the vary depth of the water. However, the更多还原