贵州寒武系底部牛蹄塘组的研究

ooids. According to the microstructures, Girvanella ooids can be further subdivided into four types: (1) Girvanella spheroids, ooid-sized grains composed entirely of meshwork of Girvanella, with the cortex-nucleus boundary poorly defined; (2) Girvanella-core ooids, having well defined Girvanella nucleus that was probably a rounded fragment of the former cyanobacterial buildup; (3) Girvanella-cortex ooids, usually larger, whose cortices are characterized by alteration of thick, dark colored Girvanella laminae and thick, light colored micritic laminae, filaments of Girvanella arranged parallel to the laminar boundary; (4) Crypto-Girvanella ooids, similar to the Girvanella-cortex ooids in microstructures of the cortex, comprising dark laminae and light laminae but lacking visible filamentous structures in dark layers, probably as a result of degradation prior to calcification.

Calcified biofilms Calcified biofilms are present as thin micrite veneers in the ooids or on the external surfaces of the ooids. The micrite veneers with irregular shapes that are dark-colored in transmission light illumination, and are most conspicuous where they contrast with the ooids; the external surfaces of the biofilms are highly irregular, with steep sides and overhanging projections , which represent surface streamers curved by the fluid flow; the internal veneer fabric, which superficially resembles dense to clotted micrite, on closer examination consisting of rounded micrite aggregates 10µm in size; millimetric pyrite particles are dotted in the external surfaces of the biofilms. The strong fluorescence reaction suggests an organic origin of the calcified veneers. These calcified veneers are easily distinguished from two generations of cements by their characterized external and internal architecture. Furthermore, the multi-stage structures of the ooids suggesting that ooid sediments were reworked by water currents after biofilms formed, and the growth of biofilms occurred in the pore spaces beneath the carbonate particles reflecting the short-term stable conditions during the two stages of the ooids formation.

关键词 Cambrian carbonate ooids microbial imprints

贵州寒武系底部牛蹄塘组的研究

杨兴莲赵元龙孙宗元

贵州大学资源与环境工程学院，贵阳550003，yangxinglian2002@

在对贵州寒武纪早期不同相区的12条地层剖面系统研究后，清理和修订了该时期牛蹄塘组岩石地层单位，认为：1）牛蹄塘组指灯影组（或老堡组、戈仲伍组、桃子冲组）与明心寺组（或九门冲组）间的一套岩层，其底部为含磷硅质岩、硅质磷块岩、硅质页岩，下部为黑色炭质泥、页岩，常具Ni、Mo等多金属的矿层；中、上部为黑色炭质页岩夹灰绿色砂质页岩和钙质页岩，含三叶虫Tsunyidiscus、高肌虫Tsunyiella及大量海绵化石；2）将原九门冲组定义缩小，底部黑色含磷硅质岩划归老堡组；中部的炭质页岩划归牛蹄塘组；上部以产大量盘虫Hupeidiscus 为特征的灰黑色灰岩偶夹页岩地层归入厘定后的九门冲组，其层位

与扬子区的明心寺组下部层位相当；3）贵州牛蹄塘组的分布范围应从原来的仅限于浅水台地区扩展至较深水的斜坡相地区。综合地层对比表明：贵州东部的老堡组上段可与贵州中西部的戈仲伍组和牛蹄塘组下部对比。牛蹄塘组下部最早三叶虫Tsunyidiscus出现之下一般有几米至几十米厚的碳质泥岩、碳质粉砂岩，这段地层与滇东的石岩头组相当，属于纽芬兰统上部地层。这也说明贵州的牛蹄塘组是跨纽芬兰统和寒武系第2统的穿时地层，而且不同地区牛蹄塘组的下限时代不同。贵州的中西部牛蹄塘组的底界普遍略低于寒武系第2统底界（习水等地除外），而东部的牛蹄塘组的底界可能等于或略高于寒武系第2统底，为解决全球寒武系第2统第3阶的界线层型剖面和点位研究提供了一定的依据和信息。

凯里生物群蠕形动物组合特征

赵元龙1)黄迪颖2)彭进1)杨宇宁1)

1) 贵州大学资环学院古生物及生物成矿研究所，贵阳550003

2) 中国科学院南京地质古生物研究所，南京210008

所谓蠕形动物，是指一些多门类、构造差异显著而又不具硬骼的蠕形状软躯体动物。凯里生物群的蠕形动物虽是凯里生物群的组成部分，但属种少，标本数量有限，由于属于软躯体化石，亦是凯里生物群重要门类化石之一。

凯里生物群中的蠕形动物共有4属、2个未定名新属新种（A、B）及1属种未定，包括门纲、目、科未定的新属新种gen. et sp. nov, indent(A)，古曵鳃虫类未定新属新种Paleopriapulids gen. et sp. indent(B)，葫芦虫（未定种）Sicyophorus sp.，古蠕虫科属种未定Palaeoscolecidae gen. et sp. uncertain，环饰蠕虫（未定种）Cricocosmia sp.，塞尔扣可虫（未定种）Selkirkia sp.，奥托虫（未定种）Ottoia sp.。

除了未定名的新属种A及葫芦虫外，其他的均属于曵鳃动物。未定名的新属A翻吻并不发育，缺少具小刺的咽，并非典型的曵鳃动物，主要产于云南澄江动物群。黄迪颖认为葫芦虫是一个特殊的属翻吻和躯干近等，两者之间为收缩的颈部，因形似葫芦而得名，他与兜甲动物关系更密切。未定名的新属种属于曵鳃类，有翻吻、颈和躯干三部分组成，同云南澄江动物群中古蠕虫Palaeopriapulites及始曵鳃虫Protopriapulites相似。凯里生物群蠕形动物中的古蠕虫类有10件标本。过去均置于古蠕虫Palascolex，但是其与真正的古蠕虫的小突起在形态及排列上有差异，暂作属种未定处理。环饰蠕虫Cricocosmia是澄江动物群常见的蠕虫，塞尔扣可虫Selkirkia既见于布尔吉斯页岩生物群，也见于澄江动物群，甚至在美国寒武纪第三世地层中亦见产出，只有数量极少的奥托虫Ottoia仅见于布尔吉斯页岩生物群。

凯里生物群中的蠕形动物，在全球三大布尔吉斯页岩型生物群中属种少，组合带有明显的澄江动物群色彩，也见少量布尔吉斯页岩生物群分子，演化上在两个动物群的蠕虫组合中起了一个承前启后的作用，这与整个凯里生物群在澄江动物群和布尔吉斯页岩生物群之间起承前启后演化作用是一致的。

关键词古蠕虫凯里生物群武陵世（寒武纪）贵州