全球维宪阶与谢尔普霍夫阶界线层的生物地层研究进展及展望

PROGRESS AND PROSPECT OF THE BIOSTRATIGRAPHIC STUDY OF THE VISEAN-SERPUKHOVIAN BOUNDARY INTERVAL

牙形刺、有孔虫和菊石是全球维宪阶与谢尔普霍夫阶界线层生物地层研究的重要化石门类。该界线定义及其候选层型剖面目前均未正式确立。详细介绍并讨论以牙形刺或有孔虫作为界线定义的可能方案 ,指出潜在的候选层型剖面存在于南乌拉尔的 Verkhnyaya Kardailovka、北美犹太州中西部的 Chainm an组等 ,我国具有潜在研究价值的剖面有广西忻城里苗剖面。

In this paper, the progress and prospect of the biostratigraphic study of the Visean-Serpukhovian Boundary beds in the world are introduced and discussed in detail. Based on the progress report of the Task Group to establish a GSSP close to the existing Visean-Serpukhovian boundary (Richards & Task Group, 2003), the most important conodont lineages which could be useful for defining the Visean-Serpukhovian boundary are: 1)Lochriea nodosa - Lochriea ziegleri or Lochriea senckenbergica, 2)Lochriea costata - Lochriea cruciformis, and 3)Lochriea nodosa - Lochriea multinodosa. Foraminifer lineages containing Neoarchaediscus postrugosus,“Millerella”tortula and Janischewskina delicata appear to be the best candidates for defining a GSSP near the Visean-Serpukhovian boundary. “Millerella”tortula, N. postrugosus and J. delicata have wide geographic distributions and can be used for global correlation. There are several excellent sections across the Visean-Serpukhovian boundary in the world. In the Urals, the best boundary stratotype candidate is the section at Verkhnyaya Kardailovka (southern Urals). This well exposed and accessible section extends from the upper Visean through the Serpukhovian and comprises relatively deep-water facies containing ammonoids, conodonts and foraminifers, and the extensive ammonoid work completed there provides a good foundation for future study. In North America, the best sections for defining a GSSP based on conodont lineages may occur in the mixed carbonate-siliciclastic successions of the Chainman Formation and its correlatives, deposited in Antler Foreland Basin of Nevada and western Utah. The Chainman Formation of west-central Utah contains an outstanding opportunity to use ammonoids to document the position of the Visean-Serpukhovian boundary. The sections comprise continuous deeper water successions containing abundant ammonoids and conodonts, and furthermore, the occurrences are in close proximity to carbonate shelf deposits containing abundant shallow-water taxa that can be correlated fairly unambiguously with the deeper water sections, and in addition, the sections are well accessible. However, in China there are three important good sections for defining a GSSP of the Visean-Serpukhovian boundary, one is the Limiao section in Xincheng County of Guangxi Province, the other two are both in Guizhou Province, one is the Old Street Reservoir section in Lanba of Shuicheng County, and another is the Nashui section in Nashui of Luodian County. All of them comprise relatively deep-water facies with mixed carbonate-siliciclastic successions containing abundant conodonts and foraminifers, therefore, one of them could be the potential candidate section for the GSSP of the Visean-Serpukhovian boundary if the biostratigraphy especially in the Visean-Serpukhovian boundary interval is well studied in the near future.