Worldwide correlation of Telychian (Upper Llandovery) strata using graptolites

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Abstract
The formal boundaries to the Telychian Stage have been stated to correlate with the bases of the Monograptus turriculatus Biozone at the bottom and the Cyrtograptus centrifugus Biozone at the top. The evidence for this, however, is far from conclusive. The Telychian has been divided, mainly using monograptids, into eight or more biozones, although fewer have been recognized in Britain due to the general paucity of recent studies of the graptolite faunas of this age and to the existence of ‘barren beds’ high within most British Telychian sections. Each biozone has a duration of only a few hundred thousand years, but most are, at present, difficult to recognize in the absence of the index species or where this species’ stratigraphical range extends beyond the limits of its biozone. Intercontinental correlation of Telychian strata using graptolites is hampered to a limited extent by provincialism and water mass specificity, and considerably by taxonomic problems. A thorough taxonomic revision of published species would provide a firm foundation for future biostratigraphical subdivision and correlation of the Telychian Stage. Knowledge of Telychian graptolite biostratigraphy would also be enhanced by restudies of two classic sections, the Trannon river section in Wales, and the Bajiaokou section, Ziyang, China.