Worldwide correlation of Telychian (Upper Llandovery) strata using graptolites

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 centrt~ugus 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.centrifugus Biozone by Rickards (1976).

Integrated biostratigraphy of the lower Silurian of the Ohesaare core, Saaremaa, Estonia

“…At present, although it is possible to correlate at subzonal scale between, for example, 'graptolitic' (that is, deeper water) facies from different palaeocontinents (see e.g. Loydell, 1993a), correlating from these 'graptolitic' facies into shallow water ('shelly') facies even within one basin is extremely difficult for much of the Silurian. Hence there is a need for an integration of the Silurian graptolite biozonation with biozonal schemes used in shallower water environments, particularly those based on conodonts, chitinozoans and brachiopods.…”

Geochemistry and potential correlation of Silurian (Telychian) metabentonites from Ireland and SW Scotland

“…They are 3.2 m linearly apart. The Lauchlan Formation, which immediately underlies the Drumyork Flags, was assigned to the lower part of the M. spiralis Biozone (Loydell 1993). Reassessment of the Drumyork Flags graptolite fauna previously referred to the griestoniensis Biozone by Cocks and Toghill (1973), together with newly recognized spiralis Biozone fauna in the overlying Blair Shale Formation, indicates that the Drumyork Flags lie entirely within the spiralis Biozone (Floyd 2001;Floyd and Williams in press).…”

The Aeronian/Telychian (Llandovery, Silurian) boundary, with particular reference to sections around the El Pintado reservoir, Seville Province, Spain

“…Whereas in Bohemia the highest graptolitic sample beneath the non-graptolitic pale mudstone yields Lituigraptus rastrum, in the El Pintado section higher parts of the Stimulograptus halli Biozone are represented within which Rastrites linnaei appears (and co-occurs with stratigraphically higher specimens of L. rastrum; Figs 9, 11) and L. rastrum itself disappears more than a metre below the first appearance of Spirograptus guerichi. The lowermost Telychian black shale horizon in the Radotín tunnel section yields Torquigraptus planus, a species that makes its first appearance in China (Loydell 1993a), Wales (Loydell 1993b) and Sweden (Loydell & Maletz 2004), and also in the El Pintado section (Fig. 10) in the upper part of the guerichi Biozone.…”

“…The Bohemian biozonation proposed by Štorch & Frýda (2012) (Temple 1988, Loydell 1993a. As a result, for practical purposes most authors have simply assumed that the base of the Telychian and that of the Spirograptus guerichi graptolite Biozone are effectively coincident, following the original contention that the boundary correlated with the base of the Spirograptus turriculatus Biozone (Bassett 1985), a biozone subsequently divided into a lower Spirograptus guerichi Biozone and an upper Spirograptus turriculatus Biozone (see Loydell et al 1993 for differences between the two taxa based upon chemically isolated material).…”

“…One such "unknown" interval has been the uppermost Aeronian to lowermost Telychian (middle to upper Llandovery Series). Recognition that the GSSP for the base of the Telychian Stage is unsatisfactory from a number of viewpoints (Temple 1988;Loydell 1993a;Davies et al 2011Davies et al , 2013 has heightened recent interest in the search for more informative sections. The aim of this paper is to document the upper Aeronian and lower Telychian graptolitic strata through sections on the shores of El Pintado reservoir in Seville Province, Spain and to discuss the bio-, chrono-and chemostratigraphy of this part of the Silurian System.…”