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The AAPG/Datapages Combined Publications Database

CSPG Special Publications

Abstract


Intl. Symposium of the Devonian system: Papers, Volume II, 1967
Pages 587-599
Biostratigraphy

Upper Silurian and Lower Devonian Biostratigraphy, Royal Creek, Yukon Territory, Canada

A. C. Lenz

Abstract

A limestone and shale sequence, some 1500 feet thick, apparently gradational from Silurian into Devonian, and made up of at least 300 feet of Ludlovian and possibly Pridoli equivalent (Upper Silurian) and 1200 feet of nearly complete Lower Devonian, is described from northern Yukon. The Upper Silurian is dominantly a graptolitic shale, but limestone bands in the upper part yielded a small brachiopod fauna including Atrypella cf. tenuis. The entire Lower Devonian part of the sequence is very fossiliferous and is one of considerable significance because of the alternation of shelly faunas with graptolites in the middle one-third. Brachiopods, of which more than one hundred species are recognized, are by far the most common fossils, and are dominated by atrypids, rhynchonellids, and orthids, but include pentamerids, strophomenids, athyrids, and spiriferids. The brachiopods at the genus, and to some extent the species, level, show affinities to the Nevada sequence and particularly to the Old World Province of the Uralian-Bohemian region; they bear no relationship to the Lower Devonian of the Appalachian Province, or to the Rhenish Community of northwestern Europe. The northern Yukon region, therefore, provides an intermediate point in possible migration routes of brachiopods between the widely separated regions of the American Great Basin and the Urals and Siberia.

The Upper Silurian and Lower Devonian stages recognized, and their six faunal subdivisions are as follows: Lower Ludlovian represented by the Monograptus nilssoni Zone; Middle or Upper Ludlovian, or possibly Pridoli equivalent: Atrypella cf. tenuis unit; Gedinnian: Gypidula cf. pelagica unit; lower Siegenian, represented by the Spirigerina cf. supramarginalis unit; upper Siegenian characterized by the Gypidula sp. 1 - Davidsoniatrypa unit; and lower Emsian: Nymphorhynchia pseudolivonica - Sieberella cf. weberi unit. The Zone of Monograptus yukonensis is concluded to be late Siegenian and early Emsian in age. Conodonts recovered from the sequence provide valuable additional information, and in general agree well with brachiopod correlations.


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