Taxonomic and biostratigraphical significance of the Tremadoc graptolite fauna from northern Yukon Territory, Canada

Abstract

Twenty-two graptolite species are described from the Tremadoc portion of the Road River Group. In a 220 m thick, graptolite-rich section on Peel River, six graptolite biozones are recognized which in ascending order are: Staurograptus dichotomus, Anisograptus matanensis, Adelograptus cf. A. tenellus, Adelograptus antiquus, Kiaerograptus pritchardi and Paradelograptus kinnegraptoides. The Psigraptus fauna appears to be confined to a single bedding-plane within a thick interval dominated by Adelograptus cf. A. tenellus, and for this reason we propose a new zone characterized by the latter species rather than identify a Psigraptus Biozone as in China. The Adelograptus cf. A. tenellus Biozone has yielded Adelograptus? bulmani Spjeldnaes 1963, which we propose as the type species for the new genus Ancoragraptus. Graptolites recorded from the Tremadoc of the Yukon for the first time are: Ancoragraptus bulmani, Clonograptus magnificus, C. cf. C. multiplex, C. cf. C. rigidus, Hunnegraptus copiosus, Kiaerograptus? bulmani and K? kutchini sp. nov.

Succession and global correlation of late Tremadoc graptolite zones from South China

“…100 m thick interval with rich Paradelograptus kinnegraptoides between the Kiaerograptus pritchardi Zone and the Tetragraptus approximatus Zone. Later on, Jackson and Lenz [6] found H. cf. copiosus in the lower part of the P. …”

“…and Didymograptus taytori. On top of [5][6][7]12,13,41,42] (Table 2). In Victoria of Australia, the Psigraptus Zone (La1b) produces Psigraptus jacksoni and some undetermined species of "Clonograptus" and Adelograptus [43,44] , of which Clonograptus sp.…”

“…In Yukon of Canada, A. victoriae is well recognized, but the interval covered by this species is not called the A. victoriae Zone but divided into two zones in ascending order: the Adelograptus antiquus Zone and the Kiaerograptus pritchardi Zone. At 3 m above the base of the K. pritchardi Zone are the FADs of Araneograptus macgillivrayi and A. pulchellus [5,6,42] . In Victoria of Australia, the A. victoriae Zone (La2) used before represented a large interval spanning from the A. victoriae Zone to the Araneograptus murrayi Zone [43,47] .…”

“…Araneograptus murrayi and/or other species of the genus are present in Scandinavia, Québec and Yukon of Canada, Tarija of Bolivia, and Victoria of Australia [5][6][7]12,14,15,[42][43][44][46][47][48] (Table 2). However, the exact vertical distributions of the different species of Araneograptus have not yet been known for lacking a meticulously described succession with fossil ranges [7] .…”

“…A two-fold division of the Tremadocian is currently accepted, and the boundary between the lower and upper parts is placed at the base of the Adelograptus tenellus Zone [3][4][5][6] or the Rhabdinopora flabelliformis anglica Zone [7] . Based on the estimation of Cooper [8] , the temporal span of the Tremadocian is about 11 Ma and, if the base of the A. tenellus Zone is taken as the boundary between the two parts, the Upper Tremadocian occupies up to 8 Ma.…”