Description and correlation of Late Ordovician conodonts from the D. ornatus and P. pacificus graptolite zones, Road River Group, northern Yukon Territory

Abstract

Upper Ordovician carbonate beds within clastic strata of the Road River Group, northem Yukon Tenitory, have yielded 403 conodont elements representing 25 species; 19 of these are illustrated. Genera present are Amorphognathus, Belodina, Besselodus, Drepanoistodus, Eocarniodus?, Gamachignathus, Icriodella, Noixodontus, Oulodus, Panderodus s.l., Paroistodus?, Plectodina, Protopanderodus, Pseudobelodina s.l., Scabbardella, Strachanognathus, and Walliserodus. The apparatus of new genus A new species A includes a symmetrical and bifurrowed rastrate element.Sparse conodont faunas from Rock River occur in strata below a level bearing graptolites of the D. omatus Zone and between this zone and the succeeding P. pacificus Zone. These conodonts have a range of "Trentonian"-Gamachian (upper Caradoc -Himantian).The fauna from Blackstone River is from a single bed that is 3 m below the G. persculptus Zone? and 13.7 m above the P. pacificus Zone. Although stratigraphically closer to the former, this fauna may be equivalent to a level within the P. pacificus Zone; the conodonts suggest correlation with the late Richmondian Fauna 12 and the lower G. ensifer Zone of Anticosti Island, Quebec. A similar fauna (G. ensifer Zone) occurs in one horizon within the P. pac$cus Zone at upper Peel River. One metre above this is the informal D. cf. D. mirus graptolite biohorizon (P. pacificus Zone).The Blackstone and Peel faunas equate to a level within the Ordovician Anceps bands C and D of the Ordovician-Silurian boundary stratotype at Dob's Linn, Scotland. The interval of Fauna 13 and the Gamachian Stage may correspond to Anceps Band E and the C.? extraordinarius Band (and contiguous strata) at Dob's Linn. The base of the G. ensifer Zone and the higher base of the Gamachian are probably late Rawtheyan. Les lits de carbonates d'ige ordovicien superieur incorpoks dans les strates clastiques du groupe de RoadRiver, dans le nord du Yukon, ont foumi 403 elements de conodontes repksentant 25 espkces et dont 19 sont illustkes ici. Strachanognathus et Walliserodus. L'appareil du nouveau genre A nouvelle espkce A inclut un Clement rastrate symktrique a deux sillons. Les faunes a conodontes peu abondantes dans le Rock River apparaissent dans les strates sous le niveau B graptolites de la zone a D. omatus, et entre cette zone et la zone suivant a P. pacificus. L'ige de ces conodontes se situe entre ~Trentonien~ -Gamachien (Caradoc suptrieur -Himantien).La faune du Blackstone River est limitke ii une seul couche localiste 3 m sous la zone a G. persculptus? et B 13,7 m au-dessus de la zone a P. pacificus. M&me si elle est stratigraphiquement plus apparentte a la premiere, cette faune peut &tre Quivalente a un niveau de la zone a P. pacificus; les conodontes suggkrent une codlation avec la faune 12 du Richmondien superieur et avec la zone a G. ensifer de l'ile d'Anticosti, Quebec. Une faune semblable (zone a G. ensifer) apparait dans un horizon de la zone B P. paciJicus a la rivibre Peel. A un mktre au-dessus se trouve le biohorizon (zone 5 P. pacificu...

Conodonts in the Upper Ordovician Keisley Limestone of northern England: taxonomy, biostratigraphical significance and biogeographical relationships

“…The morphological feature separating Birksfeldia and Gamachignathus identified by McCracken (), that is, the adenticulate vs denticulate antero‐lateral process in the Pa element, is hardly detectable in lateral view. This is the case in several previous papers in which the elements are figured in lateral view and/or are fragmentary.…”

“…There has been a long debate whether Gamachignathus McCracken et al ., , should be regarded as a junior synonym of Birksfeldia Orchard, . The most significant morphological difference, as noted by McCracken (), is the presence of a denticulated antero‐lateral process in the Pa element of Gamachignathus (McCracken et al . , pl.…”

“…The Pa (their g ) elements of Gamachignathus ensifer illustrated by Nowlan and Barnes (, pl. 3, figs 20–21), which were later assigned respectively to G. ensifer and G. hastatus by McCracken (), has no clearly visible denticles in the antero‐lateral costa. This is also the case in the elements of Gamachignathus ensifer reported from the Late Ordovician of the Gaspé Peninsula by Nowlan (, pl.…”

“…In the plate explanation, it is referred to as a dichognathiform ( g ) element, and not as a modified prioniodiform ( g ) element as stated as typical in the original diagnosis of the genus. Later McCracken (, p. 1460) suggested that Nowlan's fauna ‘may contain G. ensifer , but it may also have a new species of Birksfeldia ’ and regarded the figured elements (Nowlan, , pl. 3, figs 1–2, 5–6, 9–10) as representing Birksfeldia sp.…”

Taxonomy, biostratigraphy and biofacies of an Upper Ordovician (Katian) conodont fauna from the Casaio Formation, Northwest Spain

“…According to Dzik (1998), it resembles rather an element of Rhodesognathus from the Mójcza Limestone. McCracken (1987) regarded Noixodontus as a valid genus based on additional morphologic differences of the Pa and Pb elements.…”