Road River Group Research Articles

A long-term record of early to mid-Paleozoic marine redox change.

The extent to which Paleozoic oceans differed from Neoproterozoic oceans and the causal relationship between biological evolution and changing environmental conditions are heavily debated. Here, we report a nearly continuous record of seafloor redox change from the deep-water upper Cambrian to Middle Devonian Road River Group of Yukon, Canada. Bottom waters were largely anoxic in the Richardson trough during the entirety of Road River Group deposition, while independent evidence from iron speciation and Mo/U ratios show that the biogeochemical nature of anoxia changed through time. Both in Yukon and globally, Ordovician through Early Devonian anoxic waters were broadly ferruginous (nonsulfidic), with a transition toward more euxinic (sulfidic) conditions in the mid-Early Devonian (Pragian), coincident with the early diversification of vascular plants and disappearance of graptolites. This ~80-million-year interval of the Paleozoic characterized by widespread ferruginous bottom waters represents a persistence of Neoproterozoic-like marine redox conditions well into the Phanerozoic.

Ogilvie Platform Composite Tectono-Sedimentary Element

Abstract The Ogilvie Platform Composite Tectono-Sedimentary Element (CTSE) occupies an area of about 68 000 km 2 in the northern part of the Yukon Territory of Canada, and includes all Paleozoic- and Triassic-aged strata between a base of Cambrian unconformity and a base of Jurassic and Cretaceous unconformity. This cratonic platform is composed of two lithologically distinct sedimentary successions: a lower suite of peritidal to shallow-subtidal, carbonate-dominated, Cambrian–Middle Devonian-aged units; and an upper succession of siliciclastic-dominated alluvial fan, shelf delta, nearshore, slope and basinal strata of Middle Devonian–Late Permian and Triassic age. The lower succession is composed of a synrift tectono-sedimentary element (TSE) and an overlying passive continental-margin TSE. The upper succession is composed of an Ellesmerian orogenic foreland TSE and a syn-epeirogenic TSE. The total discovered oil reserve within the Ogilvie Platform is estimated to be 1.757 × 10 6 m 3 (11.05 MMbbl) and the total discovered gas reserve is estimated to be 2.376 × 109 m 3 (83.7 Bcf) in four oil and gas pools. A variety of stratigraphic and structural trap types have been assessed to contain additional conventional hydrocarbon reserves, with a total mean potential of 33.4 × 10 6 m 3 (210.1 MMbbl) of oil and 33.4 × 10 9 m 3 (2.63 Tcf) of gas. The organic-rich shale and siltstone-dominated petroleum source-rock units, such as within the Road River Group, the Canol and Ford Lake formations, and organic-rich strata within the Hart River and Blackie formations, are also prospective for large reserves of unconventional oil and gas, and have yet to be formally assessed.

Stratigraphy and U–Pb Zircon–Titanite Geochronology of the Aley Carbonatite Complex, Northeastern British Columbia: Evidence for Antler-Aged Orogenesis in the Foreland Belt of the Canadian Cordillera

The tectonic significance and age of carbonatite intrusions in the central Foreland Belt of the Canadian Cordillera are poorly constrained. Recent work has demonstrated that one of these carbonatite intrusions, the Aley carbonatite, was emplaced as a syn-kinematic sill, coeval with a major nappe-forming tectonic event. Determining the age of the Aley carbonatite thus provides a means of directly dating syn-tectonic magmatism. Attempts at dating carbonatite units failed due to low U–Pb content in sampled zircon; however, a U–Pb titanite age of 365.9 ± 2.1 Ma was obtained from the Ospika pipe, an ultramafic diatreme spatially and genetically related to the carbonatite. This U–Pb titanite age is further supported by respective 40Ar/39Ar phlogopite ages of 359.4 ± 3.4 Ma and 353.3 ± 3.6 Ma for the pipe and a spatially associated lamprophyre dyke. We interpret the Late Devonian U–Pb titanite age of the Ospikapipe to be the minimum possible age of the carbonatite and syn-magmatic nappe-forming tectonic event. The maximum possible age of the carbonatite is constrained by the Early Devonian age of the Road River Group, the youngest strata intruded by carbonatite dykes and involved in the nappe-forming event. Our dating results for the Aley carbonatite closely correlate with U–Pb zircon and perovskite ages obtained for the Ice River carbonatite complex in the central Foreland Belt of the southern Canadian Cordillera, and support the interpretation of carbonatite intrusions of the western Foreland Belt as genetically linked components of an alkaline-carbonatitic magmatic province. Structural, stratigraphic, and geochronological data from the Aley area indicate that deformation was similar in style to, and coeval with, structures attributable to the Antler orogeny, and are consistent with the Antler orogen having extended the length of the Cordilleran margin from the southern United States to Alaska.

The Road River Group of northern Yukon, Canada: early Paleozoic deep-water sedimentation within the Great American Carbonate Bank

Cambrian–Devonian sedimentary rocks of the northern Canadian Cordillera record both the establishment and demise of the Great American Carbonate Bank, a widespread carbonate platform system that fringed the ancestral continental margins of North America (Laurentia). Here, we present a new examination of the deep-water Road River Group of the Richardson Mountains, Yukon, Canada, which was deposited in an intra-platformal embayment or seaway within the Great American Carbonate Bank called the Richardson trough. Eleven detailed stratigraphic sections through the Road River Group along the upper canyon of the Peel River are compiled and integrated with geological mapping, facies analysis, carbonate and organic carbon isotope chemostratigraphy, and new biostratigraphic results to formalize four new formations within the type area of the Richardson Mountains (Cronin, Mount Hare, Tetlit, and Vittrekwa). We recognize nine mixed carbonate and siliciclastic deep-water facies associations in the Road River Group and propose these strata were deposited in basin-floor to slope environments. New biostratigraphic data suggest the Road River Group spans the late Cambrian (Furongian) – Middle Devonian (Eifelian), and new chemostratigraphic data record multiple global carbon isotopic events, including the late Cambrian Steptoean positive carbon isotope excursion, the Late Ordovician Guttenberg excursion, the Silurian Aeronian, Valgu, Mulde (mid-Homerian), Ireviken (early Sheinwoodian), and Lau excursions, and the Early Devonian Klonk excursion. Together, these new data not only help clarify nomenclatural debate centered around the Road River Group, but also provide critical new sedimentological, biostratigraphic, and isotopic data for these widely distributed rocks of the northern Canadian Cordillera.

A Middle Devonian basin-scale precious metal enrichment event across northern Yukon (Canada)

AbstractHyper-enriched black shale (HEBS) Ni-Mo-Zn-Pt-Pd-Au-Re mineralization is geographically widespread across the Richardson trough in northern Yukon (Canada), where it discontinuously outcrops at the regional contact between the Road River Group and overlying Canol Formation. Stratigraphic relationships indicate that the contact is Middle Devonian, but there are no precise age constraints for the HEBS. We apply Re-Os geochronology to HEBS mineralization from two localities that are 130 km apart, the Nick prospect and the Peel River showing, to date directly the age of sulfide mineralization. The Nick prospect yields an isochron age of 390.7 ± 5.1 (2σ) Ma, whereas the Peel River showing yields an isochron age of 387.5 ± 4.4 (2σ) Ma. Within error, these ages are identical and overlap with the biostratigraphically constrained age of the sedimentary host rocks, indicating that mineralization and sedimentation were coeval. Significantly, the ages of the HEBS overlap those of Middle Devonian Kačák, pumilio, and Taghanic global-scale biotic events which are characterized by eustatic sea-level rise and black shale deposition. Linkage of the Yukon HEBS to one (or more) of these bio-events indicates that sea-level rise may have been requisite to formation of basin-scale HEBS mineralization in northwestern Canada during latest Eifelian and Givetian time.

Lithogeochemical characterization of the Middle–Upper Devonian Road River Group and Canol and Imperial formations on Trail River, east Richardson Mountains, Yukon: age constraints and a depositional model for fine-grained strata in the Lower Paleozoic Richardson trough

Lithogeochemical characterization of the Road River Group and Canol and Imperial formations as exposed at an outcrop on Trail River, eastern Richardson Mountains, documents the evolution of a Laurentian-margin basin during the latest Eifelian through middle Frasnian stages. δ13Corg stable isotope data correlated to conodont-constrained global isotopic curves indicates deposition of the section from ≥387.7 to ≤376.7 Ma. The uppermost Road River Group is latest Eifelian and older in age (≥387.7 Ma) and is primarily calcareous and dolomitic shale and mudstone, representing a slope environment below a carbonate platform that experienced cyclical turbidity current deposition. A 2.3 m, metalliferous and concretionary unit lies transitionally between the Road River Group and Canol Formation and is herein designated as an informal, conformable, lithologic unit called the Road River – Canol transition zone (RCTZ), which records 4.5 Ma of condensed sediment deposition during the Givetian stage (387.7–383.2 Ma). The Canol Formation is confined to the latest Givetian to middle Frasnian stages (383.2–376.7 Ma) and consists of rhythmically bedded, biogenically sourced, siliceous shale and chert that was deposited in an anoxic (and likely euxinic) to oxic basin that evolved from moderately to strongly hydrographically restricted over time. The lowermost Imperial Formation is a siliciclastic mudstone, which documents turbidity current deposition in oxic bottom water conditions in the late Frasnian (≤376.7 Ma). Interpretation of lithofacies, whole-rock geochemistry, mineralogy, and total organic content enable the section to be grouped into eight lithochemozones that record a first-order late-stage sea-level transgression (Road River Group and RCTZ), highstand (lower Canol Formation), and early-stage regression (upper Canol Formation) followed by continued falling stage sea-level conditions with strong detrital influence from a continental collision in the high Arctic (Imperial Formation).

Helicopter AFMAG (ZTEM) EM and magnetic results over sedimentary exhalative (SEDEX) lead-zinc deposits at Howard’s Pass in Selwyn Basin, Yukon

In 2008, a regional scale 24,675 line-km survey covering a 25,000 km2 area (1 km line spacing) was flown in the Selwyn Basin. The survey footprint straddles east-central Yukon and overlaps into the western North-west Territories. In March 2013, Yukon Geological Survey purchased the survey data and, in November 2013, released the data publicly. The Selwyn Basin area is prospective for sedimentary exhalative (SEDEX)-style Pb–Zn–Ag mineralisation and the z-axis tipper electromagnetic (ZTEM) survey data provide insights into regional structures and plutons in the region. The survey overflew the Howard’s Pass SEDEX deposits at the south-eastern edge of the Selwyn Basin survey area that hosts a ~250 million tonne resource with ~4.5% Zn and ~1.5% Pb. Airborne geophysics has not been extensively used in SEDEX exploration of the Selwyn Basin and the ZTEM survey is one of the few publicly available airborne audio-frequency magnetic (AFMAG) EM-magnetic datasets that offer the opportunity to study the deposit response at Howard’s Pass in close detail.Rock physical properties indicate that the lowest resistivities are associated with the Road River Group that contains the Pb–Zn mineralised horizon at Howard’s Pass, but also include graphitic shales in the same formation. Major NW–SE to ESE and minor NNW–SSE linear conductive trends correlate with known regional geologic, structural and inferred mineral trends that were previously not visible in magnetic results. At the deposit scale, a thin NW–SE trending conductive lineament extends along the > 37-km-long ‘Zinc Corridor’ horizon at Howard’s Pass, but must include both the Pb–Zn sulphide mineralisation deposit horizon as well as the surrounding graphitic black shales. 2D and 3D ZTEM inversions reveal zones of enhanced conductivity along strike and at depth that appear to correlate with the clustering of Pb–Zn deposits, which had not been previously noticed.

Palaeomagnetism of the Howards Pass Zn-Pb deposits, Yukon, Canada

SUMMARY The Howards Pass district is located in the Selwyn Basin, Yukon. The district consists of >15 laminated clastic-dominated (CD) sphalerite–galena (Zn–Pb) deposits in the ‘zinc corridor’ that trends northwest–southeast and extends for ∼35 km. The stratiform mineralized zone, the Active Member, is hosted in carbonaceous cherts and black shales of the Early Silurian Road River Group. Using mostly thermal and then alternating field step demagnetization isolated a stable characteristic remanent magnetization (ChRM) by the core-magnetization-angle method from 18 sites (339 specimens) in 18 variably oriented exploration drill hole cores from 6 Zn–Pb mineralized panels. Rock magnetic analyses show that the main remanence carriers are single- or pseudosingle-domain pyrrhotite and titanomagnetite. The deposits’ mean ChRM direction yields a pole position of either ∼170 Ma on the North American apparent polar wander path or ∼162 Ma on a corrected path for the Intermontane Belt (IMB) terranes. A negative palaeomagnetic fold test indicates that the mineralization's ChRM is post-folding, setting a minimum age for regional metamorphic deformation of ∼170 ± 20 Ma and supporting an Early Jurassic arrival for the IMB's collision and accretion to North America. An autochthonous or para-autochthonous North American tectonic model is favoured for the ChRM of the metamorphosed Selwyn Basin strata rather than an allochthonous IMB model. Further, the palaeomagnetic age indicates that the coarse-grained Zn–Pb mineralization in fine fractures that cut the laminated fine-grained Zn–Pb mineralization at Howards Pass at least was formed by remobilization during Middle Jurassic metamorphism.

The sequence and correlation of Early Ordovician (Arenig) graptolite faunas in the Richardson Trough and Misty Creek Embayment, Yukon Territory and District of Mackenzie, Canada

Four graptolite biozones are recorded from the Arenig portion of the Road River Group in the Richardson and Mackenzie mountains in the Yukon and Northwest Territories. In ascending order, these zones are Tetragraptus approximatus, Pendeograptus fruticosus, Didymograptus bifidus, and Parisograptus caduceus australis (new). The Castlemainian stage may be represented by nongraptolitic massive bedded chert. The Arenig–Llanvirn boundary is drawn below the first occurrence of Undulograptus austrodentatus. Fifty-four graptolite taxa are present, and 16 of these species and subspecies are recorded for the first time in this deep-water biotope, namely, Didymograptus? cf. adamantinus, D. asperus, D. dilatans, D. cf. kurcki, D. validus communis, Holmograptus aff. leptograptoides, H. sp. A, Isograptus? sp. nov. A, I. ? dilemma, Keblograptus geminus, Pseudisograptus manubriatus harrisi, Ps. m. koi, Ps. m. janus, Ps. cf. tau, Xiphograptus lofuensis, and Zygograptus cf. abnormis.

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

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.

Conodont biostratigraphy of the Lower to Middle Devonian Deserters Formation (new), Road River Group, northeastern British Columbia

A new Lower to Middle Devonian basinal unit of the Road River Group, herein formally named the Deserters Formation, contains argillaceous, crinoidal limestone and black shale deposited in a linear sub-basin of the Ospika Embayment, southern Kechika Trough. The abrupt lateral facies changes in the region, facies thickness, and occurrence of volcanics indicate a period of extensional tectonism. A total of 53 (4–5 kg each) samples from the Deserters Formation yielded 7766 conodont elements assigned to 14 genera representing 33 species. The formation ranges from the Lochkovian (eleanorae Zone, or lower part of the delta Zone of the Cordilleran Region) to Eifelian (australis Zone). The temporal constraints established by conodont biostratigraphy allow correlation to the Grizzly Bear Formation, a regionally restricted Lower to Middle Devonian unit in the Selwyn Basin to the north.

CONODONTS FROM A PLATFORM-TO-BASIN TRANSECT, LOWER ORDOVICIAN TO LOWER SILURIAN, NORTHEASTERN BRITISH COLUMBIA, CANADA1

Abstract The conodont fauna from nine sections across a platform-to-basin transect in northeastern British Columbia includes species of Early Ordovician (Tremadocian) to Early Silurian (Llandovery) age. A collection of 9,110 conodont elements was recovered from 205 samples taken from nine stratigraphic sections that preserve the platform succession of the Kechika, Skoki, Beaverfoot, McCusker and Nonda Formations and their off-shelf equivalents, the Ospika, Robb, Kenny and Laurier Formations of the Road River Group. The fauna is assigned to 106 species representing 67 genera; the Ordovician species are representative of two faunal realms. One new genus, left in open nomenclature, is described. Five new species include Drepanoistodus latus and four new species left in open nomenclature assigned to the following genera: Walliserodus, Multioistodus?, Pseudooneotodus, and Belodina. The Midcontinent Realm zones recognized include, in ascending order, the Acodus kechikaensis, Oepikodus communis, Jumudontus ganan...

Conodonts from a platform-to-basin transect, lower Ordovician to lower Silurian, northeastern British Columbia, Canada

The conodont fauna from nine sections across a platform-to-basin transect in northeastern British Columbia includes species of Early Ordovician (Tremadocian) to Early Silurian (Llandovery) age. A collection of 9,110 conodont elements was recovered from 205 samples taken from nine stratigraphic sections that preserve the platform succession of the Kechika, Skoki, Beaverfoot, McCusker and Nonda Formations and their off-shelf equivalents, the Ospika, Robb, Kenny and Laurier Formations of the Road River Group. The fauna is assigned to 106 species representing 67 genera; the Ordovician species are representative of two faunal realms. One new genus, left in open nomenclature, is described. Five new species includeDrepanoistodus latusand four new species left in open nomenclature assigned to the following genera:Walliserodus, Multioistodus?,Pseudooneotodus, andBelodina. The Midcontinent Realm zones recognized include, in ascending order, theAcodus kechikaensis, Oepikodus communis, Jumudontus gananda, Tripodus laevistoPlectodina aculeatazones,Phragmodus undatusandGamachignathus ensifer? zones. Zonal species of the Atlantic Realm areMicrozarkodina flabellum, Eoplacognathus suecicus, Baltoniodus variabilis, Pygodus anserinus, andAmorphognathus tvaerensis. The Silurian fauna, of lower diversity than the Ordovician fauna, is representative of theDistomodus staurognathoidesandPterospathodus amorphognathoideszones.

Conodonts from the Kechika Formation and Road River Group (Lower to Upper Ordovician) of the Cassiar Terrane, northern British Columbia

This study examines the lower Paleozoic stratigraphy of the Cassiar Terrane from three key sections comprising an east-west transect across the terrane. The Cassiar Terrane, west of the Northern Rocky Mountain Trench, consists of a Neoproterozoic to Triassic succession and is a fragment of the Cordilleran Miogeocline that has been displaced northward. The amount of displacement from its original position remains controversial. Conodonts from the Cassiar Terrane have been previously reported from only a few reconnaissance studies. More than 3000 m of strata have been measured and examined in detail and 85 conodont samples collected. A total of 926 identifiable conodont elements are assigned to 31 species representing 21 genera. The conodonts are mainly representative of the Midcontinent Faunal Realm, but some also represent the Atlantic Realm. Conodonts from the upper Kechika Formation and base of the Road River Group are Early Ordovician (Tremadocian) in age, and those from the upper Road River Group range into the Upper Ordovician (Caradocian). The detailed Ordovician stratigraphy and temporal constraints established by conodont biostratigraphy provide for correlation to coeval facies of ancestral North America. The onset of Road River sedimentation in the mid-Tremadocian is, however, older than that in the Macdonald Platform to the east (early Arenigian). This onset timing may help link the Cassiar Terrane to a specific part of the miogeocline from which it was transported.

Conodonts from the Kechika Formation and Road River Group (Lower to Upper Ordovician) of the Cassiar Terrane, northern British Columbia

Conodonts from the Kechika Formation and Road River Group (Lower to Upper Ordovician) of the Cassiar Terrane, northern British Columbia

Some graptolites from the late Tremadoc and early Arenig of Yukon, Canada

Ten graptolite species from upper Tremadoc and lower Arenig strata are described from a 160 m thick, homoclinal, totally exposed section of the Road River Group in the Upper Canyon of Peel River, Yukon. This is believed to be one of the most complete sequences of this age range known to science. Graptolites were collected from 40 levels in the (lowest to highest) Adelograptus antiquus, Kiaerograptus pritchardi, Paradelograptus kinnegraptoides, Tetragraptus approximatus, and Pendeograptus fruticosus biozones. Two new species described are Paradelograptus rallus sp.nov. from the K. pritchardi Biozone and Kinnegraptus reclinatus sp.nov. from the Tetragraptus fruticosus Biozone.

Silurian hexactinellid sponges from northern British Columbia, Canada

Faunules of largely hexactinellid sponges have been collected from siltstones of Early Silurian Wenlock or latest Landovery age within the upper Road River Group from northern British Columbia. The assemblages include the new species: Protospongia columbiana, Hexatractiella pseudonevadensis and Cyathophycus akiensis. Other taxa described include the hexactinellids Protospongia conica Rigby and Harris, 1979, Hexatractiella nevadensis (Rigby and Stuart, 1988), Diagoniella sp., Gabelia pedunculus? Rigby and Murphy, 1983, and a specimen of the monaxonid demosponge Wareiella typicala Rigby and Harris, 1979. Also included is a fragment of what must have been a steeply obconical-cylindrical hexactinellid sponge of uncertain taxonomy; it has a skeleton of robust hexactines in an unquadruled net, above a root-tuft of 10-20 spicules. Other sponge impressions include small circular clusters of hexactines with radiating, to basketlike patterns and somewhat similar, isolated and dissociated, long probably roof tuft spicules and possible basal root tuft rosettes of monaxons. The faunules are similar to other outer continental margin, black shale, sponge assemblages of the Early Paleozoic Era, and include elements previously described from northern British Columbia and central Nevada.

Petrology of graptolites and their utility as indices of thermal maturity in Lower Paleozoic strata in northern Yukon, Canada

The optical characteristics and utility of graptolites as a measure of thermal maturity have been evaluated by measuring maximum, minimum, and random reflectance of specimens from the Lower Paleozoic Road River Group in northern Yukon. The progressive changes in optical properties of graptolites produced by increasing depth of burial are corrected to the optical properties of other organic matter (conodonts and bitumen) in the same sample. Measurement of maximum reflectance ( R o max) is the most reliable method of assessing the level of thermal maturity of gratolites because they have biaxial optical properties. At high levels of maturation the reflectance of graptolites is greater than that of vitrinite, whereas at low levels of maturation the reflectance of vitrinite is greater. In the Road River Group, the mean maximum reflectance of graptolites varies laterally from 4.0% to 6.5% R o max· R rmo max f graptolites increasing depth of burial and the relationship between reflectance and depth fits a log (reflectance)-linear (depth) relationship. The vertical increase of maximum reflectance of graptolites through an 800-m section ranges from 4.2% R o max at the top to 6.5% R o max at the bottom yielding a maturation gradientof 0.39 log % R o max km −1. A correlation of graptolite reflectance calibrated by color changes of conodonts (CAI) indicates that Road River strata are overmature (CAI = 5,4.0–6.5% R o max, graptolite reflectance) with respect to hydrocarbon generation.

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

Upper Ordovician carbonate beds within clastic strata of the Road River Group, northern Yukon Territory, 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. ornatus Zone and between this zone and the succeeding P. pacificus Zone. These conodonts have a range of "Trentonian" –Gamachian (upper Caradoc –Hirnantian).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. pacificus 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.

Middle and Late Ordovician conodont faunas and biostratigraphy of graptolitic strata of the Road River Group, northern Yukon Territory

Ordovician conodont faunas from the fine-grained clastic Road River Group in northern Yukon Territory contain a mixture of species from both warm- and cold-water regions. This group in southwestern Northwest Territories also has mixed faunas, whereas conodonts from the carbonate facies are more characteristic of the warm-water regions.Six conodont associations and biozones are identified from the Yukon. Some, such as the early Llanvirn "Cordylodus" horridus – Spinodus spinatus association, contain reworked elements. The Pygodus serra Zone (middle–late Llanvirn) is within the upper P. tentaculatus Zone and well below the G. euglyphus Zone. Genera include Ansella, Periodon, Protopanderodus, Pygodus, and Walliserodus.At Peel River, conodonts are within the P. pacificus Zone. The Blackstone River conodonts occur above the P. pacificus Zone and below the G. persculptus Zone (?) and include Oulodus rohneri, Plectodina florida, and Noixodontus. Amorphognathus ordovicicus, Gamachignathus ensifer, O. ulrichi, and Plectodina tenuis occur in both faunas. These represent Fauna 12, found in late Richmondian strata, rather than the Gamachian Fauna 13 and are assigned to the G. ensifer Zone; both occurrences of G. ensifer are biohorizons. The C.? extraordinarius and G. persculptus zones are not recognized at Peel and Rock rivers and Tetlit Creek.The Ozarkodina n. sp. A – Icriodella sp. B association occurs at Pat Lake between the G. persculptus Zone (?) and the underlying P. pacificus Zone. The Ozarkodina have a Silurian aspect but must be regarded as Ordovician.The Ordovician–Silurian boundary in the Road River Group of the Yukon is best defined using graptolites because of the rare occurrence of conodonts.