Road River Research Articles

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.

New Middle Silurian hexactinellid sponge from the Mackenzie Mountains, Northwest Territories, Canada

Several specimens of the small hexactinellid, Cyathophycus mackenziensis n. sp., were collected from pale brown, shaly mudstone of the Road River Formation. The sponges are of Wenlock age and were collected from near Avalanche Lake, Mackenzie Mountains, Northwest Territories, Canada. The small, steeply obconical sponges have skeletons in crudely ranked quadrules to at least third-order, with first-order openings generally 2 mm high and 1 mm wide. Successive orders decrease in stages approximately half that of larger elements. A moderately irregular dermal(?) layer with circular parietal gaps is suggested in some specimens. The new species is consistently finer textured than either the type species Cyathophycus reticulatus Walcott, 1879, or the later described Cyathophycus quebecensis Dawson, 1889.

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.

Alexander Mackenzie (1764-1820)

This profile recounts the two major expeditions undertaken by Alexander Mackenzie to discover a watercourse which would lead to the In 1789 he travelled down an unknown river until he perceived the rise and fall of the tide in the fog-bound delta. Although he is celebrated today for having discovered this major North American watercourse and for having made the return trip of 5000 km in a phenomenal 102 days, Mackenzie considered his expedition a failure. The river, after all, had not led to the Pacific. In 1793 Mackenzie paddled up the Parsnip River, and then made a difficult carry crossing over into the Fraser. Near the modern community of Alexandria, B.C., Indians advised him not to follow the Fraser but to go back upriver to where the West Road River flows into At that juncture, they trekked overland to reach the Pacific at the mouth of Bella Coola River. Mackenzie is lionized for his speed and efficiency in penetrating new lands as he sought a route to the Pacific, condemned and celebrated for the way he drove men as he pursued his goals, the powerfully built Alexander Mackenzie had no illusions about why he was drawn to the unexplored tracts of Rupert's Land. Soon after completing his second historic journey, he candidly expressed his feelings toward the Athabasca district in a personal letter: I think it unpardonable in any man to remain in this country who can afford to leave it. And leave it he did, returning to Britain for good in 1810.

Shelf to Basin Transition of Silurian-Devonian Rocks, Porcupine River Area, East-Central Alaska: ABSTRACT

Exposures of Silurian to lowermost Devonian strata in the Porcupine River region consist of an unnamed carbonate unit and the Road River Formation. Petrographic studies indicate that these rocks display facies representative of five depositional environments: basin, open sea shelf, deep shelf margin, open platform, and restricted shelf. The unnamed carbonate unit, exposed in the Linear Ridge area, is 390 ft (126 m) thick and records a history of restricted shelf to basinal sedimentation. Stratigraphic relations and paleontological studies suggest a Middle to Late Silurian (Ludlovian) age for this unit. The Road River Formation is Late Silurian (Ludlovian) to Early Devonian (Lochkovian) in age and is exposed near the confluence of the Porcupine-Salmontrout Rivers and downstream along the Lower Ramparts. It consists of 30-190 ft (10-61 m) of graptolitic shale with interbeds of siliceous limestone. Petrographic studies of the shales are interpreted to reflect deposition in a basinal setting, whereas the siliceous limestones represent deep shelf-margin debris flows derived from nearby, coeval shallow-water shelf environments. Together, the unnamed carbonate unit and the Road River Formation represent a shelf to basin transition on a carbonate ramp that transcends the Silurian-Devonian boundary. Petrographic examination of these rocks reveals that they are susceptible to a wide range of diagenetic processes, including (1) micritization, (2) neomorphism, (3) syntaxial overgrowths, (4) pressure solution (stylolitization), (5) trapping of dried hydrocarbons, (6) tensional stress (calcite veining), and (7) silicification. End_of_Article - Last_Page 659------------

Stratiform sulfide and barite–fluorite mineralization of the Vulcan prospect, Northwest Territories: exhalation of basinal brines along a faulted continental margin

Laminated and massive sulfide (pyrite, sphalerite, galena) mineralization and massive barite – fluorite–galena lenses occur in Upper Silurian – Lower Devonian Road River Formation shales of the Vulcan property along the eastern flank of the Selwyn Basin, Northwest Territories, Canada. The 5 km thick stratigraphic section, ranging in age from Hadrynian through Mississippian, offers insight into the nature of the Mackenzie Platform – Selwyn Basin transition. Abrupt facies changes, synsedimentary faults, debris flows, local unconformities, and the presence of high-potassium mafic flows indicate extensional tectonics during deposition of the Road River Formation. Mineralization resulted from heated, metal-rich basinal brines that vented on the sea floor up normal faults.Sulfur-isotope studies indicate that both sulfate and sulfide were derived from the exhaling metalliferous brine. Sulfur-isotope data also suggest that reduction of sulfate in the brine occurred as a result of organic decomposition, possibly during thermal maturation of hydrocarbons at temperatures greater than 80 °C. Fluid inclusion observations indicate that the brine salinity reached 26 wt.% NaCl for at least a portion of the evolution of the hydrothermal system.Cooling of the brine during venting into bottom waters caused initial rapid precipitation of fine-grained barite, resulting in a baritic buildup above vent areas. Continued percolation of the brine through the baritic mound caused recrystallization of the barite and then the deposition of interstitial fluorite and galena. In other areas the dense ore fluid collected in topographic depressions, or brine pools, in which sulfide minerals accumulated under anoxic conditions. Location of hydrothermal vents, paleotopography, and intensity of hydrothermal activity were the main controls on the thickness, distribution, and grade of Vulcan mineralization.

Ordovician Formations and Faunas, Southern Mackenzie Mountains

Ordovician strata of the South Nahanni River area occur as a western fine clastic facies with graptolitic faunas (Road River Formation) and an eastern carbonate facies with shelly faunas (Broken Skull, Sunblood, Esbataottine, and Whittaker Formations). The lithofacies are controlled by major tectonic features. In the early Ordovician the Selwyn Basin received fine clastic sedimentation (Road River) while carbonate sedimentation (Broken Skull, Sunblood, Esbataottine) was confined to the Root Basin and the fringes of the emergent Redstone Arch. Later in the Ordovician a pronounced transgression caused a marked eastwardly shift of facies belts and resulted in the flooding of the Arch and deposition of a widespread carbonate sheet (Whittaker) in the northeastern part of the study area.The carbonate facies of the Root Basin and south of the Redstone Arch contains a complete record of shelly faunas of Canadian to, probably, Maysvillian age. The Broken Skull Formation consists of craggy weathering, variably sandy carbonates and contains, in its highest parts, the Hesperonomia fauna (Canadian). The Sunblood Formation consists of generally resistant, red-orange-buff weathering limestones and minor dolostones and contains two faunas; the Orthidiella-'Goniotelina' fauna (Whiterockian) and the Bathyurus sp. 1 fauna (?Chazyan). The Esbataottine Formation (proposed) comprises moderately recessive, grey-buff weathering limestones and contains two faunas; the Mimella fauna (Chazyan) and the Doleroides fauna (Blackriveran). The lower Whittaker Formation (Trentonian to ?Maysvillian) comprises three lithosomes containing discrete faunas which appear to represent coeval communities: The Strophomena-Ceraurus fauna in thinly bedded, argillaceous limestones; the Bighornia-Thaerodonta fauna in well bedded, nonargillaceous limestones; and the Hesperorthis-Oepikina fauna in well bedded dolostones. A unique fauna of deep water aspect, the Cryptolithus-Anataphrus fauna, occurs in shales and black limestones of the Road River Formation and is, in part, equivalent to the faunas of the lower Whittaker Formation. The Sunblood, Esbataottine, and Whittaker Formations contain abundant and well preserved silicified trilobites; many of which are reported for the first time from western and northern Canada.

Regional Geology of Northern Yukon1

ABSTRACT Structurally the northernmost Yukon is part of the Eastern Cordilleran System, and in many respects it is an eastward extension of Brooks Range and the adjacent structural provinces of northern Alaska. Comparisons may also be made between the geological history of the northern Alaska - northern Yukon region and that of the Canadian Arctic Islands, a fact that has led to some speculation concerning the possible contiguity of these two areas throughout much of Phanerozoic time. This report will deal with British and Barn Mountains, Old Crow Plain and Dave Lord Ridge. Richardson Mountains will not be discussed in detail. The Ordovician, Silurian and possibly much of the Cambrian are represented east of Dave Lord Ridge by approximately 10,000 ft of fine-grained clastic sediments, the Road River Formation. Rocks of similar age in British and Barn Mountains and Brooks Range are strongly deformed metasediments (Neruokpuk Formation). Deposition of the Road River Formation took place in a basin named the Richardson Trough, which may have been a southward extension of the Franklinian Geosyncline of the Canadian Arctic Islands. A major tectonic episode, the Ellesmerian Orogeny, affected northern Yukon, northern Alaska and the Arctic Islands in several separate phases during the Devonian. The Neruokpuk underwent low-grade regional metamorphism at this time and several granite stocks were emplaced, including that at Mount Sedgwick in British Mountains. Thick syntectonic and post-tectonic clastic wedges were formed nearly everywhere near the present Alaskan and Canadian Arctic coasts, except within the Yukon, as a result of a mid-Devonian pulse of the Ellesmerian Orogeny. Between the Early Mississippian and the Late Triassic the Lisburne Group and the Sadlerochit and Shublik formations were deposited. The Lisburne and Sadlerochit are two of the most important reservoir rocks at Prudhoe Bay. Lisburne sediments, mainly carbonates, are confined (within the report area) to British and Barn Mountains. The Sadlerochit Formation (coarse-grained, porous clastic deposits) is well developed in the Dave Lord Ridge area but is thin or absent in northeastern British Mountains. The Shublik is typically developed in British Mountains. The principal sediment source area for northern Alaska and northern Yukon during the Cambrian to Jurassic period appears to have been located off the 1 Manuscript received February 9, 1972. 2 Shell Canada, P.O. Box 880, Calgary, Alberta. Present address: Institute of Sedimentary and Petroleum Geology, Calgary. This paper has developed from a field and photogeological study carried out between July 1970 and March 1971 while the author was in the employ of J. C. Sproule and Associates Ltd. The project was carried out for Charter Oil Company Ltd. Both these companies are to be thanked for granting me permission to publish the material. C. W. Drew provided an invaluable preliminary photogeological interpretation of the project area. R. Cech was my very energetic field assistant. The ideas presented herein have benefited considerably from discussions with D. K. Norris, I. Tailleur and W. O. Kupsch, all of whom have read the manuscript. Finally, grateful thanks are due to Shell Canada Limited for providing me with drafting and typing services. L. H. Taylor drew the illustrations and Mrs. J. Barnes typed the final manuscript. End_Page 81------------------------- present Arctic Coast and may have been part of the same source area that contributed detritus to the Canadian Arctic Islands region. Jurassic, Cretaceous and Tertiary sediments are almost exclusively clastic in northern Yukon. They were derived from several sources including an ancestral Brooks Range and Campbell Uplift of the Inuvik area. The Cretaceous marks a major shift in sediment dispersal patterns, particularly in northern Alaska, as a result of large-scale changes in the distribution of land and water masses at this time. These may have been caused by major continental-drift movements in the area of the Arctic Ocean Basin. A major tectonic episode, the Eurekan Orogeny, took place between Middle Cretaceous and Early Tertiary times in northern Yukon (and in Alaska and the Arctic Islands), involving all but the most recent sediments. No igneous activity has been recorded in connection with the Eurekan Orogeny in northern Yukon but most of the structural deformation of the post-Devonian rocks dates from this time.

Late Early Devonian Dacryoconarid Tentaculites, Northern Yukon Territory

The late Early Devonian succession in northern Yukon Territory contains a well-preserved dacryoconarid tentaculite fauna dominated by Turkestanella acuaria (Richter) in the upper part of the Road River Formation and T. acuaria and Nowakia parabarrandei Churkin and Carter in the overlying Michelle Formation. Based on the dacryoconarid tentaculite fauna the bulk of the Michelle Formation in the Ogilvie to Hart Rivers area is dated as late Pragian (early Emsian), and based on the graptolite and dacryoconarid tentaculite fauna the uppermost Road River Formation in the Blackstone River area is dated as Pragian (early Emsian or late Siegenian or both). The appearance of species of Nowakia in northern Yukon considerably earlier than in Bohemia is documented. It is concluded that some genera of the Dacryoconarida were influenced in their occurrence by environmental factors. New species described are Turkestanella minuta, Viriatellina michellensis, Guerichina lenini, Styliolina blackstonensis, and Metastyliolina conica.

Lower Paleozoic Rocks of Alaska [Abstract

ABSTRACT Cambrian rocks are presently known only from east-central Alaska where a succession of shelly fossils, ranging in age from Early through Late Cambrian, occurs in a thin (300 feet) carbonate section that grades downward into the Tindir Group, a thick (10,000+ feet) sedimentary series of Precambrian age. Ordovician rocks occur in a few separated areas and are widely different in facies. Thousands of feet of graywacke, shale, chert, and volcanic rocks in southeast Alaska contrast with thinner, predominantly carbonate sections in the Alaska Range, Seward Peninsula, and Porcupine River. The Road River Formation, a graptolitic shale less than 900 feet thick, seems to represent an intermediate facies in east-central Alaska that spans most of Ordovician and Silurian time. Silurian and Devonian rocks are generally similar in facies to the Ordovician rocks. In the Brooks Range, however, there is a thick (5,000 feet) succession of predominantly argillaceous rocks of Devonian age, and in southeast Alaska there are Silurian and Devonian limestones thousands of feet thick in an otherwise volcanic and detrital sequence. Coarse clastic rocks of Late Devonian age in the Brooks Range (Kanayut Conglomerate) and east-central Alaska (Nation River Formation) indicate uplift of the earlier geosynclinal deposits. 1 Reprinted, with permission, from Oilweek, v. 17, no. 14, p. 23-24. End_of_Record - Last_Page 603-------

Ordovician, Silurian, and Devonian Biostratigraphy of East-Central Alaska

A predominantly shale and chert sequence has been mapped from the Canadian border at Latitude 65°00^prime N. to the Nation River about 25 miles northwest. It has Ordovician and Silurian graptolites in the lower half, and Middle Devonian corals and Upper Devonian spores in the upper half. The lower half of the sequence consists of about 400 to 900 feet of predominantly dark gray graptolitic shale with lesser amounts of grayish black laminated chert. This unit has been traced by Green and Roddick from the international border southeastward into the Dawson area of the Yukon Territory and northeastward into the Ogilvie and Richardson Mountains where it has been mapped by Jackson & Lenz, Norris, and others as the Road River Formation. In the Tatonduk-Nation Rivers area the Road River Formation rests disconformably on a sequence of Middle and Upper Cambrian limestone that locally may include Lower Ordovician (Tremadoc) beds at its top. The sequence of graptolite faunas from the Road River Formation in Alaska is essentially the same as the graptolite zones established by Elles and Wood in Great Britain. All the standard series of the Ordovician and Silurian are probably represented in the formation with the exception of the Tremadoc and possibly the Arenig and Wenlock. Overlying the Road River Formation is a formation, 200 to 800 feet thick, consisting predominantly of thinly bedded and laminated light gray to black chert and siliceous shale that is here named the McCann Hill Chert. This new formation disconformably overlies the Road River Formation, and its lower boundary is at the base of a distinctive limestone and shale member. The basal limestone and shale member of the McCann Hill Chert contains a remarkably varied fauna including corals, brachiopods, trilobites, conodonts, ostracods, and fish of Eifelian (early Middle Devonian) age. Spores from the upper part of the formation resemble those from the overlying Nation River Formation and indicate a Late Devonian age. The McCann Hill Chert is conformably overlain by the Nation River Formation--a thick succession of inter-bedded graywacke, chert conglomerate, and silty shale of Late Devonian age. In the vicinity of Jones Ridge, only 7 miles north of exposures of the Road River Formation, Upper Cambrian limestone is overlain by a pure limestone section containing Ordovician, Middle Devonian, and perhaps Silurian shelly faunas contemporaneous with the Road River Formation and the thinner basal limestone and shale member of the McCann Hill Chert. The rapid change from graptolitic shale to limestone probably reflects changes in conditions of sedimentation, but could be a result of thrust faulting. The Tatonduk-Nation Rivers area seems to lie in a transitional zone between an early Paleozoic eugeosynclinal belt south of the Yukon River and a contemporaneous miogeosynclinal belt along the Porcupine River. One puzzling feature of the lower Paleozoic sequence in the Tatonduk-Nation Rivers area is its thinness in contrast to the much thicker volcanic and detrital sequence on the south and the considerably thicker carbonate sequence on the north.

Zonation of Ordovician and Silurian Graptolites of Northern Yukon, Canada

Twenty-two graptolite zones are recognized in the Ordovician and Silurian graptolitic shales of northern Yukon and their geographical distribution, faunal assemblages, and correlation with Europe and Arctic Islands are commented upon. All the stages and sub-series in the Ordovician and Silurian of Britain are recognized. A new formational name, Road River, is proposed for the Siluro-Ordovician graptolitic shales and carbonates of the region. At its type locality, the formation is underlain conformably by Cambrian (?) shales and argillites, and overlain disconformably by Devonian Fort Creek shale. The formation is Tremadocian to Ludlovian in age and the Siluro-Ordovician boundary is located on a faunal break.