Devo INTR ODUCTIO on P Eozoic Atf Erlie a Vast Are Million 2 Son Bay. T

CA NADA

G. TELFOR

A BSTR RACT

The M ose Riv er Basin is an in tracrat onic Paleoz oic sedim enta ry basi n un derlyin g th e Ja mes Bay L owland of n or theas tern Onta rio and containing strata rangin g from Ord dovicia n to Uppe r Devon ian age. Exce pt alo ng g th e mildly defo rmed d easte ern m argin st rata a re gene ra lly flat-lyi ing. Devonian carbon ates, sha les, evapori tes and mino ssic a nd Cretac eous clastic sediments o ve rlies the D evonian rocks inthe sout heastern pa rt of t he basin and the en tire region is blankete d by Pleist ocene glacial d eposits and Rec ent mari ne clays. Th e Devon ian suc cession com pris es, in asce nding order: Lower Devo nian Kenogam i R ver (upper part only; dolom mitic lim estone), St ooping River (mainly lim estone ) and Sextan s), M urray Islan d (lime tone) and W lli ams Island (s hal , carbo nates) Formation ; and the Up per Devoni n Long Ra pids Form ation (b lack shale, mudstone minor carbo nate s). The apparently s mple s tratigrap hy s com mpli cated by lateral fa cies variations, including a co ntinental to marine tr ansition am ong t he Low wer Devo

INTR ODUCTIO ON P eozoic atf erlie a vast are million 2 son Bay. T ibute d amon r m ain te ctonic e lem viz. are distributed am se Riv er and oxe Ba ins, and th e Foxe Chan nel-H udson S trait gra ben syst em. How ever, D Devo- nian str ins. like the ot men f the atfor m, y the w

which are nnel an d Strait , the Moose in is nn under lyi mes Bay tario (Fig. 1). A sm all segm extend s i nto the adjo eath he wate rs of J mes B ay. The underlies an are The M o2os e Rive r B ded approx of 05' a nd nd gitudes ti . M os t of t e on hore por ion of th basin is c harac- y a ve ry fla y, s parsely vegeta plain. ess is po oor, bei a single ine along the e tern margin of the low land ooson on Jam es B Bay. ossed by s al major north to no The re , includ evera ma or nort tagami rth- east flo vers merge ng t rm the Moos attagam i and farthe aib i (which m and Attaw api . O and farther n orth eozoic stricted t ps o f Paleozo or tribu ms. Th e River Basin (Fig. 1) is Th fault c ontrolled an def ined ph ysiogra north facing esca ment an d an abrupt chan ge from lly by a nort mpy cing escarpme

nd weste s of the b asin (a ive y sharp d lowland are cambrian edim swamp rain west wland passes i nto the ma ange. H However, i he M ive r is cle rly separa ted f om the H Hu dson Bay Basin by a basement struc tur al hi gh refer red to the Cape Henrietta Maria A ch (Fig. 3). Th surf ace of this no thea st trending f eature is mark ed by an area of Ar chaean and Prote roz oic r ocks kno w n as the S utton L ak es Inlier. H owever, the a rch w as not a omplete ba rrier to Paleoz oic sedim entation and , in places contains a thin seq uenc e of Upper Ordo vician and Lower Sil urian limesto nes and ly on n Prec ambrian t erra in. sequence of Devonian stra the Moose R ver Basi ratigraphic r ips w ith the Moose Ri though d ins. Parts of ne e Devo nian se ens sive inves tigation lated by po ential hy dro- carbon and i with in min eral ated by pot entia sell and Telfor d, 1984; Ru ssell etal, 1985; es source on and ssell and Te 85). There efore, th e present pap s based on and Telfo revious rep orts, pa he ma tions of the Ge log ical S urv ey o f Canada (e.g ., Sanfo d an d Norris, 1975), as w ell as o n prelimi nar y re sults an d ongoing activitie

124 Telford

Paleozoic units is from Sanford and Norris (1975). relatively stable tectonic element, as evident by the thin Phanerozoic cover of less than 1000 m. Paleozoic strata range from Middle Ordovician to Upper Devonian age (Fig. 2) and consist of approximately 700 m of marine carbonates, shales, evaporites, and minor marine and continental clastic rocks. The Ordovician to Lower Silurian strata are confined to the western and northern margins of the basin so that, in much of the remainder of the region, the Upper Silurian or Devonian rocks rest directly and unconformably on Precambrian basement (Russell et al., 1985). Composite thickness of the Ordovician and Silurian strata is about 300 m. The former consist mainly of shallow marine or supratidal carbonates, probably representing a minor transgression from the northwest over the Cape Henrietta Maria Arch/The succeeding Lower Silurian sequence is dominated by marine carbonates consisting, in part, of a basin margin reef complex and associated carbonate units positioned along the southern side of the arch. The only Silurian strata that are reasonably widespread in the basin are those of the lower and middle members of the Kenogami River Formation. Devonian strata thus make up most of the Paleozoic stratigraphic sequence in the Moose River Basin. They have a composite thickness of about 400 m and extend throughout the central and eastern parts of the basin (Fig. 1). Through much of this area the Devonian rocks rest directly upon Precambrian basement. They are well exposed near the eastern margin of the basin, along the Abitibi and Mattagami Rivers, and much of the data used in this report and previous studies has been gathered from outcrops in this region. The Paleozoic rocks of the central Moose River Basin generally comprise undisturbed, flat-lying strata, except for beds affected by depositional dips around bioherms and reef complexes. However, basin marginal areas have expe- rienced significant tectonic activity and the Devonian sequence in particular is occasionally disturbed by faults and small scale folding. Recent studies suggest that several episodes of epeirogenic activity on the Hudson Platform affected the deposition and subsequent history of the Paleozoic rocks of the Moose River Basin. This produced several regional dis- conformities and the basin margin structural complexities. The epeirogenic events are thought to have been associated with horizontal plate movements along the southeast and northeast margins of the North American continent. San- ford (1987) has demonstrated the coincidence of Hudson Devonian Moose e R . Basin , Canad BFiagsuinr.e 2: Paleozoic and Mesozoic stratigraphic units in the Moose River

Platform epeirogeny with plate movements during the Early to Middle Ordovician, Late Ordovician, Early Silurian, and Early and Late Devonian. Further tectonism, including emplacement of lamprophyric and kimberlitic intrusives in the Devonian strata of the southeastern Moose River Basin affected the region in the Middle to Late Jurassic. Devonian strata inthe southeastern part of the basin are unconformably overlain by units of Middle Jurassic (Mis- uskwia Beds) and Lower Cretaceous (Mattagami Forma- 125 tion) age (Fig. 2). These are probably the product of greater erosion of the adjoining Precambrian uplands due to tectonic events of that period. The Mesozoic deposits consist of a variable thickness of flat-lying, unconsolidated nonmarine sands and mudrocks. The Mistuskwia Beds, charac- terized by coarse quartzose sands and varicolored clays, appear to be of predominantly lacustrine origin. The disconformably overlying Mattagami Formation consists of massive silica sands, kaolinitic mudrocks and minor gravel and lignite and formed in a high constructive, possibly anastomosed segment of a major river system draining an extensive tract of the Precambrian Shield from south to north (Telford and Long, 1986). Maximum known combined thickness of the Mesozoic units is 185 m. All of the Paleozoic and Mesozoic units are blanketed by a sequence of Pleistocene glacial and glaciolacustrine deposits, and Recent marine clays, peat and muskeg. These "overburden" sediments are of variable thickness, ranging up to 200 m. Their complex depositional history has only recently begun to be unravelled (see Shilts, 1986).

PREVIOUS DEVONIAN STUDIES Much of the early geological work in the James Bay Lowland was related to lignite deposits (now known to be part of the Lower Cretaceous Mattagami Formation) on the banks of the Abitibi River near Onakawana, about 90 km south of Moosonee. Their occurrence was known as early as 1672 by the first English speaking settlers at Moose Factory (across the Moose River from the site of present-day Moos- onee). The earliest known report on the geology of the Hudson Bay territories was by Isbister (1855) but it was not until the late 19th and early 20th centuries that detailed investigations of the James Bay Lowland took place. Between 1871 and 1912 Robert Bell of the Geological Survey of Canada wrote 22 reports on the geology of the lands surrounding Hudson Bay, including aspects of the Devonian geology of the Moose River Basin. Sanford and Norris (1975) provide a comprehensive review of this early work by Bell and others so that only a selection of the pre-1975 works relevant to the Devonian geology is discussed here. For example, Savage and Van Tuyl (1919), Williams (1920a, b) and Kindle (1924) established the basic stratigraphic framework for the Devonian rocks of the Moose River Basin. Dyer (1928) summarized all known information of the Paleozoic geology of the basin and, through his own expeditions to the region, contributed significantly to knowledge of the Devonian geology. In 1930 the Ontario Department of Mines drilled Onakawana A, the first drillhole in the Moose River Basin to penetrate through the Phanerozoic sedimentary sequence to the Precambrian basement (Dyer and Crozier, 1933). The Paleozoic section in this drillhole was made up entirely of Middle and Upper Devonian strata and Onakawana A became a standard reference section for the Devonian of the eastern Moose River Basin. However, over time the impor- 126 tant drill core samples from this section were lost and application of revised stratigraphic nomenclature became difficult. Thus, fifty-five years after completion of Onakawana A, the Ontario Geological Survey drilled Onakawana B at the same location (Sanderson and Telford, 1985). Results of this recent drilling are presented in discus- sions of the individual stratigraphic units. Other than a geological reconnaissance of the Moose River Basin, aimed at establishing its petroleum potential (Martison, 1953), and a number of paleontological studies referenced by Sanford and Norris (1975), little attention was given to the Devonian geology of the region until the mid-1960's. In 1966 the Ontario Department of Mines carried out a major helicopter supported mapping program of northeastern Ontario (Operation Kapuskasing), which included part of the Moose River Basin and introduced much hitherto unpublished subsurface data (Bennett et al., 1967). Then, in 1967, the Geological Survey of Canada mounted Operation Winisk, an air-supported geological reconnaissance survey covering the entire Hudson Bay Lowlands (Sanford et al., 1968). Information on the Devo- nian geology of the lowlands, and the first modern synthesis of the Devonian stratigraphy of the Moose River Basin was reported by Sanford and Norris (1975). During the past decade the Ontario Geological Survey has carried out a number of surface and subsurface investigations in the basin (including the drilling of Onakawana B), mainly aimed at assessing the lignite, oil shale and industrial mineral resource potential of the region (e.g., Telford and Verma, 1982; Russell et al., 1985). As a result of these programs and follow-up activities a substantial vol- ume of new data has been generated, especially relating to the Devonian geology of the southeastern Moose River Basin. This forms the basis for stratigraphic refinements of the Devonian suggested in the present paper.

DEVONIAN STRATIGRAPHY The Devonian succession in the Moose River Basin consists of, in ascending order, the Kenogami River (upper middle and upper members), Sextant, Stooping River, Kwataboahegan, Moose River, Murray Island, Williams Island and Long Rapids Formations (Fig. 2). All but the Sextant and Long Rapids Formations are marine carbonate units, with significant evaporites in the Moose River For- mation and shale in the Williams Island Formation. The Sextant Formation is a mainly terrigenous unit, ascribed by Stoakes (1978) to reworking of coastal sediments, but referred to by other authors (e.g., Sanford and Norris, 1975) as a continental facies. The Long Rapids Formations consists mainly of black shales and green mudrocks with minor carbonate horizons. The following formation descriptions are drawn largely from summaries of recent important articles (e.g., Sanford and Norris, 1975; Norris, 1986), combined with new data from the Ontario Geological Survey programs and other activities in the region. Telford

KENOGAMI RIVER FORMATION This unit spans the Silurian-Devonian boundary (Fig. 2) and, as redefined by Sanford et al. (1968), consists of three members as follows # Upper member: brown and tan dolostone, dolostone breccia; 11-33 m. Middle member: red and green gypsiferous mudstone, dolostone; 145-168 m. Lower member: brown dolostone with minor anhydrite; 23-53 m. Contacts between the members are gradational. Paly- nological results reported by McGregor and Camfield (1976) suggest an Upper Silurian or Lower Devonian age for the upper part of the middle member and a Lower Devonian (Gedinnian-Siegenian) age for the upper member. All three members, generally conforming to the above descriptions, were identified in a drillhole at Schlievert Lake in the south-central Moose River Basin (Russell et al., 1985). The lower member was unusually thin (6.4 m) and the lower half was slightly silty and shaly, grading downward into the regolith of weathered Precambrian rock. This sup- ports the interpretation that Paleozoic sedimentation in the central and eastern parts of the basin was entirely post- Early Silurian. Red beds characteristic of the middle member are best exposed in a small uplifted fault block on the southern margin of the basin near Coal Creek, a tributary of the Missinaibi River. Outcrops of the upper member occur along the Albany River and its major tributary, the Ken- ogami River in the west-central part of the basin. The type section of the upper member is a composite sequence exposed in the Albany River delta (Sanford and Norris, 1975). Although they have only been observed in drill core, contacts of the Kenogami River Formation with overlying elastics of the Sextant Formation or fossiliferous limestones of the Stooping River Formation are distinct. Stoakes (1978) described the lateral facies relationships among these three units, with the supratidal upper member of the Kenogami River Formation deposited contemporaneously, in part, with the other formations during the initial Lower Devo- nian transgression of the Moose River Basin.

SEXTANT FORMATION Savage and Van Tuyl (1919) introduced the name Sex- tant sandstone and shale for clastic beds exposed along the Abitibi River in the vicinity of Sextant Rapids. Since then the unit has been examined by numerous workers, with the most complete description provided by Sanford and Norris (1975). The formation is mainly reddish arkosic sandstone, but also includes varicolored conglomerates, siltstones, shales and clays, with a maximum known thickness of about 90 m. Additional exposures of these clastic units have been reported at several localities around the southeastern margin of the Moose River Basin. Some are of problematical

Devonian Moose e R . Basin , Canad age and at least one (in Adam Creek, south of the Mat- tagami River; reported but not seen by Sanford and Norris, 1975, p. 35) is now known to be an unusually lithified horizon within the Lower Cretaceous Mattagami Forma- tion. However, the Sextant Formation does appear to be restricted to a narrow zone around the basin margin. Well preserved plant remains occur in various horizons, and particularly in micaceous shale lenses within the lower part of the formation in the Abitibi River outcrops. They have been described by W.A. Bell (in Martison, 1953), Lemon (1953), and Hueber (1983) and are one of only a few occurrences in the world of Lower Devonian land floras. Taxa include the trimerophyte Psilophyton dawsonii, zosterophyte Sawdonia ornata, and lycopods Drep- anophycus spinaeformis and Baragwanathia abitibiensis. Palynological evidence reported by McGregor and Cam- field (1976) indicates a middle to upper Emsian age for the formation. The clastic beds of the Sextant Formation are overlap- ped by, and merge northwestward with marine carbonates of the Stooping River Formation. There may also be a lateral facies relationship with the Kenogami River Forma- tion (upper member). In the Schlievert Lake drill hole (Rus- sell et al., 1985) the lower few metres of the Stooping River Formation contain silty dolostones and thin sandstone lenses which perhaps represent a far offshore facies of the Sextant Formation elastics. As noted previously, Stoakes (1978) suggested that elastics of the Sextant Formation were deposited partly in a marine environment by reworking of coastal sediments derived from erosion of the adjacent Pre- cambrian uplands. Subsequent authors (e.g., Norris, 1986; Sanford, in press) have continued to refer to the unit as a nonmarine or continental facies. The occurrence of elastics in the Schlievert Lake drill hole possibly related to the Sextant Formation, and the gradational lateral boundary between the Sextant and Stooping River Formations (and the Kenogami River Formation), imply that the Sextant Formation is unlikely to be an exclusively continental facies.

STOOPING RIVER FORMATION The name Stooping River Formation was proposed by Sanford et al. (1968) for Lower Devonian limestones and dolostones outcropping near the junction of the Albany and Stooping Rivers. As deposits of this unit (and its lateral equivalent, the Sextant Formation) form the major part of the initial Lower Devonian transgressive sequence in the Moose River Basin, these strata lie on a variety of sub- strates, including Precambrian basement rocks and Ordovician and Silurian dolostones. The Stooping River Formation consists generally of nodular or thin bedded cherty limestone with minor dolomitic limestone and dolostone. Some beds are extremely fossiliferous, with a diverse shelly fauna. Outcrops of the unit are widespread in a belt extending around the basin from the Albany River delta in the north to the Abitibi and 127

Mattagami Rivers in the southeast. Thickness is variable, being usually less than 50 m but ranging up to 143 m in the Jaab Lake (Sanford and Norris, 1975) and Schlievert Lake (Russell et al., 1985) drill holes. Conodonts obtained from the upper two-thirds of the formation, although not strongly diagnostic, suggest an Emsian age for this interval (Uyeno, in Sanford and Norris, 1975). Palynological results reported by McGregor and Camfield (1976) indicate a possible Siegenian age at the base to upper Emsian at the top of the formation. In general, the megafossil and microfossil assemblages of the Stooping River Formation have much in common with faunas of the Schoharie, Bois Blanc and lower Onondaga Formations of the Appalachian Basin. Carbonates of the Stooping River Formation were formed in intertidal or shallow subtidal environments. They represent the establishment of fully marine conditions over the Moose River Basin as a result of Lower Devonian transgression.

KWATABOAHEGAN FORMATION This unit consists of massive to thick bedded biohermal and biostromal limestones that are well developed in the central and southeastern Moose River Basin. The name Kwataboahegan was introduced and defined by Sanford et al. (1968) to replace Martison's (1953) Upper Abitibi River Formation and to resolve the problem caused by Martison having placed the unit stratigraphically above the younger Moose River Formation (his Middle Abitibi River Forma- tion). Exposures of the unit at Coral Rapids, on the Abitibi River, were selected as the type section (Sanford et al., 1968). The best outcrops of the unit are those at Coral Rapids and Grand Rapids, on the Mattagami River, where limestone cliffs rise 15 m above water level and extend for several kilometres along both sides of the river. Strat- igraphic thickness ses of strata referred to the Kwataboahegan Formation range from 24 to 77 m, this variation presumably due to the biohermal-biostromal nature of the unit. Carbonate buildups of this formation appear to be associated with topographic highs produced by relief on the Precambrian basement surface. Outcrops on the Mat- tagami River noted above overlie a feature known as the Grand Rapids Arch. Away from the highs the unit is thinner bedded, bituminous and less fossiliferous and is difficult to distinguish from the supposedly underlying Stooping River Formation or overlying Moose River Formation. Strata of the Kwataboahegan Formation are the most fossiliferous of all Devonian units inthe Moose River Basin. The fauna is dominated by corals, stromatoporoids and brachiopods and also includes a diverse assemblage of other invertebrates. In a preliminary description of the fauna Sanford and Norris (1975, p. 45-48) list 25 coral species, about 30 brachiopod species and more than 35 other inver- tebrate taxa. The coral and brachiopod assemblages have many elements in common with the Schoharie-Bois Blanc- 128

Onondaga faunas of the Appalachian Basin and those of the Michigan Basin Detroit River Group. This is in marked similarity to the Stooping River Formation and points to the possible partial contemporaneity of the two Moose River Basin lithostratigraphic units. Conodont faunas obtained from the lower part of the formation (Uyeno, in Sanford and Norris, 1975) also are similar to those from the Stooping River Formation and have a probable Emsian age. Both corals and conodonts recorded from the upper part of the Kwataboahegan For- mation are slightly younger than taxa in the Stooping River Formation, but may be correlative with sparse faunas in the Moose River Formation. This may also confirm at least partial contemporaneity of the Kwataboahegan carbonate build-ups and Moose River lagoonal or back-reef facies (see below).

MOOSE RIVER FORMATION The name Moose River Formation was introduced by Dyer (1928) but removed by Martison (1953) in favor of the term Middle Abitibi River Formation. Sanford et al. (1968) and Sanford and Norris (1975) eliminated the impreciseness of the terminology and reintroduced Moose River Forma- tion, defining the unit as the evaporitic and brecciated carbonates overlying the Kwataboahegan Formation and underlying the Murray Island Formation. Strata of the Moose River Formation are well exposed along the Abitibi, Moose and Cheepash Rivers in the eastern part of the basin. Representative sections through the unit were intersected in the recent Ontario Geological Sur- vey drill holes at Schlievert Lake (Russell et al., 1985) and Onakawana (Sanderson and Telford, 1985). The unit consists mainly of unfossiliferous to poorly fossiliferous limestone, dolostone, brecciated carbonates, gypsum and minor anhydrite. Spectacular cliffs of white gypsum form the west bank of the Moose River for several kilometres downstream from the railway bridge at Moose River Crossing. Com- monly however, the gypsum has been removed by dissolu- tion (e.g. , Schlievert Lake drillhole) leading to increased collapse and brecciation of surrounding carbonates. Also, because of this effect, thickness of the unit varies widely from about 28 to 90 m. In the Onakawana B drillhole the Moose River Formation is about 48 m thick and rests directly on Precambrian basement rocks. Stoakes (1978) interpreted much of the Moose River Formation to be a lagoonal facies developed between the carbonate buildups of the Kwataboahegan Formation. Although this may be partially correct, the strata of the Moose River Formation extend well beyond the known range of Kwataboahegan deposits, and a variety of other carbonate facies are represented. . Nevertheless the lithologies of the Moose River Formation do suggest a regressive phase, when the open platform marine conditions that allowed deposition o f the Stooping River- Kwataboahegan carbonates became restricted and environments conducive to evaporitic deposition were developed. Telford

MURRAY ISLAND FORMATION The Murray Island Formation is a thin sequence of fossiliferous limestones which succeed disconformably the evaporites and associated carbonates of the Moose River Formation and are overlain with probable disconformity by the Williams Island Formation. The limestones represent a return to open marine conditions in the basin. The unit was first defined by Sanford et al. (1968). Previous workers (e.g., Dyer, 1928; Martison, 1953) had described these strata but none had recognized them as a discrete rock unit. Outcrops of the unit only occur in the southeastern part of the basin, especially on the Abitibi River and along the Moose River near Moose River Crossing. In its type area near Moose River Crossing (Sanford and Norris, 1975), the unit consists of fossiliferous calcarenite and highly calcareous dolostone. The beds are generally closely jointed and fractured, and can be brecciated due to solution collapse of underlying evaporitic beds of the Moose River Formation. Thickness of the unit varies from 6 to 20 m. In the Schlievert Lake drill hole lithologies typical of the Murray Island Formation are absent, possibly because of erosion preceding deposition of the younger Williams Island For- mation. Brachiopods are relatively abundant and well preserved in the limestone beds of the formation. Norris (1986) indicates that the faunal assemblages have elements in common with the Onondaga Formation (Appalachian Basin), Dun- dee Formation (Michigan Basin) and Elm Point Formation (Williston Basin), as well as the Cordilleran Faunal Province of northwestern Canada. The limestones also yielded abundant conodonts indicative of an upper Eifelian age (Uyeno, in Sanford and Norris, 1975).

WILLIAMS ISLAND FORMATION Kindle (1924) proposed the name Williams Island For- mation for a sequence of shale and carbonates exposed around Williams Island and along the adjacent banks of the Abitibi River, near the eastern margin of the Moose River Basin. The formation contains a complex variety of lithological units and was divided into two members by Sanford and Norris (1975). The lower member is domin- antly grey shale with soft sandstone, gypsiferous shale, gypsiferous siltstone and sandstone, soft limestone and some brecciated limestone. At some localities basal beds of the member consist of reddish calcareous shale with a well preserved brachiopod fauna. The lower member is 36 to 47 m in thickness. The upper member consists of thin to medium bedded argillaceous limestone and calcareous shale, dolomitic limestone, oolitic limestone and zones of brecciated and vuggy limestone and dolostone. A limestone bed in the middle part of the member at Williams Island contains a rich coral fauna. The upper member is 33 to 45 m in thickness . Devonian Moos e R . Basi , Cana

Outcrops of the Williams Island Formation are restricted to the eastern part of the basin and are found only along the Abitibi, Moose and Little Abitibi Rivers. The recessive nature of the shaly lower member also precludes extensive exposure. Complete sections through the formation were intersected in the Schlievert Lake and Onakawana B drillholes. In the former the lower member and lower part of the upper member were intensely brecciated, probably as a result of removal of evaporites from the underlying Moose River Formation. During field studies by the Ontario Geological Survey in late 1984, at a time of unusually low river levels, the upper contact of the Williams Island Formation with the Long Rapids Formation was observed on the east bank of the Abitibi River adjacent to the type section on Williams Island (Russell and Telford, 1984). The contact is sharp and disconformable, with the upper part of the Williams Island Formation consisting of thick bedded, fractured and brecciated, unfossiliferous, vuggy limestone. Brachiopod-coral assemblages from the lower member of the formation are very similar to faunas from the Hamil- ton Group of the Appalachian Basin (New York State) and Michigan Basin (southwestern Ontario), which are dated as upper Middle Devonian (Givetian) (Norris, 1986). The coral fauna from the upper member has elements in common with the Traverse Group of the Michigan Basin, also dated as Givetian. As discussed by Sanford and Norris (1975), clastic beds in the lower member reflect uplift and erosion of highland areas around the basin margin. Supratidal conditions probably prevailed within the basin. Localized or restricted occurrences of marine fossils within both members suggest only intermittent intervals of subtidal conditions. LONG RAPIDS FORMATION The Long Rapids Formation is the lithostratigraphic equivalent of the extensive Upper Devonian organic-rich black shale facies of eastern North America, which is represented in the Michigan Basin by the Antrim Shale (Mich- igan) and Kettle Point Formation (southwestern Ontario) and in the Appalachian Basin by the Ohio Shale and other units (Janka and Dennison, 1980). Recent interest in the hydrocarbon content of these black shales has prompted increased attention to the stratigraphy and oil shale potential of the Long Rapids Formation. Preliminary samples from outcrops of the formation had organic carbon con- tents of greater than 10% ,which is roughly equivalent to a Fischer Assay oil yield of greater than 45 litres/tonne (Rus- sell and Telford, 1984). The name Long Rapids Shale was introduced by Savage and Van Tuyl (1919) for Upper Devonian shales exposed along the Abitibi River near Long Rapids and Williams Island, close to the eastern margin of the Moose River Basin (Fig. 1). In the type area the unit disconformably overlies the upper carbonate member of the Williams Island Formation. The Long Rapids Formation is the youngest Paleozoic unit 129 in the Moose River Basin and is disconformably overlain by unconsolidated clastic Mesozoic sediments of continental origin. Because of its recessive nature the unit is poorly exposed and outcrops have been observed only in the type area along the Abitibi River and at Grand Rapids on the Mattagami River. Current work by the Ontario Geological Survey has shown that the subsurface distribution of the Long Rapids Formation is restricted to a much smaller area (Fig. 1) than shown by Sanford and Norris (1975). The thickest reported sections of the Long Rapids For- mation in the Moose River Basin occur in the Onakawana A/Onakawana B drillholes, viz. Onakawana A: 87 m (Dyer and Crozier, 1933). Onakawana B: 79.3 m (Sanderson and Telford, 1985). The discrepancy is probably due to differing interpreta- tions of the upper and lower boundaries of the unit. Dyer and Crozier (1933) divided the formation informally into three members. This lithological subdivision was confirmed in Onakawana B and partly in the type area on the Abitibi River where the lower two members are represented in an approximate 48 m section. The lower member (about 36 m) consists of green-grey mudstone and shale alternating with fissile black shale and frequent concretionary carbonate layers. The middle member (about 29 m) is mainly black fissile shale while the upper member (15-20 m) is poorly consolidated green-grey clay and grey shale. The general characteristics (thickness, lithology, faunal content including trace fossils) of the green-grey mudstones and carbonates in the type section and Onakawana B drillhole suggest deposition in relatively shallow water. The interbedding of these facies with the black shales implies a similar shallow water depth for these rocks, with deposition of the black, organic rich sediments being accomplished by elevation of the pycnocline relative to the sediment/water interface rather than deepening of the basin. Russell (1985) proposed a similar depositional environment for the black shales of the Upper Devonian Kettle Point Formation in southwestern Ontario. Beds tentatively assigned to the Long Rapids Formation in the Hudson Bay Basin consist of evaporitic mudstone and reddish siltstone and sandstone (Norris, 1986), indicating regressive conditions and giving some support to the interpretation of restricted water cir- culation and shallow water deposition in the adjoining Moose River Basin. The biostratigraphy of the Long Rapids Formation is of particular interest. A goniatite bed, first reported by Savage and Van Tuyl (1919), was rediscovered in the Abitibi River type section during the 1984 Ontario Geological Survey field program (Russell and Telford, 1984) and contains the species Manticoceras cf. sinuosum. This goniatite also occurs in the Cashaqua Shale of New York State which has been assigned to the conodont Ancyrognathus triangularis Zone of mid-Frasnian age (Norris, 1986). Brachiopod faunas are diverse and well preserved in the

130 Telford lower part of the formation. Some twenty species have been identified, the most significant being Ladogioides pax, Leiorhynchus cf. quadracostatum, and Tecnocyrtina cf. missouriensis from the basal beds, and Calvinaria cf. vari- abilis athabascensis from higher in the section, several metres above the goniatite bed. Well preserved conodonts have been extracted in abundance from the carbonate horizons with the brachiopod faunas and have also been observed on black shale bedding surfaces. Species from the basal beds accompanying the above-noted brachiopods are characteristic of the latest Givetian lowermost asymmetricus Zone. From higher in the formation species representing at least six of the standard Upper Devonian conodont zones, ranging from the earliest Frasnian Lower asymmetricus Zone to the middle Famennian Lower rhom- boidea Zone, have been identified. Preliminary analysis of the faunas (by the author, with T.T. Uyeno and A.W. Norris, Geological Survey of Canada) suggests that the Long Rapids Formation spans most of the Upper Devo- nian, with the Middle-Upper Devonian boundary located near the base of the unit, and the Frasnian-Famennian boundary lying only 35-40 m stratigraphically higher.

INTERBASINAL RELATIONSHIPS The Devonian succession in the Moose River Basin is very similar to that of the adjoining Hudson Bay Basin and there was close connection between the basins throughout most of the period. Nevertheless some important dif- ferences occur. Thickness of the Devonian strata in the Hudson Bay Basin is almost 600 metres, about 50% greater than the Moose River Basin. Clastic deposits similar to

Devonian, Moose R. Basin, Canada those of the Sextant Formation have not been reported from the Hudson Bay Basin. In the central part of the basin the evaporitic Moose River Formation is about double the thickness of the unit in the Moose River Basin. Finally, beds in the Hudson Bay Basin considered equivalent to the Long Rapids Formation consist of evaporitic and coarse clastic lithologies, as opposed to the marine carbonates and black shales in the Moose River Basin. Many of the differing features would seem to suggest that the Hudson Bay Basin was more isolated at particular times than the Moose River Basin and suffered more severely from the regressive epeirogenic episodes that produced supratidal and evaporitic depositional conditions. At present, rocks of the Moose River Basin (and Hud- son Bay Basin) are separated from sequences in other North American Paleozoic sedimentary basins by large tracts of the Canadian Shield (Fig. 3). However, lithological and biostratigraphical similarities of the Devonian succession described herein with sequences in the distant Williston, Michigan, and Appalachian Basins (Fig. 3) suggest periodic interconnection of seaways across the Shield during Devo- nian time. The Lower Devonian units of the Moose River Basin (except for the clastic Sextant Formation, which is a local development) are very similar lithologically, faunally, and in their succession to sequences in the Appalachian and Michigan Basins of southern Ontario and neighboring U.S. states. Close correlation of megafaunal elements with those of the Appalachian Basin was noted by Sanford and Norris (1975) and Norris (1986). Also, conodont faunas reported from the Lower Devonian units of the Moose River Basin (Uyeno, in Sanford and Norris, 1975) are virtually identical to those described from southwestern Ontario (Uyeno et al., 1982). The evaporitic Moose River Formation is similar in depositional character and stratigraphic location to the Middle Devonian Lucas Formation of the Detroit River Group in the central Michigan Basin. The overlying Murray Island Formation is lithologically and faunally similar to the Dundee Formation of the Michigan Basin and has brachiopod faunal elements in common with the Elm Point Formation of the Williston Basin in southern Manitoba (Norris, 1986). Black shales of the Long Rapids Formation in the Moose River Basin represent the most northern extent of the eastern North American Upper Devonian black shale province that was centred in the Appalachian Basin. The lack of these black shales in the Hudson Bay Basin suggests that, by mid-Frasnian time the seaway connecting the Moose River Basin to the southeast may have terminated south of the Cape Henrietta Maria Arch, and that the Hudson Bay Basin was isolated or only connected to the Williston Basin in the southwest. Faunas from the Lower and lower Middle Devonian units of the Moose River Basin have elements in common with sequences in only the southeast, i.e., the Michigan and 131

Appalachian Basins. However, assemblages from younger units (Murray Island to lower Long Rapids Formations) display similarities also with Midcontinent and Cordilleran faunas (Norris, 1986). This implies that, during the Early Devonian seaway connections to the Moose River and Hud- son Bay Basins were only from the Michigan and Appalachian Basins in the southeast but, by late Middle Devonian, a connection was also established from the west or southwest, allowing mixing of faunas in the Moose River Basin. This is consistent with the increased inundation of the North American craton beginning in the late Middle Devonian and the overall cosmopolitanism of upper Middle and Upper Devonian faunas. Following regression in latest Devonian, and severing of the seaway connections the Moose River Basin has since remained isolated.

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