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 base- ment 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 REG IONAL GEO OLO GIC AL SETTING tent sedimen- tation ose ough m Bas h of Phane ite o f inte me. Nevertheles s, Copyright © 2009 by the CMaenmaodiira 11n234 S (o1c98ie8ty) of Petroleum Geologists. 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 carbon- ate 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 through- out 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 tec- tonic events of that period. The Mesozoic deposits consist of a variable thickness of flat-lying, unconsolidated non- marine sands and mudrocks. The Mistuskwia Beds, charac- terized by coarse quartzose sands and varicolored clays, appear to be of predominantly lacustrine origin. The dis- conformably 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 com- bined 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.