Early Ordavieian eustatic events in Canada

By CHRISTOPHER R. BARNES

Four areas are discussed for which the Lower Ordavieian and lower Middle Ordavieian stratigraphy, sedimentology and paleontology are well documented: southern Rocky Mountains, Mackenzie Mountains, Arctic Canada, western New­ foundland. For each area a curve is developed representing major regional facies shifts through this time interval. The four areas are widely separated around the outer passive continental margin and slope of the ancient Canadan (Laurentian) craton. In camparing these areas, similar changes in the curves suggest that these are the result of eustatic changes in sea level. A generalized curve of transgres­ sions and regressions is developed for the eraton with transgressions in the early and late Tremadoc, mid to late Arenig and late Whiterock; regressive phases occur in the early Arenig and early Whiterock with a brief regressive pulse in the late Arenig. Paleogeographic maps for the Canactian eraton during the Tremadoc, Arenig and Whiterock stages illustrate the major facies belts and the changing patterns of epeiric seas on the craton.

C. R. Barnes, Department of Earth Sciences, Memorial Un iversity of Newfound­ land, St. Joh n 's, Newfoundland, AJB 3X5, Canada.

Several attempts have been made in recent stratigraphical, sedimentological and paleonto­ years to document eustatic sea leve! changes logical information . Further, the les� deformed from Lower Paleozoic successions (e . g. Bene­ platformal sequences allow greater precision in dict & Walker 1978; McKerrow 1979; Johnson applying the various criteria available to de­ & Campbell 1980; Johnson et al. 1981; Leggett termine eustatic change (Benedict & Walker et al. 1981; Lenz 1982). Most of these studies 1982). This paper will, therefore, only consicter have used a combination of stratigraphical, se­ the platformal and slope facies of the Lower dimentological, and paleontological data to Ordavieian in Canada. There are only a few establish local apparent changes in sea level. major regions in Canada where most of this Such apparent changes can, however, be indu­ stratigraphic interval is weil exposed, and has ced by a variety of factors including eustacy, been studied in terms of its stratigraphy, sedi­ progradation, epeirogeny, tectonism which may mentology and paleontology to a degree that operate individually or in combination. Space allows interpretation of eustatic changes. These does not permit a review of this problem (see areas are confined to the outer margins of the e.g. Pitman 1978). For the discrimination of eraton because EiirlY Ordavieian seas did not unequivocal eustatic evertts the widespread transgress across the interior region of the Cana­ (preferably global) occurrence of specific sea dian Shield as shown by paleogeographic re­ leve! changes must be established. It is the constructions presented below. The areas se­ purpose of this paper to demonstrate that such lected for detailed review and for the inter­ widespread eustatic events can be recognized in pretation of eustatic change are the southern Lower Ordavieian strata in Canada, across dis­ Rocky Mountains, Mackenzie Montains, Ar­ tances of several thousand kilometers. Such ctic Canada and western Newfoundland. All events will need to be fu rther tested by compa­ were located on or adjacent to passive conti­ rative analysis of data from outer eratonic areas nental margins during the Lower Ordovician; (e . g. Australian and Siberian platforms). only in western Newfoundland was the mar­ As Lenz (1982) has noted, there is usually gin influenced by an adjacent subductian zone a larger data base available for eratonic plat­ and in this area it did not significantly affect form facies than for abyssal facies in terms of the margin until Middle Ordavieian time (mar-

In Bruton. D. L. (ed.). 19M4. A.\pt!U.\· oftht' Ort.lo\'icianSystnn. 51.--61. Palac­ omological Contributlons from the University of Oslo. No. 295. Univcrsitcts­ 51 forlaget. gin collapse and ophiolite obduction). Dis­ rather sparse fauna of trilobites, brachiopods, cussion of the biostratigraphy and stratigraphi­ gastropods, sponges and conodonts, with cal correlation of most of these areas, together thrombolites common in the upper member. with detailed references, has been presented The Outram Formation is predominantly by Barnes et al. (1976; 1981). Together, these limestone, with calcareous quartzose siltstone areas allow an analysis of eustatic events expe­ and brown shale. The limestones are of variable rienced by the northern half of Laurentia (an­ lithology, bu t thick bedded, clotted-nodular cient North American craton) during the limestone and thin beds of trilobite-brachiopod­ Early Ordovician . The object is to identify first pelmatozoan-gastropod grainstone are common; order events and to filter out local seeond or chert nodules occur throughout. The grainsto­ third order eustatic events; these events are nes become widespread toward the top of the interpreted, and then compared, through a se­ formation. There are no sedimentary structures ries of figures showing the stratigraphy and indicative of intertidal environments. The form­ interpreted depositional environments for each ation grades westwards into the graptolitic region (Figs. 1-4). Glenogle Shale. Locally developed on top of the Outram Formation, or within the Glenogle Shale, the Southem Rocky Mountains Tipperary Quartzite is thick bedded, unfossi­ The Lower Ordovician formations for western liferous and in places dolomitic. It pinches out and eastern parts of the southern Rocky Moun­ depositionally to the north and west. tain Fold Belt are shown in Figure l, together The Skoki Formation is composed of dolo­ with a general indication of the horizons with mitized limestone typically pelmatozoan grain­ accurate biostratigraphic control based on co­ stone in the lower part passing upward into nodonts (c), graptolites (g) and shelly fossils packstone and wackestone and near the top in­ (s). The two areas represent stable platform en­ to oncolitic packstone with abundant gastro­ vironments with the western sections (Kicking pods (Mae/uri tes, Falliseria ). An in terdigitating, Horse River, North White River areas) being diachronous contact with the underlying Out­ located near the ancieng platform margin. The ram Formation has been established. The sections in the Main Ranges of the Rocky formation spans the Lower-Middle Ordovician Mountains are the best documented, with the boundary. Survey Peak, Outram, Tipperary and Skoki for­ mations being approximately 515, 440, 175, Figure l includes an interpretative curve for and 185 m in thickness, respectively. These for­ the changing depositional environments within mations are predominantly, carbonate with this sequence expressed in terms of intertidal, some shale; the Tipperary is a quartzite (Aitken shallow subtidal and deep subtidal environ­ et al. 1972). ments. These changes in environment may be The Survey Peak Formation overlies with interpreted as being produced by eustatic chan­ sharp lithologic change the massive stromato­ ge . The intertidal stromatolitic facies of the up­ litic limestones and dolomites of the upward per Mistaya is replaced abruptly by open circu­ shallowing Mistaya Formation (Trempealeau­ lation conditions, bu t still relatively shallow, an). The four informal members of the Sur­ of the lower Survey Peak clastic members. The vey Peak, in ascending order, are the basal sil­ carbonate facies of the upper Survey Peak re­ ty, putty shale, middle and upper massive mem­ presents a shallowing event climaxing at the top bers. Aitken & Norford (1967) and Aitken with the massive thrombolitic limestone. The 1966, 1978) considered the formation to re­ Outram Formation is clearly a deep subtidal fa­ present a single "Grand Cycle" with the lower cies and the change at the lower formational two members comprising a predominantly clas­ boundary is relatively abrupt. In the Main tic, inner (?) detrital facies and the upper two Ranges area, the influx of the Tipperary Quart­ members representing an upward shallowing, zite marks a brief return to nearshore or inter­ prograding, middle carbonate facies. Both the iidal conditions. The overlying Skoki For­ earbonates and clastics display a variety of mation represents a complex of shallow subti­ shallow water sedimentary structures and a dal environments with a relative shallowing up-

52 ROCK Y MOUNTAIN DOMINANT FOLD-BELT EN VIRONMENT CONO DON T SHE LLY SERIES; GRAPTO LITE KICK lNG HORSE FAUNA FOSSI L MA IN S TA GE ZONE DEEP-SHALLOW INTER- ZONE RANGES ZONE NORTH WHI TE SUBTIDA L TIDA L

1-\-t-' Paroglossogroptus z � Anomalorthis JJJU!JUillillll z " Eoplacoqnothus s SKOKI o z L 0::

z :::: s (;> r-- z 3 & 4 w Prtomodus Tetrogrop. 0:: z bronch

Fig. J - Stratigraphy, biostratigraphica/ con tro/ leve/s, and curve showing major changes in depositional environ­ ment for southern Rocky Mountains (c= conodon t, g= graptolite, s = shel/y , fo ssil, as contro/ leve/s) . Chrono­ stratigraphy fr om Barne s et al. 1981. wards marked by the oncolitic and gastropad in the Selwyn Basin and Misty Creek Embay­ limestones. ent. The stratigraphy and paleontology of these areas has been detailed by Gabrielse et al. 1973; Ludvigsen 1975; 1978; 1979; 1982; Capeland Mackenzie Mountains 1977; Tipnis et al. 1978; Gordey 1980; Landing In the northwestern part of Canada, Lower Or­ et al. 1980; and Cecile 1982. dovician strata are weil exposed in the Selwyn The Broken Skull Formation consists of a and Mackenzie Fold Belts (Fig. 1). The central thick sequence of dolostones and limestones, Mackenzie Mountains preserve a carbonate plat­ commonly sandy. lt is earrelative in part with form facies and part of a transitional slope fa­ the dolostones of the Franklin Mountain For­ cies. Further west, basinal shales are preserved mation (760 m thick) of the Mackenzie Moun-

53 SELWYN MACKENZIE DOMINANT FOLD BELTS EVIRONME NT CONODON T SHE LLY SER l ES/ GRAPTOLITE FOSSIL CENTRAL FAUNA ZONE SELWYN S TA G E DEEP-SHALLOW INTER- ZON E MACKEN Z l E ZONE BASIN MOUNTAINS SUBTIOAL TIDA L

-'v-r'' Poroglossogroptus z _i__ Anomalorthis z Eoplocognorhus <( � 3 tenroculotus M - z SUeCICUS "' � u > ROAD o z Eoploc oqnothus NBLOOD a: <( 2 L RIVE c _j vcncbiiJS C w OrthJdlello B V '-- _j - I M1croz. par ve K ·�� c' l :;: P or1g 1nolis � �'---- ? Isogroptus -+- l-c___ Pnon•odus l nov1s v1Cton oe PrJOfliOdus J s l t nongula r� s Hesper- onom'c -- <: c c Pr,onJodus D•dymogroptus ev o e prOlOb If ldUS H,l Q l ROAD BROKEN s z l RIVER SKU LL � c � B c z w 3 & 4 Pr1ontOdus Tetrogrop. a: z bron ch <( Q <( elegans � c c - fruiiCOSUS- o 4 G s broner <( z <( r-- Tetroqroptus PorOJStoous u opproJCimotus proteus

c? f- c Adeloqroplus F z PcrOIStodus E Q on iQUUS i s � deltder D u o Cianograptus B. C o Lordyladus B onqulotus oureus <( KETTLE :;; - An,sogrop�us A 9 c w r1chordson• s a: Srouroqraptus >-- c A renu•s s MISSISQUOIO D. f lob. & Rod:og }.;:.J L A

Fig. 2 - Stratigraphy, biostratigraphical control levels, and curve showing major changes in depositional environ­ ment fo r Mackenzie Mo untains. tains and Franklin Mountains to the east (Nor­ Ludvigsen (1982) has shown subtie but impor­ ford & Macqueen 1975). Shelly fossils allow tant petrographic differences within the forma­ earrelation with the Ross-Hintze zones of the tion with some of the Iimestones being black Great Basin sequence in Utah-Nevada but more laminated lime mudstones whereas others be­ detailed study is needed to better document low are burrowed lime wackestones. He attri­ minor facies changes as reflected by the cyclic, buted the change to a deepening phase at the rhythmic, and cherty units. base of the Corbinia apopsis Subzone of the The Broken Skull Formation passes west­ Saukia Zone coincident to the base of the wards into the transitional slope facies of the "Hystricurid" Biornere and a Grand Cycle. The Rabbitkettle Formation. Both formations were Rabbitkettle Formation extends into the Late initiated in the Late Cambrian. The Rabbitkett­ Tremadoc in some areas (e .g. western District le Formation (up to 7 50 m thick) consists of of Mackenzie; Ludvigsen 1982) and then is thin bedded silty limestone with shaly partings. overlain by a black barren dolostone member of

54 ARCTIC PLATFORM DOMINANT

T SHE LLY ENVIRONMENT SERIES/ CONODON GRAPTO LITE BO OTHIA FOXE FAUNA FOSS l L C ELLES Is BACHE PEN. S.OEVON Is S TA G E ZONE DEEP-SHALLOW INTER- ZONE PEN BA SIN ZONE N.W.OEVON Is. E.ELLES Is SUBTIDA L TIDA L -�

PorOQIOSSOQrQPIU! z � Anornalortrus z CROCKER � Eoplocognothus tentoculotus M � z ' SUIC!CUS BAY BAY ' "' 0: F t ORD u > Eootocoqnothu �D o z E.C 0: E. C E. C MBR w � j OrthodoeJio >-

I MICfOl.QOf'o'O � " P:onqtnolls ----- � lsoqroptus Proonoodus SHtP ) I'IOVIS POINT Prtomodus NADLO trtongulorts ' POINT Hesper- E LE ANOR onomte_ RIVER E LE ANOR Proonoodus Oodymo

z MBR "' SHIP "' - POINT z w 3&4 0: Proonoodus Te!rogrop. z bron ch C.S <( "' eh�qons - frultCOSU$ / o 4

<( 8AUMANN BAUMANN z - <( Teuoqroptus FIORO ' FIORD 5 PorQoS!QdU$ u oppro�omotus E .C E,C proltus r--- AdeloQroplus z MAP UNIT Poro•slodus " OfliiQUU$ c 6 u COPES CAPE CLAY o ClonoQroptus B.C TURNER 1..-ordylodus , c o . . MINGO s 8 onqulolus ' "' RIVER CLI F FS " - An•soqroptus CASS w ncl'lordsoni c' s FIORO s 0: Stouroqroptus ? >- c MISSISQUOIO O.flob.& Rod•OQ A. _}, A

Fig. .J- Stratigraphy, biostratigraphical control levels, and curve showing major changes in depositional environ- ment fo r Arctic Canada. the Road River Formation probably reflecting area is shown on Figure 2. It must be empha­ a brief relative shallowing. In other areas (e .g. sized that this reflects changes in the areas of southwest Mackenzie Arch; Cecile 1982), the carbonate platform edge to transitional slope Rabbitkettle Formation persists to approxi­ facies and is based largely in Ludvigsen's recent mately the base of the Whiterock before being studies. He has demonstrated, in applying the overstepped by the basal Sunblood Formation Grand Cycle concept to the Rabbitkettle For­ as a result of another relative shallowing even t. mation, that a marked relative deepening in the The Sunblood Formation (up to 1400 slope facies occurs at the base of the Corbinia thick) consists of dark grey dolostone, alter­ apopsis Subzone (late Trempealeauan). The nating dark and light grey dolostone overlain black dolostone member, basal Road River by limestone, locally with interbedded sand­ Formation, and the nature of the middle Bro­ stone, and finally by grey limestone and dolo­ ken Skull Formation indicates an overall shal­ stone, locally bioclastic (stratigraphy revised by lowing phase in both slope and platform fa­ Ludvigsen 1975). The formation is character­ cies. The mo re diverse faunas of the upper Bro­ ized by vivid weathering colours due to a high ken Skull Formation and the development of silt content. Ludvigsen (1975) advocated a more anoxic conditions in the laterally equi­ shallow sublittoral, occasionally littoral envi­ valent part of the Road River Formation sug­ ronment fo r the Sunblood. gests a relative deepening. The basal Sunblood In terms of depositional environments, a ge­ Formation and its overstepping relationship to neralized curve for the Mackenzie Mountains the slope facies indicates a fairly abrupt shal-

55 lowing phase in early Whiterockian time. These Western Newfoundland changes are reflected in shifts in trilobite and conodon t biofacies (Ludvigsen 1975, 1978; This area containsexcellent exposures of Lower Tipnis et al. 1978; Landing et al. 1980). Ordavieian strata of the carbonate platform facies (St. George Group) and also in the centi­ nental slope facies of the Cow Head Group pre­ Arctic Canada served in adjacent allochthonous sheets. These In Arctic Canada, Lower Ordavieian rocks are two facies belts have Iong been studied in de­ widely exposed in many areas of the Arctic tail and much recent work has also been com­ Islands and northern mainland, together com­ pleted or is in progress. The review below is prising the Arctic Platform (Fig. 3). Formation­ based on many of these detailed studies inclu­ al names change across this vast terntory but ding Kindle & Whittington 1958; 1959; Whit­ the basic lithological successions are remarkab­ tington 1968; Hubert et al. 1977; Knight 1977 ly similar. Details of the Lower Ordavieian a, b, 1978; Fåhraeus & Nowlan 1978; Fortey stratigraphy and paleontology provides a basis 1979; Fortey & Skevington 1980; Stouge 1980, for review comments have been published by 1981, in press; Fortey et al. 1982; Stouge & several authors including Kerr 1968; Mossop Godfrey 1982. 1979; Barnes 1974; Morrow & Kerr 1977; Mayr The St. George Group (about 500 m thick) 1978; Miall & Kerr 1980. consists of four formations, in ascending order The lower and late Middle Ordovician suc­ the Watts Bight, Boat Harbour, Catoche and cession , where complete, typically consists of Port au Choix formations. It is overlain, com­ an alternation of two major facies: shallow sub­ mon1y discon formably, by the Table Head tida! carbonate , and evaporite . The Copes Bay Group. The St. George Group consists of dolo­ and Eleanor River formations represent the stones and limestones, commonly stromato­ former and the Baumann Fiord and Bay Fiord litic or bioturbated, and with chert at some ho­ formations represent the latter. rizons. There are a few brecciated horizons pro­ The Copes. Bay Formation (commonly 300- duced during karst formation following regres­ 500 m in thickness) has a lower and upper part sive phases. The pattern of shifts between ex­ that consists of thick to massive bedded, mott­ posure, intertidal and shallow subtidal facies led, limestone with a variety of sedimentary has been detailed by Stouge (in press, Fig. 6) structures indicating a shallow subtictal environ­ who has interpreted these changes in terms of ment. In many localities, an interval within the major and minor eustatic events and the ma­ formation consists of thin bedded dolostones jor ones are incorporated into the curve shown with desiccation eraeks indicative of regional on Figure 4. Important lead-zinc deposits (e.g. shallowing. Daniels Harbour) are associated with the se The overlying Bay Fiord Formation (300- paleokarst horizons. 350 m thick) is siminar in lithology to the eva­ The Cow Head Group (Ordovician part porltic Baumann Fiord and both are recessive being about 160 m thick) is a sequence of thin in outcrop. Limestones and shales predomi­ bedded ribbon limestone and graptolitic shale nate toward the top of the formation. As with that are interbedded with carbonate conglo­ the Baumann Fiord Formation, the unit is merate and breccia with clasts or blocks up to locally thin or absent and marked by an hiatus. many tens of metres in diameter. The breccias The Lower Ordavieian succession in the Arc­ were derived through down-slope slumps or tic Platform thus represents an oscillation of flows carrying carbonate blocks from the shelf shallow subtictal and evaporltic intertidal-supra­ margin (James 1981). The thin bedded Iime­ tidal environments. The facies persist for signi­ stones and graptolitic shales represent slow de­ ficant periods of time. A curve representing position on the continental slope whereas the these shifts through time is included in Figure thick breccia units represent sudden brief in­ 3; the oscillations at the b ase of the chart are fluxes of carbonate debris. There are major fau­ diagrammatic, representing the stromatolitic na! differences between the two carbonate fa­ eyeles in the lower Copes Bay Formation. cies. It has been proposed (Stouge, in press;

56 w NEWFOUNDLAN D DOMINANT EVIRONMENT CONO DON T SHE LLY SERIES/ GRAPTO LITE FO SS IL FAUNA PORT AU PORT HARE S T A G E ZONE cow DEEP�SHALLOW INTER ZONE DEEP-SHAL.OW ZONE PENINSU LA BAY HEAD SUBTIOAL TI DAL SLO PE fCOW HEAO--)

-',- Poroqlossoqroptus T HEAOCp. z AnomolorthiS c s z Eoptocoqnoll'lus � �3 t�ntoculotus ... BELLBURNS illllllillJJIJlli <{ SUeCICUS z c c HARE � ;;: o: ? UNNAMED u > ISLANO GREE N SS o z Eoptocoqnotl'll.ls L o: 2 s vor10Dolls c w j Orthldlello r---- >- 6 BED t4 ' I Mocroz. porvo K , l l ;: P: ongtnolls - tsoqroplus �- -- ? '--- ?- Pr10n10dus ---'_ nOVIS VICIOfiOf: 13 ' Pr�on•odus J ' tr•ongutoros ,, __:_ u Hes per. 6 12 ' onomoc_ ' CATOCHE � ______:__ Pr•onoodus D•dymoqroptus c evae prOIObllldUS H,l Il SOUTHERN z "- ' � "- "- <{ � AR M � o "' C>� ' - - r-- a ? ______!_ z C>� w 304 c Pnoruodus Tetragrop 6 10 ' o: bron ch z <{ lllillllilliMm"' elegans -' <{- o frUIICOSu::.- BOAT o 4 G w a broner C> ' a � 9 ' <( HAR BOUR w z w C> ' 8 I-' <( r- Tetroqroptus a c C> u PorOIStodus ' ooprox•motus 8 ' - proteus c 6 B F AdeloqrapTus • TIIilli!IIIIl][D' � z Paraoslodus �'"' o oniiQUUS ' � u ' "" dell•fer o u ______:_ B. C WAT TS o Clonoqroplus BRE NT o :�rdy'odus BIGHT ' ISLANO ' <{ B onqulolu<> aureus ::; An•soqroplus ' c ' 6 7 w r- r•chordson• ' o: Stouroqroptus ' >- ->- A tenu•s "-41SSI'>QU010 6BED 6 D f lob.& RoO•oq ' 5 - Fig. 4 Stratigraphy, biostratigraphical control levels, and curves showing major changes in depositional environment fo r western Newfoundland. Open triangles show location of main megabreccias within number­ ed units (Beds) of Cow Head Group.

N. P. James and R. K. Stevens, pers. comm. the upper Table Head. These shales are overlain 1981) that the megabreccias we re generated by a flysch sequence and by obducted ophio­ during regressive phases when the carbonate lites. The continental margin is interpreted as platform margin was exposed and brecciated being drawn down into an easterly dipping sub­ with the formation of karst surfaces. In Figure ductian zone. Some of the late Early Ordovi­ 4, the fo rmal beds numbered within the Cow cian hiatuses may have resulted from a tempo­ Head Group that contain the large megabreccias rarily upwarped margin prior to collapse. How­ are shown with an open triangle. Several, but ever, as shown below, they do correlate with not all, seem to correlate well with the hiatuses other apparent eustatic events elsewhere in Ca­ demonstrated by stratigraphic studies and cono­ nada. dont biostratigraphy (e .g. Stouge, in press) in the St. George Group strata of the earbona­ Summary te platform facies. Work in progress to try to refinefu rther these events and correlations. In four areas of Canada, the Lower Ordavieian The carbonate platform suffered a major and lower Middle Ordavieian stratigraphic re­ collapse in early Middle Ordavieian time with cord is remarkably complete and has been well the shallow water earbonates of the lower Table documented in terms of its stratigraphy, sedi­ Head Group passing up in to graptolitic shalesin mentology and paleontology: the southern

57 CANADlA N

CRATON: ROCK Y MOU NTAI N SERIES/ CONODON T GR APTO LITE SHE LLY FAUNA FOSSIL INTERPRETED S TA GE ZONE FOLD BE LT ZONE ZONE TRANSGR- RE GR. PHASES DS--+SS-IT

Poroglossogrop!us T z � Anomalorthis - - z Eoplocognothus te ntaculotus M <{ � 3 - z suecicus "" Q:: u > Eoplacoqnathus R o z L a: <{ 2 voriot>ilis w _j _j Orthidiello l- - - - I Microz. por va l K P. originolis :;: Isogroptus T f-'--- Prioniodus novis vietaria e - - Prioniodus J t nongularis R -- - Hesper- onom1c _ E Prioniodus Didymogroptus eva e pro to bif i dus H,l T z \ -<{ <:' - f--- - - z w 3& 4 Prioniodus Tetrogrop. a: z bronch <{ elegans <{ D - fruricosus - o 4 G broner R <{ z r--- <{ Tetragroptus Paraistcdu s u opproximotus proteus r--- c - - Adelogroptus F z Poroistodus E <{ ontiquus - deltifer D u o Cianograptus B,C Lordyladus o B onqulotus oureus <{ T ::;; An isogroptus A w f--- rich ordsoni a: St ourogroptus l- A tenuis Missisquoio D. f lob. & Radiog.

Fig. 5 - lnterpreted transgressive-regressive phases for the Canadian eraton during the Ear/y and ear/y Middle Ordovician, constructed by comparison of curves developed fr &m southern Rocky Mountains, Mackenzie Mountains, Arctic Canada, and western Newfoundland.

Rocky Mountains, the Mackenzie Mountains, facies ch anges ma y be a result of vari o u s factors Arctic Canada, and western Newfoundland. such as eustacy, progradation, epeirogeny, Published data, not fully repeated herein be­ tectonism, or any combination of such factors. cause of space constraints, allows a curve to be In this review paper, i t is suggested that if ma­ developed fo r each area that plots the changing jor facies changes occur at the same time in the depositional environments. First order facies four widely separated areas around the mar­ shifts are recognized and correlated against the gin of the ancient Laurentian eraton then these chronostratigraphy and zonatians adopted by are Iikely eaused by eustatic sea leve! changes. Barnes, Norford and Skevington (1981). This will need to be fu rther checked against In any particular region such major regional similar data from other cratons.

58 SELW YN- MACKENZIE ARCTIC W. NEWFOUNDLAND W. NFLD

FOLD BELTS PLATFO RM PLATFOR M SLOPE

os�ss-+IT os�ss-IT

Figure 5 provides a comparison of the cur­ Whiterock with a brief regressive phase in the ves developed in the four areas. From these, a late Arenig. These changes are portrayed as subjective generalized curve is derived which paleogeographic maps for the Tremadoc, Are­ identifies major transgressive-regressive eustatic nig, and Whiterock stages for the Canadianera­ changes that affected the Canadian eraton ton (Figs. 6-8), although such divisions cannot during the Early and early Middle Ordovician . express the several eustatic changes that occur Transgressive phases are recognized fo r the ear­ within each stage or series and must be viewed ly and late Tremadoc, the mid to late Arenig as generalized reconstructions. Although devel­ and the late Whiterock. Major regressive phases oped independently these results compare occur during the early Arenig and the early closely with the conclusions reached by

59 Fig. 6 - Paleogeographic recounstruction fo r the Canadian eraton during the Tremadoc. General areas of south­ ern Rocky Mountains, Mackenzie Mountains, Arctic Canada, and Western Newfaund/and marked by letters, A, B, C and D, respectively.

Fortey's analysis (this volume) of Earl y Ordo­ Acknow ledgements vician eustatic events from orther areas. It is stressed that while full documentation Continued support for Lower Paleozoic re­ could not be included here, it seerus evident search by the Natural Science and Engineering that eustatic events can be recognized for the Council of Canada is gratefully acknowledged. Early and early Middle Ordavieian in Canada. G. R. Vamey (Panarctic Oils Ltd.) generous­ Similar unpublished data show that more de­ ly provided some paleogeographic data fo r the tailed curves can be generated for the Middle Arctic Islands. Technical support was received and Late Ordovician. Although imperfect, it from W. Marsh, W. Howell, C. Pitts and F. would be extremely valuable to see such curves O'Brien. generated fo r many other areas of the world in order that global coverage be attained to pro­ perly test the hypothesis that the curves do tru­ ly reflecteu static events.

60 ?

o �·

Fig. 7 - Palaeogeographic reconstruction fo r the Canadian eraton during the ear/y to middle Arenig. Open trian­ gles indicate evaporite fa cies, erosses indicate local land areas.

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61 Fig. 8 - Paleogeographic reconstruction fo r the Ca nadian eraton during Wh iterock. Open triongles indicate eva­ porited fa cies.

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