Early Ordovician Eustatic Events in Canada

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 " <! Eoplocognothus s <! 3 tentoculotus M - z SUeCICUS "' 0:: RAM c u > Eoplacoqnothus s SKOKI o z L 0:: <! 2 c voriobilis g? w -' Orthidiello -' F s 1- g?- I Microz. porve K g l s s ';; P. originolis g Isogroptus ------- l-'-- Prioniodus GLENOGLE victorioe novts g B Prioniodus M triongularis J g s Hesper· _ RARY�'' onomtc E �s- � Prioniodus Oidymogroptus ev oe pratabit i dus H,l g s? z :::: s (;> r-- z 3 & 4 w Prtomodus Tetrogrop. 0:: z bron ch <! elegans s <{ D c - fruricosus 4 o G s ?- broner r-- <{ z <{ t-- Tetragroptus Paretstodus MeKAY u opproximotus proteus c SURV EY c 1----- c s s Adelogroptus PE AK z Poroistodus s s ontiQUUS <! " s c s - deltlftH D u s s o Cianograptus B.C \..Ordylodus c o oureus <{ B ongulotus s ::; Anisogroptus A s w r-- rich ardseni 0:: Stourogroptus c 1- A tenuts s s Misstsquoio c D. f lob. & Rodiog. 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.

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