Devonian geology of Banks Island, Canada, and its bearing on the tectonic development of the circum-Arctic region

ANDREW D. M1ALL Institute of Sedimentary and Petroleum Geology, 3303 33rd Street N.W., Calgary, Alberta T2L 2A7, Canada

ABSTRACT the basic data contained in this report can be found in Miall (1976). New information, predominantly from the subsurface, shows that the Devonian rocks of Banks Island comprise four units: a REGIONAL SETTING shelf carbonate formation (Siegenian? to Eifelian), a basin-slope calcareous shale (Emsian to late Givetian), a basinal cherty shale The structural setting of Banks Island is shown in Figure 1. Three (Emsian to Eifelian), and a predominantly deltaic clastic unit (Give- major Paleozoic elements are present in this area. Part of Banks Is- tian to Famennian). Paleogeographic reconstructions show south- land and the area immediately to the east and south compose a ern Banks Island as part of the stable shelf in Early Devonian time. major portion of the Central Stable region, an area of cratonic During Middle Devonian time, subsidence took place, and basinal Cambrian to Devonian sediments, mainly carbonates. The craton conditions encroached on the shelf from the north. The deep basin passes laterally into the Cordilleran and Parry Islands folded belts is considered to be part of Hazen Trough, which probably was to the west and north, respectively. The Parry Islands fold belt cor- connected with Richardson Trough of northern Yukon. responds approximately to the "miogeosynclinal" part of the Subsequent tectonic events have left the Devonian rocks of Banks Franklinian geosyncline. The latter consists of a sequence of upper Island relatively undisturbed, in comparison with those of the Parry Proterozoic to Upper Devonian rocks deformed by the Ellesmerian Islands to the north. Evidence of subduction and plate collision — orogeny, a major tectonic episode in latest Devonian or earliest such as strong deformation, the development of orogenic welts, Mississippian time. The "eugeosyncline" is now largely covered by and the production of thick, locally derived clastic wedges — is ab- upper Paleozoic to Tertiary rocks of the Sverdrup Basin, upper Ter- sent in Banks Island, in contrast to areas such as northern Ellesmere tiary rocks of the Arctic Coastal Plain, and the adjacent Arctic Island and northern Alaska. Therefore, if plate movements did take Ocean. A more complete exposure of the geosyncline is present in place in the Arctic during Devonian time, Banks Island may have northern . More detailed descriptions of these lain opposite an embayment in the advancing plate, resulting in in- tectonic units are given by Thorsteinsson and Tozer (1970) and complete suturing, as described by Dewey and Burke. However, no Trettin and others (1972). satisfactory hypothesis of plate motion in the Arctic has yet been One of the problems in making tectonic and paleogeographic re- developed, in spite of many attempts. constructions in the Canadian Arctic has always been the question of where the Franklinian geosyncline goes in the subsurface west INTRODUCTION and south of Melville Island. On Prince Patrick and Banks Islands, the Paleozoic rocks are covered largely by Mesozoic and Tertiary The gross tectonic history of the circum-Arctic region is a subject sediments, and it has not been possible, on the basis of surface about which very few geologists appear to agree. Plate tectonics geologic evidence, to fill in the gap, nearly 1,000 km wide, between theory has yet to be applied successfully to the area, although many the geosyncline of the western Arctic Islands and the outcrops of workers have made the attempt. Most of these attempts have failed Paleozoic rocks in northern Yukon. to take into account all available data. The relationship between Trettin and others (1972, p. 131) have pointed out that the de- Alaska and Siberia, for example, is one that has been ignored fre- formation constituting the Parry Islands fold belt dies out to the quently by workers dealing with a hypothetically drifting Alaska. west within Melville Island, but it is not known whether a de- Investigators dealing with the North American side of the Arctic formed eugeosynclinal belt is present beneath fall into two main groups: (1) those who have developed and or the adjacent Arctic Ocean. modified the orocline concept of Carey (1958), who proposed that As discussed elsewhere (Miall, 1975), rocks of post-Devonian Alaska rotated into its present position with a counterclockwise age in Banks Island and adjacent areas show somewhat different motion and (2) those who maintain that the distribution of the con- fades and tectonic trends from those that are now known to have tinental masses has remained relatively unchanged throughout dominated sedimentation in Devonian time (little evidence is yet Phanerozoic time. Among the first category are Tailleur and Brosge available for pre-Devonian time). The differences can be explained (1970), Tailleur (1973), Freeland and Deitz (1973), Miall (1973), in terms of changes in plate motions on a continental scale, the de- and Richards (1974). In the second category are Churkin (1969, tails of which are not immediately relevant to this paper. 1973a, 1975) and Norris (1973, 1974). Somewhat different in- terpretations involving large-scale transcurrent faulting have been STRATIGRAPHY offered by Yorath and Norris (1975) and Herron and others (1974). Devonian stratigraphy in the area discussed here is marked by The purpose of this paper is neither to lend support to one of the strong lateral fades changes. It is most readily explained with refer- available hypotheses nor to spawn a new one, although some ence to the reconstructed stratigraphic cross section shown in Fig- comments on the available models are offered at the end of the ure 2. On this diagram, four subsurface sections and four surface paper. Drilling in Banks Island has provided some new information sections have been projected onto a line of cross section oriented concerning the Devonian rocks in the subsurface (pre-Devonian approximately north-south. All the data shown in this diagram are rocks have not yet been reached by exploratory drilling), and these new, with the exception of the composite surface section through data partially fill a major gap in the record between the Canadian the Upper Devonian Melville Island Group, which was measured Arctic Islands and northern Yukon. More precise paleogeographic and described by Klovan and Embry (1971). reconstructions for Devonian time are therefore possible, and these The oldest units present are unnamed dolomite and dolomite- obviously must be taken into account in any future tectonic or shale formations (Lower Devonian or Silurian) penetrated by the palinspastic reconstruction of the area. A more detailed account of Orksut 1-44 well. These are succeeded by the Blue Fiord Formation

Geological Society of America Bulletin, v. 87, p. 1599-1608, 7 figs., November 1976, Doc. no. 61108.

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AGE OF SURFACE ROCKS

TERTIARY QUATERNARY

UPPER PALEOZOIC TERTIARY A-

UPPER PALEOZOIC- TERTIARY

Figure 1. Structural-stratigraphic pri nces in the western Canadian Arctic. (McLaren, 1963), which has a very widespread distribution in the late Emsian age (Norris, A. W., 1973, written commun.) are pres- Canadian Arctic Islands. The upper part of the Blue Fiord consists ent in the Nanuk D-76 well. Owing to lateral facies changes, the of lime mudstone with rare interbeds of bituminous shale. Beds of complete age range is never present at any one locality. fossiliferous lime packstone and lime wackestone are common and On the tiny Princess Royal Islands, located between Banks and include well-preserved corals, stromatoporoids, brachiopods, Victoria Islands, the gradational contact between the Blue Fiord nautiloids, pelecypods, and ostracodes. Lower in the section at the and the Orksut Formations is exposed. It consists of interbedded Orksut 1-44 well, the Blue Fiord consists of finely crystalline to mi- black bituminous shale and coarse, bioclastic, crinoidal limestone crocrystalline dolomite, the transition between the two lithologic showing steep depositional dips. The presence of nearby bioherms types being gradational. is suspected. Conodonts and invertebrate faunas indicate a late Sparse conodont faunas in the Blue Fiord formation indicate an Emsian or early Eifelian age for these beds (Uyeno, T. T., 1974, Early Devonian (Siegenian?) to early Middle Devonian (Eifelian) written commun.; Norris, A. W., 1972, written commun.; Ormis- age (Uyeno, T. T., 1973, 1974, written commun.). As shown in ton, 1967). Figure 2, the contact with the overlying Orksut formation is mark- The Nanuk Formation (Miall, 1976) is a lithologic variant of the edly diachronous. Orksut, consisting of black siliceous shale, commonly with much The Orksut Formation (Miall, 1976) consists of calcareous shale interbedded chert. Calcareous or silty shale beds are present in with minor amounts of silty shale, argillaceous limestone, and minor amounts. An Emsian to Eifelian age is assumed for the for- siltstone. Conodont and palynomorph assemblages indicate an mation, largely on the basis of the age of the enclosing strata. Emsian to late Givetian age for the formation (Sweet, A. R., 1973, The Weatherall Formation (Tozer and Thorsteinsson, 1964) written commun.; Uyeno, T. T., 1974, written commun.; overlies all these units and grades laterally into the Orksut Forma- McGregor, D. C., 1974, written commun.). Tentaculites remains of tion. Rock types include fine-grained to very fine grained quartzose

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FAMEN NI AN .".."..I Fluvial-deltaic

GRIPER BAY FORMATION ".."TV. Deltaic-marine

'.'.••'.'.••'.'.••'.'.HECLA ÊAV FORMATION Restricted shelf ! datum for sections 1-3

Mercy Bay Mbr Open-marine shelf

Reel and off-reef :FRASNIAN-: •WEATHERALL FORMATION- Basin slope

Deep basin

Biostratigraphic control points

Horizontal scale GIVFCTIAN ? ' Kilometres 50 i i i i i 1 30 Miles

Vertical scale

Metres Cape Crozier 500 I

Cape Vesey Hamilton 1500 Feet 2

(Klovan and Embry, 1971)

fossil localities

• 7 Princess Royal Islands

Figure 2. Restored stratigraphie cross section, Devonian rocks of Banks Island.

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sandstone, siltstone, shale, carbonaceous shale, and minor coal. land formed part of the craton on which shallow-marine carbonate The Weatherall is the lowermost of three formations composing sediments accumulated. The new subsurface evidence from Banks the Melville Island Group (Tozer, 1956; Tozer and Thorsteinsson, Island indicates that the southern part of the island remained part 1964), the other two being the Hecla Bay and Griper Bay Forma- of the stable craton until Middle Devonian time, but that com- tions. This nomenclature is used in Figure 2, although according to mencing at least as early as Emsian time, the western edge of the Embry and Klovan (1974; 1975, personal comraun.), a major revi- craton began to subside, and all the sedimentary facies and depo- sion of stratigraphic terminology is now necessary and will shortly sitional environments shifted gradually to the south and east as the be proposed by them. The subdivision is based primarily on the subsidence progressed. recognition of a prominent sandstone bed in the upper part of the The earliest period for which sufficient information is available succession. This was tentatively (and apparently incorrectly) as- to allow construction of a paleogeographic map is the late Emsian signed to the Hecla Bay Formation by Klovan and Embry (1971). (Fig. 4). At that time, and southern Banks Island Near the base of the Melville Island Group and including beds ten- formed part of the stable shelf. The rock types composing the Blue tatively assigned to the underlying Nanuk Formation by Miall Fiord Formation (Fig. 4, control points 2 and 5) indicate (1976) is an interval of interbedded shale, siltstone, and very fine shallow-water, relatively low energy marine sedimentation. A grained sandstone similar to the Blackley Member of the Weath- sharp transition into a basin-slope facies, the Orksut Formation, is erall Formation on Melville Island (Tozer and Thorsteinsson, exposed on the Princess Royal Islands (Fig. 4, loc. 6), where shelf- 1964). edge bioherms are thought to be present. The Orksut Formation is similar in lithology to the Eids Formation of the central and eastern STRUCTURE Canadian Arctic Islands (McLaren, 1963; Thorsteinsson and To- zer, 1970; Kerr, 1974); this unit has been interpreted as shelf-edge A structural cross section through Banks Island is shown in Fig- or shallow-trough facies (Kerr, 1974, p. 38; Trettin, 1974, p. 358). ure 3. Deformation is gentle, and most of it, as may be deduced The basin-slope facies belt can therefore be extended northeast- from Figure 3, is of late Cenozoic age. This confirms evidence from ward, as shown in Figure 4. [The name Eids Formation is not used surface exposures in Melville Island (referred to above) which here for the rocks in Banks Island for various reasons, as explained suggest that the Parry Islands fold belt does not extend southward in Miall (1976). The main reason is confusion over the age and into Banks Island. lithology of the Eids.] The Nanuk Formation is similar in lithology to the Lower Or- PALEOGEOGRAPHY dovician to Lower Devonian Ibbett Bay Formation of Melville Is- land (Tozer, 1956; Tozer and Thorsteinsson, 1964), but the evi- Little can be said regarding the paleogeography of the area re- dence available suggests that it may be slightly younger in age. The ported here during pre-Devonian time. Some data for late Pro- Ibbett Bay is interpreted as a relatively deep water, pelagic deposit terozoic time are available and are discussed by Miall (1976). Evi- formed in the axial regions of the Franklinian geosyncline. Trettin dence from Victoria Island (Thorsteinsson and Tozer, 1962) (1971) and Trettin and others (1972) applied the name Hazen suggests that during early Paleozoic time, part or all of Banks Is- Trough to this paleogeographic feature. The Nanuk Formation at

in < < >. CD 3 (/) r-H c o o I IO o rv a> CO (0 Q E o Q> c er cn X TD 0> a> c > c e «J ap Q> ¡Ti

Figure 3. Structural cross section through Banks Island.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/87/11/1599/3429155/i0016-7606-87-11-1599.pdf by guest on 02 October 2021 Figure 4. Paleogeography of the Banks Island area in late Emsian time. The slope-trough boundary is generalized in Melville Island because of a lack of detailed biostrati- graphic control.

• Control point

1. Cook and Aitken, 1969 2. Orksut 1-44' 3. Storkerson BayA-15' 4. Nanuk D-76* 5. Thorsteinsson and Tozer, 1962* 6. Thorsteinsson and Tozer, 1962; Ormiston, 1967' 7. Tozer and Thorsteinsson, 1964' 8. Lenz, 1972

• New biostratigraphic control in this report

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the Nanuk D-76 well is interpreted as a tongue of Ibbett Bay—type was covered entirely by deltaic sediments of the Melville Island sediments that has extended beyond the confines of the axial Group, the stratigraphy and sedimentology of which has been in- trough. The marked diachroneity displayed by all Devonian units vestigated in detail by Embry and Klovan (1974). in the area (increasing in age to the north) suggests that in northern Banks Island, the Nanuk Formation probably overlaps in age the DISCUSSION upper part of the Ibbett Bay Formation. It is therefore legitimate to interpret Hazen Trough as extending southward into the area re- The main contributions of this study are as follows: (1) The evi- ported here. A similar steady migration of the Hazen Trough dence indicates that there almost certainly is no region of folded toward the craton has been demonstrated for Ellesmere Island rocks comparable to the Parry Islands fold belt beneath Banks Is- (Trettin and others, 1972). land. (2) Paleogeographic reconstructions for Early and Middle The influence of Coppermine arch, as outlined by Lerand (1973, Devonian time suggest that Hazen and Richardson Troughs were his Fig. 7), appears to be indicated by the bend in facies belts in connected in a continuous deep-water seaway. central Banks Island. The arch in Emsian time took the form of a The existence of a link between Hazen trough and Richardson platform submerged under a shallow shelf sea. At some time prior Trough has long been assumed (Martin, 1959; Ziegler, 1969; to Cretaceous time, the arch was emergent, because at several Miall, 1973; Churkin, 1973a, 1975), but the data presented herein localities, Cretaceous rocks have overstepped all Paleozoic units provide the first actual supporting evidence. There is still a major and rest directly on Proterozoic rocks. [A regional cross section gap in the record between southern Banks Island and northern through the southwest flank of the arch which shows this relation- Yukon, but regional considerations with respect to Coppermine ship is given by Yorath (1973, his Fig. 2).] According to Cook and arch and the Eskimo Lakes fault zone provide a basis for drawing Aitken (1969), stratigraphic and structural relationships near the southern margin of the trough, as shown in Figures 4 and 5 Brock inlier (Fig. 4, loc. 1) suggest a period of post-Early Silurian, and, in a more generalized manner, in Figure 6. pre—Middle Devonian tectonism. Therefore, part of Coppermine Similar lithologic facies and lateral fades relationships are devel- arch may have been a land area during Early Devonian time, as oped along the length of this trough, as summarized in the three shown in Figure 4. By Middle Devonian time, the sea probably had regional cross sections shown in Figure 7. The Blue Fiord Forma- returned, because Cook and Aitken (1969) recorded a single out- tion is a widespread platform carbonate in the Arctic Islands; it is crop of Hume Formation on the east flank of the Brock inlier. The similar in age (in part) and lithology to the Ogilvie and Hume For- outcrop exposes coral and stromatoporoid limestone, which mations of the Arctic mainland (Lenz, 1972). The Orksut Forma- suggests a typical platform facies with no nearby terrigenous sedi- tion compares with the Eids Formation of the Arctic Islands (Kerr, ment sources. 1974) and the Prongs Creek Formation of northern Yukon (Lenz, It is possible that the Hazen Trough was linked with Richardson 1972). The Nanuk and Ibbett Bay Formations also have a counter- Trough (Fig. 6) during much of its history. Lenz (1972) showed part in the Yukon in the form of the Canol Formation. The type that the latter was undergoing deep-water sedimentation through- Canol is an Upper Devonian unit first described on the Mackenzie out most of Late Cambrian to Middle Devonian time. The eastern Platform (Bassett, 1961), but it probably represents a thin tongue margin of the trough appears to trend in a northeasterly direction of a deposit that had a much greater age range in the Richardson in the Fish River—White Mountains area of northern Yukon. This Trough. As Lenz (1972, p. 351) stated: "It is virtually impossible at trend would carry the shelf-trough margin along the Eskimo Lakes any one locality to distinguish the lithologic character of Middle fault zone [immediately north of Aklavik arch in Fig. 1; this name Devonian from Upper Devonian black, siliceous shales; that is, be- was first used by Coté and others (1974)], which, according to tween 'true' Canol shale and possibly other black, siliceous, Lerand (1973, p. 327), was active during Paleozoic time. It is pos- bituminous shales." According to Lenz (1972, p. 349), the base of sible that the present tremendous northward downthrow along this these shales varies in age from Emsian or Eifelian to late Givetian. fault zone is a reflection of a much older flexure corresponding to Churkin (1975) summarized the evidence for the existence of the the craton edge, although deep-well control is sparse in this area, ancestral Brooks geosyncline and its connection with Richardson and thus Paleozoic facies changes have not yet been mapped. This Trough. Cambrian to Lower Devonian graptolite-bearing rocks of interpretation is consistent with the paleogeography of Banks Is- the Neruokpuk "Formation" are present at several localities within land, the shelf edge "wrapping around" the northwestern end this paleogeographic unit, indicating a history parallel to that of the of Coppermine arch, as shown in Figure 4. Franklinian geosyncline. Churkin (1975, his Fig. 3) concluded by Between earliest Eifelian and earliest Givetian time, the facies presenting a regional paleogeographic map for the Ordovician belts shown in Figure 4 gradually shifted southward. To the north, Period similar to that presented here for Early and Middle Devo- on Melville Island, the fine-grained clastic material of the Blackley nian time (Fig. 6). It is similar to earlier reconstructions of a Member [of turbidite origin according to Embry and Klovan "circum-Arctic geosyncline" (Martin, 1959, p. 2435; Churkin, (1974)] represents the first distal fringe of the Melville Island 1969, 1973a) with one major difference — the three troughs Group clastic wedge. These sediments may have spread gradually (Brooks, Richardson, and Franklinian) are interpreted by Churkin southward across Banks Island, as suggested by geophysical log as the three arms emanating from a triple-joint plate junction, with character in the basal part of the succession at the Storkerson Bay Richardson Trough developing as a failed arm during early well. At Storkerson Bay, the lowermost sandstone units are of late Paleozoic time. Eifelian or early Givetian age. None of the other wells penetrates this part of the section. Carbonate sedimentation persisted at the PROBLEMS OF PALEOZOIC PLATE TECTONICS Orksut 1-44 well, and the same carbonate fades probably devel- IN THE NORTH AMERICAN ARCTIC oped all along the craton edge southward into the Mackenzie Plat- form region, where it constitutes the Hume Formation. A complete review of this controversial subject would warrant a A paleogeographic map of middle to late Givetian time (Fig. 5) paper of its own. The purpose of this section is to offer some brief shows that the shelf carbonate environment had virtually receded comments regarding the various published interpretations of the from Banks Island by this time. A major part of the area discussed tectonic history from the vantage point of Banks Island, which is here was now covered by the distal edge of the Melville Island part of the area of concern and has yielded some new and relevant Group clastic wedge. data. Little evidence is available from Banks Island for constructing a First, the question must be asked, Why involve plate tectonics in paleogeographic map for Late Devonian time. The area probably the area at all? (The opening of the Atlantic and its extension into

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Figure 6. Regional paleogeography of the North American Arctic during Early and Middle Devonian time (based on present-day continental dispositions).

the Arctic Ocean is not at issue here.) The earlier ideas suggesting a Alaska probably were derived from a geanticlinal uplift within the circum-Arctic geosyncline (Martin, 1959; Churkin, 1969, 1973a) Brooks geosyncline (Churkin, 1973a; Norris, 1974). The Melville provided a simple and straightforward means of correlating areas Island Group of the Arctic Islands was derived from the Pearya with similar geologic histories in several parts of the Arctic. How- geanticline (Trettin and others, 1972) and Caledonian uplifts in ever, Tailleur and Brosge (1970), using a modification of Carey's (Embry and Klovan, 1974). (1958) orocline concept, proposed a scissorlike opening of the There also are difficulties with the hypothesis of the circum- Canada Basin during Mesozoic time, following rifting and rotation Arctic geosyncline. Thus, if the paleogeographic outline shown in about a pivot point situated in northern Yukon. The advantages Figure 6 represents a triple-point junction, where is the plate that conferred by this hypothesis included the following: (1) It helped occupied what is now the Canada Basin? Herron and others (1974) explain the thrusting and foreshortening and the juxtaposition of invoked a separate Siberian plate corresponding to the Kolymski markedly different sedimentary facies in the pre—middle Creta- massif to explain this difficulty, but, in so doing, they violated the ceous rocks of the Brooks Range. (2) It apparently explained the Siberia-Alaska connection. Churkin (1972) demonstrated that structural deflection between the northeastern Cordillera and the there is no evidence to justify drawing a plate boundary between Brooks Range. (3) By suggesting a closing-scissor motion and a col- the Kolymski massif and easternmost Siberia. lision between Alaska and the Arctic Islands in Late Devonian time, The area that can be interpreted most readily in terms of plate the hypothesis provided a tectonic landmass from which the tectonics is the northern Arctic Islands. Trettin and others (1972, circum-Arctic Upper Devonian clastic wedge could have been de- see especially Fig. 29) have shown that the Hazen Trough probably rived. was floored by continental crust and that the Pearya geanticline Others, including Miall (1973), Richards (1974), and Freeland was an orogenic welt that developed above a southeast-dipping and Dietz (1973), have developed this idea further, and it certainly subduction zone. The movement of the Arctic Ocean plate beneath helps to explain many details of the local geology, especially in the Arctic Islands appears to have ended with the Ellesmerian northern Alaska. However, there are many difficulties with the orogeny, which may have occurred when Ellesmere Island and theory: (1) None of the authors quoted above has attempted to Greenland collided with a part of Siberia. Before the Mesozoic- account for the connection between Alaska and eastern Siberia. Tertiary opening of the Atlantic, the Barents Shelf lay close to Churkin (1972, 1973b) has shown that no plate boundary can be Ellesmere Island and Greenland, and this may have been the conti- drawn between these regions, and it is necessary, therefore, for nental mass that collided with the Canadian Arctic Islands. proponents of rotational drift to demonstrate large-scale plate Several lines of evidence suggest that the southwestern Arctic Is- motions in Siberia parallel to those of Alaska. (2) Norris (1972, lands were part of a completely different tectonic environment dur- 1974) pointed out the structural features that would be expected to ing early Paleozoic time: (1) During Middle Ordovician to Middle have resulted from oroclinal bending, including strike-slip Silurian time, the Hazen Trough in Ellesmere Island received more movements and compression on the inside of the deflection. He than 2,700 m of flysch sediments as a result of uplift along the showed that the evidence for these features is absent or contradic- Pearya geanticline (Trettin, 1970; Trettin and others, 1972, p. 95). tory. (3) There is no need to invoke a single landmass for the deri- By contrast, in the vicinity of Melville Island, the Hazen Trough vation of the Late Devonian clastic wedge. The Imperial Formation and probably Banks Island underwent pelagic sedimentation at this of northwestern Canada and the Endicott Group of northern time, giving rise to the shale and chert of the Ibbett Bay Formation.

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After Thorsteinsson and Tozer, 1970

NNW SSE Sandstone, siltstone, MELVILLE ISLANNDn/D r present erosionsiirfarp shale vr^Vr r

Siliceous shale, chert BANKS ISLAND^\^

Shale, limestone, siltstone

MACKENZIE PLATFORM

Horizontal scale Vertical scale Kilometres Metres 75 3000 I This report 40 9000 Miles Feet W Richardson Trough Mackenzie Platform

FRANKLIN MOUNTAIN FORMATION

RICHARDSON MOUNTAINS-MACKENZIE PLATFORM After Lenz, 1972 Figure 7. Comparative Devonian stratigraphy: three shelf-slope-basin stratigraphie cross sections.

(2) As discussed above, the effects of the Ellesmerian orogeny die present-day land areas, but this possibility cannot be considered in out southwestward and appear to be virtually absent in the detail without some geologic evidence from distant offshore re- Paleozoic rocks of Banks Island. (3) There is no evidence of an gions.) orogenic welt immediately to the west of Banks Island comparable My interpretation of these data is that subduction and plate col- to the Pearya geanticline. Volcanic rocks and locally derived clastic lision probably took place only along the Ellesmere Island- wedges are absent in the Devonian rocks within the island. (A gean- Greenland portion of the present Arctic Islands continental margin. ticline could have existed so far to the west of Banks Island that no The Melville Island—Banks Island region remained as an open ba- direct sedimentary or volcanic evidence for it exists within sin, toward which clastic sediments were directed throughout much

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of early and middle Paleozoic time. Paleocurrent studies in troleum provinces of Canada, their geology and potential: Canadian Ordovician-Silurian flysch (Trettin, 1970) and in the Upper Devo- Soc. Petroleum Geologists Mem. 1, p. 315—386. nian Melville Island Group (Embry and Klovan, 1974) both show Martin, L. J., 1959, Stratigraphy and depositional tectonics of north Yukon-lower Mackenzie area, Canada: Am. Assoc. Petroleum Geolo- current directions flowing along the axis of the Hazen Trough gists Bull., v. 43, p. 2399-2455. toward the southwest. A collision between plates containing em- McLaren, D. J., 1963, Southern Ellesmere Island between Goose Fiord and bayments and projections would give rise to all the observed fea- Bjorne Peninsula, in Fortier, Y. O., and others, Geology of the north- tures, in the manner described by Dewey and Burke (1974). central part of the , (Opera- The size of this basin (proto—Arctic Ocean) and the identity of tion Franklin): Canada Geol. Survey Mem. 320, p. 310—338. the continental mass opposite Banks Island (not necessarily closer Miall, A. D., 1973, Regional geology of northern Yukon: Bull. Canadian than several hundreds of kilometres distant) are questions that have Petroleum Geology, v. 21, p. 81-116. not been answered satisfactorily by any of the hypotheses proposed 1975, Post-Paleozoic geology of Banks, Prince Patrick and Eglinton Is- to date. The features of Alaskan geology that suggest plate colli- lands, in Yorath, C. J., Parker, E. R., and Glass, D. J., eds., Canada's sions (Tailleur and Brosgé, 1970; Richards, 1974) have still to be continental margins and offshore petroleum exploration: Canadian Soc. Petroleum Geologists Mem. 4, p. 557-588. explained, whether or not the orocline concept is held to be valid. 1976, Proterozoic and Paleozoic geology of Banks Island, Arctic Possibly a plate existed that comprised eastern Siberia (Kolymski- Canada: Canada Geol. Survey Bull. 258, 77 p. Chukotskiy) and the northern part of Alaska, as is shown in a Norris, D. K., 1972, En echelon folding in the northern Cordillera of promising reconstruction by Hughes (1975, his Fig. 4b). Canada: Bull. Canadian Petroleum Geology, v. 20, p. 634-642. Movements of this plate, yet to be defined, combined with strike- 1973, Tectonic styles of northern Yukon Territory and northwestern slip faulting on the Kaltag lineation (Tailleur and Brosgé, 1970; District of Mackenzie, Canada, in Pitcher, M. G., ed., Arctic geology: Norris, 1974), may explain the observed features, but much work Am. Assoc. Petroleum Geologists Mem. 19, p. 23-40. remains to be done before such ideas can be raised above the level 1974, Structural geometry and geological history of the Canadian of speculation. Cordillera, in Wren, A. E., and Cruz, R. B., eds., Proceedings of the 1973 National Convention: Canadian Soc. Explor. Geophysicists, p. 18-45. ACKNOWLEDGMENTS Ormiston, A. 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