A new Lower Devonian rock unit in the Canadian Arctic Islands

A new Lower Devonian rock unit in the Canadian Arctic Islands

ALLEN R. ORMISTON Pan American Petroleum Corporation, Tulsa, Oklahoma

Received April 14, 1969 Accepted for publication June 4, 1969

A thin, shelf-type carbonate unit with an abundant shelly fauna of Lower Devonian age is developed in the vicinity of Drake Bay, northwestern Prince of Wales Island where it rests on a dolomitic western facies of the dominantly clastic Peel Sound Formation. These limestones and shales which contrast in thickness, lithofacies, and biofacies with coeval rocks exposed in the Stuart Bay area of Bathurst Island 190 miles (306 km) to the north, represent a new stratigraphic unit.

The lithologic characteristics, stratigraphic relations, fauna, and age of the unit are documented, but no name is proposed because of the incompleteness of the exposure and because a more suitable type section is available.

Introduction

Rocks cropping out around Drake Bay, western Prince of Wales Island (see Fig. 1, locations A and B) were measured and collected in the course of stratigraphic studies made in 1960. A measured section of these strata has been published (Ormiston 1967, p. I&), but no formational terminology has been applied, nor has the exact age of the beds been established. The lithologic and faunal unique- ness of these beds was previously emphasized (Ormiston 1967, p. 6). Enough of them is now known to warrant recopition as a new stratigraphic unit. Because of the incompleteness of their exposure, formational designation is avoided, The informal name, Drake Bay beds, is an appropriate appellation for these rocks. The Drake Bay beds are much thinner and of totally different facies than are age equivalent rocks developed in the miogeosynclinal Parry Islands Fold Belt (McLaren in Fortier et al. 1963, pp. 604-610) showing that there is a rapid southward change of thick clastic sedi- ments to shelf-type deposits from the Parry Islands Fold Belt (compare Fig. 2, columns 1 and 2).

Previous Work Probably the earliest mention of the Drake

Bay strata is a report by Franklin-searcher, Sherard Osborn (1 852, p. 96), of richly fossiliferous limestone from the west coast of Prince of Wales Island. Such a description could apply only to the Drake Bay beds, as the western facies of the Peel Sound Formation in that area consists only of poorly fossiliferous (ostracodes) silty dolomites.

Canadian Journal of Earth Sciences, 6, 1105 (1969)

FIG. 1. Map of Prince of Wales showing location of outcrops (A and B) of the Drake Bay beds.

Substantive discussion of these beds begiqs with Thorsteinsson and Tozer's (in Fortier et al. 1960, p. 126) brief description of "Upper Silurian or Lower Devonian Rocks of North- western Prince of Wales Island". The localities mentioned in their discussion make it clear that the beds in question are the same as those here called the Drake Bay beds. Too few fossils were then available to decide between a Late Silurian

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ORMISTON: A NEW LOWER DEVONIAN ROCK UNIT 1107

DRAKE BAY BEDS PEEL SOUND FM., ALLEN BAY FM. A A r Y b

kLl MEASURED SECTION W

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FIG. 3. Geologic cross section along line X-X' (see Fig. 1) showing stratigraphic relations of Drake Bay>eds. Vertical exaggeration is 8X.

or Early Devonian age for these beds. Those authors did, however, advance as a working hypothesis the idea that these beds represent a western carbonate facies of the Peel Sound Formation.

Stratigraphic Relations of the Drake Bay Beds On the basis of more detailed field studies

than were possible during Thorsteinsson and Tozer's brief visit, it is clear that there is, in- deed, a western carbonate facies of the Peel Sound Formation (mainly silty dolomites), but that the Drake Bay beds are entirely younger than those beds, which they overlie (see Fig. 3). There are apparently no strata in the Peel Sound Formation to the east, which are as young as late Siegenian or early Emsian and they cannot correlate with the Drake Bay beds. Dieley (1966, p. 13) has studied vertebrate fossils from the Peel Sound Formation on Prince of Wales and Somerset Islands and mentioned none younger than Downtonian (no younger that Gedinnian in terms of the marine succession).

The influence of Thorsteinsson and Tozer's hypothesis is seen again in Geological Survey of Canada (G.S.C.) Map 3-1967 (in Blacka- dar 1967), on which beds discussed herein are mapped (map-unit 13) as "limestone, dolo- mite; mainly carbonate facies of Peel Sound Formation but probably includes some beds equivalent to Read Bay Formation and may include some beds younger than Peel Sound Formation." In fact, all of these beds are younger than the Peel Sound Formation. The relations between the Drake Bay beds and the Peel Sound Formation are shown on Fig. 3, and it is clear that while the Peel Sound Formation

does change into a silty carbonate facies to the west (beds of this type are exposed in a river about 10 miles (16 km) due east of location B, Fig. I ) , the limestones containing a good shelly fauna (Drake Bay beds) are not part of this facies (lithotope).

In lithology, stratigraphic position, and faunal content, the Drake Bay beds resemble the lower part of a thicker and more complete Lower Devonian unit on Lowther Island now being studied by R. Thorsteinsson of the Geo- logical Survey of Canada. Thorsteinsson kindly permitted examination of lithologic samples and fossils from which the foregoing conclusions are drawn. The existence of contacts with both over- and under-lying stratigraphic units as well as the greater stratigraphic thickness of the new unit within Thorsteinsson's study area make that the logical type area, if the unit under discussion is to be designated a new formation. The exposures in the vicinity of Drake Bay can serve as a reference section providing informa- tion on the age and the regional distribution of the lower part of this formation.

Lithology The measured section shown in Table I

represents the thickest single exposure in the study area, although only 80 f t (24 m) of beds are present. Exposures on the shore of Drake Bay (Fig. 4) are discontinuous and include no more than 10 ft (3 m) of beds at a single outcrop.

The gross lithologic character of the beds is clear from the measured section (Table I). Although dominantly a carbonate sequence, it includes dark shales, siltstones, and some sandstone.

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1108 CANADIAN JOURNAL OF EARTH SCIENCES. VOL. 6, 1969

FIG-4. Outcrop of Drake Bay limestones near the east shore of Drake Bay (Fig. 1, location A). Bedding in back- ground is partly obscured by drift.

FIG. 5. Limestone slab (bed 8, measured section XI) showing fossil abundance in certain Drake Bay beds.

Paleontology and Age zoans, trilobites, and conodonts are also present The abundance of fossils (see Fig. 5) is a at the measured section. Stromatoporoids, not

notable feature of the Lower Devonian rocks of seen at the measured section, are represented western Prince of Wales Island. Brachiopods by large cabbage-head forms at the head of dominate the fauna, but tabulate corals, bryo- Drake Bay.

TABLE I Measured section-Drake Bay beds

This section was measured on northwestern Prince of Wales Island 20 miles northeast of the head of Drake Bay (Fig. 1, loc. B). At this locality a low escarpment of tan weathering Devonian limestones is cut by a small creek for a distance of 0.5 mile. The section begins at the base of the escarpment and continues to the top. Measured by

A. R. Ormiston, 1960 -

Bed No. Top of exposure ft (m)

Calcareous sandstone and limestone: brownish grey, he-grained. medium-bedded, rossili- ferous sandstone, weathers tan: interbedded with dark grey. aphanitrc, thin- to mediurn- bedded Iimestonc with petrohferous odour, weathers grey. unit rorms top OF escarpment

Limeslone: brown, finely crystalline, medium-bedded. weathers tannish grey and blocky, Atr,l.pa, Reefrunia, Murifcrelh, Schizophorirr.. ....................................

CaIcareous sandstone: ltght brown, line-grained, medium-bedded, quartzose, weathers tan .................................................................. and slabby..

Argillaceous limestone: very dark brown, finely crystalline, thin-bedded, weathers tan and Raggy.Arrypa ................................................................

Limcstone and quartzose limestone: brown, finely crystalline, medium- to thick-bedded I~mestone, weathers tan; interbedded with brown, finely crystallme, medium-bedded, quartzose limestone, weathers tan, Dech~nellu (?Basideckenella) sp. .................

Argillaceous limestone; dark brown, finely cry~tatline, thin-bedded, weathers tan and slabby. somewhat resistant. Laterally this unit grades into shale: brown, fissile, with concretion-like lrmstone lenses, bryomans, Arrypu, ''S~hizoprnetoide~ sp. indet ., ?Teru- ................................................. raij>is sp., Reefranin, Mur~~erella

Sandstone and siltstone: light brown. hegrained, medium-bedded, calcareous sandstone, weathers tan and slabby; interbeddcd with dark brown, fine-grained, calcareous slltstone, weathers greyish tan and slabby, Airypa, Cyrtina, Gypidda. ...............

Limestone: dark brown, finely crystalline, medium- to thin-bedded, slightly argillaceous. slight petroliferous odour, weathers grey and slabby. Styliolino, unidentif ed pIacoderms

Limestone: dark brown, finely crystalline, med~um-bedded, slightly sandy, slight petroli- fcrous odour, weathers greyish tan and blocky, favosltids, Schrzoproe~oides sp, indet., Otarion sp., Harpes sp. indet., brachiopods, Deuhenelfa (B.) laricaudaro Ormiston (1 967)

Rests on Peel Sound dolomites, contact not exposed. Total thickness measured is 79.5 ft (24.2 m).

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ORMISTON: A NEW LOWER DEVONIAN ROCK UNIT 1109

Of the fossils present only the trilobites, brachiopods, and conodonts have been examined in any systematic way.

Trilobites Five trilobite genera are present, only one of

which is represented by sac ien t material to be specifically identiiied. The basal bed at the measured section contains Dechenella (Basi- dechenella) laticaudata Ormiston; Schizoproe- toides sp. indet.; Harpes sp. indet.; and Otarion sp. A Schizoproetoides close to that in the measured section is now known from the Em- sian Michelle Formation (Ormiston, in press) of the Yukon. Fragments that occur in bed 4 are assigned with question to the lichad genus Terataspis known from the Schoharie Forma- tion of New York State.

On the basis of a similarity of evolutionary grade between Dechenella (B.) laticaudata and Dechenella (B . ) dombrowiensis (Sobolew 1909), a Polish species which Richter and Richter (1950, p. 178) cited as coming from beds at the Lower-Middle Devonian boundary near Dombrowa, Poland, Ormiston (1967, p. 17) regarded the beds exposed at the measured section of the Drake Bay beds as comparable in age and therefore datable as Emsian and/or Eifelian. It now appears that the dechenellid stock originated in North America and subse quently migrated to Europe and that a com- parison of North American and Polish dechen- elLids may not provide a sound basis for dating the Drake Bay beds.

Brachiopods Although brachiopods abound in the cal-

carenite beds of the Drake Bay, they are not easily freed from the matrix for study. In the course of aciduing blocks from bed 8 of the measured section, a well-preserved silicified brachiopod fauna was recovered. This collec- tion was kindly examined by Dr. J. G. Johnson of the University of Pennsylvania, who reported the following genera (personal communication): Reeftonia sp. Atrypa sp. Muriferella sp. Anatrypa sp. Schizophoria sp. Nucleospira sp. Gypidula sp. (smooth) Undispirifer? sp. Skenidioides? sp. Warrenella sp. Trigonorhynchia? sp. Cyrtina sp. "Leiorhynchus" sp.

Substantially the same brachiopod fauna is

present in bed 3 of the measured section from which J. G. Johnson reported: Skenidioides sp. "Leiorhynchus" sp. Muriferella sp. A try pa "reticularis" Reeftonia sp. Spinatrypa? sp. Nucleospira sp. Undispirifer? sp. Warrenella sp. Cyrtina sp.

The presence of the genus Reeftonia is of zoogeographic interest as it was previously known only from the Lower Devonian of New Zealand, Australia, and Manchuria. On the basis of the presence of Muriferella, "Leiorhyn- chus", and Warrenella, Johnson (personal communication) suggested an Emsian age for this fauna. He pointed out, however, that Murifer- ella is both Siegenian and Emsian in age. A Siegenian age cannot be excluded, but would require extending the known ranges of War- rem/Ia and "Leiorhynchus".

Conodonts Residues from the acidized Drake Bay lime-

stones also contained well-preserved conodonts. These have been studied by Dr. Gilbert Klapper who reported (personal communication) :

bed 8 Spathognathodus sulcatus (Philip) Spathognathodus optimus Moskalenko Spathognathodus n.sp. Pelekysgnathus serratus Jentzsch Ozarkodina denckmanni Ziegler Trichonodella sp. Panderodus sp.

bed 3 Spathognathodus sulcatus (Philip) Spathognuthodus optimus Moskalenko Spathognathodus asp. Ozarkodina denckmanni Panderodus sp.

The stratigraphic distribution of both brachiopods and conodonts thus suggests no impor- tant time break within the measured section.

Concerning the age significance of this fauna, Klapper stated: "The conodont fauna seems to correlate with the interval 595 to 750 feet in Lenz's section 1 (Lenz 1966, Fig. 2) at Royal Creek, Yukon, based on the stage of evolu- tion shown by Spathognathodus sulcatus (late forms, see mapper 1969, p. 1 ) , as well as the presence of Spatbgnnthodus optimus and Pdekysgnathus serratus". Lenz ( 1968) ref er- red this interval at Royal Creek to the Gypidula 1 - Davidsoniatrypa unit (equals Gypidula 1 - Biconostrophia unit of Lenz 1966), which he considered late Siegenian in age.

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1110 CANADIAN JOURNAL OF EARTH SCIENCES. VOL. 6, 1969

From what we presently know of the faunas, the age of the Drake Bay beds could be either late Siegenian or Emsian or both. The best documented correlation of the fauna is with the Gypidula 1 - Davidsoniatrypa unit at Royal Creek (see Fig. 2, column 4) based on conodonts. For that reason, a late Siegenian age appears most reasonable for beds 3-8 in the measured section of the Drake Bay beds.

Age Equivalents to the North On central Bathurst Island some 180 miles

(290 km) north of Drake Bay, a thick succession of Lower Devonian strata is exposed in the Stuart Bay Anticline. The stratigraphy of these beds has been described by McLaren (in Fortier et al. 1963). The Bathurst Island (3000 ft or 914 m thick) and overlying Stuart Bay (1200 ft or 366 m thick) Formations of this area form a monotonous sequence of flaggy siltstones and he-grained sandstones. Rare, impersistant limestone lenses are developed in the Stuart Bay Formation, but the Bathurst Island Formation is entirely clastic with few shelly fossils. The presence of Monograptus cf. M. hercynicus in the upper part of the Bathurst Island Formation indicates a late Gedinnian and/or Siegenian age for part of the unit.

In the type area the Stuart Bay Formation is apparently of Emsian age throughout (Fig. 2). Brachiopods from the base of the formation (J. G. Johnson, personal communication) suggested this age as do conodonts (G. Klap- per, personal communication) from 400 ft (122 m) above the base. The formation must, however, be time transgressive, as 30 miles (48 km) east of its type area it has yielded Siegen- ian brachiopods.

Thus the temporal equivalents of the Drake Bay beds are represented by a considerable part of the 4200-ft (1280-m) thick interval of the combined Bathurst Island and Stuart Bay Formations. Implicit in this correlation is a signzcant change in facies and thickness of Lower Devonian strata from Bathurst Island in the north to Prince of Wales Island in the south.

Conclusions

The Drake Bay beds are part of a carbonate unit of Early Devonian age (late Siegenian or Emsian or both), which is a shelfward equivalent of a much thicker, clastic sequence (see

Fig. 2, column 2; Bathurst Island and Stuart Bay Formations) developed in the miogeosynclinal Parry Islands fold belt. Their fauna is also quite different from that of equivalent rocks on Bathurst Island. The Drake Bay beds appear to be lithologically and faunally correla- tive with the lower part of an unnamed Devon- ian unit on Lowther Island, which is now under study by R. Thorsteinsson of the Geological Survey of Canada.

Acknowledgments Stratigraphic studies on western Prince of

Wales Island were conducted under the super- vision of Professor A. H. McNair of Dartmouth College, whose guidance was most helpful. Dr. R. Thorsteinsson of the Geological Survey of Canada has discussed stratigraphic relations with me and kindly permitted examination of fossils and lithology samples collected elsewhere in the Arctic Islands. Dr. J. G. Johnson of the University of Pennsylvania and Dr. G. Klapper of the University of Iowa have provided identi- fications of brachiopods and conodonts, re- spectively.

BLACKADAR, R. G. 1967. Precambrian geology of Boothia Peninsula, Somerset Island and Prince of Wales Island, District of Franklin. Geol. Surv. Can. Bull. 151, 62 pp.

CHRISTIE, R. L. 1967. Stratigraphic sections of Palae- ozoic rocks on Prince of Wales and Somerset Islands, District of Franklin, N.W.T. Geol. SUN. Can., Paper 67-24, 21 pp.

DINELEY, D. L. 1966. Fossil vertebrates from the Read Bay and Peel Sound Formations, Somerset Island, District of Franklin. Zn Report of activ- ities, May to October, 1965. Geol. Surv. Can., Paper 66-1, pp. 12-13.

FORTIER, Y. O., et al. 1963. Geology of the north- central part of the Arctic Archipelago. N.W.T., (Operation Franklin). Geol. Surv. Can. Mem. 320, 671 pp.

KLAPPER, G. 1969. Lower Devonian conodont sequence, Royal Creek, Yukon Territory and Devon Island. Can. J. Paleontol., 43, pp. 1-27.

LENZ, A. C. 1966. Upper Silurian and Lower Devon- ian paleontology and correlation, Royal Creek, Yukon Territory, a preliminary report. Bull. Can. Petrol. Geol., 14, pp. 60L612.

1968. Upper Silurian and Lower Devonian biostratigraphy, Royal Creek, Yukon Territory, Canada. Proc. Intern. Symp. Devonian System, Calgary, 2, pp. 587-600.

ORMISTON, A. R. 1967. Lower and Middle Devonian trilobites of the Canadian Arctic Islands. Geol. SUN. Can. Bull. 153, 147 pp.

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I ORMISTON: A NEW LOWER DEVONIAN ROCK UNIT 1111

(In press). Lower Devonian trilobites from I the Michelle Formation, Yukon Territory. I n

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OSBORN, SHERARD 1852. Journal in Additional papers relative to the Arctic expedition under the orders of Captain Austin and Mr. William Penny; Great Britain, Parliament Accounts and Papers, 1852. 50, pp. 89-101.

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SOBOLEW, D. 1909. Devonien moyen de la Chaine de montagnes de Kielce-Sandomierz. MatCriel GCol. Russie, 24, St. Petersburg. (Russian with French summary.)

WASHBURN, A. L. 1947. Reconnaissance gwlogy of portions of Victoria Island and adjacent regions Arctic Canada. Gwl. Soc. Amer., Memoir 22, 142 pp.

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A new Lower Devonian rock unit in the Canadian Arctic Islands