Late Ordovician brachiopods Rafinesquina lata Whiteaves, 1 896 and Kjaerina hartae n.sp. from southern Manitoba and the Hudson Bay ~owlandsl Jisuo Jin, W.G.E. Caldwell, and B.S. Norford
Abstract: Examination of the Late Ordovician strophomenid brachiopod Rafinesquina lata Whiteaves, 1896 from the Selkirk Member of the Red River Formation of southern Manitoba reveals that the two syntypes actually represent two genera and two species, Oepikina lata and Kjaerina hartae n.sp. Specimens typically described as Rafinesquina lata by Whiteaves are large, thick-shelled, strongly but evenly concavo-convex, with randomly spaced, fine, concentric growth lamellae and a high ventral interarea. Affinity of the species to Oepikina lies in its unequal parvicostellae of the ventral valve, conspicuous dorsal peripheral rim, robust cardinal process, and strong lateral trans-muscle septa. Kjaerina hartae is easily distinguished from 0. lata by its strongly geniculate and less massive shell, a much lower ventral interarea, prominent concentric rugae, and, internally, considerably weaker trans-muscle septa. The shells of 0. lata and K. hartae are unusually large and suggest an open, shallow- and warm-water, subtidal depositional environment for the original sediments of the Selkirk Member of the Red River Formation. Common occurrences of K. hartae in the upper Portage Chute and Surprise Creek formations (Bad Cache Rapids Group) of the Hudson Bay Lowlands, together with other brachiopods and other groups of fossils, support the concept that the epicontinental seas once covering the Hudson Platform and the Williston Platform were connected during Late Ordovician (Maysvillian) time. R6sumC : L'examen du brachiopode Rafinesquina lata Whiteaves, 1896, de l'ordre des Strophomenida, Ordovicien tardif, provenant du Membre de Selkirk de la Formation de Red River dans le sud du Manitoba, rkvBle que les deux syntypes reprksentent actuellement deux genres et deux espkes, Oepikina lata et Gaerina hartae n.sp. Les spkcimens typiquement dkcrits sous le nom de Rafinesquina lata par Whiteaves sont grands, avec valves Cpaisses, une coquille fortement mais uniformkment concavo-convexe, de fines lamelles de croissance concentriques espackes alkatoirement et une interarea ventrale klevke. L'affinitk de cette espBce avec Oepikina rkside dans les parvicostules inkgales de la valve ventrale, le relief rnarquk du bourrelet pkriphkrique de la valve dorsale, le processus cardinal robuste, et les septa latkraux trans-muscles saillants. I1 est facile de distinguer K. hartae d'avec 0. lata par sa coquille fortement gknicul6e et moins massive, l'interarea ventrale beaucoup plus basse, les stries concentriques notoires et, ?i l'intkrieur, les septa trans-muscles considkrablement moins prononcks. Les coquilles de 0. lata et K. hartae sont exceptionnellement grandes, et elles suggkrent pour les skdiments originaux du Membre de Selkirk et de la Formation de Red River un dkp8t en eau chaude dans un milieu subtidal, ouvert et peu profond. La prCsence frkquente de K. hartae dans les formations de Portage Chute supkrieur et de Surprise Creek (Groupe de Bad Cache Rapids) des basses terres de la baie d'Hudson, couplke ?i d'autres brachiopodes et d'autres groupes de fossiles, plaident en faveur de l'hypothkse que les mers kpicontinentales qui couvraient jadis la plate-forme d'Hudson et la plate-forme de Williston ktaient relikes par un passage durant la pkriode de l'ordovicien tardif (Maysvillien). [Traduit par la rCdaction]
Received December 30, 1994. Accepted April 10, 1995.
J. Jin. Department of Earth Sciences, Laurentian University, Sudbury, ON P3E 2C6, Canada. W.G.E. C a l d ~ e l l Department .~ of Earth Sciences, The University of Western Ontario, London, ON N6A 5B7, Canada. B.S. Norford. Geological Survey of Canada, 3303-33rd Street NW, Calgary, AB T2L 2A7, Canada.
'
Geological Survey of Canada Contribution 41594. Corresponding author (e-mail:
[email protected]).
Introduction Despite abundance, diversity, and potential for stratigraphic correlation within western North America, the brachiopod fauna of the Upper Ordovician Red River Formation in the southern Manitoba segment of the Williston Basin has never been studied systematically. This is remarkable when the geological importance yet limited outcrop distribution of the formation is considered. The Red River and equivalent formations mark the earliest, exceptionally widespread, epicratonic, marine invasion
Can. J. Earth Sci. 32: 1255-1266 (1995). Printed in Canada 1 Imprim15au Canada
Can. J. Earth Sci. Vol. 32, 1995
Fig. 1. Geological map of Ordovician rocks in southern
Manitoba. The Red River Formation is largely undivided in areas south of Lake Winnipeg except for the Fort Garry Member. Specimens from southern Manitoba used in the present paper are from East Selkirk (GSC 4391), Lower Fort Garry (GSC 6991), and Garson Quarry (GSC locality C-205935 and University of Manitoba collection). (Adapted from McCabe and Barchyn 1982 and Lauhn-Jensen 1987).
of the North America Craton in post-Cambrian time, their distinctive carbonate rocks, algal flora, and invertebrate fauna traceable through the Western Interior of the continent, from northwestern Greenland to the borders with Mexico. The fossil assemblage, collectively dubbed the "Arctic Ordovician fauna," has been interpreted as the warm-water biota of the ancient equatorial or low-latitude belt (Flower 1946; Nelson 1959a, 1959b; Nitecki 1972), an inference subsequently confirmed by paleomagnetic reconstruction of the Late Ordovician polar and equatorial positions (see, for example, Briden et al. 1974; Jaanusson 1979; Scotese and McKerrow 1990). More locally, the formations record the oldest, widespread inundation of the Williston Platform (Cecile and Norford 1993), and their present eroded margins conservatively define the maximum known extent and shape of the Williston Basin, one of the largest intracratonic depressions in the continent (Fuller and Porter 1962). In the same way, the formations record the oldest inundation of the Hudson Platform farther east and define the southwestern margin of the equally large Hudson Bay Basin (Norris 1993). Within the Williston Basin, the Red River rocks (mainly in their upper part) offer the oldest known evidence of repeated sedimentary rhythms, implying lower-order transgressiveregressive cyclicity during a major episode of flooding (Kent 1960; Fuller and Porter 1962; Elias 1991; Cecile and Norford
1993). Within the basin too, the Red River Formation is important for its natural resources, which include some of the oldest known oil reservoirs (Johnson and McMillan 1993). The formation also contains the attractive, dolomitemottled "Tyndall Stone", Canada's preeminent building stone, used in governmental and other prominent buildings in the Prairie provinces and to a lesser extent across the country. "Tyndall Stone" is quarried in southern Manitoba, where the Red River Formation has its only substantial outcrop (Guliov 1993). The lack of systematic exposition of the Red River brachiopods is all the more remarkable when, by comparison, those of the overlying, much thinner, and less widespread Upper Ordovician Stony Mountain and Stonewall formations are relatively well understood (Okulitch 1943; Stearn 1956). The authors of this contribution have undertaken to close the gap in knowledge of the Ordovician brachiopod faunas of the Canadian Craton corresponding to the Red River and equivalent formations, and this paper is part of that effort. Large-shelled strophomenid brachiopods are fairly common in the Upper Ordovician (Maysvillian) Selkirk Member of the Red River Formation in the northeastern Williston Basin, southern Manitoba. Early collections of brachiopods were made by D. Gunn in 1858, R. Bell in 1880, T.C. Weston in 1884, and D.B. Dowling in 1891 from the Lower Fort Garry, East Selkirk, and Lake Winnipeg areas (for details see Whiteaves 1897, p. 173). Most of these collections were studied by Whiteaves (1896, 1897), who was able to date and correlate their host rocks with rocks in other regions of North America on the basis of the brachiopods and other fossils. Whiteaves (1896) established a new species, Rafinesquina lata, and illustrated three specimens (Whiteaves 1897) from a total of 14 collected to that date from the Red River Formation of southern Manitoba. Two of the three figured specimens are in the type collections of the Geological Survey of Canada (the third shell was a loan to Whiteaves by the Smithsonian Institution). It is obvious that the two Geological Survey syntypes belong to two separate genera and species, assigned respectively in the present paper to Oepikina lata and Kjaerina hartae n.sp. The Smithsonian specimen belongs to 0. lata. The purpose of this paper is to clarify the taxonomy of R. lata and to note the paleoecological and paleogeographical implications of these unusually large shells.
Regional geology and occurrences of taxa The Red River Formation (Foerste 1929) was introduced to designate the carbonate rocks between the underlying siliciclastic Winnipeg Formation and the overlying shale and limestone of the Stony Mountain Formation in southern Manitoba. Dowling (1895) had divided the rocks later referred to the Red River Formation into three units, the Lower Mottled Limestone, Cat Head Limestone, and Upper Mottled Limestone, and these units were named the Dog Head, Cat Head, and Selkirk members by Foerste (1929). The Fort Garry member subsequently was proposed for the top part of the Red River Formation by McCabe and Bannatyne (1970). The Red River Formation is exposed as a south-north belt in the Lake Winnipeg area (Fig. 1) and, from subsurface
Jin et al
Fig. 2. Stratigraphic occurrences of Oepikina lata, Kjaerina hartae, and selected brachiopod taxa of stratigraphic importance. Thicknesses of formations in the Hudson Bay Lowlands are based upon measurements at type sections taken from Nelson (1963, 1964) and Curnming (1975); thicknesses in Stony Mountain section from Elias (1982). SOUTHERN MANITOBA
x
HUDSON BAY LOWLANDS COMPOSITE SECTION
Stony Mountain Quarry Section
Y
dolomite
dolomitic limestone
LE chert
a c $ .
$ 0
s @ $ .22,s Garson Quarry Section
E
S
m
8m
O
f
'
O k C W , $52
sandstone
i i b j o a GI
11111
data (Norford et al. 1994), is known to thin from about 175 m in the south to 40 m at its erosional limit in the north. In exposed composite section, however, the formation has only an estimated thickness of 111 m (Andrichuk 1959; Elias et al. 1988). The Selkirk Member is about 40 m thick, composed of dolomitic limestone with mottled burrows. Most of the studied specimens of 0.lata and K. hartae were collected from the 8 m of the Selkirk Member exposed at Garson Quarry (Figs. 1 and 2), which produces the well-known "Tyndall Stone." Dating of the Selkirk Member is still at a preliminary stage. Elias (1991) assigned a Maysvillian early Richrnondian age to it, which accords with the middle Richmondian age of the overlying Fort Garry Member, as determined by Elias et al. (1988). The brachiopod fauna, especially the presence of the strongly lamellose rhynchonellid Hypsiptycha anticostiensis (Billings, 1862), supports a Maysvillian or younger age for the Selkirk Member (Jin et al., in press). Two species of brachiopods from the member, K. hartae and a new species of Tetraphalerella, indicate correlation with the upper Portage Chute and Surprise Creek formations (Bad Cache Rapids Group) of the Hudson Bay Lowlands, which carry the only other known occurrences of these species. The Bad Cache Rapids Group, including the Portage Chute and Surprise Creek formations, was named by Nelson (1963, 1964) and forms the basal part of the Upper Ordo-
calcareous shale
rnictitic rnudstone
vician sequence exposed along the western margin of the Hudson Platform (Figs. 2 and 3). The group is best developed in outcrops along the North Knife, South Knife, Churchill, and Nelson rivers and may extend as far south as the Winisk River. Conodonts extracted from cores of the Kaskattama Province No. 1 Well suggest a largely Edenian age (possibly extending into the Maysvillian) for the group (Le Fiivre et al. 1976). The brachiopod fauna points to a Maysvillian age for the upper Portage Chute and Surprise Creek formations, which make up the bulk of the Bad Cache Rapids Group (Jin et al., in press). Kjaerina hartae and the large-shelled new species of Tetraphalerella occur in outcrops along the South Knife and Churchill rivers and constitute characteristic elements of the Bad Cache Rapids fauna. Oepikina lata and K. hartae have unusually large shells, as do several other brachiopod species in the Selkirk Member and in the Bad Cache Rapids Group. These large sizes are perhaps the most striking feature of the Maysvillian brachiopod faunas of the two regions. Tetraphalerella (n.sp.), for example, may attain a width of 68 mm. Large shells of K. hartae exceed 50 mm in width. Oepikina lata and Strophomena undulosa Roy, 1941 (both in the Selkirk Member) are even larger, with some mature shells reaching over 70 rnrn in width. The large shell sizes, coupled with great diversity of species, indicate very favourable habitats for brachiopods and suggest the prevalence of open, shallow-
Can.J. Earth Sci. Vol. 32, 1995 Fig. 3. Geological map of Ordovician rocks in northern Hudson Bay Lowlands (adapted from
Nelson 1963, 1964; Curnrning 1975; Lauhn-Jensen 1987).
and warm-water, subtidal environments during deposition of the sediments of the Bad Cache Rapids Group and the Selkirk Member of the Hudson Platform and Williston Platform, respectively. The inferred conditions are quite in keeping with the prior suggestion that the "Arctic Ordovician fauna" lived in waters at low latitudes, close to the ancient equator (Flower 1946; Nelson 1959~).Similarly, the conditions are readily reconciled with the environmental parameters implied by the dasycladacean algae associated with the "Arctic Ordovician fauna," some of which (both cyclocrinitids and receptaculitids) are present in the Red River Formation of the eastern Williston Basin and equivalent formations in the Hudson Bay Basin (Foerste 1929; Roy 1941; Nitecki 1970; Cumrning 1975; Lee and Caldwell 1977). Elias's (1991) study of the diversity and distribution of corals in the Selkirk Member points also to the inferred conditions at the beginning of a regression following a period of transgression, presumably one of the lower-order fluctuations recorded by other lines of evidence in the Red River succession and referenced previously. Similarly large strophomenid brachiopod shells are not known in coeval Upper Ordovician rocks of the Anticosti, Michigan, and other American midcontinental basins, although unusually large shells of the orthid, Platystrophia ponderosa Foerste, 1909, are common in Cincinnatian rocks of Indiana, Ohio, and Kentucky. Occurrences of Kjaerina hartae and Tetraphalerella (n.sp.) in the Selkirk Member and the Bad Cache Rapids Group (Fig. 2), together with those of several other brachiopod species, indicate a close biogeographic link between the two regions, and they support the concept of the epicontinental seas covering the northeastern Williston Platform and the Hudson Platform being connected in Late Ordovician (Maysvillian) time.
Localities and preservation Samples from Geological Survey of Canada (GSC) localities in the Hudson Bay Lowlands were collected by S.J. Nelson
in 1951- 1952, those from GSC locality C-205935 (Garson Quarry, southern Manitoba) by J. Jin in 1993. The Garson Quarry collections loaned by the University of Manitoba were sampled by several scientists. Shells from the Hudson Bay Lowlands are primarily calcareous, with slight dolomitization, but most are single valves embedded in rock matrices. Collections from Garson Quarry contain some free, articulated shells, which, although more strongly dolomitized than the Hudson Bay specimens, are adequate for serial sectioning to reconstruct internal structures.
Hudson Bay Lowlands collections (by S.J. Nelson) Locality 3Q (GSC locality 25272): 3 -4.6 m below top of member 2, Portage Chute Formation. Bad Cache Rapids, south bank of Churchill River, locality extending about 0.8 km above and below rapids. About the same as GSC locality 81833 (204CE), Churchill River, at 95 "06.5 'W (Cumming 1975, pp. 28, 29). Locality 3Y (GSC locality 252 72): Rubble from member 1, Surprise Creek Formation, collected over 3.7 m, the total thickness of this locality. Bad Cache Rapids, south bank of Churchill River, locality extending about 0.8 km above and below rapids. About the same as GSC locality 81833 (204CE), Churchill River, at 95 "06.5 'W (Cumming 1975, pp. 28, 29). Locality IOA (GSC locality 25279): From lower 1.8 m of member 1, Surprise Creek Formation. Outcrops extending for about 0.8 km from mouth of Surprise Creek upstream, and those adjacent to mouth on north bank of Churchill River. Locality 11B (GSC locality 252 79): Lowermost 1.1-2.1 m of member 1, Surprise Creek Formation. Outcrops extending for about 0.8 km from mouth of Surprise Creek
1
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Fig. 4. Serial sections of Kjaerina hartae n.sp. Paratype, GSC 109136, Selkirk Member, Red River Formation, southern Manitoba. Note bilobate cardinal process with comb-like structures at the crests for muscle attachment. Numbers indicate distances (in mm) from ventral umbo. See also P1. 2, figs. 8 and 9.
.
.
-,..a
oseudoaunctae
1.6
muscle field
/
dorsal valve
upstream, and those adjacent to mouth on north bank of Churchill River. Locality 31SA (GSC locality 2531 1): Surprise Creek Formation, probably member 2. South bank of South Knife River, about 8 km north of sharp northwest bend, and 9 km north of latitude 58"301. Same as GSC locality 81895 (225CE, Cumming 1975, p. 20).
Southern Manitoba collection GSC locality C-205935 and collections deposited in the
Department of Geological Sciences, University of Manitoba; 8 m of Selkirk member (lower to middle part), Red River Formation, Garson Quarry (mostly from refuse of the "Tyndall Stone" factory), southern Manitoba, 50°06'N, 96O42'W.
Systematic paleontology All type specimens used in the present study are deposited in the Type Collection of Invertebrate and Plant Fossils of the Geological Survey of Canada. Descriptions of species are
Can. J . Earth Sci. Vol. 32, 1995
based primarily on specimens from southern Manitoba, with reference to some specimens from the Hudson Bay Lowlands. Order Strophomenida opik, 1934 Superfamily Strophomenoidea King, 1846 Family Rafinesquinidae Schuchert, 1893 Genus Kjaerina Bancroft, 1929
Type species Kjaerina typa Bancroft, 1929. Glynboro Member, Cheney Longville Formation (Longvillian, Caradoc), Shropshire, England. Kjaerina hartae n. sp. (Pl. 1, figs. 3-11; P1. 2, figs. 1-9; Fig. 4) Rafinesquina lata Whiteaves (in part), 1896, p. 392 (no illustrations). Rafinesquina lata Whiteaves; Whiteaves (in part), 1897, p. 172, P1. 19, fig. 3 (non figs. 2, 2a, 4, 5).
Derivation of name The name of the species was suggested by nuel el J. Nelson to honour his wife, whose maiden name is Hart. Type specimens Holotype, GSC 109077, slightly damaged, articulated shell (Pl. 1, figs. 6-9); paratypes, GSC 109078, GSC 109136 (serially sectioned). Type locality and type stratum Garson Quarry, southern Manitoba, Selkirk Member of Red River Formation (Maysvillian), from 8 m of beds in the lower to middle part of the member. Diagnosis Large, transverse, concavo-convex, roundly to sharply geniculate shells of Kjaerina with very low, orthocline ventral interarea, crudely continuous concentric rugae, commonly unequal parvicostellae in ventral valve, and equal parvicostellae in dorsal valve. Description Shell commonly large, transversely extended, semicircular to semielliptical in outline, strongly concavo-convex, roundly to rather sharply geniculate. Hingeline straight, being widest part of shell, with cardinal extremities extending into small ears. Fold and sulcus absent. Ventral umbo weakly convex, with minute beak barely protruding from hingeline; remainder of visceral disc flattened or weakly convex; interarea low, 1.O- 1.5 mm in height, orthocline to slightly apsacline; delthyrium small; pseudodeltidium either absent or not preserved; disc length in relatively large specimens attaining 20 -24 mm; trail bending dorsally, with or without sharp geniculation between 90 and 120°, reaching up to 17 mm in height (maximum depth of shell), and bearing irregular, inconspicuous, radially arranged undulations; entire ventral valve finely costellate (two to four per 1 mm), varying from equally ramicostellate to unequally parvicostellate, with irregularly accentuated
costellae; growth lines very fine, 8 to 12 per 1 mm, superimposed on concentric, more or less continuous rugae of 0.7 - 1.3 mm in thickness. Dorsal visceral disc weakly concave, with umbo slightly more depressed than rest of disc; dorsal curvature closely conforming to that of ventral valve; dorsal interarea lower than ventral interarea (generally less than 1 mm in height), anacline, interrupted by cardinal process protruding slightly toward posterior; chilidium not observed. Dorsal costellae invariably equal-sized, about two to four per 1 mm, increasing anteriorly by bifurcation and intercalation; growth lines and concentric rugae similar to those of ventral valve. Shell substance coarsely pseudopunctate, with individual pseudopunctae easily visible to naked eye, arranged in crude radial columns along interspaces. Ventral muscle field large, wide, flabellate, extending for more than one third of valve length, with strong median ridge, postero-lateral bounding ridges, small, elongate-oval adductor scars, and large diductor scars; inner surface of valve papillose. Cardinal process prominent, bilobate, with comb-like crest on each lobe for muscle attachment (Fig. 4; P1. 2, figs. 8 and 9). Hinge sockets shallow, weak. Configuration of trans-muscle septa not clearly revealed in serial sections. Length Width Estimated depth (mm) (mm) (mm)
GSC GSC GSC GSC
109080 109081 109079 109082
31.0 23.5 23.0 19.4
53.5 37.0 39.0 27.5
14.0 8.0
-
Description Ventral Ventral Ventral Ventral
valve valve valve valve
Remarks Whiteaves (1897, P1. 19, figs. 2 - 5) illustrated three specimens (all from the Red River Formation of southern Manitoba) under the name of Rafinesquina lata Whiteaves, 1896. Two of these are deposited in the type collections of the Geological Survey of Canada, and the third specimen was a loan from the Smithsonian Institution. Examination of the two syntypes, GSC 4391 and 6991, and additional specimens from the Garson Quarry (Selkirk Member, Red River Formation) clearly demonstrates that they represent two separate genera and species. Typical shells of R. lata, as stated by Whiteaves (1897, p. 172), are very large, up to 76 mm wide, with a strongly but uniformly convex ventral valve (devoid of geniculation), fine, imbricating growth lamellae, and a high (5 mm in large specimens), nearly orthocline ventral interarea, robust cardinal process, strong trans-muscle septa, and well-defined peripheral rim. Specimen GSC 6991 from east Selkirk and additional shells from the Garson Quarry, now assigned to K. hartae, are generally smaller, usually geniculate, and have strong, more or less continuous rugae, and a low ventral interarea with a height of 1.O- 1.5 mm. The internal structures of the two species are quite different. Rafinesquina lata has a robust cardinal process, consisting of two unusually large, widely separate lobes, and Oepikinalike trans-muscle septa and peripheral rim. The species is assigned to Oepikina in this paper. Rafinesquina pronis Roy, 1941 from Silliman's Fossil Mount of Baffin Island is similar to K. hartae in having con-
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Plate 1. Figs. 1, 2. Oepikina lata (Whiteaves, 1896). Hypotype, GSC 109085, dorsal and lateral views of dorsal valve showing conspicuous bilobate cardinal process and peripheral rim. Trans-muscle septa have been almost completely abraded. Selkirk Member, Red River Formation, Garson Quarry, southern Manitoba. x 1.5. Figs. 3-11. Kjaerina hartae n.sp. (3-5) Hypotype, GSC 6991, ventral, lateral, and further enlarged views of ventral valve, described as Rafinesquina lata by Whiteaves (1896, 1897, P1. 19, fig. 3), showing interrupted concentric rugae and prominent pseudopunctae. Selkirk Member, Red River Formation, East Selkirk, southern Manitoba. x 1.5 (11, x5). (6-9) Holotype, GSC 109077, dorsal, ventral, anterior, and lateral views of strongly transverse shell with sharp geniculation. Selkirk Member, Red River Formation, Garson Quarry, southern Manitoba. Note thickened median costellae on ventral, but not dorsal, valve. x2. (10, 11) Paratype, GSC 109078, ventral and enlarged postero-lateral views of broken ventral valve. Same locality. 10, x2; 11, ~ 4 .
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Can. J. Earth Sci. Vol. 32, 1995
Plate 2. Figs. 1-9. Kjaerina hartae n.sp. (1-3) Hypotype, GSC 109079, ventral and lateral views, and further-enlarged view of ornament of partly exfoliated ventral valve showing prominent pseudopunctae. Locality 11B (GSC locality 25279), Surprise Creek Formation. x 2 (3, x4). (4) Hypotype, GSC 109083, exterior of ventral valve with well-developed concentric rugae, locality 10A (GSC locality 25279), Surprise Creek Formation. X2. (5 -7) Hypotype, GSC 109082, exterior views of largely exfoliated ventral valve showing prominent pseudopunctae and papillae. Locality 3 4 (GSC locality 25272), Surprise Creek Formation. 5, X2; 6, 7, X 17. (8, 9) Paratype, GSC 109136, acetate peel taken at 2.0 mrn from apex (refer to Text-fig. 4) showing cross section of muscle field with strong median ridge and bilobate cardinal process with comb-like structure for muscle attachment. Selkirk Member, Red River Formation, Garson Quarry, southern Manitoba. 8, x 15; 9, x 45.
Jin et al.
Plate 3. Figs. 1-8. Oepikina lata (Whiteaves, 1896). (1 -3) Holotype by monotypy, GSC 4391, dorsal, ventral, and lateral views of abraded dolomitized shell, originally illustrated in Whiteaves (1897, P1. 19, figs. 2, 2a, 2b). Selkirk Member, Red River Formation, Lower Fort Garry, southern Manitoba. x 1.5. (4-7) Hypotype, GSC 109084, dorsal, ventral, and lateral views, and further-enlarged view of dorsal external ornament of large, thick, incomplete shell. X 1.5 (7, X4). Selkirk Member, Red River Formation, Garson Quarry, southern Manitoba. Note uniform convexity, high ventral interarea. (8) Hypotype, GSC 109086, dorsal interior with well-preserved trans-muscle septa and partly damaged cardinal process. Selkirk Member, Red River Formation, Garson Quarry, southern Manitoba. X1.5.
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Can. J. Earth Sci. Vol. 32, 1995 centric rugae and dorsally directed geniculation. The species from Baffin Island, however, has a smaller shell and weaker rugae, and its internal structures are unknown.
Collections (total of 28 specimens) Selkirk Member, Red River Formation (University of Manitoba collection): Garson Quarry (9 incomplete articulated shells and disarticulated ventral valves); GSC locality 205935 (4 incomplete shells embedded in matrix). Portage Chute Formation: locality 3 4 (1 ventral valve). Surprise Creek formations. Ventral valves: locality 3Y (7), 10A (5), 11B (I), and 31SA (1). Family Oepikinidae Sokolskaya, 1960 Genus Oepikina Salmon, 1942
Type species Oepikina septata Salmon, 1942. Lebanon Formation (Mohawkian), Tennessee. Remarks Recently, Rong and Cocks (1994, p. 664) redefined the Strophomenidae King, 1846 as a family whose members have type A cardinalia, which include cardinal processes with "lobes robust, often subcircular . . . , situated on the posterior part of a well-developed notothyrial platform" and "discrete, strong socket ridges often curved round laterally at their ends." These authors recognized two subfamilies, the Furcitellinae Williams, 1965 and the Strophomeninae King, 1846, and assigned Oepikina to the Furcitellinae. The cardinal process in Oepikina was described as having the lobes "fused together at the bases before merging with the notothyrial platform7' (Rong and Cocks 1994, p. 653). In a comprehensive study of the Late Ordovician and Early Silurian strophornenids of Anticosti Island, Dewing (1995, Text-fig. 7-27) serially sectioned for comparative purposes a shell of Oepikina sp. from the Lindsay Formation (Caradoc) of southern Ontario and showed that the lobes of the cardinal process change from being somewhat convergent posteriorly to entirely discrete anteriorly. In 0 . lata (described below), the range of infraspecific variation in the cardinal process spans forms in which the lobes are weakly convergent to entirely discrete at their bases (Pl. 3, fig. 8; P1. 1, fig. 1). In determining whether the lobes of the cardinal processes are convergent or discrete at their bases, caution must be exercised to differentiate, by means of their microscopic structures, the cores of the lobes from surrounding secondary shell thickening. In serial sections of K. hartae, for example, discrete lobes may appear convergent at their base because of this secondary thickening (see P1. 2, figs. 8 and 9, and relevant serial sections in Fig. 4). Although they regarded morphology of the cardinal process as one of most diagnostic characteristics of strophomenoids for classification at the familial level, Rong and Cocks (1994) did not extend their analysis to the microscopic structure of the various types of cardinal processes they recognized. On the basis of numerous serial sections and of cladistic analysis, Dewing (1995) demonstrated that microscopic shell structure (particularly size and arrangement of pseudopunctae) ranks among the most diagnostic characteristics of strophomenoids for classification at the familial and generic
levels. Rong and Cocks (1994) do not seem to have considered this characteristic in their recent classificatory revision. In Oepikina, the pseudopunctae were shown by Dewing to be fine and irregularly arranged, as in Strophomena. Rafinesquina, on the other hand, has coarse pseudopunctae arranged in radial rows and, contrary to the statement of Rong and Cocks (1994, p. 664) that the Rafinesquinidae have cardinalprocess lobes that "remain entirely discrete throughout ontogeny," Dewing's (1995, Text-fig. 7-28) serial sections of a shell of Rafinesquina altemata (Conrad 1838, the type species of Rafinesquina) from the Arnheim Formation (Ashgill) of Ohio show the two lobes to be more strongly convergent toward their bases than they are in Oepikina. In the light of the information available on microscopic structures, we agree with Dewing (1995) that continued recognition of the family Oepikinidae is warranted. Rafinesquina lata is assigned to Oepikina on the basis of its cardinal process with discrete to weakly convergent lobes, welldeveloped trans-muscle septa (up to five), anacline dorsal interarea, and prominent peripheral rim in the dorsal interior. We do recognize, however, that the species has relatively coarse pseudopunctae as in Rafinesquina, and that this combination of morphological features from two distinct families may warrant establishment of a new genus. It would be imprudent to take this step at present, however, for two reasons: (1) naturally exposed ventral interiors are unavailable for study and, (2) the taxonomic importance of microscopic structures (such as pseudopunctae) needs further investigation in strophomenoids from broader geographical and stratigraphical ranges. Oepikina lata (Whiteaves, 1896) (Pl. 1, figs. 1 and 2; P1. 3, figs. 1-8) Rafinesquina lata Whiteaves (in part), 1896, p. 392 (no illustrations). Rafinesquina lata; Whiteaves (in part), 1897, p. 172, P1. 19, figs. 2, 2a, 4, 5 (non fig. 3).
Type specimen Holotype by monotypy, GSC 4391, originally illustrated by Whiteaves (1897, P1. 19, figs. 2, 2a) as Rafinesquina lata. Type locality and type stratum "Apparently not uncommon . . . at Lower Fort Garry where it was collected by Donald Gunn in 1858, by R. Bell in 1880, by T.C. Weston in 1884, and D.B. Dowling in 1891, and at East Selkirk - where specimens were obtained by T.C. Weston and A. McCharles in 1884. From the limestones of Lake Winnipeg it has so far been collected only at Cat Head (by T.C. Weston in 1884 and D.B. Dowling in 1891), and at Jack Head Island (by D.B. Dowling and L.M. Lambe in 1890)" (Whiteaves 1897, p. 173). The collections mentioned by Whiteaves undoubtedly included both 0 . lata and K. hartae. The only specimen of 0 . lata now available from Whiteaves' collection is labelled to be from the "Selkirk Member, Red River Formation, Lower Fort Garry , Manitoba." The Selkirk Member is assigned a Maysvillian age by Jin et al. (in press). Description Shell large, transversely extended, with adult forms attaining a length of 45 rnm and width of 76 mm, strongly and uni-
Jin et al.
forrnly concavo-convex, devoid of geniculation, semielliptical in ventral view. Hingeline straight, being widest part of shell, with cardinal extremities extending into ears. Length (rnm) GSC 4391 GSC 109084 non-type GSC 109085 GSC 109086
40.5 46.0 43.0" 39.0 38.5
Width (mrn)
55.0" 62.0" 76.0" 53.0 54.0
Thickness depth (mm)
Description
18.0 20.0 20.0" 16.0 15.0
Incomplete shell Incomplete shell Ventral valve Dorsal valve Dorsal valve
Ventral valve strongly convex, galeated in some specimens; convexity relatively uniform except for flattened or deflected cardinal extremities; fold absent, but weak, radiating undulations evident in antero-medial portion of valve; interarea orthocline, about 5 mm in height; delthyrium wide, covered completely by weakly convex pseudodeltidium; foramen epithyridid (Pl. 3, fig. 4). Dorsal valve generally conforming to curvature of opposite valve; dorsal umbonal area more strongly depressed than remainder of shell; interarea low, about 2.5 rnrn in height, hypercline, forming essentially right angle with ventral interarea; chilidium welldeveloped, convex. Shell ornamentation consisting of fine (four or five per 1 mm), equal-sized costellae in dorsal valve and unequal parvicostellae in ventral valve. Development of costellae in dorsal valve erratic, increasing through bifurcation and intercalation and decreasing by coalescence (PI. 3, figs. 4 and 7). Parvicostellae in ventral valve being similar in size to costellae of dorsal valve, with accentuated costellae spaced between 1 and 2 mm apart. Shell coarsely pseudopunctate~with pseudopunctae arranged in radial pattern. Ventral interior not well known. Large, flabellate muscle field with wide median ridge discernible in partly exfoliated specimens. Dorsal interior consisting of robust, bilobate cardinal process, well-developed transmuscle septa, elongate oval adductor muscle scars, and welldefined peripheral rim (Pl. 3, fig. 8; P1. 1, fig. 1). Hinge sockets defined antero-medially by socket ridges, open distally. Two lobes of cardinal process directed posteriorly, separated by relatively wide notch of 2-3 rnm. Median septum bifurcating at short distance (about 5 mm) from anterior end of cardinal process, with, on each side, two strong lateral septa beginning immediately anterior of cardinal process. Exact length of all septa difficult to determine due to abrasion. Adductor scars located lateral to transmuscle septa, with striated floors.
Remarks Oepikinu lata differs from other congeneric species in its unusually large shell, bifurcation of the dorsal median septum, and presence of four equal-sized, lateral trans-muscle septa. Collections Total 15 specimens. Selkirk Member, Red River Formation, Garson Quarry. University of Manitoba collection (5 articulated shells, damaged, 2 ventral valves, 2 dorsal valves); GSC locality 205935 (2 fragmentary articulated shells and single valves buried in matrix).
Acknowledgments R.J. Elias, Department of Geological Sciences, University of Manitoba, kindly made available brachiopod specimens from Garson Quarry, southern Manitoba. J. Dougherty provided loans of Whiteaves' type specimens held by the Geological Survey of Canada, Ottawa. The research was made possible thorough a research grant to W.G.E. Caldwell by the Natural Sciences and Engineering Research Council of Canada.
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