A Middle Cambrian trilobite faunule from the Meguma Group of Nova ...

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A Middle Cambrian trilobite faunule from the Meguma Group of Nova Scotia. BRIAN R. PRATT. Department of Geological Sciences, University of Saskatchewan, ...
A Middle Cambrian trilobite faunule from the Meguma Group of Nova Scotia BRIANR. PRATT Department of Geological Sciences, University of Saskatchewan, Saskatoon, Sask., Canada S7N OW0 AND

JOHNW. F. WALDRON Geology Department, Saint Mary's University, Halifan, N.S., Canada B3H 3C3 Received January 25, 1991 Revision accepted May 23, 1991 The Meguma Group of southern Nova Scotia is a thick succession of mostly deep-water siliciclastic sedimentray rocks of uncertain age. Previous fossil finds have been in the Halifax Formation of the upper part of the sequence and have provided Early Ordovician ages. A newly discovered trilobite-bearing bed from the underlying Goldenville Formation yields Middle Cambrian taxa of Acado-Baltic affinity. Specimens belonging to Paradoxides (s.l.), Agraulos, Dorypyge, and Ellipsocephalidae indicate that the Meguma Group is an exotic succession with faunal similarity to the adjacent Avalon Terrane and to Middle Cambrian successions in Europe, the Middle East, and west Africa. Le Groupe de Meguma du sud de la ~ o u v e l l e - ~ c o s sest e une tpaisse succession composte pour la plupart de roches stdimentaires siliciclastiques mises en place en eau profonde mais d'un Lge incertain. Les fossiles prtctdtmment dtcouverts dans la partie supkrieure de la suite, dans la Formation de Halifax, donnent un Pge ordovicien prtcoce. Une couche rtcemment dtcouverte dans la Formation de Goldenville, au-dessous de la Formation de Halifax, produit des trilobites d'Lge cambrien moyen d'une affinitt acado-baltique. Les sptcimens identifits appartiennent a Paradoxides (s.l.), Agraulos, Dorypyge et Ellipsocephalidae, et indiquent que le Groupe de Meguma est une sCrie exotique avec une similaritt faunistique avec le terrane d'Avalon adjacent, et aussi avec les successions du Cambrien moyen de ]'Europe, le Moyen-Orient et 1'Afrique de I'Ouest. Can. J. Earth Sci. 28, 1843-1853 (1991)

Introduction The Meguma Terrane of southern Nova Scotia (Fig. 1A) forms one of the tectonostratigraphic subdivisions of the Appalachian Mountains (e.g., Williams and Hatcher 1982). It is an allochthonous terrane of uncertain provenance that was accreted onto eastern North America during the Acadian orogeny. Much of the Meguma Terrane is underlain by the Meguma Group, a thick (probably >9 km) package of metamorphosed siliciclastic sedimentary rocks. Correlation and interpretation of these strata, however, have been hampered by the scarcity of identifiable fossils, although limited evidence has suggested a general Cambro-Ordovician age for the group. We reported previously the discovery of a trilobite faunule containing Middle Cambrian taxa in the Tancook Member of the upper Goldenville Formation (Pratt and Waldron 1990a, 1990b). The purpose of this paper is to describe the elements of this faunule in detail. Regional setting and study location Stratigraphy The Meguma Group has traditionally been subdividedinto two formations. The lower, Goldenville Formation is dominated by thick-bedded to massive sandstone turbidites with locally interbedded shale now metamorphosed to slate (Phinney 1961; Schenk 1970; Harris and Schenk 1975; Waldron and Jensen 1985). The base of the Goldenville Formation is not seen, dnd estimates of its exposed thickness range up to 5600 m (Taylor 1969).The overlying Halifax Formation consists chiefly of slate, argillite, and siltstone, with subordinate thin-bedded sandstone interpreted as turbidites (Stow et al. 1984). Measured thicknesses of the Halifax Formation range from 460 m (in a highly sheared section: P. E. Schenk, personal communication, 1991) to 3550 m (Faribault 1909,1914; Taylor 1965). Schenk (1970) recorded a

thickness of 7 km, and thicknesses up to 10 km were estimated from structural cross sections by O'Brien (1986). Regionally applicable, finer lithostratigraphic subdivision has so far proved elusive, but in the Mahone Bay area south of Halifax (Fig. lB), O'Brien et al. (1986a, 19866) were able to map several members within the upper Goldenville and lower Halifax formations as traditionally recognized (Faribault 1924). The upper 870 m of the Goldenville Formation were distinguished as the Tancook Member (Fig. 2), characterized by thinto medium-bedded sandstone turbidites and slate. Slate dominates the upper 190 m of this member (Waldron 1987). The trilobite fauna described here was collected from a bed within the Tancook Member, 235 m below the top of the Goldenville Formation. Above the Tancook Member is a 200 m thick unit of Mn-enriched argillite comprising the Mosher's Island Member of the Halifax Formation. This unit is overlain by the Cunard Member which consists of black, pyrite-bearing slate and siltstone. O'Brien (1986) erected the informal Green Bay Formation to embrace both the Tancook and Mosher's Island members, but in this paper we retain the older formational nomenclature. The Meguma Group is overlain with local angular discordance by the White Rock Formation, which is composed of fine- to coarse-grainedshallow-marinesiliciclastics,with local mafic and felsic volcanics, carrying rare Upper Ordovician brachiopods (Schenk 1972b). Succeeding this unit are Upper Silurian shales of the Kentville Formation and Lower Devonian shallow-marine siliciclastics and limestone of the Torbrook Formation (Srnitheringale 1960). This entire succession was deformed and metamorphosed at ca. 400 Ma (e.g., Dallmeyer and Keppie 1987; Muecke et al. 1988) and intruded by granites at ca. 370 Ma (e.g., Clarke and Halliday 1980). Metamorphism is generally weak (chlorite

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CAN. 1. EARTH SCI, VOL. 28, 1991

FIG. 1. (A) Map of Nova Scotia showing location of the Mahone Bay area. (B) Simplified geological map of this area, with location of Big Tancook Island.

grade) in the Mahone Bay area, but elsewhere it ranges up to sillimanite grade (Keppie and Muecke 1979). Teichichnus ichnofossils in the slates of the Tancook Member of Mahone Bay indicate a strain ratio in bedding surfaces of approximately 1:1.7 (Waldron 1988).

Fossiliferous bed A nearly complete section of the Tancook Member of the upper Goldenville Formation is exposed on the east coast of Big Tancook Island (Waldron 1987) (Fig. 1B). The fossiliferous bed that yields the trilobites described here is tabular, 44 cm thick, and occurs 235 m below the top of the Tancook Member (Waldron and Graves 1987), above a slate bed and below a massive, fine-grained sandstone (Fig. 3). The fossiliferous bed consists of greenish-grey, bioclastic, well-sorted, coarse-grained siltstone to fine-grained sandstone. Exposed parts of the bed are deeply weathered, brown, and friable, but unweathered material is well indurated.

Bioclasts are 1-10 mm across, relatively well sorted, and consist of trilobite fragments and pelmatozoan echinoderm (cystoid?) ossicles (Figs. 4A, 4B). Both kinds of bioclasts are commonly broken, and by volume they constitute 10-20% of the rock; the kilobites are recrystallized to microspar. The angular to subangular matrix silt and fine and sand grains are mainly quartz, with minor amounts of alkali feldspar and muscovite and local sericite aggregates that may have been shale clasts. Blocky calcite cement fills small interparticle pores and commonly replaces the margins of siliciclastic grains. Abundant intergranular sericite was probably produced by metamorphic recrystallization of original mud in the matrix. Probe analyses indicate elevated Mn and Fe content in the calcite of both bioclasts and cement (up to 5.4 wt.% MnCO, and 2.5 wt.% FeCO,) which accounts for the brown colour of the weathered surface. Bedding-parallel orientation of the trilobite bioclasts imparts an indistinct plane lamination, which becomes a prominent

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LEGEND FOR DETAILED ,SECTION

1

SLATE

TORBROOK FM. (Early Devonian)

..:::,.. SANDSTONE .

--

KENTVILLE FM. (Late Silurian)

MIXED CARBONATE-CLASTIC

LAMINATION INTRACLASTS BIOTURBATION

I

WHITE ROCK FM. >(Late Ordovician)

0

FLUTE, SCOUR

-

--WAVY LAMINATION CROSS-LAMINATION CARBONATE CONCRETION LOAD STRUCTURE

r Member

LEGEND

1:

km

Shale, slate Sandstone Carbonate Concretions

-,

(c) '

W

i MUD T

FIG. 2. (A) Generalized stratigraphic column for the Meguma Terrane giving known biostratigraphic ages; actual age ranges of the lithostratigraphic units are probably greater. (B) Lithologic log of section on Big Tncook Island. (C) Detailed log including fossil-bearing bed, simplified from Waldron and Graves (1987).

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CAN. J . EARTH SCI. VOL. 28, 1991

FIG. 3. Outcrop of part of the Tancook Member on Big Tancook Island. Ruler (30 cm long) is resting against lower part of bioclastic bed. Light and dark bedding-parallel banding in visible part of bioclastic bed is due to variations in the depth of weathering; upper part of bed is more recessive and is partially hidden from view.

fissility in weathered material. The sedimentary lamination is cut by a tectonic fabric, defined by the preferred orientation of sericite mica grains in the matrix. Postdepositional compaction and (or) tectonic strain has caused the bioclasts to be embayed by the quartz grains. The trilobites are tectonically distorted, with a consistent elongation parallel to the bedding-cleavage intersection, and most (-80%) of the pelmatozoan ossicles show strain twinning. An unlaminated lens about 5 cm thick is present locally at the top of the bed; it appears to contain mainly pelmatozoan ossicles. The boundary with the overlying bed of grey massive sandstone (Fig. 2C) appears sharp but does not show any evidence of scouring. It is petrographically similar to the matrix of the underlying fossiliferous bed, consisting of fine-grained siliciclastic sandstone with intergranular sericite, along with rare recrystallized bioclasts and patches of blocky calcite. This sandstone may have been deposited by later stages of the sediment gravity flow that deposited the bioclastic bed; alternatively, it may represent a separate event that reworked a few bioclasts from the underlying bed. Attempts were made to locate the bioclastic bed on neighbouring coasts at Little Tancook Island and Blandford, but the equivalent part of the section is covered by sandy beach in both places. On the south coast of Big Tancook Island, the equivalent strata are near horizontal and only intermittently exposed in the core of an anticline; detailed correlation is not possible, and no bioclastic bed was observed. The broken nature of the trilobite and pelmatozoan particles and the turbiditic aspect of the succession argue that the bioclasts have been transported from shallower water. The absence of admixed lithoclastic particles or adhering cement overgrowths suggests that the bioclasts were not derived from a preexisting, lithified source. These observations discount Schenk's (1991, p. 516) suggestion that the trilobites and pelmatozoan ossicles may represent two different ' 'populations.' ' We thus interpret the fossil material as essentially contemporaneous with the host sediment. The trilobite specimens in the collection could only be studied effectively after they and the calcite cement had been removed by acid etching after splitting, which revealed sandstone and

siltstone molds (Figs. 4C, 4D). Out of some 25 kg of rock so prepared, some 50 recognizable cranidial fragments, a small number of thoracic segments, and several hypostomes, pygidia, and free cheeks were recovered.

'

Age and significance of the faunule

I

Previous fossil discoveries Prior biostratigraphic data from the Meguma Group are scarce. The Halifax Formation, between 1200 and 2720 m above its base, has yieldedDictyonemaflabellifome (s.1.) of Tremadocian (Early Ordovician) age at a number of localities in the Annapolis Valley of southwestern Nova Scotia (Smitheringale 1960; Crosby 1962). Additional specimens of Dictyonema sp. and Anisograptus sp. were obtained by Cumming (1985) from the interval 2000-2450 m above the base of the Halifax Formation at Kejirnkujik National Park in south-central Nova Scotia. Acritarchs recovered from the upper Halifax Formation at several localities are also Tremadocian (Keppie 1977b;W. A. M. Jenkins, personal communication, 1990). A poorly preserved trilobite thorax collected from the Halifax (Schenk 1982) cannot be identified (W. H. Fritz, personal communication, 1990). The underlying Goldenville Formation has hitherto yielded no confidently identifiable body fossils. Specimensof the Arenigian (Lower Ordovician) graptolite Didymograptus sp. reported from Tangier Harbour 50 km east of Halifax (B.-D. Erdtmann in Schenk 1970; Poole 1971) have been reassessed by Cumming (1985), who doubted their graptolite affinity. Pickerill and Keppie (1981) suggested an Ordovician age for the Goldenville Formation based on its trace fossil fauna. K-Ar ages of 476 19 and 496 + 20 Ma have been determined for muscovite interpreted as detrital (Wanless et al. 1972), and a maximum age limit of 552 + 5 Ma is provided by detrital titanite (Krogh and Keppie 1990).

+

New trilobite faunule The trilobite faunule from the Tancook Member contains one group of specimens identified to familial level, one group identified to generic level, and three specimens of uncertain familial assignment. Taxa present are Paradoxides (s.l.), Dorypyge, Agraulos, and ellipsocephalids. Although no detailed biostratigraphic correlationsare possible, given the imprecise nature of the identifications proposed here, a combination of generic ranges as reported elsewhere indicates a Middle Cambrian age for the fossil-bearing horizon. Paradoxides (s.1.) ranges throughout the Middle Cambrian as high as the Lejopyge laevigata Zone in Sweden (Westergird 1953; Martinsson 1974)and equivalent "Piso sin Solenopleuropsidae'' in Spain (Sdzuy 1972). Ellipsocephalids range from the upper Lower Cambrian through most of the Middle Cambrian in Spain (Sdzuy 1972). Agraulos has been recorded only in the upper part of the Middle Cambrian in Sweden, in the Jincella brachymetopa Zone, but occurs in older rocks elsewhere: in the middle Middle Cambrian of Spain (Sdzuy 1972) and southern France (Courtessole 1973) "and in the lower part of the Middle Cambrian of Bohemia (Snajdr 1958). Dorypyge is widespread in the middle and upper Middle Cambrian of the Middle East, China, Spain, and Sweden and may occur in older strata in Turkestan as well (see Schrank 1977). The Middle Cambrian age of the faunule is substantially older than that suggested by previously described fossils from the Meguma Terrane. It indicates that the remainder of the Goldenville Formation below the bioclastic bed may be as old as Early

PRATI AND WALDRON

1847

FIG.4. Lithology of bioclastic bed. (A) Thin-sectionphotomicrograph of largely recrystallized trilobite bioclasts in calcite-cemented,fine-grained sandstone. Scale bar = 1 mm. NSM 990GF37.7. (B) Thin-sectionphotomicrographof broken echinoderm (cystoid?) ossicle (right side) and trilobite fragments (left side) in calcite-cemented, fine-grained sandstone. Scale bar = 1 mm. NSM 990GF37.7. (C) Bedding-plane view of sandstone and siltstone molds of flakelike trilobite fragments after acetic-acid leaching of calcite. Scale bar = 5 mm. NSM 99OGF37.35.(D) Bedding-plane view of sandstone and siltstone molds of echinoderm (cystoid?) ossicle (centre) and trilobite fragments after acetic-acid leaching of calcite; Scale bar = 1 mm. NSM 990GF37.36.

Cambrian and that the overlying manganiferous argillite of the basal Halifax Formation may be a condensed sequence representing part of the Middle Cambrian and perhaps all of the Upper Cambrian. The condensed nature of the Halifax Formation is supported by its uniformly fine grain size, with comparative rarity of sandstones. Biogeographic and tectonic afJinity These taxa belong, in general, to the Acado-Baltic Province (Sdzuy 1972; Viking Province of Jell 1974),which encompasses Middle Cambrian sequences from the Avalon Terrane of eastern North America and from England, Scandinavia, France, Spain, central Europe, Morocco, and the Middle East. The Acado-Baltic Province can be divided into northern and Mediterranean (or Tethyan) subprovinces. The level of identification achieved here with the Meguma specimens does not permit a definite subprovincial assignment. Dewey (1969) placed the Meguma succession in an ensialic basin within the Avalon Zone. However, Schenk (1970) argued that the large volumes of siliciclastic sediment in the group imply a continent-sized source area; paleocurrent and facies analysis indicates that the source for the sediment lay to the present-day southeast. Schenk (1970, 1972a, 1973) therefore

postulated an origin as a continental rise prism adjacent to the margin of lower Paleozoic Gondwanaland in the vicinity of Morocco. Both this interpretation and that which suggests a connection with Iberia (Schenk 1978,1981; Lefort 1989) are at least consistent with the Acado-Baltic affinity of the trilobites described here. (Compare faunal lists in Destombes et al. 1985 for Morocco; Sdzuy 1961, 1967 for Spain.) On the other hand, the possibility raised by Keppie ( 1 9 7 7 ~ )that the Meguma Terrane lay adjacent to southern Mexico and Central America is not supported by paleontological data owing to the absence of Cambrian strata in that area. Current lower Paleozoic plate reconstructions (e.g., Van der Voo 1988) place Florida, the Piedmont province of the southern Appalachians, the Boston Basin, the Meguma Terrane, and the Avalon Terrane of Cape Breton Island and eastern Newfoundland as a linear belt alongside northwestern Africa and Iberia. This is not contradicted by available Middle Cambrian paleontological data for the Piedmont (Secor et al. 1983; Samson et al. 1990), Meguma (this paper), and the Avalon (Hutchinson 1952, 1962), which are all Acado-Baltic in aspect. There are, however, striking differences in primary rock type: sediments of the Avalon and the Carolina Slate Belt of the Piedmont are dominated by shales, whereas the Middle Cambrian of the Meguma

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CRANlDlUM

PI. 1,

HYPOSTOME

Q

fig.

Paradoxides FIG.5. Outline drawing of a generalized Paradoxides cranidium (left side) and hypostome with posterolateral border spines (right side), showing restored position of fragments illustrated in P1. 1, figs. 1-3.

is composed of a great thickness of well-sorted, fine-grained sandstone. This argues that, although these terranes may have been adjacent to each other at that time, the Meguma acted as a major repository of compositionally mature sand, whereas other areas were comparatively starved of coarse sediment. Paleocurrents in thick Cambro-Ordovicianfluvial sandstone sequences in the Oujeft Plateaux Group of the Taoudeni Basin, Mauritania, seem to give a general northward transport direction (B. R. Pratt, personal observation, 1988), but Middle Cambrian strata of the Anti-Atlas and High Atlas of Morocco are shaly and record complex, late pre-Cambrian and Early Cambrian rifting (e.g., Destombes et al. 1985; Bernardin et al. 1988; Geyer 1989). These observations lend support to the speculation (Schenk 1988) that the Meguma Terrane represents a wedge of deepwater sediment that lay offshore of the principal outlet of the paleo-West African Craton drainage basin, perhaps located adjacent to western Sahara.

Systematic paleontology Illustrated specimens are housed in the Nova Scotia Museum, Halifax (NSM prefix). Unfigured specimens and bulk material are housed at the Geological Survey of Canada, Ottawa (GSC localities 101727- 101730 combined). Some fragments of thoracic segments were isolated but are not illustrated or described herein. FAMILY Paradoxididae Hawle and Corda, 1847 SUBFAMILY Paradoxidinae Hawle and Corda, 1847 GENUS Paradoxides

Brongniart, 1822

Type species Entomostracitespara~oxissimus wahlenberg, 1821 from the Middle Cambrian of Sweden, designated by Barrande (1852).

Paradoxides (s.1.) sp. (spp.?) indet. (Pl. 1, figs. 1-6) Material Two cranidial fragments (NSM 990GF37.1,990GF37.2), one hypostomal fragment (NSM 990GF37.3), and three pygidia (NSM 990GF37.4, 990GF37.5,990GF37.6). Remarks Two cranidial fragments (Pl. 1, figs. 1,2) document a strongly anteriorly expanding glabella, and a palpebral lobe whose anterior end meets the divergent axial furrows, characteristic morphological attributes of Paradoxides (s.1.) (Fig. 5). A fragment of a hypostome (Pl. 1, fig. 3) exhibits a comparatively long, posteriorly directed posterolateral border spine (Fig. 5), a feature known only from some species of Paradoxides (s.l.), such as P. (Eccaparadoxides) remus Dean (1982, Fig. 20), P. (Eccaparadoxides) eteminicus Matthew, 1883 (Martin and Dean 1988, P1. 1, fig. 15), P. (Eccaparadoxides) brachyrhachis

PLATE1 All specimens are sandstone casts of ventral surfaces, except for fig. 7, which is a latex cast. FIGS.1-6. Paradoxides (s.1.) sp. (spp.?) indet. (1) Cranidium (fragment: anterior portion of left palpebral lobe and adjacent part of fixed cheek and glabella), X8. NSM 990GF37.1. (2) Cranidium (fragment: posterior portion of left fixed cheek and adjacent part of glabella), X8. NSM 990GF37.2. (3) Hypostome (fragment: posterior portion of right border, adjacent part of posterior lobe, and border spine), X6. NSM 990GF37.3. (4) Pygidium (doublure with terrace lines), X8. NSM 990GF37.4. (5) Pygidium, X7.5. NSM 990GF37.5. (6) Pygidium, X7.5. NSM 990GF37.6. FIG.7. Gen. et sp. indet. 1. Cranidium (fragment: anterior portion of left palpebral lobe, fixed cheek, anterior border, and adjacent axial furrow), X5. NSM 990GF37.32. FIGS.8-1 1. Agraulos sp. (spp.?) indet. (8) Cranidium, X 10.5. NSM 990GF37.7. (9) Cranidium, X8. NSM 990GF37.8. (10) Cranidium, X 11.5. NSM 990GF37.9. (1 1) Cranidium (fragment: frontal area, adjacent axial furrow and anterior portion of right fixed cheek), X5. NSM 990GF37.10. FIGS. 12-21. Dorypyge sp. indet. (12) Free cheek (lacking genal spine), X8.5. NSM 990GF37.11. (13) Cranidium (fragment: anterior portion of left fixed cheek, anterior border, and adjacent axial furrow), X4.5. NSM 990GF37.12. (14) Cranidium (fragment: right side of anterior border and adjacent part of glabella), X6. NSM 990GF37.13. (15) Cranidium (fragment: anterior portion of right fixed cheek, anterior border, palpebral lobe, and adjacent axial furrow), X6. NSM 990GF37.14. (16) Cranidium (fragment: anterior portion of right fixed cheek, anterior border, and palpebral lobe), X6. NSM 990GF37.15. (17) Pygidium (fragment: doublure with border spines, ventral side), X5. NSM 990GF37.16. (18) Pygidium (fragment: doublure with border spines, ventral side), X6. NSM 990GF37.17. (19) Pygidium (fragment: left pleural field and lateral border lacking border spines), X6. NSM 990GD37.18. (20) Pygidium (fragment: anterior portion of right pleural field and lateral border with border spine bases), X7. NSM 990GF37.19. (21) Pygidium (fragment: axis and right pleural field and lateral border lacking spines), X7. NSM 990GF37.20. FIG. 22. Gen. et. sp. indet. 3. Cranidium (fragment: frontal area), X5. NSM 990GF37.33. FIG. 23. Gen. et sp. indet. 2. Cranidium (fragment: anterior portion of left fixed cheek, preglabellar field, palpebral lobe, and adjacent axial furrow), X8. NSM 990GF37.34. FIGS.24-34. Ellipsocephalid gen. (genera?) et sp. (spp.?) indet. (24) Free cheek, X10. NSM 990GF37.21. (25) Cranidium, X12. NSM 990GF37.22. (26) Cranidium, X 10.5. NSM 990GF37.23. (27) Cranidium (fragment: posterior portion of right fixed cheek and adjacent part of glabella), X8.5. NSM 990GF37.24. (28) Cranidium, X 10. NSM 99OGF37.25. (29) Cranidium, X7.5. NSM 990GF37.26. (30) Cranidium, X7. NSM 990GF37.27. (31) Cranidium (fragment: left fixed cheek, palpebral lobe, frontal area, and adjacent part of glabella), X6. NSM 990GF37.28. (32) Cranidium (fragment: right fixed cheek, palpebral lobe, frontal area, and adjacent part of glabella), X7. NSM 990GF37.29. (33) Cranidium (fragment: anterior portion of left fixed cheek, frontal area, and adjacent part of glabella), X4. NSM 990GF37.30. (34) Cranidium (fragment: right fixed cheek, palpebral lobe, frontal area and adjacent area of glabella), X5. NSM 990GF37.31.

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Linnarsson, 1883 (Gil Cid 1982, P1. 1, figs. 9, 1I), Eccaparadoxidespusillus (Barrande, 1852) (Snajdr 1958, P1. 21, figs. 8, 16-18), P. pinus Holm m.s. (Westergkd 1936, P1. 6, figs. 14, 15), P. mureroensis Sdzuy, 1958 (Sdzuy 1961, P1. 16, figs. 14-17; Calonge Garcia and Gil Cid 1987, PI. 2, figs. 6, 11), and P.? enormis Sdzuy (1967, P1. 3, figs. 5,6). Two pygidia (P1. 1, figs. 5, 6) exhibit a semicircular outline and short axis, which resemble in general such species as P. (s.1.) pentagonalis Dean (1982, Fig. 25), P. (Eccaparadoxides) rouvillqi Miquel, 1905 (Courtessole 1973, P1. 4, figs. 6-10), P. gracilis (Boeck, 1827) (Snajdr 1958, P1. 13, figs. 8, 11, P1. 14, fig. 8, PI. 15, figs, 1, 2, 4), and Acadoparadoxides sacheri (Barrande, 1852) (Snajdr 1958, Pl. 16, figs. 6, 8-14, 16, 17). A third specimen (Pl. 1, fig. 4), represented only by the distinctively broad doublure with terrace lines, exhibits a sagittally elongate shape that seems to be primary. Many species of Paradoxides (s.1.) have a similarly elongate outline (e.g., Courtessole 1973, portion of the ~ i23;~~ .icid l 1984), but because the margin is not preserved in the Meguma specimen, it is not known if it possesses spines, and therefore it cannot be compared to existing taxa. It does, however, suggest that more than one paradoxidid is present in the faunule. FAMILY Ellipsocephalidae Matthew,

1887 Gen. (genera?) et sp. (spp.?) indet. (Pl. 1, figs. 24-34)

Dorypyge sp. indet. (Pl. 1, figs. 12-21) ~ ~ ~ ~ ~ i ~ l Four cranidial fragments (NSM 990GF37.12, 990GF37.13, 990GF37.14,990GF37.15), one free cheek (NSM 990GF37.11) and five pygidial fragments (NSM 990GF37.16, 990GF37.17, 990GF37.18,990GF37.19,990GF37.20),plus several cranidial fragments. &marks Kootenia Walcott, 1889(type speciesBathyuriscus (Kootenia) ~ a dawsoni Walcott, 1889) differs from D ~ v P Y in~ having subparallel- to parallel-sided glabella, an anterior border that margin, and tends to be equal in length around the pygidial border spines that are of equal to subequal length (Poulsen in Moore 1959, p. 218). The anterior border of Dorypyge cranidia, on the other hand, swells laterally, the glabella is more ovoid in outline, and the pygidium bears one pair of long spines among several pairs of shorter ones of subequal length (e.g., Whitehouse 1945; ~ e s t e r g k d1948, PI. 2, figs. 1-8; Sdzuy 1961, 22, figs. 8-16; Fhshan l973; Schra* 1977; Dean 1982, Figs. 14, 16-18). Cranidial fragments in the Meguma collection resemble more closely Dorypyge than Kootenia because the anterior border becomes longer laterally away from the glabella; the shape of the glabella is impossible to reconstruct because of tectonic distortion, but one specimen (Pl. 1, fig. 14) suggests that the glabella tapers anteriorly somewhat, which is consistent with Dorypyge.

Material T~~ cranidia and cranidial fragments (NSM 990GF37.22, 990GF37.23, 990GF37.24, 990GF37.25, 990GF37.26, Pieces of the pygidial doublure (Pl. 1, figs. 17, 18) appear to 990GF37.27, 990GF37.28, 9 9 0 ~ ~ 3 7 . 2 99, 9 0 ~ ~ 3 7 . 3 0 , have border spines that vary in length, which favours assignment to D o ~ p y g e . 990GF37.31) and one free cheek (NSM 990GF37.21), plus about a dozen cranidial fragments. FAMILY Agraulidae Raymond, 1913 Remarks GENUS Agraulos Hawle and Corda, 1847 A relatively large number of cranidia and cranidial fragments Type species exhibit a general morphology consisting of a long, parallel-sided Arion ceticephalus Barrande, 1846from the Middle Cambrian to slightly constricted, subrectangular glabella, wide fixed of Bohemia, by original designation. cheeks, relatively long, posteriorly located palpebral lobes, an axial furrow that shallows around the anterior of the glabella, and Agraulos sp. (spp.?) indet. a moderately long frontal area lacking a distinct anterior border. (Pl. 1, figs. 8-1 1) Some specimens (Pl. 1, figs. 25, 28) may have a short frontal Material area, but this is uncertain due to the tectonic distortion. A short occipital spine is present in several specimens (Pl. 1, Three cranidia and one cranidial fragment (NSM 990GF37.7, 990GF37.8,990GF37.9,990GF37.lo), plus several cranidia and figs. 28-30). One cranidial fragment (Pl. 1, fig. 34) may cranidial fragments. preserve the shallow, oblique furrow that divides the fixed cheek from the preglabellar field in some ellipsocephalid taxa (e.g., Remarks S d z u ~1961, 12*'gs 139 'gs. 149 figs' About a dozen cranidia were isolated that may be identified as 8-14). Agraulos. These specimens are characterized by a tapering A narrow free cheek I' fig' 24) has an advanced genal glabella, shallow anterior border furrow, moderately well'pine and probably an elli~soce~halid (cf. Kautsk~ impressed furrow, and shon palpebral lobes, which 19459 Pl. 169 figs. 11-14; Henningsmoen in Moore 1959, spend in general to such species as Agraulos ceticephalus Fig' 150'7)' The apparent lack a distinct lateral border (Snajdr 1958, pl. 37, figs. 1-13) andA. arenosus Sdzuy (1967, suggests it does not belong to the Protolenidae, some of which P1.8, figs. 8-1 1); the palpebral lobes of the Meguma specimens also possess advanced genal 'pines (e.g'9 S d z u ~ figs. seem to be more posteriorly located than those of A. ceti14, 15, P1.4, figs. 13-17). cephalus, however. Some specimens seem to possess a short Ellipsocephalidae exhibits wide intraspecific variability occipital spine, like that of A. longicephalus (Hicks, 1872) ~ ~lheMeguma ~ P(Sdzuy 1961, ~ ~ ~ Dean 1988, ~ (Ge~er1990)9andbecause of the P PI.~23, figs.~7-17; Mmin and PI.~3, specimens cannot be identified more precisely. figs. 9-13). -~everal'cranidialfragments (Pl. 1, fig. 11) exhibit a slightly FAMILY Dorypygidae Kobayashi, 1935 deeper anterior border furrow which recalls that of Skreiaspis GENUS Dorypyge Dames, 1883 RikZiEka, 1944, such as the type species, S. spinosus (Jahn in Type species Pompeckj 1895) (Snajdr 1958, PI. 27, figs. 14-33) and S. tosali Dorypyge richthofeni Dames, 1883fromthe Middle Cambrian Sdzuy (1967, P1.8, figs. 12, 13, 15, 16). of Wulopu, China, by original designation. 6-147

19679

37

PRATT AND WALDRON FAMILY uncertain Gen. et sp. indet. 1 (Pl. 1, fig. 7)

Material One cranidial fragment (NSM 990GF37.32). Remarks A single fragment showing the left anterior part of a cranidium preserves a relatively short preglabellar field, shallow anterior border furrow, and a well-defined palpebral lobe, the anterior end of which is level with the anterior part of the glabella. A low median preglabellar ridge may be present. No taxonomic assignment can be made, but there is a resemblance to some Protolenidae, such as Acadolenus decorus Sdzuy (1967, P1. 4, figs. 3-10), which occurs in the approximate biostratigraphic range (Sdzuy 1972) suggested by other tma in the Meguma collection.

Gen. et sp. indet. 2 (Pl. 1, fig. 23) Material One crandial fragment (NSM 990GF37.34). Remarks A fragment of the left anterior part of a cranidium is characterized by a relatively long preglabellar field, wide fixed cheek, transverse palpebral ridge, shallow palpebral furrow, and moderately short, anteriorly situated palpebral lobe. There is also a possibility that the glabella is quadrate or subrectangular in outline and anteriorly truncate. No firm identification can be made, but there is a resembla~ceto the cranidium of Ptychoparia striata (Emrnrich, 1839) (Snajdr 1958, P1. 39), which is a biostratigraphically consistent comparison.

Gen. et sp. indet. 3 (Pl. 1, fig. 22) Material One cranidial fragment (NSM 990GF37.33). Remarks A single fragment of the anterior portion of a cranidium lacks a distinct preglabellar field but has an anterior border furrow that becomes indistinct in front of the glabella. A second, transverse furrow, which seems to be real and not due to tectonic compression, is located on the fixed cheek immediately posterior to the anterior border furrow. While the specimen cannot be identified with certainty, it is reminiscent of Chelidonocephalus King, 1937 (type species C. alifrons King, 1937) because of the similar development of a pair of anterior border furrows (e.g., Fortey and Rushton 1976; Dean 1982). This genus is known from the upper part of the Middle Cambrian of the Middle East, so the comparison is biostratigraphically consistent.

Acknowledgments We thank G. S. Nowlan, P. von Bitter, and E. Landing for searching (unsuccessfully) for microfossils; J. Utting and W. A. M. Jenkins for information on palynological finds in the upper part of the Meguma; W. H. Fritz for information on an undescribed trilobite thorax collected from the Meguma; W. T. Dean, R. Ludvigsen, and H. B. Whittington for their comments on the identifications proposed for the specimens; M. Graves and M. Zentilli for loan of thin sections; and G. Geyer, D. Gil Cid, and P. E. Schenk for discussion of stratigraphic and tectonic

1851

relationships. W. A. M. Jenkins, R. Ludvigsen, and P. E. Schenk commented on the manuscript. This work has been funded through operating grants to the authors from the Natural Sciences and Engineering Research Council of Canada and a contract between the Geological Survey of Canada and Saint Mary's University as part of the Canada - Nova Scotia Mineral Development Agreement (Project 760027). BERNARDIN, C., CORNEE,J.-J., CORSINI,M., MAYOL,S., MULLER,J., and TAYEBI,M. 1988. Variations dlCpaisseur du cambrien moyen en Meseta marocaine occidentale : signification gkodynarnique des donnkes de surfaces et de subsurfaces. Canadian Journal of Earth 2104-21 17. Sciences. L!: GARCIA, A., and GIL CID, D. 1987. Deterrninacion biomCCALONGE trica de Paradoxides mureroensis Sdzuy 1958. Boletin Geoldgico y Minero. 98: 794-801. CLARKE, D. B., and HALLIDAY, A. N. 1980. Strontium isotope geology of the South Mountain batholith, Nova Scotia. Geochimica et Cosmochimica Acta, 44: 1045- 1058. COURTESSOLE, R. 1973. Le Cambrien Moyen de la Montagne Noire: biostratigraphie. Laboratoire de GCologie CEARN, FacultC des Sciences de Toulouse, Toulouse. CROSBY,D. G. 1962. Wolfville map-area, Nova Scotia. Geological Survey of Canada, Memoir 325. CUMMING, L. M. 1985. A Halifax slate graptolite locality, Nova Scotia. In Current research, part A. Geological Survey of Canada, Paper 85-1A, pp. 215-221. DALLMEYER, R. D., and KEPPIE,J. D. 1987. Polyphase late Paleozoic tectonothermal evolution of the southwest Meguma Terrane, Nova Scotia: evidence from 40~r/39Ar mineral ages. Canadian Journal of Earth Sciences, 24: 1242- 1254. DEAN, W. T. 1982. Middle Cambrian trilobites from the Sosink Formation, Derik-Mardin district, south-eastern Turkey. Bulletin of the British Museum (Natural History), Geology Series, 36: 1-41. DESTOMBES,J., HOLLARD,H., and WILLEFERT,S. 1985. Lower Palaeozoic rocks of Morocco. In Lower Palaeozoic of north-western and west-central Africa. Edited by C. H. Holland. John Wiley & Sons, London, pp. 91-336. DEWEY,J. F. 1969. The evolution of the CaledonianIAppalachian orogen. Nature (London), 222: 124- 128. FARIBAULT, E. R. 1909. Southern part of Kings and eastern part of Lunenburg counties, Nova Scotia. Geological Survey of Canada, Summary Report 1908, pp. 150-158. 1914. Greenfield and Liverpool Town map-areas, Nova Scotia. Geological Survey of Canada, Summary Report 1912, pp. 334-340. 1924. Chester Basin. Geological Survey of Canada, Map 87. FORTEY,R. A,, and RUSHTON,A. W. A. 1976. Chelidonocephalus trilobite fauna from the Cambrian of Iran. Bulletin of the British Museum (Natural History), Geology Series, 27: 321-340. GEYER,G. 1989. Late Precambrian to early Middle Cambrian lithostratigraphy of southern Morocco. Beringeria, 1: 115-143. 1990. Die marokkanischen Ellipsocephalidae (Trilobita: Redlichiida). Beringeria, 3: 1-340. GIL CID, D. 1982. Hallazgo de Paradoxides (Eccaparadoxides) brachyrhachis Linnarsson 1883, en el CBmbrico Medio de Zafra (Badajoz). Boletin Geol6gico y Minero, 93: 470-474. 1984. El gtnero Paradoxides en Espaiia; sus especies y posici6n estratigdfica. Zeitschrift der deutschen geologischen Gesellschaft, 135: 307-315. HARRIS,I. M., and SCHENK, P. E. 1975. The Meguma Group. Maritime Sediments, 11: 25-46. HUTCHINSON, R. D. 1952. The stratigraphy and trilobite faunas of the Cambrian sedimentary rocks of Cape Breton Island, Nova Scotia. Geological Survey of Canada, Memoir 263. 1962. Cambrian stratigraphy and trilobite faunas of southeastern Newfoundland. Geological Survey of Canada, Bulletin 88. JELL,P. A. 1974. ~ a u n aprovinces l and possible planetary reconstruction of the Middle Cambrian. Journal of Geology, 82: 319-350.

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I

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