First Middle Ordovician biota from southern New Brunswick ...

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First Middle Ordovician biota from southern New Brunswick: stratigraphic and tectonic implications for the evolution of the Avalon continent Ed Landing, Stephen R. Westrop, and Dong Hee Kim

Abstract: A limestone boulder in the Triassic Lepreau Formation near Saint John, New Brunswick, has yielded the first diverse marine fauna from the sub-Caradoc Ordovician of the western Avalon continent. This fauna includes the first Arenig conodonts recovered from Avalon and represents an unexposed interval in southern New Brunswick. Association of the conodonts Drepanoistodus and Baltoniodus and the trilobites Neseuretus, Nileus, and Stapeleyella emphasizes the faunal dissimilarity of Avalon and Laurentia through the late Middle Ordovician. Extension of the ranges of Neseuretus cf. Neseuretus parvifrons and Stapeleyella from Britain into New Brunswick further emphasizes that “eastern” and “western” Avalon were confluent parts of a unified, insular Avalon continent that originated in the latest Precambrian. This fauna correlates with the lower Amorphognathus (Lenodus) variabilis Zone (Kundan Stage) of Baltica and the terminal Arenig (upper Middle Ordovician; lower Darriwilian Stage) of Avalonian Britain. Available evidence suggests that an Arenig cover sequence with local shallow-water hematitic iron ore, quartz arenite, and rare limestone extended across the Avalonian marginal and inner platforms from eastern Newfoundland to the Boston, Massachusetts, region. This “western” Avalonian Arenig shows the greatest similarity with the Arenig of the Welsh Borderlands. Phosphatic fossils from the boulder have a thermal alteration index much lower than that of nearby lower Paleozoic outcrops and suggest derivation of the boulder from a weakly heated Avalonian succession brought into the Bay of Fundy region by post-Ordovician transcurrent faulting. Résumé : Un bloc de calcaire de la Formation de Lepreau (Trias) à proximité de Saint John, au Nouveau-Brunswick, a fourni la première faune marine diversifiée provenant du sous-Caradocien (Ordovicien) du continent avalonien occidental. Cette faune comprend les premiers conodontes datant de l’Arénigien récupérés d’Avalon et représente un intervalle qui n’affleure pas dans le sud du Nouveau-Brunswick. L’association des conodontes Drepanoistodus et Baltoniodus et des trilobites Neseuretus, Nileus et Stapeleyella met l’emphase sur la dissimilitude faunique entre l’Avalon et la Laurentia à travers l’Ordovicien moyen. L’extension des plages de Neseuretus cf. N. parvifrons et Stapeleyella de la Grande-Bretagne au Nouveau-Brunswick fait encore plus ressortir que les parties « Est » et « Ouest » d’Avalon étaient des parties confluentes d’un continent avalonien insulaire et unifié qui date du Précambrien terminal. Cette faune est corrélée avec la Zone à Amorphognathus (Lenodus) variabilis (étage de Kundan) inférieure de Baltica et l’Arénigien terminal (Ordovicien moyen supérieur; étage darriwilien inférieur) de la Grande-Bretagne avalonienne. Selon les évidences disponibles une séquence de couverture arénigienne avec, par endroits, du minerai de fer hématitique d’eau peu profonde, une arénite quartzique et de rares calcaires s’étendaient à travers les plate-formes marginales et internes de l’Avalon à partir de l’est de Terre-Neuve jusqu’à la région de Boston au Massachusetts. Cet Arénigien avalonien « occidental » montre sa plus grande similitude avec l’Arénigien de la Bordure galloise (Grande-Bretagne). Des fossiles phosphatiques provenant du bloc montrent un indice d’altération thermique beaucoup plus bas que ceux des affleurements avoisinants datant du Paléozoïque inférieur et portent à croire que le bloc provient d’une succession avalonienne faiblement chauffée amenée à la région de la baie de Fundy par des failles décrochantes post-ordoviciennes. [Traduit par la Rédaction]

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Received 8 July 2002. Accepted 20 December 2002. Published on the NRC Research Press Web site at http://cjes.nrc.ca on 27 May 2003. Paper handled by Associate Editor B. Chatterton. E. Landing1. New York State Museum, The State Education Department, Albany, NY 12230, U.S.A. S.R. Westrop and D.H. Kim.2 Oklahoma Museum of Natural History and School of Geology and Geophysics, University of Oklahoma, Norman, OK 73072, U.S.A. 1 2

Corresponding author (e-mail: [email protected]). Present address: School of Earth and Environmental Sciences, College of Natural Sciences, Seoul National University, Seoul 151-742, Republic of Korea.

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doi: 10.1139/E03-009

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Introduction The uppermost Precambrian–Ordovician of southern New Brunswick is a siliciclastic-dominated cover sequence on the late Precambrian Avalonian Orogen. Lithostratigraphic and biostratigraphic reevaluations of the lower Paleozoic in the Saint John region demonstrate its similarity to successions on the marginal (northwest) platform of the early Paleozoic Avalon continent (i.e., Malignant Cove autochthon, Nova Scotia; Placentia Bay, southeast Newfoundland; North Wales; see Landing 1996a; Landing and Westrop 1996, 1998; Westrop and Landing 2000; Kim et al. 2002). A previously unresolved part of the stratigraphic reevaluation of the Saint John region involved the report by Hayes and Howell (1937, p. 109) that the coarse conglomerate at Red Head (Fig. 1) has blocks of “a red limestone carrying a fauna of brachiopods and trilobites — an assemblage unfamiliar to E.M. Kindle and thought by him to represent an early Paleozoic horizon not yet described.” Fossiliferous red limestone is unknown in the early Paleozoic cover sequence in the Saint John area (see Landing 1996a). Indeed, the only known red limestone in the cover sequence on the Avalonian Orogen in this region is in much older rocks of the sub-trilobitic Lower Cambrian at Cradle Brook, 60 km northeast of Saint John (Landing 1996b, fig. 1). Thus, the Red Head limestone had the potential to provide new information on the early Paleozoic evolution of Avalon from an apparently unexposed interval in southern New Brunswick. This study documents the youngest Ordovician rocks and fossils known in southern New Brunswick and suggests the development of comparable shallow-marine facies in the terminal Arenig of Avalon from eastern Newfoundland to southern New England.

Red Head section Gently north dipping, red fanglomerate that crops out on the north side of Red Head was referred to the Carboniferous(?) Red Head Formation by Young (1913) and Hayes and Howell (1937) but is now mapped as a fault-bounded exposure of Triassic Lepreau Formation (Currie 1983). The fanglomerate forms a low, wave-cut cliff 200 m west of Red Head Road and 200 m east of Quaternary glaciomarine deposits on the tip of Red Head. The lower 2 m of the section are a weakly cemented boulder fanglomerate with clasts up to 50 cm × 50 × cm × 15 cm. The upper 2 m consist of trough cross-bedded pebble fanglomerate with cobble lenses. Clasts of white marble (Middle Proterozoic Green Head Group), red to black rhyolite, and red granite (Late Proterozoic Coldbrook Group and Golden Grove Suite, respectively) dominate the fanglomerate (see Currie 1987 for a review of local Precambrian stratigraphy).

Limestone lithology A coarse-grained, light red weathering, fossil grainstone is a minor component of both fanglomerate intervals. Although most limestone clasts are too small (granule to pebble sized) for biostratigraphic evaluation, a large block (25 cm × 30 cm × 40+ cm) was found in the lower fanglomerate. Slab and thin sections show that the red color is limited to a 5 cm thick, weakly limonite impregnated rind of the boulder, and that

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the block is a light grey, intraclast-fossil fragment (brachiopod and echinoderm hash dominated) grainstone with scattered hematite ooids and rare dark green, round (probably glauconitic) grains. The red color may reflect subaerial weathering prior to deposition in the fanglomerate and diagenetic development of a ferruginous cement. The limestone is thoroughly winnowed and shows low-angle cross-stratification, which suggest at least episodic wave or current action.

Faunas Microfossils, thermal alteration, and paleoecology A brachiopod- and ostracode-dominated microfauna was recovered from a 5.5 kg sample that was disaggregated in formic acid. Phosphatic remains include conodont elements (Table 1) dominated by Drepanoistodus Lindström, 1971 and Baltoniodus Lindström; high conical pedicle valves from an acrotretid brachiopod (approx. 1000 specimens); and several sclerites of the agathan fish Anatolepis Bockelie and Fortey, 1976. A color alteration index (CAI) of 2.0 for the conodont elements indicates mild alteration at burial temperatures of 60–140°C (see Epstein et al. 1977). By comparison, Upper Cambrian – lowest Ordovician euconodont elements from the Chesley Drive Group on the north side of Saint John harbor (Landing et al. 1978; Landing and Westrop 1998) are dull black (CAI = 5), which indicates temperatures above 300°C and much deeper burial. Hematite replacement and internal fills allowed recovery of many originally calcareous remains. These include 300 articulated specimens of two palaeocopid ostracode species; several hundred steinkerns of several snail and bivalve (Lyrodesma? Conrad, 1841) genera; approximately 100 specimens of several orthid brachiopod genera; many crinoid sclerites; and one bryozoan. The biofacies of the Red Head boulder microfauna is most similar to late Early – Middle Ordovician faunas from cool-water, unrestricted marine facies that are currently best known on the Baltic continent. Rasmussen and Stouge (1995) recognized Drepanoistodus- and Baltoniodus-dominated conodont biofacies as characteristic of open-shelf environments in southern Scandinavia, although it should be noted that these genera occur worldwide and their elements can be abundant even in successions marginal to tropical carbonate platforms (e.g., Landing 1976; An 1987; Albanesi 1998). The overall aspect of the Red Head assemblage is most comparable to low-diversity benthic faunas in Baltica, with abundant palaeocopides and small orthids as associates of Drepanoistodus and Baltoniodus (Tolmacheva et al. 2003). Trilobites Trilobites are the dominant component of a macrofaunal assemblage from the boulder which also includes orthid brachiopods. The association of Neseuretus Hicks, 1873; Nileus, Dalman, 1827; and Stapeleyella Whittard, 1955, is consistent with the open marine setting suggested earlier for the associated conodonts and other microfaunal elements. Neseuretus is the eponymous genus of the most proximal trilobite assemblage in north Gondwanan successions of Saudi Arabia (Fortey and Morris 1982), and the Neseuretus community is the most “inshore” trilobite assemblage in the © 2003 NRC Canada



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Fig. 1. Generalized locality map. (a) Uppermost Precambrian–Ordovician inliers (in black) on the Avalonian Orogen in Maine and eastern Canada. Abbreviations of localities noted in the text: BI, Bell Island; CrB, Cradle Brook; NA, northern Antigonish Highlands; SJ, Saint John. Other abbreviations: CBI, Cape Breton Island; PEI, Prince Edward Island. (b) Location of Red Head (RH) in Saint John harbor; upper Tremadoc at Reversing Falls (RF) is youngest Ordovician outcrop in the region. Lines with long dashes are faults, with upthrown block labeled (u); lines with short dashes are lithologic contacts; short wavy lines mark bodies of water. C and Carb., Carboniferous; PCao, Precambrian basement of Avalonian Orogen; PC-Ocs, uppermost Precambrian–Ordovician cover sequence. Modified from Currie (1987, fig. 1).

Arenig of Avalonian Wales (Fortey and Owens 1987; Fortey and Cocks 1992). Traynor’s (1988) synthesis of the Arenig of South Wales showed that Neseuretus occurs with orthids, bivalves, and “pelmatozoans” in wave-dominated (including hummocky cross-stratified) siltstones and mudstones with soft-sediment décollement surfaces at Ramsey Island in the west (Bates 1969) and in siltstones and mudstones deposited below wave base at Carmarthen in the east (Fortey and

Owens 1978). At Carmarthen, trinucleids (i.e., Myttonia Whittard, 1955) appear just above Neseuretus, with further deepening into graptolite-bearing mudstones (Fortey and Owens 1978; Traynor 1988), although farther west, at Whitland, Stapeleyella appears without Neseuretus higher in the succession in black, graptolitic shales (Fortey and Owens 1987). A somewhat similar prodeltaic setting with intercalated wavereworked sandstones and fan-delta debris flows is associated © 2003 NRC Canada



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Can. J. Earth Sci. Vol. 40, 2003 Table 1. Conodonts from late Middle Ordovician limestone boulder at Red Head. Element

No. of specimens

Amorphognathus (Lenodus) variabilis (Sergeeva, 1963) Pa 14 Pb 31 Sa 31 Sb 4 Sd 3 M 8 Total 91 Amorphognathus (Lenodus) sp. A (Stouge and Bagnoli, 1990) Pa 1 Total 1 Baltoniodus medius (Dzik, 1976) Pb 1 Sb 1 Sc 1 M 2 Total 5 Baltoniodus norrlandicus (Löfgren, 1978) Pa 13 Pb 83 Sb 13 Sd 6 M 11 Total 126 Drepanodus arcuatus Pander, 1856 Arcuatiform 3 Oistodiform 7 Total 10 Drepanoistodus basiovalis (Sergeeva, 1963) Drepanodiform 130 Suberectiform 33 Oistodiform 40 Total 203 Drepanoistodus cf. Drepanoistodus basiovalis sensu Stouge and Bagnoli (1990) Oistodiform 26 Total 26 Periodon sp. Sb 3 M 1 Total 4 Phragmodus? sp. aff. “Baltoniodus” crassulus (Lindström, 1955) sensu Dzik (1994) Pa 5 Sa 2 Sb 1 Sc 1 Total 9 Plectodina? sp. Sb 5 Total 5

Fig. 2. Uppermost Precambrian–Ordovician in Saint John, New Brunswick, area (stratigraphic revisions in Landing 1996a and Landing and Westrop 1998) and age of limestone boulder in Triassic Lepreau Formation. Stratigraphic column scaled proportional to Cambrian– Ordovician geochronology (see Tucker and McKerrow 1995 and reviews in Landing et al. 1997, 1998, 2000). The figure shows the Ordovician interval younger than Chesley Drive Group at Reversing Falls and older than Red Head boulder not represented by outcrop. Vertical lines indicate hiatus, and wavy lines unconformities. F.B. Mbr., Fossil Brook Member of Chamberlain’s Brook Formation; Hanf. Brook, Hanford Brook Formation; L. Is., Long Island Member; M.R. Fm., Manuels River Formation; S.M. + S.S., Saint Martins and Somerset Street members; Dep. (or D.) Seq., depositional sequence; Ser. Series; M., Middle; L. Lower; Precam., Precambrian; Cam., Cambrian; O., Ordovician.

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with the co-occurrence of Neseuretus, Myttonia, and a rich benthic fauna in the roughly coeval Henllan Ash member of the Alt Lwyd Formation in North Wales (Whittington 1966; Traynor 1990). Age and correlation of the fauna Geographically widespread conodonts allow a relatively finely resolved correlation of the Red Head boulder into Baltica. In this fauna, Amorphognathus (Lenodus) variabilis (Sergeeva, 1963) elements are abundant, with the exception of cordylodiform (Sc) elements. All of the elements recognized in this species by Dzik (1994) and Stouge and Bagnoli (1999) were recovered (Figs. 3a–3k). Most of the platforms (Pa) are small–juvenile and lack broad lateral extensions on the slightly sinuous processes. The bifid anterolateral process with branches of approximately equal length on large–mature Pa elements of the species (Stouge and Bagnoli 1999, fig. 4D) is seen in one Pa fragment (Fig. 3c). Amorphognathus (Lenodus) variabilis is the eponymous species of a conodont zone that spans the Arenig–Llanvirn boundary–interval in Baltica (Lindström 1971; Löfgren 1978, 2000) and is recognized in open marine successions in China (e.g., An 1987; Mitchell et al. 1997) and Argentina (Albanesi 1998). The lowest occurrence of this species defines the base of the A. variabilis Zone, a horizon in Baltica regarded as the base of the regional Kundan Stage (e.g., Lindström 1971; Löfgren 1978; Bagnoli and Stouge 1997) or a level slightly higher in the Kundan (Löfgren 2000). Amorphognathus (Lenodus) variabilis ranges through the Kundan from upper Arenig into lower Llanvirn equivalent strata in Baltica (Löfgren 1978). However, associated conodonts indicate that the Red Head boulder represents the lower A. variabilis Zone. A highly resolved correlation of the Red Head block into Baltica is provided by a sinistral Pa element of Amorphognathus (Lenodus) sp. A (Bagnoli and Stouge, 1990) (Fig. 3ee), a form that appears at, or whose lowest appearance is used as a proxy for, the base of the A. variabilis Zone and is limited to the lower Kundan (Stouge and Bagnoli 1990; Bagnoli and Stouge 1997; Löfgren 2000). In addition, the nomenclaturally problematical form named Phragmodus? sp. aff. “Baltoniodus” crassulus (Lindström, 1955) by Dzik (1994) is biostratigraphically useful, as it has been described from the Kundan of Polish Baltica. The presence of denticles at the bases of lateral costa in S-series elements may distinguish this taxon (Figs. 4n–4q) from the older, middle Arenig equivalent Prioniodus crassulus (Lindström, 1955) sensu Van Wamel (1972) of Sweden. Other conodonts from Red Head are less useful for correlation, as they range upward from the Volkovian into the Kundan. These forms include Drepanoistodus basiovalis (Sergeeva, 1963) (Figs. 4c–4i); Drepanodus arcuatus Pander, 1856 (Figs. 4l, 4m); and Baltoniodus norrlandicus (Löfgren, 1978) (Figs. 3l–3u, 3x, 3y) (see Löfgren 1978, 1995, 2000; Stouge and Bagnoli 1990; Bagnoli and Stouge 1997; and Tolmacheva 2000 for these species’ ranges in Baltica). M elements illustrated herein as Drepanoistodus sp. cf. D. basiovalis (Sergeeva) sensu Stouge and Bagnoli (1990) have a shorter oral edge and a weaker or obsolescent inner carina (Figs. 4j, 4k) than corresponding elements in D. basiovalis but may simply be a morphologic variant of

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the numerous M elements of D. basiovalis. Two additional forms are not identifiable to genus or species (Periodon sp., and Plectodina? sp.; Figs. 3bb–3dd, 4a, 4b) and provide little biostratigraphic resolution. The remaining conodont recovered from Red Head is Baltoniodus medius (Dzik, 1976) (Figs. 3v, 3x, 3z, 3aa), a species considered herein to be a synonym of Baltoniodus parvidentatus (Sergeeva, 1963) sensu Dzik (1976) and Baltoniodus clavatus Stouge and Bagnoli, 1990. Baltoniodus medius by this synonymy is stratigraphically long-ranging and ranges through uppermost Arenig–Llanvirnequivalent strata in Baltica. Correlation of the lower A. variabilis Zone and lower Kundan of Baltica is into the Arenig–Llanvirn boundary interval of the Avalon continent (e.g., Bagnoli and Stouge 1997). This boundary has traditionally been equated with the Lower– Middle Ordovician boundary in the cool-water successions of Avalon. However, recent work on Ordovician interprovincial correlations has focused on conodonts and graptolites from tropical Laurentia, Australia, and South China and now regards the Lower–Middle Ordovician boundary as a presently undefined level much lower in the middle Arenig (Mitchell and Chen 1995). Thus, the association of A. variabilis, D. basiovalis, and B. medius in sequences on the outer carbonate platforms in China (An 1982) and Argentina (Albanesi 1998) is regarded as Middle Ordovician. Higher strata of the lower Kundan and its terminal Arenig equivalent in Avalon are correlated into the lower Darriwilian Stage, the upper of two global stages that compose the Middle Ordovician (Mitchell et al. 1997). This reassessment of the terminal Arenig means that the Red Head limestone fauna is upper Middle Ordovician. A correlation with the Arenig of Avalonian Britain is consistent with composition of the trilobite fauna. Stapleyella cf. S. abyfrons is closely comparable to S. abyfrons Fortey and Owens, 1987 from the late Arenig (Fennian) of South Wales. Neseuretus typically occurs in the lower Arenig (Moridunian Stage) in Wales (e.g., Fortey and Owens 1987; Beckly 1989) and the Shelve Inlier of Shropshire (Whittard 1960), but as noted by Fortey and Owens (1978), this reflects the association of Neseuretus with nearshore facies at the base of a transgressive sequence. Neseuretus parvifrons (M’Coy in Sedgwick and M’Coy 1851), however, is very similar to the species described herein and has been reported to range through most of the Arenig in the Mytton Formation of the Shelve Inlier (Whittard 1966). The reevaluation by Fortey and Owens (1987, p. 238) of Whittard’s (1960, 1968) reports of Neseuretus species from the Mytton Formation led them to confirm the Moridunian occurrence of N. parvifrons and questionably refer the form from the upper Arenig (Fennian Stage) to N. parvifrons. The black shales of the Chesley Drive Group at Reversing Falls, about 2 km northwest of Red Head (Fig. 1), have long been reported as the youngest Ordovician rock in Avalonian New Brunswick (Fig. 2). The graptolites and olenid trilobite Peltocare rotundifrons (Matthew, 1892) from Reversing Falls, traditionally regarded as middle Arenig (McLearn 1915; Hayes and Howell 1937), are now known to be significantly older and of late Tremadoc age (Landing et al. 1997). Thus, the reworked limestone blocks in conglomerates of the Triassic Lepreau Formation are the only record of the Arenig in the region. © 2003 NRC Canada



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Fig. 3. Upper Arenig conodonts. (a–k) Amorphognathus (Lenodus) variabilis (Sergeeva, 1963). a–c, Pb elements, oral and lateral views, NBMG 11083 and 11084, ×45, and fragment with bifid lateral process, NBMG 11085, ×65; d and e, Pa elements, oral and anterolateral views, NBMG 11086, ×75, and NBMG 11087, ×55; f, Sb, NBMG 11088, ×80; g and i, Sa elements, NBMG 11089 and 11090, ×80; h, Sd, NBMG 11091, ×80; j and k, M elements, NBMG 11092, ×75, and NBMG 11093, ×65. (l–u, w, y) Baltoniodus norrlandicus (Löfgren, 1978). l–n, Pb elements, inner-lateral, oral, and inner-lateral views, NBMG 11094, ×75, NBMG 11095, ×75, and NBMG 11096, ×60; o and s, large Pa elements, anterior and anterolateral views, NBMG 11097 and 11098, ×70; p and u, small Pa elements, inner-lateral views, NBMG 11099 and 11100, ×100; q, r, and y, M elements, NBMG 11101, ×90, NBMG 11102, ×90, and NBMG 11103, ×80; t, Sc, NBMG 11104, ×90; w, Sb, NBMG 11105, ×90. (v, x, z, aa) Baltoniodus medius (Dzik, 1976). v, Sb, NBMG 11106, ×100; x, M, NBMG 11107, ×90; z, Pb, NBMG 11108, ×55; aa, Sc, NBMG 11109, ×90. (bb–dd) Plectodina? sp. Sb elements NBMG 11110, ×65, NBMG 11111, ×90, NBMG 11112, ×65. (ee) Amorphognathus (Lenodus) sp. A (Stouge and Bagnoli, 1990), Pa, NBMG 11113, ×65.

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Fig. 4. Upper Arenig conodonts. (a, b) Periodon sp., Sb and M elements, NBMG 11114, ×95, and NBMG 11115, ×75. (c–i) Drepanoistodus basiovalis (Sergeeva, 1963). c–e, oistodiforms, outer-lateral (NBMG 11116) and inner-lateral (NBMG 11117 and 11118) views, ×65; f and i, inner-lateral views of symmetrical and subsymmetrical drepanodiforms NBMG 11119 and 11122, ×60; g and h, suberectiforms NBMG 11120 and 11121, ×65. (j, k) Drepanoistodus cf. Drepanoistodus basiovalis (Sergeeva) sensu Stouge and Bagnoli (1990), oistodiforms NBMG 11123 and 11124, ×65. (l, m) Drepanodus arcuatus Pander, 1856, oistodiform (pipaform) and arcuatiform elements NBMG 11125 and 11126, ×65. (n–q) Phragmodus? aff. “Baltoniodus” crassulus (Lindström, 1955) sensu Dzik (1994). Pa, NBMG 11127, ×70; Sb, NBMG 11128, ×35; Sc, NBMG 11129, ×70; Sa, NBMG 11130, ×70.

Discussion The fauna described herein helps bridge a gap in the Avalonian conodont record between the terminal Cambrian – lowest Ordovician (Landing et al. 1978; Rushton 1982) and the Late Ordovician (Caradoc; e.g., Fortey et al. 2000). This is the first recovery of an Arenig conodont fauna from Avalon. This low-diversity Drepanoistodus- and Baltoniodus-dominated conodont assemblage includes geographically widespread taxa; lacks characteristic carbonate platform taxa like those known in Laurentia and south China; reflects cool-water, open-marine conditions; but does not provide evidence for Avalon’s proximity to other temperate continents, such as Baltica. The trilobite assemblage is more informative paleogeographically than the conodont fauna, although Nileus is widely distributed and occurs, for example, on the Baltic continent (Nielsen 1995), in deeper water successions around the margins of Laurentia (e.g., Whittington 1965; Fortey 1975), and from the Moroccan margin of western Gondwana (Destombes 1970). The recovery of Nileus sp. in this study now extends the range of this genus to the Avalon continent. More significantly, Stapeleyella has been recorded previously only from Avalonian Britain (Whittard 1955; Fortey and Owens 1987).

Cocks and Fortey (1982) emphasized that the Arenig– Llanvirn genus Neseuretus was useful in early Paleozoic paleogeographic reconstructions because it is absent from successions on the tropical Laurentian and temperate Baltic continents. Neseuretus, however, is characteristic of high-latitude successions in eastern Newfoundland, Wales, Normandy, Spain, and Saudi Arabia that Cocks and Fortey referred to a Gondwanan continent. Subsequent reevaluation (Landing 1996a) has dissected their Gondwana into separate Avalonian and Gondwanan continents. This distinction is based on the fact that the uppermost Precambrian – lowest Cambrian in Avalon (i.e., southern New Brunswick, eastern Newfoundland, Wales, England) is a cool-water, siliciclastic-dominated succession with no faunal similarities to the coeval carbonate platforms with evaporites and archaeocyathan faunas in Gondwanan Normandy, Spain, and Morocco (Landing 1996a). A breakdown of provincial barriers and appearance of shared trilobite genera began in the late Early Cambrian after the appearance of the oldest trilobites in Avalon (Callavia broeggeri Zone) with a dramatic shift of Gondwana into high south latitudes (Theokritoff 1979; Piper 1985) and disappearance of its warm carbonate-rich successions (e.g., Westrop and Landing 2000; Geyer and Landing 2001). With the late Early Cambrian breakdown in faunal barriers, trilobite genera, but not species, © 2003 NRC Canada



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are shared into the Late Ordovician between Avalon and Gondwana and reflect a combination of similar paleolatitudes and current systems responsible for trilobite dispersal. Just as regionally extensive lithostratigraphic units demonstrate the unity of Avalon in the latest Precambrian– Ordovician (Landing 1996a, 1996b), recovery of “British” trilobites (Stapeleyella and Neseuretus cf. parvifrons) in southern New Brunswick further helps demonstrate that “eastern” and “western” Avalon were contiguous in the Ordovician and did not comprise separate continents (e.g., compare McKerrow 1988). The recovery of Nileus in New Brunswick merely shows that this genus was widespread in the Ordovician and that its range included Laurentia, Baltica, west Gondwana, and the Avalon continents. Post-Ordovician deformation, uplift, and erosion have led to a situation in which post-Cambrian rocks are poorly represented in the Avalonian cover sequence (see Landing 1996a). Thus, the Red Head boulder is helpful in reconstructing depositional regimes on the North American part of the Avalon continent. Small areas of lowest Ordovician (Tremadoc) black and dark gray mudstone of the Chesley Drive Group occur in coastal New Brunswick, Cape Breton Island (Hutchinson 1952), and eastern Newfoundland (Hutchinson 1962). Arenig successions, however, are limited to two small areas in eastern Newfoundland and northern Nova Scotia. In eastern Newfoundland, peritidal, wave and tidal current deposited quartz arenites, dark mudstones, and oolitic iron ores with shallow trace fossils (Cruziana biofacies) of the upper Bell Island – Wabana groups (Hayes 1915; Ranger 1979; Ranger et al. 1984) are Arenig (Dean and Martin 1978). The lithologically similar Ferrona Formation in the northern Antigonish Highlands (see Murphy et al. 1979) yields the early Arenig brachiopod Sphaerobolus spissa (Billings, 1872) (Williams 1914; Dean and Martin 1978) and suggests the lateral persistence of wave and tidal current dominated sand and sedimentary iron ore deposition into northern Nova Scotia (Landing et al. 1980). An attempt at reconstructing Arenig deposition farther southwest faces the problem of lack of outcrop. The fossil grainstone of the Red Head boulder with its hematite ooids, apparent glauconite grains, and fauna dominated by orthids, gastropods, and bivalves suggests an extension of the high-energy, shallow sedimentary iron ore facies. Although available outcrops of Bell Island – Wabana – Ferrona facies are devoid of bedded carbonates, wave and current sorting presumably led to local shell lags like that of the Red Head limestone with limited iron ooid content. A caveat to use of the Red Head block in reconstructing Arenig deposition in southern New Brunswick is that the depositional site of the Red Head limestone is uncertain. As noted previously, the low thermal alteration of its conodont and other phosphatic remains, by comparison with those from adjacent lower Paleozoic outcrops, suggests deposition, burial, and thermal alteration at some distance from Saint John. Composite movements of nearly 550 km are interpreted to have taken place on dextral transform faults offshore of Saint John in the Acadian and Hercynian orogenies (Keppie 1982). Translation of an essentially thermally unaltered Avalon succession into the Bay of Fundy area and its erosion with Triassic rifting and extension may explain the origin of the Red Head boulder. If transcurrent faulting is hypothesized,


there is no way to determine whether this terminal Arenig hematitic limestone was deposited on the Avalonian marginal platform (i.e., a setting comparable to that of the Saint John area or northern Nova Scotia; Landing 1996a) or inner platform (i.e., comparable to that of the Avalon Peninsula and Conception Bay in eastern Newfoundland; Landing 1996a). The most southwesterly occurrence of Arenig deposition in North American Avalon is recorded in Rhode Island and southern Massachusetts. In this region, at least episodically high-energy depositional regimes are suggested by siliceous quartz arenite pebbles with the brachiopods Lingulobolus affinnis (Billings, 1872) and S. spissa (Billings, 1872) in Upper Carboniferous conglomerates. The latter brachiopods are also known in the upper Bell Island Group of eastern Newfoundland (see Walcott 1898; Towe 1959). Only generalized comparisons can be made between the depositional regimes of Avalonian North America and southern Britain. Arenig successions on the inner platform of South Wales (Landing 1996a) are dissimilar to the coeval shallowmarine facies of eastern Newfoundland, as they feature a progressive upward deepening into turbiditic and hemipelagic mudstones (Traynor 1988). On the marginal platform in North Wales, lower deltaic and upper tidal siliciclastic facies were deposited in fault-bounded depocenters adjacent to a developing volcanic arc. These siliciclastics are locally capped by terminal Arenig, wave-dominated hematitic ironstones of the Olchfa Member of the Alt Lwyd Formation, with fragmentary brachiopod and trilobite remains (Traynor 1990). Although poorly exposed, available descriptions (Cox and Wells 1921; Allen and Jackson 1985) of the Olchfa Member in the Arenig and Bala area suggest a resemblance to the Wabana Group of eastern Newfoundland. Persistent shallow-shelf deposition comparable to that of the Arenig of Avalonian North America is recorded farther east on the inner platform of the Shelve area of the Welsh Borderlands. Here, transgressive, lowest Arenig sandstones (Stiperstones Quartzites) are succeeded by long-term deposition of wave- and tide-dominated sandstone, siltstone, and mudstone (Mytton Formation), with sandstone lenses appearing in the Tankerville Flags and Shelve Church Beds in the uppermost Arenig (Fortey and Owens 1987).

Systematic paleontology Landing is responsible for the section on the conodonts; only those taxa regarded as taxonomically and (or) nomenclaturally problematical and biostratigraphically significant are discussed. Westrop and Kim are responsible for the trilobites; the order of their names is arbitrary and does not indicate seniority. Figured specimens are reposited in the New Brunswick Museum Geology (NBMG) collection. Conodonts Family Balognathidae, Hass, 1959, sensu Dzik, 1994 Genus Baltoniodus Lindström, 1971 TYPE SPECIES:

Prioniodus navis Lindström, 1955.

DISCUSSION: Taxonomic “splitting” seems to have led to many named species of Baltoniodus. These species have been based on differences in dentition, presence or relative length of the lateral costa in Sc, or relative curvature of the processes in S elements (compare Dzik 1976, 1994; Löfgren 1978; Stouge

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and Bagnoli 1990). Differentiation of Baltoniodus “species” from sites far away from their Swedish and Polish type areas is problematical, particularly as the range of morphologic variation in their elements is incompletely documented. Baltoniodus medius (Dzik, 1976) (Figs. 4v, 4x, 4z, 4aa) SYNONYMY:

Prioniodus alatus parvidentatus (Sergeeva). Dzik, 1976, figs. 22k–22r. Prioniodus alatus medius Dzik, 1976, p. 423, pl. 42, fig. 1, figs. 23a–23l. Prioniodus (Baltoniodus) prevariabilis medius Dzik. Löfgren, 1978, pp. 86, 87, pl. 12, figs. 27–36, pl. 13, figs. 1A, 1B, 6A–6D. Baltoniodus clavatus Stouge and Bagnoli, 1990, pp. 12, 13, pl. 2, figs. 1–12, pl. 3, figs. 1, 2. Baltoniodus parvidentatus (Sergeeva). Dzik, 1994, pp. 80–82, pl. 18, figs. 8–14, figs. 13, 14a. Baltoniodus medius (Dzik). Dzik, 1994, p. 82 (includes partial synonymy).

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Baltoniodus clavatus Stouge and Bagnoli, 1990, first described from somewhat older strata of the lower but not lowermost A. (L.) variabilis Zone, has elements fully comparable to those illustrated by Löfgren (1978) for B. medius. The latter species even seems to show B. clavatus “diagnostic” slightly upturned posterior process in Pa (Stouge and Bagnoli 1990; compare Löfgren 1978, pl. 12, fig. 29) and does not seem differentiable from B. clavatus. The circle of taxonomic uncertainty for the appropriate names for Kundan Baltoniodus is completed with Stouge and Bagnoli’s (1990) synonymization of B. clavatus with B. parvidentatus sensu Dzik (1976, 1994) and their belief that the latter’s name is inappropriate, as its apparatus did not contain F. parvidentatus as an M element. The synonomy of B. medius with B. clavatus and B. parvidentatus suggested herein means that B. medius is a long-ranging (upper Arenig–Llanvirn) taxon. Trilobites Family Calymenidae Milne-Edwards, 1840 Subfamily Reedocalymeninae Hupé, 1955 Genus Neseuretus Hicks, 1873 Neseuretus ramseyensis Hicks, 1873, from the Arenig of Ramsey Island, Wales (subsequent designation by Vogdes (1925)).

TYPE SPECIES:

In addition to Baltoniodus norrlandicus (Löfgren 1978), a second Baltoniodus species is represented at Red Head by a Pa, an Sc, and a laterally costate Sb element with alternating large and small denticles. The Pa has small denticles on a low anterior process. The lateral costa of Sb is somewhat smaller than that in B. norrlandicus. Most denticles are broken off the posterior process of the Sc, but albid bases of alternating large and small denticles could be seen in this element in reflected light. This second Baltoniodus form can be referred to any of three “species” of Baltoniodus from the A. (L.) variabilis Zone and higher strata in Baltica that also have laterally costate Sb and alternating large and small denticles. Dzik (1976) described two subspecies of Baltoniodus alatus Hadding, which he later (Dzik 1994) regarded as the successive species B. parvidentatus and B. medius. These “species” are distinguished by a somewhat longer and shorter lateral costa, respectively, in Sb. The range of variation in the relative length of this costa is undocumented and its reliability as a taxonomic character is untested. Consequently, B. parvidentatus and B. medius are considered undifferentiable. A further difficulty is that the appropriate taxonomic name of B. parvidentatus is problematical. Löfgren (1978) questioned Dzik’s (1976) assignment of the form species Fallodus parvidentatus as the M element of multielement Prioniodus alatus parvidentatus or P. a. medius. Alternatively, Stouge and Bagnoli (1990) regarded F. parvidentatus as the M element of Trapezognathus quadrangulum Lindström, 1955, but did not base this on apparatus reconstructions using topotype collections with F. parvidentatus. Although assignment of topotype F. parvidentatus to a multielement balognathid species is unresolved, Viira’s (1974, pl. 6, figs. 14–17, figs. 96, 97) illustrations of this form species are comparable to the M elements assigned by Dzik (1976, 1994) and Löfgren (1978) to B. parvidentatus and B. medius. One oistodiform from Red Head resembles some of Viira’s (fig. 97j) specimens of F. parvidentatus and is tentatively assigned to B. medius. A third Baltoniodus species with reduced anterior costa in Sb and irregular dentition is also named from the Kundan. DISCUSSION:

Neseuretus cf. Neseuretus parvifrons (M’Coy in Sedgwick and M’Coy 1851) (Figs. 5a–5h) SYNONYMY:

cf. Neseuretus parvifrons (Salter), Whittard 1960, p. 142, pl. 19, figs. 1–6 (for synonymy; see Whittington 1966, p. 501 for discussion of authorship of this species). cf. Neseuretus parvifrons (M’Coy in Sedgwick and M’Coy 1851), Whittington 1966, p. 500, pl. 4, figs. 1–13, pl. 5, figs. 1–10. cf. Neseuretus parvifrons (M’Coy in Sedgwick and M’Coy), Bates 1969, p. 26, pl. 9, figs. 4, 5, 7, 9, 10, 12–16. MATERIAL:

Ten cranidia, two pygidia, and six librigenae.

DISCUSSION: The gently inflated, long preglabellar fields, poorly defined anterior borders, and weakly arched anterior margins of the cranidia from New Brunswick are most similar to those of N. parvifrons (M’Coy in Sedgwick and M’Coy 1851) from the Arenig of Wales (Bates 1969, pl. 9, figs. 5, 16; Whittington 1966, pl. 4, figs. 1–8) and the Shelve Inlier of Shropshire (Whittard 1960, pl. 19, figs. 5, 6). The Red Head pygidia, however, have a relatively longer axis, wider pleural region, and a more conical terminal piece. The type species N. ramseyensis, from the Arenig of South Wales (Bates 1969, pl. 8, figs. 3–12, pl. 9, figs 1–3, 6; Fortey and Owens 1987, figs. 97a–97g), has a pygidial axis with eight or nine axial rings, whereas N. cf. N. parvifrons has an axis of five rings and a terminal piece. Among other species from Avalonian Britain, Neseuretus monensis (Shirley, 1936; see Beckly 1989, figs. 12a–12h) and Neseuretus caerhunensis Beckly (1989, figs. 13, 14) from the Arenig of North Wales have more posteriorly positioned palpebral lobes and, consequently, have palpebral ridges that are oblique, rather than transverse (Beckly 1989, p. 17). Neseuretus murchisoni (Salter, 1865) from the Shelve Inlier (e.g., Whittard 1960, pl. 20, figs. 6–10),

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Fig. 5. Upper Arenig trilobites. (a–h) Neseuretus cf. Neseuretus parvifrons (M’Coy in Sedgwick and M’Coy, 1851). a, pygidium, dorsal view, NBMG 11989, ×3; b, pygidium, dorsal view, NBMG 11990, ×7; c and d, cranidium, anterior-oblique and dorsal views, NBMG 11991, ×5; e, librigena, dorsal view, NBMG 11992, ×4; f, g, and h, cranidium, dorsal, anterior-oblique, and anterior views, NBMG 11993, ×4. (i–m) Nileus sp. i, cranidium, dorsal view, NBMG 11994, ×9; j, pygidium, dorsal view, NBMG 11995, ×7; k and l, cranidium, anterior oblique and dorsal views, NBMG 11996, ×8; m, pygidium, dorsal view, NBMG 11997, ×9.

South Wales (Fortey and Owens 1987, figs. 98a–98e), and North Wales (Bates 1969, pl. 9, figs. 8, 11) and Neseuretus brevisulcus Whittard (1960, pl. 19, figs. 7–14) from the Shelve Inlier both have well-defined, convex anterior borders. The former has narrower fixigenae than N. cf. N. parvifrons, whereas the latter has a distinctive, strongly tapered pygidial axis (Whittard 1960, pl. 20, fig. 3). Lastly, Neseuretus complanatus Whittard (1960, pl. 20, figs. 4, 5) is based on a

single specimen with a flattened lateral profile, but as noted by Fortey and Owens (1987, p. 240), it is difficult to determine the extent to which this feature is influenced by deformation. The only other Neseuretus species from Avalonian North America is Neseuretus vaningeni Dean in Dean and Martin (1978, pl. 4, pl. 5, figs. 1–3), which is based on a single completely articulated exoskeleton. This species is separated readily from N. cf. N. parvifrons by its shorter frontal area © 2003 NRC Canada



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and a relatively shorter and wider glabella. The pygidium of N. vaningeni has four axial rings plus a terminal piece (Dean and Martin 1978, pl. 4, figs. 2, 3, pl. 5, fig. 3), whereas the pygidium of N. cf. N. parvifrons (Figs. 5a, 5b) has five rings and a terminal piece. Numerous additional species of Neseuretus have been reported from other regions, including France, Spain, Saudi Arabia, South America, and China (see Fortey and Morris 1982, and Rábano 1990 for discussion), but many are based on limited material (e.g., Lu 1975; Chang and Jell 1983). Neseuretus tristani (Desmarest, 1817) is among the best known and most widespread, as it is recorded from Saudi Arabia (Fortey and Morris 1982), England (Sadler 1974), France (Henry 1980), and Spain (Hammann 1983). This species has a strongly arched anterior cranidial margin and a steeply upturned frontal area (Fortey and Morris 1982, figs. 3a–3c; Hammann 1983, pl. 6, figs. 62, 63; Henry 1980, pl. 10, figs. 1a, 1b) that contrasts with the weakly arched margin and gently inflated frontal area of N. cf. N. parvifrons. Family Nileidae Angelin, 1854 Genus Nileus Dalman, 1827 Asaphus (Nileus) armadillo Dalman, 1827, from the lower Holen Limestone (upper Arenig; see Månsson 1995) of Östergötland, Sweden (by subsequent designation of Hawle and Corda 1847).

TYPE SPECIES:

Nileus sp. indet. (Figs. 5i–5m) MATERIAL:

Two cranidia and six incomplete pygidia.

DISCUSSION: Nileus is represented in our collection by a few, mostly incomplete sclerites. A distinctive feature of the cranidia is a well-developed, pitted sculpture that is matched only in Nileus porosus Fortey (1975, pl. 12, figs. 1–14) and Nileus? lacunosa Whittington (1965, pl. 36, figs. 1–10). Comparisons are difficult because of their small size, but the cranidia illustrated herein (Figs. 5i, 5k, 5l) differ from those of N. porosus in having palpebral lobes that are more posteriorly located. The associated pygidia (Figs. 5j, 5m) lack the wellrounded anterior corners of similarly sized pygidia of N. porosus (e.g., Fortey 1975, pl. 12, figs. 8, 10, 13, 14). Cranidia of N.? lacunosa are more comparable in size to our specimens, which differ in having more divergent anterior branches of the facial sutures and a relatively longer area of the cranidium in front of the palpebral lobes. The pygidium tentatively attributed to N. ? lacunosa (Whittington 1965, pl. 32, figs. 8, 11) has a well-defined border that is not present on the larger pygidia illustrated herein. Other species of Nileus have cranidia with smooth surfaces, weak terrace ridges, or minute pits that are not usually evident in photographs (e.g., see Whittington 1965; Schrank 1972; Fortey 1975; Lu 1975; Nielsen 1995). The pygidia from Red Head lack borders and have weakly rounded anterior corners (e.g., Fig. 6j). In these respects, they resemble those of Nileus latifrons Nielsen (1995, figs. 157L, 158A) from the Komstad Limestone Formation of southern Scandinavia. Associated small cranidia (Nielsen 1995, figs. 153G, 153H, 153L, 154D) lack pits. A variety of other species of Nileus are separable from our pygida by possession of well-defined borders and

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border furrows (e.g., Whittington 1965, pl. 31, fig. 9, pl. 32, figs. 5, 7, 9, 14; Schrank 1972, pl. 1, fig. 3, pl. 2, figs. 6, 8, 10, pl. 3, figs. 7, 13, 14, pl. 4, fig. 2, pl. 5, figs. 4, 8, pl. 7, fig. 1c, pl. 9, figs. 2–4; Nielsen 1995, figs. 148M–148O, 149D–149M, 165H–165J, 170H, 170I, 170K–170P, 184, 196A–196L, 202A–202H, 207A–202C). Family Trinucleidae Hawle and Corda, 1847 Subfamily Trinucleinae Hawle and Corda, 1847 Genus Stapeleyella Whittard, 1955 TYPE SPECIES: Stapeleyella inconstans Whittard, 1955, from the Hope Shales Formation of the Shelve District, Shropshire, England (by original designation).

Hughes et al. (1975, pl. 2, fig. 28) illustrated an unnamed species from North Wales that combined features of the two genera Bergamia Whittard, 1955, and Stapeleyella Whittard, 1955. As in Bergamia, it has a relatively narrow fringe with two pit arcs (E1, E2) exterior to the girder, but also possesses interradial rows of pits in the E2 arc and thus resembles Stapeleyella. Hughes et al. followed Whittard (1955) in considering an E3 pit arc to be a diagnostic feature of Stapeleyella, and in the absence of this feature they questionably assigned their species to Bergamia. More recently, Fortey and Owens (1987) modified the diagnosis of Stapeleyella to accommodate another species, S. abyfrons Fortey and Owens, 1987, which has a narrow fringe with E1 and E2 arcs that include interradial pits. As redefined by them, Stapeleyella includes all species in which the presence of interradial pits results in crude to well-developed, Y-shaped branching patterns of the interradial ridges, regardless of the number of E arcs that are developed. A minimum of two E arcs are present, but E3 or even E4 may be developed in some species. The Fortey and Owens (1987) concept of Stapeleyella is followed herein. DISCUSSION:

Stapeleyella cf. Stapeleyella abyfrons Fortey and Owens, 1987 (Figs. 6, 7) SYNONYMY:

Stapeleyella abyfrons Fortey and Owens, 1987, p. 213, figs. 79a–79h (includes synonymy). MATERIAL: Twenty-eight cranidia, 11 pygidia, and one incomplete lower lamella. DESCRIPTION: Cranidium semicircular in outline, length 43–50% of width. Glabella elongate, expands forward, with strongly convex, subspherical pseudofrontal lobe; axial furrows firmly impressed. Three pairs of short, shallow lateral glabellar furrows present. Occipital ring nearly transverse medially but curved gently forward near axial furrow; occipital furrow well-incised. Bacculae weakly convex and triangular in outline; well-defined in smaller individuals (Fig. 6d), but may be obsolescent on larger specimens (Figs. 6a, 6m). Fringe approximately 25% of cranidial length at anterior but becomes reduced in width towards posterior corner of cranidium. Pit rows separated by low interradial ridges. Pit distribution highly variable with at least 16 radii, and two pit arcs external to well-defined girder (Fig. 6f). E1 and E2 arcs developed anteriorly, but may merge

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Fig. 6. Upper Arenig trilobites. (a–r) Stapeleyella cf. Stapeleyella abyfrons Fortey and Owens, 1987. a and b, cranidium, dorsal and anterior-oblique views, NBMG 11998, ×9; c, d, and e, cranidium, anterior, dorsal, and anterior-oblique views, NBMG 11999, ×12; f, fragment of lower lamella showing girder, ventral view, NBMG 12000, ×15; g, cranidium, dorsal view, NBMG 12001, ×12; h and i, cranidium, dorsal and anterior views, NBMG 12002, ×12; j, pygidium, dorsal view, NBMG 12003, ×11; k and l, cranidium, dorsal and anterior views, NBMG 12004 ×11; m, cranidium, dorsal view, NBMG 12205, ×12; n, cranidium, dorsal view, NBMG 12006, ×11; o and p, cranidium, lateral and dorsal views, NBMG 12007, ×12; q, pygidium, dorsal view, NBMG 12008, ×12; r, cranidium, dorsal view, NBMG 12009, ×12.

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Landing et al. Fig. 7. Fringe pattern of Stapeleyella cf. Stapeleyella abyfrons (based on Fig. 6k). E1, E2, and I1,2,n, pit arcs.

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The undescribed species of Stapeleyella illustrated by Hughes et al. (1975, p. 558, pl. 2, fig. 28) can be differentiated from S. cf. S. abyfrons by possession only of e2 accessory pits in the interradii. Stapleyella inconstans Whittard, 1955 (pl. 4, figs. 7–13; Fortey and Owens 1987, fig. 78), the type species, and S. murchisoni Whittard (1955, pl. 5, figs. 7, 8) have three or even four pit-arcs exterior to the girder, whereas S. cf. abyfrons has only two.

Acknowledgments

into single row of twin pits (Fig. 6k) or enlarged pits (Fig. 6n) posterior to row 7. At least two I arcs present anteriorly, become merged into single row of twin pits posterior to rows 8 or 9. On larger specimens, incomplete I2 arc present close to In (Figs. 6a, 6k). Variable e1–e2 accessory pits usually present in R0 and interradii i, ii, and viii. Between accessory pits, low interradial ridges show Y-shaped branching pattern. Genal region gently convex and depressed well below the level of the glabella in small individuals (Figs. 6c, 6o), but more inflated in larger cranidia (Fig. 6b). Posterior border furrow deep, straight to sigmoidal, and terminates at posterior fossula. Posterior border widens laterally. Finely reticulate sculpture on surfaces of glabella and genae; internal molds smooth. Pygidium subtriangular in outline, length approximately 33% of width. Axis convex, conical, extends back to inner margin of border; axial furrows shallow. Three clearly defined axial rings and terminal piece present; ring furrows deeply etched at anterior end of axis, but become increasingly shallow towards rear. Pleural fields broad, with three gently convex pleural ribs separated by shallow pleural furrows. Pleural furrows sigmoid, parallel each other, become indistinct towards border. Border slopes nearly vertically downward and increases slightly in height towards anterior corner of pygidium.

Discussion In possessing fringes with accessory pits in some interradii and, consequently, an irregular, Y-shaped branching pattern of some of the interradial ridges (Figs. 6k, 6m, 7), the cranidia illustrated herein closely resemble those of some of the early species of Stapeleyella, especially S. abyfrons Fortey and Owens (1987, figs. 79a–79h) from the Pontyfenni Formation (Arenig) of South Wales. As in the material from New Brunswick, S. abyfrons has 16 radii per half-fringe, complete E1, E2, In, and I1 arcs, and e pits in only a few interradii. The Red Head cranidia appear to differ in having an I2 arc in at least some individuals. Pygidia of S. abyfrons possess deep pleural furrows (see Fortey and Owens 1987, figs. 79b, 79d, 79f) that are not present on our specimens (Figs. 6j, 6q). The sclerites from Red Head almost certainly represent a new species, but in view of the incomplete nature of all available cranidia and lower lamellae, they are left in open nomenclature.

Support from National Science Foundation grant EAR98-05177 (to EL), Natural Sciences and Engineering Research Council of Canada grant 41197 (to SRW, held at Brock University), and Korean Research Foundation grant KRF-99-D042 and the BK 21 Project (to DHK) is gratefully acknowledged. W.A. Samsonoff provided access to scanning microscopy at the Wadsworth Center for Laboratories, New York State Health Department. L. Van Aller Hernick picked the Red Head microfossils. R.M. Owens and B.R. Pratt are thanked for manuscript reviews.

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