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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 firstdiverse marine fauna from the sub-Caradoc Ordovician of the western Avalon continent. This fauna includes the firstArenig conodonts recovered from Avalon and represents an unexposed interval in southern New Brunswick. Associationof the conodonts Drepanoistodus and Baltoniodus and the trilobites Neseuretus, Nileus, and Stapeleyella emphasizes thefaunal dissimilarity of Avalon and Laurentia through the late Middle Ordovician. Extension of the ranges of Neseuretuscf. Neseuretus parvifrons and Stapeleyella from Britain into New Brunswick further emphasizes that eastern andwestern 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 terminalArenig (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 acrossthe Avalonian marginal and inner platforms from eastern Newfoundland to the Boston, Massachusetts, region. Thiswestern Avalonian Arenig shows the greatest similarity with the Arenig of the Welsh Borderlands. Phosphatic fossilsfrom the boulder have a thermal alteration index much lower than that of nearby lower Paleozoic outcrops and suggestderivation of the boulder from a weakly heated Avalonian succession brought into the Bay of Fundy region bypost-Ordovician transcurrent faulting.

Rsum : Un bloc de calcaire de la Formation de Lepreau (Trias) proximit de Saint John, au Nouveau-Brunswick, afourni la premire faune marine diversifie provenant du sous-Caradocien (Ordovicien) du continent avalonien occidental.Cette faune comprend les premiers conodontes datant de lArnigien rcuprs dAvalon et reprsente un intervalle quinaffleure pas dans le sud du Nouveau-Brunswick. Lassociation des conodontes Drepanoistodus et Baltoniodus et destrilobites Neseuretus, Nileus et Stapeleyella met lemphase sur la dissimilitude faunique entre lAvalon et la Laurentia travers lOrdovicien moyen. Lextension des plages de Neseuretus cf. N. parvifrons et Stapeleyella de la Grande-Bretagneau Nouveau-Brunswick fait encore plus ressortir que les parties Est et Ouest dAvalon taient des parties confluentes

dun continent avalonien insulaire et unifi qui date du Prcambrien terminal. Cette faune est corrle avec la Zone Amorphognathus (Lenodus) variabilis (tage de Kundan) infrieure de Baltica et lArnigien terminal (Ordovicien moyensuprieur; tage darriwilien infrieur) de la Grande-Bretagne avalonienne. Selon les vidences disponibles une squencede couverture arnigienne avec, par endroits, du minerai de fer hmatitique deau peu profonde, une arnite quartziqueet de rares calcaires stendaient travers les plate-formes marginales et internes de lAvalon partir de lest de Terre-Neuvejusqu la rgion de Boston au Massachusetts. Cet Arnigien avalonien occidental montre sa plus grande similitudeavec lArnigien de la Bordure galloise (Grande-Bretagne). Des fossiles phosphatiques provenant du bloc montrent unindice daltration thermique beaucoup plus bas que ceux des affleurements avoisinants datant du Palozoque infrieuret portent croire que le bloc provient dune succession avalonienne faiblement chauffe amene la rgion de la baiede Fundy par des failles dcrochantes post-ordoviciennes.

[Traduit par la Rdaction] Landing et al. 730

Can. J. Earth Sci. 40: 715730 (2003) doi: 10.1139/E03-009 2003 NRC Canada

715

Received 8 July 2002. Accepted 20 December 2002. Published on the NRC Research Press Web site at http://cjes.nrc.ca on27 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 ofOklahoma, Norman, OK 73072, U.S.A.

1Corresponding author (e-mail: [email protected]).2Present address: School of Earth and Environmental Sciences, College of Natural Sciences, Seoul National University,

Seoul 151-742, Republic of Korea.


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Introduction

The uppermost PrecambrianOrdovician of southern NewBrunswick is a siliciclastic-dominated cover sequence on thelate Precambrian Avalonian Orogen. Lithostratigraphic andbiostratigraphic reevaluations of the lower Paleozoic in theSaint John region demonstrate its similarity to successions

on the marginal (northwest) platform of the early PaleozoicAvalon continent (i.e., Malignant Cove autochthon, NovaScotia; Placentia Bay, southeast Newfoundland; North Wales;see Landing 1996a; Landing and Westrop 1996, 1998; Westropand Landing 2000; Kim et al. 2002).

A previously unresolved part of the stratigraphic reevaluationof the Saint John region involved the report by Hayes andHowell (1937, p. 109) that the coarse conglomerate at RedHead (Fig. 1) has blocks of a red limestone carrying a faunaof brachiopods and trilobites an assemblage unfamiliar toE.M. Kindle and thought by him to represent an early Paleozoichorizon not yet described. Fossiliferous red limestone isunknown in the early Paleozoic cover sequence in the SaintJohn area (see Landing 1996a). Indeed, the only known red

limestone in the cover sequence on the Avalonian Orogen inthis region is in much older rocks of the sub-trilobitic LowerCambrian at Cradle Brook, 60 km northeast of Saint John(Landing 1996b, fig. 1). Thus, the Red Head limestone hadthe potential to provide new information on the early Paleozoicevolution of Avalon from an apparently unexposed intervalin southern New Brunswick. This study documents the youngestOrdovician rocks and fossils known in southern New Brunswickand suggests the development of comparable shallow-marinefacies in the terminal Arenig of Avalon from easternNewfoundland to southern New England.

Red Head section

Gently north dipping, red fanglomerate that crops out onthe 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 ofTriassic Lepreau Formation (Currie 1983). The fanglomerateforms a low, wave-cut cliff 200 m west of Red Head Roadand 200 m east of Quaternary glaciomarine deposits on thetip of Red Head. The lower 2 m of the section are a weaklycemented boulder fanglomerate with clasts up to 50 cm 50 cm 15 cm. The upper 2 m consist of troughcross-bedded pebble fanglomerate with cobble lenses. Clastsof white marble (Middle Proterozoic Green Head Group),red to black rhyolite, and red granite (Late ProterozoicColdbrook Group and Golden Grove Suite, respectively)

dominate the fanglomerate (see Currie 1987 for a review oflocal Precambrian stratigraphy).

Limestone lithology

A coarse-grained, light red weathering, fossil grainstone isa minor component of both fanglomerate intervals. Althoughmost 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 thinsections show that the red color is limited to a 5 cm thick,weakly limonite impregnated rind of the boulder, and that

the block is a light grey, intraclast-fossil fragment (brachiopodand echinoderm hash dominated) grainstone with scatteredhematite ooids and rare dark green, round (probably glauconitic)grains. The red color may reflect subaerial weathering priorto deposition in the fanglomerate and diagenetic developmentof a ferruginous cement. The limestone is thoroughly winnowedand shows low-angle cross-stratification, which suggest at

least episodic wave or current action.

Faunas

Microfossils, thermal alteration, and paleoecologyA brachiopod- and ostracode-dominated microfauna was

recovered from a 5.5 kg sample that was disaggregated informic acid. Phosphatic remains include conodont elements(Table 1) dominated by Drepanoistodus Lindstrm, 1971and Baltoniodus Lindstrm; high conical pedicle valves froman acrotretid brachiopod (approx. 1000 specimens); and severalsclerites of the agathan fish Anatolepis Bockelie and Fortey,1976. A color alteration index (CAI) of 2.0 for the conodontelements indicates mild alteration at burial temperatures of60140C (see Epstein et al. 1977). By comparison, UpperCambrian lowest Ordovician euconodont elements fromthe Chesley Drive Group on the north side of Saint John harbor(Landing et al. 1978; Landing and Westrop 1998) are dullblack (CAI = 5), which indicates temperatures above 300Cand much deeper burial.

Hematite replacement and internal fills allowed recoveryof many originally calcareous remains. These include 300articulated specimens of two palaeocopid ostracode species;several hundred steinkerns of several snail and bivalve(Lyrodesma? Conrad, 1841) genera; approximately 100 specimensof several orthid brachiopod genera; many crinoid sclerites;and one bryozoan.

The biofacies of the Red Head boulder microfauna is mostsimilar to late Early Middle Ordovician faunas fromcool-water, unrestricted marine facies that are currently bestknown on the Baltic continent. Rasmussen and Stouge (1995)recognized Drepanoistodus- and Baltoniodus-dominatedconodont biofacies as characteristic of open-shelf environmentsin southern Scandinavia, although it should be noted thatthese genera occur worldwide and their elements can beabundant even in successions marginal to tropical carbonateplatforms (e.g., Landing 1976; An 1987; Albanesi 1998).The overall aspect of the Red Head assemblage is mostcomparable to low-diversity benthic faunas in Baltica, withabundant palaeocopides and small orthids as associates ofDrepanoistodus and Baltoniodus (Tolmacheva et al. 2003).

TrilobitesTrilobites are the dominant component of a macrofaunal

assemblage from the boulder which also includes orthidbrachiopods. The association of Neseuretus Hicks, 1873;Nileus, Dalman, 1827; and Stapeleyella Whittard, 1955, isconsistent with the open marine setting suggested earlier forthe associated conodonts and other microfaunal elements.Neseuretus is the eponymous genus of the most proximaltrilobite assemblage in north Gondwanan successions ofSaudi Arabia (Fortey and Morris 1982), and the Neseuretuscommunity is the most inshore trilobite assemblage in the

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Arenig of Avalonian Wales (Fortey and Owens 1987; Forteyand Cocks 1992). Traynors (1988) synthesis of the Arenigof South Wales showed that Neseuretus occurs with orthids,bivalves, and pelmatozoans in wave-dominated (includinghummocky cross-stratified) siltstones and mudstones withsoft-sediment dcollement surfaces at Ramsey Island in thewest (Bates 1969) and in siltstones and mudstones depositedbelow wave base at Carmarthen in the east (Fortey and

Owens 1978). At Carmarthen, trinucleids (i.e., MyttoniaWhittard, 1955) appear just above Neseuretus, with furtherdeepening into graptolite-bearing mudstones (Fortey andOwens 1978; Traynor 1988), although farther west, at Whitland,Stapeleyella appears without Neseuretus higher in the successionin black, graptolitic shales (Fortey and Owens 1987). Asomewhat similar prodeltaic setting with intercalated wave-reworked sandstones and fan-delta debris flows is associated

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Landing et al. 717

Fig. 1. Generalized locality map. (a) Uppermost PrecambrianOrdovician inliers (in black) on the Avalonian Orogen in Maine andeastern 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 SaintJohn 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 PrecambrianOrdovician cover sequence. Modifiedfrom Currie (1987, fig. 1).


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Element No. of specimens

Amorphognathus (Lenodus) variabilis

(Sergeeva, 1963)

Pa 14Pb 31Sa 31Sb 4Sd 3M 8Total 91Amorphognathus (Lenodus) sp. A (Stouge

and Bagnoli, 1990)

Pa 1Total 1Baltoniodus medius (Dzik, 1976)

Pb 1Sb 1Sc 1M 2Total 5Baltoniodus norrlandicus (Lfgren, 1978)

Pa 13Pb 83Sb 13Sd 6M 11Total 126Drepanodus arcuatus Pander, 1856

Arcuatiform 3Oistodiform 7Total 10Drepanoistodus basiovalis (Sergeeva, 1963)

Drepanodiform 130Suberectiform 33Oistodiform 40Total 203Drepanoistodus cf. Drepanoistodus

basiovalis sensu Stouge and Bagnoli

(1990)

Oistodiform 26Total 26Periodon sp.

Sb 3M 1Total 4Phragmodus? sp. aff. Baltoniodus

crassulus (Lindstrm, 1955) sensu Dzik

(1994)

Pa 5Sa 2Sb 1Sc 1Total 9Plectodina? sp.

Sb 5Total 5

Table 1. Conodonts from late MiddleOrdovician limestone boulder at RedHead.

Fig. 2. Uppermost PrecambrianOrdovician in Saint John, NewBrunswick, area (stratigraphic revisions in Landing 1996a and Landingand Westrop 1998) and age of limestone boulder in Triassic LepreauFormation. Stratigraphic column scaled proportional to CambrianOrdovician geochronology (see Tucker and McKerrow 1995 andreviews in Landing et al. 1997, 1998, 2000). The figure shows theOrdovician 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 Chamberlains Brook Formation;Hanf. Brook, Hanford Brook Formation; L. Is., Long Island Member;M.R. Fm., Manuels River Formation; S.M. + S.S., Saint Martins andSomerset Street members; Dep. (or D.) Seq., depositional sequence;Ser. Series; M., Middle; L. Lower; Precam., Precambrian; Cam.,Cambrian; O., Ordovician.


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Landing et al. 719

with the co-occurrence of Neseuretus, Myttonia, and a richbenthic fauna in the roughly coeval Henllan Ash member ofthe Alt Lwyd Formation in North Wales (Whittington 1966;Traynor 1990).

Age and correlation of the fauna

Geographically widespread conodonts allow a relativelyfinely resolved correlation of the Red Head boulder intoBaltica. In this fauna, Amorphognathus (Lenodus) variabilis(Sergeeva, 1963) elements are abundant, with the exceptionof cordylodiform (Sc) elements. All of the elements recognizedin this species by Dzik (1994) and Stouge and Bagnoli (1999)were recovered (Figs. 3a3k). Most of the platforms (Pa) aresmalljuvenile and lack broad lateral extensions on the slightlysinuous processes. The bifid anterolateral process with branchesof approximately equal length on largemature Pa elementsof the species (Stouge and Bagnoli 1999, fig. 4D) is seen inone Pa fragment (Fig. 3c). Amorphognathus (Lenodus) variabilisis the eponymous species of a conodont zone that spans theArenigLlanvirn boundaryinterval in Baltica (Lindstrm1971; Lfgren 1978, 2000) and is recognized in open marinesuccessions in China (e.g., An 1987; Mitchell et al. 1997)and Argentina (Albanesi 1998). The lowest occurrence ofthis species defines the base of the A. variabilis Zone, a horizonin Baltica regarded as the base of the regional Kundan Stage(e.g., Lindstrm 1971; Lfgren 1978; Bagnoli and Stouge1997) or a level slightly higher in the Kundan (Lfgren2000).

Amorphognathus (Lenodus) variabilis ranges through theKundan from upper Arenig into lower Llanvirn equivalentstrata in Baltica (Lfgren 1978). However, associated conodontsindicate that the Red Head boulder represents the lowerA. variabilis Zone. A highly resolved correlation of the RedHead 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 lowestappearance is used as a proxy for, the base of theA. variabilis Zone and is limited to the lower Kundan (Stougeand Bagnoli 1990; Bagnoli and Stouge 1997; Lfgren 2000).In addition, the nomenclaturally problematical form namedPhragmodus? sp. aff. Baltoniodus crassulus (Lindstrm,1955) by Dzik (1994) is biostratigraphically useful, as it hasbeen described from the Kundan of Polish Baltica. The presenceof denticles at the bases of lateral costa in S-series elementsmay distinguish this taxon (Figs. 4n4q) from the older,middle Arenig equivalent Prioniodus crassulus (Lindstrm,1955) sensu Van Wamel (1972) of Sweden.

Other conodonts from Red Head are less useful for

correlation, as they range upward from the Volkovian intothe Kundan. These forms include Drepanoistodus basiovalis(Sergeeva, 1963) (Figs. 4c4i); Drepanodus arcuatus Pander,1856 (Figs. 4l, 4m); and Baltoniodus norrlandicus (Lfgren,1978) (Figs. 3l3u, 3x, 3y) (see Lfgren 1978, 1995, 2000;Stouge and Bagnoli 1990; Bagnoli and Stouge 1997; andTolmacheva 2000 for these species ranges in Baltica). Melements illustrated herein as Drepanoistodus sp. cf.D. basiovalis (Sergeeva) sensu Stouge and Bagnoli (1990)have a shorter oral edge and a weaker or obsolescent innercarina (Figs. 4j, 4k) than corresponding elements inD. basiovalis but may simply be a morphologic variant of

the numerous M elements of D. basiovalis. Two additionalforms are not identifiable to genus or species (Periodon sp.,and Plectodina? sp.; Figs. 3bb3dd, 4a, 4b) and provide littlebiostratigraphic resolution. The remaining conodont recoveredfrom Red Head is Baltoniodus medius (Dzik, 1976) (Figs. 3v,3x, 3z, 3aa), a species considered herein to be a synonym ofBaltoniodus parvidentatus (Sergeeva, 1963) sensu Dzik

(1976) and Baltoniodus clavatus Stouge and Bagnoli, 1990.Baltoniodus medius by this synonymy is stratigraphicallylong-ranging and ranges through uppermost ArenigLlanvirn-equivalent strata in Baltica.

Correlation of the lower A. variabilis Zone and lowerKundan of Baltica is into the ArenigLlanvirn boundary intervalof the Avalon continent (e.g., Bagnoli and Stouge 1997).This boundary has traditionally been equated with the LowerMiddle Ordovician boundary in the cool-water successionsof Avalon. However, recent work on Ordovician interprovincialcorrelations has focused on conodonts and graptolites fromtropical Laurentia, Australia, and South China and now regardsthe LowerMiddle Ordovician boundary as a presentlyundefined 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 carbonateplatforms in China (An 1982) and Argentina (Albanesi 1998)is regarded as Middle Ordovician. Higher strata of the lowerKundan and its terminal Arenig equivalent in Avalon arecorrelated into the lower Darriwilian Stage, the upper of twoglobal stages that compose the Middle Ordovician (Mitchellet al. 1997). This reassessment of the terminal Arenig meansthat the Red Head limestone fauna is upper Middle Ordovician.

A correlation with the Arenig of Avalonian Britain is con-sistent with composition of the trilobite fauna. Stapleyella cf.S. abyfrons is closely comparable to S. abyfrons Fortey andOwens, 1987 from the late Arenig (Fennian) of South Wales.Neseuretus typically occurs in the lower Arenig (MoridunianStage) in Wales (e.g., Fortey and Owens 1987; Beckly 1989)and the Shelve Inlier of Shropshire (Whittard 1960), but asnoted by Fortey and Owens (1978), this reflects the associationof Neseuretus with nearshore facies at the base of atransgressive sequence. Neseuretus parvifrons (MCoy inSedgwick and MCoy 1851), however, is very similar to thespecies described herein and has been reported to rangethrough most of the Arenig in the Mytton Formation of theShelve Inlier (Whittard 1966). The reevaluation by Forteyand Owens (1987, p. 238) of Whittards (1960, 1968) reportsof Neseuretus species from the Mytton Formation led themto confirm the Moridunian occurrence of N. parvifrons andquestionably refer the form from the upper Arenig (Fennian

Stage) to N. parvifrons.The black shales of the Chesley Drive Group at ReversingFalls, about 2 km northwest of Red Head (Fig. 1), have longbeen reported as the youngest Ordovician rock in AvalonianNew Brunswick (Fig. 2). The graptolites and olenid trilobitePeltocare rotundifrons (Matthew, 1892) from Reversing Falls,traditionally regarded as middle Arenig (McLearn 1915; Hayesand Howell 1937), are now known to be significantly olderand of late Tremadoc age (Landing et al. 1997). Thus, thereworked limestone blocks in conglomerates of the TriassicLepreau Formation are the only record of the Arenig in theregion.


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Fig. 3. Upper Arenig conodonts. (ak) Amorphognathus (Lenodus) variabilis (Sergeeva, 1963). ac, Pb elements, oral and lateralviews, NBMG 11083 and 11084, 45, and fragment with bifid lateral process, NBMG 11085, 65; d and e, Pa elements, oral andanterolateral views, NBMG 11086, 75, and NBMG 11087, 55; f, Sb, NBMG 11088, 80; g and i, Sa elements, NBMG 11089 and11090, 80; h, Sd, NBMG 11091, 80; j and k, M elements, NBMG 11092, 75, and NBMG 11093, 65. (lu, w, y) Baltoniodusnorrlandicus (Lfgren, 1978). ln, 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 Paelements, 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, NBMG11106, 100; x, M, NBMG 11107, 90; z, Pb, NBMG 11108, 55; aa, Sc, NBMG 11109, 90. (bbdd) Plectodina? sp. Sb elementsNBMG 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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Discussion

The fauna described herein helps bridge a gap in theAvalonian conodont record between the terminal Cambrian lowest Ordovician (Landing et al. 1978; Rushton 1982) andthe Late Ordovician (Caradoc; e.g., Fortey et al. 2000). Thisis the first recovery of an Arenig conodont fauna from Avalon.This low-diversity Drepanoistodus- and Baltoniodus-dominatedconodont assemblage includes geographically widespread taxa;lacks characteristic carbonate platform taxa like those knownin Laurentia and south China; reflects cool-water, open-marineconditions; but does not provide evidence for Avalons proximity

to other temperate continents, such as Baltica.The trilobite assemblage is more informative paleo-

geographically than the conodont fauna, although Nileus iswidely distributed and occurs, for example, on the Balticcontinent (Nielsen 1995), in deeper water successions aroundthe margins of Laurentia (e.g., Whittington 1965; Fortey1975), and from the Moroccan margin of western Gondwana(Destombes 1970). The recovery of Nileus sp. in this studynow extends the range of this genus to the Avalon continent.More significantly, Stapeleyella has been recorded previouslyonly from Avalonian Britain (Whittard 1955; Fortey and Owens1987).

Cocks and Fortey (1982) emphasized that the ArenigLlanvirn genus Neseuretus was useful in early Paleozoicpaleogeographic reconstructions because it is absent fromsuccessions on the tropical Laurentian and temperate Balticcontinents. Neseuretus, however, is characteristic of high-latitudesuccessions in eastern Newfoundland, Wales, Normandy, Spain,and Saudi Arabia that Cocks and Fortey referred to aGondwanan continent. Subsequent reevaluation (Landing 1996a)has dissected their Gondwana into separate Avalonian andGondwanan continents. This distinction is based on the factthat the uppermost Precambrian lowest Cambrian in Avalon(i.e., southern New Brunswick, eastern Newfoundland, Wales,England) is a cool-water, siliciclastic-dominated successionwith no faunal similarities to the coeval carbonate platformswith evaporites and archaeocyathan faunas in GondwananNormandy, Spain, and Morocco (Landing 1996a). A breakdownof provincial barriers and appearance of shared trilobite generabegan in the late Early Cambrian after the appearance of theoldest trilobites in Avalon (Callavia broeggeri Zone) with adramatic shift of Gondwana into high south latitudes(Theokritoff 1979; Piper 1985) and disappearance of its warmcarbonate-rich successions (e.g., Westrop and Landing 2000;Geyer and Landing 2001). With the late Early Cambrianbreakdown in faunal barriers, trilobite genera, but not species,

Landing et al. 721

Fig. 4. Upper Arenig conodonts. (a, b) Periodon sp., Sb and M elements, NBMG 11114, 95, and NBMG 11115, 75. (ci)Drepanoistodus basiovalis (Sergeeva, 1963). ce, oistodiforms, outer-lateral (NBMG 11116) and inner-lateral (NBMG 11117 and11118) views, 65; f and i, inner-lateral views of symmetrical and subsymmetrical drepanodiforms NBMG 11119 and 11122, 60; gand h, suberectiforms NBMG 11120 and 11121, 65. ( j, k) Drepanoistodus cf. Drepanoistodus basiovalis (Sergeeva) sensu Stouge andBagnoli (1990), oistodiforms NBMG 11123 and 11124, 65. (l, m) Drepanodus arcuatus Pander, 1856, oistodiform (pipaform) andarcuatiform elements NBMG 11125 and 11126, 65. (nq) Phragmodus? aff. Baltoniodus crassulus (Lindstrm, 1955) sensu Dzik(1994). Pa, NBMG 11127, 70; Sb, NBMG 11128, 35; Sc, NBMG 11129, 70; Sa, NBMG 11130, 70.


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are shared into the Late Ordovician between Avalon andGondwana and reflect a combination of similar paleolatitudesand current systems responsible for trilobite dispersal.

Just as regionally extensive lithostratigraphic unitsdemonstrate the unity of Avalon in the latest PrecambrianOrdovician (Landing 1996a, 1996b), recovery of Britishtrilobites (Stapeleyella and Neseuretus cf. parvifrons) in southern

New Brunswick further helps demonstrate that eastern andwestern Avalon were contiguous in the Ordovician and didnot comprise separate continents (e.g., compare McKerrow1988). The recovery of Nileus in New Brunswick merelyshows that this genus was widespread in the Ordovician andthat its range included Laurentia, Baltica, west Gondwana,and the Avalon continents.

Post-Ordovician deformation, uplift, and erosion have led to asituation in which post-Cambrian rocks are poorly representedin the Avalonian cover sequence (see Landing 1996a). Thus,the Red Head boulder is helpful in reconstructing depositionalregimes on the North American part of the Avalon continent.Small areas of lowest Ordovician (Tremadoc) black and darkgray mudstone of the Chesley Drive Group occur in coastal

New Brunswick, Cape Breton Island (Hutchinson 1952), andeastern Newfoundland (Hutchinson 1962). Arenig successions,however, are limited to two small areas in eastern Newfoundlandand northern Nova Scotia.

In eastern Newfoundland, peritidal, wave and tidal currentdeposited quartz arenites, dark mudstones, and oolitic ironores with shallow trace fossils (Cruziana biofacies) of theupper Bell Island Wabana groups (Hayes 1915; Ranger1979; Ranger et al. 1984) are Arenig (Dean and Martin1978). The lithologically similar Ferrona Formation in thenorthern Antigonish Highlands (see Murphy et al. 1979)yields the early Arenig brachiopod Sphaerobolus spissa(Billings, 1872) (Williams 1914; Dean and Martin 1978) andsuggests the lateral persistence of wave and tidal current

dominated sand and sedimentary iron ore deposition intonorthern Nova Scotia (Landing et al. 1980). An attempt atreconstructing Arenig deposition farther southwest faces theproblem of lack of outcrop. The fossil grainstone of the RedHead boulder with its hematite ooids, apparent glauconitegrains, and fauna dominated by orthids, gastropods, and bivalvessuggests an extension of the high-energy, shallow sedimentaryiron 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 lagslike that of the Red Head limestone with limited iron ooidcontent.

A caveat to use of the Red Head block in reconstructingArenig deposition in southern New Brunswick is that thedepositional site of the Red Head limestone is uncertain. Asnoted previously, the low thermal alteration of its conodontand other phosphatic remains, by comparison with thosefrom adjacent lower Paleozoic outcrops, suggests deposition,burial, and thermal alteration at some distance from SaintJohn. Composite movements of nearly 550 km are interpretedto have taken place on dextral transform faults offshore ofSaint John in the Acadian and Hercynian orogenies (Keppie1982). Translation of an essentially thermally unaltered Avalonsuccession into the Bay of Fundy area and its erosion withTriassic rifting and extension may explain the origin of theRed Head boulder. If transcurrent faulting is hypothesized,

there is no way to determine whether this terminal Arenighematitic limestone was deposited on the Avalonian marginalplatform (i.e., a setting comparable to that of the Saint Johnarea or northern Nova Scotia; Landing 1996a) or inner platform(i.e., comparable to that of the Avalon Peninsula andConception Bay in eastern Newfoundland; Landing 1996a).

The most southwesterly occurrence of Arenig deposition

in North American Avalon is recorded in Rhode Island andsouthern Massachusetts. In this region, at least episodicallyhigh-energy depositional regimes are suggested by siliceousquartz arenite pebbles with the brachiopods Lingulobolusaffinnis (Billings, 1872) and S. spissa (Billings, 1872) in UpperCarboniferous conglomerates. The latter brachiopods are alsoknown in the upper Bell Island Group of eastern Newfoundland(see Walcott 1898; Towe 1959).

Only generalized comparisons can be made between thedepositional regimes of Avalonian North America and southernBritain. Arenig successions on the inner platform of SouthWales (Landing 1996a) are dissimilar to the coeval shallow-marine facies of eastern Newfoundland, as they feature aprogressive upward deepening into turbiditic and hemipelagic

mudstones (Traynor 1988). On the marginal platform in NorthWales, lower deltaic and upper tidal siliciclastic facies weredeposited in fault-bounded depocenters adjacent to a developingvolcanic arc. These siliciclastics are locally capped by terminalArenig, wave-dominated hematitic ironstones of the OlchfaMember of the Alt Lwyd Formation, with fragmentarybrachiopod and trilobite remains (Traynor 1990). Althoughpoorly exposed, available descriptions (Cox and Wells 1921;Allen and Jackson 1985) of the Olchfa Member in the Arenigand Bala area suggest a resemblance to the Wabana Groupof eastern Newfoundland. Persistent shallow-shelf depositioncomparable to that of the Arenig of Avalonian North Americais recorded farther east on the inner platform of the Shelvearea of the Welsh Borderlands. Here, transgressive, lowest

Arenig sandstones (Stiperstones Quartzites) are succeededby long-term deposition of wave- and tide-dominated sandstone,siltstone, and mudstone (Mytton Formation), with sandstonelenses appearing in the Tankerville Flags and Shelve ChurchBeds 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) nomen-claturally problematical and biostratigraphically significantare discussed. Westrop and Kim are responsible for the trilobites;the order of their names is arbitrary and does not indicateseniority. Figured specimens are reposited in the NewBrunswick Museum Geology (NBMG) collection.

ConodontsFamily Balognathidae, Hass, 1959, sensu Dzik, 1994Genus Baltoniodus Lindstrm, 1971

TYPE SPECIES: Prioniodus navis Lindstrm, 1955.

DISCUSSION: Taxonomic splitting seems to have led to manynamed species of Baltoniodus. These species have been basedon differences in dentition, presence or relative length of thelateral costa in Sc, or relative curvature of the processes in Selements (compare Dzik 1976, 1994; Lfgren 1978; Stouge


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and Bagnoli 1990). Differentiation of Baltoniodus speciesfrom sites far away from their Swedish and Polish type areasis problematical, particularly as the range of morphologicvariation in their elements is incompletely documented.

Baltoniodus medius (Dzik, 1976)(Figs. 4v, 4x, 4z, 4aa)

SYNONYMY:

Prioniodus alatus parvidentatus (Sergeeva). Dzik, 1976,figs. 22k22r.

Prioniodus alatus medius Dzik, 1976, p. 423, pl. 42, fig. 1,figs. 23a23l.

Prioniodus (Baltoniodus) prevariabilis medius Dzik.Lfgren, 1978, pp. 86, 87, pl. 12, figs. 2736, pl. 13, figs.1A, 1B, 6A6D.

Baltoniodus clavatus Stouge and Bagnoli, 1990, pp. 12,13, pl. 2, figs. 112, pl. 3, figs. 1, 2.

Baltoniodus parvidentatus (Sergeeva). Dzik, 1994,pp. 8082, pl. 18, figs. 814, figs. 13, 14a.

Baltoniodus medius (Dzik). Dzik, 1994, p. 82 (includespartial synonymy).

DISCUSSION: In addition to Baltoniodus norrlandicus (Lfgren1978), a second Baltoniodus species is represented at RedHead by a Pa, an Sc, and a laterally costate Sb element withalternating large and small denticles. The Pa has small denticleson a low anterior process. The lateral costa of Sb is somewhatsmaller than that in B. norrlandicus. Most denticles are brokenoff the posterior process of the Sc, but albid bases of alternatinglarge and small denticles could be seen in this element inreflected light.

This second Baltoniodus form can be referred to any ofthree species of Baltoniodus from the A. (L.) variabilisZone and higher strata in Baltica that also have laterallycostate Sb and alternating large and small denticles. Dzik(1976) described two subspecies ofBaltoniodus alatus Hadding,which he later (Dzik 1994) regarded as the successive speciesB. parvidentatus and B. medius. These species are distin-guished by a somewhat longer and shorter lateral costa,respectively, in Sb. The range of variation in the relativelength of this costa is undocumented and its reliability as ataxonomic character is untested. Consequently, B. parvidentatusand B. medius are considered undifferentiable. A furtherdifficulty is that the appropriate taxonomic name ofB. parvidentatus is problematical. Lfgren (1978) questionedDziks (1976) assignment of the form species Fallodusparvidentatus as the M element of multielement Prioniodusalatus parvidentatus or P. a. medius. Alternatively, Stougeand Bagnoli (1990) regarded F. parvidentatus as the M elementof Trapezognathus quadrangulum Lindstrm, 1955, but didnot base this on apparatus reconstructions using topotypecollections with F. parvidentatus. Although assignment oftopotype F. parvidentatus to a multielement balognathid speciesis unresolved, Viiras (1974, pl. 6, figs. 1417, figs. 96, 97)illustrations of this form species are comparable to the Melements assigned by Dzik (1976, 1994) and Lfgren (1978)to B. parvidentatus and B. medius. One oistodiform fromRed Head resembles some of Viiras (fig. 97j) specimens ofF. parvidentatus and is tentatively assigned to B. medius.

A third Baltoniodus species with reduced anterior costa inSb and irregular dentition is also named from the Kundan.

Baltoniodus clavatus Stouge and Bagnoli, 1990, first describedfrom somewhat older strata of the lower but not lowermostA. (L.) variabilis Zone, has elements fully comparable tothose illustrated by Lfgren (1978) for B. medius. The latterspecies even seems to show B. clavatus diagnostic slightlyupturned posterior process in Pa (Stouge and Bagnoli 1990;compare Lfgren 1978, pl. 12, fig. 29) and does not seem

differentiable from B. clavatus. The circle of taxonomic un-certainty for the appropriate names for Kundan Baltoniodus iscompleted with Stouge and Bagnolis (1990) synonymizationof B. clavatus with B. parvidentatus sensu Dzik (1976,1994) and their belief that the latters name is inappropriate,as its apparatus did not contain F. parvidentatus as an Melement. The synonomy of B. medius with B. clavatus andB. parvidentatus suggested herein means that B. medius is along-ranging (upper ArenigLlanvirn) taxon.

TrilobitesFamily Calymenidae Milne-Edwards, 1840Subfamily Reedocalymeninae Hup, 1955Genus Neseuretus Hicks, 1873

TYPE SPECIES: Neseuretus ramseyensis Hicks, 1873, from theArenig of Ramsey Island, Wales (subsequent designation byVogdes (1925)).

Neseuretus cf. Neseuretus parvifrons (MCoy in Sedgwickand MCoy 1851)

(Figs. 5a5h)

SYNONYMY:

cf. Neseuretus parvifrons (Salter), Whittard 1960, p. 142,pl. 19, figs. 16 (for synonymy; see Whittington 1966,p. 501 for discussion of authorship of this species).

cf. Neseuretus parvifrons (MCoy in Sedgwick and MCoy1851), Whittington 1966, p. 500, pl. 4, figs. 113, pl. 5, figs.

110.cf. Neseuretus parvifrons (MCoy in Sedgwick and MCoy),Bates 1969, p. 26, pl. 9, figs. 4, 5, 7, 9, 10, 1216.

MATERIAL: Ten cranidia, two pygidia, and six librigenae.

DISCUSSION: The gently inflated, long preglabellar fields, poorlydefined anterior borders, and weakly arched anterior marginsof the cranidia from New Brunswick are most similar tothose ofN. parvifrons (MCoy in Sedgwick and MCoy 1851)from the Arenig of Wales (Bates 1969, pl. 9, figs. 5, 16;Whittington 1966, pl. 4, figs. 18) and the Shelve Inlier ofShropshire (Whittard 1960, pl. 19, figs. 5, 6). The Red Headpygidia, however, have a relatively longer axis, wider pleuralregion, and a more conical terminal piece. The type speciesN. ramseyensis, from the Arenig of South Wales (Bates 1969,pl. 8, figs. 312, pl. 9, figs 13, 6; Fortey and Owens 1987,figs. 97a97g), has a pygidial axis with eight or nine axialrings, whereas N. cf. N. parvifrons has an axis of five ringsand a terminal piece. Among other species from AvalonianBritain, Neseuretus monensis (Shirley, 1936; see Beckly 1989,figs. 12a12h) and Neseuretus caerhunensis Beckly (1989,figs. 13, 14) from the Arenig of North Wales have moreposteriorly 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. 610),

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South Wales (Fortey and Owens 1987, figs. 98a98e), andNorth Wales (Bates 1969, pl. 9, figs. 8, 11) and Neseuretusbrevisulcus Whittard (1960, pl. 19, figs. 714) from the ShelveInlier both have well-defined, convex anterior borders. Theformer has narrower fixigenae than N. cf. N. parvifrons,whereas the latter has a distinctive, strongly tapered pygidialaxis (Whittard 1960, pl. 20, fig. 3). Lastly, Neseuretuscomplanatus Whittard (1960, pl. 20, figs. 4, 5) is based on a

single specimen with a flattened lateral profile, but as notedby Fortey and Owens (1987, p. 240), it is difficult to determinethe extent to which this feature is influenced by deformation.

The only other Neseuretus species from Avalonian NorthAmerica is Neseuretus vaningeni Dean in Dean and Martin(1978, pl. 4, pl. 5, figs. 13), which is based on a singlecompletely articulated exoskeleton. This species is separatedreadily from N. cf. N. parvifrons by its shorter frontal area

Fig. 5. Upper Arenig trilobites. (ah) Neseuretus cf. Neseuretus parvifrons (MCoy in Sedgwick and MCoy, 1851). a, pygidium, dorsalview, NBMG 11989, 3; b, pygidium, dorsal view, NBMG 11990, 7; c and d, cranidium, anterior-oblique and dorsal views, NBMG11991, 5; e, librigena, dorsal view, NBMG 11992, 4; f, g, and h, cranidium, dorsal, anterior-oblique, and anterior views, NBMG11993, 4. (im) 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.


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and a relatively shorter and wider glabella. The pygidium ofN. vaningeni has four axial rings plus a terminal piece (Deanand Martin 1978, pl. 4, figs. 2, 3, pl. 5, fig. 3), whereas thepygidium ofN. cf. N. parvifrons (Figs. 5a, 5b) has five ringsand a terminal piece.

Numerous additional species of Neseuretus have beenreported from other regions, including France, Spain, Saudi

Arabia, South America, and China (see Fortey and Morris1982, and Rbano 1990 for discussion), but many are basedon limited material (e.g., Lu 1975; Chang and Jell 1983).Neseuretus tristani (Desmarest, 1817) is among the bestknown and most widespread, as it is recorded from SaudiArabia (Fortey and Morris 1982), England (Sadler 1974),France (Henry 1980), and Spain (Hammann 1983). This specieshas a strongly arched anterior cranidial margin and a steeplyupturned frontal area (Fortey and Morris 1982, figs. 3a3c;Hammann 1983, pl. 6, figs. 62, 63; Henry 1980, pl. 10,figs. 1a, 1b) that contrasts with the weakly arched marginand gently inflated frontal area of N. cf. N. parvifrons.

Family Nileidae Angelin, 1854

Genus Nileus Dalman, 1827

TYPE SPECIES: Asaphus (Nileus) armadillo Dalman, 1827, fromthe lower Holen Limestone (upper Arenig; see Mnsson 1995)of stergtland, Sweden (by subsequent designation of Hawleand Corda 1847).

Nileus sp. indet.(Figs. 5i5m)

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 cranidiais a well-developed, pitted sculpture that is matched only inNileus porosus Fortey (1975, pl. 12, figs. 114) and Nileus?lacunosa Whittington (1965, pl. 36, figs. 110). Comparisonsare difficult because of their small size, but the cranidiaillustrated herein (Figs. 5i, 5k, 5l) differ from those of N.porosus in having palpebral lobes that are more posteriorlylocated. The associated pygidia (Figs. 5j, 5m) lack the well-rounded anterior corners of similarly sized pygidia of N.porosus (e.g., Fortey 1975, pl. 12, figs. 8, 10, 13, 14). CranidiaofN.? lacunosa are more comparable in size to our specimens,which differ in having more divergent anterior branches ofthe facial sutures and a relatively longer area of the cranidiumin front of the palpebral lobes. The pygidium tentativelyattributed to N. ? lacunosa (Whittington 1965, pl. 32, figs. 8,11) has a well-defined border that is not present on thelarger pygidia illustrated herein.

Other species ofNileus have cranidia with smooth surfaces,weak terrace ridges, or minute pits that are not usually evidentin photographs (e.g., see Whittington 1965; Schrank 1972;Fortey 1975; Lu 1975; Nielsen 1995). The pygidia from RedHead lack borders and have weakly rounded anterior corners(e.g., Fig. 6j). In these respects, they resemble those of Nileuslatifrons Nielsen (1995, figs. 157L, 158A) from the KomstadLimestone Formation of southern Scandinavia. Associatedsmall cranidia (Nielsen 1995, figs. 153G, 153H, 153L, 154D)lack pits. A variety of other species of Nileus are separablefrom our pygida by possession of well-defined borders and

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. 24; Nielsen 1995, figs. 148M148O,149D149M, 165H165J, 170H, 170I, 170K170P, 184,196A196L, 202A202H, 207A202C).

Family Trinucleidae Hawle and Corda, 1847Subfamily Trinucleinae Hawle and Corda, 1847Genus Stapeleyella Whittard, 1955

TYPE SPECIES: Stapeleyella inconstans Whittard, 1955, fromthe Hope Shales Formation of the Shelve District, Shropshire,England (by original designation).

DISCUSSION: Hughes et al. (1975, pl. 2, fig. 28) illustrated anunnamed species from North Wales that combined featuresof the two genera Bergamia Whittard, 1955, and StapeleyellaWhittard, 1955. As in Bergamia, it has a relatively narrowfringe with two pit arcs (E1, E2) exterior to the girder, butalso possesses interradial rows of pits in the E2 arc and thusresembles Stapeleyella. Hughes et al. followed Whittard (1955)in considering an E3 pit arc to be a diagnostic feature ofStapeleyella, and in the absence of this feature they questionablyassigned their species to Bergamia. More recently, Forteyand Owens (1987) modified the diagnosis of Stapeleyella toaccommodate another species, S. abyfrons Fortey and Owens,1987, which has a narrow fringe with E1 and E2 arcs thatinclude interradial pits. As redefined by them, Stapeleyellaincludes all species in which the presence of interradial pitsresults in crude to well-developed, Y-shaped branching patternsof the interradial ridges, regardless of the number of E arcsthat are developed. A minimum of two E arcs are present,but E3 or even E4 may be developed in some species. TheFortey and Owens (1987) concept of Stapeleyella is followed

herein.Stapeleyella cf. Stapeleyella abyfrons Fortey and Owens,

1987(Figs. 6, 7)

SYNONYMY:

Stapeleyella abyfrons Fortey and Owens, 1987, p. 213,figs. 79a79h (includes synonymy).

MATERIAL: Twenty-eight cranidia, 11 pygidia, and one incompletelower lamella.

DESCRIPTION: Cranidium semicircular in outline, length 4350%of width. Glabella elongate, expands forward, with stronglyconvex, subspherical pseudofrontal lobe; axial furrows firmlyimpressed. Three pairs of short, shallow lateral glabellar furrowspresent. Occipital ring nearly transverse medially but curvedgently forward near axial furrow; occipital furrow well-incised.Bacculae weakly convex and triangular in outline; well-definedin smaller individuals (Fig. 6d), but may be obsolescent onlarger specimens (Figs. 6a, 6m). Fringe approximately 25%of cranidial length at anterior but becomes reduced in widthtowards posterior corner of cranidium. Pit rows separated bylow interradial ridges. Pit distribution highly variable with atleast 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. (ar) Stapeleyella cf. Stapeleyella abyfrons Fortey and Owens, 1987. a and b, cranidium, dorsal andanterior-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 andanterior views, NBMG 12004 11; m, cranidium, dorsal view, NBMG 12205, 12; n, cranidium, dorsal view, NBMG 12006, 11; oand p, cranidium, lateral and dorsal views, NBMG 12007, 12; q, pygidium, dorsal view, NBMG 12008, 12; r, cranidium, dorsalview, NBMG 12009, 12.


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Landing et al. 727

into single row of twin pits (Fig. 6k) or enlarged pits (Fig. 6n)posterior to row 7. At least two I arcs present anteriorly, becomemerged 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 e1e2 accessory pits usually presentin R0 and interradii i, ii, and viii. Between accessory pits,low interradial ridges show Y-shaped branching pattern. Genalregion gently convex and depressed well below the level ofthe glabella in small individuals (Figs. 6c, 6o), but moreinflated in larger cranidia (Fig. 6b). Posterior border furrowdeep, straight to sigmoidal, and terminates at posterior fossula.Posterior border widens laterally. Finely reticulate sculptureon surfaces of glabella and genae; internal molds smooth.

Pygidium subtriangular in outline, length approximately33% of width. Axis convex, conical, extends back to innermargin of border; axial furrows shallow. Three clearly definedaxial rings and terminal piece present; ring furrows deeplyetched at anterior end of axis, but become increasingly shallowtowards rear. Pleural fields broad, with three gently convexpleural ribs separated by shallow pleural furrows. Pleuralfurrows sigmoid, parallel each other, become indistinct towardsborder. Border slopes nearly vertically downward and increasesslightly in height towards anterior corner of pygidium.

Discussion

In possessing fringes with accessory pits in some interradiiand, consequently, an irregular, Y-shaped branching patternof some of the interradial ridges (Figs. 6k, 6m, 7), the cranidiaillustrated herein closely resemble those of some of the earlyspecies of Stapeleyella, especially S. abyfrons Fortey andOwens (1987, figs. 79a79h) from the Pontyfenni Formation(Arenig) of South Wales. As in the material from NewBrunswick, S. abyfrons has 16 radii per half-fringe, completeE1, E2, In, and I1 arcs, and e pits in only a few interradii. TheRed Head cranidia appear to differ in having an I 2 arc in atleast some individuals. Pygidia of S. abyfrons possess deeppleural furrows (see Fortey and Owens 1987, figs. 79b, 79d,79f) that are not present on our specimens (Figs. 6j, 6q). Thesclerites from Red Head almost certainly represent a newspecies, but in view of the incomplete nature of all availablecranidia and lower lamellae, they are left in open nomenclature.

The undescribed species of Stapeleyella illustrated by Hugheset al. (1975, p. 558, pl. 2, fig. 28) can be differentiated fromS. cf. S. abyfrons by possession only of e2 accessory pits inthe interradii. Stapleyella inconstans Whittard, 1955 (pl. 4,figs. 713; Fortey and Owens 1987, fig. 78), the type species,and S. murchisoni Whittard (1955, pl. 5, figs. 7, 8) havethree or even four pit-arcs exterior to the girder, whereas S.

cf. abyfrons has only two.

Acknowledgments

Support from National Science Foundation grantEAR98-05177 (to EL), Natural Sciences and EngineeringResearch Council of Canada grant 41197 (to SRW, held atBrock University), and Korean Research Foundation grantKRF-99-D042 and the BK 21 Project (to DHK) is gratefullyacknowledged. W.A. Samsonoff provided access to scanningmicroscopy at the Wadsworth Center for Laboratories, NewYork State Health Department. L. Van Aller Hernick pickedthe Red Head microfossils. R.M. Owens and B.R. Pratt arethanked for manuscript reviews.

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