Lower Ordovician (Ibexian) trilobites from the Tribes ...

1618

Lower Ordovician (Ibexian) trilobites from the Tribes Hill Formation, central Mohawk Valley, New York State STEPHEN

R.

WESTROP AND LEANNE

A.

KNOX

Department of Earth Sciences, Brock University, St. Catharines, ON L2S 3A1, Canada AND ED LANDING

New York State Geological Survey, State Education Department, Albany, NY 12230, U.S.A.

Received February 19, 1993

Revision accepted June 30, 1993

The Early Ordovician Tribes Hill Formation of east-central New York State is a sequence of peritidal to subtidal carbonates and minor shales that rests disconformably on Late Cambrian carbonates and is , in turn, succeeded disconformably by Middle Ordovician strata . More than 800 trilobites from 24 coI\ections are assigned to six species: Bellefontia gyracantha (Raymond), Clelandia parabola (Cleland), Hystricurus ellipticus (Cleland), Hystri curus cf. Hystricurus oculilunatus Ross, Symphysurina convexa (Cleland), and Symphysurina cf. Symphysurina woosteri Ulrich. Two distinct biofacies are present: the Bellefontia Biofacies in subtidal shales with thin, storm-generated bioclastic interbeds, and the Gastropod - rostroconch Biofacies in shallow, carbonate bank lithofacies . The trilobites of the Tribes Hill Formation are assigned to a single, informal biostrati­ graphic unit, the Clelandia parabola Fauna, which is correlative with trilobite Zone B of the Garden City Formation of Utah and with the Bellefontia franklinense Subzone of the McKenzie Hill Formation of Oklahoma. La Formation de Tribes Hill, d'age ordovicien precoce, de l'est-central de J'Etat de New-York est une sequence form ee de carbonates peritidaux a subtidaux et de shales, qui repose en discordance sur Jes carbonates d'age cambrien tardif, et qui est, a son tour, surmontee avec discordance pdf des strates de l'Ordovicien moyen. Plus de 800 trilobites, provenant de 24 collections, sont ass ignes a six especes : Bellefontia gyracantha (Raymond), Clelandia parabola (Cleland), Hystricurus ellipticus (Cleland), Hystricurus cf. Hystricurus oculilunatus Ross, Symphysurina convexa (Cleland) et Symphysurina cf. Symphysurina woosteri Ulrich. Deux biofacies distincts sont presents: Ie Biofacies a Bellefontia dans les shales subtidaux incluant de minces interlits bioclastiques de tempestites, et Ie Biofacies a gastropodes - rostroconchia dans Ie lithofacies de banes de carbonates de faible profondeur. Les trilobites de la Formation de Tribes Hill sont assignes a une seule unite biostratigraphique infor­ melle, la Faune a Clelarulia parabola, est mise en correlation avec la Zone B a trilobites de la Formation de Garden City de I'Utah et avec la Sous-zone a Bellefontia franklinens e de la Format ion de McKenzie Hill de l'Oklahoma. [Traduit par la redaction) Con. 1. Earth Sc i. 30. 161 8 -1633 (1993)

Introduction The trilobite fauna of the Tribes Hill Formation of New York State was first described by Cleland (1900, 1903), but only a single species, Clelandia parabola (Cleland), has been the subject of a modem systematic treatment (Norford 1969). Fisher (1954) illustrated a few specimens and described the general stratigraphic distribution of Cleland's species, but the fauna was all but ignored in the studies of sequences in the western (Ross 1951 ; Hintze 1953) and southern (Stitt 1977, 1983) United States which laid the foundations of North American Lower Ordovician trilobite biostratigraphy. Here, we revise the trilo­ bites of the Tribes Hill Formation using new collections from' stratigraphic sections at five localities (Fig . 1) and document their abundance and distribution patterns. A subseqdent paper (Landing et a!. I) will deal with the stratigraphy of t e Tribes Hill Formation and its conodont fauna. The Early to Middle Ordovician was a critical perlod in the evolution of marine benthic communities, during wpich new community types became established (Sepkoski and Sheehan 1983; Sepkoski and Miller 1985). Trilobites became less important components of paleocommunities that w J re domi­ nated by articulate brachiopods and, in nearshore h+itats, by molluscs. The community replacements were apparently dia­ chronous, with "archaic" trilobite-rich assemblages persisting for longer in deeper water sites (Sepkoski and shee1 an 1983; IE. Landing, S.R . Westrop, L.A. Knox . Lower Ordovician stratigraphy and conodont faunas of New York State. In preparation. Pri nled in CJn:H.1:i , Imprimc au Canada

Sepkoski and Miller 1985). However, details of this change­ over remain obscure, partly because of the lack of detailed information on Lower Ordovician paleocommunities. The large collections assembled during the course of this study enable an evaluation of the paleocommunities of the Tribes Hill Forma­ tion to be made.

Stratigraphic setting Outcropping in a narrow belt in the central Mohawk Valley, the Tribes Hill Formation (Ulrich and Cushing 1910) records predominantly carbonate sedimentation in a shallow shelf set­ ting (Braun and Friedman 1969). Fisher (1954) divided the Tribes Hill into four members that lay disconformably above the Late Cambrian Little Falls Dolomite and that were in turn succeeded by two dolostone units, the Chucktanunda Creek and Cranesville formations. In subsequent work , Fisher (1980) reduced the Chucktanunda Creek and Cranesville formations to member status within an expanded Tribes Hill Formation. We found Fisher's nomenclature difficult to apply consistently in the field and, in this paper, we simply recognized an undivided Tribes Hill Formation as a disconformity-bound sequence between the underlying Little Falls Dolomite and the Black River or Trenton groups above.

Faunal associations Two recurrent, lithofacies-related faunal aSSOCiatIOns are present in the Tribes Hill Formation. Gastropods and rostro­ conchs are common elements in bioclastic - intraclastic pack-

16 19

WESTROP ET AL.

- ____ -1j.:2Q~_2~LTO~~_ MONTGOMERY CO.

FIG. 1. Map showing location of measured sections. CCr, Canajoharie Creek (locality 9 , Fisher 1980); FC, Flat Creek (locality 11, Fisher 1980); BR , Van Wie Creek at Borden Road (locality 13, Fisher 1980); NY67, quarry on New York Highway 67 (locality 14, Fisher 1980); ARC , road cut on New York Highway 5, Amsterdam (locality 16, Fisher 1980).

Gastropod - rostroconch Biofacies

8el/efontia Biofacies CCr 5.7 NY6712.85 SR 1.35 N=72 N= 52 N = 125

ARC 2.8 N=57

ARC 2.5 N=30

FC 24 N=82

ARC 1.65 N=61

ARC 5.75 CCr 10.6 N=114 N=60

FC 30.7 N = 75

SR 8.7 N= 108

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60

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o FIG . 2 . Collections may be divided into two intergrading biofacies based on relative abundances (percent) of dominant taxa. The abundance of each trilobite genus in each sample was expressed as the number of the most common sclerite type (in all cases, either cranidia or pygidia), rather than the combined total of all sclerites . The Bellefontia Biofacies is dominated by the eponymous genus, with Clelandia ranked second; rostroconchs and molluscs are very rare or absent. Gastropods and rostroconchs are a conspicuous element of the other biofacies; Bellefontia is rare or absent, and Clelandia is the dominant trilobite genus.

stones, grainstones, and rudstones that were associated with intervals of bioturbated lime mudstones and wackestones in the upper part of the formation. However, these molluscs were very rare in bioclastic - intraclastic packstones and rudstones from a shaly interval in the middle of the formation, which contained abundant sclerites of the trilobite Bellefontia. Relative abundances of taxa in 11 large collections form an intergrading series from those dominated by Bellefontia to those dominated by gastropods and rostroconchs (Fig. 2). This continuum was somewhat arbitrarily divided into two biofacies: the Bellefontia and Gastropod - rostroconch biofacies. Bellefontia Biofacies Seven collections are assigned to the Bellefontia Biofacies and are dominated by the eponymous genus, with Clelandia ranked second. The gastropods Ophilita, Bucanella, and Raphistomina are very rare elements, as is the trilobite genus Hystricurus. Total diversity is low, ranging from two to five species, with an average of three. Apart from one collection

from the upper carbonate sequence (CCr 5.7; Fig. 2), all occur­ rences of the Bellefontia Biofacies are from a thin, regionally correlative interval of shales, bioclastic packstones and rud­ stones, and intrac1astic packstones and rudstones.

Gastropod - rostroconch Biofacies Four mollusc-rich collections from the upper carbonate sequence are dominated by gastropods, especially Ophilita and Raphistomina; the rostroconch Riberia is a persistent but less important associate. Clelandia and, to a lesser extent, Hystri­ curus are the most important trilobite genera present, and Bellefontia is rare or absent from all but one collection . The articulate brachiopod Finkelnburgia occurs as a minor compo­ nent ( < 5 %) in most collections. Diversity is slightly higher than the Bellefontia Biofacies, with five to six species per collection. Discussion Some taphonomic sorting is evident in collections from the Bellefontia Biofacies, all of which show a marked enrichment

CAN. 1. EARTH SCI. VOL. 30, 1993

1620

Quarry on NY67

Bellefontla gyracantha: relative abundances of cranidia and pygidia

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Pygidial length (mm) FIG. l1. Reduced major axis regression of pygidial dimensions of Bellefonlia gyracantha . (A) Pygidial width vs. pygidial length. (B) Axis length vs . pygidial length.

surfaces. Ill-defined , roughly transverse pleural bands separated by very shallow pleural furrows may be present on parietal sur­ faces. Border is gently concave and occupies about one-fifth of pygidial length . Inner margin of pygidial doublure forms smooth curve that is interrupted by short embayment beneath posterior tip of axis, lateral margins of which are formed by small triangular projections . External surface is smooth, except for terrace ridges along pygidial margin, doublure, and on articulating facet.

Remarks In previous work (Raymond 1910; Fisher 1954), this species was assigned to the genus Asaphellus Callaway. However, the recent reevaluation of the type species of Asaphellus, A. homfreyi (Salter), by Fortey and Owens (1991, figs. 31-3u, 7a -7g, 8a, and 8b) indicates that there are few similarities with B. gyracantha other than effacement. Asaphellus homfreyi differs by possessing smaller, more anteriorly positioned pal­ pebrallobes and, consequently , much longer (exsag.) posterior

fixed cheeks . The facial sutures of A. holmfreyi proceed back­ wards along a curved course, whereas those of B. gyracantha follow a straight path (PI. 2, fig. 3). The anterior cranidial margin of B. gyracanlha is a smooth curve (PI. 2, figs. 1 and 3 -7), whereas A. homfreyi has a small triangular apex mark­ ing the junction of the anterior branches of the facial sutures (e.g., see Fortey and Owens 1991, fig. 31) . The median glabeUar tubercle of A. homfreyi is located well behind the level of the palpebral lobes but lies between the palpebral lobes in B. gyracanlha (PI. 2 , figs. 1 and 3) . Finally, the hypostome of B. gyracanlha is sub rectangular with narrow borders (PI. 2, fig. 8), whereas that of A. homfreyi is elliptical in outline and has broad borders (Fortey and Owens 1991, fig . 7f). Boyce (1989) placed B. gyracantha in his new genus, Randaynia, which he regarded as closely comparable to Belle­ jonlia. However, similarities between these genera seem to be related to effacement, and Randaynia is different from B. gyracantha and other species of Belle/ontia. In particular , Randaynia has a parallel-sided glabella that is evenly rounded

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CAN. J. EARTH SCI. VOL. 3D, 1993

PLATE

3

All from the Tribes Hill Quarry "lower bed" (Fisher 1952). All x9 except (8), which is x7. FIGS. 1-9, Hystricurus ellipticus (Cleland). (1, 2) Cranidium (T (testate material)), NYSM 15224, (3, 4) Cranidium (T), NYSM 15225. (5,6) Cranidium (T), NYSM 15226. (7) Cranidium (T), NYSM 15227. (8) Pygidium (E (exfoliated material)), NYSM 15228. (9) Pygidium (T), NYSM 15229. FIGS. 10-12. Hystricurus cf

H. oculiluna/us Ross . (10,12) Cranidium (T), NYSM 15230. (11) Pygidium (T), NYSM 15331.

WESTRO? ET AL.

anteriorly, long palpebral lobes, and a broadly based genal spine (Boyce 1989, PI. 36, figs. 5-9, PI. 38, figs. 1-3) which, although not characteristic of Bellefontia, are matched in bath­ yurellines such as Uromystrum (Boyce 1989, PI. 33, figs. 7­ 10). Pygidia attributed to Uromystrum (see Boyce 1989, PI. 34, fig. 5) compare favourably to those of Randaynia (Boyce 1989, PI. 37, figs . 1-10, PI. 38, figs. 8-11), differing only in their greater degree of effacement. Thus, we regard Randaynia as a bathyurelline genus that is most closely related to Uromystrum. Pygidia from the McKenzie Hill Formation of southern Oklahoma which were identified by Stitt (1983, PI. 3, fig. 9) as Parabellafontia? sp.indet. fall within the range of varia­ tion of those of B. gyracantha and are probably conspecific. However, a final decision must await the discovery of cranidia. Similarly, we regard fragmentary pygidia and free cheeks from the Beekmantown of New Jersey (Weller 1903, PI. 5, figs. 5 and 6) that were included in B. gyracantha by Raymond (1910) as inadequate for a confident identification. T he effacement of the axial furrows on testate surfaces, even in small individuals, separates B. gyracantha from all other members of the genus except Bellefontia cocinna (Hintze 1953, PI. 3, figs. 1 - 8). However, this species lacks an anterior border and the genal spines are lost in large holaspids . Belle­ fontia gyracantha also differs from B. franklinense (Ross 1951, PI. 24, figs. 10 and 14, PI. 25, figs. 1-5; Stitt 1983, PI. 3, figs . 1, 2, 4, and 5) and B. acuminiferentis Ross (1951, PI. 24, fig. 18, PI. 25, figs. 6-9) in having a very short anterior border and in lacking a median pygidial spine. Bellefontia ibexensis Hintze (1953, PI. 4, figs. 1, 3, 5a , 5b, and 8) and B. chamberlaini Clark (Ross 1951, PI. 25, figs. 10-15; Hintze 1953, PI. 4, figs. 13a and 13b; Stitt 1983, PI. 3, figs. 4 and 5) both differ from B. gyracantha in having broader pygidial borders and doublures, and firmly impressed border furrows. ORDER Proetida

Hystricuridae Hupe, 1953

Hystricurus Raymond, 1913

FAMILY GENUS

Type species Bathyurus conicus Billings, 1859 from the Beekmantown Group at St. Timothy, Quebec (by original designation). Hystricurus ellipticus (Cleland, 1900) (PI. 3, figs. 1-9) Synonymy 1900 Bathyurus ellipticus Cleland, p. 17, PI. 16, figs. 5 and 6. 1954 Hystricurus ellipticus, Fisher, PI. 4, figs. 12 and 13. Holotype A cranidium (PRI 5073) from the Tribes Hill Formation, New York State, illustrated by Fisher (1954, PI. 4, fig. 12). Diagnosis A species of Hystricurus with a strongly convex, subovoid glabella outlined by deep axial furrows; lateral glabellar furrows are represented only by smooth areas on sides of glabella. Frontal area is subequally divided into gently inflated pre­ glabellar field and slightly longer, convex anterior border.

1631

12.85, 17.8; Tribes Hill Quarry "lower bed " and "upper bed" (Fisher 1952). Description Strongly convex glabella is subovoid in outline, with width equal to four-fifths of length and occupies two-thirds of cranidial length; axial, preglabellar furrow and occipital furrows are deeply incised. Lateral glabellar furrows are represented only by smooth areas on sides of glabella. Fixed cheeks are convex and are equal to two-fifths of glabellar width at glabellar mid­ length. Palpebral lobes are large, crescentic, and equal to half of glabellar length; midpoint is opposite glabellar mid-length. Frontal area is subequally divided into gently inflated pre­ glabellar field and slightly longer, convex anterior border by firmly impressed border furrow. Posterior border is separated from cheek by deep border furrow. Anterior branches of facial suture diverge gradually before swinging abruptly upward along anterior cranidial margin. Posterior branches diverge abruptly backwards. External surface of cranidium carries prosopon of coarse tubercles that may be poorly defined on parietal surfaces. Pygidium is semielliptical in outline. Convex axis occupies one-third of pygidial width and is outlined by well-defined axial furrows; deep, roughly transverse ring furrows separate three axial rings and terminal piece . Pleural fields are weakly inflated. They are crossed by finely etched pleural furrows that define three pairs of pleurae that are subequally divided by deep pleural furrows. Border forms narrow rim. External and parietal surfaces carry fine and coarse tubercles. Remarks Among more than 20 previously described species of Hys­ tricurus (see Poulsen 1927, 1937; Ross 1951; Hintze 1953; Stitt 1983; Fortey 1983; Boyce 1989; Fortey and Peel 1989), only H. hillyardensis Stitt (1983, PI. 4, figs. 3 - 6) and H. globosus Stitt (1983, PI. 5, figs . 1-6) are comparable to H. ellipticus in glabellar outline and convexity. Cranidia of H. hillyardensis from Oklahoma (Stitt 1983, PI. 4, figs . 3 and 4) and Utah (identified by Ross (1951, PI. 9, figs . 35,36, and 38-41) as Hystricurus sp. D; see Stitt 1983, p. 25) differ from H. ellipticus in lacking palpebral ridges and in possessing shorter , less con­ vex anterior borders. Cranidia of H. globosus (see Stitt 1983, PI. 5, figs. 1 and 2) are separated readily from those of H. ellipticus on the basis of their short, weakly convex anterior borders that are poorly differentiated from the much longer pregJabellar fields. Hystricurus cf. H. oculilunatus Ross, 1951 (PI. 3, figs. 10 - 19) Synonymy 1900 Bathyurus sp. (?) Cleland, p. 17, PI. 16, fig. 9. 1951 Hystricurus oculilunatus Ross, p. 47, PI. 10, figs. 1-3, 5, 8, 9, and 12. 1989 Hystn'curus oculilunatus, Boyce, p. 38, PI. 8, figs. 1 - 8, PI. 9, figs. 1-10, PI. 10, figs. 1-10, PI. 11, figs. 1-13 (see for synonymy). Material One illustrated cranidium (NYSM 15230) and one illustrated pygidium (NYSM 15231); plus five cranidia.

Material Four illustrated cranidia (NYSM 15224, 15225, 15226, 15227) and two illustrated pygidia (NYSM 15228, 15229) ; plus 81 cranidia and 9 pygidia.

Occurrence Tribes Hill Formation, New York State, "lower bed," Tribes Hill Quarry (Fisher 1952).

Occurrence

Discussion

Tribes Hill Formation, New York State, collections ARC 2.8 ; BR 8.7; CCr 5.7, 8.06,9.1, 10.6; FC 30.7,31.35; NY67

Hystricurus cf. H. oculilunatus resembles H. oculilunatus Ross (1951, pp. 47-48, PI. 10, figs. 1-3,5,8,9, and 12 ;

CAN. 1. EARTH SCI. VOL. 3D, 1993

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Boyce 1989, pp. 38-40, PIs. 8-11) in its bluntly rounded anterior glabellar margin, steeply downsloping preglabellar field, broad, nontuberculate anterior margin, and narrow pre­ glabellar furrow. More material will be required for a confi­ dent identification. Hystncurns cf. H. oculilunatus is separable from co-occurring cranidia of H. ellipticus on the basis of the longer preglabellar field, less convex glabella, and a prosopon of large and small tubercles, augmented by terrace ridges on the anterior border.

Acknowledgments This paper is an expanded and revised version of a B.Sc. honours thesis by Knox, supervised by Westrop. Funding was provided by Natural Sciences and Engineering Research Council of Canada operating grant 41197 to Westrop and by the New York State Geological Survey. We thank Rolf Ludvigsen, Brian Pratt, and Jim Stitt for their comments on the manuscript. Divino Mucciante processed our negatives.

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Raymond, P.E. 1913. A revi sion of the species which have been referred to the genus Bathyurus. Geological Survey of Canada, Me moir of the Victoria Museum, No.1, pp. 51-69. Robison . R.A ., and Pantola-Alor, J. 1968. Tremadocian trilobites from the Nochixtl