lower ordovician faunas, stratigraphy, and sea-level history ... - BioOne

J. Paleont., 80(5), 2006, pp. 958–980 Copyright 䉷 2006, The Paleontological Society 0022-3360/06/0080-958$03.00

LOWER ORDOVICIAN FAUNAS, STRATIGRAPHY, AND SEA-LEVEL HISTORY OF THE MIDDLE BEEKMANTOWN GROUP, NORTHEASTERN NEW YORK ED LANDING1

AND

STEPHEN R. WESTROP2

New York State Museum, State Education Department, Albany, New York 12230, ⬍[email protected]⬎ and 2Oklahoma Museum of Natural History and School of Geology and Geophysics, University of Oklahoma, Norman 73072, ⬍[email protected]⬎

1

ABSTRACT—The Lower Ordovician middle Beekmantown Group is a very thin carbonate platform succession on the northern New York Promontory that thickens north into the Ottawa aulacogen near Montreál. The Tribes Hill Formation (Rossodus manitouensis Zone) records the earliest Ordovician (late Skullrockian, late early Tremadocian) eustatic high that submerged Laurentia, and produced the lowest Ordovician sequence along the New York Promontory. These dolostones are succeeded in the Beekmantown, New York, area by late Tulean?–Blackhillsian transgressive systems tract quartz arenites of the lower Fort Cassin Formation (Ward Member). The ‘‘Fort Ann Formation’’ (middle Stairsian, upper Tremadocian) of the southern Lake Champlain lowlands (⫽Theresa Formation sandstones in the Ottawa graben) is absent at Beekmantown, and moderate Stairsian (late Tremadocian) eustatic rise apparently did not inundate the Beekmantown area after Skullrockian–Stairsian boundary interval offlap. Highstand carbonates of the upper Fort Cassin Formation [Sciota Member ⫽ ‘‘Spellman Formation’’ and ‘‘Ogdensburg Member’’ of the ‘‘Beauharnois Formation’’ in the Montreál area; designations abandoned] at Beekmantown yield diverse conodonts seemingly characteristic of the Oepikodus communis–Fahraeusodus marathonensis Zone (new). However, associated trilobites, particularly Carolinites tasmanensis (Etheridge, 1919), show a correlation with the upper Trigonocerca typica (trilobite) Zone of the Utah and the overlying Reutterodus andinus (conodont) Zone. This abrupt early Blackhillsian lithofacies change features the appearance of chitinozoans and conodonts known from marginal successions, and records the Laignet Point highstand (new). This highstand is recognized across Laurentia on the west Newfoundland and southern Midcontinent platforms. It is recorded on the east Laurentian continental slope by lower Oepikodus evae Zone dysoxic black mudstone in the Taconian allochthons. Taxonomic re-evaluations include Ulrichodina Branson and Mehl, 1933, with its genotype species U. abnormalis (Branson and Mehl, 1933) emend., as the senior synonym of Colaptoconus Kennedy, 1994; Eucharodus Kennedy, 1980; and Glyptoconus Kennedy, 1980. Paraserratognathus An in An et al., 1983, emend. is the senior synonym of Wandelia Smith, 1991 and Stultodontus Ji and Barnes, 1994. Tropodus Kennedy, 1980 is the senior synonym of Chionoconus Smith, 1991. The trilobite fauna of the Sciota Member includes species of Isoteloides, Benthamaspis, Acidiphorus and Carolinites, of which I. fisheri is new.

INTRODUCTION

T

Formation was proposed (Clarke and Schuchert, 1899) to replace Brainerd and Seely’s (1890) Calciferous Formation, a dolostone and limestone-dominated interval on the carbonate platform of eastern New York and western Vermont. The Beekmantown is underlain by sandstones of the upper Middle-lower Upper Cambrian Potsdam Formation and overlain by upper Middle Ordovician Chazy Group limestones. Although named from exposures near Beekmantown village, northeast New York, Clarke and Schuchert (1899) designated the type section at the then well-exposed succession at East Shoreham, Vermont (Figure 1.1). The Beekmantown area has limited outcrops, with macrofossils reported at only one locality (Whitfield, 1889). Over the following century, the Beekmantown was variously regarded as a formation- or group-level unit, as well as a chronostratigraphic unit (see Wilmarth, 1938), that comprised the Lower Ordovician of the east Laurentian carbonate platform (e.g., Twenhofel et al., 1954). In somewhat later discussions of the Laurentian Lower Ordovician, or Canadian Series, the Fort Cassin Formation near the top of the Beekmantown Group was used as the basis for an uppermost Lower Ordovician Cassinian Stage (Flower, 1968). However, in this report, currently used Laurentian chronostratigraphic divisions will be applied to the Beekmantown succession; these include the Ibexian Series and its constituent stages for the terminal Upper Cambrian through Lower Ordovician (Ross et al., 1997). The term ‘‘Beekmantown’’ is appropriate for use as a grouplevel lithostratigraphic unit in eastern Laurentia (e.g., Fisher, 1968; Bernstein, 1992). Recent work on the Beekmantown Group in New York and Vermont shows that it extends from the middle Upper Cambrian through much of the Middle Ordovician (e.g., Ludvigsen and Westrop, 1983; Landing, 2002; Landing et al., 2003), but did not reevaluate the Beekmantown area succession. In this report, we compare the succession of the Beekmantown HE BEEKMANTOWN

area with that to the north in southern Ontario, as well as with the thicker successions further east in southeastern Ontario and southern Que´bec in the northwest-trending Ottawa aulacogen (Williams, 1978; Salad Hersi et al., 2003). Comparative successions also lie farther south on the New York Promontory in the southern Lake Champlain and Mohawk River lowlands (Landing et al., 1996, 2003, fig. 2; Landing, 2002; Fig. 1.1). In the course of our work, we developed new information on the conodont and trilobite faunas and revised the biostratigraphy of this classic succession. GEOLOGIC SETTING AND LOCALITIES

The Cambrian–Ordovician of the Beekmantown area nonconformably overlies middle Proterozoic (ca. 1.0 Ga) metamorphics and intrusives of the Adirondack Mountains massif (Figs. 1, 2). To the east, parautochthonous, synorogenic, Upper Ordovician mudstones underlie much of Lake Champlain and mark the outer margin of the Taconian orogen (e.g., Fisher et al., 1970). Lower Ordovician outcrop is limited, with few quarries and road cuts in an almost flat-lying succession (Fisher, 1968, pls. 1, 2). Although most exposures are low pasture outcrops, we found that the stratigraphic completeness of much of the Lower Ordovician could be evaluated in a composite section (Fig. 1.2, 1.3). Locality 22.⎯Whitfield (1889, p. 42) described abundant fossils (orthids, hypseloconids, gastropods, orthoconic nautiloids, trilobites, ostracodes) collected by H. M. Seely from ‘‘a low bank exposing about seventeen or eighteen feet of rock’’ ‘‘about one and a half miles north of Beekmantown Station, on the Delaware and Hudson Railroad.’’ This locality description is problematical, as the 1907 edition of the Rouses Point, New York, 15⬘ quadrangle shows that the modern route of the Delaware & Hudson Railroad is unchanged from that of the early twentieth century. This rail line runs through East Beekmantown, not Beekmantown (Fig. 1.2), and follows a marshy area without exposed rock. However,

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LANDING AND WESTROP—IBEXIAN FAUNAS OF NORTHEASTERN NEW YORK

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FIGURE 1—Generalized locality maps. 1, Location of the Beekmantown area; abbreviations: B, Beekmantown; Sh, Shoreham. 2, Sample localities DurQ, KeB, WD&H, 22. 3, Composite section of the Beekmantown Group in the Beekmantown, New York, area; fossiliferous samples (Tables 1, 2) numbered in meters above base of section at each sample locality; dash ⫽ barren samples.

a low cliff with 5.1 m of dolostones and fossiliferous limestone is located 2.8 km (1.7 mi) north of the intersection of Route 22 and Haynes Road in Beekmantown (Fig. 1.2, 1.3). This section (locality 22) corresponds in approximate location and lithology to Whitfield’s (1889) locality. It was the only fossiliferous Lower Ordovician locality found by Fisher (1968, NYSM locality 6645) during mapping of the Beekmantown area, and yielded the only trilobites found during this study. As discussed below, this is a different fauna that is younger than the one described by Whitfield. The section is ca. 35 m east of Route 22 and crops out just below and south of the Hobbs Hill Farm barn. Fifteen centimeters of interbedded gray shale and thin echinoderm grainstone in a

creek that flows east under Route 22 forms the top of the section. Fisher (1968) assigned these strata to his newly proposed ‘‘Spellman Formation.’’ (Here and below, the use of quotation marks around lithostratigraphic designations indicates that they are abandoned in this report or were inadequately defined on their proposal.) Locality WD&H.⎯This is a pasture outcrop of flat-lying dolostone 225 m east of locality 22 and 375 m west of the Delaware & Hudson Railroad tracks (Fig. 1.2, 1.3). It is 6 m below locality 22, and was mapped by Fisher (1968) as ‘‘Spellman Formation.’’ Locality KeB.⎯Thin- to medium-bedded quartz arenites lie ca. 13 m below locality WD&H just west of the Delaware & Hudson

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JOURNAL OF PALEONTOLOGY, V. 80, NO. 5, 2006

FIGURE 2—Upper Middle Cambrian–upper Middle Ordovician stratigraphy on the northern New York Promontory. ‘‘V’’ is Van Wie Member.

tracks and south of Spellman Road (Fig. 1.2, 1.3). These flatlying sandstones, which Fisher (1968) mapped as ‘‘Cutting Formation,’’ can be traced south almost to East Beekmantown. They form low waterfalls in Kennan Brook (locality KeB) just west of the Durand Road bridge. Oddly, Fisher (1968, pl. 1) mapped the Kennan Brook sandstones as ‘‘Spellman,’’ rather than ‘‘Cutting.’’ The 10.9 m of quartz arenite with a 1.0 m thrombolitic dolostone cap at KeB lie ca. 10 m below locality WD&H. Locality DurQ.⎯‘‘Cutting Formation’’ dolostone mapped in Kennan Brook downstream from locality KeB (Fisher, 1968, pl. 1) proved to be subaqueous exposures of white, Champlain Sea varved clay. The only ‘‘Cutting’’ dolostone we found in the Beekmantown area is in an abandoned quarry (locality DurQ) just west of Durand Road and 1.4 km east southeast of KeB. An outcrop

of quartz arenite along Stafford Road comparable to that at locality KeB is 9 m higher and 800 m west of the DurQ dolostone (Fig. 1.2, 1.3). BIOTAS, BIOSTRATIGRAPHY, AND STRATIGRAPHIC CONTINUITY

Conodonts.⎯Two distinct conodont faunas were recovered from the Lower Ordovician of the Beekmantown, New York, area. The conodont elements are dark brown, and have a color alteration index (C.A.I.) of 3, indicating a burial temperature of 110⬚– 200⬚C (Epstein et al., 1977). Dolostones of the ‘‘Cutting’’ at DurQ yielded only a few elements from Clavohamulus densus Furnish, 1938; Rossodus beimadaoensis (Chui and Zhang in An et al., 1983); Laurentoscandodus triangularis (Furnish, 1938); and Variabiloconus? lineatus


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TABLE 1—Lower Ordovician faunas from productive sample in the Tribes Hill Formation. Number in parentheses below sample horizon is mass (in kg) of acid-disaggregated sample. ‘‘P,’’ present; ‘‘el.,’’ is element. DurQ-1.3 (6.0) GASTROPODS INDET. CONODONTS Clavohamulus densus Laurentoscandodus triangularis Drepanodiform el. Oistodiform el. Rossodus beimaidoensis M el. Variabiloconus? lineatus

P 2 1 1 1 2

(Furnish, 1938) (Table 1, Fig. 3). These characteristic conodonts of the Rossodus manitouensis Zone in Laurentia (Landing et al., 1986) are known from the Lower Ordovician (middle-upper Skullrockian) Tribes Hill Formation in the southern Lake Champlain and Mohawk River lowlands, with C. densus and R. beimadoensis appearing only in the upper Tribes Hill (Landing et al., 1996, 2003). Clavohamulus densus suggests correlation into the middle R. manitouensis Zone in the type area of the Ibexian Series (Ross et al., 1997, pl. 1b). No conodonts persist from the ‘‘Cutting’’ into the ‘‘Spellman.’’ The ‘‘Spellman’’ locally shows quite diverse conodont assemblages (Table 2; the alphabetic listing of conodont taxa in Table 2 corresponds to their ordering in the figures: Figure 4, Bergstroemognathus extensus (Graves and Ellison, 1941)–Oepikodus communis (Ethington and Clark, 1964); Figure 5, ‘‘Oistodus’’ ectyphus Smith, 1991–Protopanderodus sp.; and Figure 6, Pteracontiodus bransoni (Ethington and Clark, 1981)–Ulrichodina simplex Ethington and Clark, 1981). The thrombolitic dolostone capping section KeB (Fig. 1) yielded only Ulrichodina abnormalis (Branson and Mehl, 1933) (Fig. 6.22–6.29). This is a post-Rossodus manitouensis Zone species reported under many names (see Systematic Paleontology) through much of the Laurentian middle–upper Lower Ordovician (Repetski, 1982; Smith, 1991; Ji and Barnes, 1994; Ross et al., 1997). Only ca. 10 m higher in the composite section, Ulrichodina abnormalis is part of a low-yield (18 elements, 5 species) conodont assemblage from the bioturbated dolostone at WD&H. This fauna has the characteristic Laurentian middle–upper Lower Ordovician taxa Drepanoistodus? concavus (Branson and Mehl, 1933) (Fig. 4.16–4.22), Paraserratognathus costatus (Ethington and Brand, 1981) (Fig. 5.8–5.10), and Tropodus comptus (Branson and Mehl, 1933) (Fig. 6.7–6.21). This fauna persists into similar dolostone of the lower 1.3 m of locality 22. Both dolostone intervals have Oepikodus communis (Fig. 4.27–4.30), the eponymous species of the Laurentian upper Lower-lowest Middle Ordovician O. communis Zone sensu stricto of Ethington and Repetski (1984). Higher at locality 22, conodont element abundance increases abruptly with a resultant increase in the number of represented taxa in wave-rippled, trilobite-echinoderm grainstones (Fig. 1.3, Table 2). All taxa appearing above the KeB sandstones persist into this facies, which yields such characteristic Laurentian inner platform taxa (see Ethington and Repetski, 1984) as Cristodus ethingtoni Ji and Barnes, 1994 (Fig. 4.4); C. loxoides Repetski, 1982 (Fig. 4.5, 4.6); Pteracontiodus bransoni (Fig. 6.1–6.6); and Parapanderodus striatus (Graves and Ellison, 1941) (Fig. 5.2– 5.7). In addition, conodonts regularly encountered in continental slope successions marginal to Laurentia also make their appearance. The latter include Bergstroemognathus extensus (Fig. 4.1–

FIGURE 3—Lower Ordovician conodonts (Rossodus manitouensis Zone), Tribes Hill Formation, Wolf Hollow Member, sample DurQ-1.3, hypotypes. 1, 2, Laurentoscandodus triangularis (Furnish, 1938), drepanodiform, lateral view ⫻57, and oistodiform, inner-lateral view ⫻108, NYSM 17138 and NYSM 17139. 3, Rossodus beimadoensis (Chui and Zhang in An et al., 1983), oistodiform element, inner-lateral view ⫻73, NYSM 17140. 4, 7, Variabiloconus? lineatus (Furnish, 1938), shortand long-based elements with albid elements of the species, ⫻94 and ⫻90, NYSM 17141 and NYSM 17142. 5, 6, Clavohamulus densus Furnish, 1938, aboral and posterior views, ⫻55 and ⫻72, NYSM 17143 and NYSM 17144.

4.3); Drepanodus arcuatus Pander, 1856 (Fig. 4.12–4.15); Fahraeusodus marathonensis (Bradshaw, 1969) (Fig. 4.23–4.26); and Periodon primus Stouge and Bagnoli, 1988 (Fig. 5.13–5.15) (see Bradshaw, 1969; Landing, 1976; Stouge and Bagnoli, 1988). An occurrence of Oistodus ectyphus Smith, 1991, sensu formo (Fig. 5.1) allows a more precise correlation of the upper part of locality 22. Smith (1991) and Ross et al. (1997, pl. 1b) reported O. ectyphus s.f. from the middle Oepikodus communis Zone s.s. on the west and northeast Laurentian platform, where it appears a few meters below and overlaps the range of Reutterodus andinus Serpagli, 1974. The latter species was not recovered from locality 22, and its absence could be explained in several ways— either locality 22 is older than the range of R. andinus in other sections or locality 22 is coeval with sections with R. andinus and the species is absent due to the small number of samples processed or to paleoenvironmental factors. Ross et al. (1997, p. 25–27) divided Ethington and Repetski’s (1984) Oepikodus communis Zone s.s. into three zones. Unfortunately, they created and Smith (1991) maintained an objective homonym by retaining ‘‘O. communis Zone’’ for the lowest zone. This ‘‘undesirable restriction’’ of the O. communis Zone means that Ross et al.’s ‘‘O. communis Zone’’ must be abandoned (North American Commission on Stratigraphic Nomenclature, 1983, articles 19g, 20a). We propose Smith’s (1991) ‘‘Oepikodus communis–Fahraeusodus marathonensis Interval’’ (i.e., the ‘‘Oepikodus communis–‘Microzarkodina’ marathonensis Interval’’ of Ethington and Clark, 1981) as a replacement and that it be regarded as a biostratigraphic zone, with the lowest occurrence of O. communis defining the base (see Ross et al., 1997, pl. 1b). The top of the O. communis–F. marathonensis Zone is the base of the

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TABLE 2—Lower Ordovician faunas from productive samples in the Fort Cassin Formation. Number in parentheses below sample horizon is mass (in kg) of acid-disaggregated sample. ‘‘P,’’ present; ‘‘el.,’’ element; ‘‘s.f.,’’ sensu formo. KeB-11.9 (26.3) BRACHIOPODS Linguloid fragments ‘‘Orthis’’ sp. GASTROPODS UNDET. NAUTILOIDS UNDET. CONODONTS Bergstroemognathus extensus M el. S el. Cristodus ethingtoni Unidenticulate el. C. loxoides Unidenticulate el. Multidenticulate el. Diaphorodus delicatus M el. P el. Sc el. Diaphorodus sp. B M el. Drepanodus arcuatus M el. (graciliform) M el. (pipaform) Drepanodiform (short-based) Drepanodiform (long-based) Drepanodiform (scoloponeaform) Drepanoistodus? concavus M el. (graciliform) Drepanodiform (scoloponeaform) Drepanodiform (short-based) Drepanodiform (long-based) Suberectiform Fahraeusodus marathonensis M el. P el. Sb el. Sc el. Oepikodus communis M el. P el. Sa el. Sb sl. Sc el. Oistodus eutyphus s.f. Parapanderodus striatus Acontiodiform el. Drepanodiform el. Paraserratodontus costatus P. guyi Periodon primum M el. P el. Sc el. Protopanderodus sp Acontiodiform el. Scandodiform el. Pteracontiodus bransoni M el. Sa el. Sb el. Sc el. Sd el. Tropodus comptus M el. (S. ethingtoni s.f.) M el. P el. Sb el. (tricostate)

WD&H (6.0)

22-0.1 (6.0)

22-1.0 (6.0)

22-2.45 (6.0)

22-4.35 (6.0)

6,645 (5.7)

22-4.75 (6.0)

22-5.15 (6.0)

1

4 1

2

1 1 1

1

3 1

1

1 1 7 3

4 1 3 1

1 2 1

5

3

7

12

17 8

11 8

2

7 5

2 5

1 1 1 1

2

1 2 1

1 1 1

3 2 1 1 1

10 2 4 15 4

2 2

4 2

1

4

1 5 1 2 1 1

2 1

2

3

2

2 7 10 1

7 20

1 3 1

3

4

1 4 1 3 4 10 2 5 4 1 1 4

5

1 8 7

7 15 11

2 7 2 6

2 10 21 31

4

2 2 4

8

6 6 4

1 5 1 1


963

TABLE 2—Continued. KeB-11.9 (26.3) Sb? el. (comptaform) Sc el. (scandodiform) Sd el. (tetracostate) Sd? el. (pentacostate) Ulrichodina abnormalis Tricostate Tetracostate Drepanodiform Suberectiform Ulrichodina? simplex s.f. CHITINOZOANS Conochitina exilis Lagenochitina boja

2 2

WD&H (6.0)

22-0.1 (6.0)

22-1.0 (6.0)

22-2.45 (6.0)

22-4.35 (6.0)

1

5 2

4 6

4 9

14

13

16

1 3

7 5

Reutterodus andinus Zone of Ross et al. (1997). In the absence of R. andinus it is impossible to make an unequivocal conodontbased correlation of upper locality 22 with the Ibexian succession of the Great Basin. The co-occurrence of O. communis and O. ectyphus s.f. indicates either the uppermost O. communis–F. marathonensis Zone or the lower R. andinus Zone. The trilobite data (see below) support the latter alternative, which equates with the lower Blackhillsian Stage and upper Trigonocerca typicalis Zone of the Great Basin. The presence of Oepikodus communis, Bergstroemognathus extensus, and Fahraeusodus marathonensis in upper locality 22 permits correlation into marginal Laurentian and cool-water Baltoscandian successions. These species overlap in marginal Laurentian sequences with the upper stratigraphic range of Prioniodus elegans Pander, 1856 and lower range of Oepikodus evae (Lindstro¨m, 1954), the eponymous species of two successive Arenigian conodont zones in Baltoscandia (see Ethington, 1972; Landing, 1976; Landing and Ludvigsen, 1984; Stouge and Bagnoli, 1988). These data suggest that the best correlation is with the Baltoscandian upper Prioniodus elegans or lower Oepikodus evae zones, as well as the Laurentian Pendeograptus fruticosus 3 ⫹ 4 branched–lower Didymograptus protobifidus zones (graptolites) (see conodont-graptolite correlations of Landing, 1976; Webby et al., 2004). Chitinozoans.⎯Pyrite-infilled chitinozoan tests were recovered from upper locality 22 (Table 2). The elongate form Conochitina exilis Bockelie, 1980 and the necked tests of Lagenochitina boja Bockelie, 1980 are stratigraphically long ranging (middle Arenigian–lowest Llanvirnian) in outer Laurentian platform sections in Spitsbergen (Bockelie, 1980) (Fig. 6.31, 6.32). Their lowest recorded occurrence in the Didymograptus protobifidus Zone in Spitsbergen is consistent with the upper limit of the conodontbased correlation of upper locality 22 into marginal successions. Bockelie (1980) noted that chitinozoans are typically absent in shallow-platform settings in the Early Ordovician, suggesting that their occurrence at locality 22 records immigration related to a relative sea-level rise. Trilobites.⎯The discovery of Carolinites tasmanensis (Etheridge, 1919) at locality 22 (Fig. 7.4–7.6) has important biostratigraphic implications. This species (identified in earlier work as Carolinites genacinaca nevadensis Hintze, 1953; see Jell and Stait, 1985) has been recorded from Australia (Jell and Stait, 1985), Spitsbergen (Fortey, 1985), Newfoundland (Fortey, 1979b), Alberta (Dean, 1989), and the Great Basin (Hintze, 1953). In the last area, it occurs in the upper part of the Blackhillsian Trigonocera typicalis Zone (collections H-23 and H-24; Hintze, 1953, p. 34), which is equivalent to Zone H in earlier zonations (Ross et al., 1997). According to Fortey (1975), occurrences in Spitsbergen lie in the Pendeograptus fruticosus (graptolite) Zone.

1 8 4 1 1

10 7 5 5 2

2 19 6

12

6,645 (5.7) 6 2 4

5 4 1

22-4.75 (6.0)

22-5.15 (6.0)

4 6

2 3 1 1

1 2

1 3

14 1

Other elements of the trilobite fauna at locality 22 are either identical to (Isoteloides peri Fortey, 1979a), or are closely related to, species described by Brett and Westrop (1996) from the Fort Cassin Formation farther south in New York (Whitehall area) or in Vermont [i.e., Benthamaspis cf. B. striata (Whitfield, 1897), Isoteloides fisheri n. sp.]. Significantly, neither of the two trilobites collected from the Beekmantown area by Seely and described by Whitfield (1889; see Boyce, 1989 for photographic illustration and discussion) are present in our new collections. The latter trilobites include an undescribed species of Hystricurus Raymond, 1913 (misidentified by Boyce, 1989 as H. oculilunatus Ross; see Landing et al., 2003 and Adrain et al., 2003). The second is Paraplethopeltis seelyi (Whitfield, 1889). Moreover, the occurrences of these latter two species are in well-documented stratigraphic sections in Newfoundland (Boyce, 1989), and this indicates that they are entirely older than the trilobite fauna described herein. From the associated conodont fauna in Newfoundland (Boyce, 1989, fig. 4), Whitfield’s (1889) fauna most likely came from the ‘‘Fort Ann Formation.’’ There are two possible explanations for the absence of this fauna at locality 22. First, Seely’s collecting locality is not the same as locality 22, and the trilobites are from older strata in the Beekmantown area that are no longer exposed. We consider this alternative unlikely because the general locality and physical description of the succession provided by Whitfield is very close to that of locality 22. Second, there may have been miscommunication between Seely and Whitfield as to the provenance of the trilobites, and they were actually collected from Shoreham, Vermont, the other locality studied by Seely. We consider this hypothesis to be more likely, but it needs to be evaluated by further work in Vermont. Calibration of almost all of the Lower Ordovician in New York by conodont zones prompts a review of the parallel, trilobitebased biostratigraphy (Fig. 2). The Tribes Hill Formation (upper Skullrockian Rossodus manitouensis Zone) yields a fauna (Westrop et al., 1993) dominated by Clelandia parabola (Cleland, 1900) and Bellefontia gyrocantha (Raymond, 1910) that is designated the C. parabola Fauna. Trilobite collections from the overlying Fort Ann Formation are limited (e.g., Flower, 1968), but Whitfield’s (1897) assemblage is almost certainly from this unit and provides the basis for the Paraplethopeltis seelyi Fauna (Fig. 2). Trilobites have yet to be recovered from the Ward Member of the basal Fort Cassin Formation and overlying Providence Island Formation, but the Sciota Member of the Fort Cassin Formation yields abundant sclerites (Brett and Westrop, 1996; this paper). The Sciota assemblage is designated the Isoteloides peri– I. canalis Fauna and is lower Blackhillsian. Stratigraphic continuity.⎯As data on the conodont and trilobite faunas have accumulated in recent years (Westrop et al.,

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FIGURE 4—Lower Ordovician conodonts (upper Oepikodus communis–Fahraeusodus marathonensis Zone or lower Reutterodus andinus Zone), Fort Cassin Formation, Sciota Member, hypotypes. 1–3, Bergstroemognathus extensus (Graves and Ellison, 1941) from 22–2.45, inner-lateral views. 1, 3, M elements, ⫻65 and ⫻52, NYSM 17145 and NYSM 17146; 2, bipennate S element, ⫻60, NYSM 17147. 4, Cristodus ethingtoni Ji and Barnes, 1994, inner-lateral view of monodenticulate element ⫻84, NYSM 17148, NYSM locality 6645. 5, 6, Cristodus loxoides Repetski, 1982, multi- and monodenticulate elements, ⫻94 and ⫻62, NYSM 17149 and NYSM 17150, 22–2.45. 7–10, Diaphorodus delicatus (Branson and Mehl, 1933). 7, Sc (subsymmetrical drepanodiform) element, inner-lateral view ⫻160, NYSM 17151, 22–2.45; 8, P element, inner-lateral view ⫻135, NYSM 17152, NYSM locality 6645; 9, 10, Sa (symmetrical tricostate) elements, posterolateral and lateral views ⫻67 and ⫻90, NYSM 17153 and NYSM 17154, 22–2.45. 11, Diaphorodus sp. B Smith, 1991, M element, ⫻73, NYSM 17155, 22–4.75. 12–15, Drepanodus arcuatus Pander,

LANDING AND WESTROP—IBEXIAN FAUNAS OF NORTHEASTERN NEW YORK 1993; Brett and Westrop, 1996; Landing et al., 1996, 2003; this report), it has become evident that the Lower Ordovician of eastern New York and western Vermont preserves only a fraction of the type Ibexian of Utah (Ross et al., 1997). There is firm biostratigraphic evidence only for the presence of the upper Skullrockian (Rossodus manitouensis Zone), middle Stairsian (Macerodus dianae Zone), and lower to middle Blackhillsian (upper Oepikodus communis–Fahraeusodus marathonensis? and lower Reutterodus andinus zones); most, if not all, of the Tulean Stage is missing. The Lower-Middle Ordovician boundary interval is missing beneath the Providence Island Formation, and the gap encompasses the upper Blackhillsian and all of the overlying Rangerian (lower Whiterockian) stages. The slivers of strata that are preserved in New York and Vermont record major highstands (see below). Even within New York, there is evidence to suggest variation in stratigraphic completeness. The composite middle Beekmantown Group section near Beekmantown is very thin and, at locality 22, only about 38 m separates Rossodus manitouensis Zone dolostones from limestones in the lower Reutterodus andinus Zone. This stratigraphic separation may be considerably less as the top of the R. manitouensis Zone is not exposed, and, as discussed below, may even lie ca. 9 m higher at the base of the KeB quartz arenites. Field work farther south shows that New York Promontory sections are thicker with 60 m separating the R. manitouensis Zone (and top of the Tribes Hill Formation) from the lowest occurrence of Fahraeusodus marathonensis and Oepikodus ectyphus s.f. in the Fort Cassin Formation in the Whitehall, New York, area (E. Landing, personal data, 2004). Although limited outcrop does not allow a definitive explanation for the condensed aspect of the middle Beekmantown Group in the Beekmantown area, multiple unconformities in the section and low rates of sedimentary rock accumulation are the likely reasons. This interpretation follows from a comparison with coeval strata in the eastern and southern Lake Champlain lowlands (Fig. 1.2). In the latter area, the Lower–lower Middle Ordovician part of the Beekmantown Group consists of four successive formations (Fig. 2). Each formation is an unconformity-bound depositional sequence with a lower transgressive systems tract sandstone and an upper carbonate highstand facies (Landing, 2002; Landing et al., 2003). The Rossodus manitouensis Zone in the DurQ dolostones characterizes the highstand facies of the upper Skullrockian Tribes Hill Formation (Landing et al., 1996, 2003). The Oepikodus communis–Fahraeusodus marathonensis Zone(?) of locality WD&H and Reutterodus andinus Zone interval at locality 22 is a Blackhillsian Stage interval known from the upper Fort Cassin Formation (Landing, 2002; E. Landing, personal data, 2004). No evidence for Stairsian rocks and conodonts [lower Fauna D of Ethington and Clark (1971)] of the ‘‘Fort Ann Formation’’ in the southern Champlain lowlands (Landing et al., 2003) is present in the Beekmantown area. The only interval which

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might correspond to the Fauna D interval in the Beekmantown composite section is the ca. 22 m interval bracketed by the base of the KeB sandstones and the WD&H dolostone. As locality WD&H has an O. communis–F. marathonensis Zone assemblage, the underlying 22 m could be referable to the upper Fauna D interval. STRATIGRAPHIC REVISIONS

Tribes Hill Formation.⎯In a revision of the Beekmantown Group in the Mohawk and Champlain valleys, Landing et al. (2003; also Landing, 2002) abandoned the ‘‘Cutting’’ and ‘‘Great Meadows’’ Formations as junior synonyms of the Tribes Hill Formation, the lowest Ordovician depositional sequence on the New York Promontory. The same action is appropriate in the Beekmantown area, where the upper ‘‘Cutting’’ at DurQ is also a carbonate-dominated unit with Rossodus manitouensis Zone faunas. Like the upper Tribes Hill Formation throughout the Mohawk and Champlain valleys (Landing et al., 1996, 2003), the upper ‘‘Cutting’’ at DurQ has thrombolite buildups. Fort Cassin Formation.⎯Fisher (1968) referred limestone and dolostone above the ‘‘Cutting’’ to the ‘‘Spellman Formation.’’ His mapping of locality KeB in the ‘‘Spellman’’ outcrop belt indicates that sandstones comprise the lower ‘‘Spellman’’ (Fisher, 1968, pl. 1). Proposal of the ‘‘Spellman’’ did not include designation and measurement of a type section or definition of upper and lower contacts, and thus did not meet the standards for proposal of a lithostratigraphic unit (see North American Commission on Stratigraphic Nomenclature, 1983). In proposing the ‘‘Spellman,’’ Fisher (1968) equated it with the ‘‘Fort Ann Formation’’ of the southern Champlain lowlands. However, as shown in this report, the ‘‘Spellman’’ is entirely equivalent to the Fort Cassin Formation. With lower sandstone and an upper carbonate-dominated interval with minor shale interbeds, the ‘‘Spellman’’ is lithologically comparable to the Fort Cassin Formation in the southern Champlain lowlands (see Fisher, 1984). The lower sandstones at KeB can be referred to the Ward Member of the lower Fort Cassin (see Fisher, 1984), whereas the overlying carbonates and minor shales are assigned to the carbonate-dominated Sciota Member of the upper Fort Cassin Formation (Fig. 2). Consequently, the ‘‘Spellman Formation’’ is abandoned as a junior synonym of the Fort Cassin Formation. EUSTATIC INTERPRETATION

Tribes Hill Formation.⎯Stratigraphic developments in the Beekmantown area can be related to the dramatic eustatic changes recognized through the Early Ordovician (see Leggett, 1978; Barnes, 1984; Fortey, 1984; Ross and Ross, 1995; Nielsen, 2004). The Tribes Hill Formation of the Champlain and Mohawk valley lowlands records a late Skullrockian/early Tremadocian eustatic high that brought tropical carbonate deposition as far into the interior of Laurentia as the upper Mississippi River valley (e.g.,

← 1856. 12, Long-based drepanodiform (arcuatiform) element, ⫻74, NYSM 17156, 22–2.45; 13, oistodiform (graciliform) element, inner-lateral view ⫻76, NYSM 17157, 22–2.45; 14, short-based drepanodiform (arcuatiform) element, ⫻85, NYSM 17158, 22–2.45; 15, oistodiform (pipaform) element, inner-lateral view ⫻53, NYSM 17159, 22–2.45. 16–22, Drepanoistodus? concavus (Branson and Mehl, 1933). 16, Drepanodiform (scoloponeaform) element, ⫻64, NYSM 17160, 22–2.45; 17, 18, oistodiform (graciliform) elements, inner-lateral views ⫻31 and ⫻61, NYSM 17161 and NYSM 17162, 22–2.45; 19, 20, long-based drepanodiform (arcuatiform) elements, ⫻100 and ⫻64, NYSM 17163 and NYSM 17164, 22–2.45 and NYSM locality 6645; 21, short-based drepanodiform (arcuatiform) element, ⫻36, NYSM 17165, 22–2.45; 22, suberectiform element, ⫻79, NYSM 17166, 22–2.45. 23–26, Fahraeusodus marathonensis (Bradshaw, 1969) from 22–2.45, inner-lateral views. 23, P element, ⫻87, NYSM 17167; 24, Sb element, ⫻81, NYSM 17168; 25, Sc element, ⫻117, NYSM 17169; 26, M element, ⫻137, NYSM 17170. 27–30, Oepikodus communis (Ethington and Clark, 1964). 27, P element, inner-lateral view ⫻175, NYSM 17171, NYSM locality 6645; 28, Sb element showing only inner costa, ⫻148, NYSM 17172, NYSM locality 6645; 29, Sa element, lateral view ⫻128 showing only one costa, NYSM 17173, 22–2.45; 30, M element, inner-lateral view, ⫻145, of broken element lacking posterior process, NYSM 17174, 22–2.45; 31, Sc element, ⫻140, NYSM 17175, NYSM locality 6645.

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FIGURE 5—Lower Ordovician conodonts (upper Oepikodus communis–Fahraeusodus marathonensis Zone or lower Reutterodus andinus Zone), Fort Cassin Formation, Sciota Member, hypotypes. 1, Oistodus eutyphus Smith, 1991, sensu formo, lateral view ⫻112, NYSM 17176, 22–2.45. 2–7, Parapanderodus striatus (Graves and Ellison, 1941). 2, 3, Acontiodiform elements with posterior sulcus, lateral and posterior views ⫻120 and ⫻61, NYSM 17177 and 17178, 22–2.45; 4, 5, Posteriorly sulcate drepanodiforms [⫽Scolopodus gracilis Ethington and Clark, 1964 s. f.], lateral and slightly posterolateral views ⫻85 and ⫻94, NYSM 17179 and NYSM 17180, 22–2.45; 6, drepanodiform with wide posterior sulcus bordered by two posterolateral costae [⫽variant of Scolopodus triangularis Ethington and Clark, 1964 s. f.], posterolateral view ⫻139, NYSM 17181, NYSM locality 6645; 7, posteriorly nonsulcate drepanodiform (⫽Scolopodus filosus Ethington and Clark, 1964 s. f.), ⫻120, NYSM 17182, 22– 2.45. 8–10, Paraserratognathus costatus (Ethington and Brand, 1981) from 22–4.35; NYSM 17183–17185, ⫻84, ⫻125, ⫻156, respectively. 11, 12, Paraserratognathus guyi (Smith, 1991), lateral and aboral views ⫻135 and ⫻120, NYSM 17186 and NYSM 17187, NYSM locality 6645 and 22–2.45. 13–15, Periodon primum Stouge and Bagnoli, 1988. 13, Sc element, ⫻79, NYSM 17188, 22–2.45; 14, P element, inner-lateral view ⫻75, NYSM 17189, 22–2.45; 15, M element, inner-lateral view ⫻92, NYSM 17190, NYSM locality 6645. 16–20, Protopanderodus sp. from 22–2.45. 16, 17, Acontiodiform elements, ⫻40 and ⫻59, NYSM 17191 and NYSM 17192; 18–20, scandodiform elements, views showing inner-lateral costae, NYSM 17193–17195, ⫻66, ⫻82, and ⫻69.

Oneota Dolostone) (Landing, 1988; Landing et al., 1992; Ross and Ross, 1995) and cool-water siliciclastic mudstones across much of southern Baltica. Absence of ‘‘Fort Ann Formation.’’—Many reports propose cumulative eustatic rise beginning in the earliest Ordovician and continuing through the Tremadocian, followed by dramatic eustatic fall in the Tremadocian–Arenigian boundary interval, and single or multiple rise-fall events through the Arenigian (e.g.,

Barnes, 1984; Fortey, 1984; Ethington et al., 1987; Landing et al., 1992). Ross and Ross’s (1995) summary of Ordovician sea levels deviated from this synthesis by distinguishing two successive, strong eustatic rise-fall couplets in Laurentia that corresponded to the lowest Ordovician stages in the Ibex area—the older corresponding to the Skullrockian Stage and peaking in the Rossodus manitouensis Zone (described above) and the younger equating to the Stairsian. On the New York Promontory (and

LANDING AND WESTROP—IBEXIAN FAUNAS OF NORTHEASTERN NEW YORK Beekmantown area), the Skullrockian rise corresponds to the Tribes Hill Formation (Fig. 2). The subsequent Stairsian rise-fall couplet is late Tremadocian (see Webby et al., 2004, fig. 2.1, 2.2) and coincident with deposition of the ‘‘Fort Ann’’ Formation with its ‘‘low diversity’’ and Macerodus dianae (conodont) Zone assemblages in the southern Lake Champlain valley (Landing et al., 2003). Ross and Ross (1995, fig. 1) represented Stairsian sea-level rise as comparable in magnitude to that of the preceding Skullrockian. However, part of their interpretation was based on miscorrelation of the ‘‘Ogdensburg Formation’’ on the northwest New York-Ontario border. As detailed below, the ‘‘Ogdensburg’’ is best correlated with, and referred to, the late Tulean?–Blackhillsian Fort Cassin Formation, and no evidence suggests that Stairsian submergence and transgression extended west of easternmost New York. Indeed, Stairsian lithostratigraphic units such as the ‘‘Fort Ann Formation’’ and the Rochdale Formation, its senior synonym, in southeastern New York, as well as the Roubidoux and Cool Creek Formations in the southern Midcontinent, are restricted to more marginal regions of the Laurentian platform (see Ross et al., 1982). This geographic restriction in Laurentia is consistent with the more moderate late Tremadocian eustatic rise recorded in Baltica (e.g., Nielsen, 2004). Thus, the apparent absence of the ‘‘Fort Ann Formation’’ in the Beekmantown area suggests that Stairsian/late Tremadocian eustatic rise was not sufficient to allow transgression across the eastern margin of the Proterozoic Adirondack Mountains massif. Fort Cassin Formation and Laignet Point eustatic high (new).⎯Work in the Beekmantown area emphasizes that the entire Fort Cassin Formation records the dramatic Arenigian eustatic rise proposed by Barnes (1984) and Landing et al. (1992). Fortey (1979b) also reported a ‘‘sudden deepening event’’ equated with the Catoche Formation of western Newfoundland and Ross-Hintze Zone H; he regarded the onset of the deepening as early Arenigian. The timing of the onset of this deepening is seemingly corroborated by subsequent work showing that the bases of the Oepikodus communis–Fahraeusodus marathonensis Zone and Catoche Formation are almost coincident (compare Ji and Barnes, 1994 with Boyce and Stouge, 1997, p. 192) and allow a correlation into the lowest Arenigian (Webby et al., 2004, fig. 2.1, 2.2). The actual onset of this ‘‘Arenigian’’ eustatic rise in Laurentia may prove to be somewhat earlier. The upper conodont Fauna D interval and terminal Tremadocian record inundation of an unconformity on the ‘‘pebble bed’’ in the upper Boat Harbour Formation in western Newfoundland (Knight and James, 1987). Consequently, the Fort Cassin Formation, which has been broadly correlated with the Catoche (e.g., Brett and Westrop, 1996) may more accurately prove to correlate with the upper Boat Harbour– Catoche, with both intervals recording a cumulative eustatic rise in northeastern Laurentia. Evidence of a truly ‘‘sudden deepening event’’ within the Arenigian is recorded within the Fort Cassin Formation at locality 22, the Catoche Formation, and by lithofacies/biotic changes at a number of other localities across Laurentia. The lithofacies change in upper locality 22, with replacement of dolostones by fossil hash grainstones with high-diversity upper Oepikodus communis–Fahraeusodus marathonensis zone faunas, including conodonts and chitinozoans more characteristic of marginal settings, is best explaned by abrupt eustatic rise. A similar and coeval abrupt appearance of diverse conodont assemblages with taxa better represented in marginal facies is seen in Reutterodus andinus Zone black limestones of the informal ‘‘Laignet Point Member’’ of the Catoche Formation (Knight, 1977a, 1977b). The ‘‘Laignet Point Member’’ shares taxa that also have their lowest appearance in upper locality 22 and features marginal platform/continental slope taxa [e.g., Bergstroemognathus extensus, Drepanodus arcuatus, F. marathonensis, Paroistodus parallelus (Pander, 1856),

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Polonodus? corbatoi (Serpagli, 1974), Reutterodus andinus; see Stouge, 1982; Boyce and Stouge, 1997]. ‘‘Laignet Point highstand’’ is proposed as a new Laurentian designation for a rapid eustatic deepening correlated with the then-unnamed lower Blackhillsian Stage eustatic rise proposed by Ross and Ross (1995). It is named for Laignet Point in the Northern Peninsula, western Newfoundland, where Reutterodus andinus Zone faunas occur in a black limestone interval of the middle Catoche Formation (Knight, 1977a, 1977b; Boyce and Stouge, 1997). An abrupt appearance of diverse conodont assemblages with taxa identical to those seen at locality 22 takes place in the upper Oepikodus communis–Fahraeusodus marathonensis–Reutterodus andinus zones in upper Cape Weber Formation (846–992 m) at Ella Ø, central East Greenland. However, no corresponding lithologic change has been reported in the massive limestones and dolomitic limestones of this interval (Smith, 1991). Landing et al. (1992) showed that middle Arenigian eustatic rise was coincident with development of strongly dysoxic, black mudstones in the Pendeograptus fruticosus 3 ⫹ 4 br.–Didymograptus protobifidus zones on the east Laurentian continental shelf in Spitsbergen (Olenidsletta Member of the Valhallfonna Formation; e.g., Fortey and Barnes, 1977) and from west Newfoundland to New Jersey. With eustatic rise, this dysoxic, graptolite-bearing mudstone facies onlapped the platform in the southern Midcontinent and Great Basin. Specifically, Didymograptus protobifidus Zone assemblages occur in the Black Rock Member of the Smithville Formation in southern Arkansas (Decker, 1936); a thin interval in the middle West Spring Creek Formation in the Arbuckle Mountains, central Oklahoma (Decker, 1936, 1939); and in the Nine Mile Formation in the western Great Basin (Ethington and Clark, 1981, p. 11; Ross et al., 1982). In addition, Braithwaite (1976) described several provincial species of Didymograptus M’Coy (in Sedgwick and M’Coy, 1851) with geographically widespread species of Phyllograptus Hall, 1858, in Ross-Hintze zones H and I in the type Ibexian. This graptolite assemblage from the Calcarenite Member correlates with the D. protobifidus Zone, and provides further evidence that the ‘‘Laignet Point’’ highstand may be recognizable in western Laurentia. As the D. protobifidus Zone correlates into the lower Prioniodus evae Zone (Landing, 1976) and the latter with the uppermost Oepikodus communis–Fahraeusodus marathonensis–Reutterodus andinus zonal interval, these D. protobifidus Zone highstands all indicate the trans-Laurentian extent of the ‘‘Laignet Point’’ highstand. The correlation of this ‘‘sudden deepening event’’ with the upper Prioniodus elegans–lower Oepikodus evae (conodont) zones (discussed above) shows that it is broadly equivalent with the ‘‘mid Arenig Highstand Interval’’ and specifically coeval with the ‘‘Oepikodus evae Drowning Event’’ of Baltoscandia (Nielsen, 2004) and Ross and Ross’s (1995) upper Tulean eustatic high. ´ BEC CORRELATIONS INTO SOUTHERN ONTARIO AND QUE

Data from this study and related work on the faunas and sequence stratigraphy of the New York Promontory allow reevaluation of the poorly exposed Beekmantown Group further north in the Montreál, Que´bec, region. Traditionally, comparisons between the Beekmantown Group in the eastern New York-Vermont and southern Que´bec-Ontario regions have been confounded by three factors: 1) regional differences in stratigraphic nomenclature; 2) limited biostratigraphic control on the Canadian successions that has allowed a surprising fluidity in correlations between and even within individual studies (e.g., compare Champlain valley-southeast Ontario-southwest Que´bec correlations in Bernstein, 1992, figs. 8, 11); and 3) a Waltherian stratigraphic approach that often shows continuous successions without unconformities and posits significant lateral diachroneity in formation contacts over

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FIGURE 7—Trilobites from the Sciota Member, Fort Cassin Formation, from 22-4.75, except 1, 7, 8 from NYSM locality 6645. 1, 7, 8, Benthamaspis cf. B. striata (Whitfield, 1897), cranidium, NYSM 17268, dorsal, anterior, and lateral views, ⫻8. 2, 3, Acidiphorus sp., cranidium, NYSM 17269, dorsal and anterior views, ⫻4. 4–6, Carolinites tasmanensis (Etheridge, 1919), cranidium, NYSM 17270, lateral, anterior, and dorsal views, ⫻12.

short distances and interprets lateral transitions between formations even in the absence of adequate biostratigraphic control (e.g., Bernstein, 1992, fig. 10; Salad Hersi et al., 2003, figs. 5, 12). Salad Hersi et al. (2003) applied Bernstein’s (1992) tripartite division of the Beekmantown into a lower Theresa Formation (siliciclastics), middle Beauharnois Formation (fossiliferous dolostones), and an upper Carillon Formation, (laminated dolostones

and higher cyclic [lower laminated-upper fossiliferous] carbonates). They improved an understanding of the succession by using cores to show that the thick Beekmantown at Montreál (ca. 340 m) thickens southwest into the Ottawa aulacogen (see Williams, 1978). They used available conodont evidence to show that a major unconformity intervenes between Upper Cambrian sandstones and the Theresa Formation. Salad Hersi et al. (2002, 2003)

← FIGURE 6—Lower Ordovician conodonts and chitinozoans (upper Oepikodus communis–Fahraeusodus marathonensis Zone or lower Reutterodus andinus Zone), Fort Cassin Formation, Sciota Member, Beekmantown area, northeast New York, hypotype specimens. 1–6, Pteracontiodus bransoni (Ethington and Clark, 1981), most elements from 22–2.45, Figure 8.6 from 22–4.35. 1, 2, Sb elements, inner-lateral views basally broken and complete elements, ⫻56 and ⫻71, NYSM 17196 and NYSM 17197; 3, 4, Sa elements, lateral and posterior views, ⫻61 and ⫻38, NYSM 17198 and NYSM 17199; 5, Sd element, inner-lateral view ⫻82, NYSM 17200; Sc element, ⫻73, NYSM 17201. 7–21, Tropodus comptus (Branson and Mehl, 1933), most specimens from 22–2.45, Figure 7.7 from 6645. 7–9, Large-based M elements (⫽Scandodus ethingtoni Smith, 1991 s. f.), innerlateral views, ⫻55, ⫻53, and ⫻60, NYSM 17202–17204, NYSM locality 6645; 10–12, M elements, inner-lateral views ⫻47, ⫻40, and ⫻61, NYSM 17205–17207; 13, 14, P elements, inner-lateral views ⫻59 and ⫻68, NYSM 17208 and NYSM 17209; 15, Sc (scandodiform) element, inner-lateral view ⫻42, NYSM 17210; 16, 17, comptiform elements, outer- and inner-lateral views ⫻64 and ⫻67, NYSM 17211 and NYSM 17212; 18, 19, Sb? (asymmetrical tricostate) elements, oral and outer-lateral views, ⫻67 and ⫻72, NYSM 17213 and NYSM 17214; 20, Sd (tetracostate) element, lateral view ⫻78, NYSM 17215; 21, Sd? (pentacostate) element, oral view ⫻81, NYSM 17216. 22–29, Ulrichodina abnormalis Branson and Mehl, 1933, from 22–2.45. 22, Drepanodiform element with weak anterolateral costa, ⫻65, NYSN 17217; 23, 24, shortand long-based laterally noncostate drepanodiform elements, NYSM 17218 and NYSM 17219, ⫻100 and ⫻81; 25, 26, symmetrical tetracostate elements (⫽Scolopodus quadraplicatus Branson and Mehl, 1933 s. f.), lateral and posterior views ⫻100 and ⫻111, NYSM 17220 and NYSM 17221; 27–29, suberectiform (ulrichodiniform) elements (⫽U. deflexus s. f. and U. abnormalis s. f.), lateral views ⫻78, ⫻72, and ⫻78, NYSM 17222–17224, 22–4.35. 30, Ulrichodina? simplex Ethington and Clark, 1981 s. f., lateral view ⫻68, NYSM 17225, 22–2.45. 31, Lagenochitina boja Bockelie, 1980, ⫻100, NYSM 17226, 22–4.75. 32, Conochitina exilis Bockelie, 1980, ⫻104, NYSM 17227, 22–4.75.

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reported Striatognathus prolificus Ji and Barnes, 1994, a conodont known from the ‘‘Fort Ann Formation’’ in New York (Landing et al., 2003), low in the Theresa northwest of Montreál. This suggests that the Stairsian depositional sequence of the ‘‘Fort Ann Formation,’’ which is absent at Beekmantown, New York, is the lateral equivalent of the Theresa in the Ottawa aulocogen. The typical Upper Cambrian–Stairsian unconformity separating Potsdam sandstones from the Theresa is reduced at an isolated dolostone outcrop south of Montreál, from which Salad Hersi et al. (2003, locality 16) recovered a Rossodus manitouensis Zone assemblage comparable to that at locality DurQ. Although assigned to the generally younger ‘‘Beauharnois Formation’’ by Salad Hersi et al., we suggest that this dolostone underlies the Theresa and lies at the northern end of late Skullrockian depositional sequence that comprises the Tribes Hill Formation along the New York Promontory. Available evidence indicates that the Fort Cassin Formation, the Blackhillsian (Arenigian) depositional sequence along the New York Promontory, correlates into the post-Theresa ‘‘Beauharnois Formation,’’ a unit divided by Bernstein (1992) into a lower ‘‘Ogdensburg Member’’ (fossiliferous dolostones) and an upper ‘‘Huntingdon Member’’ (lower laminated dolostones interbedded upward with fossiliferous dolostones). [It should be noted that ‘‘Beauharnois’’ underwent an undesirable restriction when Bernstein (1992) divided the Beauharnois Formation of Raymond (1913) and subsequent authors (e.g., Globensky, 1982a, 1982b) into an upper ‘‘Carillon Formation’’ and created a homonym by retaining ‘‘Beauharnois’’ for the lower. Thus, use of ‘‘Beauharnois’’ should be abandoned in Ontario and Quebec (i.e., North American Commission on Stratigraphic Nomenclature, 1983, articles 19g, 20a).] Higher-diversity conodont (Oepikodus communis–Fahraeusodus marathonensis Zone) and trilobite (Isoteloides peri–I. canalis Fauna) collections from an outcrop of the upper ‘‘Ogdensburg’’ in southern Quebec (Desbiens et al., 1996; Salad Hersi et al., 2003) indicate correlation with the Fort Cassin. Conodont collections from small core samples lower in the ‘‘Ogdensburg’’ have very low diversity and are referable either to conodont Fauna D or the O. communis–F. marathonensis Zone (Salad Hersi et al., 2003), and are consistent with correlation with the Fort Cassin Formation. Despite the absence of biostratigraphically definitive faunas from the lower part of the ‘‘Ogdensburg,’’ it is important to note the overall lithologic similarity of the thinto medium-bedded fossiliferous dolostones with thin shale interbeds of the ‘‘Ogdensburg’’ to the Fort Cassin Formation. We regard the ‘‘Ogdensburg’’ simply as a pervasively dolomitized, sandier facies of the Fort Cassin. This lithologic similarity was noted in the Ogdensburg, New York, type area of the ‘‘Ogdensburg Dolomite’’ by Chadwick (1919). Abandoning the ‘‘Ogdensburg’’ for the Fort Cassin Formation, its senior synonym, is further strengthened by the lithology and correlation of the overlying ‘‘Huntingdon Member’’ of the ‘‘Beauharnois Formation.’’ Both the lithology (lower laminated dolostones and upper interbedded laminated and fossiliferous dolostones) and presence of lowermiddle Whiterockian conodonts in the ‘‘Carillon Formation’’ (Salad Hersi et al., 2003) are identical to the lithofacies succession and biota of the Providence Island Formation, the terminal Beekmantown depositional sequence of the Beekmantown Group in eastern New York and adjacent Vermont (Landing, personal data). We suggest that further work will demonstrate the synonymy of the ‘‘Carillon’’ with the Providence Island Formation. CONCLUSIONS

The middle Beekmantown Group in the Beekmantown, New York, area is a thin and incomplete Lower Ordovician platform succession. Part of the reason for this ‘‘condensation’’ is the apparent absence of the ‘‘Fort Ann Formation,’’ a Stairsian/upper

Tremadocian, unconformity-bound depositional sequence known further south and east on the New York Promontory (Landing, 2002; Landing et al., 2003). Presence of the older Tribes Hill Formation and an unconformably overlying Fort Cassin Formation reflects deposition during eustatic highstands that inundated large areas of Laurentia in the late Skullrockian/early Tremadocian and late Tulean?–Blackhillsian/middle Arenigian. Abrupt middle Arenigian eustatic rise resulting in the ‘‘Laignet Point highstand’’ is recorded in a number of regions across the Laurentian platform from Newfoundland to Oklahoma to Nevada. Regional correlations of the Beekmantown Group indicates that a unified stratigraphic nomenclature and sequence stratigraphy is appropriate for the Lower Ordovician of the New York Promontory and Ottawa graben. A unified stratigraphic nomenclature is significant as it will contribute to a simplified and readily comprehensible geological history of this large region of eastern Laurentia. Indeed, if stratigraphic successions are lithologically identical, are coeval, and share comparable sequence boundaries, their named lithostratigraphic divisions should cross state, provincial, and national boundaries. SYSTEMATIC PALEONTOLOGY

Specimens are reposited in the New York State Museum (NYSM). Discussion is limited to those taxa for which new systematic proposals or morphologic observations have been made. For trilobites, measurement data (proportions in percent) are reported as mean values with the range in parentheses. Landing is responsible for the section on conodonts, and Westrop is responsible for the treatment of the trilobites. Class CONODONTA Eichenberg, 1930 Genus DREPANOISTODUS Lindstro¨m, 1971 Type species.⎯Oistodus forceps Lindstro¨m, 1954, sensu formo from the Upper Planilimbata Limestone, southern Sweden. DREPANOISTODUS?

(Branson and Mehl, 1933) Figure 4.16–4.22

CONCAVUS

Oistodus concavus BRANSON AND MEHL, 1933, p. 59, pl. 4, fig. 6. Drepanodus concavus (BRANSON AND MEHL). KENNEDY, 1980, p. 55– 57, pl. 1, figs. 26–34; SMITH, 1991, p. 28–31, fig. 17a–j (sources include partial multielement reconstruction and synonymy). Drepanoistodus lucidus STOUGE AND BAGNOLI, 1988, p. 117, pl. 3, figs. 1–6. Drepanoistodus suberectus? (BRANSON AND MEHL). SMITH, 1991, p. 31, 32, fig. 18d, e (with synonymy through 1991). Drepanoistodus concavus (BRANSON AND MEHL). JI AND BARNES, 1994, p. 34, 35, pl. 1, figs. 1–6 (includes synonymy through 1990). Drepanoistodus angulensis (HARRIS). DESBIENS ET AL., 1996, p. 1148, pl. 5, figs. 22–25.

Material examined.⎯One hundred forty-six elements from localities WD&H and 22 (Table 2). Discussion.⎯The elements assigned by Smith (1991) to Drepanodus concavus were all recovered in this study. These elements are typically the largest in the Beekmantown collections. However, the species’ apparatus is more complex than that of multielement Drepanodus Pander, 1856, because suberectiforms (Fig. 5.22) comparable to those included by Ji and Barnes (1994) in Drepanoistodus concavus are also present (see Fig. 4.22, also Desbiens et al., 1996, pl. 5, fig. 25). As noted by Smith (1991, p. 32), a number of reports on the Laurentian platform Lower Ordovician have associated these suberectiforms with a generalized drepanodiform element in a bimembrate Drepanodus suberectus apparatus. However, these suberectiforms are best associated in a Drepanoistodus concavus apparatus sensu Ji and Barnes (1994).

LANDING AND WESTROP—IBEXIAN FAUNAS OF NORTHEASTERN NEW YORK The assignment of the species to Drepanoistodus is herein considered tentative. Indeed, species of Drepanoistodus from Baltica have M elements with more elongate bases (e.g., Van Wamel, 1974), and, in our observations, have cusps that are completely and opaquely albid, rather than showing the albid growth axes of D.? concavus elements. For these reasons, D.? concavus and related Laurentian species may not be confidently referable to Drepanoistodus, and a question mark is appended to the generic assignment. Genus PARASERRATOGNATHUS An in An et al., 1983 emend. Type species.⎯Paraserratognathus obesus Yang in An et al. (1983; ⫽Scolopodus abruptus Repetski, 1982) from the Lower Ordovician of North China (by original designation). Generic synonymy.⎯Wandelia Smith, 1991; Stultodontus Ji and Barnes, 1994. Proposed diagnosis.⎯Euconodonts with apparatus consisting of albid, non- to strongly costate elements with circular to oval cross sections; a transition is present from rapidly tapering, broadly curved, conelike elements to elements in which the distal part of the cusp is small, peglike, and recurved to reclined above a large costate base. Discussion.⎯Stouge and Bagnoli (1988, p. 127) noted that the type elements of Paraserratognathus obesus appear to be comparable to those of Scolopodus abruptus s.f. Repetski (1982, p. 45, 46, pl. 21, figs. 1, 3) earlier showed that elements of S. abruptus s.f. range from abruptly tapering, costate cones to forms in which a peglike cusp is reclined above a strongly costate, relatively large base. In their proposal of Oneotodus costatus, Ethington and Brand (1981) showed the association of longitudinally microstriated, non- to multicostate elements in one apparatus (see Fig. 5.8–5.10), and remarked on the presence of ‘‘rejuvenated cusps’’ (i.e., small cusps) in some specimens. Smith (1991, fig. 27e–i) and Ji and Barnes (1994, pl. 22, figs. 21, 22) illustrated elements with small cusps that are reclined above a large base as variants in O. costatus, which was designated as the genotype species of Stultodontus. All of these data outlined above suggest that Stultodontus is a junior synonym of Paraserratognathus, and that O. costatus should be referred to Paraserratognathus. Similarly, the genotype species Wandelia guyi Smith, 1991 has elements with reduced cusp reclined over a large, costate base (Fig. 5.11, 5.12). In addition, Wandelia guyi has elements identical to and consequently must be regarded as the senior synonym of Stultodontus ovatus Ji and Barnes, 1994. Thus, W. guyi and its junior synonym, S. ovatus, are assigned herein to Paraserratognathus, and Wandelia is considered a junior synonym of Paraserratognathus. Based on the morphology of O. costatus elements, Smith (1991, p. 46) suggested that Oneotodus Lindstro¨m, 1954 could prove to be the senior synonym of Paraserratognathus. However, the genotype species of Oneotodus, Distacodus? simplex Furnish, 1938, has noncostate elements not known to have peglike cusps (see Ethington and Brand, 1981), and it is unlikely that Oneotodus is the senior synonym of Paraserratognathus. Genus PROTOPANDERODUS Lindstro¨m, 1971 Type species.⎯Acontiodus rectus Lindstro¨m, 1954, s. f. from the Upper Planilimbata Limestone of southern Sweden. PROTOPANDERODUS sp. Figure 5.16–5.20 Material examined.⎯Seven elements from 22–2.45. Discussion.⎯Protopanderodus is represented by albid acontiodiform and scandodiform elements from 22–2.45. The acontiodiforms have low posterolateral costae most strongly developed

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in the zone of maximum element curvature. The laterally deflected scandodiforms have a broadly rounded outer-lateral surface, keeled anterior and posterior margins, and up to four low costae on the inner-lateral surface. The elements have the broadly oval basal cross sections of P. leonardi Serpagli, 1974, and include laterally multicostate scandodiforms that resemble those of P. gradatus Serpagli, 1974. The morphological variation in elements in both of Serpagli’s (1974) Argentinian Protopanderodus species may be incompletely documented, and they may prove to be synonomous with each other and with the Beekmantown form. Genus TROPODUS Kennedy, 1980, s. Bagnoli et al., 1988 Type species.⎯Paltodus comptus Branson and Mehl, 1933, from the Jefferson City Formation in central Missouri. Genus synonymy.⎯Chionoconus Smith, 1991. TROPODUS

COMPTUS

(Branson and Mehl, 1933) s. Stouge and Bagnoli, 1988 Figure 6.7–6.21

?Diaphorodus delicatus (BRANSON AND MEHL). KENNEDY, 1980, p. 52– 54, pl. 1, figs. 12, 13, 20–22 (pl. 1, figs. 3–11, 14–19 ⫽ D. delicatus); DESBIENS ET AL., 1996, p. 1147, pl. 5, figs. 4–13. Diaphorodus delicatus vulgaris (BRANSON AND MEHL). KENNEDY, 1980, p. 53, 54, pl. 1, figs. 23–25. Tropodus comptus (BRANSON AND MEHL). KENNEDY, 1980, p. 65, 66, pl. 2, figs. 20–27 (partial multielement reconstruction and synonymy); STOUGE AND BAGNOLI, 1988, p. 141, 142, pl. 16, figs. 1, 2 (includes synonymy). Tropodus comptus comptus (BRANSON AND MEHL). STOUGE AND BAGNOLI, 1988, p. 142, pl. 16, figs. 6–9. Chionoconus avangna SMITH, 1991, p. 22–24, fig. 14a–h (includes partial synonymy). Acodus comptus (BRANSON AND MEHL). JI AND BARNES, 1994, p. 26, 27, pl. 2, figs. 1–20, fig. 23a (?pl. 2, fig. 21); DESBIENS ET AL., 1996, p. 1147, pl. 5, figs. 1–3. in part Acodus delicatus (BRANSON AND MEHL). DESBIENS ET AL., 1996, p. 1147, pl. 5, figs. 4, 5, 7–13 (pl. 5, fig. 6 is symmetrical tricostate Sa of Diaphorodus delicatus).

Material examined.⎯Two hundred fifty-eight elements from localities WD&H and 22 (Table 2). Discussion.⎯Elements of Tropodus comptus are common in many Laurentian Lower Ordovician successions, but conflicting reconstruction of the apparatus of this genus and its species have been published. In the Beekmantown collections, a symmetry transition series is readily recognized with asymmetrical tricostate-comptaform (asymmetrical tricostate variants with additional costa on the outer-lateral surface)-symmetrical tetracostate-symmetrical pentacostate elements (Fig. 6.16–6.21). These S elements correspond to Smith’s (1991) reconstruction of the T. comptus apparatus. To these S elements must be added a laterally noncostate, scandodiform element (Figure 6.15) with the same features (i.e., longitudinal microstriae, diffusely albid and gently curved cusp) as in the symmetry transition series. This scandodiform was included by Smith (1991) as the q element in Chionoconus avangna. P and M elements proposed as part of a much more elaborate Tropodus apparatus (see Bagnoli et al., 1988) were recovered in this study (Fig. 6.10–6.14), and corroborate the apparatus reconstructions of T. comptus and ‘‘Acodus’’ comptus by Stouge and Bagnoli (1988) and Ji and Barnes (1994). Morphologically identical P and M elements were referred to C. avangna by Smith (1991). However, similarity in size and longitudinal microstriae and the fact that the anterolateral costa of the P elements is elongated below the aboral plane, as in most of the associated S elements of T. comptus, all suggest that these P and M elements are part of T. comptus. Consequently, C. avangna is synonymized in this report with T. comptus. Smith (1991, p. 62) considered it possible that Scandodus ethingtoni Smith, 1991 s. f. (see Fig. 6.7–

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6.9) might prove to be a long-based, short-cusped variant of the M element in C. avangna. This proposal is supported by the stratigraphic overlap and co-occurrence of S. ethingtoni s.f. with T. comptus/C. avangna in Laurentian platform successions in East Greenland (Smith, 1991), southern Que´bec (Desbiens et al., 1996), and northern New York. Genus ULRICHODINA Furnish, 1938, emend. Landing et al., 2003 Type species.⎯Acontiodus abnormalis Branson and Mehl, 1933 (⫽Ulrichodina prima Furnish, 1938; see Lindstro¨m, 1964, p. 176; Kennedy, 1980; and Ethington and Clark, 1981, p. 112) from the Jefferson City Formation in central Missouri. Genus synonymy.⎯Eucharodus Kennedy, 1980, Glyptoconus Kennedy, 1980, and Colaptoconus Kennedy, 1994 (see Landing et al., 2003, p. 95, 96). ULRICHODINA

(Branson and Mehl, 1933) emend. Figure 6.22–6.32

ABNORMALIS

Acontiodus abnormalis BRANSON AND MEHL, 1933, p. 57, pl. 4, figs. 24, 25. Drepanodus parallelus BRANSON AND MEHL, 1933, p. 59, pl. 4, fig. 17. Scolopodus quadraplicatus BRANSON AND MEHL, 1933, p. 63, pl. 4, figs. 14, 15. Ulrichodina? deflexus FURNISH, 1938, p. 335, 336, pl. 41, figs. 19, 20, fig. 1c. Scolopodus triplicatus ETHINGTON AND CLARK, 1964, p. 700, pl. 115, figs. 20, 22, 24,? 23. Eucharodus parallelus BRANSON AND MEHL. KENNEDY, 1980, p. 58–60, pl. 1, figs. 35–38 (includes synonymy through 1980); SMITH, 1991, p. 33–35, fig. 19d–f. Ulrichodina abnormalis (BRANSON AND MEHL). ETHINGTON AND CLARK, 1981, p. 112, pl. 12, fig. 31; REPETSKI, 1982, p. 53, 55, pl. 26, fig. 9; SMITH, 1991, p. 69–71, fig. 40a–c (sources includes synonymy). Glyptoconus quadraplicatus (BRANSON AND MEHL). SMITH, 1991, p. 38– 40, fig. 22a–d (includes synonymy); JI AND BARNES, 1994, p. 41, 42, pl. 10, figs. 8–20, fig. 27b (includes synonymy). Colaptoconus quadraplicatus (BRANSON AND MEHL). DESBIENS ET AL., 1996, p. 1148, pl. 5, figs. 19, 20 (in part, coarsely microstriated element in pl. 5, fig. 18 is Parapanderodus striatus acontiodiform; compare Fig. 5.2, 5.3); SALAD HERSI ET AL., 2002, fig. 10l, 10 m.

Emended diagnosis.⎯Species of Ulrichodina with apparatus consisting of elongate, gently tapering, finely longitudinally striated elements that include: 1) reclined, laterally compressed drepanodiforms with sharp to broadly rounded anterior and posterior margins, some elements with subtle anterolateral costae; 2) proclined to reclined, asymmetrical, tri-, and symmetrical tetracostate elements; and 3) symmetrical, proclined to erect ulrichodiniforms (i.e., suberectiforms) with (rare) tetracostate (showing antero- and posterolateral costae) to (common) bicostate (anterolateral costae and sharp posterior margin) cross sections. Material examined.⎯One hundred one elements from localities KeB, WD&H, and 22 (Table 2). Discussion.⎯An understanding of the Ulrichodina apparatus has slowly emerged over the last 20 years. Landing et al. (2003) noted that Dzik (1976) figured diagrammatic reconstructions of multielement Ulrichodina that are comparable to those proposed by Ji and Barnes (1994) for a number of species of Glyptoconus (⫽Colaptoconus). Landing and Barnes (1981) proposed an association of Scolopodus quadraplicatus sensu formo and Ulrichodina? deflexus s. f. in an Ulrichodina apparatus. These two latter form species are dominantly hyaline and have white matter concentrated in a growth axis, finely longitudinally microstriated elements, and tetracostate cross sections. Repetski (1982, p. 55) also remarked on the similarity of the tetracostate cross sections of the cusps of U.? deflexus s. f. and S. quadraplicatus s. f., as well as the similarity between Laurentian Scolopodus Pander,

1856 s. f. and Ulrichodina s. f. elements. Subsequently, these two form species were associated in Glyptoconus quadraplicatus in Ji and Barnes’s (1994) reconstuction. Indeed, the supposed Ulrichodina wisconsinensis Furnish, 1938 element illustrated by Ji and Barnes is a U.? deflexus s. f. variant with a keeled (Fig. 6.27), not sulcate (Fig. 6.29), posterior cusp margin. This latter element is essentially identical to Acontiodus abnormalis s. f. Ji and Barnes (1994) also included Drepanodus parallelus s. f. [and its many synonymous form species named by Branson and Mehl (1933) and Furnish (1938); see Kennedy (1980) for Eucharodus parallelus’s synonymy] as the drepanodiform element in G. quadraplicatus. This reconstruction, by which Ji and Barnes (1994) made Eucharodus a junior synonym of Glyptoconus, actually followed Kennedy’s (1980) and Ethington and Clark’s (1981) suggestions that E. parallelus might prove to be part of the G. quadraplicatus apparatus. This suggestion is further strengthened by our work in northeastern New York and the recovery of morphologically transitional forms that bridge the form species D. parallelus and S. quadraplicatus. These transitional forms are seen in specimens of D. parallelus s. f. with subtle, low anterolateral costa in the zone of maximum cusp curvature (Fig. 6.22). This association of non- to strongly sulcate elements is consistent with Brand and Rust’s (1977, p. 2005) association of D. parallelus s.f. and S. quadraplicatus s.f. in one apparatus. Ji and Barnes’s (1994) assembly of D. parallelus–S. quadraplicatus (and its asymmetrical tricostate variant Scolopodus triplicatus)– U.? deflexus (the latter reported as U. wisconsinensis and synonymized with U. abnormalis s. f. in this report) in one apparatus is further supported by the regular association and overlapping stratigraphic ranges of these form species in northeastern New York and in other studies on the Laurentian Lower Ordovician (e.g., Ethington and Clark, 1981; Repetski, 1982; Smith, 1991). For example, the form species S. quadraplicatus, U. abnormalis and its variant U. deflexus, and D. parallelus overlap throughout most of the middle and upper Ibexian Series in its type area (Ross et al., 1997, pl. 1). It should also be noted that Ross et al. (1997, pl. 1) show E. parallelus ranging lower into older strata of the Rossodus manitouensis Zone in Utah. However, these E. parallelus specimens, which do not occur with other elements of the U. abnormalis apparatus as reconstructed herein and by Ji and Barnes as G. quadraplicatus, have not yet been illustrated, and they may be referable to multielement Acanthodus lineatus (Furnish, 1938) (see Landing et al., 1996). Synonymy.⎯The oldest genus name for conodonts with an apparatus having Furnish’s (1938) form genus Ulrichodina as a suberectiform element with symmetrical to subsymmetrical, noncostate and costate elements is Ulrichodina (Landing et al., 2003). Kennedy (1980), Smith (1991), and Ji and Barnes (1994) selected quadraplicatus as the oldest species name, from all the formspecies’ names proposed by Branson and Mehl (1933), for a species bearing S. quadraplicatus, S. triplicatus, and S. robustus Ethington and Clark, 1964 elements. However, recognition that Ulrichodina s. f. is the symmetrical suberectiform of the apparatus (Ji and Barnes, 1994; Landing et al., 2003, this report) requires naming the species after the oldest available component Ulrichodina form species—in this case U. abnormalis s.f. Class TRILOBITA Walch, 1771 Family TELEPHINIDAE Marek, 1952 Genus CAROLINITES Kobayashi, 1940 Type species.⎯Ptychoparia (?) tasmanensis Etheridge, 1919 [⫽Carolinites bulbosa Kobayashi, 1940; see Jell and Stait (1985)] from the Caroline Creek Sandstone, Tasmania (by original designation). Discussion.⎯Species of Carolinites have been regarded as

LANDING AND WESTROP—IBEXIAN FAUNAS OF NORTHEASTERN NEW YORK having broad geographic ranges that encompass several Ordovician continents (e.g., Fortey, 1975; Jell and Stait, 1985), and some quantitative support for this view has been provided by morphometric analysis of C. genacinaca Ross, 1951 (McCormick and Fortey, 1999). However, many occurrences of other species remain documented by a limited number of figured specimens (e.g., Fortey, 1979a; Dean, 1989), and more data are needed to corroborate the species-level taxonomy. CAROLINITES

(Etheridge, 1919) Figure 7.4–7.6

TASMANENSIS

Carolinites tasmanensis (ETHERIDGE, 1919). JELL AND STAIT, 1985, p. 40, pl. 15, figs. 1–17 (see for synonymy); MCCORMICK AND FORTEY, 1999, fig. 3.8–3.10; MCCORMICK AND FORTEY, 2002, fig. 2k–n. Carolinites genacinaca nevadensis HINTZE, 1953. FORTEY, 1979a, p. 68, pl. 36, figs. 14–17. Carolinites aff. C. tasmanensis (ETHERIDGE, 1919). DEAN, 1989, p. 29, pl. 18, figs. 4, 8, 9, 11, 12.

Material studied.⎯One cranidium from 22-4.75. Discussion.⎯As revised by Jell and Stait (1985), Carolinites tasmanensis is characterized by small bacculae that produce little or no indentation of the base of the glabella, a librigena with a straight genal spine and conspicuous, inflated band beneath the base of the spine, and a pygidium with two well-defined and a third weakly impressed axial ring furrow. Fortey (1975) used these features to diagnose C. genacinaca nevadensis, which Jell and Stait regarded as a synonym of C. tasmanensis. The single specimen from locality 22 has small bacculae that do not indent the axial furrows and, in this respect, it is closely comparable to the type and other material of C. tasmanensis from Tasmania (Jell and Stait, 1985, pl. 15, figs. 1–8), and to the holotype cranidium of C. genacinaca nevadensis (Hintze, 1953, pl. 20, fig. 3). Cranidia from the basal Olenidsletta Member of the Valhallfonna Formation in Spitsbergen (Fortey, 1975, pl. 38, figs. 4–6, 8) also have small bacculae, but the axial furrows are somewhat more strongly indented. The associated librigena is similar to those in both Tasmania (Jell and Stait, 1985, pl. 15, figs. 11– 13) and Utah (Hintze, 1953, pl. 20, fig. 4) in a having posteriorly positioned spine and inflated band beneath the visual surface. However, it is worth noting that a librigena (Dean, 1989, pl. 19, figs. 7, 8) from the Outram Formation of Alberta that occurs low in the local range of C. genacinaca is unusual in possessing both the advanced genal spine typical of that species and the welldefined band beneath the eye thought to be diagnostic of C. tasmanensis. Family BATHYURIDAE Walcott, 1886 Subfamily BATHYURINAE Walcott, 1886 Genus ACIDIPHORUS Raymond, 1925 Type species.⎯Acidiphorus spinifer Raymond, 1925 from the Table Head Formation, western Newfoundland (by original designation). ACIDIPHORUS sp. Figure 7.2, 7.3 Material studied.⎯One incomplete cranidium from 22-4.75. Discussion.⎯A single, incomplete cranidium is illustrated here to document the presence of Acidiphorus in the Sciota Member at locality 22. It is similar to A. whittingtoni Brett and Westrop (1996, fig. 16.1–16.4), also from the Sciota Member, but has a glabella that is less tapered anteriorly. Subfamily BATHYURELLINAE Hupe´, 1953 Genus BENTHAMASPIS Poulsen, 1946 Type species.⎯Benthamaspis problematica Poulsen, 1946 [⫽Dolichometopus? gibberulus Billings, 1865; Fortey, 1979a]

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from Lower Ordovician strata of Ellesmere Island (by original designation). BENTHAMASPIS cf. B. STRIATA (Whitfield, 1897) Figure 7.1, 7.7, 7.8 cf. Benthamaspis striata (WHITFIELD, 1897). BRETT 1996, p. 425, fig. 19.11, 19.12 (includes synonymy).

AND

WESTROP,

Material studied and occurrence.⎯One cranidium from NYSM loc. 6645. Discussion.⎯This specimen resembles the holotype of Benthamaspis striata (Whitfield, 1897; Brett and Westrop, 1996, fig. 19.11, 19.12) in the degree of effacement of the anterior border and preglabellar furrow, but the L0 furrow is incomplete, rather than firmly impressed along its entire width. However, the holotype is smaller than the cranidium figured herein, so that the difference in the expression of L0 could be ontogenetic, although more data are required to evaluate this hypothesis. The type species, B. gibberula (Billings, 1865; Fortey, 1979a, pl. 34, figs. 1, 5, 7), also has an incomplete L0 but is differentiated from our cranidium by possession of a clearly defined anterior border (Fortey, 1979a, pl. 34, figs. 2, 4). Fortey (1979a, pl. 34, figs. 8–13) assigned two distinct pygidial morphs that differ in length (sag.) and in the expression of a postaxial ridge to B. gibberula. He regarded them as recording intraspecific variation but, as the figured specimens of these morphs occur in different collections that are separated stratigraphically by 34 m, more data would be desirable to confirm this interpretation. Finally, our cranidium has a relatively long, narrow glabella that recalls B. sera Fortey and Droser, 1999 (fig. 4.1, 4.2) from basal Whiterockian strata at Meiklejohn Peak, but that species has a narrow but clearly defined anterior border (e.g., Fortey and Droser, 1999, fig. 4.10). Family ASAPHIDAE Burmeister, 1843 Subfamily ISOTELINAE Angelin, 1851 Genus ISOTELOIDES Raymond, 1910 Type species.⎯Asaphus canalis Whitfield, 1886, from the Fort Cassin Formation, Fort Cassin, Vermont (see Fortey, 1979a). ISOTELOIDES PERI Fortey, 1979a Figure 8.1–8.11 Isoteloides peri Fortey, 1979a. BRETT AND WESTROP, 1996, p. 418, fig. 13.1–13.11. (includes synonymy); DESBIENS ET AL., 1996, p. 1143, pl. 3, fig. 16; pl. 4, figs. 7–19 [only; pl. 2, figs. 1–3, 25 ⫽ I. canalis (WHITFIELD, 1886)].

Material studied.⎯Two cranidia and five pygidia from 22-4.75. Discussion.⎯Two species of Isoteloides co-occur in collections from locality 22 and differ, among other features, in the length of the pygidial border. The short-bordered morph is closely comparable to material from the Fort Cassin Formation of Vermont and in the Whitehall, New York, area that were assigned to I. peri by Brett and Westrop (1996, fig. 13.3, 13.4, 13.6, 13.7, 13.10, 13.11). This species has also been documented recently from the lower ‘‘Beauharnois Formation’’ of the Montreál, Que´bec, area by Desbiens et al. (1996, pl. 4, figs. 7–19), although some of their specimens (pl. 2, figs. 1–3, 25) have broad pygidial borders and are better assigned to I. canalis. ISOTELOIDES FISHERI new species Figures 8.12, 8.13, 8.14? 9, 10 Diagnosis.⎯A species of Isoteloides with large palpebral lobe set far back on cranidium, so that distance (exsag.) from posterior margin to posterior tip of palpebral lobe is no more than onethird (27%–33%) of glabellar length (sag.) (Fig. 11). Anterior branches of facial sutures moderately divergent, so that maximum

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FIGURE 8—Trilobites from the Sciota Member, Fort Cassin Formation, from 22–4.75. 1–11, Isoteloides peri Fortey, 1979a. 1, Cranidium, NYSM 17271, dorsal view, ⫻5; 2–4, cranidium, NYSM 17272, lateral, dorsal, and anterior views, ⫻9; 5–7, pygidium, NYSM 17273, posterior, lateral, and dorsal views, ⫻7; 8, 9, pygidium, NYSM 17274, dorsal and posterior views, ⫻9; 10, 11, pygidium, NYSM 17275, dorsal and posterior views, ⫻9. 12, 13,? 14, Isoteloides fisheri n. sp. 12, 13, Librigena, NYSM 17276, dorsal and lateral views, ⫻5; ?14, hypostome, NYSM 17277, dorsal view, ⫻9.

→ FIGURE 9—Isoteloides fisheri n. sp., Sciota Member, Fort Cassin Formation, from 22–4.75. 1, Cranidium, NYSM 17278, dorsal view, ⫻3.5; 2, cranidium, NYSM 17279, dorsal view, ⫻3.5; 3, cranidium, NYSM 17280, dorsal view, ⫻8; 4, cranidium, NYSM 17281, dorsal view, ⫻8; 5–7, cranidium, NYSM 17282, dorsal, anterior, and lateral views, ⫻8; 8–10, cranidium, NYSM 17283, lateral, anterior, and dorsal views, ⫻ 8; 11–13, cranidium, NYSM 17284, lateral, anterior, and dorsal views, ⫻7.5.


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FIGURE 10—Isoteloides fisheri n. sp., Sciota Member, Fort Cassin Formation, from 22–4.75. 1, Pygidium, NYSM 17285, dorsal view, ⫻3.5; 2, 3, pygidium, NYSM 17286, dorsal and lateral views, ⫻3.5; 4, pygidium prepared to show doublure, NYSM 17287, dorsal view, ⫻7.5; 5, pygidium, NYSM 17288, dorsal view, ⫻8; 6, 7, pygidium, NYSM 17289, dorsal and posterior views, ⫻9; 8, pygidium, NYSM 17290, dorsal view, ⫻9; 9– 11, pygidium, NYSM 17291, dorsal, lateral, and posterior views, ⫻9; 12, pygidium, NYSM 17292, dorsal view, ⫻9.


FIGURE 11—Plot of the ratio between posterior fixigenal length (A) and glabellar length (B) against cranidial length (sag). Data for I. canalis and I. peri are from specimens in Brett and Westrop (1996).

width of frontal area is ca. 80% (66%–94%) of glabellar length (sag.). Larger pygidia (greater than 5 mm sag.) with relatively long border and, consequently, short axis that occupies about three-quarters (73%–79%) of pygidial length. Glabella, palpebral lobe, and posterior fixigena with punctate sculpture (Fig. 9.12) that becomes subdued (Fig. 9.2) or lost (Fig. 9.1) in larger individuals. Axis and pleural field of pygidium also punctate, with terrace ridges on border (Fig. 10.9); sculpture lost or subdued on large individuals (Fig. 10.1). Description.⎯Cranidium moderately arched and, excluding posterior fixigenae, subrectangular in outline, with width across palpebral lobes equal to 93% (87%–100%) of cranidial length. Axial and preglabellar furrows shallow, ill-defined grooves. Glabella occupies 82% (79%–87%) of cranidial length; subrectangular in outline, width equal to 55% (51%–60%) of glabellar length, gently rounded anteriorly and slightly hourglass-shaped opposite posterior end of palpebral lobe; gently convex, raised slightly above level of palpebral lobes. Palpebral lobe large, flat, arcuate band, length (exsag.) equal to ca. 24% (20%–30%, with lower values in larger cranidia) of cranidial length, and separated by faint palpebral furrows from narrow palpebral area of fixigena (Fig. 9.3, 9.13); set far back on cranidium, so that distance (exsag.) from posterior margin to posterior tip of palpebral lobe is no more than one-third (27%–33%) of glabellar length (Fig. 11). Anterior branches of facial sutures moderately divergent, so that maximum width of frontal area is ca. 80% (66%–94%) of glabellar length; posterior branches abruptly divergent, following roughly S-shaped course. Posterior fixigenae broad, so that cranidial length is 86% (85%–87%) of cranidial width (tr.) along posterior margin. Gently convex posterior border separated from remainder of fixigena by shallow border furrow. Glabella, palpebral lobe, and posterior fixigena with punctate sculpture (Fig. 9.12) that becomes subdued (Fig. 9.2) or obsolescent (Fig. 9.1) in larger individuals. Moderately arched librigena with long genal spine equal to at least half of length of librigenal field. Broad, shallow, lateral border expressed largely as break in slope between librigenal field and border; border flat to gently down-sloping, and narrows (tr.) backward, extending onto genal spine. Posterior border and border furrow absent. Doublure broad anteriorly but narrows posteriorly. Surface of exoskeleton smooth except for terrace ridges on outer edge of lateral border and on genal spine. Hypostome deeply forked, with lateral margins bowed outward opposite macculae. Median body convex, roughly oval in outline, and separated from lateral border by well-incised border furrows. Posterior lobe measures about 20% of median body length, and is transversely semielliptical in outline; anterior lobe subelliptical in outline; macculae prominent. Lateral border nearly flat, narrow

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(tr.) anteriorly, but expands towards rear. Anterior wing incomplete, but apparently triangular in outline. Surface of median body with weak terrace ridges; border and posterior projections with well-defined terrace ridges that run parallel to margin. Pygidium semielliptical in outline, length ca. 70% (59%–75%) of pygidial length, and moderately arched; well-defined articulating facets at anterior corners. Axis narrow, width at anterior equal to ca. 27% (23%–29%) of maximum pygidial width. Axis length, and therefore length of border, is size-related. Larger pygidia (greater than 5 mm sag.) with relatively long border and, consequently, with short axis that occupies about three-quarters (73%– 79%) of pygidial length. Small pygidia (less than 5 mm sag) have a relatively longer axis that accounts for ca. 86% (79%–91%) of pygidial length. Posterior end of axis underlain by distinct embayment in inner margin of doublure (Fig. 10.4). Pleural field weakly convex with faint pleural furrows on both testate and exfoliated surfaces; greater width of border results in relatively narrower pleural field on larger specimens (e.g., Fig. 10.2). Edge of pleural field corresponds to inner edge of doublure, and is separated from border by a break in slope. Border more steeply sloping than pleural field and gently concave in lateral profile. Axis and pleural field of pygidium punctate, with terrace ridges on border (Fig. 10.9); sculpture obsolescent or subdued on large individuals (Fig. 10.1). Etymology.⎯For Dr. Donald W. Fisher (see Landing and Yochelson, 1992), who discovered the locality that yielded the trilobites illustrated herein. Types.⎯Holotype cranidium NYSM 17284 (Fig. 9.11–9.13); paratype cranidia (NYSM 17278–17283); paratype pygidia (NYSM 17285–NYSM 17292), paratype librigena (NYSM 17276), and ?paratype hypostome (NYSM 17277). Material studied.⎯Seven cranidia, twelve pygidia, one librigena, and one hypostome (assigned tentatively) from 22-4.75. Discussion.⎯Isoteloides fisheri is similar to the genotype species I. canalis (see Brett and Westrop, 1996, figs. 9, 10). The primary difference lies in the size and position of the palpebral lobe and, consequently, the length (exsag.) of the posterior fixigenae. In I. fisheri, the palpebral lobe is larger and more posteriorly positioned, so that the distance from the posterior tip of the lobe to the posterior cranidial margin is no more than 33% (27%– 33%) of glabellar length (Fig. 11). This distance is longer (average 38%; range 28%–44%) in I. canalis (Fig. 11; see also Brett and Westrop, 1996, fig. 9.7, 9.9), although the difference disappears in the smallest individuals, which are comparable to similarly sized cranidia of I. fisheri (Fig. 11). Smaller, more anteriorly positioned palpebral lobes and longer (exsag.) posterior fixigenae are also characteristic of I. polaris Poulsen, 1937 (Hintze, 1953, pl. 17, figs. 9, 14); I. flexus (Hintze, 1953, pl. 17, fig. 4); I. peri (Figs. 8.1–8.4, 11); and I. saxosimontis (Dean, 1989, pl. 31, figs. 8, 13, 15, pl. 32, figs. 1, 2). The anterior branches of facial sutures are moderately divergent in I. fisheri, so that the maximum width of frontal area averages 80% (66%–94%) of glabellar length (sag.). These sutures are more strongly divergent in I. canalis, so that maximum width of the frontal area averages 104% (98%–110%; data from specimens measured by Brett and Westrop, 1996) of glabellar length. All cranidia of I. canalis have smooth external surfaces, whereas smaller cranidia of I. fisheri (Fig. 9.3–9.5, 9.11–9.13) have punctate sculpture on the glabella, palpebral lobes, and posterior fixigenae. Pygidia of I. fisheri (Fig. 10) fall in the range of variability exhibited by I. canalis (see Brett and Westrop, 1996, fig. 10). ACKNOWLEDGMENTS

This project was supported by the New York State Museum. Dan and Nancy Hobbs of Hobbs Hill Farm are thanked for access.

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Use of facilities at the Electron Microscopy Unit, Center for Laboratories and Research, New York State Health Department (via W. Samsonoff), under National Science Foundation grant 0116551 is greatly appreciated. R. H. Fortey and M. P. Smith are thanked for constructive reviews. REFERENCES

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