upper silurian and lower devonian graptolites and graptolite biostratigraphy, northern yukon, canada

Upper Silurian and Lower Devonian graptolites and graptolite biostratigraphy, northern Yukon, Canada

ALFRED C. LENZ Department of Geology, The University of Western Ontario, London, Ont., Canada N6A 5B7

Received April 1, 1987

Revision accepted June 10, 1987

Upper Silurian and Lower Devonian graptolite biostratigraphy of the northern Canadian Cordillera is revised in the light of new data. The zones, listed in order of oldest to youngest, are Lobograptus progenitor, Saetograptus fritschi linearis, and Bohemograptus bohemicus tenuis: Ludlow; Monograptus formosus, Pristiograptus ultimus, Pristiograptus chelmiensis, Monograptus bouceki, and Pristiograptus transgrediens praecipuus: Pridoli; Monograptus uniformis and M. hercynicus: Lochkov; and Monograptus falcarius?, M. fanicus, M. thomasi?, and M. yukonensis: Prag.

The following taxa, inclusive of new species, are described: Pristiograptus separabilis Teller, Pseudomonoclimacis tetlitensis n. sp., P. richardsonensis n. sp., P.? bispinosus n. sp., Monograptus cerahrs n. sp., M. aequabilis bardoensis Poqbska, M. cf. anerosus Koren', M. fanicus Koren', M. hercynicus hercynicus Pemer, M. uniformis parangustidens Jack- son and Lenz, Saetograptus fritschi linearis (BouEek), and Abiesgraptus? sp.

La biostratigraphie des graptolites du Silurien supCrieur et du DCvonien infkrieur du nord de la Cordillkre canadienne est kvistk ?i la 1umiBre de nouvelles donnCes. Les zones, dans l'ordre de plus LgC 2 plus jeune, sont Lobograptus progenitor, Saetograptusfn'tschi linearis et Bohemograptus bohemicus tenuis : Ludlow; Monograptus formosus, Pristiograptus ultimus, Pristiograptus chelmiensis, Monograptus bouceki et Pristiograptus transgrediens praecipuus : Pridoli; Monograptus uniformis et M. hercynicus : Lochkov; et Monograptus falcarius?, M. fanicus, M. thomasi? et M. yukonensis : Prag.

Les taxons suivants, incluant les nouvelles espkces, sont dtcrits : Pristiograptus separabilis Teller, Pseudomonoclinacis tetlitensis n. sp., P. richardsonensis n. sp., P.? bispinosus n. sp., Monograptus ceratcls n. sp., M. aequabilis bardoensis Poqbska, M. cf. anerosus Koren', M. fanicus Koren', M. hercynicus hercynicus Pemer, M. uniformis parangustidens Jack- son et Lenz, Saetograptus fntschi linearis (BouEek) et Abiesgraptus? sp.

[Traduit par la revue] Can. 1. Earth Sci. 25, 355-369 (1988)

Introduction third of the Road River Grouv (Jackson and Lenz 1962) of

Upper Silurian and Lower Devonian graptolites of the northem Canadian Cordillera have been the focus of studies for more than 20 years (Jackson and Lenz 1962, 1963, 1969, 1972; Lenz and Jackson 1971; Lenz and Pedder 1972; Jackson et al. 1978; Lenz 1979, 1984). Concurrently, intense studies were carried out in Poland (Teller 1964, 1966, 1969; Poqbska 1984), the USSR (e.g., Koren' 1971, 1973, 1974, 1975,1983, 1986; Mikhailova 1975; Ul'st 1974; PashkeviEius 1974; Obut 1974), Czechoslovakia (Pii'byl 1981, 1983; Jaeger in KM et al. 1986), and Germany (Jaeger 1959, 1975, 1977, 1979). The impact of these studies on the northem Cordilleran graptolite sequence was twofold: ( i ) the diversity of the Canadian faunas seemed relatively depauperate in comparison with those of Poland, the USSR, and Czechoslovakia; and ( i i ) a revision of the zonal scheme used in northern Cordilleran graptolitic succession was called for.

Two sections, Tetlit Creek and "Falcon Creek" (see Fig. I), were collected in detail during the summer of 1986. The resulting faunas, added to those re-examined from Hart River (Jackson and Lenz 1972), provide the main faunal basis for this study. Five other sections collected only cursorily in the past provided supplementary material.

The objectives of this study are to describe and illustrate new and (or) important species and to partially revise the biostratigraphic scheme in light of the new data. The initial goal of "filling in" apparent faunal and biostratigraphic gaps was, however, only partially successful; that is, the species diversity of the northern Canadian Cordillera does appear to be genuinely lower than that of Poland, Czechoslovakia, or the USSR. An explanation for this is not evident.

I Collection localities and species occurrences Graptolites were collected from approximately the upper one

Printed in Canada I lmprimt au Canada

Tetlit Creek, the type section for the formation (66"44 '~ , 135"46'W), and an unnamed tributary of Peel River, infor- mally called "Falcon Creek" in the field (65"53'45"N, 135 "55'25 "W). Previously collected sections comprise the well-sampled Hart River (65"34'N, 136"55'W), as well as Porcupine River (67"35'N, 138" 10tW), upper canyon of Peel River (65 O52'36"N, 134"42'40"W), lower canyon of Peel River (65"55'30"N, 135"53'46"W), Rock River (66"48'N, 136"18'W), and Prongs Creek (65"17'N, 135"411W) (see Fig. 1).

Biostratigraphy Ludlow

Lobograptus progenitor Zone This is identical to the Neodiversograptus nilssoni Zone of

Jackson et al. (1978). A name change is warranted because an examination of old, as well as new, material shows that the so-called N. nilssoni is, in fact, assignable to Lobograptus progenitor (see Palmer 1971). This species also occurs in the Arctic Islands (Jackson et al. 1978, p. 19). Commonly associated species include Bohemograptus bohemicus bohemicus, Pristiograptus tumescens, Saetograptus colonus compactus, S. roemeri, S. varians, and Monograptus uncinatus.

Saetograptus fritschi linearis Zone This zone is synonymous with the S. leintwardinensis

primus Zone of Lenz and Jackson (1971) and Jackson et al. (1978) and is probably closely correlative with the S. leintwardinensis Zone of Great Britain (see Rickards 1976). The zonal name change is necessitated by the fact that S. leintwardinensis primus is considered synonymous with S. fntschi linearis (see Jaeger 1959, p. 40). Saetograptusfritschi cf. linearis, recently described from the Arctic Islands (Lenz and Melchin 1986), is unquestionably conspecific with the Yukon species. The zone

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356 CAN. J. EARTH SCI. VOL. 25.1988

is characterized by the name species, most of the taxa occurring in the underlying progenitor Zone, and the first appearance of Pseudomonoclimacis tetlitensis and P.? bispinosus. The zone appears thin wherever recognized.

Bohemograptus bohemicus tenuis Zone The generally consistent stratigraphic position above

B. bohemicus bohemicus, the absence of most typical lower Ludlow species, and the relatively long range of the name subspecies are justification for the zone. The stratigraphic position of the subspecies above the leintwardinensis Zone in the United Kingdom (Holland and Palmer 1974) further justifies its use as a separate zone. Associated fauna in the Yukon may include other bohemograptids, such as B. helicoides and B. cf. comutus (see Jackson and Lenz 1972).

Pridoli Monograptus formosus Zone This zone is recognized primarily by the occurrence of the

zonal species and is arbitrarily assigned to the Pridoli, although it is recognized that the zonal species ranges across the Ludlow -Pridoli boundary (Jaeger in Kni et al. 1986). The new species, Pseudomonoclimacis richardsonensis, appears to be confined to the zone. Monograptus paraformosus Jack- son and Lenz (1969) is now considered conspecific with M. formosus BouEek (see Koren' 1986, p. 97; Jaeger in Kiii et al. 1986).

Pristiograptus ultimus Zone This zone was earlier named the bugensius Zone; Jaeger

(1977 and in Kiii et al. 1986) now, however, places P. bugensius Teller in synonymy with P. ultimus Pemer. The zone is marked by the first appearance of the zonal species. It has been well documented in Jackson and Lenz (1969), Lenz and Jackson (1971), and Jackson et al. (1978).

Pristiograptus chelmiensis Zone This zone is widely known and attains a moderate thickness

in the northem Cordillera (see Jackson et al. 1978). It is associated with closely similar pristiograptids, including P. separabilis and P. no$ordi. Although P. chelmiensis and P. separabilis are considered synonyms of P. transgrediens (s.1.) by Jaeger (in Kiii et al. 1986), the writer prefers to retain these as discrete taxa at the present time.

Monograptus bouceki Zone To date, the zonal species has been recognized only at

Falcon Creek, but its stratigraphic position above P. chelmiensis and below monograptids of the M. uniformis parangustidens type supports a separate zonal designation. The zone is well known in Czechoslovakia (Jaeger in Kiii et al. 1986).

Pristiograptus transgrediens praecipuus Zone This zone has been well documented in several localities in

the northern Yukon (see Jackson et al. 1978) and, in addition, is now tentatively recognized on Tetlit Creek. Its presence on Falcon Creek may coincide with the occurrence of M. cf. uniformis parangustidens. Jaeger (in Kiii et al. 1986) considers the name species a synonym of P. transgrediens (Pemer).

Lochkov (Devonian) Monograptus uniformis Zone The zone is best documented on Hart River, where the zonal

species, M. aequabilis aequabilis and M. cf. hercynicus sub- hercynicus, co-occur (Jackson and Lenz 1972) and might be demonstrated by the occurrence of M. aequabilis aequabilis on

FIG. 1. Map of northern Yukon Tenitory, showing localities of sections referred to in text: (1) Porcupine River; (2) Rock River; (3) Tetlit Creek; (4) Peel River, lower canyon; (5) Peel River, upper canyon; (6) Falcon Creek; (7) Hart River; (8) Prongs Creek.

Peel River upper canyon (Lenz and Pedder 1972), although the species is not restricted to the uniformis Zone. The zone is not recognized with certainty elsewhere but is probably represented by the occurrence of M. uniformis parangustidens on Falcon Creek and in the lower canyon of Peel River. Mono- graptus praehercynicus, which occurs somewhat higher stratigraphically in Nevada (Berry 1970), has not been recognized in any of the collections.

Monograptus hercynicus Zone The zone was earlier recognized in only one locality: Prongs

Creek (Jackson et al. 1978). Two additional localities, Falcon Creek and the upper canyon of Peel River, may now be added. In the latter locality, the zonal species lies 13 m above M. aequabilis aequabilis.

Prag Monograptus falcarius Zone? The recognition of this zone is based tentatively and solely

on the morphologic characteristics of the sicula of M. aequabilis bardoensis, a species found without association and only on Tetlit Creek. Poqbska (1984) pointed out that the sicula of stratigraphically lower (i.e., falcarius Zone) occurrences of that species is consistently longer and narrower, respectively, than those of the stratigraphically higher morphs. The Tetlit Creek specimens conform well to the averages of the older (i.e., falcarius Zone) Polish occurrences. It is of interest to note that the closely related subspecies of M. aequabilis notoaequabilis occurs in probable early Pragian strata in the lower canyon of Peel River and Rock River. The falcarius Zone is

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LBNZ 357

TABLE 1 . Upper Silurian, Lower Devonian graptolites, Tetlit Creek-range chart of presence or absence by lowest appearance

Level

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358 CAN. J. EARTH SCI. VOL. 25,1988

TABLE 2. Upper Silurian, Lower Devonian graptolites, Falcon Creek-range chart of presence or absence by lowest appearance

Level (m)

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well known in earliest Pragian strata of the USSR (Koren' 1971, 1975).

Monograptus fanicus Zone The zone is well known in the USSR (Koren' 1975) and

Poland (Poqbska 1984). The zonal index, previously reported only from the lower canyon of Peel River (Lenz 1979), is abundantly represented on Tetlit Creek. It is without association, but like the Polish and Russian occurrences, it lies beneath the M. yukonensis - M. telleri - M. craigensis group. The species has also been recognized in Arctic Canada (Jackson et al. 1976).

Monograptus thomasi Zone? The thomasi Zone was proposed for the Yukon by Jackson

et al. (1978) for two occurrences of the name species underlying the lowest appearance of M. yukonensis. The zone was already recognized by Jaeger (1966). Recently, however, M. thomasi was recovered from about the middle of the range of M. yukonensis in the Yukon, and the validity of a separate zone based on M. thomasi is now questionable.

Monograptus yukonensis Zone This zone, based primarily on the occurrence of the name

species, is very widely known in the Canadian Cordillera and Arctic, as well as in other countries and continents. Various authors have paid much attention to the delicateness or robust- ness and curvature of the proximal region of the rhabdosome of the distinctive J-shaped monograptids, and, consequently, a plethora of species and subspecies has been erected, some on extremely narrow morphologic criteria. Some of the earlier named taxa include M. craigensis (Churkin et al. 1970), M. yukonensis fangensis (Jaeger et al. 1969), and M. lang- gunensis (Jones 1973). More recently, Mu and Ni (1975) and Ni and Jiao (1983) proposed a large number of species and subspecies involving variations of the yukonensis morphology. Jaeger (1979) has already commented that most of those species appear to be based on very narrow criteria and are therefore probably synonymous with other species. This problem is presently under study.

Systematic paleontology Specimens of species described in this section are housed

with the Geological Survey of Canada and are given Survey (GSC) type collection numbers.

GENUS Pristiograptus Jaekel 1889 Pristiograptus? separabilis Teller (Pl. 1, figs. P, Q; Figs. 2A-2D)

Catalogue listing 1964 Pristiograptus separabilis Teller, p. 49, P1. 2, figs. 2,

10; P1. 7, figs. 16, 17; Figs. 9a-9c.

Material Ten mature and immature, flattened specimens of moderate

preservation, from 180 and 181.5 m of Tetlit Creek.

Discussion This is the first report of this species in North America. It is

distinguished chiefly by its long, narrow sicula, a moderately strongly hooked theca 1 with three to four weakly hooked subsequent thecae, a rhabdosome of moderate width, and relatively low inclination of the thecae. In addition, the distal nonhooked thecae may possess a weak lip, and the apertural margin may form an acute angle with the axis of the theca. It differs from the similar and associated P. chelmiensis in pos-

sessing four to five hooked proximal thecae, a narrower rhabdosome, and, generally, thecae with a lower inclination.

Dimensions of the species are as follows: length of sicula 2.2-2.3 mm; thecal spacing about 6 in 5 rnrn proximally and 5 -5: in 5 mm distally; rhabdosome widening gradually to a maximum of about 1.9 mm; and thecae inclined 30 - 35".

Age Found within the chelmiensis Zone.

GENUS Pseudomonoclimacis Mikhailova 1975

Type species: Pseudomonoclimacis elegans Mikhailova 1975.

Discussion This genus is very similar to Monoclimacis (s.s.). Its chief

diagnostic feature, according to Mikhailova (1975), appears to be that the traces of the interthecal septa of the prothecae are more or less perpendicular to the dorsal wall of the rhabdosome.

Pseudomonoclimacis tetlitensis n. sp. (Pl. 1, figs. I, J; Figs. 2E-21)

Catalogue listing 1978 Pristiograptus aff. P. haupti (Kiihne) or P. ultimus

(Pemer) Jackson, Lenz, and Pedder, P1. 2, Figs. 1 - 3. 1984 Pristiograptus cf. haupti (Kiihne) Lenz, p. 969,

Figs. le, lh- lj.

Origin of name Tetlitensis, refemng to Tetlit Creek, the locality of the type

species.

Material About 20 specimens, 2 preserved in partial relief, the

remainder flattened but reasonably well preserved, from 44.5, 49.5, 51, and 73.5 m of Tetlit Creek. A few specimens also occur on Hart River at 85 ft (27 m) (see Jackson and Lenz 1972).

Diagnosis Rhabdosome small, dorsal side gently dorsally curved,

sicula strongly ventrally curved. Thecae steeply inclined, outer margin glyptograptid in profile. Interthecal septa distinct.

Description Rhabdosome small, greatest length 6.6 rnrn, weakly but con-

sistently dorsally curved between levels of thecae 4 - 7, straight thereafter. Width increases rapidly from 0.6 -0.7 mm across theca 1 to 1.1 - 1.2 mm in the region of theca 4 or 5 and is constant distally. The7ae inclined 40 - 50°, overlap increases rapidly from about 2 between thecae 1 and 2, to about : or 2 by theca 3 and beyond. Ventral margin of thecae prorni- nently glyptograptid in profile, prothecal septum straight or curved, more or less perpendicular to dorsal wall of rhabdosome. Thecae densely packed, numbering 9- 12 in 5 rnm.

Sicula 1.4 - 1.8 mm long, strongly ventrally curved, aperture distinctly concave, virgella long, straight, sicular apex at level of, or beyond aperture of, theca 2. Discussion

The species resembles P. dalejensis BouEek (= P. haupti Kiihne: fide Jaeger in KKi et al. 1986) primarily in the strong ventral curvature of its sicula and, to some extent, in the thecal profile (cf. Kiihne 1955; Urbanek 1958; Jaeger 1978 and in Kiii et al. 1986). It differs in possessing a more strongly ventrally curved sicula, a much more rapidly widening rhabdosome, much more densely spaced thecae, and greater overlap of the thecae.

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360 CAN. J. EARTH SCI. VOL. 25,1988

The species differs from P. ? ultimus and P. parultimus (see Jaeger 1975 and in Kiii et al. 1986) in lacking a hooked first theca and in its much more rapidly widening rhabdosome.

The same species occurs in strata of about mid-Ludlow age in northern Cornwallis Island (Jackson et al. 1978).

Age Found on Tetlit Creek within the probably mid-Ludlow

fritschi linearis Zone in association with the zonal species, P.? bispinosus n. sp., B. bohemicus bohemicus, and others. On Cornwallis Island it is associated with similar taxa.

Pseudomonoclimacis richardsonensis n. sp. (Figs. 2 0 - 2T)

Catalogue listing 1969 Monograptus aff. M. kosoviensis (BouEek) Jackson

and Lenz, p. 26, P1. 3, fig. 5; P1. 5, figs. 1, 5. 1978 "Monograptus" aff. " M . kosoviensis (BouEek)

Jackson, Lenz, and Pedder, P1. 3, fig. 9.

Origin of name Richardsonensis, after the Richardson Mountains, in which

the species occurs.

Material Several dozen specimens, all flattened, mostly only

moderately preserved, from 8 1.5, 82.5, 86, 87.5, and 95 m of the Falcon Creek section. Well-preserved specimens are, in addition, present on the Porcupine River (Jackson and Lenz 1969), and dozens were recovered from Hart River (Jackson and Lenz 1972).

Diagnosis Rhabdosome long, essentially straight. Sicula straight to

weakly ventrally curved, with long virgella. Thecae glyptograptid in profile, except theca 1, which is orthograptid.

Description Rhabdosome may exceed 30 mm in length, straight through-

out or with a weak ventral curvature at the level of thecae 4 -6. Width increases very gradually from 0.8-0.9 mm across theca 1, attaining a maximum width that may exceed 2.0 mm, but is generally 1.6- 1.9 mm, about the level of thecae 15 - 17. Theca 1 essentially orthograptid in profile with concave ventral margin and markedly isolated from theca 2. Remainder of thecae distinctly glyptograptid in rofile, overlapping 1-5, P inclined about 30". Thecal spacing 5 2 - 4 in 5 rnm proximally and 7-8 in 10 mm distally. Interthecal septa not clearly dis-

Discussion The orthograptid outline of theca 1 and glyptograptid outline

of the remainder of the thecae, as well as the straight to slightly ventrally curved sicula with its long virgella, make the species unique.

It differs from P. kosoviensis in its monoclimacid thecal profile and distinctive sicula. This is particularly evident in comparison with P. aff. kosoviensis of Koren' (1986).

Koren' (1986) illustrates a number of species of Pseudo- monoclimacis, but all differ from the Yukon species in the nature of the sicula and the unique, isolated, orthograptid-like theca 1.

Age Found primarily in the formosus Zone of Falcon Creek,

Porcupine River, and Hart River. Its occurrence on Hart River may begin in the overlying chelmiensis Zone.

Pseudomonoclimacis? bispinosus n. sp. (Figs. 2J-2N)

Origin of name Bispinosus, after the possession of two prominent sicular

spines.

Material About 15 specimens, all flattened, of moderate preservation,

from 44.5,47, and 49.5 m of Tetlit Creek and a few specimens from 4.5 m of Falcon Creek.

Diagnosis Rhabdosome very small, very gradually widening, straight.

Sicula slightly ventrally curved, with long, divergent virgellar and anti-virgellar spines.

Description Rhabdosome small and immature, straight throughout

length, largest specimen with 5 -6 thecae. Thecae weakly and uniformly monoclimacid in profile, inclined about 20°, overlapping at least one half length. No hint seen of perpendicular prothecae interthecal septa. Rhabdosome widens very gradually to a maximum of about 0.75 mm, thecae number about 61 in 5 rnrn.

Sicula relatively long and narrow, gently ventrally curved, 1.4 - 1.7 mm in length, apex attaining level of about midpoint of ventral wall of theca 2. Sicula provided with long (probably in excess of 1.0 mm), stout virgella and an equally long and stout anti-virgellar spine. Spines diverge about 130".

cernible, but those of prothecae appear to be perpendicular to Discussion the rhabdosome axis. Pits or nodes generally present in area of The assignment of this taxon to Pseudomonoclimacis is ten- probable junction between prothecal and metathecal septa. tative, primarily because of the absence of a clear indication of

Sicula straight to, generally, ventrally curved, 2.2 -2.3 mm a protheca interthecal septum. in length, apex attaining level of theca 2 or 3. Virgella long The species is unique because of its possession of two long, and stout, projecting proximo-ventrally; anti-virgellar process divergent sicular spines and the narrow, very delicate and very short and robust. gradually widening rhabdosome. The possibility that this spe-

PLATE 1 FIGS. A-E. Abiesgraptus? sp. Tetlit Creek, 256.6 m, x 1. Note: A, D, and E show apparently single (unpaired) primary and secondary

cladial stipes. GSC 86188, 86189, 86190, 86191, and 86192. FIGS. F-H. Monograptus fanicus Koren', Tetlit Creek, x5 . F, H, 287 m, H partially pyritized, GSC 86193 and 86165. G, 275.5 m, partially

pyritized, GSC 86166. FIGS. I, J. Pseudomonoclimacis tetlitensis n. sp. Tetlit Creek, 49.5 m, x 10. 1, pyritized and in relief, holotype GSC 86135; J , paratype

GSC 86137. FIGS. K - 0 . Monograptus aequabilis bardoensis Po~bska . Tetlit Creek, 246.5 m, ~ 5 . GSC 86152, 86153, 86155, 86194, and 86195. FIGS. P, Q. Pristiograptus separabilis Teller. Tetlit Creek, 181.5 m, x5 . GSC 86134, and 86196.

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362 CAN. I. EARTH SCI. VOL. 25.1988

cies might be merely a Linograptus juvenile was raised by one of the referees. The continuous widening of the (albeit short) rhabdosome would seem to preclude this.

Age From the fritschi linearis Zone of Tetlit Creek and Falcon

Creek.

GENUS Monograptus Geinitz 1852 Monograptus aequabilis bardoensis Porqbska

(Pl. 1, figs. K-0; Figs. 3A-3F)

Catalogue listing 1984 Monograptus aequabilis bardoensis Poqbska, p. 194,

Figs. 2811 -28116.

Material Dozens of specimens, all flattened and of fair to good preser-

vation, from 246.5 and 247 m of Tetlit Creek.

Discussion This species is, according to Poqbska (1984), characterized

by a more or less straight rhabdosome, which is generally weakly ventrally curved in the region of thecae 4-6 (6-8 in the Tetlit Creek material); a dorsally curved proximal region, primarily due to the presence of a broadly triangular sicula; and two to four hooked proximal thecae.

The Tetlit Creek specimens are very similar in every respect, except that the first two thecae are generally more strongly hooked than the two subsequent ones. The remaining thecae of the Yukon material are, like those of the Polish material, fur- nished with short apertural processes.

Parameters are as follows: rhabdosome generally less than 20 mm long, width increasing fairly rapidly from 0.9 - 1.3 mm across theca 1 to level of thecae 6-8, then slowly to a distal maximum of 1.8 - 2.3 mm. Thecae spaced 6: -7 in 5 mm proximally and 5;-6 in 5 mm distally. Sicula moderately to broadly triangular, attaining a length of 1.8 -2.3 mm.

According to Poqbska (1984), stratigraphically lower specimens possess a longer and narrower sicula (1.8 - 2.3 mm) than those from higher strata (1.6- 1.8 mm). On that basis, it is tentatively suggested that the Tetlit Creek specimens are representative of the falcarius Zone.

The subspecies differs from the coeval M. aequabilis notoaequabilis Jaeger and Stein in possessing a more broadly triangular sicula, a distinct proximal dorsal curvature, and generally a greater width.

cf. 1986 Monograptus anerosus (Koren') Koren', p. 87, P1. 17, figs. 1-7; Fig. 11.

Material A single, flattened specimen of moderate preservation, from

the upper canyon of Peel River.

Discussion Distinctive of the species is the weak to moderate dorsal cur-

vature of the proximal region, the strong ventral curvature of the sicula, and the long, claw-like thecal hoods. The latter may occupy up to one third of the rhabdosomal width.

Although only moderately well preserved, the Peel River specimen generally coincides with the parameters of the Kazakhstan material in length of sicula (1.7 mm), number of thecae (7; in 5 mm proximally and 6 in 5 mm distally), and a maximum width of 2.2 mm. Furthermore, it appears to be similar in possessing very long thecal hoods, although comparison is difficult with the much better preserved Kazakhstan specimens.

Age Probably within the latest Pridoli transgrediens praecipuus

Zone. According to Koren' (1983, 1986) the species ranges through the bouceki and the lower part of the transgrediens-pemen Zone in the USSR.

Monograptus ceratus n. sp. (Figs. 3G-31)

Catalogue listing 1984 Monograptus uncinatus (Tullberg)? Lenz, p. 97, Figs.

If, lg.

Origin of name Cerato, Greek for homed, referring to the long, stout virgel-

lar and anti-virgellar spines.

Material Seven specimens, including UW02672 (see Lenz 1984),

flattened but moderately well preserved from 49.5 m of Tetlit Creek.

Diagnosis Rhabdosome straight, slightly ventrally curved proximally.

Thecae hooded throughout, hoods tend to increase in size distally. Sicula long, provided with long, stout virgellar spine and anti-virgellar spine, diverging about 130".

Age Description Tentatively correlated with the falcarius Zone of Koren' Rhabdosome small, maximum 15 mm in length, generally

(1975) and Poqbska (1984). straight or very weakly ventrally curved to the level of thecae

Monograptus cf. anerosus Koren' 5 -7. Width increases gradually from 0.6-0.7 mm across

(Fig. 2U) theca 1 to a maximum of 1.7 mm, inclusive of thecal hoods, distally. Thecae hooded throughout rhabdosome, hoods gen-

Catalogue listing erally weakly defined at theca 1 but strong thereafter and cf. 1983 Monograptus anerosus Koren', p. 412, P1. 49, showing a tendency to become more robust distally. Inter-

figs. 1-5; Fig. 3. thecal septa sigmoidal; pustules, probably at the juncture

FIG. 2. (A-D) Pristiograptus separabilis Teller. Falcon Creek (locality 6), 181.5 m, x7 . GSC 86131, 86132, 86133, and 86134. (E- I) Pseudomonoclimacis tetlitensis n. sp. Tetlit Creek (locality 3), X 14. E-G, 49.5 m; H, I, 51 m. G, holotype GSC 86135, partially pyritized; E, F, H, I, paratypes GSC 86136, 86137, 86138, and 86139. Specimen H slightly tectonically broadened. (J-N) Pseudomonoclimacis? bispinosus n. sp. Tetlit Creek, X 14. J, K, 47 m; L-N, 44.5 m. N, holotype GSC 86140; J-M, paratypes GSC 86141, 86142, 86143, and 86144. ( 0 -T) Pseudomonoclimacis richardsonensis n. sp. Falcon Creek, x7 . 0, Q, R, T, 81.5 m; P, S, 87.5 m. S, holotype GSC 86145; 0 -R, T, paratypes GSC 86146, 86147, 86148, 86149, and 86150. (U) Monograptus cf. anerosus Koren'. Peel River upper canyon (locality 5), 957 m (2975A), x7 . GSC 86151.

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364 CAN. 1. EARTH SCI. VOL. 25, 1988

between prothecae and metathecae, may be present. Thecae 6 - 7 in 5 mm proximally and 5; - 6 in 5 mm distally.

Sicula narrow, 1.8 - 2.1 mm long, apex attaining level of about theca 2. Virgella and anti-virgella spine at least 0.9 mm long, stout; former directed ventrally to proximo-ventrally, latter directed proximo-dorsally, diverging about 130".

Discussion As noted in Lenz (1984), the species resembles M. unci-

natus in rhabdosomal and thecal characteristics; it differs markedly, however, from that and any other species in the possession of the long, diverging virgellar and anti-virgellar spines.

M. aequabilis bardoensis and M. a. notoaequabilis, a fact fully appreciated by Porebska (1984). It differs in the more persistent and un i fody developed thecal hoods, a trumpet- shaped sicula, and a strongly ventrally hooked sicular dorsal process.

The species is now widely known, having been already reported from south central USSR (Koren' 1975), Arctic Islands (Jackson et al. 1976), and Poland (Poqbska 1984). It constitutes the basis of a separate zone, the fanicus Zone in the USSR and Poland, and its Yukon occurrence stratigraphically below the lowest appearance of M. telleri and M. yukonensis supports a separate zonal assignment.

Age Age

Assigned to the fanicus Zone. On Tetlit Creek, it is Probably from thefntschi linearis Zone. It is associated with separated by 58 of banen shales from the lowest occurrence Bohemograptus b. bohemicus and lies 3.5 m below the lowest of yukonensis; in the Peel River lower canyon, it occurs

occurrence of B. b. tenuis. 10 m above M. aequabilis notoaequabilis. Monograptus fanicus Koren'

(Pl. 1, figs. F-H; Figs. 3K-3R) Monograptus hercynicus hercynicus Pemer

(Figs. 4A -4D) Catalogue listing Catalogue listing

1975 Monograptus fanicus Koren', p. 9, P1. 2, figs. 4 -8; 1899 Monograptus hercynicus Pemer, p. 19, Fig. 13. P1. 3, figs. 1-3; P1.4, figs. 3-8;Pl. 8, figs. 6-21. 1959 Monograptus hercynicus (Pemer) Jaeger, p. 87, P1. 1,

lg76 Monogra~nrr fanicus (Karen') lackson, Kerr, and f igs 1, 10; PI. 2; P I 3, fig. 1 ; Figs. 15a- 15h. Morrow, p. 39, Figs. 21, 22. 1960 Monograptus hercynicus (Pemer) Teller, p. 331,

1979 Monograptus fanicus (Koren') Lenz, p. 1122, Fig. 1 Figs. a- i . (1 -4). 1968 Monograptus hercynicus (Pemer) Obut, p. 947,

1984 Monograptus fanicus (Koren') Poqbska, p. 198, .6 - .7a. Figs. 2912 -2917. 1969 Monograptus hercynicus (Perner) Koren' , p. 1325, Material Figs. 2.1-2.3.

Dozens of specimens, flattened, many well preserved, from 1971 Monograptus hercynicus (Pemer) Lenz, and Jackson, 275.5,277,281?, 282.5,285?, and 287 m of Tetlit Creek; and P. 7, PI. 1, figs. 1-6; Figs. 2A-2F. from 485 ft (155 m) of a poorly collected section in the lower 1984 Monograptus hercynicus hercynicus (Pemer) canyon of Peel River (see Lenz 1979). Poqbska, p. 162, Figs. 2011 -20119.

Description Rhabdosome seldom more than 20 mm long, straight

throughout or with a gentle ventral or dorsal curvature, in the proximal region. Width increases at a moderate rate from 0.9- 1.0 mm across theca 1 to the level of thecae 5-7, then gradually thereafter to attain a maximum width of 1.5- 2.0 mm distally, 1.8 mm being average.

Thecae hooded, theca 1 generally strongly hooked, seldom exposing aperture, subsequent thecae generally exposing aperture and hoods becoming progressively smaller distally. Inter- thecal septa sigmoidal. Thecae 6;-73 in 5 mm proximally, 53 - 6 in 5 mm distally.

Sicula broadly triangular to, more commonly, flaring toward aperture and imparting strong dorsal curvature to proximal end of rhabdosome. Sicula 1.8 -2.1 rnrn in length, apex attaining level of theca 2 or 3. Virgella short, projecting proximo- ventrally; dorsal process large, linguloid, sharply curved in ventral direction.

Material Eight specimens of poor to moderate preservation from

158 m of Falcon Creek and a few from Peel River, 3435 ft (1097 m) of Jackson et al. (1978). In addition, 22 specimens were reported by Lenz and Jackson (1971) from Prongs Creek (Fig. 1, locality 8).

Discussion The subspecies is well known in Europe, North Africa,

China, southeast Asia, and the USSR, and a closely allied subspecies, M. hercynicus nevadensis, is reported from Nevada (Beny 1967).

This distinctive subspecies is characterized by strongly hooded thecae and a moderately to strongly flaring, trumpet- shaped sicula, which is, however, devoid of a dorsal process. In the last feature, it is quite unlike Monograptus aequabilis bardoensis.

According to Poqbska (1984), the stratigraphically higher morphs possess a much more flared sicular aperture than the

Discussion lower forms, which are more or less confined the hercynicus This species is very distinctive and is comparable only to Zone proper. On the basis of this, the Yukon specimens much

FIG. 3. (A-F) Monograptus aequabilis bardoensis Poqbska. Tetlit Creek, 246.5 m, ~ 7 . GSC 86152, 86153, 86154, 86155, 86156, and 86157. Specimens B and D slightly twisted. (G-I) Monograptus ceratus n. sp. Tetlit Creek, 49.5 m, x 7. G, holotype GSC 86158; H, I, paratypes GSC 86159 and 86160. (J-R) Monograptus fanicus Koren'. Tetlit Creek. K, L, N, x14; M, 0 - R , ~ 7 . K-M, 0 - R , 275.5 m; J , N, 287 m. GSC 86161, 86162, 86163, 86164, 86165, 86166, 86167, 86168, and 86169. (S -X) Saetograptusffitschi linearis (BouEek). S, V , X, Falcon Creek, 13.5 m, x7, X14, x7 . T, Tetlit Creek, 47 m, x7 . U, W , Hart River (locality 7), 10.3 m (32 ft), X7. GSC 86170, 86171, 86172, 86173, 86174, and 86175.

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366 CAN. J . EARTH SCI. VOL. 25,1988

more resemble the older morphs (sicular widths 0.5 -0.7 mm) and therefore are probably representative of the restricted hercynicus Zone.

Age From the hercynicus Zone on Falcon Creek, Prongs Creek,

and Peel River. It is associated with M. uniformis parangustidens at Falcon Creek.

Monograptus uniformis parangustidens Jackson and Lenz (Figs. 4E -4L)

Catalogue listing 1972 Monograptus uniformis parangustidens Jackson and

Lenz, p. 594, Figs. ID-11, 1M-10. 1984 Monograptus uniformis parangustidens (Jackson and

Lenz) Poqbska, p. 144, Figs. 1411 -14111.

Material Dozens of specimens, all flattened, from 148, 148.5, 150,

and 158 m of Falcon Creek, and about 20 specimens from Peel River 3315 ft (1059 m) of Jackson et al. (1978). This is in addition to the dozens of samples from Hart River, the section from which the type was described in Jackson and Lenz (1972).

Discussion This subspecies is distinguished from other members of the

uniformis group, i.e., M. uniformis uniformis and M. uniformis angustidens, by its narrower average width, by its gentle but persistent dorsal proximal curvature, and, most importantly, by its very gradual widening. It is further differ- entiated in lacking ventral curvature in the region of thecae 5-6, so common in the other subspecies. The dorsal sicular process is thin and generally straight but may be moderately ventrally curved.

Parameters are as follows: sicula attains a length of 1.8 - 2.1 mm, thecae are spaced 6 -6; in 5 mm proximally and 5; - 51 in 5 mm distally, and width ranges from 0.7-0.8 mm across theca 1, reaching 1.1 - 1.4 mm across theca 5, to a maximum of 1.7 - 1.9 mm at or beyond theca 15.

The newly collected material ranges higher stratigraphically than reported in Jackson and Lenz (1972), in that it extends to the hercynicus Zone. Poqbska (1984) reported it from the uniformis zone.

In some respects the subspecies is similar to M. craigensis (see Churkin et al. (1970) and especially Koren' (1975)). It differs in possessing a much less delicate-looking and much less dorsally curved proximal end, lacking the "hump- backed" profile of the dorsal wall, and in lacking the robust and strongly ventrally incurved dorsal sicular process.

Age Latest Silurian Pridoli and (or) earliest Devonian uniformis

Zone to the hercynicus Zone but probably most common in the uniformis Zone.

FIG. 4 . (A-D) Monograptus hercynicus hercynicus Pemer. A, C, D, Falcon Creek, 158 m, X 7, X 7, X 14; B, Peel River upper canyon (locality 5), 1104.5 m (3435 ft), x 7 . GSC 86176, 86177, 86178, and 86179. (E-L) Monograptus uniformis parangustidens Jackson and Lenz. E, I, K, Falcon Creek, 148 m, X7; F, G, J, Hart River, 138.3 m (430 ft), x 7 ; H, L, Peel River upper canyon, 1066 m (3315 ft), x 7 . GSC 86180, 86181, 86182, 86183, 86184, 86185, 86186, and 86187.

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LENZ 367

GENUS Saetograptus Pfibyl 1942 Description Saetograptus fitschi linearis (BouEek) Specimens fragmentary, obviously of a large species. Multi-

(Figs. 3s - 3X) branching; primary stipe straight and robust, first- and second- order cladia straight to gently curved. First- and second-order

Catalogue listing cladia arising in pairs from a common point or apparently aris- 'g36 Monogra~tus fitschi linearis BouEek, p. 148, Figs.

ing Spacing between first- or second-order cladia vari- 3r-3u. able, observed to be 20-50 mm. Primary cladium robust, at

1979 Monogra~tus fritschi linean's (BouEek) Jaeger and least 1.5 - wide; second-order cladia 0 9 - 1.1 mm wide Robardet, P1. 1, fig. 6. Thecae simple tubes, inclined about 30°, with overlzp of not

1986 Saetogra~tus fn'tschi cf. linearis (BouEek) h n z , and more than one half, and numbering 6 in 5 mm. Sicular region Melchin, p. 1856, Figs. 1, 2a, 2b. not seen. Material

About two dozen specimens of fair to moderate preservation, from 13.5 m of Falcon Creek, and three from Tetlit Creek, 47 m. In addition, approximately two dozen complete and fragmented, mostly poorly preserved specimens from Hart River were assigned to M. leintwardinensis primus by Jackson and Lenz (1972). These specimens, some of which show bifur- cated "spines," are clearly assignable to M. fritschi linearis.

Discussion This subspecies is readily recognizable by its straight rhab-

dosome; its flaring sicula, which imparts a distinct dorsal curvature to the proximal region of the rhabdosome; a ventrally directed sicular dorsal process; and its highly inclined and basically simple tube-like thecae, which possess long, bifur- cating spines or lappets.

Parameters are as follows: sicula 1.7 - 1.9 mm long, thecae number 6:-7 in 5 mm proximally and about 6 in 5 mm distally, and the rhabdosome attains a maximum width of 1.7 - 1.9 rnm, inclusive of "spines."

The poor illustrations of the sicular and thecal details of M. fntschi linearis by BouEek (1936), Pinlbyl (1942), and Munch (1952) made positive comparison impossible. However, the specimen illustrated as that subspecies by Jaeger and Robardet (1979) is clearly of the same species as occurs in the northern Yukon, and only for that reason are the Arctic specimens now unequivocally assigned to BouEek's subspecies. The parameters and thecal characteristics of the Yukon specimens coincide exactly with those from the Arctic Islands (Lenz and Melchin 1986).

The subspecies differs from Saetograptus pilosus Jackson and Lenz (= S. chimaera alaskaensis (Ruedemann)) in being relatively much straighter and wider and in possessing a flaring sicula and generally more continuous and robust thecal ' 'spines. "

The presence of this subspecies in about the same part of the stratigraphic column in three sections and its consistent position just below the lowest occurrence of Bohemograptus bohemicus tenuis are considered a good basis for the establishment of a separatefritschi linearis Zone.

Age About mid-Ludlow, occurring within the zone of the same

name.

GENUS Abiesgraptus Hundt 1935 ?Abiesgraptus sp. (Pl. 1, figs. A-E)

Material Numerous fragments of branches, some long and branching

more than once, from 256.5 m of Tetlit Creek.

Discussion The first report of the North American occurrence of Abies-

graptus was from lower Lochkovian strata of Nevada (Berry 1968, 1970). The genus had been previously recognized only from central Europe (Hundt 1935, 1965; Munch 1952; Jaeger 1959) and from Morocco (Willefert 1966).

The Yukon species appears to differ from known species in the possession, sometimes, of apparently nonpaired cladia, although illustrations by Hundt (1935, 1965) show some specimens without paired cladia-a feature that could be a preserva- tional phenomenon. More importantly, however, the Yukon specimens differ from any known species in possessing secondary cladia.

The species differs from Linograptus in possessing first- and second-order cladia that are spread out along the (presumably) primary stipe.

Abiesgraptus? sp. occurs in strata that are younger than Nevadan, European, or Moroccan occurrences of Abies- graptus.

Age The species lies above Monograptus aequabilis bardoensis

and below M. fanicus and may, therefore, be assignable to either the falcarius? or the fanicus zones, both being Pragian in age.

NOTE ADDED IN PROOF: Subsequent to the final revision of this paper, H. Jaeger examined some of the writer's specimens. He is of the opinion that the so-called Monograptus aequabilis bardoensis Poqbska of this paper falls readily within the morphological range of Monograptus fanicus Koren'. The writer is now in agreement with Jaeger. The ramifications of this are threefold: Monograptus aequabilis bardoensis of this study becomes M. fanicus, the tentatively recognized falcarius Zone is eliminated, and the fanicus Zone is expanded.

Acknowledgments The cheerful and able field assistance provided by

M. Melchin during the summer of 1986 is gratefully acknowledged. Logistic support provided by the Geological Survey of Canada, in particular through D. W. Morrow, is heartily acknowledged. Financial support for travel and incidentals, as well as for laboratory costs, was provided by a Natural Sciences and Engineering Research Council of Canada operat- ing grant. The valuable comments of the referees, particularly H. Jaeger, are acknowledged.

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upper silurian and lower devonian graptolites and graptolite biostratigraphy, northern yukon, canada

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