Palaeophycus bolbitermilus isp. nov. from the Lower Silurian Upsalquitch Formation of New Brunswick, Eastern Canada.
Le Palaeophycus bolbitermilus, une nouvelle ichnoespece de Palaeophycus Hall, a ete releve dans des strates turbiditiques de la Formation du Silurien inferieur d'Upsalquitch dans le Nord du Nouveau-Brunswick, dans l'Est du Canada. Cette ichnoespece est non ramifiee, elle est marquee de lignes fines, elle est unie et sans relief, et, par opposition aux ichnoespeces precedemment definies de Palaeophycus, elle se caracterise par une terminaison piriforme uniformement developpee a une extremite.
Traduit par la redaction
The ichnogenus Palaeophycus was first defined by Hall (1847, p. 7) as "Stem terete, simple or branched, cylindric or subcylindric; surface nearly smooth, without transverse ridges, apparently hollow". It was originally considered by Hall (1847) as the stem of a "fucoid" but later interpreted as a trace fossil (e.g., James 1885). Over the next century or so, numerous ichnospecies of Palaeophycus were defined, particularly during the years 1847 to 1883, but in a seminal and exhaustive review Pemberton and Frey (1982) reduced the then known 54 ichnospecies to a taxonomically recognizable 5. These were P. tubularis Hall, 1847, P. striatus Hall, 1852, P. heberti (Saporta, 1872), P. sulcatus (Miller and Dyer 1878) and P. alternatus Pemberton and Frey, 1982. Pemberton and Frey (1982) distinguished these on the nature of the burrow linings (thin or thick) and external surface characteristics (unornamented, striate, annulate or alternately striate and annulate). They regarded the remainder of historically defined form s as synonyms of the 5 they recognized, as nomina oblita, nomina dubia, nomina nuda, inorganic or assignable to alternative ichnogenera (Pemberton and Frey 1982, pp. 852 - 853). The simplified nomenclature proposed by Pemberton and Frey (1982) was, and continues to be, widely adopted by the ichnological fraternity. Nevertheless, it is clear that it cannot always be universally applied because several additional, apparently aberrant, ichnospecies have subsequently been formulated. These include P. ferrovittatus Hofmann, 1983; P. subornatus Ghare and Kulkarny, 1986; P. annulatus Badve, 1987; P. anulatus McCann and Pickerill, 1988; P. canalis Walter, Elphinstone and Heys, 1989; P. serratus McCann, 1993; P. beifengwanensis Luo, Tao and Gao, 1994 and P. crenulatus Buckman, 1995. In a review of most of these ichnospecies, Buckman (1995) regarded several as nomina dubia (P. annulatus, P. anulatus, P. canalis, P. serratus), a conclusion with which we agree. Notwithstanding, herein we recognize and describe an additio nal ichnospecies, namely P. bolbitermilus, isp. nov. that we regard as ichnotaxonomically distinct.
LOCATION AND GEOLOGICAL SETTING
The material documented herein was collected from two inland locations within the Lower Silurian Upsalquitch Formation in the Upsalquitch Forks area of northern New Brunswick, eastern Canada (Fig. 1), specifically:
1. On a logging road adjacent to Cravens Gulch, 1.1 km west of the Northwest Upsalquitch River, 3.6 km southwest of Upsalquitch Forks; Lat. 47[degrees] 39' 15" N, Long. 66[degrees] 44' 54" W, and
2. On Dalhousie Road, 3.6 km northwest of the bridge over the Southeast Upsalquitch River, 2.7 km east-northeast of Upsalquitch Forks; Lat. 47[degrees] 40' 44" N, Long. 66[degrees] 40' 22" W.
In the Upsalquitch Forks area, the Upsalquitch Formation is the oldest lithostratigraphic unit and forms the basal sequence of the Early Silurian Chaleurs Group (Fig. 1). The formation is approximately 1800 m in thickness (Wilson 2000). It is comprised of dominantly thin to very thin (10-40 mm) calcareous siltstones and shales, with interbeds of sporadically distributed and thicker (10-40+ mm) fine-grained sandstones and calcarenites (St. Peter 1978; Wilson 2000). Partial Bouma sequences in the siltstones and sandstones, several slump horizons and flutes and grooves on the soles of several layers collectively attest to its origin as a deep-water turbiditic sequence, most probably deposited on a slope.
Thirty ichnospecies have been recognized in the Upsalquitch Formation (Kim et al., unpublished data). At the two aforementioned locations, P. bolbitermilus isp. nov. occurs in association with Calycraterion isp., Cochlichnus anguineus Hitchcock, 1858, Didymaulichnus lyelli (Rouault 1850), Furculosus carpathicus Roniewicz and Pienkowski, 1977, Helminthopsis hieroglyphica Wetzel and Bromley, 1996, Palaeophycus heberti, Planolites annularius Walcott, 1890, Planolites montanus Richter, 1937, Planolites terraenovae Fillion and Pickerill, 1990 and Teichichnus rectus Seilacher, 1955.
The material described herein is housed in the New Brunswick Museum, Saint John, New Brunswick, Canada and is prefixed NBMG.
Ichnogenus Palaeophycus Hall, 1847
Type ichnospecies: Palaeophycus tubularis Hall, 1847, by subsequent designation (Miller 1889, P. 130).
Diagnosis: Branched or, more typically, unbranched, straight to curved to slightly undulose, smooth or ornamented, lined, predominantly horizontal cylindrical structures of variable diameter; fill typically structureless and similar to the host rock; when present bifurcation is not systematic, nor does it result in swelling at the site of the branching (after Pemberton and Frey 1982; Fillion and Pickerill 1990).
Discussion: Following several discussions with respect to differentiation of Palaeophycus from the morphologically similar ichnotaxon Planolites Nicholson (e.g., Osgood 1970; Pemberton and Frey 1982; Fillion 1989; Fillion and Pickerill 1990, Keighley and Pickerill 1995) there is now general agreement that the presence of a lining in the former and an absence in the latter is the significant ichnotaxobase (sensu Fursich 1974) enabling ichnogeneric distinction. As noted by Keighley and Pickerill (1995) other ichnotaxobases and ethological considerations are, without exception, subordinate to this directive.
Palaeophycus bolbitermilus isp. nov. Figs. 2, 3
Diagnosis: Horizontal to slightly oblique, thinly lined, unbranched, smooth and unsculptured, cylindrical burrow typically, though not exclusively, with a massive, structureless fill and characterized by a bulb-like termination at one extremity.
Etymology: Greek bolbi = bulb-like and Latin termilus = ending, in reference to the characteristic morphology of the ichnospecies.
Material: Sixteen specimens on 4 rock slabs, NBMG 11013 - 11016. Rock slabs NBMG 11013 - 11015 are from locality 2 of Fig. 1; NBMG 11016 is from locality 1.
Holotype: NBMG 11013/I
Paratypes: NBMG 11013/2 - II
Additional specimens: NBMG 11014/1 - 2; NBMG 11015/1 - 2; NBMG 11016/1
Description: Descriptive terminology is illustrated schematically in Fig. 4, and size and morphological data for each specimen, where available, are indicated in Table 1. All specimens are preserved in convex hyporelief, more rarely in full relief, on the soles of 10-40 mm thick, parallel-to cross-laminated, fine-grained sandstone layers and comprise two basic elements, namely a horizontal cylindrical tube and a bulb-like termination at one extremity.
The cylindrical tubes are straight and typically parallel to stratification, although two specimens (NBMG 11015/1 and 11016/1) occur at 35-45[degrees] to bedding. They are up to 20 mm long but are typically truncated as a result of weathering and also invaginated into the terminal bulb; presumably, therefore, they were originally longer. Cross-sectional shape is elliptical, a result of compaction and/or deformation, with long axes varying from 5.4-10.5 mm and short axes from 3-9 mm; the resultant cross-sectional ratios (length/width) vary from 1.1-2.0. Tube-fill is either massive and structureless and similar in grain size to the host rock, or, less commonly (Table 1), possesses weakly developed concave-downward laminae at and towards the base of the tubes. Where observable, tubes possess a distinct but thin (approximately 0.1mm) mudstone lining. Outer surfaces of tubes are typically smooth; superficial and irregularly developed wrinkles/striations on NBMG 11014/1 -2, 11016/1 are considered compactional and n ot primary features.
The terminal bulbs are typically hemispherical to hemielliptical and superficially resemble the cap of a button-shaped mushroom; they curve steeply at their lateral margins and then steeply inward within the host rock. Vertical sectioning of several examples indicated a structureless infill but no additional vertical or oblique continuity into the overlying substrate, though admittedly this is the typical situation with trace fossils preserved in semi-relief on turbidite soles. The obliquely preserved specimen 11016/1 (Fig. 3d) does, however, suggest that the bulbs were originally spheroidal or elliptical structures and had no such continuity, as also illustrated by us schematically in Fig. 4. Each bulb possesses at least 8, possibly up to 12, radial grooves; interspersed with these may be regular to irregular, less deeply impressed fine grooves. Several also possess concentric regular to irregular grooves or ridges. The bulbs are 4-8 mm in length and 8.5-24 mm in width (Table 1); width/tube diameter ratio is 1.1-2.5; width/length ratio is 1.6-3.0.
Discussion: It is tempting to equate P. bolbitermilus, as formulated and described herein, with several previously established ichnotaxa, particularly as the material is essentially preserved in semi-relief. The ichnogenera Arthraria Billings, Bifungites Desio and Diplocraterion Torell are obvious candidates in semi-relief preservation. However, these ichnogenera all possess expanded terminations at both extremities and the latter two have vertical components extending from these. Arthraria, although lacking vertical elements, is also characterized by a dumb-bell morphology, and as with Bifungites and Diplocraterion but unlike P. bolbitermilus, the expanded terminations are unsculptured (see Fillion and Pickerill 1984). Furthermore, these ichnotaxa consistently exhibit a dumb-bell morphology, a feature totally absent in P. bolbitermilus. Additionally, a minor consideration is that these ichnogenera are almost invariably associated with neritic and not turbiditic sequences. Superficially, the material describe d herein also closely resembles several ichnospecies of Phycodes Richter; however, these possess flabellate or broom-like (not bulb-like) terminations (see Han and Pickerill 1994). It also resembles several plug-shaped ichnotaxa (e.g., Calycraterion Karaszewski), as reviewed by Pemberton et al. (1988), but all these are vertical structures and clearly differ from the essentially horizontally oriented specimens of P. bolbitermilus. Specimens of the recently formulated Sphaerichnus lobatus Fursich, 1998 are also broadly comparable in that this ichnotaxon is also essentially a horizontal tube that, at least schematically (Fursich 1998, p. 269), possesses irregular spherical structures along its course. The latter does, however, differ substantially from the material described herein (see below).
Following the recommendations of Pickerill (1994), we consider the significant features (morphology related to distinct behaviour -- sensu Fursich 1974) of this material to be the presence of a generally horizontal, more rarely oblique, cylindrical and lined tube that typically possesses an internally structureless fill (see also Schlirf 2000). Accordingly, at the ichnogeneric level, it is best assigned to Palaeophycus, most commonly interpreted ethologically as a dwelling structure (domichnion), produced infaunally, and subsequently passively infilled (Pemberton and Frey 1982; Keighley and Pickerill 1995). That the tubes were in fact infaunal open structures and subsequently passively infilled is supported, respectively and collectively, by preservation of several specimens in full relief, the presence of (albeit thin) distinct linings and the occurrence in several examples of a basal concave-upward laminate fill. Indeed, had the material not possessed the bulb-like terminations, it could have easily been as signed to P. tubularis, itself characterized by a thin lining and smooth external surface.
We regard the bulb-like termination, although an integral component, as an accessory feature (minor variation of trace maker behaviour -- sensu Fursich 1974). Its presence distinguishes it not only from P. tubularis but also from all other previously documented ichnospecies of Palaeophycus, none of which possess such a feature. The origin and function of the bulb remain enigmatic. As noted above, however, S. lobatus also possesses bulb-or ball-like structures along its course. These differ from the bulb-like terminations of P. bolbitermilus in several respects. First, S. lobatus comprises irregularly spherical structures with radial lobes and cylindrical horizontal axial extensions; second, the lobes possess chevron-patterned external ridges; and, third, they possess a fill of faecal pellets. Nevertheless, as also suggested by Fursich (1998) for his material, it seems likely that the terminal cavity of P. bolbitermilus served some specific purpose. Based on the presence of abundant faecal pellets in S. lobatu s, Fursich (1998) interpreted its bulb-like structures as refuse dumps. P. bolbitermilus bulbs contain no faecal pellets and, therefore, a similar origin is unlikely. Alternative functions could possibly be related to breeding, bacterial farming, or as "turn around" structures but there is no definitive evidence to substantiate any of these possibilities.
Table 1 Size and morphological data, in millimeters, for most specimens of P. bolbitermilus from the Lower Silurian Upsalquitch Formation of northern New Brunswick (see Fig. 4 for legend) Tube Tube Bulb Bulb Sample length diameter length diameter Lining (long/short) NBMG 11013/1 14 6.7/5 7 14 n.o. NBMG 11013/2 11 7/5.5 7 11.5 0.2 NBMG 11013/3 9 10.5/6 8 15 n.o. NBMG 11013/4 4 7/3.5 4 11.3 0.1 NBMG 11013/5 4 5(?)/3.5 5 (?) 10 (?) 0.1 NBMG 11013/6 4 7.5/4.5 5 9.5 0.1 NBMG 11013/7 4 12/6.5 5 15 0.1 NBMG 11013/8 2 7.5/4 5 8.5 0.1 NBMG 11013/9 21 9.4/5.8 8 13.5 0.1 NBMG 11013/10 7 8/4 (?) 7 13 n.o. NBMG 11013/11 15 8.5 (?) 8 12 n.o. NBMG 11014/1 13 6.7/4 (?) 4.6 8.5 n.o. NBMG 11014/2 8 (?) 5.4/3 (?) n.o. 10,4 n.o. NBMG 11015/1 5 7.8/7 n.o. 12 0.1 NBMG 11015/2 7 (?) 8/n.o. 5 (?) 10 n.o. NBMG 11016/1 7 9.5/9 n.o. 24 0.1 Bulb Sample Tube fill ornament NBMG 11013/1 Massive RG,CR NBMG 11013/2 Laminate RG,CR NBMG 11013/3 Massive RG,CG NBMG 11013/4 Massive RG,CR NBMG 11013/5 Massive n.o. NBMG 11013/6 Laminate RG NBMG 11013/7 Massive RG NBMG 11013/8 Laminate RG NBMG 11013/9 Massive RG NBMG 11013/10 n.o. RG,CG NBMG 11013/11 n.o. RG,CG NBMG 11014/1 Massive n.o. NBMG 11014/2 Massive n.o. NBMG 11015/1 Massive RG,CG NBMG 11015/2 Massive RG NBMG 11016/1 Laminate CG (?), approximate value; RG, radial grooves; CG, concentric grooves; CR, concentric ridges; n.o., not observed
We thank A. Gomez, R. McCulloch and K. Shea for technical assistance and D. Keighley and D. Mossman for encouraging reviews. R.K.P. acknowledges a National Sciences and Engineering Council of Canada grant that supported this research. J.Y. Kim thanks the University of New Brunswick for providing facilities during his sabbatical leave. Fieldwork by R.A. Wilson in the Upsalquitch Forks area was carried out as part of the Appalachian Foreland and Platform NATMAP Project.
Date Received: March 14, 2001
Date Accepted: June 19, 2001
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Jeong Yul Kim (1)
Ron K. Pickerill (2)
Reg A. Wilson (3)
(1.) Department of Earth Science Education, Korea National University of Education, Cheongwon, Chungbuk 363-791, Korea
(2.) Department of Geology, University of New Brunswick, Fredericton, NB E3B 5A3, Canada
(3.) New Brunswick Department of Natural Resources and Energy, Geological Surveys Branch, P.O. Box 50, Bathurst, NB E2A 3Z1, Canada
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