Of Western Cape Breton Island, Eastern Canada, 2: Surface Markings Dave G
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Document généré le 28 sept. 2021 00:15 Atlantic Geology Systematic ichnology of the Mabou and Cumberland groups (Carboniferous) of western Cape Breton Island, eastern Canada, 2: surface markings Dave G. Keighley et Ron K. Pickerill Volume 34, numéro 2, summer 1998 Résumé de l'article Des strates du Carbonifere (Namurien-Westphalien A) des groupes de Mabou et URI : https://id.erudit.org/iderudit/ageo34_2art01 de Cumberland affleurent sur une surface etendue dans l'ouest de l'tle du Cap-Breton. On releve en outre dans ces strates une collection diversified de Aller au sommaire du numéro terriers, de pistes, de trous et de coprolites decrits anterieurement; un grand nombre de marques au sol, en majeure partie des pistes, comme celles du Diplichnites cf. logananus (Marsh), du Diplichnites isp. (types A et B), du Éditeur(s) Gluckstadtella eooperi Savage, de YHexapodichnus horrens Hitchcock, duMonomorphichnus cf. lineatus Crimes et colli, du Protichnites cf. Atlantic Geoscience Society carbonarius Dawson, du Protichnites cf. kennediea (Smith), du Protichnites cf. scoticus Salter, du Protichnites cf. variabilis (Linck), du Protichnites isp. (types ISSN A, B, C et D) et de la Stiallia cf. pilosa Smith, des marques d'appendices (types A et B), une trace "d'arthropode au repos", des traces en surface en forme de 0843-5561 (imprimé) corne et des pistes de vertebres (types A, B, C, D, E, et F). 1718-7885 (numérique) [Traduit par la redaction] Découvrir la revue Citer cet article Keighley, D. G. & Pickerill, R. K. (1998). Systematic ichnology of the Mabou and Cumberland groups (Carboniferous) of western Cape Breton Island, eastern Canada, 2: surface markings. Atlantic Geology, 34(2), 83–112. All rights reserved © Atlantic Geology, 1998 Ce document est protégé par la loi sur le droit d’auteur. L’utilisation des services d’Érudit (y compris la reproduction) est assujettie à sa politique d’utilisation que vous pouvez consulter en ligne. https://apropos.erudit.org/fr/usagers/politique-dutilisation/ Cet article est diffusé et préservé par Érudit. Érudit est un consortium interuniversitaire sans but lucratif composé de l’Université de Montréal, l’Université Laval et l’Université du Québec à Montréal. Il a pour mission la promotion et la valorisation de la recherche. https://www.erudit.org/fr/ A tlantic G eology 83 Systematic ichnology of the Mabou and Cumberland groups (Carboniferous) of western Cape Breton island, eastern Canada, 2: surface markings Dave G. Keighley* and Ron K. Pickerill Department of Geology, University of New Brunswick, Fredericton, New Brunswick E3B 5A3, Canada Date Received July 17, 1997 Date Accepted February 9, 1998 Carboniferous (Namurian- Westphalian A) strata of the Mabou and Cumberland groups outcrop extensively in western Cape Breton Island. As well as a diverse collection of burrows, trails, pits, and coprolites described previ ously, numerous surface marks, mostly trackways, were encountered in these strata: Diplichnites cf. logananus (Marsh), Diplichnites isp. (types A and B), Gluckstadtella cooperi Savage, Hexapodichnus horrens Hitchcock, Monomorphichnus cf. lineatus Crimes et al., Protichnites cf. carbonarius Dawson, Protichnites cf. kennediea (Smith), Protichnites cf. scoticus Salter, Protichnites cf. variabilis (Linck), Protichnites isp. (types A, B, C, and D), Stiallia cf. pilosa Smith, Appendage Marks (types A and B), an “Arthropod Resting” Trace, Horn-shaped Surface Traces, and Vertebrate Trackways (types A, B, C, D, E, and F). Des strates du Carbonif&re (Namurien-Westphalien A) des groupes de Mabou et de Cumberland aifleurent sur une surface dtendue dans l’ouest de l’ile du Cap-Breton. On rel&ve en outre dans ces strates une collection diversifide de terriers, de pistes, de trous et de coprolites ddcrits antdrieurement; un grand nombre de marques au sol, en majeure partie des pistes, comme celles du Diplichnites cf. logananus (Marsh), du Diplichnites isp. (types A et B), du Gluckstadtella cooperi Savage, de 1’Hexapodichnus horrens Hitchcock, da Monomorphichnus cf. lineatus Crimes et colli., da Protichnites cf. carbonarius Dawson, du Protichnites cf. kennediea (Smith), du Protichnites cf. scoticus Salter, du Protichnites cf. variabilis (Linck), du Protichnites isp. (types A, B, C etD) et de la Stiallia cf. pilosa Smith, des marques d’appendices (types A et B), une trace “d’arthropode au repos”, des traces en surface en forme de come et des pistes de vertdbrds (types A, B, C, D, E, et F). [Traduit par la rddaction] I ntroduction vertebrate and invertebrate trackways and explain the prin This paper describes and discusses several of the trace ciples behind our nomenclatural decisions. As stated in Keighley fossils encountered at various localities in western Cape Breton and Pickerill (1996b, 1997) and Pickerill and Keighley (1997), Island (Fig. 1). The numerous surface markings described (pri an ichnotaxon can only be formally named (and hence diag marily trades and trackways) occur in Carboniferous (Namurian- nosed) from distinguishing morphological features, follow Westphalian A) Mabou and Cumberland Group strata that ing the guidelines of the International Code of Zoological have been confidently inferred to be the products of fluvial, Nomenclature (I.C.Z.N., 1985). Criteria such as (a) the phy floodplain, and lacustrine sedimentation in half grabens main togeny of the producer, (b) stratigraphic limitation of the trace tained by a transtensional tectonic regime (Keighley and Pickerill, fossil, or (c) the environment in which the trace fossil was 1996a). The surface markings may occur exclusive of, or asso produced, are not criteria that can be directly, or objectively, ciated with, the trace fossils already described from these observed or proven in a type specimen. Therefore they re strata by Keighley and Pickerill (1997); Baird (personal com main hypothetical concepts and so cannot be used to pro munication, 1989,1994) and his co-workers have collected vide a name based upon the ‘Principle of the Name-bearing additional material that remains undescribed. Future work will Type’ (I.C.Z.N., 1985, p. xiii, Article lb-1). Specifically, fora assess the palaeoenvironmental distribution of our specimens. name now to be available, it must upon introduction include a description of characteristics that purport to make the N omenclatural p r o b l e m s and terminology (trace-) fossil unique (I.C.Z.N., Article 13a-i), which the above criteria cannot conclusively provide. Saijeant and Kennedy Before presenting our taxonomic classification of the trace (1973), Saijeant (1975,1990), andMagwood (1992), amongst fossils from the study area, it is necessary to first comment others, have also provided excellent and compelling reasons on the chaotic taxonomic nomenclature that exists for both for rejecting such criteria in favour of a morphologically based nomenclature. Saijeant (1990) further noted that there is nothing •Current Address: Department of Earth Sciences, University of to prevent use of parallel names based on systematic affinity Liverpool, Brownlow Street, Liverpool, England, L69 3BX where the investigation being undertaken requires such a Atlantic Geology 34, 83-112 (1998) 0843-5561/98/020083-3085.50/0 84 K eighley and P ickerill behaviour at a high level of significance (significant features), and ichnospecies from features considered to result from behaviour of less importance (secondary features). Such in terpretations of significant behaviour are highly subjective and, fiithermore, morphological terminology itself is not cov ered by the I.C.Z.N. or any other code. Accordingly such terms often have different definitions attached to them, re sulting in nomenclatural confusion. For clarity, therefore, our use of certain morphological terms follows Keighley and Pickerill (1997) and the definitions below. A ‘trackway’ is herein defined as a succession of indi vidual marks that collectively form a ribbonlike structure at a sedimentary (or, potentially, an extrusive igneous) interface (in contrast, a trail represents a continuous mark left on the substrate: no separate marks are preserved—Trewin, 1994). A trackway should be characterized by two ‘rows’ of imprints, or two ‘track rows’ (or, interpretively, two rows of appendage marks, Fig. 2A). Typically the rows would represent records of both the left- and right-sided appendages of an animal that were produced while supporting itself above the substrate during locomotive activity, since almost all animals known to be capable of such locomotion have bilateral symmetry. If it cannot be determined whether two rows of imprints are present, then they can simply be described as a sequence of ‘tracks’ (Fig. 2). The shapes of individual prints also varies, and the terminology we use is given in Figure 2B. Within a row, a ‘natural track cycle’ (Anderson, 1975) contains a single im print from each of the producing appendages (but that may include imprints of separate digits extending from one ap pendage) from one side of the body (Fig. 2C—this term is preferred to Trewin’s ‘imprint series’). Essentially, only two phylogenetic groups, the vertebrates and arthropods, produce trackways (but vagile Echinoder- mata are a potential exception, and need not have bilateral symmetry either, e.g., Sutcliffe, 1997). Trackways formed by vertebrates can usually be distinguished from those produced by invertebrates, primarily by their form and geometry. Thus, when the qualifiers ‘vertebrate’ or ‘invertebrate’ are applied Fig. 1. Location map of trace-fossil localities