No abstract

Sixty-six suites of trace fossils from thirty-four different localities were collected or observed in the Carboniferous Mabou and Cumberland groups of western Cape Breton Island. Recurrent suites have been compiled into thirteen ichnocoenoses. Twelve of these ichnocoenoses, together with others from the Carboniferous elsewhere in the Maritimes, can be considered representative of two revised ichnofacies and their related composite ichnofacies. The remaining ichnocoenosis is currently anomalous. In our view, some ichnofacies identifi ed in the nonmarine realm have been too broadly defi ned. They allow for the inclusion of ichnocoenoses that are better considered representatives of composite ichnofacies. The Mermia ichnofacies is thus emended to consist primarily of systematic-coverage interface burrows and trails, irregular interface burrows and trails, non-striate pits, sinusoidal burrows and trails, migrating burrows, systematic-coverage burrow networks, (dense coverage) simple burrows and, if present, subordinate trackways. It remains an ichnofacies indicative of quiet water, oxygenated, permanently subaqueous conditions with signifi cant organic input. Two Cape Breton Island ichnocoenoses are representative of the revised Mermia ichnofacies. The Scoyenia ichnofacies is emended to consist primarily of bilobate or striate pits and trails, trackways, meniscate burrows, (sparse coverage) simple burrows and, if present, subordinate vertical burrows. It remains an ichnofacies indicative of transitional environments, specifi cally quiet water conditions that regularly dry out, or periodically inundated fl oodplains. Four Cape Breton Island ichnocoenoses are representative of the revised Scoyenia ichnofacies. Six ichnocoenoses from Cape Breton Island contain some trace fossils considered typical of both the Mermia and Scoyenia ichnofacies as emended. Two interpretations are possible. These ichnocoenoses might indicate instances where the trace-fossil producers were environmentally tolerant animals that could inhabit and behave similarly in either setting. Alternatively, they may represent cases where producers active in different environments had their traces juxtaposed or even overprinted due to a change in environmental conditions. In this latter case, the ichnocoenoses can be considered examples of composite ichnofacies that are taphonomic successors of combinations of the Mermia, Scoyenia, and the well-established Skolithos ichnofacies. RÉSUMÉ Soixante-six ensembles d'ichnofossiles de 34 emplacements différents ont été prélevés ou observés dans les groupes carbonifères de Mabou et de Cumberland dans l'ouest de l'île du Cap-Breton. Les ensembles répétitifs ont été compilés au sein de 13 ichnocoenoses. Douze de ces ichnocoenoses, auxquelles on peut ajouter les autres exemplaires du Carbonifère présents ailleurs dans les Maritimes, peuvent être considérées comme des types représentatifs de deux ichnofaciès révisés et de leurs ichnofaciès composites connexes. Les autres ichnocoenoses constituent actuellement des types...

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) 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) [Traduit par la rddaction] I n t r o d u c t io nThis paper describes and discusses several o f the trace fossils encountered at various localities in western Cape Breton Island (Fig. 1). The numerous surface markings described (pri marily trades and trackways) occur in Carboniferous (Namurian-W estphalian A) M abou and Cumberland Group strata that have been confidently inferred to be the products of fluvial, floodplain, and lacustrine sedimentation in half grabens main tained by a transtensional tectonic regime (Keighley and Pickerill, 1996a). The surface markings may occur exclusive of, or asso ciated with, the trace fossils already described from these strata by Keighley and Pickerill (1997); Baird (personal com munication, 1989Baird (personal com munication, ,1994 and his co-workers have collected additional material that remains undescribed. Future work will assess the palaeoenvironmental distribution of our specimens.N o m e n c l a t u r a l p r o b l e m s and t e r m in o l o g y Before presenting our taxonomic classification o f the trace fossils from the study area, it is necessary to first comment on the chaotic taxonomic nom enclature that exists for both •Current Address: Department of Earth Sciences, University of Liverpool, Brownlow Street, Liverpool, England, L69 3BX vertebrate and invertebrate trackways and explain the prin ciples behind our nomenclatural decisions. As stated in Keighley and Pickerill (1996b, 1997) and Pickerill and Keighley (1997), an ichnotaxon can only be formally nam ed (and hence diag nosed) from distinguishing morphological features, follow ing the guidelines o f the International Code o f Zoological Nomenclature (I.C.Z.N., 1985). Criteria such as (a) the phy togeny of the producer, (b) stratigraphic limitation of the trace fossil, or (c) the environm ent in which the trace fossil was produced, are not criteria that can be directly, or objectively, observed or proven in a type specimen. Therefore they re main hypothetical concepts and so cannot be used to pro vide a name based upon the 'Principle o f the Name-bearing Type' (I.C.Z.N., 1985, p. xiii, Article lb-1). Specificall...

Strata of the Mabou and Cumberland groups (Namurian-Westphalian A) outcrop extensively in western Cape Breton Island. Trace fossils were encountered at various localities, and include: Circulichnus montanus (nom. correct.), Cochlichnus anguineus, Cochlichnus isp., Conichnus isp., Cruziana problematica, Didymaulichnus cf. lyelli, Diplopodichnus biformis, Gordia marina, Helminthopsis abeli, Helminthopsis hieroglyphica, Palaeophycus striatus, cf. Palaeophycus,Phycodespedum, Planolites beverleyensis,Planolites terraenovae, cf. Planolites, Rusophycus carbonarius, cf. Rusophycus, Selenichnites isp., Taenidium barretti, cf. Taenidium, Thalassinoides suevicus, Undichnus binus (nom. correct.), Undichnus consulcus (nom. correct.), cf. Undichnus, coprolites, interface trails (types A, B, and C), plug-shaped burrows, small ovate pits (types A, B, and C), and vertical 'escape' structures. In total (including tracks and trackways not described herein), twenty-two ichnogenera have been identified that comprise a total of eighteen named ichnospecies, eight ichnospecies retained in open nomenclature, and thirteen unnamed ichnospecies. A further ten trace-fossil morphologies (comprising twenty different types) are retained in the ver nacular.On trouve de vastes affleurements de strates des groupes de Mabou et de Cumberland (Namurien -Westphalien A) dans l'ouest de Tile du Cap-Breton. On y a releve des ichnofossiles en divers endroits, notamment: le Circulichnus montanus (nom corrige), le Cochlichnus anguineus, le Cochlichnus isp., le Conichnus isp., le Cruziana problematica, le Didymaulichnus cf. lyelli, le Diplopodichnus biformis, le Gordia marina, le Helminthopsis abeli, le Helminthopsis hieroglyphica, le Palaeophycus striatus, cf. le Palaeophycus, le Phycodes pedum, le Planolites beverleyensis, le Planolites terraenovae, cf. le Planolites, le Rusophycus carbonarius, cf. le Rusophycus, le Selenichnites isp., le Taenidium barretti, cf. le Taenidium, le Thalassinoides suevicus, VUndichnus binus (nom corrige), VUndichnus consulcus (nom corrige), cf. P Undichnus, des coprolites, des pistes de reptation de jonction (types A, B et C), des trous de forme cylindrique, de petites fossettes ovees (types A, B et C) et des structures de " fuite " verticales. On a releve au total (et ce, y compris des traces et des traces non decrits aux presentes) 22 ichnogenres comprenant 18 ichnoesp&ces nominees, huit ichnoespeces retenues dans une nomenclature ouverte et 13 ichnoespeces sans nom. On retient en plus les noms vulgaires de dix autres formes d'ichnofossiles (qui comprennent 20 types differents). Morphological terminology is not covered by the I.C.Z.N. and, unfortunately, such term inology frequently has differ ent definitions attached to it, potentially causing nomenclatural confusion. For clarity, therefore, it should be noted that our use o f 'burrow', 'w all', 'lin in g', 'm eniscus', and 'branching' follow s K eighley and Pickerill (1 9 9 4 ,1 9 9 5 ). A 'm ould' is a 'negative' o f the original structure and a 'cast' is a reproduction ...