Lower Ordovician Trilobites from the Baumann Fiord Formation, Ellesmere Island, Arctic Canada

1523 Lower Ordovician trilobites from the Baumann Fiord Formation, Ellesmere Island, Arctic Canada Jonathan M. Adrain and Stephen R. Westrop Abstract: Sections through member B of the Baumann Fiord Formation on the Bache Peninsula, Ellesmere Island, Arctic Canada, contain a range of lithofacies indicating deposition in shallow subtidal settings above storm wave base. Macrofossils are generally rare, but low-diversity trilobite-dominated faunas occur in a section near Sanddöla Creek. The only other fossils common in the collections are poorly preserved gastropods. All of the trilobite species are apparently new, and four are formally named: Licnocephala sanddoelaensis, “Peltabellia” baumannensis, Bolbocephalus ellesmerensis, and Ceratopeltis bachensis. The species Ceratopeltis forteyi is introduced for material previously described from North Greenland. Rare additional species of Licnocephala and Jeffersonia are reported in open nomenclature. The trilobites occur in three stratigraphically and lithologically distinct associations, with species diversity ranging from two to four. Closest comparisons of the trilobite species all indicate that member B should be assigned to the Tulean Stage of the Ibexian Series. Rananasus Cullison, 1944, is placed in synonymy of Bolbocephalus Whitfield, 1890. Résumé : Des coupes dans le membre B de la formation de Baumann Fiord, dans la péninsule Bache de l’île d’Ellesmere, dans l’Arctique canadien, présentent divers lithofaciès qui témoignent de milieux de dépôt infralittoraux peu profonds situés au-dessus de la zone d’action des vagues de tempête. Les macrofossiles y sont généralement rares, mais des assemblages fauniques de faible diversité dominés par des trilobites sont présents dans une coupe exposée à proximité du ruisseau Sanddöla. Les seuls autres fossiles répandus dans ces collections sont des gastéropodes en mau- vais état de conservation. Toutes les espèces de trilobites qui s’y trouvent sont vraisemblablement nouvelles, et des noms formels ont été assignés à quatre de celles-ci, soit Licnocephala sanddoelaensis, « Peltabellia » baumannensis, Bolbocephalus ellesmerensis et Ceratopeltis bachensis. L’espèce Ceratopeltis fortey est introduite pour du matériel dé- crit antérieurement provenant du nord du Groenland. D’autres rares espèces de Licnocephala et Jeffersonia sont égale- ment signalées en nomenclature ouverte. Les trilobites se présentent dans trois associations distinctes sur les plans stratigraphique et lithologique, comptant chacune de deux à quatre espèces. La comparaison des espèces de trilobites aux assemblages d’autres régions indique que le membre B de la formation de Baumann Fiord devrait être affecté au stade tuléen de l’Ibexien. Rananasus Cullison, 1944, est placé en relation de synonymie avec Bolbocephalus Whitfield, 1890. [Traduit par la Rédaction] Adrain and Westrop 1546 Introduction Ellesmere Island by Mossop (1979). Here, we describe the trilobite fauna and sedimentology of the middle part The Lower Ordovician Baumann Fiord Formation is a (member B) of the formation at two localities on the Bache shallow-water unit developed on the Arctic Platform across Peninsula, east-central Ellesmere Island (Fig. 1). the southern and eastern Canadian Arctic Archipelago (Kerr Lower Ordovician (Ibexian) trilobite faunas have been 1967, 1968, 1974; Thorsteinsson and Kerr 1968; McGill documented from northern Greenland (Poulsen 1927, 1937; 1974; Morrow and Kerr 1977; Mayr 1978, 1980; Mossop Fortey 1986; Fortey 1979, 1989, 1990), but Poulsen (1946) 1979; Mayr and de Freitas 1992; Turner and Mayr 1999). is the only substantial publication to date on those of Arctic The formation is represented in northern Greenland as the Canada. Shallow-water faunas similar to those from Green- Poulsen Cliff and Nygaard Bay formations (see Peel and land have been described from western Newfoundland (Fortey Christie 1982) and was studied in detail across central and Peel 1983; Boyce 1989) and from the Laurentian Hebridean Terrane in Scotland (Fortey 1992). The faunas from member B of the Baumann Fiord Formation are not Received 29 July 2004. Accepted 28 April 2005. Published precisely age equivalent to any previously described from on the NRC Research Press Web site at http://cjes.nrc.ca on 23 November 2005. the northern and eastern Laurentian regions, and all of the species present are apparently new. Paper handled by Associate Editor B. Chatterton. J.M. Adrain.1 Department of Geoscience, University of Iowa, Iowa City, IA 52242, USA. Stratigraphic setting S.R. Westrop. Oklahoma Museum of Natural History and The Baumann Fiord Formation (Kerr 1967) is part of a School of Geology and Geophysics, University of Oklahoma, thick Cambrian–Devonian package deposited on the Arctic Norman, OK 73072, USA. Platform, a region in the southern and eastern Arctic in 1Corresponding author (e-mail: [email protected]). which the Phanerozoic strata have not been deformed on a Can. J. Earth Sci. 42: 1523–1546 (2005) doi: 10.1139/E05-054 © 2005 NRC Canada 1524 Can. J. Earth Sci. Vol. 42, 2005 Fig. 1. (a) Position of Bache Peninsula on east-central Ellesmere Island (box, enlarged in b). (b) Position of measured sections at Sanddöla Creek (SCr) and Bartlett Bay (BB). regional scale (Trettin 1991). During the Late Cambrian – Mossop (1979) regarded the evaporite cycles of members Middle Ordovician, the southeastern portion of the platform A and C as coastal sabkha deposits that formed under appears to have been in the form of a rimmed shelf, rather supratidal conditions. More recently, Trettin et al. (1991) than a carbonate ramp, with extensive peritidal deposits suggested a subaqeous origin in a broad, shallow, saline basin, (Mossop 1979; Trettin et al. 1991). The rim itself is pre- and Higgins et al. (1991) favoured a similar interpretation served only locally (Trettin et al. 1991, p. 178, fig. 8B.2), for correlative evaporites of northwestern Greenland. The and the succession in the study area was deposited in what carbonates of member B were treated briefly by Mossop, has been interpreted as an intrashelf basin inboard of the who regarded them as having formed in a restricted, shallow, rim. Evaporites are developed locally in the Late Cambrian shelf lagoon. Here, we describe the lithofacies of member B peritidal successions of the Cass Fjord Formation of eastern in the study area and present an environmental interpretation. Ellesmere Island (Christie 1967; Trettin et al. 1991, p. 175, fig. 8B.12), whereas the Baumann Fiord Formation records a Study area regionally extensive, Early Ordovician episode of evaporite deposition that extended across Ellesmere, Bathurst, and Sections were measured on the west and east ends of the Cornwallis islands. The evaporites can also be traced east- Bache Peninsula, central Ellesmere Island, at Sanddöla Creek ward across the Kane Basin into Washington Land, north- (SCr) and Bartlett Bay (BB), respectively (Figs. 1, 2). The western Greenland, where they are assigned to the Poulsen study site at Sanddöla Creek (Figs. 3a,3b) lies just to the Cliff and Nygaard Bay formations (Peel and Christie 1982; east of locality 9 of Christie (1967) and section 5 of Mossop Higgins et al. 1991). (1979, p. 7). The lower contact is not exposed, but the 29 m The Baumann Fiord Formation is divided into three infor- section through member B (Fig. 2) is nearly complete be- mal members, in ascending order, members A, B, and C cause Mossop (Table 2) recorded a thickness of 33 m at his (Kerr 1968) (Figs. 3a,3b). Members A and C are composed section. Trilobites were recovered from float in two thin, of metre-scale, carbonate–evaporite cycles (Mossop 1979, talus-covered intervals in the lower half of the member fig. 10), whereas member B is composed exclusively of car- (Fig. 2). The section at Bartlett Bay was measured on the bonates. Member A accounts for most of the formation and, south side of the bay, along the east side of a stream gully according to Mossop (1979, Table 2), is 188 m in thickness that is occupied by the major fault indicated in Christie’s at Sanddöla Creek, Ellesmere Island; members B and C map. Only 13 m of member B is exposed at Bartlett Bay reach 33 m and 44 m in thickness, respectively, at Sanddöla (Fig. 2) and, from the presence of thrombolites at the base, Creek. In Washington Land, northeastern Greenland, the this interval probably correlates with the lower half of the Poulsen Cliff Formation (100–125 m) consists of interbedded section at Sanddöla Creek, about 40 km to the west. No carbonates and evaporites, and the overlying, thinner Nygaard trilobites were recovered, and the section is illustrated to aid Bay Formation (40 m) is divided into a lower carbonate unit understanding of the depositional environments. and an upper evaporite-rich interval that are equal in thickness (Peel and Christie 1982; Higgins et al. 1991). Thus, the Lithofacies Poulsen Cliff Formation can be correlated with member A, and the Nygaard Bay Formation is equivalent to members B Intraclastic rudstone and bio-intraclastic packstone and C. This lithofacies occurs in units that range from 5 cm to © 2005 NRC Canada Adrain and Westrop 1525 Fig. 2. Stratigraphic columns of sections at Sanddöla Creek (showing position of collections SCr-L and SCr-U) and Bartlett Bay. The inset shows a generalized stratigraphic column of the Princess Marie Bay region. Camb., Cambrian; M.O., Middle Ordovician. more than1minthickness, with the latter comprising several posed of clasts of, and interbedded with, microbial

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