Palaeoecology of transported brachiopod assemblages embedded in black shale, Cape Phillips Formation (Silurian), Arctic Canada Pengfei Chen, Jisuo Jin ⁎, Alfred C. Lenz Department of Earth Sciences, University of Western Ontario, London, Ontario, Canada N6A 5B7 abstract article info Article history: Received 3 December 2010 Received in revised form 9 July 2011 Accepted 12 November 2011 Available online 21 November 2011 Keywords: Brachiopod assemblage Palaeoecology Sea level Silurian Arctic Canada Brachiopod communities have been widely used for palaeoecological studies and reconstruction of sea-level changes in Earth history. Previous studies of brachiopod communities emphasised sampling benthic shelly fossils preserved in situ to avoid preservation bias. Silurian (Wenlock) brachiopod assemblages are well pre- served as debris-turbidity flows, including calcareous concretions, embedded in thick sequences of black shale of the Cape Phillips Formation, with a mixture of deep-water brachiopods and transported shallow- water forms. In this study, the first attempt is made to use the transported assemblages to reconstruct Silu- rian brachiopod communities that once lived along a palaeogradient from the shallow-water Arctic Platform to the deep-water Franklinian Basin. Seven transported brachiopod assemblages were recognised using mul- tivariate analyses (cluster analysis and principal components analysis), with varying ratios of shallow- versus deep-water shells, segregated according to their known palaeobathymetric ranges in other regions. The Wenlock– early Ludlow sea-level fluctuations in the study area, reconstructed using the percentage values of shallow- and deep-water brachiopod specimens as a proxy, have a high degree of agreement with the Arctic Silurian sea-level curve and moderate agreements with global sea-level histories of other regions such as the British Isles and Got- land interpreted from graptolite abundance and diversity changes, and sequence and event stratigraphical methods, respectively. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Large deposits of black shale or other types of organic carbon-rich sediments are extremely rare in modern oceans, which is in sharp contrast to the widespread distribution of black shale or organic- rich mudrock during the Palaeozoic and Mesozoic eras (for a recent summary, see Page et al., 2007; Negri et al., 2009). In the palaeocon- tinent of Laurentia, black shales are common, especially in Ordovi- cian, Silurian, and Devonian systems, with kilometre-thick sequences in deep basins along the palaeocontinental margin extending into thinner tongues in intracratonic basins. It is generally believed that such black shale successions recorded long episodes of intense oceanic anoxia. In Arctic Canada, the Silurian strata contain kilometre-thick suc- cessions of black shale, commonly interbedded with varying amount of allochthonous and autochthonous limestones, including nodules and nodular beds, such as in the Cape Phillips Formation in the Corn- wallis Fold Belt and the Road River Formation in the Selwyn Basin and Richardson Trough (Lenz, 1972; Norford, 1997a,b). Laterally, the deep-water shale-dominated facies grades relatively abruptly into the carbonate rocks of the Arctic Platform. Because of the lack of modern analogues in comparable scales of time and space, however, the exact depositional environment of the black shale has been difficult to interpret, especially regarding the water depth and the mechanisms controlling long periods of intense anoxia over vast areas of seemingly open seas. Yet, large fluctuations of graptolite diversity recorded in the thick Silurian black shale successions imply episodes of major changes in ocean water chemistry, temperature, and circulation, which are difficult to decipher from the relatively monotonous strata alone. In the black shale sequences, however, there are numerous car- bonate interbeds, mostly derived from debris-turbidity flow deposits with abundant brachiopod shells from shallow-water platforms telescoping into deeper-water basin slopes and preserved with the deeper-water species entrained and transported downslope. These benthic shelly components hold significant information (such as fluctuations in water depth, oxygen content, and proximity to basin edge) about the predominantly anoxic–dysoxic depositional environ- ments, but the palaeoecology of such transported and mixed brachio- pod assemblages is difficult to interpret, and has been commonly avoided in most previous reconstructions of brachiopod communities. In the classic works on depth-related early Silurian brachiopod commu- nities or benthic assemblages (e.g. Ziegler, 1965; Boucot, 1975), for ex- ample, the reconstruction of palaeoenvironments, palaeobathymetry and sea-level emphasises in-situ preservation of the shelly benthos (e.g. Ziegler et al., 1968; Hancock et al., 1974; Cocks and McKerrow, 1978; Johnson and Campbell, 1980; Johnson et al., 1981, 1985, 1991a, Palaeogeography, Palaeoclimatology, Palaeoecology 367–368 (2012) 104–120 ⁎ Corresponding author. E-mail address: jjin@uwo.ca (J. Jin). 0031-0182/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2011.11.013 Contents lists available at SciVerse ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo