https://doi.org/10.1130/G48060.1 Manuscript received 22 June 2020 Revised manuscript received 30 July 2020 Manuscript accepted 30 July 2020 © 2020 The Authors. Gold Open Access: This paper is published under the terms of the CC-BY license. Nailed to the craton: Stratigraphic continuity across the southeastern Canadian Cordillera with tectonic implications for ribbon continent models M.E. McMechan1, K.G. Root2, P.S. Simony3 and D.R.M. Pattison3 1 Geological Survey of Canada, Natural Resources Canada, 3303 33 Street NW, Calgary, Alberta T2L 2A7, Canada 2 Consultant, 54 Wildwood Drive SW, Calgary, Alberta T3C 3C5, Canada 3 Department of Geoscience, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada ABSTRACT The debate over whether there is a hidden Cambrian and Upper Devonian to Mississippian strata can be confidently traced westward, or cryptic suture has identified the need to reas- without strike-slip offset, from the autochthonous section above North American basement sess the stratigraphic succession in the south- into the southeastern Canadian Cordillera, and are thus “nailed” to the craton. These strata eastern Canadian Cordillera. In this study, we are in turn stratigraphically pinned to older (Mesoproterozoic Belt-Purcell Supergroup, analyzed the stratigraphic succession in terms Neoproterozoic Windermere Supergroup, and Ediacaran), intermediate-aged (Ordovician– of its linkage to the adjacent North American Silurian), and younger (Permian to Middle Jurassic) strata found only in the mountains, craton. Here, we briefly summarize stratigraphic thus linking them to the adjacent autochthonous craton. The overlapping distribution of information accumulated by systematic map- linking successions, regionally traceable unique stratigraphic horizons in the Belt-Purcell ping, stratigraphic studies, and subsurface drill- and Windermere Supergroups, and across-strike stratigraphic features show that the entire ing. We focus on key units and features within Cariboo, northern Selkirk, Purcell, and Rocky Mountains are directly tied to the adjacent the Belt-Purcell, Windermere, and Paleozoic to North American craton without discernible strike-slip or oblique displacement, or substan- Middle Jurassic successions to document their tial purely convergent plate-scale (>400 km) horizontal displacement. They link the entire stratigraphic continuity with the adjacent North width of the Belt-Purcell and Windermere basins in the southeastern Canadian Cordillera American craton and test whether there is an to the adjacent craton and show that any proposed Cretaceous ribbon continent suture, with identifiable gap in stratigraphic continuity as its thousands of kilometers of proposed displacement, cannot run through the southeastern proposed by ribbon continent models. Canadian Cordillera. STRATIGRAPHIC LINKAGES INTRODUCTION et al., 2019) or continue southward (John- Five main tectono-stratigraphic sequences Several hypotheses have been proposed in ston, 2008). According to these models, all comprise the stratigraphic succession exposed recent decades postulating that there is a major pre-Cretaceous strata west of the proposed in the southeastern Canadian Cordillera: (1) suture or subduction zone of Cretaceous age suture would have moved north thousands of the Mesoproterozoic Belt-Purcell Supergroup within the foreland of the Canadian and Amer- kilometers and represent exotic units. In the (BPSG); (2) Neoproterozoic Windermere ican Cordillera that separates far-traveled or Rubia ribbon continent models, this includes Supergroup (WSG); (3) Ediacaran–Silurian non–North American terrane or “ribbon conti- all exposures of Mesoproterozoic Belt-Purcell and (4) Middle Devonian–Middle Jurassic nent” rocks from North American rocks. These and most exposures of Neoproterozoic Winder- sedimentary strata deposited along the rifted include the Cordilleria (Lambert and Chamber- mere strata. In addition, an implicit assumption margin of the North American craton; and (5) lain, 1988), SAYBIA (Siberia–Alaska–Yukon– in the ribbon continent models is that there was Upper Jurassic–Paleocene foreland basin strata British Columbia; Johnston, 2008; Chen et al., substantial removal of intervening oceanic(?) (e.g., Price, 1981). Our analysis is restricted to 2019), and Rubia ribbon continent models crust and lithosphere between the craton and high-level discussions of stratigraphic details in (Hildebrand, 2013, 2014). In the southeastern ribbon continent. There is little discussion in each pre–foreland basin sequence. We used the Canadian Cordillera, the surface location of any of these papers about specific geologi- “nails and links” principle, which states that if a the suture is interpreted to be along the South- cal evidence that supports the identification stratigraphic unit c is observed, in outcrop and/ ern Rocky Mountain Trench in the Cordilleria of the suture in outcrop, and Johnston (2008) or in boreholes, to lie with depositional contact model, or adjacent to or at the Kicking Horse and Chen et al. (2019) referred to the suture on cratonal basement, with no tectonic inter- Rim Lower Paleozoic facies change in the as “cryptic.” Major stratigraphic and structural ruptions, it is there “nailed” to the craton. At SAYBIA and Rubia models (Fig. 1). Where summaries of the southeastern Canadian Cor- a place to the west, where units b-c-d can be this facies change disappears to the south, the dillera by regional experts (e.g., Price, 1981, demonstrated to lie in depositional contact, the suture is interpreted to swing eastward to the 1994; Simony and Carr, 2011) have found no sequence b-c-d is nailed together and linked by Lewis thrust (Fig. 1; Hildebrand, 2013; Chen evidence for a suture. unit c to the craton. CITATION: McMechan, M.E., et al., 2020, Nailed to the craton: Stratigraphic continuity across the southeastern Canadian Cordillera with tectonic implications for ribbon continent models: Geology, v. 49, p. , https://doi.org/10.1130/G48060.1 Geological Society of America | GEOLOGY | Volume XX | Number XX | www.gsapubs.org 1 Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/doi/10.1130/G48060.1/5147752/g48060.pdf by Univ Calgary Library user on 19 November 2020 o 118Wo 54o N 116Wo 54 N 116Wo 116Wo 114Wo 114Wo o 52o N 52 N 52o N 11 9 10 8 Calgary Q 5 4 1 2 3 7 6 o EasternLimit of 50 N Quesnellia (Q)or SlideMountain(SM) Terranes Q 4 100km 100km 1 3 2 7 5 a b 6 8 Cambrian facies Easternlimit of Devonian Mesoproterozoic Foreland Basin Archaeochyathid change FairholmeGp UpperBelt-Purcell -bearing volcanics Proposed Suture Neoproterozoic to PaleozoicNorth American distal continentalmargin limestones Ediacaran-Cambrian LowerBelt-Purcell Cordilleria Transgressive MesoproterozoictoJurassic ‘markers’ sandstones SAYBIA NorthAmericancontinental margin Northern limit of Montania Neoproterozoic Stratigraphically Rubia OldFortPoint overlapping Monashee Complex Channelbetween Fm,Windermere sequences Normal fault Southern Rocky Devonian reef Supergroup Mountain Trench complexes Well drilledtocratonicbasement Thrust fault Line of stratigraphiccross section Fairholme unconformable over Belt-Purcell outcropsection,well Figure 1. (A) Generalized geology of the southeastern Canadian Cordillera showing locations of postulated ribbon continent sutures (after Lambert and Chamberlain, 1988; Johnston, 2008; Hildebrand, 2013) and lines of stratigraphic cross sections A-A′ and B-B′ (Fig. 2). AB—Alberta, BC—British Columbia, HR—Hughes Range, LR—Lizard Range, LT—Lewis thrust. (B) Distribution of key stratigraphic linkage horizons and features in the southeastern Canadian Cordillera. North edge of Montania is after McMechan (2012) and Zaitlin et al. (2002). Geological base map was modified from Wheeler and McFeely (1991). Linear trends in part B, e.g., Devonian channel trends, are shown to continue unbroken into the Canadian Cordillera because they occur at a high angle to thrusting and are not significantly broken or displaced at regional scale. Devonian–Middle Jurassic edge of the prominent northeast-southwest– they occur in autochthonous sections above Upper Devonian and Mississippian strata trending paleogeographic feature called Mon- basement and above a transgressive middle have been subdivided into multiple formations tania (Fig. 1B; Deiss, 1941), the Upper Devo- Cambrian “basal sandstone,” into outcrops in and members that have been traced in detail in nian Fairholme Group sits directly on middle the Rocky Mountains (Slind et al., 1994), as far petroleum wells on the autochthonous cratonic and upper BPSG strata (Fig. 1B; Benvenuto and as the Kicking Horse Rim (Figs. 1B and 2, sec- basement in the Alberta Plains and in outcrops Price, 1979). Unconformably underlying Middle tion A-A′). In the southern part of the study area, across the Rocky Mountains (e.g., Fig. 2, section Devonian, Ordovician, Cambrian, and Meso- the middle Cambrian succession can be traced B-B′). In particular, prominent northeast-trend- proterozoic BPSG strata and overlying Penn- from the plains, where it unconformably over- ing reefs, channels, and barriers in the Upper sylvanian to Middle Jurassic strata are linked lies Paleoproterozoic and Archean basement, Devonian Leduc Formation (part of the Wood- to the adjacent craton by the Upper Devonian to the Rocky Mountains, where it unconform- bend Group in the plains and Fairholme Group to Mississippian succession to which they are ably overlies BPSG strata as far as the Rocky in the cordillera) have been mapped