Canadian Journal of Earth Sciences Revised stratigraphy of the middle Simcoe Group (Ordovician, upper Sandbian-Katian) in its type area: an integrated approach Journal: Canadian Journal of Earth Sciences Manuscript ID cjes-2018-0023.R2 Manuscript Type: Article Date Submitted by the 28-Dec-2018 Author: Complete List of Authors: Paton, Timothy; University of Tennessee, Knoxville, Earth and Planetary Sciences; University of Cincinnati, Geology Brett, Carlton;Draft University of Cincinnati, Geology Upper Ordovician, Kirkfield Formation, Bobcaygeon Formation, sequence Keyword: stratigraphy, chemostratigraphy Is the invited manuscript for consideration in a Special Not applicable (regular submission) Issue? : https://mc06.manuscriptcentral.com/cjes-pubs Page 1 of 50 Canadian Journal of Earth Sciences 1 Revised stratigraphy of the middle Simcoe Group (Ordovician, upper 2 Sandbian-Katian) in its type area: an integrated approach 3 4 Timothy R. Paton1 and Carlton E. Brett2 5 6 [email protected] 7 Department of Geology, University of Cincinnati, Cincinnati, OH 45221, USA 8 Currently [email protected] 9 Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, Tennessee 10 37996-1410 11 12 [email protected] 13 Department of Geology, University of Cincinnati,Draft Cincinnati, OH 45221, USA 14 15 Timothy Robert Paton 16 1621 Cumberland Avenue, 602 Strong Hall, Knoxville TN 37996-1526 17 Phone: 901-292-7976 18 Fax: 865-974-2368 19 Email: [email protected] https://mc06.manuscriptcentral.com/cjes-pubs Canadian Journal of Earth Sciences Page 2 of 50 20 Abstract 21 The Upper Ordovician Bobcaygeon Formation of southern Ontario is a widespread unit 22 that spans the Sandbian-Katian stage boundary and contains exceptionally preserved invertebrate 23 fossil assemblages, including the famed ‘Kirkfield echinoderm fauna.’ However, the precise 24 correlation of this interval remains poorly understood. This paper presents new data on high- 25 resolution sequence and carbon isotope chemostratigraphy of the Bobcaygeon interval based on 26 new quarry exposures and introduces refined definitions of unit boundaries based on 27 allostratigraphic criteria. Sequence, chemo-, and biostratigraphic evidence indicate that the 28 Bobcaygeon Formation represents a composite unit as it encompasses a major erosional th 29 unconformity. The Coboconk and KirkfieldDraft formations, described in the early 20 century, were 30 merged into a single unit, the Bobcaygeon, for concern that the original lithostratigraphic 31 divisions would be conflated with biostratigraphic zones of the same names. However, these 32 biostratigraphic zones are no longer favoured, and the lower member of the Bobcaygeon is here 33 elevated again to the status of formation (Coboconk Formation) and represents the uppermost 34 portion of the Sandbian M4 sequence. The middle and upper members of the Bobcaygeon, herein 35 reassigned to the Kirkfield Formation, represent the upper Sandbian to lower Katian M5A and 36 M5B sequences recognized widely in the eastern and central United States. The term 37 Bobcaygeon is retained and elevated to the rank of subgroup. The Kirkfield Formation is divided 38 into three members and contacts are refined, placing a 1–2 m transgressive grainstone at the base 39 of each sequence. These units are correlated with equivalent strata of New York and the 40 Cincinnati Arch. 41 https://mc06.manuscriptcentral.com/cjes-pubs Page 3 of 50 Canadian Journal of Earth Sciences 42 Keywords: Upper Ordovician, Kirkfield Formation, Bobcaygeon Formation, sequence 43 stratigraphy, chemostratigraphy Draft https://mc06.manuscriptcentral.com/cjes-pubs Canadian Journal of Earth Sciences Page 4 of 50 44 Introduction 45 Upper Ordovician sedimentary rocks in the Lake Simcoe area of southern Ontario, 46 Canada (Fig. 1), dominated by shallow-water subtropical carbonates, provide key insights into 47 paleoenvironments, sea level fluctuations, and basin dynamics. These rocks are well exposed in 48 several quarries in the City of Kawartha Lakes and neighboring townships, as well as a few road 49 cuts, but contacts between certain stratigraphic units are rarely exposed and few formations are 50 continuously exposed in any given locality. The Simcoe Group of southern Ontario (equivalent 51 to the Black River–Trenton groups of New York) was studied and documented from the mid-19th 52 century to the early-21st century by many researchers, including Logan et al. (1863), Johnston 53 (1911), Kay (1943), Sinclair (1954), LibertyDraft (1969), Brookfield and Brett (1988), Melchin et al. 54 (1994), Armstrong (1999; 2000), Brunton et al. (2009), and Armstrong and Carter (2010). 55 However, some of these units have been overly generalized and advances in sequence 56 stratigraphy and chemostratigraphy (Holland and Patzkowsky 1996, Holland and Patzkowsky 57 1998; Bergström et al., 2010) reveal a need for revision. The Bobcaygeon Formation, as defined 58 by Liberty (1969), has been disfavoured as a lithological unit by many geologists involved in 59 active study and mapping of the geology in south-central Ontario, who instead retain Johnston’s 60 (1911) Coboconk and Kirkfield formations (Winder and Sanford, 1972; Johnson et al., 1992; 61 Sanford, 1993; Melchin et al., 1994; Armstrong, 1999; Armstrong, 2000; Brunton et al., 2009; 62 Armstrong and Carter, 2010; Haeri-Ardakani et al., 2012; Haeri-Ardakani et al., 2013; Pancost et 63 al., 2013). 64 The objectives of the present study include: a) documentation of high-resolution 65 stratigraphy of the Bobcaygeon interval in new reference sections and comparisons with data 66 from the Kirkfield Quarry; b) proposal of an objectively defined lithostratigraphy; c) production https://mc06.manuscriptcentral.com/cjes-pubs Page 5 of 50 Canadian Journal of Earth Sciences 67 of a high resolution carbonate carbon isotope curve tied to detailed litho- and biostratigraphy; d) 68 identification of key surfaces and lithologic trends to develop a sequence stratigraphic 69 framework; and e) correlation of that framework with the established Mohawkian sequences of 70 the Cincinnati Arch region and New York (Holland and Patzkowsky, 1996; Brett et al., 2004). 71 Geologic Setting 72 The lower Paleozoic strata of south-central Ontario are exposed at the surface in east- 73 west trending outcrop belts that extend for several hundred kilometres, controlled by a slight 74 (<0.5°) dip to the south (Fig. 1). These undeformed strata are bounded to the north by the 75 metamorphic and granitic shield rocks of the Proterozoic Grenville Province. The Upper 76 Ordovician strata (the Basal, Simcoe, andDraft Nottawasaga groups of Liberty, 1969) onlap exposed 77 crystalline Grenville-age rocks, which would have supplied coarse siliciclastic sediments to the 78 basal transgressive Paleozoic strata, and locally to younger carbonate strata, from 79 paleotopographic basement highs which would have formed islands. Silurian carbonate rocks 80 form the Niagara Escarpment to the south and west. The Ordovician strata create a relatively 81 continuous outcrop belt to the northeast of the escarpment, connected in the subsurface with 82 equivalent rocks of the Michigan Basin and Appalachian Basin, and are slightly offset from the 83 Ottawa Embayment by a thin belt of exposed crystalline basement. 84 The Upper Ordovician strata preserved in southern Ontario record shallow, possibly cool- 85 water environments of the Trenton carbonate platform (Brookfield, 1988). This platform, on the 86 southeastern margin of Laurentia, was situated adjacent to the cratonic margin of the Taconic 87 peripheral foreland basin and was subjected to pulses of muddy sediments from the Taconic 88 Highlands and periodic volcanic ash accumulation as the Taconic volcanic island arc collided https://mc06.manuscriptcentral.com/cjes-pubs Canadian Journal of Earth Sciences Page 6 of 50 89 with Laurentia during the Late Ordovician. The Trenton carbonate platform lay in the southern 90 subtropics at ~20° south latitude (Mac Niocaill et al., 1997) and hosted a rich invertebrate fauna. 91 Subdivisions of the Simcoe Group, defined by Liberty (1969), include the Gull River, 92 Bobcaygeon, Verulam, and Lindsay formations. Underlying the Simcoe Group is the Basal 93 Group (Jacobsville and Mount Simon formations, which only occur in the subsurface) and 94 overlying is the Nottawasaga Group, which includes the Blue Mountain (previously the upper 95 Whitby Formation; Russell and Telford, 1983), Georgian Bay, and Queenston formations. 96 Although originally included by Liberty (1969) in the Basal Group, the Shadow Lake Formation 97 is now assigned as the basal member of the Simcoe Group (Noor, 1989; Melchin et al., 1994; and 98 Armstrong and Dodge, 2007). The GullDraft River Formation and lower member of the Bobcaygeon 99 Formation consist of clean-water micrites and grainstones, respectively, of the ‘pre-Taconic 100 foreland’ (Holland and Patzkowsky, 1996), which preserve little evidence of tectonic influence, 101 although the Bobcaygeon Formation does host several bentonitic clays indicative of volcanic 102 activity associated with the approaching Taconic magmatic arc (Armstrong, 2000). The middle 103 and upper members of the Bobcaygeon Formation, Verulam Formation, and Lindsay Formation 104 contain a higher fraction of siliciclastic mudstones and shales derived from the prograding clastic 105 wedge and exhibit a strong back-stepping pattern associated with a major marine transgression 106 enhanced by tectonic loading and