Supercontinents and the case for Pannotia R. DAMIAN NANCE 1 * & J. BRENDAN MURPHY 2 1 Department of Geological Sciences, 316 Clippinger Laboratories, Ohio University, Athens, OH 45701, USA 2 Department of Earth Sciences, St Francis Xavier University, Antigonish, Nova Scotia, B2G 2W5, Canada R.D.N., 0000-0001-9431-0963 *Correspondence: nance@ohio.edu Abstract: Disagreement about the existence of the late Neoproterozoic supercontinent Pannotia highlights the limitation of defining supercontinents simply on the basis of size, which, for pre-Pangaean supercontinents, is difficult to determine. In the context of the supercontinent cycle, however, supercontinent assembly and break- up, respectively, mark the end of one cycle and the beginning of the next and can be recognized by the tectonic, climatic and biogeochemical trends that accompany them. Hence supercontinents need only be large enough to influence mantle circulation in such a way as to enable the cycle to repeat. Their recognition need not rely solely on continental reconstructions, but can also exploit a variety of secular trends that accompany their amalgam- ation and break-up. Although the palaeogeographical and age constraints for the existence of Pannotia remain equivocal, the proxy signals of supercontinent assembly and break-up in the late Neoproterozoic are unmistak- able. These signals cannot be readily attributed to either the break-up of Rodinia or the assembly of Gondwana without ignoring either the assembly phase of Pan-African orogenesis and the changes in mantle circulation that accompany this phase, or the reality that Gondwana cannot be a supercontinent in the context of the supercon- tinent cycle because its break-up coincides with that of Pangaea. Over the past two decades, data from a wide variety of sources have led to a growing recognition that Pangaea (Wegener 1915, 1920), rather than being Earth’s only supercontinent, was simply the most recent in a series of supercontinents that have punc- tuated Earth history for billions of years (e.g. Dalziel 1997, 2013; Rogers & Santosh 2003; Santosh & Zhao 2009; Meert 2014a; Nance & Murphy 2013; Nance et al. 1986, 2014). This history of episodic supercontinent assembly and break-up was first pro- posed by Worsley et al. (1984, 1985, 1986). Known as the supercontinent cycle (Nance et al. 1988), it is now widely recognized as having profoundly influ- enced the course of the Earth’s geological history (e.g. Brown 2007a; Goldfarb et al. 2010; Hawkes- worth et al. 2010, 2016; Condie 2011; Pisarevsky et al. 2015), as well as the evolution of its hydro- sphere, atmosphere and biosphere (e.g. Hoffman et al. 1998; Lindsay & Brasier 2002; Santosh 2010a, b; Bradley 2011; Strand 2012; Young 2012, 2013a, b; Melezhik et al. 2013; Müller et al. 2013). Proposals for the existence of pre-Pangaean supercontinents date to the early days of the applica- tion of plate tectonics to the geological past (e.g. Val- entine & Moores 1970; Piper 1974, 1976), but it took almost 20 years for their existence to gain traction (e.g. Hoffman 1989, 1991; Dalziel 1991, 1992; Moores 1991; Williams et al. 1991; Stump 1992; Powell et al. 1993; Powell 1995), the first synopsis for the Neoproterozoic incorporating the available palaeomagnetic, geological and faunal data being that of Dalziel (1997). Even today, their number and configuration remain a matter of debate (e.g. Piper 2013). Best known is the supercontinent Rodinia (McMenamin & McMenamin 1990), the assembly of which is recorded in worldwide Mesoproterozoic orogenesis of broadly Grenville age (c. 1.19– 0.98 Ga) (e.g. Rino et al. 2008) and the configura- tion and break-up history (at c. 825–740 Ma) of which are reasonably well constrained (e.g. Li et al. 2008). Earlier supercontinents are less well understood, but include Columbia (c. 2.1–1.5 Ga; Rogers & Santosh 2002; Zhao et al. 2002, 2004) or Nuna (Hoffman 1997), Kenorland (c. 2.7– 2.1 Ga; Williams et al. 1991; Arctica of Rogers 1996), Ur (c. 3 Ga; Rogers 1993, 1996) and Vaalbara (c. 3.6–2.8 Ga; Cheney 1996). Ironically, however, the most controversial supercontinent is Pannotia (c. 650–540 Ma; Stump 1987, 1992; Powell 1995; Dalziel 1997, 2013), the very existence of which is debated (e.g. Cogné & Humler 2008; Oriolo et al. 2017) despite the fact that it is the youngest of all those proposed to have predated Pangaea. Fuel for this argument comes from palaeomagnetic data, which is permissive of a From:WILSON, R. W., HOUSEMAN, G. A., MCCAFFREY, K. J. W., DORÉ, A. G. & BUITER, S. J. H. (eds) Fifty Years of the Wilson Cycle Concept in Plate Tectonics. Geological Society, London, Special Publications, 470, https://doi.org/10.1144/SP470.5 © 2018 The Author(s). Published by The Geological Society of London. All rights reserved. For permissions: http://www.geolsoc.org.uk/permissions. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics by guest on March 2, 2018 http://sp.lyellcollection.org/ Downloaded from