Downloaded from gsabulletin.gsapubs.org on May 2, 2014 Geological Society of America Bulletin Volcanosedimentary paleoenvironments of Ediacaran fossils in Newfoundland Gregory J. Retallack Geological Society of America Bulletin 2014;126, no. 5-6;619-638 doi: 10.1130/B30892.1 Email alerting services click www.gsapubs.org/cgi/alerts to receive free e-mail alerts when new articles cite this article Subscribe click www.gsapubs.org/subscriptions/ to subscribe to Geological Society of America Bulletin Permission request click http://www.geosociety.org/pubs/copyrt.htm#gsa to contact GSA Copyright not claimed on content prepared wholly by U.S. government employees within scope of their employment. Individual scientists are hereby granted permission, without fees or further requests to GSA, to use a single figure, a single table, and/or a brief paragraph of text in subsequent works and to make unlimited copies of items in GSA's journals for noncommercial use in classrooms to further education and science. This file may not be posted to any Web site, but authors may post the abstracts only of their articles on their own or their organization's Web site providing the posting includes a reference to the article's full citation. GSA provides this and other forums for the presentation of diverse opinions and positions by scientists worldwide, regardless of their race, citizenship, gender, religion, or political viewpoint. Opinions presented in this publication do not reflect official positions of the Society. Notes © 2014 Geological Society of America Downloaded from gsabulletin.gsapubs.org on May 2, 2014 Volcanosedimentary paleoenvironments of Ediacaran fossils in Newfoundland Gregory J. Retallack† Department of Geological Sciences, University of Oregon, Eugene, Oregon 97302, USA ABSTRACT INTRODUCTION felsic volcanic eruptions (Fisher and Schminke, 1984), but felsic eruptions of the deep sea are A new perspective on paleoenvironments The Ediacaran Conception Group of New- inferred mainly from ancient volcanic rocks of Ediacaran fossils of the upper Concep- foundland (Figs. 1 and 2) is best known because (Cas and Wright, 1987; Busby, 2005; Allen tion Group (Newfoundland) comes from of its diverse assemblage of the earliest known and McPhie, 2009). An important distinction geochemical and sedimentological study of large organisms (Lafl amme et al., 2004, 2007, for volcanosedimentary sequences is between volcanic tuffs and sedimentary rocks. Tuffs 2012a, 2012b; Narbonne et al., 2005; Clapham rocks produced by volcanic eruptions and those in the Conception Group have major- and et al., 2003, 2004; Gehling and Narbonne, 2007; produced by redeposition of older erupted mate- trace-element compositions and U-Pb ages Bamforth et al., 2008; Flude and Narbonne, rial (pyroclastic vs. epiclastic of Fisher and comparable with those of source volcanics 2008; Hofmann et al., 2008; Bamforth and Nar- Schminke, 1984; Cas and Wright, 1987; or pri- on the nearby Burin and Bonavista Penin- bonne, 2009; Liu et al., 2011, 2012). These large mary volcaniclastic vs. sedimentary of White sulas and the islands of St. Pierre and quilted fossils remain evolutionary enigmas and Houghton, 2006). Furthermore, tuff and Miquelon. Loss of silica and alkalies in best assigned to the extinct group Vendobionta sediment geochemistry can be used to constrain some ashes indicates weathering on land, (Seilacher, 1992; Retallack, 2007; Brasier and paleotectonic setting (Bhatia, 1983; Bhatia and not marine diagenesis. Volcanic crystal and Antcliffe, 2009; Erwin et al., 2011). Were they Crook, 1986; Roser and Korsch, 1986; Gorton lapilli tuffs fail to show grading and have la- fungi (Peterson et al., 2003), lichens (Retallack, and Schandl, 2000; Ryan and Williams, 2007). pilli and highly vesicular scoria scattered in 2013a), xenophyophore foraminifera (Seilacher This is the fi rst geochemical and petrographic a fi ne-grained matrix, and so they were de- et al., 2005), sponges (Clapham et al., 2004; study of tuffs and sedimentary rocks of the Con- posited on land, not in water. These as well Sperling et al., 2011), sea pens (Jenkins, 1992), ception Group of Newfoundland. as block-and-ash fl ows, volcanic spindle or anemones (Gehling et al., 2000; Liu et al., A postulated forearc tectonic setting of the bombs, and degassing features are evidence 2010a, 2010b)? Did they live on land (Retal- Conception Group (Hughes and Brückner, of eruptions from nearby subaerial volcanic lack, 2013a), or were they marine organisms 1971; Nance et al., 1991; Barr and Kerr, 1997) edifi ces. (Hofmann et al., 2008; Bamforth and Narbonne, has stimulated volcanosedimentary models The fossiliferous Conception Group accu- 2009; Sperling et al., 2011)? Whether they were of marine burial of vendobiont fossils by non- mulated within a forearc basin, formed on marine or terrestrial organisms is fundamental to erosive volcanic ash (Jenkins, 1992; Seilacher, continental crust, inboard of the Holyrood understanding their biological affi nities, paleo- 1992, 1999). As a forearc sequence, other bed- horst, and uplifted as part of an ancient sub- ecology, and role in the Cambrian explosion of scale models are also worth consideration, duction complex or accreted terrane. Like life (Retallack, 2013a; Erwin et al., 2011). including contourites (Stow, 1979; Stow et al., analogous forearc basins in Oregon-Wash- This study is focused on volcanic tuffs and 1998), tempestites (Seilacher, 1982), seismites ington, southern Chile, and Japan, the Con- tuffaceous sedimentary rocks that host vendo- (Wheeler, 2002; Greb and Dever, 2002; Stewart ception Group includes not only marine bay bionts in order to understand more about their et al., 2002; Agnon et al., 2006), tsunamites turbidites, but also a variety of intertidal paleoenvironment. Preservation by tuff has (Atwater et al., 1992; Atwater and Hemphill- and terrestrial tsunamites, seismites, tem- been considered a distinctive “Conception-style Haley, 1997; Kelsey et al., 2005; Cisternas pestites, and paleosols. Traditional marine taphonomy” of these fossils (Narbonne, 1995), et al., 2005), ash-fall and ash-fl ow tuffs (Sparks turbidite models explain deposition of the which have holdfasts, tiering, and equidistant and Huang, 1980; Cas and Wright, 1987; Allen Mall Bay, lower Drook, and lower Briscal spacing indicating that they lived on the bed- and Cas, 1998), and paleosols (Retallack, 1997, Formations of the Conception Group, but ding planes where they are preserved (Clapham 2012a, 2013a). the Gaskiers, upper Drook, upper Briscal, and Narbonne, 2002; Clapham et al., 2003; Hof- Previous hypotheses of a deep-sea paleoenvi- and Mistaken Point Formations were depos- mann et al., 2008). Volcanic tuffs show a variety ronment for Newfoundland vendobionts have ited in coastal plains and intertidal zones. of features, depending on whether they were been based on interpretation of their substrates Paleoenvironments of vendobiont fossils erupted entirely on land or from, into, or within as turbidites (Anderson and Misra, 1968; Misra, preserved in life position in Newfoundland lakes or oceans (Table 1). Differences between 1971; Gardiner and Hiscott, 1988; Benus, were terrestrial to marginal marine, not volcanic environments can be related to the 1988; Clapham and Narbonne, 2002; Clapham deep sea. higher pressure, heat capacity, bulk density, and et al., 2003; Wood et al., 2003; Narbonne et al., viscosity of water compared with air (White 2005; Ichaso et al., 2007). However, turbidites †E-mail: [email protected]. et al., 2003). Much is known about subaerial may form in lakes, and at all depths of the GSA Bulletin; May/June 2014; v. 126; no. 5/6; p. 619–638; doi: 10.1130/B30892.1; 12 fi gures; 2 tables; Data Repository item 2014091; published online 13 February 2014. For permission to copy, contact [email protected] 619 © 2014 Geological Society of America Downloaded from gsabulletin.gsapubs.org on May 2, 2014 G.J. Retallack geologically younger (Ediacaran-Devonian) GANDER ZONE TECTONIC BREAK 5 - to marine transgression AVALON ZONE 550–540 Ma non-marine, Signal Hill Group and Crown Hill Formation 560–550 Ma marine, St Johns Group BONAVISTA PENINSULA TECTONIC BREAK 4 - to arc-parallel tilting 590–560 Ma coastal-marine, Conception Group Bonavista Bay north 590–560 Ma subaerial volcanics and sediments of Marystown, Musgravetown, Long Harbour, Catalina St Pierre and Belle Rivière Groups 590–560 Ma Harbour Breton granite EDIACARAN TECTONIC BREAK 3 - to new arc alignment localities 620–590 Ma marine Connecting Point Group fault 620–590 Ma subaerial volcanics of cross Harbour Main and Connaigre Bay Group section 620–590 Ma Holyrood Granite TECTONIC BREAK 2 - to continental arc N48° geologically older (Cryogenian, 670–760 Ma) Trinity Bay AVALON PENINSULA Ackley Granite stitching pluton Conception A Bay hns St Jo St GANDER Head Green ZONE Holyrood Horst AVALON ZONE CONNAIGRE PENINSULA Salmonier B Fortune Bay + Cambrian stratotype + + N47° Miquelon Placentia Bay y St Pierre BURIN PENINSULA Portugal Cove South 0204060 km St Marys Ba Pigeon Cove St Shotts Mistaken Point E56° E54° Bristy Cove CROSS SECTION AVALON PENINSULA A east B Holyrood Horst Trinity Bay Synclinorium Conception Bay Anticlinorium Bulls Bay Syncline Figure 1. Simplifi ed geological map and study sites in the Avalon zone of Newfoundland (after King, 1988; Dec et al., 1992; O’Brien et al., 1996, 2006; O’Brien and King, 2002, 2005; Pisarevsky et al., 2012). ocean (Bouma, 1962; Ludlam, 1974; Talling 1971; Benus, 1988; Dalrymple et al., 1999). These suggestions of varied paleoenvironments et al., 2012). Turbidites have been generated Geochemical indices for the Mistaken Point are here tested with an array of new fi eld, geo- in fl umes as shallow as 0.5 m (Sumner et al., and Gaskiers Formations of the Conception chemical, and petrographic observations. 2009). Previous indications of shallow-marine Group, such as freshwater C/S ratios >2.8 and paleoenvironments for the Conception Group soil ratios <0.2 of highly reactive iron over MATERIALS AND METHODS include frondose shapes and spreading orienta- total iron (Retallack, 2013b), are also incon- tions of vendobionts like those of modern algae sistent with a deep-marine setting.