740 Ma Vase-Shaped Microfossils from Yukon, Canada: Implications for Neoproterozoic Chronology and Biostratigraphy

740 Ma vase-shaped microfossils from Yukon, Canada: Implications for Neoproterozoic chronology and biostratigraphy

Justin V. Strauss1, Alan D. Rooney1, Francis A. Macdonald1, Alan D. Brandon2, and Andrew H. Knoll1 1Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, USA 2Department of Earth and Atmospheric Sciences, University of Houston, Houston, Texas, 77204, USA

ABSTRACT global stratigraphic correlation that goes beyond Biostratigraphy underpins the Phanerozoic time scale, but its application to pre-Ediacaran previous broad morphoclass-based biostrati- strata has remained limited because Proterozoic taxa commonly have long or unknown stratigraphic comparisons. graphic ranges, poorly understood taphonomic constraints, and/or inadequate geochronological context. Here we report the discovery of abundant vase-shaped microfossils from the STRATIGRAPHY Callison Lake dolostone of the Coal Creek inlier (Yukon, Canada) that highlight the potential The Coal Creek inlier in the Ogilvie Moun- for biostratigraphic correlation of Neoproterozoic successions using species-level assemblage tains (Yukon, Canada) hosts an ~3-km-thick se- zones of limited duration. The fossiliferous horizon, dated here by Re-Os geochronology at quence of ca. 780–540 Ma Windermere Super- 739.9 ± 6.1 Ma, shares multiple species-level taxa with a well-characterized assemblage from group strata (Fig. 1; Mustard and Roots, 1997). the Chuar Group of the Grand Canyon (Arizona, USA), dated by U-Pb on zircon from an The Mount Harper Group consists of three interbedded tuff at 742 ± 6 Ma. The overlapping age and species assemblages from these two informal units; in stratigraphically ascending deposits suggest biostratigraphic utility, at least within Neoproterozoic basins of Laurentia, order , these are (1) the Callison Lake dolostone, 13 and perhaps globally. The new Re-Os age also confi rms the timing of the Islay δ Ccarbonate an ~400-m-thick mixed siliciclastic and carbon- anomaly in northwestern Canada, which predates the onset of the Sturtian glaciation by ate deposit; (2) the Mount Harper conglomer- >15 m.y. Together these data provide global calibration of sedimentary, paleontological, and ate, an ~1100-m-thick rift-related clastic suc- geochemical records on the eve of profound environmental and evolutionary change. cession; and (3) the Mount Harper volcanics, an ~1200-m-thick intermediate to mafi c volcanic INTRODUCTION (Porter and Knoll, 2000; Porter et al., 2003). complex (Mustard and Roots, 1997; Macdon- Neoproterozoic sedimentary deposits of west- Given their abundance, diversity, preservation, ald et al., 2010). Age constraints on the Mount ern North America record large fl uctuations in and time-calibrated record, VSMs could rep- Harper Group are provided by U-Pb chemical global biogeochemical cycles (e.g., Narbonne resent the fi rst temporally well-resolved bio- abrasion–thermal ionization mass spectrometry et al., 1994; Karlstrom et al., 2000; Halver- stratigraphic assemblage zone for pre-Ediacaran (CA-TIMS) ages on zircon of 811.51 ± 0.25 Ma son et al., 2005), the diversifi cation of multiple strata, opening a new window for regional and from a tuff in the underlying Fifteenmile Group, eukary otic clades (e.g., Porter and Knoll, 2000; Samuelsson and Butterfi eld, 2001; Cohen and Greenland Knoll, 2012), the fragmentation of Rodinia ac- Coal Creek Inlier, Ogilvie Mountains, Yukon companied by localized mafi c volcanism (e.g., Alaska Jefferson and Parrish, 1989; Prave, 1999; Mac- Upper Group Mount Gibben δ13 Corg(‰) donald et al., 2010), and multiple global glacia- Hay Creek Group 500 m Section J1204 –35 –30 –25 Yukon 33.1 tions (e.g., Aitken, 1991; Hoffman et al., 1998). Te r r i t o r y Rapitan Group Understanding the causal relationships among 716.47±0.2 Ma these events requires accurate stratigraphic cor- Mount Harper 717.43±0.1 Ma CANADA volcanics relation in the context of geochronologically constrained age models. However, the geograph- U.S.A. Mount Harper conglomerate 20 ically disparate Neoproterozoic sedimentary rec- 141°W Hyland Group 739.9±6.1 Ma ords along the length of western North America 68°N Windermere SG Callison Lake have yet to be clearly linked in time and space Mackenzie Mtns SG dolostone due a paucity of radiometric age constraints, Pinguicula Group 10 Wernecke SG non-unique chemostratigraphic ties, abundant Craggy Coal Creek synsedimentary tectonism and associated lat- M Dolostone Inlier acken 811.51±0.1 Ma eral facies change, and a lack of biostratigraphi- zie 0 m M –8 –4 0 4 cally useful microfossils. Correlations have been o 13 u Conglomerate VSM δ C (‰) n Reefal carb proposed for pre-glacial Neoproterozoic strata t Sandstone Cover

Mount a Assemblage i in the southwestern United States (e.g., Dehler n Shale Nodular U-Pb Age

Gibben Ogilvie s

Evaporite Chert Re-Os Age

et al., 2001, 2010), but these schemes have not Mtns GroupFifteenmile Harper Gp. Mount Diamictite Chandindu Intraclasts Exposure been extended to the rich sedimentary archives 400 km Dolostone Fine lamination surface

of northwest Canada, due primarily to a lack of Whitehorse Mackenzie Mountains SG Windermere Supergroup Gibben Fm. Basalt/Rhyolite Stromatolite/Microbial age control. Here we document new vase-shaped microfossil (VSM) assemblages from Yukon, Figure 1. Simpliﬁ ed map locations and schematic lithostratigraphy of the Coal Creek inlier, Canada, that are indistinguishable in taxonomic Yukon, Canada. Vase-shaped microfossils (VSMs) described herein are from Callison Lake dolostone. Measured section J1204 highlights location of fossil and Re-Os age horizon, as composition and age from those described from δ13 δ13 well as bounding Ccarb and Corg (blue data points) data from the Islay anomaly. Geologic the Chuar Group of the Grand Canyon (Arizona, map of Yukon is adapted from Wheeler and McFeely (1991). Abbreviations: SG—Supergroup; USA) and successions of similar age worldwide Gp.—Group; Fm.—Formation; Mtns—mountains.

GEOLOGY, August 2014; v. 42; no. 8; p. 1–8; Data Repository item 2014244 doi:10.1130/G35736.1 | Published online XX Month 2014 GEOLOGY© 2014 Geological | June Society 2014 | ofwww.gsapubs.org America. For permission to copy, contact Copyright Permissions, GSA, or [email protected]. 1 data-point error ellipses are 2 717.43 ± 0.14 Ma from rhyolite in the upper 3.4 member of the Mount Harper volcanics, and G 716.47 ± 0.24 Ma from a tuff interbedded with 3.0 E H diamictite correlated with the glacially inﬂ u- F 2.6 Os C enced Rapitan Group in the Mackenzie Moun- B 188 tains (Fig. 1; Macdonald et al., 2010). / 2.2 H D

The lower Mount Harper Group records Os I

mixed marine and terrestrial deposition inti- 187 1.8 mately associated with an east-west–trending, A Age = 739.9 ± 6.1[6.5] Ma 1.4 187 188 syndepositional north-side-down fault scarp that J Initial Os/ Os = 0.609 ± 0.01 outlines the remnants of a Proterozoic half-gra- MSWD = 0.62 1.0 ben (Mustard and Roots, 1997). Basal deposits Figure 2. Neoproterozoic vase-shaped micro- 20 60 100 140 180 220 of the Callison Lake dolostone unconformably 187 188 fossils (VSMs) from Callison Lake dolo- Re / Os overlie brecciated and silicifi ed strata of the stone, Yukon, Canada. (Slide number and Fifteenmile Group, and consist of an ~4–30-m- England Finder Coordinates are given for Figure 3. Re-Os isochron for upper Callison each image.) A: Low-magnifi cation image thick interval of sandstone, siltstone, and dis- Lake dolostone (Yukon, Canada) with an age showing abundance of VSM tests, with uncertainty of 6.5 m.y. (in brackets) when un- continuous beds of quartz and chert pebble centrally located specimen of Melano- certainty of 187Re decay constant is included. conglomerate that transition into ~5–30 m of cyrillium hexodiadema (J1204.16.8; K23/0). MSWD—mean square of weighted deviates. black to varicolored and mud-cracked shale Scale = 100 µm. B: Palaeoarcella athanata Isotope composition and abundance data interbedded with laterally discontinuous stro- (J1204.16.8; H31/1). Scale = 50 µm. C: Cross are presented in the Data Repository (see section of Melanocyrillium hexodiadema footnote 1). matolitic bioherms that host poorly preserved aperture (F930.15.5; O33/4). Scale = 50 µm. VSMs. Basal Callison Lake siliciclastic depos- D: Bombycion micron (J1204.18.1; H32/2). its are sharply overlain by an ~15–100-m-thick Scale = 40 µm. E: Bonniea dacruchares medium gray dolostone characterized by (J1204.18.1; W31/1). Scale = 50 µm. F: Cyclio- GEOCHRONOLOGY cyrillium torquata (J1204.18.1; L43/1). Scale = piso litic grainstone, microbial laminae, mor- 50 µm. Silicifi ed black shale of the Callison Lake phologically diverse stromatolites, evaporite dolostone was collected from a VSM-bearing pseudomorphs, intraclast conglomerate, and outcrop near Mount Gibben in the Coal Creek mechanically bedded dolomicrite and/or dolo- inlier (Fig. 1; section J1204, 16.8–18.2 m). This siltite, which also contains intercalated black pole opposite a tapered oral end with aperture; 2.4-m-thick exposure was sampled at high reso- shale composed predominantly of authigenic (3) broad size ranges, from ~20 to 200 µm in lution for Re-Os geochronology, and bounding talc [Mg3Si4O10(OH2)] (Tosca et al., 2011). length and ~15 to 120 µm in width; (4) morpho- stromatolitic dolostone was collected at ~1 m δ13 δ13 These strata are overlain by 200–300 m of logically diverse apertures ~10–40 µm wide; resolution for Ccarb and Corg chemostratig- dolo stone characterized by abundant microbial and (5) ~1–3-µm-thick test walls. Most sections raphy (Fig. 1; details of the sampling proce- lamination, domal stromatolitic bioherms, and through Callison Lake specimens do not yield dure and analytical methods are provided in cross-bedded oolitic grainstone, with abun- systematically diagnostic characters; however, the GSA Data Repository1). A Re-Os age of dant early diagenetic chert. The Callison Lake because the fossils are so abundant, each thin 739.9 ± 6.1 Ma (±6.5 m.y. if including 187Re dolostone culminates with another recessive section includes many dozens of individuals decay constant uncertainty; n = 10, mean square ~10–40-m-thick unit of fossiliferous black that permit species-level comparison to Chuar of weighted deviates, MSWD = 0.62, 2σ, initial shale, locally silicifi ed and interbedded with Group populations (Porter et al., 2003). Thus, 187Os/188Os = 0.609 ± 0.01) was obtained from stromatolitic and microbial dolostone, that is we can identify Melanocyrillium hexodiadema this horizon (Fig. 3). This Re-Os age is within gradationally to abruptly overlain by sandstone (Figs. 2A and 2C), Palaeoarcella athanata error of the U-Pb zircon age of 742 ± 6 Ma from and conglomerate of the Mount Harper con- (Fig. 2B), Bombycion micron (Fig. 2D), Bon- a reworked tuff interbedded with VSM-bearing glomerate (Fig. 1). Callison Lake strata record niea dacruchares (Fig. 2E), and Cycliocyrillium black shale of the upper Chuar Group (Fig. 4), peritidal to shallow subtidal deposition in an torquata (Fig. 2F), as well as Bonniea pytinaia, providing a distinct geochronological tie for our episodically restricted marginal marine basin, C. simplex, Hemisphaeriella ornata, and other paleontological comparisons. the subsidence of which was largely driven by long-necked unnamed forms (not illustrated). regional extension. All observed VSMs refl ect a taphonomic his- DISCUSSION tory similar to that of Chuar Group populations; Early fragmentation of Rodinia ca. 780– PALEONTOLOGY they are siliceous or calcareous internal molds 720 Ma generated local tectonism, mafi c vol- A diverse VSM assemblage (Fig. 2) occurs commonly coated with thin layers of pyrite, canism, and regional basin subsidence in west- in the uppermost organic-rich silicifi ed shale iron oxide, or organic matter (Fig. 2; Porter and ern North America (e.g., Jefferson and Parrish, of the Callison Lake dolostone (Fig. 1; section Knoll, 2000). Porter and Knoll (2000) outlined 1989; Prave, 1999; Karlstrom et al., 2000). In J1204, 16.8–18.2 m). Because of pervasive the taphonomic processes that preserved such northwestern Canada, the Mount Harper Group silici fi ca tion, the fossils cannot readily be freed microfossils and summarized previous inter- and Coates Lake Group were deposited in a se- from their matrix and so must be evaluated in pretations of their biological affi nities, making ries of narrow, fault-bounded basins between ca. petrographic thin section. Individual thin sec- a strong case for viewing Chuar Group VSMs as tions contain many hundreds of essentially ran- testate amoebae placed phylogenetically within 1GSA Data Repository item 2014244, a summary dom cross sections through VSMs (Fig. 2A). As the Amoebozoa and Rhizaria. As such, these of sampling techniques, detailed analytical methods, in the Chuar Group assemblage (Porter et al., fossils provide our earliest direct evidence of data tables containing all isotopic and geochrono- 2003), nearly all preserved fossils are tear- protistan predation, including the evolutionarily logical data, and a compilation of global vase-shaped microfossil occurrences, is available online at www shaped tests characterized by (1) circular out- important innovation of eukaryvory, the capture .geosociety .org /pubs /ft2014 .htm, or on request from line in transverse section; (2) radially or bilat- and ingestion of other eukaryotic cells (Porter, editing@geosociety .org or Documents Secretary, erally symmetrical form with a rounded aboral 2011; Knoll, 2014). GSA, P.O. Box 9140, Boulder, CO 80301, USA.

2 www.gsapubs.org | June 2014 | GEOLOGY Figure 4. Schematic litho- Ogilvie Mtns, Yukon Mackenzie Mtns, NWT Death Valley, California Uinta Mtns, Utah Grand Canyon, Arizona stratigraphy, geochronol- RAP. –6–4 –2 0246 RAP. –6–4–2 024 6 8 KP2 –4–2 024 6 Camb. -30 –25 –20 –15 60 Mile –30 –25–20 –15 ogy, and carbon isotope 716.47±0.2 Ma VS ? 742 ± 6 Ma chemostratigraphy of 717.43±0.1 Ma basal Windermere Super- 732.2±3.9 Ma Walcott group strata from western 13 North America. All δ Corg data are shown with blue Awatubi Mount Harper volcanics Kwagunt Formation data points. Data are Formation Coppercap summarized from (1) this CB paper and Macdonald Red Pine Shale et al. (2010); (2) Jeffer- son and Parrish (1989) Beck Springs Dolomite

and Rooney et al. (2014); Mount Harper conglom. Harper Mount (3) Macdonald et al. (2013) 739.9±6.1 Ma Chuar Group Pahrump Group Coates Lake Group Carbon Canyon Member

and Mahon et al. (2014); Mount Harper Group Uinta Mountain Group (4) Dehler et al. (2010) Formation Redstone River ~ 4 km strata and Nelson et al. (2011); not shown Galeros Formation (5) Karlstrom et al. (2000) and Dehler et al. (2010). <766 Ma Jupiter Member Numbers correlate to in- 200 m 200 m 200 m set map. Abbreviations: dolostone Lake Callison 100 m 200 m AK—Alaska; Mex.—Mex- Fm. Thundercloud Tanner ico; carb—carbonate; 15 Mi. –6–4 –2 0246 LDB –6–4–2 024 6 8 formations unspecified lower δ13 δ13 Nk. Fm. <770 Ma Horse Thief Springs Formation KP1 –20 –15 org—organic; VSM— 811.51 ± 0.1Ma Ccarb(‰) 777.7 ± 2.5 Ma Ccarb(‰) RCQ –30 –25 –20 –15 13 Unk. Gp. 13 vase-shaped micro- >1650 Ma δ C (‰) δ C (‰) CANADA USA <787 Ma org org ex. 1. Ogilvie Mountains, Yukon 1070 ± 70 Ma fossil; Mtns—Mountains; 2 M 4 5 2. Mackenzie Mountains, VSM Horizon Northwest Territories Conglomerate Dolostone Limestone conglom.—conglomer- 1 3 LCS –4–2 024 6 U-Pb CA-ID-TIMS AK N 3. Death Valley, California δ13 Sandstone Evaporite Basalt/Diabase ate; 15 Mi.—Fifteenmile 4. Uinta Mountains, Utah 1069 ± 3 Ma Ccarb(‰) Re-Os Isochron Shale/Siltstone Diamictite Basement Pacific Ocean 400 km 5. Grand Canyon, Arizona U-Pb Baddelyite Group; LDB—Little Dal U-Pb Detrital Zircon LA-ICPMS Rb-Sr Isochron Ar-Ar Hornblende basalt; RAP.—Rapitan Group; KP—Kingston Peak Formation; VS—Virgin Spring limestone; LCS—Lower Crystal Spring Formation; RCQ—Red Creek Quartzite; Camb.— Cambrian; CB—Carbon Butte Member; NK. Fm.—Nankoweap Formation; Unk. Gp.—Unkar Group; LA-ICP-MS—laser ablation–inductively coupled plasma–mass spectrometry; CA-TIMS—chemical abrasion–thermal ionization mass spectrometry.

777 and 720 Ma (Jefferson and Parrish, 1989; (Fig. 4; Macdonald et al., 2013). We correlate Globally, strata above the Bitter Springs δ13 δ13 Mustard and Roots, 1997). Farther south, the these Ccarb anomalies with the pre-Sturtian Ccarb anomaly (younger than 811 Ma; Mac- Chuar, Pahrump, and Uinta Mountain groups Islay anomaly because of their stratigraphic donald et al., 2010) but below Sturtian glacio- were also deposited in extensional basins be- position below glacial deposits and their broad genic rocks are characterized by an increased δ13 tween ca. 780 Ma and 740 Ma (Fig. 4; Timmons covariance with Corg and lack of covariance diversity of eukaryotes that includes morpho- δ18 et al., 2001; Dehler et al., 2001, 2010). Based with Ocarb (Fig. 1; Table DR1 in the Data Re- logically complex acritarchs, diverse VSM δ13 on a compilation of previously published carbon pository; Rooney et al. 2014). This Ccarb ex- populations (see Table DR3 for a summary of isotope chemostratigraphy, the new Re-Os age cursion is commonly associated with a distinct global VSM occurrences), complex protistan δ13 constraints discussed herein, and the fi rst ap- recovery to enriched Ccarb values prior to the scales, and a number of simple multicellular pearance of VSMs in different basins along the onset of glacial sedimentation (e.g., Prave et al., and coenocytic taxa (Knoll et al., 2006; Cohen length of the Cordillera, we can begin to cor- 2009; Hoffman et al., 2012), clearly seen in the and Knoll, 2012). Of these, VSMs are particu- relate these pre-Sturtian basins with confi dence Coates Lake Group but masked by siliciclastic larly well suited for biostratigraphic correlation, throughout western North America (Fig. 4). deposits in the Mount Harper Group (Fig. 4). given their distinctive forms, relative ease of Interestingly, all of these ca. 780–720 Ma ba- Tziperman et al. (2011) suggested that acceler- preservation, wide facies distribution, and lim- sins in western North America host VSM assem- ating eukaryotic diversifi cation led to increased ited stratigraphic range; they meet the require- blages and/or pronounced carbon isotopic fl uc- export production, triggering dynamic effects in ments of biostratigraphic index fossils. Previ- tuations below Sturtian glacial deposits (Fig. 4), the carbon cycle due to anaerobic respiration, ous workers have noted the potential utility of hinting at complex links between tectonics, bio- consumption of CO2, and the initiation of gla- VSMs for Neoproterozoic biostratigraphy (e.g., geochemical cycling, and climate (Karlstrom ciation. Our data are consistent with this model Knoll and Vidal, 1980; Porter and Knoll, 2000; δ13 et al., 2000). In conjunction with the U-Pb CA- insofar as it relates the Islay Ccarb anomaly Dehler et al., 2001); however, these suggestions TIMS zircon ages from the Mount Harper and to the abundant preservation of diverse VSMs; were based on broad morphoclass comparisons Rapitan Groups of the Coal Creek inlier and the however, the apparent ~15 m.y. age disparity be- without tight radiometric age constraints. In Re-Os age of 732.2 ± 3.9 Ma within a large neg- fore the onset of the Sturtian glaciation suggests contrast, we suggest that VSMs in the Callison δ13 ative Ccarb anomaly in the Coates Lake Group that any evolutionary infl uence on the Neo- Lake and Chuar strata constitute a species-level of the Mackenzie Mountains (Rooney et al., proterozoic Earth system must be interpreted assemblage zone comparable to those used to 2014), the Re-Os geochronology and chemo- broadly and not specifi cally in terms of the Islay delimit time in Phanerozoic successions. Tra- stratig raphy presented herein suggest a clear event. Our new geochronological data sever the ditionally, Proterozoic taxa were held to have correlation between the Mount Harper Group proposed link between the Islay anomaly and long stratigraphic ranges, far different from and Coates Lake Group (Fig. 4). Furthermore, the onset of global glaciation (Tziperman et al., most Phanerozoic species (Knoll, 1994), but the δ13 this Ccarb isotopic pattern is indistinguishable 2011; Hoffman et al., 2012), unless there are advent of eukaryote-ingesting predators would δ13 from that of the Beck Spring Dolomite in Death multiple Islay-like Ccarb anomalies recorded be predicted to increase protistan turnover Valley, which also hosts VSMs in association in ca. 745–716 Ma preglacial strata or an earlier rates, much as carnivory did among Cambrian with a large negative carbon isotope anomaly episode of glaciation. animals (Knoll, 2014), and this may underpin

GEOLOGY | June 2014 | www.gsapubs.org 3 the limited stratigraphic longevity inferred for Hoffman, P.F., Kaufman, A.J., Halverson, G.P., and letin, v. 106, p. 1281–1292, doi:10 .1130 /0016 Chuar Group–Callison Lake dolostone VSMs. Schrag, D.P., 1998, A Neoproterozoic Snow- -7606(1994)106 <1281: ICABOT>2 .3 .CO;2 . ball Earth: Science, v. 281, p. 1342–1346, doi: Nelson, S.T., Hart, G.L., and Frost, C.D., 2011, A re- At most, the Chuar–Callison Lake assemblage 10 .1126 /science .281 .5381 .1342 . assess ment of Mojavia and a new Cheyenne Belt zone characterizes an interval comparable in Hoffman, P.F., Halverson, G.P., Domack, E.W., alignment in the eastern Great Basin: Geosphere, length to a Phanerozoic epoch or period, and our Maloof, A.C., Swanson-Hysell, N.L., and v. 7, p. 513–527, doi: 10 .1130 /GES00595 .1 . radiometric dates suggest that its duration could Cox, G.M., 2012, Cryogenian glaciations on Porter, S.M., 2011, The rise of predators: Geology, have been considerably shorter, more akin to the southern tropical paleomargin of Lauren- v. 39, p. 607–608, doi: 10 .1130 /focus062011 .1 . tia (NE Svalbard and East Greenland), and a Porter, S.M., and Knoll, A.H., 2000, Testate amoe- Phanerozoic ages. Lower Callison Lake fossils primary origin for the upper Russøya (Islay) bae in the Neoproterozoic Era: Evidence from occur about one-third of the way between the carbon isotope excursion: Precambrian Re- vase-shaped microfossils in the Chuar Group, well-characterized upper fossiliferous horizon search, v. 206–207, p. 137–158, doi: 10 .1016 /j Grand Canyon: Paleobiology, v. 26, p. 360– and a subjacent ca. 811 Ma tuff in the Fifteen- .precamres .2012 .02 .018 . 385, doi:10 .1666 /0094 -8373 (2000)026 <0360: Jefferson, C.W., and Parrish, R., 1989, Late Protero- TAITNE>2 .0 .CO;2 . mile Group. Consistent with data from other zoic stratigraphy, U-Pb zircon ages, and rift Porter, S.M., Meisterfeld, R., and Knoll, A.H., 2003, basins (Fig. 4), this suggests that VSMs in gen- tectonics, Mackenzie Mountains, northwestern Vase-shaped microfossils from the Neo protero- eral occur through an interval tens of millions of Canada: Canadian Journal of Earth Sciences, zoic Chuar Group, Grand Canyon: A clas- years in duration; but, because of poor preserva- v. 26, p. 1784–1801, doi: 10 .1139 /e89 -151 . sifi cation guided by modern testate amoebae: tion, the lower fossils do not provide information Karlstrom, K.E., et al., 2000, Chuar Group of the Journal of Paleontology, v. 77, p. 409–429, Grand Canyon: Record of breakup of Rodinia, doi: 10 .1666 /0022 -3360 (2003)077 <0409: on the stratigraphic ranges of individual species. associated change in the global carbon cycle, VMFTNC>2 .0 .CO;2 . Thus, the new results promise a transition from and ecosystem expansion by 740 Ma: Geol- Prave, A.R., 1999, Two diamictites, two cap carbon- established Proterozoic biostratigraphic links, ogy, v. 28, p. 619–622, doi:10 .1130 /0091 -7613 ates, two δ13C excursions, two rifts: The Neo- where morphoclass correlations are coarse and (2000)28 <619: CGOTGC>2 .0 .CO;2 . proterozoic Kingston Peak Formation, Death Knoll, A.H., 1994, Proterozoic and Early Cambrian Valley, California: Geology, v. 27, p. 339–342, many of the taxa used to correlate among basins protists: Evidence for accelerating evolution- doi: 10 .1130 /0091 -7613 (1999)027 <0339: have long ranges, to species-level assemblage ary tempo: National Academy of Sciences TDTCCT>2 .3 .CO;2 . zone correlation constrained by radiometric age Proceedings, v. 91, p. 6743–6750, doi:10 .1073 Prave, A.R., Fallick, A.E., Thomas, C.W., and Graham , constraints. /pnas .91 .15 .6743 . C.M., 2009, A composite C-isotope profi le for Knoll, A.H., 2014, Paleobiological perspectives on the Neoproterozoic Dalradian Supergroup of early eukaryotic evolution: Cold Spring Har- Scotland and Ireland: Geological Society ACKNOWLEDGMENTS bor Perspectives in Biology, v. 6, 14 p., doi: 10 of London Journal, v. 166, p. 129–135, doi:10 We thank the Yukon Geological Survey, the Na- .1101 /cshperspect .a016121 . .1144 /0016 -76492007 -126 . tional Science Foundation (NSF) Graduate Research Knoll, A.H., and Vidal, G., 1980, Late Proterozoic Rooney, A.D., Macdonald, F.A., Strauss, J.V., Dudás, Fellowship to Strauss; NSF Sedimentary Geology and vase-shaped microfossils from the Visingsö F.O., Hallmann, C., and Selby, D., 2014, Re-Os Paleobiology grant EAR-1148058, and the NASA As- Beds, Sweden: Geologiska Föreningen i Stock- geochronology and coupled Os-Sr isotope trobiology Institute for fi nancial and logistic support; holm Förhandlingar, v. 102, p. 207–211, doi: 10 constraints on the Sturtian snowball: National Fireweed Helicopters for transportation; D. Schrag for .1080 /11035898009455157 . Academy of Sciences Proceedings, v. 111, the use of the Laboratory for Geochemical Oceanog- Knoll, A.H., Javaux, E.J., Hewitt, D., and Cohen, p. 51–56, doi: 10 .1073 /pnas .1317266110 . raphy at Harvard University; C. Roots, G. Halverson, P., 2006, Eukaryotic organisms in Proterozoic Samuelsson, J., and Butterfi eld, N.J., 2001, Neo- P. Cohen, N. Tosca, E. Sperling, E. Smith, E. Kennedy, oceans: Royal Society of London Philosophi- protero zoic fossils from the Franklin Moun- and A. Gould for assistance in the fi eld and stimulat- cal Transactions, ser. B, v. 361, p. 1023–1038, tains, northwestern Canada: Stratigraphic and ing discussions; and N. Butterfi eld, C. Dehler, and an doi: 10 .1098 /rstb .2006 .1843 . palaeobiological implications: Precambrian Re- anonymous reviewer for constructive comments. Macdonald, F.A., Schmitz, M.D., Crowley, J.L., search, v. 107, p. 235–251, doi:10 .1016 /S0301 Roots, C.F., Jones, D.S., Maloof, A.C., Strauss, -9268 (00)00142 -X . REFERENCES CITED J.V., Cohen, P.A., Johnston, D.T., and Schrag, Timmons, J.M., Karlstrom, K.E., Dehler, C.M., Aitken, J.D., 1991, Two Late Proterozoic glaciations, D.P., 2010, Calibrating the Cryogenian: Geissman, J.W., and Heizler, M.T., 2001, Mackenzie Mountains, northwestern Canada: Science, v. 327, p. 1241–1243, doi: 10 .1126 Proterozoic multistage (ca. 1.1. and 0.8 Ga) Geology, v. 19, p. 445–448, doi:10 .1130 /0091 /science .1183325 . extension in the Grand Canyon Supergroup -7613 (1991)019 <0445: TLPGMM>2 .3 .CO;2 . Macdonald, F.A., Prave, A., Petterson, R., Smith, and establishment of a northwest- and north- Cohen, P.A., and Knoll, A.H., 2012, Scale microfos- E.F., Pruss, S., Oates, K., Waechter, F., Trot- trending tectonic grain in the southwestern sils from the mid-Neoproterozoic Fifteenmile zuk, D., and Fallick, A., 2013, The Laurentian United States: Geological Society of America Group, Yukon Territory: Journal of Paleontol- record of Neoproterozoic glaciation, tectonism, Bulletin, v. 113, p. 163–181, doi:10 .1130 /0016 ogy, v. 86, p. 775–800, doi: 10 .1666 /11 -138 .1 . and eukaryotic evolution in Death Valley, Cali- -7606 (2001)113 <0163: PMCAGE>2 .0 .CO;2 . Dehler, C.M., Elrick, M., Karlstrom, K.E., Smith, fornia: Geological Society of America Bulletin, Tosca, N.J., Macdonald, F.A., Strauss, J.V., John- G.A., Crossey, L.J., and Timmons, J.M., 2001, v. 125, p. 1203–1223, doi: 10 .1130 /B30789 .1 . ston, D.T., and Knoll, A.H., 2011, Sedimentary Neoproterozoic Chuar Group (~800–742 Ma), Mahon, R.C., Dehler, C.M., Link, P.K., Karlstrom, talc in Neoproterozoic carbonate successions: Grand Canyon: A record of cyclic marine depo- K.E., and Gehrels, G.E., 2014, Geochronologic Earth and Planetary Science Letters, v. 306, si tion during global cooling and superconti- and stratigraphic constraints on the Meso protero- p. 11–22, doi: 10 .1016 /j .epsl .2011 .03 .041 . nent rifting: Sedimentary Geology, v. 141– zoic and Neoproterozoic Pahrump Group, Death Tziperman, E., Halevy, I., Johnston, D.T., Knoll, 142, p. 465–499, doi:10 .1016 /S0037 -0738 Valley, California: A record of the assembly, sta- A.H., and Schrag, D.P., 2011, Biological in- (01)00087-2 . bility, and break of Rodinia: Geological Society duced initiation of Neoproterozoic snowball- Dehler, C.M., Fanning, C.M., Link, P.K., Kingsbury, of America Bulletin, v. 126, p. 652–664, doi:10 Earth events: National Academy of Sciences E.M., and Rybczynski, D., 2010, Maximum .1130 /B30956 .1 . Proceedings, v. 108, p. 15091–15096, doi:10 depositional age and provenance of the Uinta Mustard, P.S., and Roots, C.F., 1997, Rift-related vol- .1073 /pnas .1016361108 . Mountain Group and Big Cottonwood Forma- canism, sedimentation, and tectonic setting of Wheeler, J., and McFeely, P., 1991, Tectonic assem- tion, northern Utah: Paleogeography of rift- the Mount Harper Group, Ogilvie Mountains, blage map of the Canadian Cordillera and ad- ing western Laurentia: Geological Society of Yukon Territory: Geological Survey of Canada jacent parts of the United States of America: America Bulletin, v. 122, p. 1686–1699, doi:10 Bulletin, v. 492, 92 p., doi: 10 .4095 /208670 . Geological Survey of Canada A series Map .1130 /B30094 .1 . Narbonne, G.M., Kaufman, A.J., and Knoll, A.H., 1712A, scale 1:200,000. Halverson, G.P., Hoffman, P.F., Schrag, D.P., Maloof, 1994, Integrated chemostratigraphy and bio- Manuscript received 1 April 2014 A.C., and Rice, A.H.N., 2005, Toward a Neo- stratigraphy of the Windermere Supergroup, Revised manuscript received 13 May 2014 proterozoic composite carbon isotope rec- northwestern Canada: Implications for Neo- Manuscript accepted 14 May 2014 ord: Geological Society of America Bulletin, proterozoic correlations and the early evolution v. 117, p. 1181–1207, doi: 10 .1130 /B25630 .1 . of animals: Geological Society of America Bul- Printed in USA

4 www.gsapubs.org | June 2014 | GEOLOGY