Neoproterozoic glaciation on a carbonate platform margin in Arctic Alaska and the origin of the North Slope subterrane Francis A. Macdonald† Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, Massachusetts 02138, USA William C. McClelland Department of Geological Sciences, University of Idaho, Moscow, Idaho 83843, USA Daniel P. Schrag Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, Massachusetts 02138, USA Winston P. Macdonald Biology Department, Boston University, 5 Cummington Street, Boston, Massachusetts 02215, USA ABSTRACT former aragonite crystal fans, rests on a nal bend of the northernmost Cordillera (Carey, silicifi ed surface. Chemostratigraphic cor- 1955, 1958). This was later refi ned to the rota- The rotation model for the opening of relations also indicate a large increase in tion model, which called for a Cretaceous 66° the Canada Basin of the Arctic Ocean pre- sedimentation rate in the upper ~1 km of counterclockwise rotation of the Arctic Alaska– dicts stratigraphic links between the Alas- the Katakturuk Dolomite and in the over- Chukotka Plate (Fig. 1) away from the Cana- kan North Slope and the Canadian Arc- lying lower Nanook Limestone. We suggest dian Arctic islands about a pole in the Mack- tic islands. The Katakturuk Dolomite is a that the accompanying increase in accom- enzie River Delta (Hamilton, 1970; Grantz et 2080-m-thick Neo protero zoic carbonate suc- modation space, along with the presence of al., 1979). While this model is the most widely cession exposed in the northeastern Brooks two low-angle unconformities within these accepted (for a review of the models, see Lawver Range of Arctic Alaska. These strata have strata, are the product of late Ediacaran and Scotese, 1990), the tectonic movements previously been correlated with the pre– rifting along the southern margin of the that precipitated the opening of the Arctic Basin 723 Ma Shaler Supergroup of the Amund- North Slope subterrane. There are no strata remain controversial (Lane, 1997). This uncer- son Basin. Herein we report new composite present in the Amundson Basin that are tainty is due in large part to the paucity of mag- δ13C profi les and detrital zircon ages that potentially correlative with the late Neopro- netic anomalies in the Canada Basin, since much test this connection. We go further and use terozoic Katakturuk Dolomite, as the Cam- of the ocean crust was formed during the Cre- stratigraphic markers and a compilation brian Saline River Formation rests on the taceous Long Normal Interval (Sweeney, 1985). of δ13C chemostratigraphy from around ca. 723 Ma Natkusiak Formation. Detrital Moreover, paleomagnetic constraints are com- the world, tied to U-Pb ages, to derive an zircon geochronology, chemostratigraphic plicated by pervasive mid-Cretaceous overprints age model for deposition of the Kataktu- correlations, and the style of sedimentation in the Brooks Range (Hillhouse and Grommé, ruk Dolomite. In particular, we report the are inconsistent with both a Canadian Arc- 1983). Yet all is not lost, for Neoproterozoic and identifi cation of ca. 760 Ma detrital zircons tic origin of the North Slope subterrane and Paleozoic sequences on the Arctic margins pro- in strata underlying the Katakturuk Dolo- a simple rotation model for the origin of the vide geologic tests of the rotation model. mite. Moreover, a diamictite present at the Arctic Ocean. If the rotation model is to be The Katakturuk Dolomite is a 2080-m-thick base of the Katakturuk Dolomite is capped retained, the exotic North Slope subterrane Neoproterozoic carbonate succession exposed by a dark-colored limestone with peculiar must have accreted to northwest Laurentia in the northeastern Brooks Range of Arctic roll-up structures. Chemostratigraphy and in the Early to Middle Devonian. Alaska (Fig. 1). The rotation model predicts lithostratigraphy suggest this is an early- that these strata are a northern extension of Cryogenian glacial diamictite-cap carbonate Keywords: Neoproterozoic, snowball Earth, pre–723 Ma “Succession B” intracratonic couplet and that deposition of the Kataktu- cap carbonates, Arctic Alaska terrane, Kat- deposits of northwestern Laurentia (Rainbird ruk Dolomite spanned much of the late Neo- akturuk, Nanook, chemostratigraphy, detrital et al., 1996), such as the Shaler Supergroup of proterozoic. Approximately 500 m above the zircon geochronology, carbon isotope, oxygen Victoria Island (Young, 1981), the Little Dal diamictite, a micropeloidal dolomite, with isotope, glaciation. Group in the Mackenzie Mountains (Aitken, idiosyncratic textures that are characteris- 1981), and the Lower Tindir Group of Yukon- tic of basal Ediacaran cap carbonates, such INTRODUCTION Alaska border area (Young, 1982). Herein we as tubestone stromatolites, giant wave rip- report lithostratigraphic, chemostratigraphic, ples, and decameters of pseudomorphosed In his Alaskan orocline hypothesis, Sam and geochronologic studies that test both this Carey proposed that the Arctic Ocean opened correlation with Laurentian strata and the rota- †E-mail: [email protected] as a sphenochasm complementary to the orocli- tion model for the opening of the Arctic Ocean. GSA Bulletin; March/April 2009; v. 121; no. 3/4; p. 448–473; doi: 10.1130/B26401.1; 14 fi gures; Data Repository item 2008190. 448 For permission to copy, contact [email protected] © 2008 Geological Society of America Neoproterozoic carbonates in Arctic Alaska FR South Anyuy Suture LA LA SI FR Figure 1. Location and tec- LA ARCTIC ALASKA– tonic map superimposed on EST HST CHUKOTKAWrangel MICROPLATE the bathymetry of the Arctic Tatonduk Island Ocean, modifi ed and simpli- Inlier NST fi ed from Johnston (2001), Romanzof Mts. East Siberian Mackenzie Moore et al. (1994), Persits and Shelf Mountains Shublik and Sadlerochit Ulmishek (2003), and Colpron Mountains et al. (2007), with the Arctic New Siberian Alaska–Chukotka microplate NA Chukchi Islands Borderland shaded gray. Abbreviations for terranes and subterranes: the Canada Basin North Slope subterrane (NST), the Endicott Mountains sub- Banks terrane (EST), the Hammond Island subterrane, including the Ang- ayucham, Coldfoot, De Long Prince Patrick Victoria Island Mountains, Slate Creek subter- Island ranes (HST); FR—Farewell- Ruby terranes; NA—ancestral North America; LA—late accreted terranes; SI—Siberia. Taimyr Stars are locations addressed in the text and Figure 14. Lomonosov Ridge Furthermore, a redefi nition of the age of the this gap, integrated, high-resolution studies of unique isotopic variability of the era (Kaufman Katakturuk Dolomite integrates this sequence Late Neoproterozoic–Cambrian successions and Knoll, 1995; Halverson et al., 2005). Car- into our understanding of environmental change are necessary, and where possible, new sections bon-isotope records have played a central role in the terminal Neoproterozoic. need to be added to the record of this tumultu- in studies of Neoproterozoic climate extremes Neoproterozoic strata contain evidence of ous period. (Hoffman and Schrag, 2002), ocean carbon multiple low-latitude glaciations (Harland, 1964; dynamics (Rothman et al., 2003; Hotinski et al., Hambrey and Harland, 1981; Evans, 2000), the BACKGROUND 2004), carbonate production (Bartley and Kah, breakup of Rodinia and assembly of Gondwana- 2004), and the end-Neoproterozoic extinction land (Hoffman, 1991), the putative oxygenation Neoproterozoic Carbon-Isotope event (Amthor et al., 2003). of the deep oceans (Logan et al., 1995; Roth- Chemostratigraphy The Neoproterozoic represents one of only man et al., 2003; Fike et al., 2006), several high- two periods in Earth history (the other being amplitude carbon-isotope excursions (Knoll et Carbon-isotope records from marine carbon- 2.0–2.2 Ga) when the δ13C of carbonates devi- al., 1986; Burns and Matter, 1993; Halverson et ate strata are widely used for global stratigraphic ates strongly from 0 to 3‰ for long periods al., 2005), the acanthomorphic acritarch radia- correlation (Knoll et al., 1986; Saltzman et al., (Shields and Veizer, 2002), hovering around 5‰ tion (Grey et al., 2003; Grey, 2005), the rise 2000; Halverson et al., 2005) and for studying for most of a 300-m.y. interval (Halverson et and fall of the Ediacaran fauna (Glaessner and the interplay between climate and biogeochemi- al., 2005). From this heavy baseline, there are Wade, 1966; Cloud and Glaessner, 1982), and cal cycling (Summons and Hayes, 1992; Zachos several sharp, global, negative carbon-isotope the advent of bilaterians and calcifying metazo- et al., 2001; Saltzman, 2005). Carbonate carbon excursions. The Rasthof (Yoshioka et al., 2003), ans (Grotzinger et al., 1995; Fedonkin and Wag- isotopes are a particularly valuable proxy in Trezona (McKirdy et al., 2001; Halverson et goner, 1997; Martin et al., 2000). However, both the Neoproterozoic because of their resistance al., 2002), and Maieberg (Kaufman and Knoll, relative and absolute age uncertainties preclude to alteration (Banner and Hanson, 1990; Veizer 1995; Kennedy, 1996; Hoffman et al., 1998b) a better understanding of the origins and inter- et al., 1999), the relative lack of calibrated bio- isotope excursions are intimately associated relationships of these events. In order to bridge stratigraphy (Knoll and Walter, 1992), and the with Neoproterozoic glaciations. A pronounced Geological Society of America Bulletin, March/April 2009 449 Macdonald et al. carbon-isotope excursion also occurs in the thin