Geochemical Constraints on the Provenance of Pre-Mississippian Sedimentary Rocks in the North Slope Subterrane of Yukon and Alaska

Home , Cambrian Stage 3, Cambrian Stage 4

The Geological Society of America Special Paper 541

Geochemical constraints on the provenance of pre-Mississippian sedimentary rocks in the North Slope subterrane of Yukon and Alaska

Lyle L. Nelson Department of Earth and Planetary Sciences, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, USA

Justin V. Strauss Department of Earth Sciences, Dartmouth College, HB6105 Fairchild Hall, Hanover, New Hampshire 03755, USA

Peter W. Crockford Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot 76100, Israel Department of Geosciences, Princeton University, Princeton, New Jersey 08544, USA

Grant M. Cox Centre for Tectonics, Resources and Exploration (TraX), Department of Earth Sciences, The University of Adelaide, Adelaide, South Australia 5005, Australia

Benjamin G. Johnson Department of Geology and Geography, West Virginia University, 98 Beechurst Avenue, Morgantown, West Virginia 26506, USA

William Ward Department of Earth and Environmental Sciences, University of Iowa, 115 Trowbridge Hall, Iowa City, Iowa 52242, USA

Maurice Colpron Yukon Geological Survey, P.O. Box 2703 (K-14), Whitehorse, Yukon, Y1A 2C6, Canada

William C. McClelland Department of Earth and Environmental Sciences, University of Iowa, 115 Trowbridge Hall, Iowa City, Iowa 52242, USA

Francis A. Macdonald Department of Earth Science, University of California, Santa Barbara, 1006 Webb Hall, Santa Barbara, California 93106, USA

Nelson, L.L., Strauss, J.V., Crockford, P.W., Cox, G.M., Johnson, B.G., Ward, W., Colpron, M., McClelland, W.C, and Macdonald, F.A., 2018, Geochemical constraints on the provenance of pre-Mississippian sedimentary rocks in the North Slope subterrane of Yukon and Alaska, in Piepjohn, K., Strauss, J.V., Reinhardt, L., and McClelland, W.C., eds., Circum-Arctic Structural Events: Tectonic Evolution of the Arctic Margins and Trans-Arctic Links with Adjacent Orogens: Geologi- cal Society of America Special Paper 541, p. 1–20, https://doi.org/10.1130/2018.2541(24). © 2018 The Geological Society of America. All rights reserved. For permission to copy, contact [email protected].

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ABSTRACT

The North Slope subterrane of Arctic Alaska extends from the northeastern Brooks Range of Alaska into adjacent Yukon, Canada, and includes a pre- Mississippian deep- water sedimentary succession that has been historically correlated with units exposed in the Selwyn basin of northwestern Laurentia. Sedimentary provenance data, including Sm-Nd isotopes and major and trace element geochemistry, provide detailed geochemical characterization of the regional pre- Mississippian strata of the North Slope subterrane. Combined with paleontological and geochronological age constraints, these new data record a marked shift in provenance in the Ordovician–Devonian(?) Clarence River Group, evidently linked to an inﬂ ux of juvenile, arc-derived material. The timing and nature of this provenance change are consistent with early Paleozoic tectonic reconstructions of the Arctic margin that restore the North Slope subterrane to northeastern Laurentia (present coordinates), proximal to the Appalachian- Caledonian orogenic belt. Such a restoration requires signiﬁ cant post-Early Devonian sinistral strike-slip displacement to later incorporate the North Slope subterrane into the composite Arctic Alaska terrane.

INTRODUCTION remain particularly enigmatic (e.g., Miller et al., 2006), posing an outstanding barrier to accurate tectonic reconstructions of the The North American Cordillera contains numerous exotic Arctic (Fig. 1A). The Arctic Alaska terrane was once thought to crustal fragments with uncertain origins and displacement his- represent a single contiguous Neoproterozoic−Paleozoic terrane tories that were accreted to autochthonous western Laurentia (e.g., Blodgett et al., 2002; Dumoulin et al., 2002; Miller et al., throughout the late Paleozoic and Mesozoic (Fig. 1A; e.g., Coney 2006), but it has recently been shown to represent a composite of et al., 1980; Silberling et al., 1994; Colpron and Nelson, 2009). In multiple subterranes that likely have distinct pre-Devonian tec- the northernmost Cordillera, the origin and subsequent tectonic tonic histories (Fig. 1B; e.g., Strauss et al., 2013; Amato et al., evolution of Arctic Alaska and Chukotka (northeastern Siberia) 2015; Johnson et al., 2016). Neoproterozoic to early Paleozoic

B GREENLAND A 162°W 141°W Beaufort Sea Franklinian basin North Slope beneath NE Brooks (Patchett et al., 1999) 69°N Range PearyaPearya

Doonerak Fig. 2

Ba in B Fenster USA 67°N CAN EllesmereE Island

n i Arctic Alaskan subterranes g r North Slope Angayucham a m Hammond Cover n Figure 1. Generalized study location maps ia De Long Mountains n 200 km li showing: (A) distribution of paleo-Arctic ter- Endicott Mountains k Chukchi n a ranes and Laurentian basins in the northern Coldfoot Devonian r Study Area Borderland F ChukchiSlate Sea Creek Canadaplutons Cordillera (after Colpron and Nelson, 2011; Basin VictoriaV Johnson et al., 2016), and (B) subterranes of B Island Arctic Alaska (after Strauss et al., 2013). Stars Chukotka indicate study areas.

1 Paleo-Arctic realm terranes 1

1 Arctic 1 YYukon block Laurentian off-shelf margin

Alaska 1 1 1 Laurentian on-shelf margin Bering Sea

1 1 Selwyn North Slope subterrane basinBasin Farewell Limit of Cordilleran deformation 500 km

Alexander

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strata, faunal assemblages, and detrital zircon data suggest that Early to Middle Ordovician due to the arrival of peri- Laurentian the southwestern portions of the Arctic Alaska terrane (e.g., and exotic island arcs (e.g., Hiscott, 1978; Hurst et al., 1983; Hammond subterrane; Fig. 1B) are exotic to Laurentia (Moore Surlyk and Hurst, 1984; Botsford, 1988; Andersen and Sam- et al., 1997; Dumoulin et al., 2002; Miller et al., 2011; Till et son, 1995; Macdonald et al., 2017). The early Paleozoic tectonic al., 2014a, 2014b; Hoiland et al., 2017; Strauss et al., 2017). In history of the northern margin of Laurentia is less constrained, contrast, the northeastern part of Arctic Alaska, the North Slope but an Ordovician change in provenance from cratonic base- subterrane, has strong ties to Laurentia, based on stratigraphic ment sources to arc-derived juvenile siliciclastic material has relationships and distinctly Laurentian faunas and detrital zircon been documented (e.g., Trettin et al., 1991; Patchett et al., 1999). populations (Strauss et al., 2013, this volume, Chapters 22 and Critically, early Paleozoic arc-derived sediments do not appear 23; McClelland et al., 2015; Lane et al., 2016; Johnson et al., to have reached northwestern Laurentia until the Middle(?) 2016, this volume; Colpron et al., this volume). However, there Devonian–Early Mississippian, when the Ellesmerian clastic remains controversy regarding where along the Laurentian mar- wedge delivered recycled components of juvenile material to the gin the North Slope subterrane originated and when it attained passive margin (Boghossian et al., 1996; Garzione et al., 1997; its current position (e.g., Lane et al., 2016; Johnson et al., 2016). Beranek et al., 2010; Lemieux et al., 2011). In this study, we pres- Some studies maintain that pre-Mississippian strata of the ent new sedimentary geochemical data, specifi cally major and North Slope were deposited in-situ along the Neoproterozoic− trace element analyses coupled with Sm-Nd isotopes, in order to Early Devonian passive margin of the Yukon block of north- characterize the provenance of the pre-Mississippian sedimen- western Laurentia (e.g., Lane, 1991, 1997, 1998; Moore et al., tary succession of the North Slope subterrane and test possible 1994; Cecile et al., 1999; Beranek et al., 2010; Lane and Gehrels, links to northwestern or northeastern Laurentia. 2014; Lane et al., 2016), while others argue for deposition of these strata near the Franklinian basin of northeastern Laurentia GEOLOGICAL SETTING with subsequent translation prior to the opening of the Amerasian basin of the Arctic Ocean (Fig. 1A; e.g., Sweeney, 1982; Oldow North Slope Subterrane et al., 1987; Strauss et al., 2013; Cox et al., 2015; Johnson et al., 2016). Specifi cally, paleogeographic links between the North In the northeastern salient of the Brooks Range, the North Slope subterrane and northeastern Laurentia have been supported Slope subterrane is composed of three distinct sedimentary suc- with biogeographic data and by relating detrital zircon popula- cessions: the pre-Mississippian Franklinian sequence, the Upper tions to sources in the Caledonian orogenic belt (Dumoulin et Devonian−Cretaceous Ellesmerian sequence, and the Jurassic− al., 2000; Strauss et al., 2013, this volume, Chapters 22 and 23; Cenozoic Brookian sequence (Fig. 2A; Lerand, 1973; Moore et Johnson et al., 2016, this volume; Colpron et al., this volume). al., 1994). The Franklinian sequence is characterized by a pen- Owing to the distinct tectonic and sedimentation histories of the etrative fabric that is absent from the younger successions, and it northeastern and northwestern margins of Laurentia during the is locally intruded by Late Devonian plutons (Moore et al., 1994). early Paleozoic, these two competing paleogeographic recon- These pre-Mississippian sedimentary units are unconformably structions have different predictions for the provenance of basinal overlain by the Upper Devonian−Mississippian Endicott Group pre-Mississippian strata within the North Slope subterrane. of the Ellesmerian sequence, which forms a prominent clastic Samarium-neodymium isotopes are a useful sedimentary wedge succession that has been attributed to either rifting or fore- provenance tool because these elements have short residence land basin sedimentation (Nilsen, 1981; Moore et al., 1994). At times in seawater and their isotopic ratios are not signifi cantly the headwaters of the Kongakut River in the northeastern Brooks affected by low-grade metamorphism, weathering, or diagenesis Range (Fig. 2A), pre-Mississippian rocks are unconformably (e.g., McLennan et al., 1993, 2003; Taylor and McLennan, 1995). overlain by siliciclastic strata of the Middle Devonian Ulunga- ε Therefore, the calculated initial epsilon Nd ( Nd) values of fi ne- rat Formation, which is itself tilted and unconformably overlain grained sedimentary rocks largely refl ect mixing of the source by the Upper Devonian−Mississippian Endicott Group (Fig. 3; terranes from which the sediment is derived. In addition, major Anderson et al., 1994). and trace element compositions can be analyzed from the same All of the pre-Mesozoic sedimentary successions of the mudstone sample to provide further insights into the specifi c tec- North Slope were affected by north-directed Jurassic−Tertiary tonic environment of the source region, particularly where there deformation during the Brookian orogen, but locally this defor- is a demonstrated juvenile contribution (e.g., McLennan et al., mation clearly overprints an older fabric (Oldow et al., 1987; Wal- 1993, 2003). Consequently, these geochemical fi ngerprints can lace and Hanks, 1990; Moore et al., 1994; Lane, 2007; Johnson et link sedimentary deposits to ancient source regions through time al., 2016). The Ulungarat Formation lacks the penetrative fabric and help identify different basement domains and tectonic events of the underlying older successions, implying that most of the (e.g., Boghossian et al., 1996; Li and McCulloch, 1996; Patchett early Paleozoic deformation occurred prior to the Middle Devo- et al., 1999; Barovich and Foden, 2000; Li et al., 2003). nian (Anderson et al., 1994)—this apparent pre-Middle Devonian Along the Appalachian-Caledonian margin of Laurentia, deformation has been referred to as the Romanzof orogeny (Lane, distal sedimentary basins began to receive juvenile detritus by the 2007). To the north, the pre-Mississippian sequence is truncated

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WMT WMT Clarence River Group (Upper Ordovician–Lower Devonian) Whale Mountain allochthon (Upper Cambrian–Lower Devonian) Neruokpuk/Leffingwell formations (Cambrian–Middle Ordovician) Firth River Group (Neoproterozoic–middle Cambrian(?)) Carbonate Platform (Neoproterozoic–Lower Devonian) Ulungarat Formation (Middle Devonian) go

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Sadlerochit Mts. Mts. Sadlerochit Sadlerochit

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Frankli Frankli Sample Localities: A Figure 2. Sample locality maps showing: (A) simpliﬁ ed geology of eastern half northeastern Brooks Range (after Johnson et al., 2016), and (B) detailed Clarence (A) simpliﬁ Figure 2. Sample locality maps showing: locality F1 from Dutro et al. (1971); 1). Fossil Table fossil locations (see (after Lane et al., 1995). Diamonds indicate sample locations; circles are key Yukon area of northern River Thrust; RMT—Romanzof Mountain Thrust; WMT—Whale Mountain Thrust; River FRT—Firth Abbreviations: F2 from Lane and Cecile (1989); F3 et al. (1995). Thrust; Fm—formation; Gp—group. CDT—Continental Divide

Figure 3. Schematic stratigraphic architecture of the basinal pre-Mississippian succession of the North Slope subterrane (after Strauss et al., this volume, Chapter 23). Stars indicate approximate stratigraphic positions of analyzed samples with colors corresponding to those in Figure 2. Approximate ages are assigned from a compilation of available age constraints presented in Table 1.

by strata of the Mesozoic Canada basin; to the southwest, it is Pre-Mississippian Rocks of the North Slope Subterrane juxtaposed against the southwestern subterranes of Arctic Alaska; and to the southeast, it is juxtaposed against the Yukon block by Pre-Mississippian rocks of the North Slope subterrane the Porcupine shear zone (Fig. 1A; Churkin et al., 1980). This are composed of two distinct stratigraphic successions in the shear zone has been interpreted as a continuation of the right- northeastern Brooks Range (Fig. 2A): a Neoproterozoic−Lower lateral Kaltag fault, which has up to 130 km of Tertiary strike-slip Devonian basinal succession of mixed siliciclastic, volcanic, displacement in east-central Alaska (e.g., Dillon, 1989; Norris and and carbonate rocks exposed in the Franklin, Romanzof, British, Yorath, 1981), but Lane (1992) argued against continuation of the and Barn Mountains (Figs. 3 and 4; Moore et al., 1994; Lane fault into northern Yukon. However, the Porcupine shear zone may et al., 2016; Johnson et al., 2016; Strauss et al., this volume, still represent a major, but older, tectonic boundary (e.g., Oldow et Chapter 23), and a Neoproterozoic−Lower Devonian platformal al., 1987; von Gosen et al., 2015, this volume, Chapter 21). carbonate succession exposed in the Shublik and Sadlerochit

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A B

Figure 4. Field photographs of sampled strata. (A) Clarence River Group in Clarence River area of British Mountains, Yukon, demonstrating general exposure of outcrop belts in this region (photo looking NW towards Beaufort Sea). (B) Interbedded black sandy limestone and shale of Firth River Group near Firth River, Yukon; hammer for scale is 33 cm long. (C) Red and green Oldhamia-bearing argillite of Neruokpuk Formation near Firth River, Yukon; hammer for scale is 33 cm long. (D) Maroon siltstone interbedded with basalt ﬂ ows (green arrow) of Whale Mountain volcanic rocks and trilobite-bearing limestone beds (blue arrows) of Egaksrak formation in southern British Mountains near Yukon- Alaska border; geologist for scale. (E) Bedded chert and phyllite with channelized lithic sandstone of Romanzof formation on upper Aichilik River, Alaska; geologist for scale. (F) Isoclinally folded argillite of Clarence River Group in Clarence River area, British Mountains, Yukon; Canadian one dollar coin (2.65 cm) for scale.

Mountains (Moore et al., 1994; Clough and Goldhammer, 2000; were most likely collected from the Leffi ngwell formation (Lenz Macdonald et al., 2009; Strauss et al., this volume, Chapter 22). and Perry, 1972; Lane and Cecile, 1989), and therefore this unit The stratigraphic relationship between these two successions is tentatively considered latest Cambrian to Middle Ordovician remains poorly constrained, but they are at least partially coeval in age. (e.g., Mull and Anderson, 1991; Strauss et al., this volume, The youngest part of the pre-Mississippian succession of Chapter 23). The basinal succession, which is the focus of this the northeastern Brooks Range is the Clarence River Group, study, is composed of fault-bounded sedimentary units that have an imbricated succession of deep-water siliciclastic rocks that been structurally imbricated by both Romanzof and Brookian disconformably overlies the Neruokpuk and Leffi ngwell for- deformation (Figs. 2B and 4A). As a result, the true thickness of mations (Johnson et al., 2016; Lane et al., 2016; Strauss et al., these deep-marine strata is unknown, but has been estimated to this volume, Chapter 23). The Clarence River Group is mainly be anywhere from ~2.5 to 13.4 km (Norris, 1985a; Lane, 1991). composed of fi ne-grained siliciclastic strata (Fig. 4F), but locally These strata have mostly been mapped separately across the includes lithic arenite and wacke, chert-pebble conglomerate, United States and Canadian border (Fig. 2B; Reiser et al., 1971, and redeposited shallow-water carbonate rudstone and olio- 1980; Dutro et al., 1972; Norris, 1981a, 1981b, 1985a, 1985b, strome (Lane et al., 2016; Johnson et al., 2016; Strauss et al., 1986; Lane and Cecile, 1989; Cecile and Lane, 1991; Kelley et this volume, Chapter 23). A tectonic mélange containing hetero- al., 1994; Lane et al., 1995). However, many of the disparate lithic megaclasts within a black phyllitic matrix (locally part of map units have recently been placed in an updated stratigraphic map unit Cp of Reiser et al., 1980) locally occurs structurally framework based on regional mapping, stratigraphic studies, beneath the overlying Whale Mountain volcanic rocks and is and new and preexisting age constraints (Lane et al., 2016; John- also considered part of the Clarence River Group (Johnson et al., son et al., 2016, this volume; Strauss et al., this volume, Chapter 2016; Strauss et al., this volume, Chapter 23). Devonian rocks 23). Figure 3 presents an updated lithostratigraphic framework within the Clarence River Group have been previously referred for the pre-Mississippian basinal succession; a compilation of to as the informal Buckland Hills formation (Lane et al., 2016; current age constraints for these strata is provided in Table 1 Johnson et al., 2016); however, because of the imbrication and with select fossil localities marked on the inset geologic map in scarcity of fossils within these strata, we are generally unable to Figure 2B. determine the precise age of collected samples within the Clar- The oldest strata in the basinal succession make up the Firth ence River Group. Several samples were collected along strike River Group, which is largely composed of black to dark gray of units containing Ordovician and Silurian fossil localities (e.g., sandy limestone of the informal Cryogenian–Ediacaran(?) Mal- J1318, J1320, J1321), hence we are confi dent that some of the colm River formation (Fig. 4B; Strauss et al., this volume, Chap- Clarence River Group samples are older than Devonian (Figs. 2B ter 23). The Firth River Group also includes minor calcareous and 3). In the Barn Mountains, the Clarence River Group con- siltstone and sandstone, phyllite, argillite, limestone, and chert tains Silurian (Llandovery and early Ludlow) graptolites (Lenz that comprise the Redwacke Creek and Fish Creek formations and Perry, 1972; Cecile, 1988), and in the British Mountains this (Strauss et al., this volume, Chapter 23). The Firth River Group Group contains Late Ordovician (Sandbian-Katian) graptolites is regionally overlain by the Neruokpuk Formation, which is a (F1 in Fig. 2B; Dutro et al., 1971), Silurian (Telychian) grapto- thick siliciclastic unit composed primarily of quartz sandstone lites (F2 in Fig. 2B; Lane and Cecile, 1989), Silurian (Telychian- and wacke with minor phyllite, argillite, and conglomerate (Fig. Wenlock) graptolites (F3 in Fig. 2B; Lane et al., 1995), and late 4C; Leffi ngwell, 1919; Reed, 1968; Reiser et al., 1978; Norris, Silurian (Pridoli)−Early Devonian (earliest Pragian) conodonts 1985a; Lane, 1991; Lane et al., 2016; Johnson et al., 2016). In (Kelley et al., 1994; Lane et al., 1995). In the northeastern Brit- the British and Barn Mountains, Oldhamia trace fossils occur in ish Mountains, near the Loney syncline, there are late Silurian green and maroon argillite of the Neruokpuk Formation (Cecile, (Pridoli) graptolites (Norris, 1976); on the lower Firth River in 1988; Lane, 1991; Hofmann et al., 1994; Lane et al., 1995; the northernmost British Mountains, Early Devonian (Emsian?) Strauss et al., this volume, Chapter 23), which are thought to conodonts were identifi ed from black shale units exposed in talus represent distinctly middle Cambrian (Global Stage 3–Stage 5) (Norris, 1986). A Silurian (Wenlock) maximum depositional age deep-marine ichnofossils (Herbosch and Verniers, 2011; Mac- for at least part of the Clarence River Group is supported by the Naughton et al., 2016). The Firth River Group and Neruokpuk youngest populations of U-Pb detrital zircon ages from the Clar- Formation are both characterized by Bouma sequences, fl utes, ence River Group (Johnson et al., 2016; Strauss et al., this vol- channel morphologies, and load structures, collectively sug- ume, Chapter 23). Although some strata of the Clarence River gesting a slope to basin-fl oor depositional setting (Lane, 1991; Group could be as young as latest Early Devonian (late Emsian), Strauss et al., this volume, Chapter 23). The Neruokpuk Forma- the only fossil locality that supports this claim (Norris, 1986) tion is overlain by the informal Leffi ngwell formation, a thin lacks stratigraphic context and could also represent a previously package of black chert and maroon phyllite that contains radio- unrecognized deposit of the Devonian Ulungarat Formation (e.g., larian ghosts, indicating a late Cambrian (Furongian) or younger Anderson, 1991). Collectively, these fossil constraints suggest age (Strauss et al., this volume, Chapter 23). In the British and that the Clarence River Group has a Late Ordovician (Katian) to Barn Mountains, Early to Middle Ordovician graptolite fossils Early Devonian (Pragian) age.

Downloaded from https://pubs.geoscienceworld.org/books/chapter-pdf/4554404/spe541-24.pdf by GSA Content on 17 November 2018 8 Nelson et al. Reference 1991; Dillon et al., 1987; Ward et al., Ward Dillon et al., 1987; 1991; this volume Norris, 1986 Norris, 1976 et al., 1994 Kelley Lane et al., 1995; Mortensen and Bell, 1977; Sable, Lenz and Perry, 1972 Lenz and Perry, Reiser et al., 1980 Lane et al., 1995 Dutro et al., 1972 Strauss et al., this volume, Chapter 22 Strauss et al., this volume, Dutro et al., 1972 Chapter 23 Strauss et al., this volume, Reiser et al., 1980 Dutro et al., 1971 1972 Lenz and Perry, 1989 Lane and Cecile, Lane and Cecile, 1989 Lane and Cecile, Anderson et al., 1994 Lenz and Perry, 1972 Lenz and Perry, Moore and Churkin, 1984 Lenz and Perry, 1972 Lenz and Perry,

, M. M. sp., sp.,

cf. cf. sp.; sp.; (?), and pendens geinitzianus sp., sp., sp., (?) sp., sp., sp., O. pandora O. cf. cf. , Cardiograptus Saetograptus cf. T cf. sp.; brachiopods: brachiopods: sp.; inversus cf. , ﬁ sp., sp., T. , P. , mbriatus , var. var. hughesi , Orthograptus Phyllograptus Phyllograptus Retiolites , Cryptograptus transgrediens praecipuus Didymograptus decipiens , Adelograptus – straight thecae, Phyllograptus sp., Goniograptus sp., cf. cf. , compressus , (?), sp.–biserial graptolite, graptolite, sp.–biserial Monograptus sp., , serra T. sp., sp., sp., cf. cf. (?) cf. cf. (Herbosch and Verniers, 2011)Verniers, (Herbosch and Hofmann et al., 1994 1991; Lane, sp., sp., sp., Saratogia sp., cf. cf. T. sp. sp. sp., Glossograptus sp., confertus sp., sp., M. turriculatus M. (?) sp. , cf. cf. Locality Description

aff. Novus aff. sp., D. sp., aff. abnormis, aff. (?) (?) (?) sp., Goniophoria (?) sp., Warrenella sp. Ozarkodina remscheidensis Ozarkodina serotinus Polygnathus Didymograptus Monograptus Dechenella Geragnostus Glossograptus hincksii , Glossograptus hincksii Sigmagraptus , Linograptus posthumus tenuis Clonograptus Phyllograptus the Mount Sedgwick pluton in northern Yukon and the Yukon pluton in northernthe Mount Sedgwick Okpilak batholith in Alaska trilobites: trilobites: varians Pseudoplegmatograptus angustidens Billingsella sp. Retiograptus geinitzlanus nudus Monograptus cf. primulus exiguus Tetragraptus sp., sp., Goniograptus Didymograptus Amplexograptus Amplexograptus schaferi Didymograptus gracilis, sp., sp., Didymograptus Didymograptus ilicifolius Range* 497–? Ma Radiolarian ghosts 497–? Ma Radiolarian ghosts 521.0–? Ma Echinoderm debris (?) 380–368 Ma Pb-alpha, U–Pb zircon, and titanite ages from 521–509 Ma Olenellus s.s. Trolobites: < ca. 430 Ma< ca. U-Pb detrital zircon maximum depositional age Johnson et al., 2016 < ca. 500 Ma< ca. U-Pb detrital zircon maximum depositional age Johnson et al., 2016 423.0–407.6 Ma Conodonts: 407.6–393.3 Ma Conodonts: 423.0–419.2 Ma Graptolites 393.3–387.7 Ma Brachiopods: 427.4–423.0 Ma Pristiograptus bohemicus Graptolites: 438.5–433.4 Ma Monograptus Graptolites: 438.5–427.4 Ma Cyrtograptus Graptolites: 477.7–467.3 Ma Graptolites: 477.7–467.3 Ma Tetragraptus Graptolites: 458.4–445.2 Ma Orthograptus quadrium cronatus Graptolites: 443.8–433.4 Ma Monograptus Graptolites: 443.8–433.4 Ma Climacograptus Graptolites: Radiometric Age 467.3–458.4.5 Ma pendens Tetragraptus Graptolites: Age ogenian–Ediacaran 662–541 Ma Strontium and Carbon isotopic values Pridoli–Pragian late Emsian Eifelian Pridoli Late Devonian Wenlock early Ludlow late Cambrian (Furongian) 497–485.4 Ma Trilobites: Telychian Telychian–Wenlock Cambrian Series 3 Cambrian (Stage 4–Stage 5) 513–505 Ma < ca. U-Pb detrital zircon maximum depositional age Johnson et al., this volume Cambrian (Series 2)–? Floian–Dapingian Floian–Dapingian Furongian–? Sandbian–Katian Llandovery Llandovery Cambrian (Stage 2) Cambrian (Stage 3–Stage 5) 521–504.5 Ma Oldhamia fossils: Trace Furongian–? Darwillian TABLE 1. AGE CONSTRAINTS FROM PRE–MISSISSIPPIAN ROCKS IN THE NORTH SLOPE OF YUKON AND ALASKA YUKON SLOPE OF THE NORTH IN PRE–MISSISSIPPIAN ROCKS CONSTRAINTS FROM AGE 1. TABLE *Radiometric ages from Cohen et al., 2013. Ulungarat Formation Clarence River Group Clarence River Group Clarence River Clarence River Group Clarence River plutonic rocks Devonian Clarence River Group Clarence River Group (?) Clarence River Ekaluakat formation Whale Mountain volcanic rocks Whale Mountain volcanic Romanzof formation Romanzof Group Clarence River Group Clarence River Marsh Fork volcanic rocks volcanic Marsh Fork Neruokpuk Formation rocks Whale Mountain volcanic formation Romanzof Group Clarence River ngwell formation Leffi (?) formation ngwell Leffi Firth River Group (Malcolm River formation)Firth Group (Malcolm River River Cry formation ngwell Leffi Clarence River Group Clarence River Group (?) Clarence River Formation Leffi ngwell formation (?) formation ngwell Leffi

Distinct belts of dominantly maﬁ c volcanic and volcani- plasma-atomic emission spectroscopy (ICP-AES) and induc- clastic rocks of the Whale Mountain allochthon are structurally tively coupled plasma-mass spectrometry (ICP-MS). juxtaposed with different units of the basinal succession (Fig. 2; Johnson et al., 2016, this volume; Strauss et al., this volume, Samarium-Neodymium Isotope Analytical Procedures Chapter 23). The Marsh Fork and Whale Mountain volcanic rocks are composed of amygdaloidal aphanitic and porphyritic The remainder of each powdered sample was ignited at basalt that is locally intercalated with pelagic limestone and ~1000°C to remove all volatiles and organic matter. Approxi- dolostone units of the informal Egaksrak formation (Fig. 4D; mately 0.3 g was weighed into a 5 mL Teﬂ on beaker, spiked with Moore, 1987; Lane, 1991; Strauss et al., this volume, Chapter enriched 150Nd-149Sm tracer, and dissolved under pressure with

23; Johnson et al., this volume) and regionally overlain by chert, a concentrated HF-HNO3 mixture. The resulting solutions were

phyllite, and minor volcaniclastic sandstone of the informal evaporated and dissolved in aqua-regia (2:1, 6N HCl:7N HNO3), Romanzof formation (Fig. 4E; Strauss et al., this volume, Chap- then evaporated and dissolved again in 6N HCl. Pure Sm and Nd ter 23). Limestone units of the Egaksrak formation are found extracts of each sample were separated via column chromato- both in blocks and interbedded with the volcanic rocks, and in graphy in a three-stage process. First, Fe was removed by passing places they contain late Cambrian (Furongian, Global Stage 4− the sample through columns fi lled with 200−400 mesh AG1X8 Stage 5) trilobites and brachiopods of peri-Laurentian affi nity ion exchange resin. Second, the rare earth element (REE) com- (Dutro et al., 1972; Reiser et al., 1980; Johnson et al., this vol- ponent was concentrated by passing the sample through columns ume). Volcaniclastic units within the Whale Mountain volcanic fi lled with Eichrom TRU Resin SPS 50−100 µm. Third, the Sm rocks yield ca. 560−440 Ma (peak age ca. 500 Ma) U-Pb zircon and Nd fractions were purifi ed by passing the samples through ages, which broadly align with the late Cambrian trilobite ages columns fi lled with 600 mg of Eichrom LN Resin 100−150 µm. from the Egaksrak formation (see Johnson et al., this volume). The reported 143Nd/144Nd and 147Sm/144Nd ratios (Table 2) Radiolarian ghosts within chert of the overlying Romanzof were measured with a Thermo Triton thermal ionization mass formation broadly establish a late Cambrian (Furongian) and spectrometer (TIMS) in the Geotop laboratories at Université du younger age (Anderson et al., 1994); the Romanzof formation Québec à Montréal. A double fi lament array was used with Nd also contains Silurian (Llandovery) graptolites (Moore and extracts loaded onto outgassed Re fi laments, parallel to outgassed Churkin, 1984), and the youngest detrital zircon grains in lithic Re ionization fi laments. Sm and Nd were measured in dynamic sandstone from this unit yield U-Pb ages of ca. 410 Ma (Strauss mode; the total combined blank for Sm and Nd is less than 150 et al., this volume, Chapter 23). In the northern British Moun- pg. 146Nd/144Nd was normalized to 0.7219 for mass fractionation tains, upper Cambrian–Lower Ordovician mafi c volcanic and corrections. During the analysis period, repeated measurements volcaniclastic rocks and chert of the informal Ekaluakat forma- of the Nd isotopic reference JNdi-1 yielded values within error tion (Figs. 2 and 3; Strauss et al., this volume, Chapter 23) are of that obtained by Tanaka et al. (2000); repeated measurements either correlative with the Whale Mountain volcanic rocks or of BHVO-2 yielded values within error of the accepted value form part of the younger Clarence River Group (Johnson et al., (Jochum et al., 2005). For the data presented herein, chondritic 2016, this volume; Strauss et al., this volume, Chapter 23). meteorites serve as a reference for the isotopic ratio of undifferentiated bulk Earth (Jacobsen and Wasserburg, 1984), and ANALYTICAL METHODS the deviations above or below the chondritic value (CHUR for “Chondritic Uniform Reservoir”) are written in parts per 10,000, Major and Trace Element Analytical Procedures yielding epsilon notation, where:

ε 143 144 143 144 Thirty-two samples of mudstone and phyllite were collected Nd = [( Nd/ Nd)sample – ( Nd/ Nd)CHUR] / 143 144 from pre-Mississippian map units in the North Slope subterrane (Nd/ Nd)CHUR x 10000. (1) of northeastern Alaska and northwestern Yukon during the 2013 ε Circum-Arctic Structural Events (CASE) 15 expedition to north- The chondritic reference values used for Nd calculations are: 143 144 147 144 ern Yukon (Fig. 2). Each sample was collected during regional Nd/ NdCHUR = 0.512638, Sm/ NdCHUR = 0.1966. The decay mapping and stratigraphic studies; many were collected in con- constant for 147Sm was assumed to be 6.54 x 1012 a-1 (Goldstein cert with sandstone samples obtained for detrital zircon geochro- et al., 1984). nology (Strauss et al., this volume, Chapter 23). The weathered The reported Sm and Nd concentrations and 147Sm/144Nd edges of each sample were removed using a lapidary saw, and ratios have less than 0.5% error, corresponding to an error of less ε ε the remaining material was homogenized with a SPEX 8500 than 0.5 Nd units, and most reported Nd values have an error of ε shatterbox using a tungsten carbide grinding mill. Small aliquots less than 0.2 Nd units (Table 2). The possible age range for each (~5 grams) of each powdered rock sample were sent to SGS sample was assigned using the available age constraints for the Analytical Services, where the powders were dissolved using a unit (Table 1; Fig. 3). The average of the assigned age range was standard 4-acid digestion and analyzed for major and trace ele- used as the approximate depositional age when calculating the ε ment compositions using a combination of inductively coupled Nd value; however, horizontal error bars are shown to indicate the

Downloaded from https://pubs.geoscienceworld.org/books/chapter-pdf/4554404/spe541-24.pdf by GSA Content on 17 November 2018 10 Nelson et al. DM (Ga) (t) error T Nd ε (t) Nd ε Nd 144 Nd/ 143 Nd 144 Sm/ 147 Nd (ppm) Sm (ppm) (°W) Longitude Location (°N) Latitude Age (Ma) 588.0 ± 47.0588.0 ± 47.0 69.44250522.8 ± 18.2 69.16278522.8 ± 18.2 140.45889 69.22250522.8 ± 18.2 140.16222 69.21611522.8 ± 18.2 140.97250 3.47 69.46806522.8 ± 18.2 140.92528 6.80 69.46361522.8 ± 18.2 19.80 140.95611 5.33 69.46361522.8 ± 18.2 38.92 140.95861 7.26 69.41472522.8 ± 18.2 23.60 140.95861 5.08 0.1058 69.48672 40.06 140.50806 2.99 0.1057 69.13563474.2 ± 40.8 28.19 140.53351 5.70 0.1366 0.511325474.2 ± 40.8 15.17 139.21286 6.18 0.1096 69.11861 0.511265474.2 ± 40.8 30.31 6.56 0.1090 −18.8 69.11303 0.511499460.3 ± 52.7 37.11 143.27564 4.42 0.1192 −20.0 69.11242 0.511539460.3 ± 52.7 37.05 143.15039 0.1137 −18.2 69.43417 0.05 0.511421434.5 ± 23.9 25.52 143.15094 4.69 0.1006 −15.6 69.43472 0.04 0.511414434.5 ± 23.9 140.95944 5.90 0.1069 −17.9 69.44944 0.08 0.511399434.5 ± 23.9 27.87 140.95889 2.46 0.1047 2.55 −18.7 69.44056 0.06 0.511272 17.83434.5 ± 23.9 30.81 140.95833 2.63 −18.7 69.43750 0.07 0.511363 15.64434.5 ± 23.9 14.73 140.95611 0.1017 3.21 −20.3 94.99 69.43639 0.05 0.511405434.5 ± 23.9 140.95778 4.50 0.1158 2.33 −18.9 78.75 69.41306 0.08434.5 ± 23.9 140.95833 4.89 0.1008 2.48 −17.9 69.41245 0.07 0.511652 0.1135434.5 ± 23.9 23.37 140.51278 4.97 2.76 69.41056 0.11 0.511813 0.1200434.5 ± 23.9 25.17 140.72926 3.05 2.63 −13.5 69.40194 0.14 0.511668434.5 ± 23.9 24.43 140.51472 4.88 0.1165 2.50 −11.2 0.512609 69.40056434.5 ± 23.9 16.19 140.52889 4.48 0.1175 −13.1 2.52 0.512635 68.56776 0.06434.5 ± 23.9 25.41 140.56667 4.86 0.1229 2.41 68.44482 0.06 0.511948 4.3434.5 ± 23.9 22.18 138.32867 3.61 0.1141 69.19389 0.06 0.511986 4.5434.5 ± 23.9 22.31 138.07237 4.92 0.1161 2.02 69.12425 −9.0 0.511954434.5 ± 23.9 13.18 0.10 140.89972 4.20 0.1221 2.06 69.34047 −8.3 0.512028434.5 ± 23.9 26.52 0.05 143.21433 2.44 0.1318 1.98 69.34653 −9.3 0.512171 22.29 0.05 142.67625 3.90 0.1658 69.34653 −7.3 0.511971 0.82 10.51 0.06 142.65403 3.70 0.1121 −4.6 0.512258 0.83 17.79 0.04 142.65403 4.65 0.1138 1.86 −8.9 0.512307 20.48 0.06 3.85 0.1402 1.82 −3.8 0.512015 26.52 0.05 4.81 0.1325 1.98 −4.8 0.512040 20.86 0.07 0.1093 1.70 −7.5 0.512142 23.79 0.06 0.1060 1.51 −7.1 0.512101 0.06 0.1117 1.94 −6.5 0.512038 0.38 0.1222 1.64 −6.9 0.512009 0.12 2.62 −6.9 0.512374 0.05 1.68 −7.2 0.511992 0.07 1.68 −0.4 0.06 2.06 −8.5 0.06 1.94 0.06 1.61 0.06 1.60 1.15 1.90 Formation TABLE 2. SAMARIUM-NEODYMIUM ISOTOPIC DATA FROM PRE-MISSISSIPPIAN ROCKS IN THE NORTH SLOPE OF YUKON AND ALASKA YUKON SLOPE OF THE NORTH IN PRE-MISSISSIPPIAN ROCKS FROM DATA ISOTOPIC SAMARIUM-NEODYMIUM 2. TABLE J1332J1311J1355 Firth Group River J1348 Firth Group River J1331 Neruokpuk Formation J1328 Neruokpuk Formation J1329 Neruokpuk Formation J1338 Neruokpuk Formation 13MC054 Neruokpuk Formation 13MC079 Neruokpuk Formation Neruokpuk Formation J1353 Neruokpuk Formation J1471J1473 rocks Whale Mountain volcanic J1474 formation Romanzof J1314 formation Romanzof 499.2 ± 13.8J1316 formation Romanzof J1324 69.17667 Ekaluakat formation J1321 Ekaluakat formation 140.92417J1320 Group Clarence River J1318 Group Clarence River 8.13J1340 Group Clarence River 13MC053 Group Clarence River 39.51J1342 Group Clarence River Group Clarence River J1344J1345 0.1244 Group Clarence River 13MC050 Group Clarence River 13MC072 Group Clarence River Group Clarence River 0.512634J1351 Group Clarence River J1472 4.5J1479 Group Clarence River J1481 Group Clarence River J1483 0.04 Group Clarence River Group Clarence River Group Clarence River 0.87 Sample number

10 Depleted Mantle Firth River Gp Neruokpuk Fm 5 Whale Mtn volcanic rocks Romanzof fm Ekaluakat fm CHUR 0 Clarence River Gp Franklinian basin (Ellesmere Island) −5

−10 Epsilon Nd

−15 Canadian Shield

−20

−25 700 600 500 400 300 200 100 0 Stratigraphic Age (Ma)

Figure 5. Initial epsilon Nd (ε ) values for pre-Mississippian sedimentary rocks of the North Slope subterrane. Colors of data points cor- Nd ε respond to symbols in Figures 2 and 3. Initial Nd values for strata from the Franklinian basin of Ellesmere Island, plotted in dark gray, are from Patchett et al. (1999).

ε possible age range, and the possible variation in the Nd calcula- Major and Trace Element Data tion is within the diameter of the data points (Fig. 5). The major element data for the 32 samples analyzed herein GEOCHEMICAL RESULTS are illustrated in a ternary diagram (Fig. 6A; Table DR11), plot-

ting mole fractions of Al2O3–(CaO+Na2O+K2O)–(FeO+MgO), Samarium-Neodymium Isotopic Data as well as simpliﬁ ed compositions of typical crystalline rock types and clay minerals with generalized weathering trends for Results of the Sm-Nd whole-rock analyses are presented different lithologies (after McLennan et al., 1993). Trends in the ε in Table 2 and Figure 5. Four distinct Nd signatures exist in the bulk-rock major element chemistry of sedimentary rocks are pre-Mississippian strata of the North Slope subterrane (Fig. 5). dominated by the conversion of feldspars and volcanic glass to All of the samples from the Firth River Group and Neruokpuk clay minerals through weathering and can be quantiﬁ ed using ε Formation have moderate to highly negative Nd values (-20.3 to molecular proportions to calculate a Chemical Index of Altera- -15.6), which is consistent with derivation from evolved base- tion (CIA; Nesbitt and Young, 1982), where: ment sources such as Archean and Proterozoic crystalline rocks

of the Canadian Shield (Fig. 5; e.g., Villeneuve et al., 1993). CIA = Al2O3 / [Al2O3 + K2O + Na2O + CaO] x 100. (2) A single sample from volcaniclastic mudstone interbedded with basalt ﬂ ows of the Whale Mountain volcanic rocks and Distinct groupings of major element compositions broadly ε limestone beds of the Egaksrak formation has a highly juvenile correlate with the distinct Nd signatures of the different sample ε Nd value of +4.5; samples from mudstone interbedded with the populations (Fig. 7A). Based on the major element geochemistry, volcaniclastic rocks of the Ekaluakat formation have similarly samples from the Firth River Group and Neruokpuk Formation ε positive Nd values of +4.3 and +4.5. Mudstone samples from record a predominance of upper crustal granitic sources having the Romanzof formation of the Whale Mountain allochthon relatively intense weathering and recycling histories, with CIA ε have Nd values ranging from -13.5 to -11.2, distinct from the older Firth River Group and Neruokpuk Formation. Finally, mudstone samples from the Clarence River Group have a range of moderately juvenile ε values that range from -9.3 to -0.4, 1GSA Data Repository Item 2018379, Table DR1: Major and trace element Nd data, is available at www.geosociety.org/datarepository/2018/, or on request indicating mixed sedimentary components with a signiﬁ cant from [email protected] or Documents Secretary, GSA, P.O. Box 9140, juvenile contribution. Boulder, CO 80301-9140, USA.

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Al2O3 1000

A ed B c r s

-sou ay Firth River Gp c cl

Neruokpuk Fm elsi Whale Mtn volcanic rocks Felsic-sourcedF 100 Romanzof fm Ekaluakat fm Clarence River Gp Weathering Trends

10 Granodiorite Andesite

Basalt clays ppm / Average Chondrite

1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Yb CaO + Na2O + K2O FeO + MgO

Th/U = 27.5 12 CDContinentally-derived 10 200

8 g Trend 150 6 Th/U Th/U Weatherin 100

4 Upper Crust Cr (ppm)

2 50 Depleted Mantle Sources 0 0 100 101 102 0 20 40 60 80 100 120 140 160 180 190 200 Th (ppm) Ni (ppm)

Figure 6. Geochemical data from the pre-Mississippian basinal succession of the North Slope subterrane. Colors correspond to Figures 2, 3, and

5. (A) Ternary plot of mole fractions of Al2O3–(CaO+Na2O+K2O)–(FeO+MgO). Also plotted are simpliﬁ ed compositions of typical crystalline rock types and clay minerals, as well as generalized weathering trends of different rock types; after McLennan et al. (1993). (B) Rare earth element (REE) abundance patterns normalized to average chondritic value, using average C1 chondrite composition from Sun and McDonough (1989). (C) Plot of Th/U ratios versus Th concentrations in ppm. Approximate upper crustal igneous value and depleted mantle ﬁ eld plotted after McLennan et al. (1993). (D) Plot of Cr concentrations (ppm) versus Ni concentrations (ppm).

values ranging from 72 to 81. In contrast, data for samples from 7B; Table DR1). Whereas mudstone samples from the Firth River the Whale Mountain volcanic rocks and the Ekaluakat formation Group and Neruokpuk Formation have negative Eu anomalies indicate a localized provenance dominated by mafi c sources and (Eu/Eu* ~0.6−0.8) characteristic of upper continental crust, sam- a general lack of sedimentary recycling, with CIA values of 48 ples from the Whale Mountain volcanic rocks and the Ekaluakat to 54. Mudstone samples from the Clarence River Group and formation lack this anomaly (Eu/Eu* ~1.0) and suggest an Romanzof formation appear to have mixed provenance compo- undifferentiated volcanic provenance in which plagioclase is nents, with CIA values ranging from 67 to 78 (Figs. 6A and 7A; unfractionated (McLennan et al., 1993). Europium anomalies Table DR1). are less pronounced in samples from the Clarence River Group Rare earth element patterns are plotted in Figure 6B, nor- (Eu/Eu* ~0.7−0.9), which may refl ect a mixture of both upper malized to the average composition of C1 chondrites (Sun and continental crust and undifferentiated magmatic sources. The ε McDonough, 1989; Table DR1). Differences in Eu anoma- variations in Eu anomalies clearly correlate with the different Nd lies visible in the REE plot (Fig. 6B) are quantifi ed here using signatures of each succession (Fig. 7B). One sample (13MC072) Eu/Eu*, calculated after Bhatia (1985) as an arithmetic mean of has a fairly large positive Eu anomaly, falling off of the broad ε SmN and GdN, using the chondritic values of Taylor and McLen- trend with Nd, and two samples (J1316, J1353) have small

nan (1981), such that, Eu/Eu* = EuN / [(SmN + GdN) / 2] (Fig. positive Eu anomalies (Fig. 7B). These positive anomalies may

refl ect post- depositional hydrothermal or diagenetic alteration ~1.0, the approximate value of upper continental crust, refl ects (e.g., Bau, 1991; MacRae et al., 1992). a relatively felsic, continental provenance, whereas a lower Observed stratigraphic changes in the relative abundance of Th/Sc ratio generally refl ects less differentiated provenance con- trace elements are also consistent with changes in provenance tributions, typically indicating appreciable mafi c components throughout the pre-Mississippian succession. A Th/Sc ratio of (McLennan et al., 1993). The Firth River Group and Neruok- puk Formation have Th/Sc ratios of ~1.0, whereas the Whale Mountain volcanic rocks and Ekaluakat formation have low 10 Th/Sc ratios of ~0.1−0.3; the Clarence River Group and Roman- A Firth River Gp Neruokpuk Fm zof formation have intermediate ratios of ~0.5−0.8 (Fig. 7C; 5 Whale Mtn volcanic rocks Table DR1). Differences in this proxy correlate well with the Romanzof fm ε 0 Ekaluakat fm differences in Nd, and data from the Clarence River Group and Clarence River Gp Romanzof formation plot along a mixing line between the other −5 two groups of samples (Fig. 7C; Table DR1). In addition, low −10 Th/U ratios accompanied by low Th contents, commonly seen in active margin sediments, refl ect geochemically depleted mantle −15 sources (McLennan et al., 1993). The Neruokpuk Formation and Initial Epsilon Nd −20 Firth River Group have relatively high Th/U ratios of 5.7−11.4, the Whale Mountain volcanic rocks and Ekaluakat formation −25 45 50 55 60 65 70 75 80 85 90 95 have low Th/U ratios of 2.5−3.0 consistent with a local volcanic Chemical Index of Alteration source, and the Clarence River Group has variable but relatively low Th/U ratios of 2.1−5.0 (Fig. 6C; Table DR1). B 10 Elevated abundances of Cr and Ni in fi ne-grained sedimen- 5 tary rocks can indicate the presence of mafi c or ultramafi c rocks in the source region because oceanic and mantle rocks contain 0 high concentrations of Cr- and Ni-bearing minerals and Cr and −5 Ni are unfractionated in fi ne-grained sediment (Goles, 1967; Garver et al., 1996). Chromium can also be enriched in shale −10 ontinental Crust without an igneous component (e.g., Slack et al., 2015); however, −15 these examples likely refl ect specifi c local redox conditions in Initial Epsilon Nd the bottom waters and pore fl uids of the basin. Chromium and Ni −20 concentrations of samples from the pre-Mississippian succession Old Upper C Young Undifferentiated Arc −25 of the North Slope subterrane (Fig. 6D; Table DR1) are strongly 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 correlated (r = 0.79) and are most elevated in the Whale Moun- Eu/Eu* tain volcanic rocks and Ekaluakat formation, consistent with a provenance dominated by local mafi c sources. Most samples C 10 MORB Arc Felsic from the Clarence River Group have higher Cr and Ni concentra- 5 tions than those from the Firth River Group, Neruokpuk Forma- Mafic tion, and Romanzof formation (Fig. 6D). 0 −5 DISCUSSION

−10 On the Fidelity of Sedimentary Geochemical Signals in −15 Upper Crust Pre-Mississippian Rocks of the North Slope Subterrane Initial Epsilon Nd

−20 Old Crust Due to their limited solubility, Sm and Nd are generally −25 immobile during sedimentary processes, and their isotopic ratios 10−2 10−1 100 101 are robust with respect to alteration, diagenesis, and low-grade Th/Sc metamorphism (e.g., McLennan et al., 1993, 2003; Taylor and Figure 7. Plots of initial ε values versus geochemical composition. McLennan, 1995). Neither Sm nor Nd has a biological function, Nd ε Colors correspond to Figures 2, 3, 5, and 6. (A) Initial Nd values ver- and with a sole +3 oxidation state, neither is affected by Eh or pH sus Chemical Index of Alteration (CIA). (B) Initial ε values versus Nd changes (Brookins, 1983). Although there is some evidence for Eu/Eu* ratios, which quantiﬁ es differences in Eu anomalies visible in ε the fractionation of REE during hydraulic grain-size sorting (e.g., Figure 6B. (C) Initial Nd values versus Th/Sc ratios. Values for typical mid-ocean ridge basalt (MORB), arc andesite, upper continental crust, McLennan et al., 1990), this study avoids this bias by analyzing and mixing line are plotted after McLennan et al. (1993). only mudstones and their low-grade metamorphic equivalents.

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Some REE may be fractionated in weathering profi les, but rarely Within the Whale Mountain allochthon, mudstone in the ε is there any signifi cant change in Sm or Nd concentration from Whale Mountain volcanic rocks exhibits very juvenile Nd values, weathering (McLennan et al., 1993). Diagenesis can also redis- major element compositions indicative of very low degrees of tribute REE among various minerals; however, this process does sedimentary recycling, and trace element signatures of an undif- not tend to result in signifi cant mobilization of REE into or out ferentiated mafi c source (Figs. 5−7). Sandstone from the volca- of the system (Ohr et al., 1994), and hence would make no differ- niclastic units is composed primarily of plagioclase grains, mafi c ence to the Sm-Nd whole-rock isotope systematics of this study lithic fragments, and heavy minerals (Johnson et al., 2016, this given the latest Neoproterozoic to middle Paleozoic depositional volume; Strauss et al., this volume, Chapter 23). These lines of age of the sample set. evidence indicate local derivation from volcanic sources within If isotopically different REE were mobilized into the system the Whale Mountain allochthon. Owing to their geochemical during diagenesis or hydrothermal alteration, these secondary composition, physical characteristics, and association with car- processes generally result in Ce anomalies (e.g., McDaniel et al., bonates bearing shallow water faunas, these volcanic rocks are 1994). Cerium anomalies are calculated using normalization to interpreted as fl ows that erupted in a bathymetrically elevated the average C1 chondrite composition of Sun and McDonough oceanic setting such as an island arc or atoll (Moore, 1987;

(1989) as an arithmetic mean of LaN and PrN, such that, Ce/Ce* = Johnson et al., this volume). This oceanic assemblage was sub-

CeN / [(LaN + PrN) / 2]. For most of the sample set presented here, sequently juxtaposed structurally against the rest of the basinal Ce/Ce* values range from 0.9 to 1.1 (Table DR1). Two samples pre- Mississippian succession during the emplacement of the of phyllite from the Romanzof formation, J1471 and J1473, have Whale Mountain allochthon (Johnson et al., 2016, this volume). small positive Ce anomalies with Ce/Ce* values of 1.2 and 1.5, The similar geochemical compositions of mudstones within the respectively, indicating that these rocks likely experienced some Ekaluakat formation of the northern British Mountains are con- REE mobilization. These samples are from the southernmost sistent with the interpretation of this belt being a dismembered sample area in Alaska (Fig. 2), where the rocks are of slightly component of the Whale Mountain allochthon (Figs. 5−7); how- higher metamorphic grade due to Brookian deformation. ever, it remains possible that this belt is also part of the Clarence River Group that is dominated by detrital contributions from the Provenance Evolution in Pre-Mississippian Strata of Whale Mountain volcanic rocks. The Romanzof formation of the the North Slope Subterrane Whale Mountain allochthon has a considerably more evolved geochemical signature than the Whale Mountain volcanic rocks The geochemical data from fi ne-grained siliciclastic rocks (Figs. 5−7), indicating an appreciable detrital component from presented herein, together with fi eld observations and current age continental sources combined with a minor contribution from constraints, allow for interpretation of the provenance and tectonic local mafi c volcanic rocks. This mixed provenance is consis- environments of different parts of the basinal pre-Mississippian tent with an interpretation that these strata were deposited in a succession of the North Slope subterrane. The Sm-Nd isoto- relatively starved, deep-marine basin in advance of structural pic data, combined with major and trace element compositions, emplacement of the Whale Mountain allochthon onto the passive indicate four distinct provenance signatures. Comparing the tim- margin succession (Johnson et al., this volume). ing and nature of provenance change to existing data from the The Upper Ordovician–Lower Devonian Clarence River northern margin of Laurentia provides constraints on the early Group is the youngest part of the basinal pre-Mississippian suc- ε Paleozoic paleogeographic position of the North Slope subterrane cession and is dominated by relatively juvenile Nd values and by because of the distinct tectonic histories of northeastern and north- major and trace element compositions indicating of a mixture western Laurentia. of evolved continental sources and juvenile undifferentiated arc The Firth River Group and Neruokpuk Formation have major sources (Figs. 5−7). The introduction of this juvenile siliciclas- ε and trace element compositions and initial Nd values (Figs. 5−7) tic material into the basinal succession of the North Slope sub- that are indicative of evolved continental crustal sources. Based on terrane represents the erosion of arc terranes and deposition of the Laurentian affi nities of the North Slope subterrane (e.g., Strauss their detritus along the northern margin of Laurentia, most likely et al., 2013, this volume, Chapter 23), this succession was most associated with the accretion of the Whale Mountain allochthon likely deposited in a basinal setting along the late Neoproterozoic− onto the late Neoproterozoic–Ordovician passive margin (John- Cambrian passive continental margin of northern Laurentia (pres- son et al. 2016, this volume; Strauss et al., this volume, Chapter ent coordinates), with siliciclastic infl ux derived from the Cana- 23). The Clarence River Group also includes beds of volcani- dian Shield and/or recycled sedimentary sources. This interpreta- clastic wacke and chert-pebble conglomerate, both of which are tion is consistent with published detrital zircon results from these typical of syn-orogenic deposits (e.g., Floyd, 1982). In addition, units, which also indicate extensive sediment recycling along the the prominent ca. 470−420 Ma detrital zircon populations in continental margin with Mesoproterozoic, Paleoproterozoic, and sandstone units from the Clarence River Group further support Archean age populations (Strauss et al., 2013, this volume, Chap- this interpretation of a profound transition from passive to active ter 23; McClelland et al., 2015; Lane et al., 2016; Johnson et al., margin sedimentation (Johnson et al., 2016; Strauss et al., this 2016, this volume; Colpron et al., this volume). volume, Chapter 23).

This fundamental shift in sedimentary provenance occurs in hamia (e.g., Cecile, 1988; Lane, 1991; Norford, 1996; Lane et samples along strike with units containing Ordovician to Silu- al., 2016). The Firth River Group and Neruokpuk Formation rian biostratigraphic constraints (Fig. 2B). Such a shift implies were correlated to late Neoproterozoic−Cambrian strata of the an infl ux of juvenile material at this time, which we interpret to Hyland Group in the Selwyn basin, and Ordovician−Devonian refl ect the exhumation of an arc proximal to the North Slope sub- units in the British and Barn Mountains were correlated with the terrane. The tectonic setting of this provenance change remains Ordovician−Devonian Road River Group of the Selwyn basin poorly constrained, particularly because the northeastern Brooks and Richardson trough (Fig., 1A; Norris, 1986; Lane, 1991; Lane Range lacks arc-related intrusive rocks or subduction-related et al., 2016). However, these lithological correlations are non- metamorphism of this age; however, evidence for south-vergent, unique because lower Paleozoic basinal turbidite successions pre-Mississippian deformation suggests southward tectonic deposited anywhere along the northern margin of Laurentia are transport (present coordinates) (Oldow et al., 1987; Lane, 2007). likely to preserve similar lithofacies and contain Oldhamia fos- Three areas that host arc-type igneous rocks that could relate sils. For example, the Hazen Formation of the Franklinian basin to the pre-Mississippian succession of the North Slope are the in Ellesmere Island, the Sillery Group in southern Québec, and Doonerak arc complex of the central Brooks Range, the Pearya the Nassau Formation in New York also host Oldhamia-bearing terrane in northern Ellesmere Island, and the Clements Markham mixed siliciclastic and carbonate deposits that are lithologically and Northern Heiberg fold belts in northern Ellesmere and Axel similar to those of the North Slope basinal succession (Fig. 1A; Heiberg islands (Fig. 1). In the Doonerak window, Ordovician Walcott, 1894; Sweet and Narbonne, 1993; Hofmann et al., to Silurian volcanic rocks of the Apoon assemblage have been 1994). Furthermore, the Road River Group of the Richardson interpreted as fragments of a juvenile island arc complex (Julian trough, although itself lithologically diverse with complex facies and Oldow, 1998; Strauss et al., 2017); in the Pearya terrane, Suc- relationships, shows signifi cant differences from the coeval rocks cessions 3 and 4 include Ordovician calc-alkaline volcanic rocks of the Clarence River Group (Johnson et al., 2016; Strauss et al., with minor ultramafi c units, which have also been interpreted as this volume, Chapter 23). The Road River Group is composed of arc-related (Trettin, 1987, 1998). In the Clements Markham and shale, limey shale, argillaceous limestone, limestone, dolostone, Northern Heiberg fold belts, inboard of the Pearya terrane, Upper and diagenetic chert with intervals of carbonate debris-fl ow Ordovician volcanic rocks and serpentinites of the Kulutingwak deposits, slumps, and turbidites derived from proximal Paleozoic Formation and Mount Rawlinson complex have been interpreted carbonate banks of the Ogilvie and Mackenzie platforms (Nor- as vestiges of an island arc complex (Klaper, 1992), and Silu- ford, 1996, and references therein). The Clarence River Group, rian volcanic rocks (Llandovery to Wenlock) of the Fire Bay while superfi cially similar, lacks these carbonate-rich facies Formation and Svartevaeg Formation have been used to infer the and contains abundant lithic wacke, chert-pebble conglomerate, presence of an early Silurian arc outboard of northern Laurentia lithic volcanic conglomerate, and zones of tectonic mélange, all (Trettin, 1998). The specifi c tectonic relationships between these of which are absent from the Road River Group of the adjacent different arc rocks are beyond the scope of this paper, but all are Yukon block. interpreted to represent elements of the northern extension of the The deep-water basins adjacent to the Paleozoic carbonate Appalachian-Caledonian orogenic belt into the Arctic realm that platforms of the Yukon block are thought to have formed through were subsequently dismembered by sinistral translation along localized continental rifting during which potassic volcanic rocks the margin of northern Laurentia (e.g., McClelland et al., 2012; were intermittently emplaced along rift-parallel normal faults Beranek et al., 2015; Strauss et al., 2017). The Whale Mountain between the Cambrian and Devonian (Goodfellow et al., 1995). allochthon may also be a dissected fragment of this arc system The geochemical compositions of the volcanic rocks of the Selwyn that was later emplaced onto basinal rocks of the North Slope basin are consistent with a model involving partial melting of pre- subterrane during the Early−Middle Devonian (Johnson et al., viously metasomatized lithospheric mantle during episodic exten- 2016, this volume). Regardless of the precise source of juvenile sion of continental crust (Goodfellow et al., 1995). Recent U-Pb detritus to the Ordovician−Devonian Clarence River Group, the dating of the Old Cabin Formation in the Selwyn basin indicates sedimentary geochemical data presented herein reveal an early a late Cambrian age (~500 Ma) for these volcanic rocks (Mac- Paleozoic history of arc exhumation proximal to the North Slope Naughton et al., 2016). Although the volcanic rocks of the Whale subterrane that predates metamorphism and magmatism related Mountain allochthon are broadly coeval, they are geochemically to the Early−Middle Devonian Romanzof orogeny (Lane, 2007; distinct and more consistent with asthenospheric melts (Moore, Johnson et al., 2016). 1987; Goodfellow et al., 1995; Johnson et al., this volume). Sparse Sm-Nd isotopic data from basinal rocks of the Yukon Implications for the Origin of the North Slope Subterrane block indicate juvenile input into the Selwyn basin as early as middle Cambrian, which is attributed mainly to contribution Pre-Mississippian basinal rocks of the North Slope subter- from local extensional volcanism and/or the weathering of proxi- rane have been previously correlated to deep-marine strata of mal volcanic rocks of the Neoproterozoic Franklin large igneous the northwestern margin of Laurentia based on age, broad lith- province (Garzione et al., 1997; Holmden et al., 2013). Because ological comparisons, and the presence of the ichnofossil Old- this juvenile signature appears by the Cambrian, it predates

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initiation of any evident orogenesis in northern Laurentia (Garzi- and evolved sources to orogenic-derived and juvenile sources one et al., 1997). Sedimentary geochemical data from the Selwyn (Fig. 5; Patchett et al., 1999). In contrast, the major depocenters basin indicates that this basin was at times restricted; there also are of northwestern Laurentia were experiencing passive margin or both sedimentary-exhalative Ba-Pb-Zn deposits within the basin localized rift-related sedimentation at this time. Thus, the new and enriched levels of volcanic-related trace elements in parts of geochemical constraints from the North Slope basinal succession the Road River Group (Goodfellow and Jonasson, 1984; Good- reported herein are consistent with paleogeographic proximity, in fellow et al., 1995; Norford, 1996; Goodfellow, 2007). Because the early Paleozoic, to Ellesmere Island and the northern extent of the high REE contents of the potassic volcanic rocks within of the Appalachian-Caledonian orogenic belt (Fig. 1A). This the Selwyn basin, only 10−20 vol % of volcanic material mixed early Paleozoic paleogeographic restoration for the North Slope with Canadian Shield sources could create the observed juvenile subterrane requires a major sinistral strike-slip boundary along ε Nd signatures observed in the early Paleozoic strata (Garzione et the Arctic margin of Laurentia during the Paleozoic or Mesozoic ε al., 1997). Despite the presence of these older juvenile Nd values in order to explain its modern juxtaposition against parautochtho- in the basins of the Yukon block, there was no infl ux of orogenic- nous northwestern Laurentia. derived juvenile material until deposition of the northerly derived Imperial Formation in the Late Devonian (Boghossian et al., CONCLUSIONS 1996; Garzione et al., 1997; Beranek et al., 2010; Lemieux et al., 2011), coinciding with signifi cant arc magmatism in the Yukon- Sedimentary geochemical data presented herein charac- Tanana terrane (e.g., Pecha et al., 2016). From Late Devonian terize the pre-Mississippian provenance of basinal strata in the to Early Mississippian time, the northerly derived Ellesmerian North Slope subterrane of Arctic Alaska, recording sedimenta- clastic wedge, including strata of the Earn Group and coeval tion in roughly four different tectonic settings. Siliciclastic mate- Besa River assemblages, was deposited throughout the northern rial in the late Neoproterozoic−Cambrian Firth River Group Cordillera and dominated clastic sediment supply in the region and Neruokpuk Formation was derived from recycled cratonic (Gordey et al., 1991). sources, consistent with deposition in a passive margin setting. In contrast, in the Canadian Arctic Islands, Sm-Nd isotopic The siliciclastic strata of the Whale Mountain allochthon were data from the Hazen Formation in the Franklinian basin on Elles- initially dominated by local mafi c volcanic sources, but during mere Island indicate arrival of juvenile orogenic-derived material deposition of the overlying Romanzof formation, the relatively by the Late Ordovician (Fig. 5; Patchett et al., 1999). Cambrian starved deep-water basin received increased continental input. ε through Lower Ordovician samples have a very evolved Nd signa- Sediment deposited in the Upper Ordovician−Lower Devonian ture dominated by Canadian Shield sources; subsequently, there Clarence River Group was derived from a mixture of sources that is a prominent Late Ordovician transition to a signifi cantly more included both evolved continental and juvenile undifferentiated ε juvenile Nd signature, which is attributed to sediment infl ux from components, consistent with a provenance generated during the collisional arc-continent tectonism associated with closure of the obduction and erosion of a volcanic arc. The timing of this major Iapetus Ocean in the northern extent of the early Paleozoic Appa- change in provenance, together with fundamental differences lachian-Caledonian orogenic belt (Fig. 5; Patchett et al., 1999). from coeval basinal rocks of the Yukon block, suggests a tectonic ε This shift in Nd values in the Franklinian basin was accompanied origin for the North Slope subterrane in northeastern Laurentia by the delivery of thick turbidites of the Silurian−Devonian Dan- with potential paleogeographic ties to Ellesmere Island, Pearya, ish River Formation, with petrological, paleocurrent, and detrital and the northernmost extent of the Appalachian-Caledonian oro- zircon data also supporting a source region in the northern part gen in Laurentia. of the Appalachian-Caledonian orogen in northeastern Laurentia (Trettin et al., 1991; Trettin, 1998; Anfi nson et al., 2012; Hadlari ACKNOWLEDGMENTS et al., 2014; Beranek et al., 2015). A direct comparison of Sm-Nd isotopic data from the North We thank the Yukon Geological Survey (YGS) and the Bunde- Slope subterrane of Arctic Alaska to data from the Franklinian sanstalt für Geowissenschaften und Rohstoffe (BGR), par- basin of Ellesmere Island shows a discrepancy because the sam- ticularly Dr. Karsten Piepjohn, for supporting our fi eld work ples from the Whale Mountain allochthon and Ekaluakat forma- in northern Yukon during the CASE 15 Program. Nelson was tion exhibit very juvenile Cambrian signatures (Fig. 5). However, supported by a Herchel Smith-Harvard undergraduate science the allochthon model of Johnson et al. (2016) predicts that these research fellowship and the Department of Earth and Planetary rocks were deposited outboard of the Laurentian margin at this Sciences at Harvard University. Strauss was supported by a time and hence were unrelated to the passive margin deposits of National Science Foundation (NSF) graduate research fellow- the North Slope subterrane. Critically, Upper Ordovician−Lower ship, a Geological Society of America (GSA) graduate student ε Devonian strata of the Clarence River Group have a similar Nd research grant, and NSF Tectonics grant EAR-1624131. Crock- signature to those of coeval Caledonian-derived strata of the ford was supported by the NSERC CREATE CATP program. Hazen and Danish River formations on Ellesmere Island, indi- Field work was funded in part by NSF EAR-1049368 (McClel- cating an approximately synchronous shift from craton-derived land) and EAR-1049463 (Macdonald), as well as by the YGS.

Samarium-neodymium isotopes were measured at Geotop Boghossian, N.D., Patchett, P.J., Ross, G.M., and Gehrels, G.E., 1996, Nd iso- laboratories at Université du Québec à Montréal, and we thank topes and the source of sediments in the miogeocline of the Canadian Cordillera: The Journal of Geology, v. 104, no. 3, p. 259–277, https://doi André Poirier for assistance. We thank the Aklavik Hunters .org/10.1086/629824. and Trappers Committee, the Inuvialuit Game Council, and the Botsford, J., 1988, Stratigraphy and sedimentology of Cambro–Ordovician Wildlife Management Advisory Council for the North Slope deep water sediments, Bay of Islands, western Newfoundland [Ph. D. the- sis]: St. John’s, Memorial University of Newfoundland, 473 p. for their support of the CASE 15 Program. Sample collection Brookins, D.G., 1983, Eh-pH diagrams for the rare earth elements at 25°C and within Ivavvik National Park was done under Parks Canada one bar pressure: Geochemical Journal, v. 17, no. 5, p. 223–229, https:// Research and Collection Permit #IVV-2013-13733. We thank doi.org/10.2343/geochemj.17.223. Cecile, M., 1988, Corridor traverse through Barn Mountains, northernmost Canadian Helicopters, Aklak Air, Wright Air, and Kirk Sweetsir Yukon: Geological Survey of Canada, Current Research, Part D, Paper for providing safe transportation to fi eld localities. We thank 88-1D, p. 99–103. Luke Beranek and John Slack for thoughtful and constructive Cecile, M.P., and Lane, L.S., 1991, Geology of the Barn uplift, northern Yukon: Geological Survey of Canada, Open File Map 2342, scale 1:50,000. feedback that improved this manuscript. This is Yukon Geologi- Cecile, M.P., Lane, L.S., Khudoley, A.K., and Kos’ko, M.K., 1999, Lower cal Survey contribution #030. Paleozoic rocks around today’s Arctic Ocean: Two ancestral continents and associated plates; Alaskan rotation unnecessary and unlikely: Polar- forschung, v. 69, p. 235–241. 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