Detrital Zircon U-Pb Geochronology of Mesozoic Sandstones from the Lower Yana River, Northern Russia

Home , Adycha, Baikalia, Verkhoyansk, Verkhoyansk Range, Yana (river)

Detrital zircon U-Pb geochronology of Mesozoic sandstones from the Lower Yana River, northern Russia

D.B. Harris1,*, J. Toro1,*, and A.V. Prokopiev2,* 1DEPARTMENT OF GEOLOGY AND GEOGRAPHY, WEST VIRGINIA UNIVERSITY, MORGANTOWN, WEST VIRGINIA 26506-6300, USA 2DIAMOND AND PRECIOUS METAL GEOLOGY INSTITUTE, SIBERIAN BRANCH OF THE RUSSIAN ACADEMY OF SCIENCES, YAKUTSK, RUSSIAN FEDERATION

ABSTRACT

The formation of the Amerasian Basin of the modern Arctic remains enigmatic in terms of both timing and method of formation. Most models used to describe its formation involve movement of the Arctic Alaska-Chukotka microplate across the basin’s current location. Detrital zircon U-Pb geochronology has been shown to be an inexpensive yet powerful method by which the tectonic correlation and proximity between multiple terranes over geologic time can be approximated. Five detrital zircon samples were collected from Late Jurassic sandstones from the Lower Yana River area and compared to previous results from detrital zircons collected from nearby Triassic strata. Jurassic samples had detrital zircon age populations of 147–210 Ma, 223–396 Ma, 1639–2183 Ma, and 2281–3116 Ma. Comparison of all detrital zircon ages from the Lower Yana River to those dated from Triassic and Jurassic sandstones of Chukotka, the Verkhoyansk fold-and-thrust belt, and the In’yali-Debin synclinorium supports the interpretation that Chukotka was separated from the Kular area during the Triassic. Jurassic detrital zircon age populations suggest that the Anyui Ocean had closed by the Tithonian, bringing Chukotka to a location where it could be fed by similar depositional systems as the Verkhoyansk fold-and-thrust belt and the Lower Yana River area. Sedimentological and detrital data presented here also suggest that the Yana fault does not represent a regional suture between the Kolyma-Omolon superterrane and the Siberian craton.

LITHOSPHERE; v. 5; no. 1; p. 98–108; GSA Data Repository Item 2012336 | Published online 26 October 2012 doi: 10.1130/L250.1

INTRODUCTION sedimentary provenance and for tectonic recon- vidual zircon grain dating has gone down, along structions when source regions can be identifi ed with a concomitant rise in accuracy, speed, and The tectonic history responsible for forma- (Andersen, 2005; Carrapa, 2010). Studies of ease of analysis. tion of the major basins of the Arctic has long modern river systems have shown that along a The Lower Yana River area, describing the been a topic of debate despite an increasing body river transect, input of zircons from downstream general area east of the Kular Dome surrounding of research. These efforts typically focus on the sources can overprint upstream sources, despite the Yana fault and lower Yana River, was selected Amerasian Basin and its internal Canada Basin higher erosive rates in the headwaters (Cawood for this study because it is located between the (see review in Lawver and Scotese, 1990) since et al., 2003). Though headwater zircon preser- Verkhoyansk fold-and-thrust belt and the Arctic the Eurasian Basin, located more proximal to the vation may diminish downstream compared Alaska-Chukotka microplate, two areas that are Barents Shelf, is younger and has a more easily to more proximal sources, these signatures are well studied and have abundant detrital zircon interpreted tectonic history (Fig. 1A). Seafl oor present nonetheless and require long-distance U-Pb data for the Mesozoic. Several studies by spreading models utilize multiple interpretations transport. Results from a study of detrital zir- Miller et al. (2006, 2008, 2010) have already of the movement and function of prominent fea- cons from sedimentary rocks in the Verkhoyansk compared detrital zircon geochronologic results tures in and around the Amerasian Basin, includ- Range of Siberia require transport of zircons for from several areas surrounding the Amerasian ing the Lomonosov Ridge, the Alpha and Men- thousands of kilometers as well as persistence of Basin. Our data will serve as a supplement to the deleev Ridges, the Chukchi Cap, the Northwind the river responsible for deposition for up to 200 ongoing formation of a comprehensive Meso- Ridge, and the Arctic Alaska-Chukotka micro- m.y. (Prokopiev et al., 2008). A similar study of zoic detrital zircon data set (i.e., Miller et al., plate (Fig. 1A). The Arctic Alaska-Chukotka marine and fl uvial sandstones collected in the 2012), and will add insight from Jurassic sam- microplate includes the North Slope and Seward Colorado Plateau of the U.S. Cordillera sug- ples to the Mesozoic tectonic setting of northern Peninsula of Alaska, as well as Chukotka, the gests transport of detrital zircons from source Siberia and the Arctic. For brevity, the Lower New Siberian Islands, Wrangel Island, and the regions in eastern and central Laurentia at times Yana River area will be referred to as the Kular East Siberian Shelf of northeast Russia. Because as far away as the Appalachian orogen along a area, as it only includes data collected along the of access diffi culties to the Arctic basins, most transcontinental river system with headwaters Yana River east of the Kular Dome. studies are limited to research of the landmasses in the southern Appalachian Mountains (Dick- surrounding the Amerasian Basin. More spe- inson and Gehrels, 2009). These studies provide GEOLOGICAL FRAMEWORK cifi cally, detrital zircon geochronology has been strong support that long-distance transport of shown to be a powerful tool for determining detrital zircons is possible under the right cir- Arctic Tectonics cumstances. With the advent of laser-ablation– *E-mails: [email protected]; [email protected]; multicollector inductively coupled plasma–mass Similarities of stratigraphic records, mag- [email protected]. spectroscopy (LA-MC-ICP-MS), the cost of indi- netic anomalies, basin correlations, and seismic

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s Chukotka k u 8 in this study with the Kular fi eld area marked as location 2. Fig- th 5 Alaska A 160° ure modifi ed from Miller et al. (2006). (B) Simplifi ed version of ny NE Russia ui Z SP the rotational model for opening of the Canada Basin (Embry, on W 60°E e 1 1990; Embry and Dixon, 1994; Grantz and May, 1983; Grantz et 1: Verkhoyansk 8: Lisburne Hills al., 1979; Lawver et al., 2002). In both fi gures, the dashed outline 1000 km 2: Kular Dome 9: Sadlerochit Mts. represents the approximate boundary of the Arctic Alaska-Chu- kotka microplate, and background bathymetry image is from 3: In’Yali Debin 10: Sverdrup Basin AE1 the International Bathymetric Chart of the Arctic Ocean (IBCAO) 4: Stobovoi Island 11: Sverdrup Basin AE2 (Jakobsson et al., 2008). Abbreviations are: AAC—Arctic Alaska- 5: South Anyui Zone 12: Novaya Zemlya Chukotka microplate; AR—Alpha Ridge; CC—Chukchi Cap; LR— 6: Chukotka 13: Taimyr Lomonosov Ridge; MR—Mendeleev Ridge; NR—Northwind 7: Wrangel Island Ridge; NSI—New Siberian Islands; SP—Seward Peninsula.

profi les comparing northern Alaska to the Cana- it is not possible to restore the Arctic Alaska- the Taimyr Peninsula and Ural Mountains, were dian Arctic Islands all support an opening of the Chukotka microplate back to this prerift posi- deposited and severed Baltican sedimentation Canada Basin involving counterclockwise rotation if it is treated as a rigid, coherent block, from the rest of the Arctic Alaska-Chukotka tion of the Alaskan portion of the Arctic Alaska- due to large overlap of prerift landmasses and microplate. Miller et al. (2006) also used linear Chukotka microplate away from an original signifi cant space problems during continental arrays of normal faults from bathymetric data to position along the Canadian Arctic Islands, with drift (Miller et al., 2006). Using detrital zircon support later formation of the Makarov Basin proposed rifting ages from the Early Jurassic to geochronologic data, Miller et al. (2006, 2008, involving rift formation parallel to the Lomono- the Early Cretaceous (Embry, 1990; Embry and 2010) suggested that the Arctic Alaska-Chu- sov Ridge and orthogonal to the Canadian Arc- Dixon, 1994; Grantz and May, 1983; Grantz kotka microplate must have been a unifi ed frag- tic Islands, consistent with previous studies et al., 1979; Lawver et al., 2002) (Fig. 1B). ment in the late Paleozoic and that Chukotka (i.e., Sweeney et al., 1982; Taylor et al., 1981; While there is an abundance of support for the was instead located closer to the Barents Shelf Vogt et al., 1982). Under this reconstruction, pre–Canada Basin location of northern Alaska and Ural Mountains prior to formation of the Pacifi c-directed move-out of subduction zones adjacent to the Canadian Arctic Islands, there is Amerasian Basin, according to similarities in found along northern Eurasia was associated less well-documented evidence for the original detrital zircon ages from Upper Paleozoic strata with rifting parallel to the Barents Shelf, result- location of Chukotka. According to the rota- collected from Wrangel Island, the Lisburne ing in formation of the Amerasian Basin during tional model, Chukotka and the Siberian Shelf Peninsula, and the Seward Peninsula of Alaska. the Cretaceous (Miller et al., 2010). This rifting were attached to the North Slope of Alaska A model presented by Miller et al. (2006) and event was also correlated with as much as 100% akin to their current geometry and experienced later expanded upon in Miller et al. (2008, 2010, extension of the Siberian Shelf in an east-west a similar rotational movement away from an 2011) shows an updated pre–Amerasian Basin direction and movement of Chukotka along a original location along the northern Canadian location for the various pieces of the Arctic transform boundary represented by the modern Arctic Islands near Greenland with strike-slip Alaska-Chukotka microplate, where Chukotka South Anyui zone (Miller et al., 2006, 2008). or transform motion along the Lomonosov and Wrangel Island were located more proxi- A prerift location of Chukotka closer to the Ridge during the Mesozoic (i.e., Embry, 1990; mal to Baltica and east of the Uralides during Taimyr region also ties in with another recon- Lawver and Scotese, 1990; Grantz et al., 1979). sedimentation prior to rifting. Permian–Triassic struction by Kuzmichev (2009) involving rota- However, under current interpretations regard- rifting provided the basin in which sediments tion of Chukotka and Arctic Alaska about two ing the Mesozoic location of Arctic landmasses, of Chukotka and Wrangel Island, derived from separate poles, where Chukotka experienced

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clockwise rotation away from the Lomonosov (103 Ma) biotite granite plutons (Layer et al., 2007; Konstantinovsky, 2007; Oxman, 2003; Ridge margin concurrently with counterclock- 2001) that crop out in multiple exposures along Parfenov, 1991) (Figs. 2 and 3). The Adycha- wise rotation of the North Slope of Alaska away a northeast-southwest trend. Within our fi eld Taryn thrust fault, located west of the Kular- from the Canadian Arctic Islands, though retain- area, the unit surrounding the Kular pluton is a Nera slate belt (Fig. 2), is more commonly inter- ing their connection near the modern Chukchi biotite- and muscovite-rich andalusite-bearing preted to represent the regional suture between Sea. The specifi c movement pathway of the metapelite, which displays top-down shear the Siberian craton and the Kolyma-Omolon various pieces of the Arctic move in this model away from the pluton, involving gently plung- superterrane, though the Chai-Yuryue-Indigirka by way of an opening parallelogram in order to ing stretched andalusites and mantled porphy- reverse fault system, located directly east of the overcome various geometrical problems such roblasts, suggestive of extensional emplacement Kular-Nera slate belt, has also been interpreted as the modern acute angle between Chukotka conditions during intrusion of the pluton. These as a suture. The Jurassic sediments southeast and western Alaska and the rectangular shape of metapelites were likely formed under local of the Yana fault are openly folded along axes the Makarov Basin (Kuzmichev, 2009). Under moderate-temperature, low-pressure conditions striking approximately east-west and are cut this model, the South Anyui suture zone turns associated with intrusion of the Kular pluton, by several southward-vergent thrust faults with south via the “Chroma Loop” to connect with as suggested by prevalence of andalusites. The minor displacement. the Kolyma Loop on the outer border of the next units outward from the pluton are Trias- Kolyma-Omolon superterrane, which is thought sic sandstones with shale interbeds that display Stratigraphy to have collided with the Siberian platform in open folds along axes paralleling the long direc- the Late Jurassic, rather than turning north tion of the Kular granite (Figs. 2 and 3). Trias- Geologic maps of northeastern Russia place toward the Anjou Islands, as is more commonly sic sandstone units are separated from Jurassic the Kular Dome and Triassic sequences of the suspected (e.g., Spektor et al., 1981; Parfenov sandstone units in the Kular area by the Yana Kular area within the Kular-Nera slate belt, et al., 1993, and references within; Kuzmichev, fault, which has traditionally been interpreted as which has traditionally been described as an 2009), or continuing west toward the Taimyr either a local reverse fault within the Kolyma- ~900–1200 km long belt of Late Permian, Tri- Peninsula (Sokolov et al., 2002). Omolon superterrane, a branch of the Adycha- assic, and Early Jurassic black shale and tur- While the specifi cs of movement for the Taryn suture fault, or a part of the Chai-Yuryue- bidite deposits, which extend from the Laptev various pieces of the modern Arctic are con- Indigirka suture fault (Khudoley and Prokopiev, Sea in the northwest to the Sea of Okhotsk in troversial, conclusions from Miller et al. (2006, 2008, 2010, 2011) regarding the close proximity between Chukotka and the Taimyr Peninsula 132° E 134° E 136° E 138° E or Uralian sources prior to the Triassic have 72° N Ust’ Yana Graben K particular merit because this geometry allevi- Laptev Sea Kular pluton ates the problem of overlap between the Arctic Alaska-Chukotka microplate and Greenland

created by closing the Amerasian Basin using C Cenozoic deposits the rotational model. The Chukotka part of the Arctic Alaska-Chukotka microplate is assumed VFB Verkhoyansk Fold-Thrust Belt to have reached its fi nal position during the Late 71° N C Cretaceous along the northern Kolyma-Omolon KN Kular-Nera belt superterrane, which deformed passive-margin Yana River sequences along the eastern edge of the Siberian PS Polousnyi Synclinorium craton to form the Verkhoyansk fold-and-thrust Yana fault belt in the Late Jurassic (Fig. 1). The South Anyui zone represents a suture between Chu- Thrust fault kotka and northern Russia, though the specifi cs 70° N of this suture are still a topic of much debate. K While the main body location of the suture is Normal fault generally agreed upon, the location of the suture around and west of the New Siberian Islands is KN very much in question (see review in Kuzmi- PS Adycha-Taryn Fault chev, 2009). 69° N ? Kular Dome Chai-Yuryue-Indigirka Fault The Kular Dome is located at ~70.0°N, ? Anticlinal fold axis 134.3°E, ~135 km south of the Laptev Sea and VFB ~30 km west of the Lower Yana River and Ust’ Kuyga, Siberia (Fig. 2). In this area, granites of 50 km the Kular pluton intrude Paleozoic metasedi- 68° N ments and Mesozoic sandstones of the Kular- Figure 2. Generalized tectonic and terrane map of the Kular area, modifi ed from Specktor Nera slate belt (Parfenov, 1991) (Fig. 3). The (1995), Konstantinovsky (2007), and Oxman (2003). See Figure 1 for location. The central Kular Range contains multiple Early Cretaceous boxed area indicates the location of Figure 3.

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J 3km T3 (Late Triassic), J3ox (Oxfordian), J3km (Kim- 134°30'E 134°45'E 135°E 135°15'E 135°30'E 135°45'E meridgian), and J3t (Tithonian) (Oleshko, 1981). A t Q Quaternary cover Q ul All observed Triassic units were lithologically Q fa X l Cretaceous granite Meta a J Ust’-Kuyga m 3t similar, despite age differences, though different r Jurassic sandstone Kgr T o 2a n Q 70°N from Jurassic units, which were also generally a Triassic sandstone 50 10 n 10 15 a identical in terms of lithology. Eight thin sec- 75 08DH33 Y T3 Late Paleozoic Kgr 7 30 25 tions were prepared using two samples from 45 metasediments 19 20 50 J3ox 6 26 Detrital zircon T2l and six from J3ox, though several outcrops 20 K Yana River J3km 60 y 30 sample location were studied in the fi eld from all mappable 8 u 30 12 c h J3t 24 u 60 20 Thrust fault units. Unfortunately, in-place sedimentary out- s 45 J 25 R 15 3ox i J 35 crop was diffi cult to fi nd away from the Yana v T2l 3km 10 45 e 20 Normal fault r 08DH30 J3km River, so most data collection and observation 35 25 J3ox Stretching 40 30 24 10 30 40 occurred along a transect of this river from Ust’ Q lineation 45 08DH01 J X‘ Kuyga to the Kyuchus mining operation near the 69° 3km 20 7 45'N 45 30 52 30 Bedding S confl uence with the Kyuchus tributary (Fig. 3). 08DH3235 T 0 60 J 30 3 30 08DH29 J 2a 20 3ox Due to the similarities in lithology between all Q 08DH03 15 Foliation S 40 08DH02 J 1 Triassic units and all Jurassic units, for descrip- T2l 3km 30 N Foliation S2 tive purposes, all mapped units will be referred 03 6 12 18 24 30 30 to as either Triassic or Jurassic sandstones. Kilometers Triassic sandstones found west of the Yana X X′ fault have 20%–25% lithics, mostly meta- B J3ox morphic fragments and minor chert, 35%–40% 2 S foliation S foliation J J3t J J2a 2 1 3km 3km J3ox quartz, mostly monocrystalline with few poly- 0 K T2l J3ox T2a crystalline grains, 20%–25% feldspars, 2%–15% -2 Meta1 T3 (km) -4 opaque iron-oxide material, likely diagenetic Elevation T2l hematite, and occasional (<1%) calcite rhombs. -6 ? P T2a P Total biotite with minor associated muscovite Figure 3. (A) Kular fi eld area and location of detrital zircon samples collected for U-Pb geo- may locally comprise as much as 10% of sample chronology analysis in this study. (B) Cross section is drawn along profi le X-X′ seen in A. volume, though it is in general much less com-

Unit abbreviations indicate age: Meta1—Paleozoic metasediments; P—Paleozoic sediments; mon. All grains are generally medium sized and

T2a—Anisian; T2l—Ladinian; T3—Late Triassic; J2a—Aalenian; J3ox—Oxfordian; J3km—Kimmer- angular with poorly defi ned grain boundaries. idgian; J t—Tithonian; K —Cretaceous granite. Geology is from Oleshko (1981) and this study. 3 gr Laminated black shales and red-colored mudstone interbeds, generally <1 mm thick, are also common and often show thin, soft-sediment, the southeast (Konstantinovsky, 2007; Oxman, and Prokopiev, 2007) (Fig. 2). Despite original fl uid-supported slump folds with wavelengths 2003; Parfenov, 1991). Konstantinovsky (2007) placement of the Kular area within the Kular- of 1 m or less, and occasional cross-beds, rip- described the Kular-Nera belt as the north- Nera slate belt, sedimentary rocks found in the up clasts of partially lithifi ed mud, and burrows. western segment of a larger terrane extending Kular area are Middle to Late Triassic sand- Ripple marks are also exposed, which, together for over 1500 km from northwest to southeast stones and Middle to Late Jurassic sandstones with structures described previously, are in called the Kular-Ayan-Yuryakh terrane. Tur- with lithologies, sedimentary structures, and agreement with deposition in a delta or prodelta bidite sequences of the Kular-Nera belt are faunal assemblages more suggestive of depo- environment just offshore and are inconsistent thought to have been deposited as continental sition within a delta or prodelta system more with deposition in a continental slope environ- rise and marginal sea deep-water fan deposits, proximal to the Siberian craton than rocks tra- ment commonly invoked for deposition of the which formed after middle to late Paleozoic ditionally described as Kular-Nera slate belt Kular-Nera slate belt. Well-preserved ammonites rifting on thinned continental or oceanic crust assemblages. are also found within Triassic rocks of the Kular of the Oimyakon sedimentary basin (Oxman, In the Kular area, the relevant stratigraphy area, which further preclude deposition within a 2003; Parfenov, 1991). Unconformably above for this geochronologic study includes Triassic turbidite fl ow like those described for the Kular- the Kular-Nera belt, and located directly to the sandstone sequences of the Kular-Nera slate belt Nera belt. Three Triassic units have been mapped east in the south (Fig. 1A), there are the low- west of the Yana fault and open folds of Jurassic in our fi eld area previously based on their pale-

est units of the In’yali-Debin terrane, which are mud-rich sandstones within the Polousnyy syn- ontological ages, T2a, T2l, and T3, with thick- composed of Middle to Late Jurassic siltstone, clinorium east of the Yana fault (Fig. 3). Russian ness variations from 1.5 to 2.5 km (Oleshko, mudstone, sandstone, and olistostrome deposits geologic maps further separate these units by age 1981; Spektor, 1995). These units generally dip (Oxman, 2003). The Polousnyy synclinorium is as determined by paleontology (Oleshko, 1981; gently to the southeast but are sometimes verti- directly east of the Kular-Nera belt in the north Spektor, 1995). These ages are in agreement cal (Fig. 4A) and also commonly display near- (Fig. 2) and is composed of Early–Late Juras- with maximum depositional ages suggested by vertical to vertical pencil cleavage related to sic synorogenic silty-sandy turbidite deposits the detrital zircon data described by Miller et al. formation of the Verkhoyansk fold-and-thrust (Gusev, 1979; Oxman, 2003; Konstantinovsky, (2012) and this text, though generally younger, belt during the Late Jurassic. A ternary plot 2007). To the west, the Kular-Nera slate belt is and were therefore adopted in our updated maps of monocrystalline quartz, feldspar, and total separated from the Verkhoyansk fold-and-thrust for the area. Russian maps name the units based lithic content (QmFLt) based on multiple 300

belt by the Adycha-Taryn fault zone (Khudoley on their ages as T2a (Anisian), T2l (Ladinian), point-count analyses of thin sections of Triassic

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Qm ing approximately east-west within northward- A vergent imbricated thrust packages east of the Yana fault (Fig. 3). Unit thicknesses range from 0.6 to 1.3 km (Oleshko, 1981). A QmFLt plot based on multiple 300 point-count analyses of RO thin sections suggests that a continental source m is most likely for Jurassic samples (Dickinson et al., 1983) (Fig. 5), though different from Triassic sedimentation due to prevalence of volcaniclas- MA tic grains in Jurassic samples. CB B F Lt GEOCHRONOLOGY Figure 5. Ternary plots based on multiple 300 point counts from thin-section samples, plot- Geochronologic analysis of detrital zircons ted in fi elds defi ned by Dickinson et al. (1983), was performed on seven samples (two Triassic, showing Triassic data as triangles and Jurassic fi ve Jurassic) collected along the Yana River data as circles. Abbreviations for the ternary diagrams are: Qm—monocrystalline quartz; south of Ust’ Kuyga (Fig. 3) using LA-MC- F—feldspar; Lt—total lithics. Provenance fi eld ICP-MS at the University of Arizona Laser- abbreviations are: CB—continental block; MA— Chron Center. Samples were crushed and sepa- magmatic arc; RO—recycled orogen; m—mixed. rated using standard gravimetric and magnetic Sample locations are given in Figure 3A. separation techniques at West Virginia Univer- sity. Following separation, grain mounts were created and polished at the LaserChron Cen- ter and were imaged using refl ected light and Figure 4. (A) Vertical bedding in Triassic sandstones west of the Yana River. Two separate cathodoluminescence (CL). No fewer than 100 shear bands can be seen cutting the strata. grains per sample were randomly ablated using View to the north. Cleavage at this location is a 35-µm-diameter laser. For every fi ve sample 082/50S. (B) Flute casts commonly seen along grains ablated, one standard grain (also added the bottom bedding surface of Jurassic strata to each mount) was targeted. For this study, along the Yana River. Orientations of the casts standard R33 was used, which yields an isotope suggest an approximate paleocurrent direction toward 163° upon bed restoration. dilution–thermal ionization mass spectrom- etry (ID-TIMS) age of 419.3 ± 0.4 Ma (Black et al., 2004). Individual zircon grain ages were determined using 238U/206Pb ratios for grains samples yields a magmatic arc as the most likely younger than 1.4 Ga and 207Pb/206Pb ratios for provenance, according to diagrams developed by Figure 6. Photomicrograph of volcaniclastic grain grains older than 1.4 Ga, due to higher preci- Dickinson et al. (1983) (Fig. 5), though the lack (outlined in yellow) characteristic of those seen sion within these respective ranges (Gehrels and in samples collected from Jurassic units of the of volcaniclastic grains in Triassic samples sug- Kular area. Imaged under cross-polarized light. Pullen, 2010). Analyses with greater than 30% gests that a mixed source may more accurately discordance or greater than 5% reverse discor- describe the source for Triassic rocks. dance between 238U/206Pb and 207Pb/206Pb ages Jurassic units east of the Yana fault are fi ne to were discarded. Of the grains ablated, 87% had coarse grained and have a high amount of muddy those found in Triassic units were also common a U/Th ratio less than 3, indicating a magmatic matrix. Grains are angular and poorly sorted, along both the top and bottom of beds in Juras- source (Hoskin and Black, 2000). For more with sizes ranging from <30 µm to 0.5 mm. sic units. Reverse grading was visible in multiple detailed information on the analytical process, Samples are composed of 20%–35% matrix, locations, along with prevalent slump folding see review of operating procedure in Gehrels 5%–10% lithic fragments with subequal propor- and abundant 1–2-m-thick conglomerate lenses, and Pullen (2010) and Gehrels et al. (2006). tions of volcaniclastic grains and chert, 20%– suggesting the likelihood of rapid subaqueous Results from geochronologic analysis of the 30% quartz, mostly monocrystalline, 30%–35% fan deposition potentially within a prodelta envi- Kular samples are listed in Appendix 1 of the feldspars, and minor amounts of white mica, bio- ronment, with preservation of wood and faunal GSA Data Repository1 and are shown in prob- tite, and diagenetic hematite. Volcaniclastic lithic assemblages within the delta plain segment of ability density plots in Figure 7. Detrital zircon fragments are basaltic or andesitic and show an overall prograding delta system. Impressive data from the Kular area are plotted in Figure 8 characteristic plagioclase-rich matrix (Fig. 6). fl ute casts several centimeters in thickness were along with data compiled from previous stud- Bedding of Jurassic units is massive, with beds also commonly visible on the underside of tilted ies in areas surrounding the Amerasian Basin 5–6 m thick, showing abundant laminated layers, suggestive of a paleocurrent toward the organic-rich black shale interbeds and occa- SE upon restoration of bedding (Fig. 4B). Four 1GSA Data Repository item 2012336, which includes sional conglomerate lenses up to 2 m in diam- previously mapped units were adopted for this Appendices 1 (full detrital results from the Lower eter containing aligned, rounded lithic clasts. study based on previously published paleonto- Yana River area) and 2 (compiled detrital age ranges from various publications), is available online at www Wood fragments were also noticed in some sec- logical ages and new detrital zircon ages from .geosociety.org/pubs/ft2012.htm, or on request from tions, supporting a depositional location near the J3ox, J3km, and J3t occurring within our fi eld [email protected] or Documents Secretary, continent. Flat, rounded rip-up clasts similar to area. These units are exposed as open folds strik- GSA, P.O. Box 9140, Boulder, Colorado 80301, USA.

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assic data from the Kular area show peak ages at 08DH01 n = 68 242, 301, 370, 501, 789, and 1851 Ma, with age 239 Ma ranges of 224–337, 341–387, 413–568, 738– 825, and 1759–2011 Ma (Miller et al., 2012). 08DH33 Combined Jurassic data show peak ages at 167, n = 85 203, 255, 269, 287, 321, 339, 1921, 2544, and 2739 Ma, with age ranges of 147–210, 223–396,

Triassic samples Triassic 244 Ma 1639–2183, and 2281–3116 Ma. Age ranges common to both Triassic and Jurassic Kular 08DH02 samples occur in the ranges of 223–396 Ma and n = 82 1639–2183 Ma. Jurassic samples differ from 165 Ma Figure 7. Probability den- Triassic samples in that they have young zircon sity plots for Kular data. ages at 147–210 Ma that are absent from Trias- Ages listed for each sam- sic samples due to their younger age of deposi- ple are inferred to be the 08DH03 tion, but they also display differences in older maximum possible deposi- populations of zircons that cannot be explained n = 64 tional age for each unit and by timing of deposition alone (Fig. 7). All Juras- 171 Ma are based on overlap of at least three youngest ages sic samples show a range of very old zircons of 08DH29 within error as calculated 2200–3100 Ma that is not evident in the Trias- n = 91 by AGEPICK (Gehrels and sic samples. Jurassic samples are also missing a 167 Ma Pullen, 2010). Triassic data Late Proterozoic–early Paleozoic (413–825 Ma) are from Miller et al. (2012). population of zircons that is abundant in the Tri- Jurassic samples Jurassic 08DH30 assic samples. n = 61 159 Ma DISCUSSION

When possible, age ranges and peak ages 08DH32 using complete data sets from all samples n = 73 were calculated with AGEPICK and compiled 178 Ma into sets of representative age ranges for each location (Appendix 2 [see footnote 1]; Fig. 8). 0 200 400 600 800 1000 1500 1700 1900 2100 2300 Most representative age ranges were based on Age (Ma) multiple samples. Detrital zircon populations were compiled from the literature from multiple sources surrounding the Amerasian Basin (Appendix 2 of the GSA Data Repository [see product of random sampling of the same par- and are described in the following sections, footnote 1]). Statistically likely age peaks and ent population. P values of zero imply that any though zircons collected in northern Chukotka ranges (those that display greater than three similarity between the two samples is likely due and along the Dyanyshka River within the overlapping ages within error) for each sample to random chance. P values near the maximum Verkhoyansk fold-and-thrust belt are most rel- were chosen using the Arizona LaserChron value of 1.0 suggest that there is low chance that evant to this discussion (Fig. 1). Center AGEPICK program. AGEPICK uses the similarity is due to random chance alone Zircons from Chukotka’s Triassic 5.5-km- calculated weighted mean ages, mean square of and that the two populations are likely from the thick sequences of distal turbidites (Bychkov, weighted deviates (MSWD), and uncertainty of same “parent,” or in this case magmatic source. 1994) near Bilibino, Russia, were dated by individual grain ages to objectively determine Because the calculated P value among Trias- Miller et al. (2006) and were supplemented peak ages and age ranges for detrital zircon sam- sic samples was 1.000 (Table 1), these samples with Jurassic zircons from nearby massive, ples (Gehrels and Pullen, 2010). For Kular data were combined for subsequent analysis into one well-cemented arkosic sandstones collected analyses, any age errors from the original anal- plot diagnostic of Triassic sandstones (Fig. 8). north of Bilibino to Pevek (Miller et al., 2008). ysis that had a 1σ less than 2% were adjusted For the Jurassic samples, 08DH02, 08DH03, Pennsylvanian–Jurassic detrital zircon samples up to 2% based on reproducibility of standards and 08DH30 were determined to be similar, and diagnostic of Siberian cratonal passive-margin (McClelland, 2011, personal commun.). samples 08DH29 and 08DH32 were determined sequences collected from the central Verkhoy- All samples were compared using Kol- similar (Table 1). The main statistical (P value) ansk fold-and-thrust belt were described in mogorov-Smirnov (K-S) tests using error from difference between individual Jurassic samples greater detail by Prokopiev et al. (2008) and the calculated cumulative distribution function seems to be the contribution of grains older than Miller et al. (2006). Units of the Verkhoyansk (Gehrels and Pullen, 2010; Press et al., 1992). 1.0 Ga (Fig. 7). fold-and-thrust belt are well exposed along the Output values from K-S tests compare the dif- Combined data sets for Kular Triassic Dyanyshka River just east of the Vilyui graben. ference between two distributions as a measure (Miller et al., 2012) and Jurassic detrital zircon Triassic samples from this area were from the of the vertical separation of their cumulative peak ages were compared to similar data sets Tolbon and Khedalichen Formations, which probability plots. The output P value from a K-S for regions surrounding the Amerasian Basin were previously dated as Anisian-Ladinian and test is a measure of the probability that the mea- that potentially shared source areas during their Carnian-Norian based on faunal data (Grad- sured difference between the two samples is the respective periods of deposition. Combined Tri- stein et al., 2004).

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Triassic Detrital Zircon Data

3000 Aldan Shield Results from the Triassic samples of the Kular area (Miller et al., 2012) are in agreement with interpretations by Miller et al. (2006, 2008) that detrital zircon data from Chukotka

Chuk and western Alaska place these areas closer

Stol to the Taimyr Peninsula and the Verkhoyansk SAZ 2500 Aldan Shield fold-and-thrust belt than to the Canadian Arctic during the early Mesozoic. This observation is

Verk based on abundance of detrital zircons in Chu- Kular In’Y kotka likely derived from Uralian sources and a higher degree of similarity of detrital zircon populations between Chukotka and Siberian Siberian craton 2000 areas than between Chukotka and Laurentian areas (Fig. 8). In Triassic samples, Chukotka Verk In’Y Kular

Chuk Central Asian fold belt and western Alaska display a different range of SAZ Lisb

Chuk zircon ages than the Verkhoyansk Range, while Stol AE2 Verk Triassic data from Kular show similarities to AE1 Kular both Chukotka and Verkhoyansk. Speciﬁ cally, both Kular and Chukotka Triassic samples have 1500 225–260 Ma and 730–850 Ma zircons that are Lisb

Age (Ma) Age absent from Verkhoyansk Triassic samples (Fig. Aldan Shield 8). However, both Kular and the Verkhoyansk AE2 AE1 Sad Baltica signatures Range lack 800–1000 Ma and 1000–1315 Ma ca. 900-2000 Ma zircon populations that are present in Triassic Chuk Wran Chukotka samples (Miller et al., 2006). The 1000 presence of Permian–Triassic zircons in Kular and Chukotka is signiﬁ cant since granitic rocks

Taimyr granitoids of this age are uncommon in northern Siberia. Potential source areas for Permian–Triassic zircons are the southern Taimyr Mountain range, where doleritic sills aged 220–230 Ma and 250 Sad Ma A-type granites are common (Walderhaug AE1 500 AE2 Central Asian fold belt et al., 2005; Vernikovsky et al., 2003), and the Alaska and Chukotka widespread Siberian Traps south of Taimyr, Devonian granitoids Angara Vitim Batholith which contain maﬁ c volcanics with mean ages Taimyr Peninsula of ca. 250 Ma (Dalrymple et al., 1995; Reichow Verk et al., 2002; Renne and Basu, 1991). Though Lisb Kular Chuk Wran In’Y Verk

Stol mafi c sources are unlikely to contribute substan- Kular SAZ Chuk 0 tial amounts of detrital zircons to sedimentary WEWE samples, widespread syenite and quartz syenite Triassic sandstones Jurassic sandstones intrusions with mafi c components not exceed- ing 15% total content, as well as lesser quartz Figure 8. Age ranges of detrital zircons collected from locations surrounding the Amerasian Basin. Vertical dark-gray boxes show age ranges compiled from literature and calculated with AGEPICK monzonite, subalkaline granite, alkaline syenite, (Gehrels and Pullen, 2010). Bold outlines emphasize data from the Kular and In’yali-Debin areas and granite are found in the northwestern Tai- described in this study. Data are ordered west to east from left to right with Triassic data on the far myr Peninsula (Vernikovsky et al., 2003). These left and Jurassic data on the far right (locations shown in Fig. 1). Light-gray lines within age ranges intrusions have been dated via U-Pb analysis of show peak ages within their respective populations. Wide light-gray boxes, labeled on the right, zircons and have a likely emplacement age of show potential granitic sources for the detrital zircons displayed. Jurassic Kular and In’yali-Debin 241–249 Ma, i.e., coeval or shortly following (In’Y) data are from this study, with all other data listed in Appendix 2 (see text footnote 1) and compiled from the following sources: Triassic data: Verkhoyansk (Verk) from Prokopiev et al. (2008); Siberian Trap magmatism, and are suggested Kular (Kular) from Miller et al. (2012); Chukotka (Chuk), Wrangel Island (Wran), Lisburne Peninsula to be related to the Permian–Triassic northern (Lisb), Sadlerochit Mountains (Sad), Sverdrup Bain AE1 (AE1) and Sverdrup Basin AE2 (AE2) from Eurasian superplume that generated the Sibe- Miller et al. (2006). Jurassic data: Verkhoyansk (Verk) from Prokopiev et al. (2008); Stolbovoi Island rian Traps (Vernikovsky et al., 2003). Assuming (Stol), Chukotka (Chuk), and South Anyui zone (SAZ) from Miller et al. (2008). Magmatic source a Taimyrian source, zircons of these ages were ages were compiled from Miller et al. (2006, 2008), Scarrow et al. (2002), Prokopiev et al. (2008), likely carried northward along the paleo–Tai- Parfenov and Kuz’min (2001), and references listed in GSA Data Repository Item 2008177. Note that myr River system (Miller et al., 2012) which the magmatic age range of 560–850 Ma described in the body of this document was collected from the Zhdanov granite of the Taimyr Peninsula and is excluded from this fi gure because the lower age supplied clastic material to the northern part of intercept from U-Pb zircon analysis is poorly constrained, showing more concordant ages near 850 the platform (modern coordinates), the Kular Ma (Pease and Vernikovsky, 2000, and references within). area, and to the Polousnyy synclinorium, but

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TABLE 1. KOLMOGOROV-SMIRNOV (K-S) TEST RESULTS FOR ALL SAMPLES FROM THE KULAR AREA WITH AGES YOUNGER THAN 229 Ma REMOVED (AGE OF THE YOUNGEST TRIASSIC ZIRCON) Triassic Jurassic Triassic 08DH01 08DH01 08DH33 08DH33 1.000 08DH02 Jurassic 08DH02 0.006 0.003 08DH03 08DH03 0.106 0.074 0.936 08DH29 08DH29 0.000 0.000 0.001 0.001 08DH30 08DH30 0.005 0.003 0.827 0.939 0.016 08DH32 08DH32 0.000 0.000 0.001 0.017 0.791 0.009 Note: Zircons younger than 229 Ma are not considered because they represent additions based on depositional age. Speciﬁ c P-values discussed in text are emphasized in bold. See Figure 3 for sample locations.

not to the more southern Verkhoyansk region, deposition in the Paleozoic to a Taimyr or Ura- cons of similar ages found in the Verkhoyansk which was fed mostly by the paleo–Lena River lian source in the Late Permian–Triassic (Miller fold-and-thrust belt along the Dyanyshka River, (Prokopiev et al., 2008). Permian–Triassic et al., 2010). The presence of Middle to Late having traveled northward along the paleo–Lena zircons are also absent from the Sadlerochit Proterozoic zircons in Upper Paleozoic samples River system (Prokopiev et al., 2008). Presence Mountains and Sverdrup Basin data (Miller et from Chukotka and Wrangel Island suggests a of volcaniclastic lithic fragments in Jurassic al., 2006) (Fig. 1), despite other similarities to prior connection to intrusions found in Baltica samples is further indication of an arc source Triassic data from the Arctic Alaska-Chukotka that is further supported by deposition in these for these younger zircons, and the low percent- microplate. Perhaps more important for Trias- areas across Upper Paleozoic platformal sedi- age of volcaniclastic fragments is in agreement sic detrital zircon data is the lack of 730–850 ments underlain by Neoproterozoic rocks of the with the low numbers of Middle–Late Jurassic Ma zircons in the Verkhoyansk Range, but their Timanides also associated with Baltica (Bingen zircons in Jurassic samples (average of 2% Main presence in both Kular and Chukotka. In Miller et al., 2008, and references within; Miller et al., belt–aged zircons per sample), supportive of et al. (2006), these zircons are suggested to have 2010). Triassic samples from Kular, Chukotka, diminishing percentages caused by the long dis- also been from the Taimyr region as age ranges and Verkhoyansk all contain zircons in the range tances traveled, overprint of upstream sources by of zircons are within error of samples collected of 1600–2100 Ma, which match basement ages downstream sources (Cawood et al., 2003), and from granitic and metamorphic rocks of the from the Siberian craton. Similarities between inﬂ uence from the incoming Kolyma-Omolon Central Belt of Taimyr (Pease et al., 2001; Pease all three sites (Chukotka, Kular, and Verkhoy- superterrane. The Kular area was situated closer and Vernikovsky, 2000, and references within). ansk) suggest that they shared some sedimen- to the colliding terrane than was the Dyanyshka Another potential source for zircons of this age tation sources during the Triassic, though Chu- River (Verkhoyansk in Fig. 1A), which remained is the Baikalia region (Transbaikalia and Prebai- kotka and to a lesser extent, the Kular region more insulated from the effects of collision with kalia) to the south, which is known to have gra- seem to have been fed by more varied sources, the Kolyma-Omolon superterrane in the Juras- nitic intrusions ranging in age from 772 to 831 because they contain zircons from age ranges sic. Samples collected from Jurassic units in the Ma, though the lack of zircons of this age in the not seen in the Verkhoyansk Range. These inter- In’yali-Debin synclinorium, located directly east Verkhoyansk Range suggests that the Taimyr pretations, including the similarity of detrital of the central Kular-Nera slate belt (Fig. 1A), region is a more likely source for Chukotka and zircon ages collected from Chukotka to igneous show a nearly identical zircon age distribution Kular. Zircons in the range of 850–1000 Ma and ages from the Taimyr Peninsula and similarity to the Kular area samples, despite being located 1000–1315 Ma are prevalent in Triassic Chu- between Chukotka and Kular area detrital zir- some 650 km to the southeast (Fig. 8), suggest- kotka samples (Miller et al., 2006) but are con- con data, put Chukotka closer to northern Rus- ing the likelihood of a similar arc source for spicuously absent from both Kular and the Verk- sia and the Barents Shelf prior to development Middle Jurassic zircons. Western zircon source hoyansk Range. Interestingly, zircons of this age of the Amerasian Basin, supporting original areas for older detrital grains are compatible with were also seen in Triassic samples from Wran- conclusions by Miller et al. (2006, 2008, 2010). the interpretation that the Kular-Nera belt was a gel Island, western Alaska (Lisburne Hills), and series of eastward-deposited continental-slope eastern Alaska (Sadlerochit Mountains and the Jurassic Detrital Zircon Data fans, which likely also applies to deposition Sverdrup Basin) (Fig. 8), though percentages within the In’yali-Debin terrane. This interpreta- of this age range are greatly diminished relative Deposition of the Kular Jurassic units must tion is further supported by the presence of SE- to late Paleozoic samples from the same areas have occurred following initiation of collision directed paleocurrent indicators seen in Jurassic (Miller et al., 2010). Though all three areas have between the incoming Kolyma-Omolon superter- strata along the Yana River, as described earlier. Precambrian zircons of varying age ranges (Fig. rane and the Siberian craton based on differences In’yali-Debin sediments have been described 8), differences in younger populations of zircons between Triassic and Late Jurassic Kular detrital as synorogenic and are inferred to have been (less than 400 Ma) suggest that Chukotka and data. Potential sources for the 162 Ma peak seen deposited synchronously with collision of the western Alaska may have shared sedimentation in Jurassic samples are the Selenga (135–295 Kolyma-Omolon superterrane from the east sources that were different from those feeding Ma), Uda-Murgal, and Stanovoy (96–203 Ma) (Oxman, 2003), which could be a potential eastern Alaska during the Triassic. Decreased subduction-related arcs that formed during sub- source for the Late Jurassic–aged zircons found amounts of Late Proterozoic zircons found in duction of the Mongol-Okhotsk Ocean plate both in the In’yali-Debin and Kular areas, as pre- Triassic samples from Chukotka and Wrangel under the North Asian cratonal margin (Parfenov viously described. Differences in the detrital sig- Island relative to upper Paleozoic samples from et al., 2009). The Selenga volcanic-plutonic belt nal strength between the In’yali-Debin and Kular the same areas suggest a change from Baltican was also suggested to have provided detrital zir- areas may be related to their large geographical

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separation. Both the In’yali-Debin terrane and geographic locations near modern northern Rus- than 2200 Ma and a matching age peak at 1920 Kular lack a 450–550 Ma range of zircons (com- sia (South Anyui suture, Chukotka, Verkhoy- Ma, in Jurassic samples, matching Aldan Shield monly attributed to the Central Asia fold belt) ansk, Kular, Stolbovoi Island, and In’yali-Debin) ages seen in Triassic Verkhoyansk data. The that is present in the Verkhoyansk Range, sup- displays zircons with ages ranging from 750 to Aldan Shield is commonly invoked as a source porting a disconnect between parts of the paleo– 1300 Ma at all (Miller et al., 2010). This sug- of Precambrian zircons because it represents the Lena River and the Kular Nera terrane caused gests that by the Jurassic, these areas had likely largest exposure of Precambrian basement in the by deformation associated with the impending become more closely linked geographically than Siberian platform (Glebovitsky and Drugova, Kolyma-Omolon superterrane collision. they were in the Triassic and that they were also 1993). The change in sedimentation source separated from the source of the Middle–Late that added older zircon populations by the Late Triassic to Jurassic Transition Proterozoic zircons by this time. Chukotka, Jurassic (possibly Aldan Shield or equivalent Verkhoyansk, and the Kular areas are, however, basement) affected both Kular and Chukotka, The differences in Triassic and Jurassic similar in terms of other age distributions and suggesting connection to a sedimentation sys- Kular detrital signatures suggest a large distur- prominent peak ages in Triassic samples (Fig. tem that had previously only reached the Verk- bance in the sedimentation system for northern 8), indicating some similarity in sedimentation hoyansk area. Absence of the 2200–3000 Ma Russia between 242 Ma and 167 Ma. While systems during the Triassic and further evidence signature in the Verkhoyansk Jurassic samples Triassic and Jurassic detrital data are relatively that Chukotka was not separated from northern suggests both a change in the paleo–Lena River consistent in the Dyanyshka River area of Siberia during the Triassic, as is suggested by deposition (as suggested in Prokopiev et al., the Verkhoyansk Range, with the only major the rotational model. Chukotka, however, may 2008), as this age range was present in Triassic changes being the expected addition of younger have begun separation from Baltican sources by samples, and also that the paleo–Lena River was signatures to the Jurassic samples and the loss the Triassic due to rifting along northern Siberia, not responsible for transport of Aldan Shield of zircons older than 2300 Ma, the Kular and separating Baltica and Uralian sediments from zircons to Chukotka and the Kular area in the Chukotka Triassic detrital signatures are differ- Chukotka and the Taimyr regions. This separa- Jurassic. It could be that as collision with the ent from their Jurassic counterparts despite close tion is evidenced by diminished percentages in Kolyma-Omolon superterrane began, it formed proximity of sample collection within each area 1000–1300 Ma detrital zircons from Triassic a NW-SE–oriented watershed where sediments (Fig. 8). A K-S test of only Kular ages older than samples collected in Wrangel Island, Lisburne from the Aldan Shield could have traveled up 229 Ma (the age of the youngest Triassic zircon Hills, Alaska, and Chukotka as compared with the northeast edge of the continent, bypassing dated) from both Triassic and Jurassic samples late Paleozoic samples collected from the same the paleo–Lena River. So, in the Triassic, this supports two different populations based on areas (Miller et al., 2010), though it is noted that extra sedimentation source was likely just mov- calculated P values (Table 1). Upon removal of Uralian sources for Chukotka sediments cannot ing eastward into the basin, and most sediments all zircons with ages younger than 229 Ma (the be ruled out (Miller et al., 2006). These data are to Kular were coming through the Verkhoyansk Jurassic input pulse), the highest P value when also consistent with conclusions of Miller et al. area along the paleo–Lena River (Prokopiev comparing Jurassic Kular samples to Triassic (2006), who stated that source regions for Perm- et al., 2008) or along the paleo–Taimyr River Kular samples was 0.106. Triassic samples col- ian–Triassic zircons found in Triassic samples of system (Miller et al., 2012). Following Juras- lected from the Kular area include a dominant Chukotka could have included the Taimyr region sic accretion, this new pathway from the Aldan 400–500 Ma signature and a smaller 730–850 or a Uralian source, provided they included river Shield could have bypassed the paleo–Lena Ma signature, which are completely absent from systems passing through the Taimyr and Sibe- River to the east and supplied an additional Jurassic samples collected from the same area rian Trap regions. Incorporating Jurassic detrital older population to both Chukotka and Kular. (Figs. 7 and 8). These age ranges are most likely zircon data into emplacement models for Chu- representative of source regions in the Central kotka suggests that by the Tithonian, Chukotka Tectonic Implications of Detrital Zircon Asian fold belt, which were cut off from deposi- was situated north of the Kular area, which is Data tion in the Kular area and In’yali-Debin (which in agreement with the Miller et al. (2008) con- also lacks Central Asian fold belt signatures in clusion that the South Anyui suture must have Extensive work performed around the Can- Jurassic samples) by the Late Jurassic (Fig. 1A) begun to form by the Tithonian, closing the ada Basin supports a Late Jurassic–Early Cre- due to compressional deformation to the west Anyui Ocean. The youngest age in Kular Juras- taceous opening, which is at odds with detrital in the Verkhoyansk fold-and-thrust belt, block- sic sediments is ca. 160 Ma, and Kular Jurassic data presented here if the Alaskan and Chu- ing eastward ﬂ ow input from the paleo–Taimyr data match Chukotka Jurassic data, precluding kotkan portions of the Arctic Alaska-Chukotka River system. separation of the two areas by an oceanic basin microplate are treated as a coherent block dur- Though Taimyr (560–850 Ma and 885–940 by the Late Jurassic, despite likely separation in ing opening of the Canada Basin. Resolutions to Ma; Pease et al., 2001; Pease and Vernikovsky, the Triassic. Further evidence supporting closure this problem involve either rifting of the Arctic 2000, and references within) and Baltica (900– of the South Anyui Ocean by the Tithonian is the Alaska-Chukotka microplate away from the 2000 Ma, with greatest proportions in the range presence of detrital zircons with likely source Canadian Arctic Islands earlier, during the Mid- of 1400–1800 Ma; Miller et al., 2010, and ref- areas from south of the South Anyui suture (1.7– dle to Late Jurassic, as one coherent block simi- erences within) zircon ages from 750 to 1000 2.1 Ga) found in Late Jurassic samples from lar to the rotational model (Fig. 1B), or separa- Ma and 1000–1300 Ma are present in Triassic Chukotka (Miller et al., 2008). tion of the Alaskan and Chukotkan portions of samples from Chukotka and western Alaska Kular and Chukotka appear to have similar the Arctic Alaska-Chukotka microplate, which (Miller et al., 2006), suggesting close proxim- detrital zircon signatures for the Jurassic despite would allow Chukotka to be near the Kular area ity between these areas in the Triassic, they are differences in the Triassic. Neither one has zir- during opening of the Canada Basin. Due to the present in diminished amounts relative to their cons older than 2200 Ma in Triassic samples; strong support for Late Jurassic–Early Creta- Paleozoic counterparts (Miller et al., 2010). By they both have zircons ranging in age from ceous opening of the Canada Basin involving the Jurassic, none of the samples from similar 1600 to 2800 Ma, with wide age ranges older rifting of the North Slope of Alaska away from

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the Canadian Arctic Islands (evidence summa- zircon data presented here show that the paleo– wegian belt, S. Norway: U-Pb, Th-Pb and Re-Os data: Norwegian Journal of Geology, v. 88, p. 13–42. rized in Lawver and Scotese, 1990; Lawver et Lena River system likely provided sediments to Black, L.P., Kamo, S.L., Allen, C.M., Davis, D.W., Aleinikoff, al., 2002), the tectonic movement pathway for the Kular area during the Triassic, as demon- J.N., Valley, J.W., Mundil, R., Campbell, I.H., Korsch, Chukotka may have been independent of the strated by the similarity in the detrital zircon data R.J., Williams, I.S., and Foudoulis, C., 2004, Improved 206Pb/238U microprobe geochronology by the monitor- Alaskan portion of the Arctic Alaska-Chukotka sets between the Kular area and the Dyanyshka ing of a trace-element–related matrix effect; SHRIMP, microplate in the Mesozoic. River system of the Verkhoyansk fold-and-thrust ID-TIMS, ELA-ICP-MS and oxygen isotope documenta- Detrital zircon data from these areas also sug- belt, though the paleo–Taimyr River system also tion for a series of zircon standards: Chemical Geology, v. 205, p. 115–140, doi:10.1016/j.chemgeo.2004.01.003. gest that the eastern margin of the Siberian cra- likely provided sediment to the Kular area in Bychkov, Y.M., 1994, Structural-Facies Zonation and Biostra- ton and the location of the downgoing slab that the Triassic, according to similarities to detrital tigraphy of the Triassic in Chukotka: Magadan, Russia, resulted in suturing of incoming terrane material zircon records of Chukotka. The detrital zircon Northeast Scientifi c Centre, 53 p. (in Russian). Carrapa, B., 2010, Resolving tectonic problems by dating to the Verkhoyansk passive margin would have record from Triassic sediments of Chukotka detrital minerals: Geology, v. 38, p. 191–192, doi:10.1130 been further east of its presently interpreted suggests a depositional source from Baltica /focus022010.1. Cawood, P.A., Nemchin, A.A., Freeman, M., and Sircombe, location along the Adycha-Taryn fault west of that is not present in Kular or the Verkhoyansk K., 2003, Linking source and sedimentary basin: Detri- the Kular-Nera belt. Interpretations that place a fold-and-thrust belt, though Taimyr and Sibe- tal zircon record of sediment fl ux along a modern large thrust fault (the Yana fault) as a Late Juras- rian sources are also evident, putting Chukotka river system and implications for provenance studies: Earth and Planetary Science Letters, v. 210, p. 259–268, sic–Early Cretaceous suture of separate terranes near the Taimyr Peninsula and Barents Shelf in doi:10.1016/S0012-821X(03)00122-5. just east of the Kular Dome are likely in error, the Triassic (Miller et al., 2006). By the Late Condie, K.C., and Aster, R.C., 2009, Zircon age episodicity since the detrital data from this study link the Jurassic, collision between the Kolyma-Omolon and growth of continental crust: Eos (Transactions, American Geophysical Union), v. 90, p. 364, doi:10.1029 Verkhoyansk Range to the Jurassic strata east of superterrane and the Siberian craton disrupted /2009EO410003. the Yana fault. Similar detrital zircon signatures deposition in the Dyanyshka and Kular areas. Dalrymple, G.B., Czamanske, G.K., Fedorenko, V.A., Simonov, O.N., Lanphere, M.A., and Likhachev, A.P., 1995, A between Triassic samples from the Kular area Comparison of these results with those col- reconnaissance geochronologic study of ore-bearing and Jurassic samples from both the Kular area lected from landmasses surrounding the modern and related rocks, Siberian Russia: Geochimica et Cos- and the In’yali-Debin synclinorium (A. Pro- Amerasian Basin provides support for the sepa- mochimica Acta, v. 59, p. 2071–2083, doi:10.1016/0016 -7037(95)00127-1. kopiev, 2012, personal obs.) further dispute the ration of the Chukotka part of the Arctic Alaska- Dickinson, W.R., and Gehrels, G.E., 2009, U-Pb ages of existence of a large suture between the Triassic Chukotka microplate from the Baltican sources detrital zircons in Jurassic eolian and associated sand- and Jurassic units of the Kular-Nera slate belt in the Late Triassic–Early Jurassic and involving stones of the Colorado Plateau: Evidence for transcontinental dispersal and intraregional recycling of sedi- and the eastern Polousnyy-Debin and In’yali- dextral strike-slip movement of Chukotka along ment: Geological Society of America Bulletin, v. 121, Debin terranes. Paleocurrent measurements the northern Siberian Shelf to a position more p. 408–433, doi:10.1130/B26406.1. Dickinson, W.R., Beard, L.S., Brakenridge, G.R., Erjavec, J.L., from Jurassic sandstones also suggest a south- proximal to the Kular area by the Middle–Late Ferguson, R.C., Inman, K.F., Knepp, R.A., Lindberg, F.A., eastern transport direction during deposition, Jurassic. Detrital zircon age peaks seen in Kular and Ryberg, P.T., 1983, Provenance of North American matching inferred Triassic depositional condi- samples also match well with global records Phanerozoic sandstones in relation to tectonic setting: Geological Society of America Bulletin, v. 94, p. 222– tions within the same prograding delta system, for prominent zircon age peaks, contributing to 235, doi:10.1130/0016-7606(1983)94<222:PONAPS>2.0 which further disputes the presence of a suture the global supercontinent cycle record of zircon .CO;2. separating Triassic units of the Kular area from preservation (Condie and Aster, 2009). Sedi- Embry, A.F., 1990, Geological and geophysical evidence in support of the hypothesis of anticlockwise rotation of Jurassic units. Sedimentary evidences including mentological and detrital data collected from the northern Alaska: Marine Geology, v. 93, p. 317–329, prevalence of slump folds, ripple marks, reverse Kular area are also strong evidence against the doi:10.1016/0025-3227(90)90090-7. grading, and thick conglomerate lenses, as well presence of a large regional suture represented Embry, A.F., and Dixon, J., 1994, The age of the Amerasia basin, in Thurston, D.K., and Fujita, K., eds., Proceed- as preservation of ammonites and wood frag- by the Yana fault in the Kular area. ings of the 1992 International Conference on Arctic Mar- ments, are all suggestive of depositional condi- gins, MMS94-0040: Anchorage, Alaska, United States Department of the Interior, p. 289–294. tions within a prograding deltaic system near the ACKNOWLEDGMENTS Gehrels, G., and Pullen, A., 2010, Introduction to U-Th-Pb shore rather than the traditional interpretation Geochronology Using a Laser-Ablation Multicollector of continental rise or marginal sea deep-water This work was supported by funding from BP ICP Mass Spectrometer: Anaheim, California, Geologi- cal Society of America Short Course, 78 p. deposition of the Kular-Nera slate belt as turbi- contract CON-ARC-08-003 and the Chesapeake Gehrels, G., Valencia, V., and Pullen, A., 2006, Detrital zircon dite fl ows. Fellowship. Special thanks go to Elizabeth geochronology by laser-ablation multicollector ICPMS Miller for providing several critical reviews and at the Arizona Laserchron Center, in Olszewski, T., ed., Geochronology: Emerging Opportunities: Paleontology CONCLUSIONS helpful comments. Thanks also go to Elizabeth Society Papers, v. 12, p. 67–76. Miller, Dmitry A. Vasiliev, and Alexei I. Ivanov Glebovitsky, V.A., and Drugova, G.M., 1993, Tectonothermal evolution of the Western Aldan Shield, Siberia: Pre- In recent years, detrital zircon studies focus- for contributions during fi eld work performed in cambrian Research, v. 62, p. 493–505, doi:10.1016/0301 ing on Wrangel Island and the Chukotka Pen- 2008, to the members of the Kyuchus mining -9268(93)90018-W. insula have suggested that the Chukotka part facility, and to the technicians of the University Gradstein, F.M., Ogg, J.G., and Smith, A.G., eds., 2004, A Geologic Time Scale 2004: Cambridge, UK, Cambridge of the Arctic Alaska-Chukotka microplate may of Arizona LaserChron Center for their assis- University Press, 585 p. have been closer to Siberia during the Neoco- tance while using their facilities and equipment. Grantz, A., and May, S.D., 1983, Rifting history and structural mian than previously considered. 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MANUSCRIPT RECEIVED 20 JULY 2012 2002, 40 39 Miller, E.L., Gehrels, G.E., Pease, V., and Sokolov, S., 2010, Ar/ Ar dates from the West Siberian Basin: MANUSCRIPT ACCEPTED 23 SEPTEMBER 2012 Stratigraphy and U-Pb detrital zircon geochronology Siberian fl ood basalt province doubled: Science, v. 296, of Wrangel Island, Russia: Implications for Arctic paleo- p. 1846–1849, doi:10.1126/science.1071671. Printed in the USA

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