Hornbrook Formation, Oregon and California: a Sedimentary Record of the Late Cretaceous Sierran Magmatic Flare-Up Event GEOSPHERE; V

Research Paper

GEOSPHERE Hornbrook Formation, Oregon and California: A sedimentary record of the Late Cretaceous Sierran magmatic flare-up event GEOSPHERE; v. 11, no. 6 Kathleen D. Surpless Department of Geosciences, Trinity University, One Trinity Place, San Antonio, Texas 78212, USA doi:10.1130/GES01186.1

11 figures; 1 table; 2 supplemental files ABSTRACT cally punctuated by short-term, high-volume magmatic flare-ups (e.g., Ducea, 2001; de Silva et al., 2015; Ducea et al., 2015; Paterson and Ducea, 2015). A key to CORRESPONDENCE: [email protected] Early Late Cretaceous time was characterized by a major magmatic flare-up the accurate interpretation of the episodic magmatic history of continental arcs event in the Sierra Nevada batholith and early phases of magmatism in the is the integration of age distributions from the arc itself and from detrital zircons CITATION: Surpless, K.D., 2015, Hornbrook Forma- Idaho batholith, but the sedimentary record of this voluminous magmatism in eroded from the arc that are typically archived in forearc, intra-arc, and backarc tion, Oregon and California: A sedimentary record of the Late Cretaceous Sierran magmatic flare-up the U.S. Cordillera is considerably less conspicuous. New detrital zircon U-Pb basins (e.g., Gehrels, 2014; Ducea et al., 2015; Paterson and Ducea, 2015). event: Geosphere, v. 11, no. 6, p. 1770–1789, doi:10 ages from the Hornbrook Formation in southern Oregon and northern Califor- The first 15 m.y. of Late Cretaceous time was characterized by a significant .1130/GES01186.1. nia reveal a significant and sustained influx of 100–85 Ma detrital zircons into magmatic flare-up event in the Sierra Nevada (Coleman and Glazner, 1997; the broader Hornbrook region beginning ca. 90 Ma. Detrital zircon ages and haf- Ducea, 2001; Ducea and Barton, 2007; Cao et al., 2015) that reached spatial Received 9 March 2015 nium isotopic compositions, combined with whole-rock geochemistry, suggest addition rates of up to 1000 km2/km/m.y. (Paterson et al., 2011) and accounted Revision received 18 August 2015 Accepted 22 September 2015 that sediment was largely derived from the Sierra Nevada, requiring uplift and for nearly 78% of the California arc magmatic volume (Ducea, 2001). Magma Published online 10 November 2015 erosion of the Sierra Nevada batholith during and immediately following the addition to the Sierran arc during the Late Cretaceous flare-up was 100–1000 Late Cretaceous magmatic flare-up event. Sediment derived from the eroded times greater than during the preceding magmatic lull, and the vast majority arc may have been transported northward along the axis of the arc, between of that magma crystallized at depth, resulting in a plutonic to volcanic ratio of a western drainage divide along the arc crest and the rising Nevadaplano to 30:1 or greater (Paterson and Ducea, 2015). In addition, the first phase of mag- the east. Although the Klamath Mountains and Blue Mountains Province pre matism in the Idaho batholith occurred ca. 98–87 Ma, and although these rocks sent more proximal potential sources of Jurassic and Early Cretaceous detrital are now exposed only as outlying stocks and roof pendants, they may have zircons in the Hornbrook Formation than the Sierra Nevada, Late Cretaceous originally formed an extensive and continuous igneous complex at a higher deposition on the Klamath Mountains 80 km west of Hornbrook Formation structural level than current exposure (Gaschnig et al., 2010, 2011). outcrops, and Late Cretaceous deep-water deposition on the Blue Mountains Given the ubiquity of zircon in silicic igneous rocks (e.g., Gehrels, 2012) and in the Ochoco Basin suggest that these regions were the locus of subsidence exhumation of the plutonic system beginning ca. 90 Ma (e.g., Cecil et al., 2006; and sedimentation, rather than erosion, during Late Cretaceous time. The lim- Giorgis et al., 2008), the sedimentary record of this Late Cretaceous magma- ited outcrop extent of the Hornbrook Formation may represent only a sliver of tism is surprisingly sparse. Detrital zircons of 100–85 Ma age are more abun- a much larger Late Cretaceous Hornbrook basin system. Complete characteri- dant in the retroarc than the forearc regions of the California-Oregon segment zation of the episodic magmatic history of continental arcs requires integration of the Cordillera, but they do not dominate the retroarc detrital zircon age sig- of age distributions from the arc itself and from detrital zircons eroded from nature (Barth et al., 2004; Dickinson and Gehrels, 2008; Dickinson et al., 2012), the arc; it is critical to recognize the potential of drainage systems to transport and they form only a minor component of the Cenomanian–Coniacian (ca. sediment to depocenters not directly linked to present-day arc exposures. 100–86 Ma) Great Valley forearc basin (DeGraaff-Surpless et al., 2002; Sharman et al., 2015). Although 100–85 Ma detrital zircons are more abundant in Santo- nian and younger forearc strata of the Great Valley forearc (deposited after ca. INTRODUCTION 86 Ma), they are typically part of a broader spectrum of Mesozoic grains, likely reflecting expanding catchments rather than deeper erosion of the Late Creta- The complex history of Late Cretaceous plate convergence and arc magma- ceous plutons (DeGraaff-Surpless et al., 2002; Sharman et al., 2015). tism in the U.S. Cordillera may be deciphered from the eroded remnants of Cor- This study presents new detrital zircon U-Pb ages from the Hornbrook For- dilleran arcs exposed at the surface today, as well as from basins that received mation in southern Oregon and northern California, as well as from coeval sedi sediment eroded from magmatic arcs and associated terranes (e.g., Barth et al., mentary rocks deposited on Klamath Mountains’ basement near the southern For permission to copy, contact Copyright 2013; Gehrels, 2014). The batholiths that comprise the bulk of continental mag- Oregon town of Cave Junction (Figs. 1 and 2). These new data are integrated Permissions, GSA, or [email protected]. matic arcs form incrementally through long-term magmatism that is episodi- with detrital zircon hafnium isotopic data, and whole-rock major- and trace-

GEOSPHERE | Volume 11 | Number 6 Surpless | Hornbrook Formation, Oregon and California Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/6/1770/4333694/1770.pdf 1770 by guest on 28 September 2021 Research Paper

element geochemical data from Hornbrook Formation sandstone, siltstone, GEOLOGIC SETTING and mudstone samples. The results document a significant and sustained influx of 100–85 Ma detrital zircon into the broader Hornbrook region beginning The Hornbrook Formation crops out in two northwest-trending belts within at ca. 90 Ma and continuing for at least 10 m.y., into Campanian time. Detrital the Bear Creek valley in southern Oregon and the Cottonwood Creek valley in zircon ages and hafnium isotopic composition and whole-rock geochemistry northern California (Fig. 2A). The strata unconformably rest on Klamath Moun- results suggest that this sediment was largely derived from the Sierra Nevada, tains basement terranes and are overlain by Paleogene sedimentary and vol- although a portion may have been from the early phase of the Idaho batho- canic rocks of the Cascade Range (McKnight, 1971). The Hornbrook Formation lith. Thus, Sierran-derived sediment may have been funneled northward and is considered a forearc basin (e.g., Nilsen, 1984; Miller et al., 1992), with sedi- westward into the Hornbrook basin beginning ca. 90 Ma, suggesting increased ment sources during Albian–Turonian time (ca. 113–90 Ma; Fig. 2C) in the ac- uplift and erosion of the Late Cretaceous Sierra Nevada batholith during and creted terranes and plutons of the Klamath Mountains and the Sierra Nevada immediately following the Late Cretaceous magmatic flare-up event. Foothills metamorphic belt, as well as possible sources in northern Nevada Uplift of the Nevadaplano (e.g., DeCelles, 2004) and Sierra Nevada (e.g., (Surpless and Beverly, 2013). Hornbrook sediment sources also included Late Cecil et al., 2006), combined with a Cretaceous drainage divide within the Cretaceous plutons of the Sierran batholith and/or early phases of the Idaho Sierra Nevada that precluded west-directed transport of eastern Sierran sedi batholith during Turonian–Maastrichtian time (ca. 90–66 Ma; Surpless and ment into the Great Valley forearc basin (e.g., Sharman et al., 2015), may have Beverly, 2013). Sandstone samples are quartzofeldspathic with minor volcanic resulted in the northward transport of abundant Sierran arc detritus into the lithic fragments, and they plot in recycled orogen and dissected arc prove- subsiding Hornbrook region during Late Cretaceous time. These results under nance fields on quartz-feldspar-lithic ternary diagrams of Dickinson et al. (1983; score the potential of intra-arc drainage systems to transport sediment to Golia and Nilsen, 1984; Surpless and Beverly, 2013). These sandstone compo- depocenters not directly linked to present-day arc exposures; these transport sitions suggest that volcanic sources provided little sediment, and therefore pathways are critical to recognize if the detrital zircon record is to provide an that the detrital zircon in the Hornbrook sandstone was derived largely from integrated, long-term history of magmatic activity. plutonic and metamorphic sources.

Cretaceous contractional belt (WISZ—western Idaho shear zone) 48°N WA WISZ Cretaceous to Cenozoic dextral OR strike-slip fault Jurassic-Cretaceous and Cretaceous sedimentary basins (outcrop area; N HF—Hornbrook Formation) HF BLUE MTNS. PROVINCE Mid-Late Cretaceous plutonic belts 44°N KLAMATH IDAHO MOUNTAINS OR ID BATHOLITH Discontinuous mid- to Late Cretaceous Figure 1. Generalized map of the U.S. Cor- NV plutonic belts dillera (modified from Wyld et al., 2006). Hornbrook Formation (HF) outcrop area Cretaceous subduction complex is shown in green. State abbreviations: WA—Washington, OR—Oregon, ID—Idaho, assemblages RMA NV—Nevada, UT—Utah, AZ—Arizona. GA Triassic and Paleozoic basinal terranes; 40°N GA—Golconda allochthon; RMA—Roberts Mountains allochthon Paleozoic and/or Early Mesozoic volcanic arc assemblages SIERRA UT NEVADA 0 300 AZ Late Paleozoic to early Mesozoic subduction complexes KILOMETERS 36°N 120°W 116°W112°W Late Proterozoic to Permian miogeocline

Medford A BE A R CR E E K VA Ashland LLEY Cave Junction

Suncrest Road Quarry

OREGON CALIFORNIA COTT C Hornbrook Formation REEK Upper Cretaceous ONWOOD Hornbrook OREGON VA Lower(?) Cretaceous LL Figure 2. (A) Simplified geologic map of E the Hornbrook Formation (from Nilsen, fault (dotted where inferred) Y 1993) showing the distribution of outcrop in the Bear Creek and Cottonwood Creek Highway valleys and the location of the Suncrest

CALI Road Quarry near Cave Junction, Oregon. Topographic image from Google Earth. F OR (B) Hornbrook Formation member names NIA N Yreka and depositional ages from Nilsen (1984); proposed new members and depositional 0 10 20 ages for the Bear Creek valley from Wiley KILOMETERS et al. (2011). (C) Geologic time scale with age names and boundary age picks (Ma) for the Cretaceous Period (from Walker PICKS PERIOD EPOCH AGE et al., 2012). B Hornbrook Formation Members Depositional Ages (Ma) 66.0 Blue Gulch Mudstone (BGM) Campanian–Maastrichtian MAASTRICHTIAN 72.1

Rocky Gulch Sandstone (RGS) Campanian(?) CAMPANIAN

TE 83.6 Ditch Creek Siltstone (DCS) upper Turonian–lower Coniacian(?) SANTONIAN LA 86.3 CONIACIAN 89.8 TURONIAN Osburger Gulch Sandstone (OGS) Turonian–lower Coniacian 93.9 CENOMANIAN s 1) Barneburg Hill (BH) middle Turonian(?) 100 CEOU S Medford Mudstone middle Turonian ALBIAN

Pioneer Road Sandstone middle Turonian 113 Dark Hollow Siltstone lower to middle Turonian APTIAN Klamath River Ashland Sandstone lower to middle Turonian CRE TA 126 Conglomerate (KRC) Jacksonville upper (?) Albian to middle EAR LY

Bear Creek valley member BARREMIAN named by Wiley et al. (201 Cenomanian 131 HAUTERIVIAN 134 VALANGINIAN 139 C BERRIASIAN

Hornbrook Formation strata record an overall marine transgression, with improve depositional age constraints and resulting potential correlation of this fluvial and alluvial deposition at the base of the section and slope and deep isolated Cretaceous outlier, which rests unconformably on Jurassic rocks of the basin plain in the middle and upper sections (McKnight, 1971; Elliott, 1971; Galice Formation (Imlay et al., 1959; Walker and McLeod, 1991). Zircons were Nilsen, 1984, 1993). Building on previous work (Peck et al., 1956; Jones, 1959; isolated using standard separation techniques (e.g., Gehrels et al., 2006), and a McKnight, 1971; Elliott, 1971), Nilsen (1984) recognized five members of the random subset of zircon grains from each sample was mounted in epoxy and Hornbrook Formation (Fig. 2B): (1) the basal Klamath River Conglomerate polished. U-Pb dating and Lu-Hf isotopic analysis were completed at the Uni- member formed in fluvial and alluvial depositional environments, with depo- versity of Arizona LaserChron Center, following methods described in Gehrels sition beginning as early as late Albian time (ca. 102 Ma) in the north (Nilsen, et al. (2006) and Cecil et al. (2011). Following DeGraaff-Surpless et al. (2003), I 1993) and middle Cenomanian time (ca. 95 Ma) to the south (Jameossanaie include grains younger than 600 Ma that plot within 10% of Tera-Wasserburg and Lindsley-Griffin, 1993); (2) the late Albian–early Coniacian (ca. 102–87 Ma) concordia along a mixing line from the common Pb value (207Pb/206Pb ratio of Osburger Gulch Sandstone member formed in nearshore to wave-dominated 0.86; Cumming and Richards, 1975) through the data to concordia. For grains middle-shelf environments; (3) the Turonian–Coniacian, ca. 94–86 Ma, Ditch older than 600 Ma, only grains with less than 10% discordance are included Creek Siltstone member formed in outer-shelf environments; (4) the Rocky in the probability density plots. Ages reported are 206Pb/238U ages for grains

SUPPLEMENTAL TABLE 1. U-Pb DATA Isotope ratios Apparent ages (Ma) Best age (Ma) Analysis U (ppm) 206Pb/204Pb U/Th 206Pb*/ 207Pb* ± (%) 207Pb*/235U* ± (%) 206Pb*/ 238U± (%)error corr. 206Pb*/ 238U* ± (Ma) 207Pb*/ 235U± (Ma) 206Pb*/ 207Pb*± (Ma) Best age (Ma) ± (Ma) 207 206 Suncrest Road Quarry 13-KOB-03-76 423 17793 1.4 20.7450 5.3 0.0895 6.2 0.01353.2 0.51 86.3 2.787.15.1 109.3124.7 86.3 2.7 13-KOB-03-55 406 11331 1.6 20.4662 7.0 0.0913 7.1 0.01351.4 0.19 86.8 1.288.76.0 141.2164.3 86.8 1.2 Gulch Sandstone member of uncertain age formed in a slope environment, younger than 900 Ma and Pb/ Pb ages for grains 900 Ma and older (all U-Pb 13-KOB-03-48 258 13737 1.9 21.9013 14.0 0.0859 15.8 0.01367.3 0.46 87.4 6.483.712.7-20.3 339.387.46.4 13-KOB-03-78 487 5735 1.4 21.0143 5.9 0.0899 6.1 0.01371.5 0.25 87.7 1.387.45.1 78.7 141.387.71.3 13-KOB-03-64 475 12816 1.5 20.2945 7.2 0.0934 7.4 0.01371.7 0.22 88.0 1.490.76.4 160.9167.9 88.0 1.4 13-KOB-03-25 179 7279 1.2 18.1895 18.9 0.1051 19.4 0.01394.3 0.22 88.8 3.7101.5 18.7 411.3426.9 88.8 3.7 13-KOB-03-22 287 20297 2.0 20.7108 4.7 0.0926 5.1 0.01392.0 0.40 89.1 1.890.04.4 113.2110.0 89.1 1.8 1 13-KOB-03-05 63 3174 1.7 27.3857 34.9 0.0702 36.2 0.01399.4 0.26 89.2 8.468.924.1-592.2972.8 89.2 8.4 13-KOB-03-23 327 17130 1.4 20.3046 5.5 0.0947 6.4 0.01403.3 0.51 89.3 2.991.95.6 159.7128.7 89.3 2.9 and it unconformably overlies the Ditch Creek Siltstone in the type section; and data are given in Supplemental Table 1 ). Lu-Hf isotopic compositions were col- 13-KOB-03-18 165 8979 1.6 25.8995 31.3 0.0743 31.4 0.01402.9 0.09 89.4 2.672.822.0-443.1839.3 89.4 2.6 13-KOB-03-50 487 9216 1.5 21.3205 4.2 0.0904 6.3 0.01404.7 0.74 89.5 4.287.95.3 44.3 101.489.54.2 13-KOB-03-72 250 10275 1.9 23.4145 14.9 0.0824 15.2 0.01402.6 0.17 89.6 2.380.411.7-184.5375.1 89.6 2.3 13-KOB-03-87 549 30196 1.5 19.7773 3.9 0.0977 4.1 0.01401.1 0.28 89.7 1.094.63.7 221.090.489.71.0 13-KOB-03-53 360 28259 2.3 21.0989 8.1 0.0917 8.2 0.01401.1 0.13 89.9 1.089.17.0 69.2 192.589.91.0 13-KOB-03-99 703 41813 2.9 20.8226 5.2 0.0932 5.4 0.01411.4 0.26 90.1 1.390.54.6 100.5122.3 90.1 1.3 13-KOB-03-27 210 1067 1.5 16.0283 14.8 0.1213 15.7 0.01415.3 0.34 90.3 4.7116.3 17.2 687.5317.1 90.3 4.7 13-KOB-03-80 72 4202 1.3 26.7717 68.7 0.0729 69.0 0.01426.6 0.10 90.6 6.071.447.7-531.02080.090.66.0 (5) the Campanian–Maastrichtian (ca. 84–66 Ma) Blue Gulch Mudstone mem- lected from all grains dated in the Ditch Creek Siltstone sample from the Bear 13-KOB-03-40 371 14584 1.8 20.9656 10.2 0.0931 10.5 0.01422.3 0.22 90.6 2.190.49.1 84.3 243.790.62.1 13-KOB-03-45 340 7375 1.7 19.7769 6.7 0.0988 7.1 0.01422.2 0.31 90.7 2.095.76.5 221.0155.6 90.7 2.0 13-KOB-03-71 419 34981 2.1 22.1509 6.3 0.0883 6.5 0.01421.5 0.23 90.8 1.485.95.3 -47.8152.8 90.8 1.4 13-KOB-03-03 214 25844 2.6 19.3188 16.5 0.1014 16.9 0.01423.4 0.20 91.0 3.198.115.8274.9 380.591.03.1 13-KOB-03-75 356 35349 1.8 20.3478 5.8 0.0967 6.3 0.01432.4 0.39 91.4 2.293.85.6 154.8136.2 91.4 2.2 13-KOB-03-14 173 14989 1.9 23.0032 17.2 0.0858 17.6 0.01433.4 0.19 91.6 3.183.614.1-140.5429.8 91.6 3.1 13-KOB-03-04 169 26545 1.6 19.5085 17.3 0.1028 17.4 0.01452.6 0.15 93.1 2.499.316.5252.6 399.593.12.4 ber formed in outer-shelf to basin plain environments. Depositional ages are Creek valley (I-5 sample) and from all grains younger than 110 Ma in the Ditch 13-KOB-03-11 160 792 1.2 17.9771 17.0 0.1125 18.6 0.01477.4 0.40 93.9 6.9108.3 19.1 437.5381.6 93.9 6.9 13-KOB-03-92 378 17985 1.3 20.1617 6.1 0.1025 6.2 0.01501.2 0.19 95.9 1.199.15.8 176.2141.4 95.9 1.1 13-KOB-03-09 323 16436 1.4 21.3793 9.3 0.0972 9.9 0.01513.3 0.33 96.4 3.194.28.9 37.7 224.096.43.1 13-KOB-03-16 253 20070 3.4 24.1897 9.3 0.0859 9.8 0.01513.1 0.32 96.4 3.083.77.9 -266.6 236.796.43.0 13-KOB-03-01 226 11189 1.3 21.0124 13.2 0.0993 13.5 0.01512.9 0.21 96.9 2.896.212.479.0314.7 96.9 2.8 13-KOB-03-43 1224 49192 1.5 20.7480 2.0 0.1020 2.5 0.01531.5 0.60 98.2 1.598.62.4 109.047.898.21.5 13-KIB-44 224 19307 2.1 18.7479 10.2 0.1134 10.7 0.01543.1 0.29 98.6 3.1109.0 11.0 343.3231.7 98.6 3.1 13-KOB-03-98 635 17163 1.7 20.4516 4.0 0.1044 5.1 0.01553.2 0.63 99.1 3.2100.8 4.9142.8 93.6 99.1 3.2 based on macro- and microfossils and suggest time-transgressive deposition, Creek Siltstone sample from the Cottonwood Creek valley (Rickety Bridge sam- 13-KOB-03-65 1650 11271 1.3 20.3776 2.4 0.1064 4.7 0.01574.1 0.86 100.64.0 102.74.6 151.355.4100.6 4.0 13-KOB-03-02 552 41512 1.2 21.2202 3.1 0.1055 3.9 0.01622.4 0.61 103.82.5 101.83.8 55.6 73.3 103.82.5 13-KOB-03-51 713 7323 1.4 20.1030 5.5 0.1115 7.0 0.01634.4 0.63 103.94.5 107.37.1 183.0127.3 103.94.5 13-KOB-03-89 93 4258 1.3 19.2772 18.3 0.1217 18.8 0.01704.0 0.22 108.74.4 116.620.7279.9 422.6108.7 4.4 13-KOB-03-13 75 1662 1.5 22.3572 21.7 0.1073 22.2 0.01744.8 0.21 111.25.3 103.521.9-70.4 535.4111.2 5.3 13-KOB-03-91 41 4608 3.1 -0.6852 6120.2 -3.8133 6120.2 0.01908.7 0.00 121.010.5#NUM!#NUM!NANA121.0 10.5 13-KOB-03-67 74 1852 1.9 15.6512 22.0 0.1718 23.2 0.01957.2 0.31 124.58.9 161.034.5738.1 471.5124.5 8.9 with deposition becoming younger to the south (Nilsen, 1993). Paleocurrent ple), using laser ablation of the same spot created during U-Pb analysis (all Hf 13-KOB-03-73 75 8690 3.0 20.1572 27.6 0.1435 28.5 0.02107.4 0.26 133.99.8 136.236.4176.7 654.0133.9 9.8 13-KOB-03-85 1211 58480 1.1 20.1328 1.2 0.1529 4.9 0.02234.7 0.97 142.46.7 144.56.6 179.628.7142.4 6.7 13-KOB-03-59 122 14534 1.5 20.2479 8.5 0.1527 9.1 0.02243.2 0.35 143.04.5 144.312.2166.3 198.5143.0 4.5 13-KOB-03-07 96 6772 1.0 22.1606 16.5 0.1436 16.8 0.02313.1 0.18 147.14.5 136.321.5-48.9 404.8147.1 4.5 13-KOB-03-46 381 2083 1.2 18.8267 8.8 0.1708 8.9 0.02331.4 0.16 148.62.0 160.113.1333.8 198.7148.6 2.0 2 13-KOB-03-68 297 24254 2.0 19.5309 4.9 0.1696 5.0 0.02400.8 0.15 153.11.2 159.17.3 249.9112.8 153.11.2 13-KOB-03-94 119 18089 2.8 21.6716 9.8 0.1533 10.6 0.02414.0 0.38 153.56.1 144.814.35.1 237.1153.5 6.1 13-KOB-03-86 224 33976 1.8 19.8681 6.0 0.1693 6.3 0.02441.6 0.25 155.42.4 158.89.2 210.3140.3 155.42.4 measurements are dominantly north-directed, with considerable scatter to the data are given in Supplemental Table 2 ). These Ditch Creek Siltstone samples 13-KOB-03-62 461 41865 1.2 20.2371 2.2 0.1665 2.4 0.02440.8 0.35 155.71.3 156.43.4 167.552.1155.7 1.3 13-KOB-03-82 372 2961 2.1 19.2537 7.1 0.1755 7.4 0.02452.1 0.28 156.13.2 164.211.3282.7 163.4156.1 3.2 13-KOB-03-63 130 9779 2.2 20.3421 12.7 0.1661 12.9 0.02452.1 0.16 156.13.2 156.118.6155.4 298.7156.1 3.2 13-KOB-03-19 274 6629 0.8 19.5767 4.3 0.1735 5.1 0.02462.7 0.53 156.94.2 162.47.6 244.599.5156.9 4.2 13-KOB-03-29 36 3600 2.0 25.1007 31.8 0.1359 32.7 0.02477.7 0.24 157.512.1129.4 39.7 -361.3 839.4157.5 12.1 13-KOB-03-30 198 13583 1.6 20.6195 8.4 0.1655 8.7 0.02482.4 0.27 157.63.7 155.512.6123.6 197.7157.6 3.7 13-KOB-03-93 213 4012 2.0 20.0008 9.8 0.1709 10.0 0.02481.8 0.18 157.92.8 160.214.8194.9 228.1157.9 2.8 east and west (Nilsen, 1984). were chosen for Hf analysis because detrital zircon age analysis revealed that 13-KOB-03-35 135 13921 2.2 20.9893 17.1 0.1636 17.2 0.02492.1 0.12 158.63.3 153.824.681.6408.9 158.63.3 13-KOB-03-42 147 2726 1.8 22.3349 10.2 0.1545 10.4 0.02501.9 0.18 159.33.0 145.814.1-68.0 249.8159.3 3.0 13-KOB-03-96 149 3347 1.7 23.4601 8.1 0.1484 8.4 0.02522.3 0.27 160.73.6 140.511.1-189.4203.5 160.73.6 13-KOB-03-28 123 4543 1.7 19.9675 13.8 0.1753 14.3 0.02543.6 0.25 161.65.8 164.021.6198.8 321.8161.6 5.8 13-KOB-03-12 137 4392 1.5 19.8993 16.2 0.1771 16.3 0.02561.5 0.09 162.72.4 165.624.9206.7 377.7162.7 2.4 13-KOB-03-88 174 15074 2.6 20.2758 9.6 0.1749 10.0 0.02572.8 0.28 163.74.6 163.715.2163.0 225.6163.7 4.6 Wiley et al. (2011) suggested that the Hornbrook Formation within the Bear the Ditch Creek Siltstone records the first occurrence of the prominent Late Creek valley represents four transgressive sequences separated by three pos- Cretaceous detrital zircon age peak, which is the focus of this study. 1Supplemental Table 1. U-Pb data. Please visit http:// dx.doi .org /10 .1130/GES01186 .S1 or the full-text article sible unconformities, and they proposed six new members within the basal Mesozoic detrital zircon age distributions for all samples (20 samples; 11 on www.gsapubs.org to view Supplemental Table 1. upper Albian–middle Turonian section of Bear Creek valley that replace, in from this study and 9 from Surpless and Beverly, 2013) from Bear Creek and part, Nilsen’s (1984) Klamath River Conglomerate member (Fig. 2B). Only the Cottonwood Creek valleys are shown in stratigraphic order by members within

SUPPLEMENTAL TABLE 2. HAFNIUM DATA Sample name + 176Lu) / 176H Volts Hf 176Hf/177Hf ± (1σ) 176Lu/177Hf 176Hf /177Hf (T) E Hf (0) E Hf (0) ± (1σ E Hf (T)Age (Ma) middle Turonian(?) Barneburg Hill member, which was formerly mapped as each valley, and they are aligned between valleys by similar age distributions, Surpless#2/I-5:828.2 1.80.282383 0.000035 0.000543 0.282383 -14.2 1.3 -12.3 89 Surpless#2/I-5:12 15.21.4 0.282922 0.000066 0.001091 0.282920 4.82.3 6.890 Surpless#2/I-5:699.4 1.90.282368 0.000038 0.000572 0.282367 -14.8 1.3 -12.8 92 Surpless#2/I-5:89 17.01.5 0.282463 0.000044 0.001150 0.282461 -11.41.6 -9.494 the lower conglomerate of the Paleogene Payne Cliffs Formation (McKnight, such that members in the northern Bear Creek valley are older than the same Surpless#2/I-5:13 26.82.0 0.282855 0.000037 0.001683 0.282851 2.51.3 4.6 100 Surpless#2/I-5:41 26.91.1 0.282898 0.000082 0.001985 0.282894 4.02.9 6.2 105 Surpless#2/I-5:18 12.41.5 0.283069 0.000047 0.000879 0.283067 10.01.7 12.7 124 Surpless#2/I-5:9 19.62.1 0.283017 0.000038 0.001300 0.283014 8.21.3 11.0 129 1971), was sampled in this study. member in the southern Cottonwood Creek valley (Fig. 3). Also shown is one Surpless#2/I-5:36 19.01.7 0.282921 0.000043 0.001191 0.282919 4.81.5 7.6 129 Surpless#2/I-5:1 12.41.8 0.283070 0.000028 0.000910 0.283068 10.11.0 12.9 132 Surpless#2/I-5:2 19.32.0 0.283116 0.000041 0.001463 0.283113 11.7 1.5 14.5 133 Cretaceous sedimentary rocks mapped in the southern Klamath Moun- sample from the Suncrest Road Quarry in the Klamath Mountains. All samples Surpless#2/I-5:5 22.12.3 0.282984 0.000036 0.001522 0.282980 7.01.3 9.9 133 Surpless#2/I-5:19 12.51.5 0.282977 0.000036 0.000828 0.282975 6.81.3 9.7 133 Surpless#2/I-5:22 22.51.9 0.283037 0.000040 0.001656 0.283033 8.91.4 11.8 134 Surpless#2/I-5:30 17.71.7 0.283020 0.000042 0.001232 0.283017 8.31.5 11.2 136 tains near the town of Cave Junction (Fig. 2A) have variously been considered contain a majority of Mesozoic ages, with Paleozoic and Precambrian grains Surpless#2/I-5:537.9 2.10.283053 0.000037 0.0005110.283051 9.51.3 12.4 136 Surpless#2/I-5:45 22.81.1 0.283052 0.000051 0.001809 0.283048 9.51.8 12.3 137 Surpless#2/I-5:103 15.61.4 0.283059 0.000077 0.001079 0.283056 9.72.7 12.7 138 part of the Great Valley Group (Knoxville Formation; e.g., Mankinen and Irwin, comprising 2%–14% in Bear Creek valley, and 7%–19% in Cottonwood Creek Surpless#2/I-5:4911.81.8 0.283006 0.000033 0.000742 0.283004 7.81.2 10.9 141 Surpless#2/I-5:54 65.11.7 0.283053 0.000038 0.004324 0.283042 9.51.3 12.2 141 Surpless#2/I-5:17 14.51.8 0.283058 0.000038 0.000918 0.283056 9.71.3 12.7 142 Surpless#2/I-5:62 23.91.4 0.282932 0.000052 0.001880 0.282927 5.21.8 8.2 142 1982), Myrtle Group (Days Creek Formation; Imlay et al., 1959), and Hornbrook valley. In total, 14 samples from both Bear Creek and Cottonwood Creek val- Surpless#2/I-5:63 10.81.9 0.283091 0.000031 0.000774 0.283089 10.81.1 13.9 142 Surpless#2/I-5:98 19.71.4 0.283002 0.000049 0.001299 0.282998 7.71.7 10.7 142 Surpless#2/I-5:48 16.51.8 0.282961 0.000044 0.001103 0.282958 6.21.6 9.3 143 Surpless#2/I-5:34 15.12.0 0.282997 0.000040 0.001107 0.282994 7.51.4 10.6 146 Formation (Batt et al., 2010). Very limited outcrop extent and poor age control leys contain a significant proportion of mid- to Late Cretaceous detrital zircons Surpless#2/I-5:4 12.91.9 0.283054 0.000039 0.000796 0.283052 9.51.4 12.7 149 Surpless#2/I-5:42 23.11.5 0.283057 0.000046 0.001553 0.283053 9.61.6 12.8 150 Surpless#2/I-5:76 25.31.8 0.282944 0.000045 0.002022 0.282938 5.61.6 8.8 151 make correlation of these Cretaceous outliers difficult, but detrital zircon age (120–85 Ma), with more variable proportions of Jurassic and Early Cretaceous Surpless#2/I-5:87 26.71.5 0.283052 0.000042 0.001784 0.283046 9.41.5 12.8 160 Surpless#2/I-5:10 18.01.7 0.282975 0.000054 0.001436 0.282971 6.71.9 10.3 167 Surpless#2/I-5:32 54.90.7 0.283015 0.000101 0.004455 0.283001 8.13.6 11.4 168 Surpless#2/I-5:84 17.51.5 0.283067 0.000048 0.001179 0.283063 10.01.7 13.6 168 signatures obtained here help to constrain depositional age and therefore po- grains (Fig. 3). Only the Klamath River Conglomerate, Osburger Gulch Sand- Surpless#2/I-5:38 32.91.4 0.282977 0.000045 0.002925 0.282968 6.81.6 10.2 169 Surpless#2/I-5:7 3.02.1 0.282900 0.000029 0.000287 0.282900 4.11.0 7.8 170 Surpless#2/I-5:95 10.51.4 0.283001 0.000057 0.000705 0.282998 7.62.0 11.3 170 tential correlations. stone, and Bear Creek valley sample of the Ditch Creek Siltstone member lack Surpless#2/I-5:2411.62.0 0.282891 0.000040 0.000950 0.282887 3.71.4 7.4 171 Surpless#2/I-5:28 18.51.5 0.282932 0.000047 0.001325 0.282928 5.21.7 8.9 171 Surpless#2/I-5:928.0 2.00.282987 0.000040 0.000684 0.282984 7.11.4 10.9 171 Surpless#2/I-5:91 10.61.9 0.282989 0.000033 0.000707 0.282986 7.21.2 10.9 172 abundant mid- to Late Cretaceous zircons. Surpless#2/I-5:39 26.81.6 0.282992 0.000033 0.001834 0.282986 7.31.2 10.9 173 Surpless#2/I-5:25 36.51.6 0.282885 0.000041 0.002541 0.282877 3.51.5 7.1 174 Surpless#2/I-5:27 15.61.8 0.282964 0.000037 0.000938 0.282961 6.31.3 10.1 174 Surpless#2/I-5:658.2 1.20.283055 0.000052 0.000716 0.283052 9.51.8 13.3 174 The detrital zircon age distribution of the newly recognized Barneburg Hill Surpless#2/I-5:21 15.42.3 0.283048 0.000026 0.001057 0.283044 9.30.9 13.1 176 Surpless#2/I-5:14 20.22.0 0.283025 0.000044 0.001786 0.283019 8.51.6 12.2 178 Surpless#2/I-5:59 63.51.1 0.283005 0.000069 0.004007 0.282992 7.82.4 11.3 178 DETRITAL ZIRCON AGE DISTRIBUTIONS AND member in the Bear Creek valley (Wiley et al., 2011) is nearly identical to that of Surpless#2/I-5:79 46.00.8 0.283030 0.000052 0.003021 0.283020 8.71.9 12.3 179 Surpless#2/I-5:33 15.61.6 0.283071 0.000041 0.001082 0.283068 10.11.5 14.1 183 Surpless#2/I-5:94 10.81.8 0.283031 0.000040 0.000691 0.283029 8.71.4 12.7 183 Surpless#2/I-5:156.3 2.20.282905 0.000026 0.000433 0.282903 4.20.9 8.3 185 HAFNIUM ISOTOPIC SIGNATURES the Ditch Creek Siltstone member in the Cottonwood Creek valley and the Sun- Surpless#2/I-5:68 10.41.4 0.282986 0.000045 0.000657 0.282984 7.11.6 11.2 185 Surpless#2/I-5:77 23.72.0 0.282951 0.000048 0.001399 0.282946 5.91.7 9.8 185 Surpless#2/I-5:8 18.52.3 0.282954 0.000026 0.001244 0.282950 6.00.9 10.0 187 crest Road Quarry sample, and it is very similar to the Rocky Gulch Sandstone Surpless#2/I-5:85 19.51.6 0.282994 0.000038 0.001406 0.282989 7.41.3 11.4 188 Surpless#2/I-5:866.9 1.80.282971 0.000044 0.000423 0.282970 6.61.5 10.7 189 Surpless#2/I-5:60 26.72.0 0.282978 0.000040 0.002069 0.282970 6.81.4 10.8 193 Surpless#2/I-5:72 13.91.5 0.282239 0.000041 0.001213 0.282214 -19.3 1.43.5 1057 Eleven sandstone samples and three quartzite cobbles were collected from sample in the Bear Creek valley. All of these samples are characterized by a the Ditch Creek Siltstone, Rocky Gulch Sandstone, and Barneburg Hill mem- dominant Late Cretaceous peak (ca. 90 Ma), few Early Cretaceous grains, and 2 Supplemental Table 2. Hafnium data. Please visit bers of the Hornbrook Formation. In addition, one sandstone sample from Cre- more Middle–Late Jurassic than Early Jurassic grains. Therefore, the Barne- http://dx .doi .org /10 .1130/GES01186 .S2 or the full-text article on www.gsapubs.org to view Supplemental taceous siliciclastic rocks in the Suncrest Road Quarry in the Klamath Moun- burg Hill member is placed stratigraphically above the Ditch Creek Siltstone Table 2. tains, ~80 km west-southwest of Ashland, Oregon (Fig. 2A), was collected to member within the Bear Creek valley section, although Wiley et al. (2011) con-

Figure 3. Histograms and superimposed probability density plots of detrital zircon age data for Mesozoic grains in the members of the Hornbrook Formation. Curves are composites of one to five samples from each member, are arranged in stratigraphic order within the Bear Creek and Cottonwood Creek valleys, and are aligned horizontally based on similar depositional age and similar detrital zircon age signatures. Green vertical bars highlight the age of the main Cretaceous batholith of the Sierra Nevada (e.g., Chen and Moore, 1982), with darker-green color indicating the age of the Late Cretaceous magmatic flare-up event in the Sierra Nevada (e.g., Ducea, 2001) and the early phase of magmatism in the Idaho batholith (Gaschnig et al., 2011). Data are from Surpless and Beverly (2013) for Cottonwood Creek valley Klamath River Conglomerate and Blue Gulch Mudstone samples, and for Bear Creek valley Osburger Gulch Sandstone (OGS), Rocky Gulch Sandstone (RGS), and Blue Gulch Mudstone (BGM) samples. DCS—Ditch Creek Siltstone; KRC—Klamath River Conglomerate.

sidered it to be stratigraphically lower than the Ditch Creek Siltstone member by an abundance of Middle–Late Jurassic to earliest Cretaceous ages (170– and disconformably overlain by the Blue Gulch Mudstone member. 130 Ma). The middle group contains abundant Late Cretaceous zircons with a The Mesozoic detrital zircon age distribution of these samples can be sub- dominant peak at 92 Ma, few Early Jurassic or Early Cretaceous zircons, and divided into three groups: (1) a lower group that includes the Klamath River a broad distribution of Middle–Late Jurassic zircons (175–145 Ma). The upper Conglomerate, Osburger Gulch Sandstone, and the Ditch Creek Siltstone in the group contains abundant Cretaceous and Jurassic zircons but is more variable Bear Creek valley; (2) a middle group that includes the Ditch Creek Siltstone in than the lower two groups. Very few earliest Cretaceous (140–125 Ma) grains the Cottonwood Creek valley, Barneburg Hill, and the Suncrest Road Quarry are present in any of these samples. sample; and (3) an upper group that includes the Rocky Gulch Sandstone and Paleozoic detrital zircons are present in several samples, but they are lim- Blue Gulch Mudstone (Fig. 4). The lower group contains no Late Cretaceous ited to a total of only 28 grains ranging from 538 to 252 Ma, with the ma- zircons and variable amounts of Early Jurassic zircons, and it is characterized jority of ages between 370 and 260 Ma (Fig. 5). Precambrian detrital zircons

100% are more abundant in the Cottonwood Creek valley samples than in the Bear 90% UPPER Creek valley samples, comprising up to 19% of any single sample, but they 80% typically constitute less than 10%. Precambrian ages from all Hornbrook 70% sandstone samples have been combined into one distribution (Fig. 6A) that includes two prominent modes ca. 1780 and 1400 Ma, with smaller modes 60% ca. 2470 Ma, 1100 Ma, and 556 Ma, and a spread of grains between 2000 and 50% 1300 Ma. Detrital zircon ages from quartzite cobbles collected from conglom- 40% erate units within the Klamath River Conglomerate, Rocky Gulch Sandstone, 30% BGM and Barneburg Hill members have been combined into one distribution (Fig. 20% 6B). Precambrian age modes are similar to those in the sandstone samples, 10% RGS but with only one prominent mode spanning 1850–1700 Ma, smaller modes at 0% ca. 1446 Ma, 1108 Ma, and 668 Ma, and several Late Archean–Paleoproterozoic 100% grains spanning 2900–2400 Ma. Lu-Hf isotopic analysis of selected Jurassic and Cretaceous grains from t 90% MIDDLE Rocky Gulch Sandstone, Ditch Creek Siltstone, Osburger Gulch Sandstone, 80% and Klamath River Conglomerate samples yielded positive, isotopically juve- 70% nile eHf values of +16 to +5 for all Jurassic and Early Cretaceous grains, and a Percen 60% larger spread of eHf values from +13 to –17 for Late Cretaceous grains (Fig. 7). 50% 40% SRQ (KM) 30% WHOLE-ROCK GEOCHEMISTRY BH 20% Cumulative 10% DCS (CCV) Geochemical analysis can help delineate the effects of weathering and 0% sedimentary sorting as well as characterize provenance composition (e.g., McLennan, 1989; McLennan et al., 1993). In total, 24 mudstone, siltstone, and 100% sandstone samples from the Hornbrook Formation were analyzed by induc- 90% LOWER tively coupled plasma–mass spectrometry (ICP-MS) and X-ray fluorescence 80% (XRF) at Washington State University, following procedures of Knaack et al. 70% (1994) and Johnson et al. (1999); data are presented in Table 1. 60% 50% 40% DCS (BCV) Major-Element Geochemistry 30% OGS Major elements are susceptible to postdepositional mobility resulting from 20% chemical weathering and diagenesis, so the degree of weathering can be esti 10% KRC mated using the chemical index of alteration (CIA; Nesbitt and Young, 1982). 0% The CIA is a ratio of the mole proportions of Al O over the sum of Al O , K O, 50 75 100 125150 175 200225 250 2 3 2 3 2 Na O, and CaO*, where CaO* is calculated by correcting for apatite using val- Age (Ma) 2 ues of P2O5 following McLennan et al. (1993). If the remaining CaO is less than

Figure 4. Cumulative probability plots of Mesozoic detrital zircon ages from the Hornbrook Na2O, then this value is used as CaO*; if the remaining CaO is more than Na2O, Formation, grouped into lower (Klamath River Conglomerate [KRC], Osburger Gulch Sand- then Na2O is considered equivalent to CaO*. Because weathering generally stone [OGS], and Ditch Creek Siltstone [DCS] in the Bear Creek valley), middle (Ditch Creek removes Ca faster than Na, this method to determine CaO* produces mini- Siltstone in Cottonwood Creek valley, Barneburg Hill [BH], and Suncrest Road Quarry [SRQ]), and upper members (Rocky Gulch Sandstone [RGS] and Blue Gulch Mudstone [BGM]) based mum CIA values (by up to ~3%; Mongelli et al., 2006). The ratio is multiplied by on depositional age and detrital zircon age signatures; CCV—Cottonwood Creek valley; BCV— 100, such that fresh igneous and metamorphic rocks have CIA values of 45–55, Bear Creek valley; KM—Klamath Mountains. Green vertical bars highlight the age of the main shale has CIA values of 65–75, and pure aluminosilicate weathering products, Cretaceous batholith of the Sierra Nevada (e.g., Chen and Moore, 1982), with darker-green color indicating the age of the Late Cretaceous magmatic flux event in the Sierra Nevada (e.g., such as kaolinite, have a CIA value of 100 (Taylor and McLennan, 1985; Mc- Ducea, 2001) and the early phase of magmatism in the Idaho batholith (Gaschnig et al., 2011). Lennan et al., 1993). Weathering trends depicted on A-CN-K and A-CNK-FM

5 Hornbrook Formation 4 All Sandstone Samples n=28 3

1 Number of grains

250300 350400 450500 550 Age (Ma)

Figure 5. Composite histogram and superimposed probability density plot of all Paleozoic detrital zircon grains from all members of the Hornbrook Formation. Data are from Surpless and Beverly (2013) and this study.

diagrams (where A = Al2O3, C = CaO*, N = Na2O, K = K2O, F = total Fe as FeO, Trace-Element Geochemistry and M = MgO; after Nesbitt and Young, 1984, 1989) largely result from the con- version of feldspar and glass to clay minerals (McLennan et al., 1990). Mixing Trace elements (large ion lithophile elements [LILEs], high field strength provenance components of different weathering histories or compositions, as elements [HFSEs], and rare earth elements [REEs]) can be powerful prove- well as diagenetic reactions involving addition or loss of these elements, will nance indicators because of low postdepositional mobility and exclusion from shift samples away from expected weathering trends. seawater (McLennan et al., 1993). In addition, immobile trace elements can Hornbrook Formation samples separate according to grain size on A-CN-K highlight differences between samples (Ryan and Williams, 2007), revealing and A-CNK-FM diagrams (Fig. 8). Sandstone samples have CIA values of 62–67, changes within basin stratigraphy and between basins. with an average of 64, suggesting extensive weathering and/or diagenetic al- Comparing incompatible elements Th and Zr against the compatible element teration, and siltstone and mudstone CIA values range from 71 to 89, with an Sc provides a measure of the relative importance of magmatic versus sedimen- average value of 77 (Fig. 8A). The finer-grained samples plot largely in the trail- tary processes within the source region (e.g., Fralick, 2003). Th/Sc ratio increases ing edge (passive margin) tectonic setting for mudstones of McLennan et al. with magmatic differentiation, whereas sedimentary recycling concentrates zir- (1990), and sandstone samples plot between the forearc tectonic setting for con and thereby increases the Zr/Sc ratio (McLennan et al., 1990). A plot of Zr/Sc sands and trailing edge tectonic setting for muds, within a region typified by versus Th/Sc shows enrichment in Zr in all sandstone relative to fine-grained sands within continental collision, strike-slip, and/or backarc tectonic settings samples, and most samples plot along a trend between andesite and upper-crust (Fig. 8A; McLennan et al., 1990). Only the Klamath River Conglomerate sam- granodiorite values, with Blue Gulch Mudstone sandstone clustering around ple plots along the weathering trend of island-arc andesite; all other samples granodiorite values (Fig. 9A; values from Taylor and McLennan, 1985). plot between the weathering trends for island-arc andesite and upper crust A ternary plot of incompatible elements La and Th and compatible ele- on the A-CN-K diagram (Fig. 8A). Hornbrook Formation samples largely plot ment Sc provides another discriminator between juvenile (Sc-enriched) and between weathering trends for andesite and granodiorite compositions on an evolved (La- and Th-enriched) crust (Bhatia and Crook, 1986; McLennan et al., A-CNK-FM diagram, with a greater spread in apparent source rock composi- 1990, 1993). Hornbrook samples plot between island-arc andesite and upper tions in the sandstone samples than the fine-grained samples (Fig. 8B). The continental crust, with lower Hornbrook samples (Klamath River Conglomer- lower Hornbrook Formation samples (Klamath River Conglomerate, Osburger ate, Osburger Gulch Sandstone, and Ditch Creek Siltstone) plotting closest to Gulch Sandstone, and Ditch Creek Siltstone) appear more intermediate in com- island-arc andesite, upper Hornbrook Blue Gulch Mudstone samples closest to position, whereas the upper Hornbrook Formation (Rocky Gulch Sandstone North American shale composite (values from Gromet et al., 1984) and upper and Blue Gulch Mudstone) straddles the granodiorite weathering trend, and continental crust, and upper Hornbrook Rocky Gulch Sandstone samples the Blue Gulch Mudstone sandstone samples show the most felsic sources. showing the greatest spread (Fig 9B). The higher proportion of Precambrian detrital zircons in the three detrital zir- A negative europium anomaly is associated with intracrustal differentiation con samples from the Blue Gulch Mudstone (14% and 19%; Fig. 3) suggests an or crystallization of a plagioclase-rich mantle melt that separates plagioclase increase in nonarc sediment sources, perhaps contributing to the more felsic through partial melting and/or crystal fractionation (e.g., McLennan et al., 1993). geochemical signature of the Blue Gulch Mudstone sandstone samples (Fig. The europium anomaly is given as Eu/Eu*, where Eu* is the square root of the 8). The Hornbrook samples are more extensively weathered and/or altered product of Sm and Gd concentrations (ppm). Therefore, a plot of Th/Sc versus than samples expected in typical forearc basins, and they include abundant Eu/Eu* can differentiate different provenance types (Fig. 9C). All but two Horn- intermediate to felsic source material. brook samples plot within the young differentiated arc field (Eu/Eu* ~0.5–0.9

20 Southwestern Klamath Mountains & Grenville Laurentia Northern Laurentia western Sierra Nevada 15 Hornbrook Formation A All Sandstone Samples; n=102 Data from Surpless and Beverly (2013) 10 and this study 5

Hf(i ) 0

Ɛ Sierra Nevada Fine Gold Intrusive Suite -5 Hornbrook Formation B All Quartzite Cobbles; n=353 -10 RGS Data from Surpless and Beverly (2013) Idaho Batholith DCS and this study (early metaluminous phase) -15 OGS KRC -20 50 75 100125 150 175 200 225 Age (Ma) Snow Lake pendant, Sierra Nevada C Figure 7. Detrital zircon vs. age plot for selected zircon grains from Hornbrook Formation n = 226; Memeti et al. (2010) and εHf Grasse et al. (2001) sandstone samples. Data for Klamath River Conglomerate (KRC), Osburger Gulch Sandstone (OGS), and Rocky Gulch Sandstone (RGS) samples are from Surpless and Beverly (2013); data for two Ditch Creek Siltstone (DCS) samples are from this study. Shaded areas represent the

range of zircon εHf values vs. age for plutons in the Klamath Mountains and western Sierran terranes (Todt et al., 2011), the Fine Gold intrusive suite in the Sierra Nevada (Lackey et al., 2012), and the Idaho batholith (Gaschnig et al., 2011).

Central North American Passive Margin D n = 1237; Gehrels and Pecha (2014) and Th/Sc <1; field values from McLennan et al., 1993). Two Blue Gulch Mud- stone samples plot within the overlapping old upper continental crust and recycled sedimentary rocks fields (Eu/Eu* ~0.6–0.7 and Th/Sc values = 1; field values from McLennan et al., 1993), consistent with the higher proportion of Precam- brian detrital zircon in the Blue Gulch Mudstone (Fig. 3). Chondrite-normalized rare earth element diagrams reveal little variability between Hornbrook sam-

Blue Mountains Jurassic strata ples; all samples show light (L) REE enrichment and intermediate europium E n = 163; LaMaskin et al. (2011) anomalies (Fig. 10).

DISCUSSION Depositional Ages and Stratigraphy

700100013001600190022002500280031003400 Maximum depositional ages interpreted from the youngest robust detrital Age (Ma) zircon ages present in a sample can increase the precision of biostratigraph- ically determined depositional age ranges and thereby improve estimates of Figure 6. Detrital zircon age signatures for Precambrian grains from the Hornbrook Formation sedimentation rate, provenance changes, and correlation within the Horn- and possible source regions (only grains older than 550 Ma are plotted). Colored vertical shading brook Formation. Following Dickinson and Gehrels (2009), the maximum highlights inferred original crystalline sources of zircon. Plots show composite probability density plots of detrital zircon from: (A) all Hornbrook Formation sandstone samples; (B) Hornbrook deposi tional age for Hornbrook Formation samples is estimated by calculat- Formation quartzite cobbles collected from the Klamath River Conglomerate, Rocky Gulch ing the weighted mean of the youngest three or more grains that overlap at Sandstone, and Barneburg Hill members; (C) the Snow Lake pendant in the central Sierra Ne- 2s. In addition, I report the age and uncertainty of the youngest Gaussian age vada (data from Memeti et al., 2010; Grasse et al., 2001); (D) the Central North American passive margin (Gehrels and Pecha, 2014); and (E) Blue Mountains Jurassic strata (LaMaskin et al., 2011). distribution within the sample, as determined by the “Unmix ages” routine in Isoplot version 4.15.11.10.15 (Ludwig, 2011).

TABLE 1. WHOLE-ROCK MAJOR- AND TRACE-ELEMENT GEOCHEMICAL DATA Member Klamath River Cgl Osburger Gulch Sandstone Ditch Creek Siltstone Rocky Gulch Sandstone Sample: 07-KRC-03 07-OGS-17 07-OGS-14 07-OGS-13 07-OGS-11 07-DCS-16 13-DCS-0113-DCS-0307-RGS-30 07-RGS-29 13-RGS-04 13-RGS-05 13-RGS-09 Rock type: ms ss ss ss ss ss ms ms ss ms ms ms ms

SiO2 (wt%) 47.59 58.41 61.27 57.76 57.97 61.42 55.03 56.97 63.66 53.45 53.45 55.67 58.41

TiO2 (wt%) 1.152 0.852 0.860 0.990 1.089 0.829 0.8880.781 0.5650.796 0.8640.822 0.748

Al2O3 (wt%) 22.92 14.71 15.33 15.46 14.59 14.36 18.28 17.22 15.00 17.49 19.02 18.32 17.95 FeO* (wt%) 7.03 6.84 6.48 7.00 8.54 5.27 6.86 5.57 4.19 6.40 6.71 6.32 5.63 MnO (wt%) 0.057 0.113 0.095 0.112 0.114 0.096 0.0590.060 0.0520.045 0.0580.053 0.053 MgO (wt%) 2.75 2.54 2.41 2.55 3.36 1.79 3.45 3.38 2.35 3.18 3.69 3.35 2.87 CaO (wt%) 0.91 4.53 2.83 4.57 3.28 3.54 1.84 3.24 2.97 2.06 1.74 1.55 1.26

Na2O (wt%) 0.53 3.37 3.61 3.29 3.24 2.59 1.32 2.12 3.37 1.17 1.45 1.73 1.84

K2O (wt%) 1.82 2.20 2.50 2.47 2.31 2.68 2.67 2.81 2.38 3.11 3.35 3.17 3.00

P2O5 (wt%) 0.037 0.144 0.125 0.125 0.136 0.101 0.1820.191 0.1720.168 0.1600.1620.162 Sum (wt%) 84.79 93.71 95.52 94.35 94.63 92.67 90.57 92.35 94.70 87.85 90.48 91.15 91.91 Inductively coupled plasma–mass spectrometry (ICP-MS) data (ppm) La 30.02 18.18 17.52 16.46 16.43 15.31 23.2019.58 24.1420.18 26.7617.69 26.94 Ce 62.13 38.95 37.59 35.07 35.79 30.18 46.0737.64 46.3534.50 46.9234.27 52.53 Pr 7.98 5.13 4.90 4.60 4.63 3.62 5.73 4.38 5.53 4.88 6.04 4.17 6.37 Nd 30.80 20.92 20.12 19.15 19.33 14.03 22.3816.35 20.5218.96 23.1316.05 24.48 Sm 6.28 5.02 4.86 4.59 4.62 3.13 4.91 3.37 4.16 4.24 4.75 3.51 5.09 Eu 1.51 1.27 1.26 1.19 1.18 0.80 1.19 0.76 1.03 0.99 1.11 0.90 1.13 Gd 5.08 4.76 4.58 4.45 4.50 2.92 4.38 2.68 3.49 3.93 4.22 3.18 4.56 Tb 0.80 0.79 0.76 0.71 0.73 0.51 0.71 0.42 0.54 0.66 0.67 0.54 0.72 Dy 4.66 4.88 4.60 4.44 4.48 3.15 4.26 2.62 3.18 4.03 4.03 3.49 4.46 Ho 0.88 1.00 0.93 0.90 0.92 0.68 0.86 0.54 0.63 0.85 0.81 0.71 0.89 Er 2.45 2.75 2.58 2.43 2.52 1.89 2.38 1.55 1.69 2.38 2.21 2.09 2.47 Tm 0.37 0.40 0.38 0.36 0.36 0.28 0.36 0.24 0.25 0.36 0.34 0.32 0.37 Yb 2.33 2.60 2.40 2.26 2.32 1.80 2.31 1.62 1.57 2.34 2.27 2.112.36 Lu 0.36 0.41 0.39 0.35 0.36 0.29 0.37 0.26 0.25 0.38 0.37 0.34 0.37 Ba 451 589 666 687 592 748 670714 831650 705760 928 Th 9.74 9.08 7.67 5.93 6.68 6.90 7.83 8.52 7.90 7.79 8.62 7.74 9.07 Nb 13.41 7.31 6.85 6.04 6.03 6.64 11.7112.11 9.83 10.70 12.2011.23 11.68 Y 20.96 25.01 23.42 22.50 23.23 17.24 21.3913.17 16.1221.60 20.8718.92 22.78 Hf 4.51 8.33 7.35 5.18 5.25 6.13 3.05 3.19 4.11 3.09 3.04 3.01 3.44 Ta 0.92 0.56 0.51 0.46 0.47 0.51 0.83 0.86 0.77 0.73 0.86 0.78 0.83 U 2.00 2.80 2.43 2.02 2.27 2.56 3.19 3.01 3.06 4.61 3.98 3.01 3.41 Pb 10.27 7.28 7.02 7.32 6.99 7.72 20.2025.47 12.1219.52 22.8020.55 21.24 Rb 73.9 61.8 65.9 62.2 53.1 77.0 106.9109.5 77.4 145.0134.3 123.4114.8 Cs 3.95 3.15 3.56 2.33 1.87 3.81 8.29 6.92 2.18 7.07 9.69 7.16 6.20 Sr 115 284 323 305 299 235 142244 412355 158170 168 Sc 33.1 22.7 21.1 19.7 21.6 14.5 22.7 17.3 11.0 21.2 21.3 19.9 18.4 Zr 156 303 265 183 189 219 105112 146105 106104 120 X-ray ﬂuroescence (XRF) data (ppm) Cr 227 136 110 89 101 48 89 62 45 95 80 86 76 Ni 170 31 34 25 24 9 51 38 19 50 44 48 41 V 230 219 184 159 173 131 186 148 99 191 183 172 140 Ga 25 16 16 15 16 13 23 22 16 25 25 24 24 Cu 163 34 41 35 34 33 91 61 20 75 93 75 64 Zn 117 80 78 70 71 76 149 128 73 152 146 133 126 (continued)

TABLE 1. WHOLE-ROCK MAJOR- AND TRACE-ELEMENT GEOCHEMICAL DATA (continued) Member Blue Gulch Mudstone Sample: 07-BGM-04 07-BGM-05 07-BGM-06 07-BGM-21 07-BGM-250 07-BGM-2607-BGM-2807-BGM-2207-BGM-2307-BGM-2713-BGM-01 Rock type: ss ss ss ss (concretion) ss ss ss ms ms ms ms

SiO2 (wt%) 66.41 66.74 67.74 53.93 63.49 59.81 62.04 56.16 56.99 60.43 59.11

TiO2 (wt%) 0.522 0.510 0.496 0.449 0.643 0.6600.631 0.7970.774 0.6920.745

Al2O3 (wt%) 15.11 14.78 14.61 10.53 13.46 12.87 12.47 18.45 18.22 16.30 17.66 FeO* (wt%) 3.90 3.60 3.38 2.60 5.08 4.66 3.92 5.80 5.96 6.73 5.76 MnO (wt%) 0.040 0.038 0.038 0.310 0.110 0.2040.149 0.0600.032 0.0360.054 MgO (wt%) 1.89 1.75 1.56 0.99 1.92 1.83 1.78 2.33 2.29 2.79 2.94 CaO (wt%) 1.54 1.78 1.80 13.44 3.27 6.31 5.63 0.82 0.90 0.82 1.53

Na2O (wt%) 3.52 3.55 3.75 2.46 2.56 2.37 2.39 1.40 1.36 1.93 1.86

K2O (wt%) 2.51 2.42 2.37 1.49 1.70 1.92 1.83 2.68 2.65 2.30 2.92

P2O5 (wt%) 0.143 0.154 0.156 0.090 0.257 0.1780.192 0.1470.206 0.1690.177 Sum (wt%) 95.59 95.33 95.90 86.29 92.49 90.81 91.03 88.64 89.38 92.19 92.75 Inductively coupled plasma–mass spectrometry (ICP-MS) data (ppm) La 26.99 31.58 32.15 15.36 20.34 22.8723.50 24.4525.34 21.9626.81 Ce 53.86 62.74 64.39 29.50 39.83 44.7947.46 48.5449.20 42.6752.53 Pr 6.27 7.31 7.51 3.58 5.04 5.55 6.19 6.08 6.26 5.30 6.35 Nd 23.71 27.64 27.92 13.64 19.66 21.3425.07 24.0624.32 20.3324.06 Sm 4.78 5.53 5.57 2.76 4.32 4.52 5.66 5.32 5.38 4.35 5.02 Eu 1.05 1.14 1.10 0.69 1.21 1.06 1.44 1.32 1.27 1.04 1.11 Gd 4.16 4.69 4.66 2.37 3.97 3.99 5.54 4.73 4.72 3.87 4.33 Tb 0.64 0.73 0.72 0.37 0.65 0.64 0.91 0.78 0.77 0.64 0.69 Dy 3.73 4.28 4.13 2.22 3.82 3.83 5.57 4.82 4.67 3.92 4.20 Ho 0.74 0.85 0.84 0.45 0.80 0.78 1.14 0.98 0.98 0.81 0.83 Er 2.02 2.29 2.24 1.27 2.19 2.17 3.03 2.76 2.76 2.28 2.36 Tm 0.30 0.33 0.33 0.19 0.32 0.32 0.43 0.41 0.42 0.34 0.35 Yb 1.88 2.08 2.10 1.23 2.03 2.04 2.56 2.60 2.63 2.19 2.28 Lu 0.30 0.33 0.33 0.20 0.32 0.33 0.39 0.42 0.43 0.35 0.36 Ba 850 820 887 676 871 857991 816864 853804 Th 7.88 9.28 9.62 4.50 6.39 7.34 6.85 10.259.247.828.79 Nb 9.47 9.51 9.63 4.94 6.77 7.38 7.12 9.00 9.33 8.15 11.75 Y 18.55 21.71 21.49 12.14 21.64 21.0432.73 25.6224.90 20.5821.25 Hf 5.23 6.22 6.26 3.22 4.57 5.67 5.08 3.43 3.62 3.55 3.78 Ta 0.70 0.74 0.75 0.37 0.52 0.57 0.55 0.67 0.67 0.61 0.82 U 2.37 2.58 2.57 1.53 2.53 2.74 2.71 3.40 3.04 2.92 3.24 Pb 12.46 12.06 12.61 6.11 8.92 9.60 10.7522.56 19.98 16.9622.91 Rb 84.6 79.4 75.5 42.0 55.0 58.9 59.5 110.3105.1 90.8 105.5 Cs 2.80 2.55 2.26 1.54 3.07 2.93 3.36 9.90 8.13 6.72 5.97 Sr 328 331 332 260 185 244243 150143 155187 Sc 10.3 9.7 9.7 8.3 13.3 13.7 11.2 18.1 18.2 15.8 17.2 Zr 183 219 221 117 163 204185 116123 122133 X-ray ﬂuroescence (XRF) data (ppm) Cr 47 50 47 31 48 50 50 82 79 63 73 Ni 15 13 13 6 17 17 17 39 34 29 41 V 90 86 82 80 120 126 111 196 188 173 136 Ga 17 17 16 10 14 12 13 21 21 17 23 Cu 10 8 8 7 25 21 24 69 69 48 61 Zn 67 63 60 41 75 72 79 158 152 145 132

AB A Kaolinite, A Kaolinite, 100 Chlorite, sandstone Gibbsite Gibbsite shale/silty shale 90 BGM Illite Muscovite 80 RGS

Smectite DCS Muscovite 70 Feldspar

CI A OGS KRC 60 Granodiorite Andesite Plagioclase 50 K-Feldspar Basalt Upper crust Island arc andesite 40 CN (40%) K (40%) CNK FM forearc tectonic setting for sands

forearc tectonic setting for muds

trailing edge tectonic setting for sands

trailing edge tectonic setting for muds

Figure 8. (A) A-CN-K plot vs. chemical index of alteration (CIA), after McLennan et al. (1990), where A—Al2O3, CN—CaO (silicate fraction only) + Na2O, and K—K2O (after Nesbitt and Young, 1984, 1989). Arrows indicate predicted paths for increasing weathering intensities; Hornbrook Formation samples form a mix between trailing

edge and forearc tectonic settings. (B) A-CNK-FM plot after McLennan et al. (1993) where A—Al2O3, CNK—CaO (silicate fraction only) + Na2O + K2O, and FM—FeO + MgO (after Nesbitt and Young, 1984, 1989). Also plotted are compositions of major minerals and rock types; arrows indicate general weathering trends typical of the various rock types. KRC—Klamath River Conglomerate; OGS—Osburger Gulch Sandstone; DCS—Ditch Creek Siltstone; RGS—Rocky Gulch Sandstone; BGM—Blue Gulch Mudstone.

The Ditch Creek Siltstone member contains pelecypods, gastropods, am- nifera collected from a site east of Medford (northern Bear Creek valley) monites, and foraminifera that indicate middle Turonian (92.2–90.5 Ma) depo- that was previously mapped as part of the Rocky Gulch Sandstone member sition in the Bear Creek valley and late Turonian–Coniacian (90.5–86.3 Ma) by Nilsen (1984, 1993). Detrital zircon ages presented here are from sam- deposition in the Cottonwood Creek valley (Nilsen, 1993). In the Bear Creek ples collected south of this locality, within the Barneburg Hill conglomer- valley, the I-5 sample from the middle of the Ditch Creek Siltstone has a maxi ate, which was previously mapped as the basal conglomerate of the Paleo- mum depositional age of 90.5 ± 2 Ma, with the same value resulting from a gene Payne Cliffs Formation (McKnight, 1971) and is now considered part weighted mean of the youngest four grains and the Unmix routine. Both Ditch of the upper Barneburg Hill member by Wiley et al. (2011). These samples Creek Siltstone samples from the Cottonwood Creek valley have maximum have maximum depositional ages within Turonian–Santonian time (93.9– depositional ages within Coniacian time: The Rickety Bridge sample from the 83.6 Ma). Sample 13-HBF-01 has a late Turonian–early Coniacian maximum middle-upper Ditch Creek Siltstone has a maximum depositional age of 87.4 ± depositional age of 89.1 ± 1.6 Ma (n = 9, weighted mean) or 91.3 ± 1.1 Ma 0.9 Ma (n = 15, weighted mean age) or 87.0 ± 1.3 Ma (Unmix), and sample (Unmix), whereas sample 08-PC-02 has a Santonian maximum depositional 13-DCS-02 from the upper Ditch Creek Siltstone has a maximum depositional age of 84.5 ± 0.7 Ma (n = 7, weighted mean) or 84.5 ± 0.8 Ma (Unmix). These age of 87.2 ± 1.2 Ma (n = 10, weighted mean) or 89.1 ± 0.8 Ma (Unmix). Thus, detrital zircon maximum depositional ages suggest that the Barneburg Hill detrital zircon maximum depositional ages are consistent with time-transgres- member at this location is slightly younger than the Turonian Ditch Creek sive deposition in the Ditch Creek Siltstone member. Siltstone member in the Bear Creek valley, and the same age or younger The proposed Barneburg Hill member of the Bear Creek valley was con- than the Coniacian Ditch Creek Siltstone member in the Cottonwood sidered middle Turonian (92.2–90.5 Ma; Wiley et al., 2011) based on forami Creek valley.

AB10 La

Upper crust ) (granodiorite) BGM zircon addition 1 RGS (sedimentary recycling DCS Passive c continental OGS margin mudstone

Th/S KRC UCC Andesite sandstone NASC 0.1 island-arc andesite

Magmatic-arc MORB related compositional variation 0.0 0.11 10 100 1000

Zr/Sc N-MORB Th Sc 10.00 C EVOLVED recycled Figure 9. (A) Th/Sc vs. Zr/Sc plot after McLennan et al. (1990, sedimentary 1993); values for andesite and upper crust granodiorite are from

rocks c Taylor and McLennan (1985), mid-ocean-ridge basalt (MORB) 1.00 value is from Sun and McDonough (1989). Hornbook Formation old upper sandstone and mudstone samples plot along similar trends, c continental with sandstone samples showing higher Zr/Sc ratios than mud- crust stone samples. (B) Ternary plot of La-Th-Sc; upper continental

Th/S crust (UCC), North American shale composite (NASC), island-arc andesite, and normal MORB (N-MORB) are from Taylor and Mc- young differentiated arc 0.10 Lennan (1985) and McLennan et al. (1993). Passive-margin and magmatic-arc–related fields are from McLennan et al. (1993). young undifferentiated ar (C) Th/Sc vs. Eu/Eu* after McLennan et al. (1993) to distinguish potential source regions. KRC—Klamath River Conglomerate; OGS—Osburger Gulch Sandstone; DCS—Ditch Creek Siltstone; JUVENILE 0.01 RGS—Rocky Gulch Sandstone; BGM—Blue Gulch Mudstone. 0.40.6 0.81 Eu/Eu*

Nilsen (1993) reported that the Rocky Gulch Sandstone lacks fossil age depositional age, requiring that deposition of the Rocky Gulch Sandstone in control, with the exception of the middle Turonian foraminifera collected the Cottonwood Creek valley began no earlier than Coniacian time (89.8 Ma) from a section east of Medford that Wiley et al. (2011) remapped as part of and may have extended into Santonian time (beginning 83.6 Ma). the Barneburg Hill member. Surpless and Beverly (2013) reported a maximum Wiley et al. (2011) noted the presence of a possible middle Coniacian–middle depositional age of 86 Ma in one Rocky Gulch Sandstone sample from the Campanian disconformity between the Ditch Creek Siltstone and the Rocky Bear Creek valley near Ashland. Five detrital zircon samples were collected Gulch Sandstone in the Bear Creek valley, on the basis of the absence of de- from a continuous section of the Rocky Gulch Sandstone in the Cottonwood finitive middle–late Coniacian, Santonian, and early–middle Campanian fossil Creek valley; the basal sample, 13-RGS-01, has a maximum depositional age of assemblages (Peck et al., 1956; Elliott, 1971), but Nilsen (1993) suggested only 89.7 ± 1.3 Ma (n = 11, weighted mean) or 91 ± 1 Ma (Unmix), and the uppermost local erosion based on his collection of mega- and microfossil ages within that sample, 13-RGS-08, has a maximum depositional age of 86.3 ± 1.7 Ma (n = 6, time span. In the Bear Creek valley, detrital zircon ages yield a late Turonian weighted mean) or 86.7 ± 2 Ma (Unmix). These ages permit deposition begin- maximum depositional age for the middle Ditch Creek Siltstone member and a ning as early as late Turonian and continuing through at least Coniacian time. Santonian maximum depositional age for the Rocky Gulch Sandstone member, However, these Rocky Gulch Sandstone samples were collected from a contin- consistent with a possible disconformity between these members (Surpless uous stratigraphic section above 13-DCS-02, which has a Coniacian maximum and Beverly, 2013). However, in the Cottonwood Creek valley, Coniacian maxi-

1000 the Myrtle Group (Imlay et al., 1959), was deposited no earlier than Coniacian A time and is time-correlative with the Hornbrook Formation. Idaho Batholith: Taken together, these maximum depositional ages are consistent with Early metaluminous phase time-transgressive deposition of the Hornbrook Formation; deposition oc- (Gaschnig et al., 2011) 100 curred first in the Bear Creek valley to the north before deposition in the Cot- tonwood Creek valley to the south. In addition, these detrital zircon deposi tional age constraints, combined with biostratigraphic ages, suggest that most Hornbrook Formation deposition took place in Coniacian–Campanian time (89.8–72.1 Ma). However, estimation of sedimentation rates through this 10 period is hampered by the variable thickness of members, time-transgressive Hornbrook Formation deposition, and the possible presence of one or more disconformities within the section.

1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Y Sediment Sources 1000 B Given that the Hornbrook basin lies inboard of proposed translated ter-

All Sierra Nevada data ranes associated with the Baja–British Columbia hypothesis (e.g., Cowan et al., (Cecil et al., 2011) 1997), and that the Klamath Mountains were displaced westward in Late Ju- 100 rassic or Early Cretaceous time (Irwin, 1960; Jones and Irwin, 1971; Constenius Northern Sierran Cretaceous plutons (Cecil et al., 2011) et al., 2000; Ernst et al., 2008; Batt et al., 2010; Ernst, 2013), the current config- uration between the Sierra Nevada Foothills metamorphic belt and correla tive units in the Klamath Mountains was established prior to deposition of 10 the Hornbrook Formation on the eastern Klamath Mountains. Restoring 38° of post-Albian clockwise rotation (Housen and Dorsey, 2002) places the Blue Mountains Province of central and eastern Oregon close to the Hornbrook For- Hornbrook Formation mation by 90 Ma (Fig. 11). Nilsen (1993) and others (summarized in Nilsen, 1984) suggested that Horn- 1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Y brook Formation sediment was wholly derived from the Klamath Mountains,

Figure 10. Comparison of chondrite-normalized rare earth element but detrital zircon U-Pb age and hafnium isotopic compositions led Surpless (REE) plots for the Hornbrook Formation (shown in diagonal line and Beverly (2013) to suggest that only the lower Hornbrook Formation pattern) with (A) the early metaluminous phase of the Idaho batho- (Klamath River Conglomerate, Osburger Gulch Sandstone, Ditch Creek Silt- lith (data from Gaschnig et al., 2011), and (B) all available REE data from the central and southern Sierra Nevada batholith (light-gray stone in Bear Creek valley) could have had solely Klamath Mountains prove- shading; data compiled by Cecil et al. [2012] from the North Amer- nance, and that much of the Hornbrook Formation sediment was derived from ican volcanic and intrusive rock database [NAVDAT; www.navdat the Sierra Nevada and northern Nevada, with additional sediment input .org]) and Cretaceous plutons of the northern Sierra Nevada (blue from the Blue Mountains possible. lines; data from Cecil et al., 2012). Chondrite values are from Sun and McDonough (1989). The Coniacian and younger members of the Hornbrook Formation, particularly in the middle group (Fig. 4), are characterized by abundant 100–85 Ma

detrital zircon with eHf values that range from +13 to –17 (Fig. 7). Whole-rock mum depositional ages for both the Ditch Creek Siltstone and the Rocky Gulch geochemical analysis of these Hornbrook members (Ditch Creek Siltstone, Sandstone indicate no major disconformity between these members, suggest- Rocky Gulch Sandstone, and Blue Gulch Mudstone) indicates provenance ing that any Coniacian–Santonian disconformity was not basinwide. in the young differentiated arc field, with source-rock average compositions The Suncrest Road Quarry sample collected from the Suncrest Road between island-arc andesite and the North American shale composite and Quarry ~80 km west-southwest of Ashland, Oregon (Fig. 2A), yields a maxi- upper continental crust (Fig. 9). The Late Cretaceous age range that charac- mum depositional age of 89.3 ± 0.7 Ma (n = 23, weighted average) or 89.4 ± terizes most of the Coniacian and younger Hornbrook strata aligns well with 0.8 Ma (Unmix). Thus, this Cretaceous outlier in the Klamath Mountains, previ- a volumetrically significant magmatic flare-up event in the Sierra Nevada ously considered part of the Valanginian–Barremian Days Creek Formation of batholith and with the early phase of magmatism in the Idaho batholith, but it

Cretaceous sedimentary basins (outcrop area; ? HF—Hornbrook Formation; SRQ—Suncrest Road Quarry) 90–85 Ma Blue Mountains Cretaceous plutonic belts of the Sierra Nevada

? Possible extent of early (98–87 Ma) metaluminous

Klamath Z plutons of the Idaho batholith and border zone suite Mountains IS Figure 11. Paleogeographic cartoon for W Discontinuous mid- to Late Cretaceous 90–85 Ma showing inferred drainage path- ? plutonic belts ways into the Hornbrook basin region from the south and east. Following Wyld Cretaceous subduction complex ? HF et al.’s (2006) reconstruction, Cenozoic assemblages Basin and Range extension, western Cali SRQ ? Hornbrook fornia strike-slip faulting, and post-Creta- ? Basin ? Triassic and Paleozoic basinal terranes ceous rotation of the Blue Mountains have been restored. The extent of Cretaceous Paleozoic and/or Early Mesozoic volcanic Sierran magmatism is based on the paleo- ? arc assemblages (BRT—Black Rock Terrane) geographic map of Van Buer et al. (2009), BRT and the possible extent of Idaho batho- Late Paleozoic to early Mesozoic lith magmatism was estimated based on subduction complexes present mapped exposure of the batholith. Location of the margin of the elevated Nevadaplano is after Sharman et al. (2015), Elevated Nevadaplano Late Proterozoic to Permian miogeocline Great and Cretaceous sea level is after Surpless Valley and Beverly (2013), Sharman et al. (2015), Approximate extent of Cretaceous sea Basin and this study.

N Sierra Approximate boundary of elevated Nevadaplano Nevada 100 km Fluvial systems

western Idaho shear zone (WISZ)

does not have a source within the Klamath Mountains or the Blue Mountains. formed a larger, more continuous igneous complex than modern preserva-

Although they may be nonunique discriminators, eHf values and whole-rock tion suggests. geochemical signatures from the Hornbrook strata help differentiate between West and southwest of the Late Cretaceous Idaho batholith, the Blue Moun- Late Cretaceous sources entirely within the Idaho batholith, the Sierran arc, or tains Province includes Paleozoic and early Mesozoic island-arc and subduc- a combination of the two. tion-accretion assemblages that are unconformably overlain by Triassic–Juras- sic clastic deposits (Dickinson and Thayer, 1978; Dorsey and LaMaskin, 2007; LaMaskin et al., 2008). The Blue Mountains contain Triassic–Lower Jurassic Idaho Batholith ± Blue Mountains Source (238–187 Ma; Northrup et al., 2011), Upper Jurassic (162–150 Ma), and Lower Cretaceous plutons (148–141 Ma and 124–111 Ma; Walker, 1995; Anderson et al., The Late Cretaceous Idaho batholith is largely younger than 85 Ma, with 2011; Schwartz et al., 2011), as well as Triassic and Jurassic clastic strata that up to 120 Ma magmatism documented along its western and northwest- contain abundant Precambrian detrital zircons (LaMaskin et al., 2008, 2011). ern margins (Lewis et al., 1987). U-Pb geochronology of the Idaho batholith Jurassic strata contain detrital zircon age modes between 500 and 650 Ma and revealed an early metaluminous suite of plutons that are 98–85 Ma in age between 1000 and 1300 Ma, with additional ages spanning 1300–2300 Ma, and

(Gaschnig et al., 2011), with eHf values that range from –6 to –12 (Gaschnig a few Archean grains (Fig. 6E; LaMaskin et al., 2011). Two 153–150 Ma plutons

et al., 2011). These metaluminous plutons occur as outlying stocks and roof yielded very positive eHf values, ranging from +16 to +10, and four 148–146 Ma

pendants within the younger Atlanta lobe (Gaschnig et al., 2011). The 90 Ma plutons have slightly less positive eHf values that range from +14 to +4 (Ander- border zone suite, immediately east of the western Idaho shear zone, has geo- son et al., 2011). chemical and isotopic compositions similar to the early metaluminous phase, Uplift recorded by the western Idaho shear zone from 100 to 90 Ma ex- leading Gaschnig et al. (2011) to speculate that the two magmatic suites once humed midcrustal rocks (e.g., Giorgis et al., 2008; Benford et al., 2010) and

could have led to rapid erosion of a volumetrically significant early meta Sierra Nevada Source luminous phase and border zone suite of the Idaho batholith, providing abundant 98–87 Ma detritus to catchments draining the uplifted region. Although The terranes of the Sierra Nevada Foothills metamorphic belt are com- the early phase of the Idaho batholith is characterized by a less-evolved iso- posed of serpentinized ultramafic rocks, blueschists, chert-argillite-limestone topic signature than later phases of peraluminous magmatism (Gaschnig mélange, metasedimentary rocks including deep-water quartzites, phyllite,

et al., 2011), the eHf values of the early metaluminous phase range from –6 to and chert of the Cambrian–Ordovician Shoo Fly complex, and ophiolites (Miller –12, overlapping with only the most-evolved Late Cretaceous detrital zircons et al., 1992, and references therein; Snow and Scherer, 2006; Ernst et al., 2008),

within the Hornbrook Formation (eHf values range from +13 to –16; Fig. 7). and they have been correlated with similar terranes in the Klamath Mountains Hornbrook whole-rock geochemistry reflects all sources of sediment, not (e.g., Irwin, 2003; Ernst, 2013). Passive-margin deposits preserved in a belt of only plutonic sources, and therefore it would not be expected to perfectly quartzite-rich metasedimentary roof pendants within the axial Sierra Nevada match Idaho batholith whole-rock samples, but the mismatch between them occur east of the Shoo Fly complex within the Western metamorphic belt and is significant: Idaho batholith samples show greater LREE enrichment than west of Sierran roof pendants of the Roberts Mountain allochthon in the East-

Hornbrook Formation samples (Fig. 10), with mean LaN /YbN values of 22 ± 12 ern metamorphic belt (Memeti et al., 2010).

(Gaschnig et al., 2011), compared with upper Hornbrook mean LaN /YbN values Mesozoic magmatism in the Sierra Nevada arc includes magmatic flare-up of only 8 ± 2. Taken together, these mismatches between Idaho batholith and events during the Triassic (250–200 Ma), Middle and Late Jurassic (180– Hornbrook samples suggest that the Late Cretaceous detrital zircon grains in 145 Ma), and mid-Early to Late Cretaceous (124–76 Ma; Barth et al., 2013; Pater- the Hornbrook Formation were not derived solely from the Idaho batholith. son and Ducea, 2015). The Late Cretaceous flare-up event produced the main However, it remains possible that at least some of the sediment eroded off Cretaceous batholith (Chen and Moore, 1982; Bateman, 1992; Irwin, 2003) and

the rapidly exhumed early magmatic phase of the Idaho batholith was shed peaked at 99 Ma (Paterson and Ducea, 2015). The eNd values for Sierra Nevada westward and comprises a portion of the Late Cretaceous detritus in the Horn- plutonic rocks range from +6.5 to –7.9 (DePaolo, 1981; Cecil et al., 2012), with

brook Formation. eNd values of northern plutons ranging from +2.7 to –7.5 (Cecil et al., 2012). Transport across the Blue Mountains Province could then have added Lower Cretaceous (ca. 138 Ma) plutons in the Sierra Nevada Foothills arc have

older, Early Cretaceous and Jurassic sediment to the Hornbrook basin as flu- positive eHf values that range from +7 to +19 (Todt et al., 2011). The eHf values vial systems traversed west and southwest. The result would be a mix of de- in 124–105 Ma zircons from the Fine Gold intrusive suite in the central and tritus with Jurassic, Early Cretaceous, and Late Cretaceous ages. The older western Sierra Nevada batholith range from +6.4 to –4.7, with more negative

plutons would contribute detrital zircon with positive eHf values ranging from eHf values in younger plutons to the east within the suite (Fig. 7; Lackey et al., +4 to +16, and the Late Cretaceous detrital zircon would have much more- 2012). Additional Hf data for younger Sierra Nevada batholith rocks are not yet

evolved eHf values from –6 to –12. Whole-rock geochemical results would re- available, precluding further comparison. However, the wide range in Sierran

flect mixing of sediment derived from a young, differentiated arc and from eNd values and the >11 epsilon unit spread in eHf values for the Fine Gold in-

the island arc and continental arcs of the Blue Mountains terranes. However, trusive suite suggest that eHf values of Late Cretaceous Sierran plutons may

even a combined Idaho batholith–Blue Mountains source area does not pro- also be quite variable. Importantly, the better-characterized eHf values from the vide the abundant 120–100 Ma late Early Cretaceous detrital zircons that char- early phase of the Idaho batholith show an evolved signature with much lower acterize the upper Hornbrook samples, particularly in the Cottonwood Creek variability than either the Early Cretaceous Fine Gold intrusive suite or the Late valley (Fig. 3). Furthermore, Blue Mountains sources would likely contribute Cretaceous detrital zircon in the Hornbrook Formation, suggesting that the abundant Precambrian detrital zircon, as Jurassic and Triassic clastic cover Idaho batholith could not be the sole source of the Late Cretaceous zircon in sequences (e.g., LaMaskin et al., 2008, 2011) would be eroded as well as base- the Hornbrook region. ment terranes and Mesozoic plutons. Although provenance assessment based Plutons in the northern Sierra Nevada intruded episodically in Middle to on Precambrian ages within active tectonic settings must be viewed cautiously Late Jurassic and middle Cretaceous time, with Late Cretaceous plutons oc- due to dilution of Precambrian signatures by abundant arc-derived grains as curring to the northeast, up to 200 km east of the modern Sierran range crest well as the likelihood of sedimentary recycling (e.g., LaMaskin et al., 2011), the (Barton et al., 1988; Van Buer and Miller, 2010; Cecil et al., 2012); a potentially Precambrian ages that characterize the Blue Mountains strata (Fig. 6E) are a significant portion of the Late Cretaceous arc may be buried by younger sedi poor match for the Precambrian age signature of the Hornbrook Formation ment and volcanic rocks in northern California, northwestern Nevada, and (Figs. 6A and 6B). Further, the presence of isolated Cretaceous sedimentary southeastern Oregon (Lerch et al., 2007; Van Buer et al., 2009). Whole-rock rocks deposited unconformably on the western Blue Mountains terranes (e.g., geochemistry from plutons of the northern Sierra Nevada show LREE enrich-

Oles and Enlows, 1971; Dickinson, 1979) suggests that at least the western Blue ment, with LaN /YbN ratios ranging from 5 to 35, consistent with the general Mountains region underwent subsidence and deposition during the middle to pattern for plutons of the greater Sierra Nevada (Cecil et al., 2012). Cretaceous Late Cretaceous Period. plutons trend north-northeast into Nevada, including the Sahwave batholith in

northwestern Nevada, which has similar geochemistry and zonation pattern given the near-absence of Late Cretaceous detrital zircon and abundance of Ju-

as plutons of the greater Sierran batholith (Van Buer and Miller, 2010; Cecil rassic and pre–125 Ma Early Cretaceous detrital zircon with juvenile eHf values et al., 2012). Thus, the northern Sierra Nevada batholith may be much wider (Surpless and Beverly, 2013). These samples contain very little pre-Mesozoic than the 60 km width of the exposed southern Sierra Nevada, reaching more detrital zircon (2%–7%; Fig. 3), and they plot near island-arc andesite values in than 180 km width at 40°N latitude (Cecil et al., 2012). Cecil et al. (2012) suggest a La-Th-Sc ternary diagram (Fig. 9B). By late Turonian or Coniacian time, Horn- that the northward widening of the batholith resulted in more rapid eastward brook sediment sources had shifted into the Late Cretaceous Sierra Nevada migration of Cretaceous magmatism and a more dispersed Late Cretaceous batholith and possibly Idaho batholith, resulting in widespread sedimentation magmatic flare-up event that occurred over a longer period of time in the throughout the Hornbrook region that was characterized by abundant Late

northern batholith than in the south. Cretaceous detrital zircons with variable eHf values, scarce Early Cretaceous The 100–85 Ma magmatic flare-up event in the Sierra Nevada matches the grains, and a broad distribution of Jurassic grains (middle group of Fig. 4, in- Late Cretaceous age peak that characterizes the middle and upper Hornbrook cluding the Ditch Creek Siltstone in the Cottonwood Creek valley, Barneburg Formation, and plutons of the northern Sierra, including northwestern Nevada, Hill, and the Suncrest Road Quarry sample). These samples contain small but could also provide the Jurassic and Early Cretaceous detrital zircons that occur variable amounts of pre-Mesozoic detrital zircon (2%–13%) and also plot near

throughout the Hornbrook Formation. Moreover, the variability of eNd values island-arc andesite, but relatively closer to North American shale composite

in the northern Sierran Nevada is consistent with the range in eNd values in and upper continental crust than the older samples (Fig. 9B). Following the

the Hornbrook Formation (Surpless and Beverly, 2013). The eHf data from the Coniacian pulse of Late Cretaceous detrital zircon, upper Hornbrook strata

Idaho batholith are a poor match for the wide-ranging eHf values from Late (upper group of Fig. 4, including the Rocky Gulch Sandstone and Blue Gulch

Cretaceous detrital zircon in the Hornbrook Formation (Fig. 7), but limited eHf Mudstone) continued to receive Late Cretaceous detrital zircon, but also abun- data for Sierran plutons preclude making a positive comparison of Sierran and dant Early Cretaceous zircon (125–100 Ma), and variable abundance of Early

Hornbrook eHf data. Although nonunique, whole-rock geochemistry of Horn- and Middle–Late Jurassic detrital zircon (Figs. 3 and 4). These upper samples brook samples is consistent with Sierran sources, and REE distributions match contain up to 19% pre-Mesozoic detrital zircon and plot closer to the North well with Cretaceous plutons of the northern Sierra (Fig. 10; Cecil et al., 2012). American shale composite and upper continental crust values on a La-Th-Sc Detrital zircon geochronology of Neoproterozoic through Triassic central ternary diagram (Fig. 9B). North American passive-margin deposits (Utah and Nevada) yield three main Precambrian age populations of 1000–1200 Ma, 1350–1500 Ma, and 1650– 1850 Ma, with additional ages between 2500 and 2900 Ma (Fig. 6D; Gehrels Tectonic Implications and Pecha, 2014). Metasediments in roof pendants in the central Sierra Nevada record similar Precambrian detrital zircon age ranges, albeit with variable pro- Sharman et al. (2015) suggested that a Cenomanian–Coniacian drainage portions (Fig. 6C; Memeti et al., 2010). This passive-margin Precambrian age divide along the axis of the Cretaceous Cordilleran arc precluded westward signature provides a compelling match for the Hornbrook Precambrian age transport of 100–85 Ma zircon into the forearc region, and results presented signatures (Fig. 6), with abundant grains originally derived from southwestern here suggest that much of the detritus eroded from the Late Cretaceous rocks Laurentian sources and likely recycled through Paleozoic and early Mesozoic of the Sierran Crest intrusive suite and/or coeval plutons in the northern Sierra passive-margin deposits (perhaps entirely within the roof pendants within the Nevada may have been transported northward and westward into the Horn- central Sierra Nevada) before Late Cretaceous deposition in the Hornbrook brook basin beginning as early as late Turonian time (ca. 90 Ma; Fig. 11). basin. These Sierran sources of Precambrian zircon also provide a better match DeCelles (2004) suggested that shortening in the Sevier thrust belt led to to the Hornbrook age signature than the Precambrian age ranges within Juras- crustal thicknesses of 50–60 km and development of an elevated Nevadaplano sic strata of the Blue Mountains (Fig. 6E). Thus, the northern Sierra Nevada in conjunction with voluminous mid- to Late Cretaceous magmatism in the region, combined with possible input from the early phase of the Idaho batho- Sierra Nevada batholith. Paleoelevation studies by Mulch et al. (2006) and lith, represents the most likely source of much of the Coniacian and younger Cassel et al. (2009) concluded that the Sierra Nevada uplift occurred in Late Hornbrook sediment (Fig. 11). This extensive source region includes the Sierra Cretaceous or early Cenozoic time, and continuity of Eocene paleodrainage Nevada batholith and possibly the Idaho batholith, and currently exposed as systems suggests that the Sierra Nevada formed the western flank of the well as now-buried plutons in northwestern Nevada, and it also may have in- Nevadaplano (e.g., Faulds et al., 2005; Henry, 2009). Snell et al. (2014) used car- cluded the Black Rock terrane (Surpless and Beverly, 2013). bonate isotope thermometry to suggest that the Nevadaplano stood at ≥2 km The oldest Hornbrook strata (lower group of Fig. 4, including the Klamath elevation during the latest Cretaceous. Bonde et al. (2014) compared verte- River Conglomerate, Osburger Gulch Sandstone, and Ditch Creek Siltstone brate fauna in Early and Late Cretaceous units of east-central Nevada to show in Bear Creek valley) may have received locally derived sediment from the that regional uplift of the Nevadaplano was entirely a Late Cretaceous event, Sierran Foothills belt, western Sierran batholith, and Klamath Mountains, and it may have reached its maximum during Maastrichtian time. Thermo-

chronology of the northern Sierra Nevada indicates exhumation and erosional comparison of large data sets of bedrock and detrital zircons from the Sierra denudation of the region from 90 to 60 Ma, as a result of earlier orogenic thick- Nevada arc demonstrates that the detrital zircon record accurately reflects ening of the crust and emplacement of the Late Cretaceous batholith (Cecil the timing of magmatic flare-ups and lulls in the Sierran arc, but it provides et al., 2006). Resulting sediment derived from eroded arc rocks may have been a poor proxy for estimating the volume of magmatic addition during each transported northward along the axis of the arc, between the western drainage flare-up event (Paterson and Ducea, 2015). Sedimentary successions are un- divide along the arc crest and the rising Nevadaplano to the east (Fig. 11). likely to accurately reflect the volume of magmatic flare-up events because The abrupt appearance of abundant 100–85 Ma detrital zircons in the de- they may include nonarc sources and may over- or underrepresent mag- trital age signatures of Coniacian Hornbrook strata, even extending onto the matic arc age distributions, depending on zircon fertility of sources (e.g., Klamath Mountains at the Suncrest Road Quarry, suggests that regional uplift Moecher and Samson, 2006), catchment size (e.g., Ingersoll, 1990), and dep- of the Sierran arc and Nevadaplano began during Coniacian time. Late Creta- ositional age. However, closer approximation of the timing, duration, and ceous detrital zircons persist in the Hornbrook samples through Maastrichtian volume of magmatic flare-up events also depends on thorough sampling of deposition, but they are relatively less abundant in the detrital age signatures, arc-derived strata. Intra-arc drainage systems may have transported a sig- with additional contribution of more Early Cretaceous and Jurassic detrital zir- nificant volume of sediment eroded from Late Cretaceous Sierran plutons cons (Figs. 3 and 4). This broadening of the detrital zircon age signature may northward into the Hornbrook region, rather than westward into the Great reflect increased catchment size as fluvial systems eroded east- and south- Valley forearc or eastward into the retroarc region. Detrital zircon ages from eastward into the elevated Nevadaplano and the Sierran arc rocks that formed the forearc and retroarc regions would therefore underrepresent the Late its western flank. In addition, the gradual increase in 100–85 Ma zircons in the Cretaceous magmatic flare-up event. This potential for sediment transport Santonian to Paleogene Great Valley forearc, concomitant with the relative de- to depocenters not directly linked to present-day arc exposures is critical to crease of this Late Cretaceous age peak in the Hornbrook region, may have recognize so that the detrital zircon record forms a detailed record of mag- resulted from breaching of the western drainage divide within the arc and en- matic activity, providing a powerful, and necessary, complement to bedrock suing westward transport of sediment eroded from Late Cretaceous plutons geochronology. of the eastern Sierra Nevada (e.g., Sharman et al., 2015). The presence of the elevated Nevadaplano during the Late Cretaceous (DeCelles, 2004; Snell et al., 2014) meant that relatively little arc-derived detritus was shed to the east, and CONCLUSIONS even less crossed the Nevadaplano into the foreland basin (Dickinson et al., 2012; Sharman et al., 2015). Deposition in the Hornbrook basin may have begun as early as Albian It is possible that Jurassic and Early Cretaceous sediment present through- time (e.g., Surpless and Beverly, 2013), but most of the Hornbrook strata were out the Hornbrook strata was derived from the Klamath Mountains and/or deposited during the Late Cretaceous, and provenance results presented here the Blue Mountains, but the presence of Late Cretaceous deposition on the suggest that the Hornbrook region received abundant sediment derived from Klamath Mountains at the Suncrest Road Quarry (Fig. 2), 80 km west of Horn- the Late Cretaceous Sierra Nevada batholith and possibly the early magmatic brook Formation outcrops, and Late Cretaceous deep-water deposition on the phase of the Idaho batholith beginning in Coniacian time. The Coniacian in- Blue Mountains in the Ochoco basin (e.g., Dickinson, 1979; Kleinhans et al., flux of Late Cretaceous detrital zircon into the Hornbrook region may signal 1984; Dorsey and Lenegan, 2007) suggest that these regions were the locus the rise of the Nevadaplano and the Sierran arc rocks that formed its western of subsidence and sedimentation, rather than erosion, during the Late Creta- flank, as well as erosion of rapidly exhumed rocks in the western Idaho shear ceous. Thus, the limited outcrop extent of the Hornbrook Formation may rep- zone. Uplift of the Sierran arc and Nevadaplano from overthickening of the resent only a sliver of a much larger Late Cretaceous Hornbrook basin (Fig. 11). crust and emplacement of voluminous Late Cretaceous magmatism in the Subsidence of the Hornbrook region may have been in part a response to Late Sierran arc, combined with transpressive uplift along the western Idaho shear Cretaceous uplift of the early Idaho batholith (e.g., Giorgis et al., 2008), north- zone, may have led to subsidence in the greater Hornbrook region, resulting ern Sierra Nevada (e.g., Cecil et al., 2006), and Nevadaplano (e.g., DeCelles, in more widespread Late Cretaceous deposition than modern outcrop extent 2004; Snell et al., 2014). suggests. Sediment was transported north-, northwest-, and westward into the subsiding Hornbrook region by fluvial systems draining the rising Sierran arc and Idaho batholith during the early Late Cretaceous, with catchments Improved Record of Episodic Magmatism increasing as fluvial systems reached further east and south with time. Thus, the sedimentary record of the Late Cretaceous magmatic flare-up event in Unlike bedrock analyses, detrital zircon ages are unlikely to reflect sam- the northern Sierran arc may be best documented in the Hornbrook basin pling of a single pluton or isolated part of an arc, but rather they provide an northwest of the arc, rather than either the forearc or retroarc systems that averaged long-term history of arc magmatism (e.g., de Silva et al., 2015). A flank the Sierra Nevada.

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