Lamaskin et al. 2011 Oregon reef

PALAIOS, 2011, v. 26, p. 779–789 Research Article DOI: 10.2110/palo.2011.p11-006r DETRITAL RECORD OF UPPER TRIASSIC REEFS IN THE OLDS FERRY TERRANE, BLUE MOUNTAINS PROVINCE, NORTHEASTERN OREGON, UNITED STATES TODD A. LAMASKIN,1* GEORGE D. STANLEY, JR.,2 ANDREW H. CARUTHERS,3 and MEGAN R. ROSENBLATT 2 1Department of Geography and Geology, University of North Carolina at Wilmington, 601 South College Road, Wilmington, North Carolina 28403-5944, USA, lamaskint@uncw.edu; 2Department of Geosciences, University of Montana, 32 Campus Drive #1296, Missoula, Montana 59812-1296, USA, george.stanley@umontana. edu, megan.rosenblatt@umontana.edu; 3Department of Earth and Ocean Science, University of British Columbia, 6339 Stores Road, Vancouver, B.C., Canada, V6T 1Z4, acaruthe@eos.ubc.ca ABSTRACT We report a coral-sponge dominated reef lithofacies in detrital boulders of carbonate-clast conglomerate from the Olds Ferry terrane, Blue Mountains Province, Willow Spring locality, northeastern Oregon. This discovery constitutes the first report of Triassic reefal lithofacies from the Olds Ferry terrane. Corals at the site include a high-growing, dendroidphaceloid species that acted as a framework or sediment baffle, and a lowgrowing, cerioid, encrusting coral and a sponge that acted as sediment binders. The co-occurrence of coral taxa in the Wallowa intraoceanic arc and Olds Ferry pericratonic arc terranes suggests that during the Late Triassic, these regions were in proximity to one another. With this report, Upper Triassic carbonate rocks are known from all of the major terranes of the Blue Mountains Province and a Tethyan affinity is established for the fauna of the Olds Ferry terrane. We suggest that the source of this Late Triassic coral-sponge reef fauna in the upper member of the Huntington Formation was intrabasinal and that the source rocks are no longer exposed in the region. Numerous possible regional source areas for these detrital limestone clasts rule out the need to call upon an exotic terrane source area. Quesnel terrane of central British Columbia, Canada (Stanley and Nelson, 1996), and the Wallowa terrane of northeastern Oregon, United States (Stanley and Senowbari-Daryan, 1986; Stanley et al., 2008). Many of the reef builders of these Upper Triassic deposits represent the same species as those in the Eurasian Tethys. The dispersal and paleogeography of the fossil biota have been the subject of considerable discussion in the literature (e.g., Newton, 1988; Smith and Westermann, 1990). Here, we report the first discovery of a coral-sponge dominated reef lithofacies in detrital boulders of a carbonate-clast conglomerate from the Olds Ferry terrane, Blue Mountains Province, northeastern Oregon. With this finding, Upper Triassic carbonate rocks are now known from all of the major terranes of the Blue Mountains Province and a Tethyan affinity is established for the fauna of the Olds Ferry terrane. GEOLOGIC SETTING * Corresponding author. The Blue Mountains Province is an amalgamated assemblage of accreted Paleozoic–Mesozoic volcanic arcs, sedimentary basins, subduction mélange complexes, and post-tectonic stitching plutons (Fig. 1; Brooks and Vallier, 1978; Silberling et al., 1984; Vallier, 1995). Four major terranes have been recognized in this region: the Wallowa, Baker, Olds Ferry, and Izee (Vallier, 1995; Fig. 1). These four terranes represent two late Paleozoic–early Mesozoic volcanic island-arc assemblages (Wallowa intraoceanic and Olds Ferry pericratonic arc terranes; Vallier, 1995; LaMaskin et al., 2008), a Paleozoic–early Mesozoic subduction-accretionary complex (Baker terrane; Jones et al., 1976; Brooks and Vallier, 1978; Dickinson and Thayer, 1978; Coward, 1983; Schwartz et al., 2010), and a Triassic–Jurassic clastic sedimentary succession (Izee terrane; Silberling et al., 1984). Mudrock geochemistry and detrital zircon U-Pb geochronology suggest that the Wallowa terrane was an intraoceanic island arc, whereas the Olds Ferry terrane was an island arc fringing the North American craton (LaMaskin et al., 2008, 2009, 2011). Note that the Baker, Olds Ferry, and Izee terranes are not all fault bounded with respect to one another and do not necessarily have origins wholly distinct from one another. Thus, to varying degrees, the Baker, Olds Ferry, and Izee terranes of the Blue Mountains are genetically related and represent portions of a western North American arc-trench complex (Dorsey and LaMaskin, 2007, 2008; Dickinson, 2008; LaMaskin et al., 2008, 2011; Schwartz et al., 2010). The spatial relationship between the Olds Ferry and the Wallowa terranes as well as the timing of their amalgamation remains unclear. The Wallowa, Baker, and Olds Ferry terranes were either amalgamated offshore during the Late Triassic–Early Jurassic before being accreted to the margin of North America during the Jurassic–Cretaceous (Dorsey and LaMaskin, 2007; LaMaskin et al., 2011), or amalgamation occurred during the Late Jurassic prior to Cretaceous accretion to the continent (Dickinson, 1979; Avé Lallemant, 1995; Schwartz et al., 2011). Rocks of the Blue Mountains Province are overthrust in the Copyright 0883-1351/11/0026-0779/$3.00 INTRODUCTION The Late Triassic is generally considered to be a time of extensive carbonate deposition worldwide, especially in the former Tethys region of central Europe where extensive reef complexes are well known. The Norian Stage, in particular, records one of the greatest reef blooms since the Permian (Flügel, 2002). Many of these early Mesozoic reef complexes are thousands of meters thick and contain evidence of extensive and vigorous reef building; the organisms that constitute the framework range from the northern Calcareous Alps to the southeastern Pamirs. As summarized by Flügel (2002), the reef constituents are chiefly calcified algae, foraminifers, microproblematica, calcified sponges, scleractinian corals, hydrozoans, and mollusks. Upper Triassic coral and sponge-rich faunas also appear to have formed around volcanic seamounts(?) and arcs in the ancient Panthalassic Ocean. Many of these faunas yield a predominance of Tethyan-type organisms and are now incorporated into the terrane collage of western North America (Blodgett and Stanley, 2008). Tethyan reef-type faunas are present in North America from central Alaska to Sonora, Mexico as coral and sponge-rich complexes. Late Carnian–Rhaetian examples from North America, however, are best generally described as beds, lenses, or biostromes, as only a few sites produce true reef lithofacies or structures comparable to those present in the Eurasian Tethys (Stanley and Senowbari-Daryan, 1986; Stanley, 1988; Flügel, 2002; Stanley, 2003, 2006). Late Triassic reefs most akin to those of the Tethys are present in the Stikine terrane of the Canadian Yukon (Reid and Templeman-Kluit, 1987; Yarnell et al., 1999), the G 2011, SEPM (Society for Sedimentary Geology) 780 LAMASKIN ET AL. FIGURE 1—Regional geologic map of Blue Mountains Province (northwestern United States) showing distribution of terranes. OR 5 Oregon; ID 5 Idaho; WA 5 Washington state. Modified from Dickinson (1979), Mann and Vallier (1989), and Gray and Oldow (2005). northeast by high-grade metamorphic rocks of the Salmon River Belt (Lund and Snee, 1988; Manduca et al., 1992, 1993; Selverstone et al., 1992; Lund, 2004; Gray and Oldow, 2005; Lund et al., 2008). The Salmon River Belt is bounded on the east by the western Idaho shear zone (Fig. 1), a complex structural boundary with the Laurentian continental margin (McLelland et al., 2000; Giorgis et al., 2005, 2008). PALAIOS The Wallowa terrane contains a thick sequence of clastic and volcanic rocks representing Permian–Jurassic island-arc volcanism (Vallier, 1977, 1995; Tumpane and Schmitz, 2009). In the southern Wallowa Mountains, the Upper Triassic (Carnian–Norian) Martin Bridge Formation includes Tethyan-type reefs in the Summit Point member (Summit Point reefs; Stanley and Senowbari-Daryan, 1986; Stanley et al., 2008). The Martin Bridge Formation grades both laterally and upward into deep-marine clastic rocks of the Upper Triassic–Lower Jurassic (Norian–Pliensbachian) Hurwal Formation. In the eastern portions of the Baker accretionary-subduction complex, extensive outcrops of strongly recrystallized carbonate are present (Prostka, 1967; Brooks et al., 1976). This unit, the Nelson Marble, is found in association with quartz phyllite, metasandstone, and metaconglomerate, and contains Middle–Late Triassic conodont faunas (Morris and Wardlaw, 1986; Ashley, 1995). Recent investigations suggest that the Nelson Marble may be an olistostromal body (A. Snoke, personal communication, 2010). The Olds Ferry terrane represents a Middle Triassic–Lower Jurassic pericratonic volcanic arc succession that is distinct from the Wallowa intraoceanic arc terrane (LaMaskin et al., 2008; Tumpane et al., 2008). Rocks of the Olds Ferry terrane (Fig. 2) include hypabyssal and extrusive volcanic rocks and interbedded volcaniclastic rocks of the Huntington Formation, which contains the Late Triassic detrital coralsponge reef fauna presented in this paper (Brooks, 1979). The informal lower member of the Huntington Formation includes volcanic flows composed of monolithologic mafic volcanic breccia, pillowed greenstone, andesite porphyry, and minor rhyolite and rhyodacite (Brooks and Vallier, 1978; Brooks, 1979; Charvet et al., 1990; Tumpane, 2010). A thin-bedded, deep-water limestone unit has previously been described from the lower Huntington Formation; however, no in situ reefs or reef- FIGURE 2—Mesozoic chronostratigraphy of the Huntington, Oregon region. Modified from LaMaskin (2008). PALAIOS DETRITAL RECORD OF UPPER TRIASSIC REEF FACIES 781 FIGURE 4—Detailed geologic map of conglomerate outcrop area. Additional unpublished mapping by R. Dorsey, T. LaMaskin, and P. Wright (ca. 2007). Jw 5 Jurassic Weatherby Formation; Trhl 5 Triassic Huntington Formation, informal lower member; Trhu 5 Triassic Huntington Formation, informal upper member; Qls 5 Quaternary landslide deposits. FIGURE 3—Geologic map of the Huntington, Oregon area. Modified from Juras (1973) and Brooks (1979). like facies have been reported (Brooks, 1979; LaMaskin, 2008). Ammonite and bivalve age assignments indicate that this unit spans the upper Carnian–lower Norian (Brooks, 1979; LaMaskin, 2008). High precision U-Pb ages on zircons from volcanic rocks of the lower member of the Huntington Formation are Late Triassic, ca. 221– 220 Ma (late Carnian; Ogg et al., 2008; Walker and Geissman, 2009; Tumpane, 2010). The informal upper member of the Huntington Formation includes laminated shale and thin- to medium-bedded sandstone turbidites interlayered with thick-bedded, cobble-to-boulder conglomerate and abundant thick-bedded rhyolite, and rhyodacite porphyry. High precision U-Pb zircon ages from rhyolite in the upper portion indicate an Early Jurassic crystallization-depositional age of ca. 188–187 Ma (early Pliensbachian; Ogg et al., 2008; Walker and Geissman, 2009; Tumpane, 2010). DESCRIPTION Locality Information We have recovered a Late Triassic coral-sponge reef fauna from a thick-bedded cobble-to-boulder conglomerate in the informal upper member of the Huntington Formation (Olds Ferry terrane) at a locality herein named Willow Spring (Figs. 3–4, 5A; 44u249530N, 117u149400W). The site is ,15 kms north of the town of Huntington, Oregon on the Snake River. The conglomerate exposures discussed here are within the upper Huntington Formation, stratigraphically below the dated Pliensbachian tuff units of Tumpane (2010), and are thus Lower Jurassic. The fauna is preserved in reworked (i.e., detrital) limestone clasts that are present within a steep, east-dipping, ,100-m-thick succession of conglomerate and sandstone, interbedded with rhyolite and rhyodacite volcanic-flow deposits. Clasts range from pebble sized to .1.5 m and are composed of rhyolite, rhyodacite porphyry, basalt, andesite, and limestone. Trace numbers of mudstone-argillite clasts are also present; additional clast types have not been identified. Lithic framework grains in sandstone that is interbedded with the Willow Spring conglomerate are restricted to a range of volcaniclastic mafic-tosilicic compositions and textures. Specimens are reposited at the University of Montana Paleontology Center, Missoula, Montana; Locality ID# MI 8839. Carbonate Lithofacies Types Detrital carbonate clasts found at Willow Spring vary from fossiliferous limestone to mixed fossiliferous limestone-volcaniclastic lithologies (Fig. 5B). Three distinct lithofacies types are recognized in the clasts comprising Upper Triassic reef facies (Table 1). On the basis of grain type, texture, and fossil content, they are classified according to Dunham (1962, 1970) and supplemented by Embry and Klovan (1971) as: (1) coral boundstone-framestone lithofacies, (2) crinoid packstonegrainstone lithofacies, and (3) spongiomorph-algal grainstone lithofacies. Coral Boundstone-Framestone Lithofacies.—This lithofacies, consisting of fine- to coarse-grained, light-gray to pink detrital limestone clasts, is the dominant carbonate clast lithology at the site (Figs. 5C–E; 6F). The fauna, recognized in thin sections and polished samples from these clasts (Table 2), includes a high-growing, dendroid-phaceloid 782 LAMASKIN ET AL. PALAIOS FIGURE 5—Representative outcrop and exposure images. A) Exposures of limestone-clast conglomerates on ridge above Snake River near Huntington, Oregon. Dashed lines indicate approximate bedding. Jw 5 Jurassic Weatherby Formation; Trh 5 Triassic Huntington Formation. B) Typical exposure of detrital reef facies showing two large limestone boulders encased in volcaniclastic matrix. C) Dark, detrital silt-filled voids and associated coral bafflestone textures. D) Coarse cement-filled voids. E) Coralline boundstone composed almost exclusively of low-relief, encrusting corals; hammer head ,15 cm long. F) Crinoid packstone grainstone. (branching) coral, Paracuifia sp., which acted as a framework or sediment baffle, and to a lesser extent, Kuhnastraea cowichanensis (Clapp and Shimer), a low-growing, cerioid, encrusting coral (Fig. 7A– E). These typical colonial reef corals are found in association with the branching reef sponge taxon, Spongiomorpha ramosa (Frech) (Fig. 7F). Together, these organisms produced at least a 10–50-cm-high bios- tromal framework (height estimates limited by clast size). The carbonate sand matrix is dominated by skeletal allochems consisting of echinoderm (crinoid and echinoid) and mollusk (bivalves and gastropods) fragments with lesser intraclastic peloidal material. This well-rounded skeletal-peloidal debris suggests abundant abrasion and reworking of detrital carbonate material. PALAIOS DETRITAL RECORD OF UPPER TRIASSIC REEF FACIES 783 TABLE 1—Descriptions of lithofacies in limestone clasts from the upper Huntington Formation. Lithofacies Coral boundstonebafflestone Crinoid packstonegrainstone Spongiomorph-algal grainstone Predominant biota Subordinate biota Fossil taxa Sedimentary structures and textures Environmental interpretation Fragmental algae, crinoids, Paracuifia sp., Kuhnastraea Detrital silt filled voids (,3–15 cm) Shallow subtidal, Colonial corals including high-energy reef containing red-pink, hematitic cowichanensis, echinoids, bivalves, and dendroid-phaceloid and setting quartz, feldspar, and carbonate Spongiomorpha ramosa cerioid morphologies, and gastropods sand. Coarse cement-filled voids sponges are (,0.5–4 cm). Well-rounded skeletal grains ‘‘Pentacrinus’’ Well-rounded skeletal grains Shallow subtidal, high Crinoid occicles Foraminifers, fragmental energy back-reef or calcareous algae and fore-reef shoals molluscan debris Shallow-subtidal, high Spongiomorpha ramosa Well-rounded skeletal grains, Spongiomorphs, algae Fragmental calcareous energy back-reef rounded intraclasts of encrusting platy green Spongiomorpha ramosa algae and molluscan debris Characteristic reef-void fillings are observed in many of the clasts, including both detrital silt and coarse cement fillings (Figs. 5C–D). Detrital silt-filled voids are large areas (,3–15 cm) containing red-pink, hematitic quartz, feldspar, and carbonate sand that display welldeveloped depositional lamination and other geopetal features. These infilled voids are interpreted as post-depositional infilling of inter-reef void spaces. Coarse cement-filled voids are smaller areas (,0.5–4 cm) filled with a meniscus-rim cement of medium crystalline calcite spar that grades inward to coarsely crystalline calcite spar (Fig. 5D). Crinoid Packstone-Grainstone Lithofacies.—Subordinate detrital clasts at the locality are composed of well-sorted and well-rounded crinoid packstone-grainstone (Figs. 5B, 6A–B). The assignment of crinoid ossicles to ‘‘Pentacrinus,’’ a typical Triassic–Jurassic form, is made only on the fragments of columnals. Lesser amounts of foraminifers, fragments of calcareous algae, and molluscan skeletal debris also are present. This crinoid packstone-grainstone facies is interpreted to represent a shallow-water, subtidal back-reef or fore-reef shoal (Lehrmann et al., 1998; Chablais et al., 2009; Flügel and Munnecke, 2010). The dominance of well-rounded crinoid ossicles and, to a lesser extent, other well-rounded skeletal grains is indicative of redeposition and transport in a high-energy setting. Spongiomorph-Algal Grainstone Lithofacies.—Other clasts in the Willow Spring conglomerate consist of a spongiomorph-algal grainstone (Figs. 6C–E), characterized as a fine-grained, light-gray limestone containing encrusting platy green algae and the late Triassic Spongiomorpha ramosa, traditionally regarded as a hydrozoan but also interpreted as a sponge or coral (Ezzoubair and Gautret, 1993; Roniewicz, 2011). Allochems associated with this facies include wellsorted and well-rounded intraclasts of S. ramosa, molluscan and echinoderm fragments, and unidentified calcified algae. The dominance of spongiomorphs and calcified algae, paired with echinoderm and molluscan debris, suggests a high energy shallow-subtidal, back-reef environment (Flügel and Munnecke, 2010). DISCUSSION Triassic Reef-Building Organisms in the Olds Ferry Terrane This study marks the first discovery of Upper Triassic reefal lithofacies and reef-building fossils in the Olds Ferry terrane. Kuhnastraea cowichanensis was first described from Rhaetian rocks on Vancouver Island by Clapp and Shimer (1911) and later from Alaska by Caruthers and Stanley (2008). The spongiomorph, S. ramosa, is a well-known Norian–Rhaetian reef builder that is widely distributed across the Tethys and western North America (Smith, 1927; Stanley and Whalen, 1989; Flügel, 2002; Caruthers and Stanley, 2008). Both of these taxa are previously known from the Martin Bridge Formation of the Wallowa terrane (Stanley and Whalen, 1989) and also are distributed in Upper Triassic carbonate rocks of Wrangellia and the Alexander terrane, Alaska (Caruthers and Stanley, 2008). The branching coral Paracuifia sp. is closely related to P. magnifica, previously identified from the Pamir Mountains (Melnikova, 2001). This genus also was identified from the Alexander terrane (Caruthers and Stanley, 2008); however, the specimen present at the Willow Spring locality appears to be a new taxon. The low diversity of corals may reflect incomplete sampling and limited availability of material for study. In order to evaluate potential source areas for these limestone clasts it is necessary to understand the known distribution of coral taxa from the North American Cordillera, especially from terranes that are thought to have been in close paleogeographic proximity to the Olds Ferry terrane. A recent compilation of Late Triassic coral data shows several taxa that are common throughout the Tethys Ocean and the North American Cordillera and therefore interpreted to be cosmopolitan in nature (Caruthers and Stanley, 2008, table 2). Genera such as Distichophyllia, Retiophyllia, Gablonzeria, Kuhnastraea, Crassistella, Meandrostylis, and Astraeomorpha are generally diverse at the species level and widespread in terrane localities from southern Alaska to Mexico. They are also common in localities comprising the Wallowa, Alexander, and Wrangellia terranes, as well as an isolated locality near Lewiston, Idaho, which is suspected to be part of the Wallowa terrane (Stanley and Whalen, 1989; Nützel and Erwin, 2004; Caruthers and Stanley, 2008); however, the latter site does not contain Kuhnastraea or Crassistella (Squires, 1956; Caruthers and Stanley, 2008). Of the abovementioned cosmopolitan genera, the new fauna from the Olds Ferry terrane contains only Kuhnastraea and is therefore somewhat problematic. If the source area for these eroded limestone clasts was one of the well-known terrane sources (i.e., Wallowa, Alexander, and Wrangellia terranes), then the fauna would most probably contain a higher diversity of cosmopolitan genera, but again, limited sampling and exposure of the Willow Creek locality may have affected diversity. Paracuifia has previously been identified only from the Alexander and northern Wrangellia terranes; its presence in the Olds Ferry terrane is compelling because it may suggest either a paleobiogeographic tie to these terranes or a broadening of the geographic distribution of this taxon. Because there does not seem to be a strong influence of other cosmopolitan or endemic coral genera within the Olds Ferry terrane, a wider geographic distribution of Paracuifia may be indicated. Reef-Clast Source Area The distinctive limestone-clast conglomerate of Willow Spring was deposited during the Early Jurassic, prior to ca. 188–187 Ma (Tumpane, 2010), and thus represents reworking of older, Upper Triassic reef deposits. Regionally, we know of two possible source areas of Upper Triassic reefal limestone and suggest a third possibility: (1) reefs in the Wallowa intraoceanic arc terrane (Stanley and Senowbari-Daryan, 1986; Stanley et al., 2008), (2) marble currently exposed in the Baker 784 LAMASKIN ET AL. PALAIOS FIGURE 6—Photomicrographs of carbonate lithofacies types. A–B) Crinoid grainstone-packstone. C–E) Spongiomorph-algal grainstone. F) Coral boundstone-bafflestone. terrane subduction-accretionary complex (Prostka, 1967; Morris and Wardlaw, 1986), and (3) reefs associated with the Olds Ferry pericratonic arc terrane that are no longer exposed in the region. Wallowa Terrane Source.—The Upper Triassic Summit Point member reef facies of the Wallowa terrane contains two coral taxa also found in the Willow Spring conglomerate, K. cowichanensis and S. ramosa. If the Willow Spring limestone clasts were eroded from the Summit Point reef, it would indicate proximity of the Wallowa and Olds Ferry terranes by the early Jurassic. This scenario supports evidence for late Triassic–early Jurassic collision of the Wallowa and Olds Ferry terranes (i.e., Dorsey and LaMaskin, 2007) and is in contrast to models of late Jurassic collision between the two island arc terranes (i.e., Dickinson, 1979, 2004; Avé Lallemant, 1995; Schwartz et al., 2011). Reef facies and fossils of the Summit Point member type also occur in middle Norian to Pliensbachian clastic turbidites (Excelsior Gulch member of the Hurwal Formation) of the Wallowa terrane, where they occur in conglomerate-breccia clasts along with volcanic and chert PALAIOS DETRITAL RECORD OF UPPER TRIASSIC REEF FACIES 785 TABLE 2—Cross-reference of late Triassic reef taxa between major western North American terranes. Blue Mountains Species Olds Ferry Paracuifia sp. P. smithi n. sp. P. jennieae n. sp. 3 Wallowa Wrangelia S N Stratigraphic range and North American locations 3 Huntington Formation, Olds Ferry terrane, Oregon Early Norian, Gravina Island, Alaska (Caruthers and Stanley, 2008) Early Norian, Cornwallis Limestone, Keku Strait, southeastern Alaska; Chitistone Formation, Wrangell Mountains (Caruthers and Stanley, 2008) Early Norian, Nehenta Formation, Gravina Island, southeastern Alaska (Caruthers and Stanley, 2008) Early Norian–Rhaetian; Vancouver Island, Canada; Gravina Island, Keku Strait, Wrangell Mountains, Alaska; Hells Canyon, Oregon (Smith, 1927; Montanaro-Gallitelli et al., 1979; Melnikova and Bychkov, 1986; Stanley and Whalen, 1989; Caruthers and Stanley, 2008) Rhaetian, Vancouver Island, Canada; Northern Calcareous Alps; Norian, Gravina Island, Keku Strait, Wrangell Mountains, Iliamna Lake, Peninsula, Alaska; Hells Canyon, Oregon; Shasta County, California; Pilot Mountains, Nevada (Roniewicz, 1989; Stanley and Whalen, 1989; Caruthers and Stanley, 2008) Rhaetian, Vancouver Island, Canada; Norian–Rhaetian; early Norian, Hells Canyon, Oregon (Roniewicz, 1989; Stanley and Whalen, 1989; Caruthers and Stanley, 2008) Early Norian–Rhaetian, Long Creek, Alaska; Cedar Creek, Shasta County, California; Brock Mountain, California, Hosselkus Limestone Formation; Martin Bridge Formation, Hells Canyon, Oregon (Smith, 1927; Stanley and Whalen, 1989; Stanley and Yarnell, 2003; Caruthers and Stanley, 2008) 3 3 3 3 3 K. decussata 3 3 3 3 K. incrassata 3 3 3 3 Spongiomorpha ramosa Tethys 3 3 P. anomala n. sp. Kuhnastraea cowichanensis Alexander 3 3 3 3 3 clasts (Flügel et al., 1989; Follo, 1992, 1994). Ongoing research by Rosenblatt and Stanley suggests that this material was reworked subaerially from the Summit Point reefs and redeposited. It is also possible that reef deposits of Wallowa affinity became a source area for detritus only after they were tectonically incorporated into the northern margin of the Baker terrane. This margin has been interpreted as a .25-km-wide zone that includes metamorphosed Upper Triassic rocks of possible Wallowa terrane affinity infaulted with rocks of the Baker terrane (Schwartz et al., 2010). In this scenario, Upper Triassic reefs would have been tectonically transferred from an offshore, intraoceanic arc (Wallowa terrane) to a subduction-accretionary complex (Baker terrane) following Upper Triassic deposition and subsequently uplifted, eroded, and deposited into a pericratonic arc succession (Olds Ferry terrane) in the early Jurassic. Baker Terrane Source.—These clasts may be derived from Upper Triassic carbonate rocks of the Nelson Marble, currently exposed in the Baker terrane subduction-accretionary complex. Conodonts recovered from exposures of the marble and probable equivalents include Neogondolella navicula, N. polygnathiformis, and Xaniognathus sp., suggesting a range of middle–late Triassic (Morris and Wardlaw, 1986). The marbles are strongly recrystallized as a result of late Jurassic deformation (Avé Lallement, 1995) and abundant local quartz diorite intrusions (Prostka, 1967), and macrofossil identification has not been possible to date. Derivation of these clasts from the Nelson Marble would indicate proximity of the Baker subduction-accretionary complex and the Olds Ferry pericratonic arc by early Jurassic time. This paleogeographic interpretation is supported by numerous studies and reinforces the concept that portions of the Baker terrane represent forearc crust and the accretionary prism to the Olds Ferry terrane (e.g., Dickinson, 1979; Avé Lallemant, 1995; Vallier, 1995; Dorsey and LaMaskin, 2007; Schwartz et al., 2010). If the Nelson Marble is itself an olistostromal body, it may be intrabasinal with respect to the Baker terrane subduction-accretionary complex, or extrabasinal, having a Wallowa-terrane provenance. This suggests, in turn, that the detrital coral fauna of Willow Spring described here may be a multicyclic deposit. In this scenario, the first cycle is represented by olistostromal sliding of carbonate megaclasts of Wallowa- or Baker-terrane affinity into a marine basin floored by Baker terrane subduction-accretionary complex rocks. The second cycle 3 involves post-Norian, pre-Pliensbachian uplift and erosion (,10 myr duration) of the Baker terrane-floored basin and subsequent deposition of the Willow Spring carbonate conglomerate in a marine forearc basin floored by pericratonic arc rocks of the Olds Ferry terrane. Olds Ferry Terrane Source.—Willow Spring limestone clasts may be wholly intrabasinal, eroded from Upper Triassic reefal limestone that is not currently exposed in the Olds Ferry terrane. Exposures of thinbedded, Upper Triassic deep-water limestones are locally present, but have been interpreted to represent a heterozoan faunal assemblage (i.e., non-tropical-type deposition represented by fragmental allochems of echinoderms and mollusks; LaMaskin, 2008). These observations and interpretations suggest that typical reef deposition did not occur in the Olds Ferry pericratonic arc region during the late Triassic and therefore, a source area within the Olds Ferry terrane is not supported. Conversely, it is believed that a wide range of factors can restrict growth of photozoan carbonates and lead to deposition of a heterozoan cool-water community in a regionally warm-water setting (Westphal et al., 2010). These factors may include both global-regional factors (e.g., elevated trophic conditions, oceanographic instability, increased nutrient load from runoff, or cold-water intrusion in upwelling zones) and more local factors (e.g., high water energies or geographical isolation; Whalen, 1995; James, 1997; Parrish et al., 2001, Pomar et al., 2004; Westphal et al., 2010). Thus, it is possible that during the late Triassic, both heterozoan- and photozoan-favoring conditions existed in the Olds Ferry terrane. If so, then both the in situ Upper Triassic deep-water limestone (LaMaskin, 2008) and the Upper Triassic detrital limestone clasts in the upper member of the Huntington Formation represent deposits of Olds Ferry affinity. The observation that non-limestone clast and framework grain types appear to be restricted to rhyolite, rhyodacite porphyry, and basalt to andesite is suggestive of an intrabasinal, local source; these rock types are interbedded locally with the conglomerate deposits and are present in the lower and upper Huntington Formation. All of the observed detritus in the Willow Spring conglomerate, except for the Upper Triassic reefal lithofacies, can be accounted for locally (Brooks and Vallier, 1978; Brooks, 1979; Charvet et al., 1990; Tumpane, 2010). The lack of other recycled Wallowa terrane or Baker terrane detritus (e.g., quartzose metasedimentary, radiolarian chert) in associated sandstones or conglomerate matrix is strong evidence for an intrabasinal origin. 786 LAMASKIN ET AL. PALAIOS FIGURE 7—Representative faunal elements. A–B) Kuhnastraea cowichanensis; A) Colony showing corallite arrangement; B) Longitudinal view of septal growth; C–E) Paracuifia n. sp.; C) Close up of corallite showing lonsdaleiod dissepiments; D) Longitudinal view; E) Colony illustrating varying ontogenetic corallite size; F) Spongiomorpha ramosa; transverse view illustrating branching character. The first and second scenarios above require that any sediment transport and deposition system carrying detrital limestone clasts eroded from the uplifted Wallowa intraoceanic arc or Baker terrane subduction-accretionary complex would include detrital grains and clasts representative of other Wallowa or Baker terrane lithologies. Detrital grains and clasts of quartzose metasedimentary lithologies and radiolarian chert are absent from the Willow Spring location. Based on this key observation, we suggest that the source of late Triassic coralsponge reef faunas in the upper member of the Huntington Formation (Lower Jurassic) was intrabasinal and that the source rocks are no longer exposed in the region. This interpretation suggests that during the late Triassic, conditions were favorable for deposition of reefal limestone in all of the terranes of the Blue Mountains Province. As such, the presence of Upper Triassic limestone cannot be used to infer lithologic correlation between the terranes of the region (including the Salmon River Belt). Importantly, the potential regional source areas discussed above preclude the need to call upon sourcing from other, more exotic terranes of the Cordillera. Furthermore, the absence of key cosmopolitan and endemic genera from the Willow Spring site of the Olds Ferry terrane does not support the Wallowa, Alexander, or Wrangellia terranes as being potential sources for the limestone clasts of the upper Huntington Formation. Similarly, the absence of Kuhnastraea from the Lewiston, Idaho locality also argues against this area as a potential source. Thus, faunal data suggest that this low- PALAIOS 787 DETRITAL RECORD OF UPPER TRIASSIC REEF FACIES TABLE 3—Late Triassic reef faunas in allochthonous terranes of the western North American Cordillera. Terrane name Location(s) Alexander Southeastern Alaska Antimonio Chulitna Eastern Klamath Luning Allochthon Quesnel Sonora, Mexico Alaska Northern California–Southern Oregon Nevada British Columbia Stikine Formation Age Reference Nehenta Fm. Cornwallis Fm. Hound Island Volcanics Antimonio Fm. Chulitna sequence Hosselkus Ls. Early Norian Caruthers and Stanley, (2008a, 2008b) Early–mid. Norian Norian Norian González-León et al., 2005 Stanley and Yarnell, 2003 Smith, 1927; Stanley, 1979 Luning Fm. Takla Group Carnian–early Norian Early–middle Norian British Columbia Hancock Ls. Late Carnian–late Norian Wallowa Oregon, southern Wallowa mountains Martin Bridge Fm., Summit Point member Early Norian Wrangellia, North Wrangellia, South Peninsular Terrane Lewiston, Idaho Alaska Vancouver Island Alaska Lewiston, Idaho Chitistone Ls. Parson Bay Fm. Kamishak Formation Martin Bridge–Hurwal Formations Early Norian (kerri) Rhaetian Mid-Norian Late Norian Sandy and Stanley, 1993 Stanley and Nelson, 1996; Stanley and Senowbari-Daryan, 1999 Reid and Templeman-Kluit; 1987; Yarnell et al., 1999 Stanley and Senowbari-Daryan, 1986; Stanley and Whalen, 1989; Stanley et al., 2008 Caruthers and Stanley, 2008 Caruthers and Stanley, 2008 Blodgett, 2008 Nützel and Erwin, 2004 diversity coral assemblage from the Olds Ferry pericratonic arc terrane was likely derived locally. In detrital reef deposits, careful analysis of possible uplift-and-erosion scenarios, in combination with petrographic observations, is required to make an accurate determination of clast origin. Significance of Discovery The reefal, coral-sponge fauna described herein indicates a Tethyan affinity for Upper Triassic rocks of the Olds Ferry terrane. This is in concurrence with halobiid bivalve and ammonite collections from the thin-bedded, deep-water limestone unit of the Huntington Formation (Brooks, 1979; LaMaskin, 2008). As shown in Table 3, late Triassic faunas, including reef lithofacies, are preserved in allochthonous terranes throughout the western North American Cordillera. Our discovery at Willow Spring in the Olds Ferry terrane represents a new western North American Cordilleran record of Upper Triassic reef deposits. Identical taxa (Kuhnastraea cowichanensis and Spongiomorpha ramosa) have been found in numerous terranes of the western North American Cordillera. The co-occurrence of these taxa in the Wallowa and Olds Ferry terranes suggests that during the late Triassic these regions may have been in proximity to one another, an interpretation that supports tectonic models wherein the Wallowa, Baker, and Olds Ferry terranes were amalgamated offshore during the late Triassic– early Jurassic (Dorsey and LaMaskin, 2007; LaMaskin et al., 2011). The presence of these taxa in northern and southern Wrangellian locations (i.e., Alaska and Vancouver Island, British Columbia, respectively) and within the Alexander terrane in southeastern Alaska, however, suggests that these taxa had a cosmopolitan distribution and are not necessarily good indicators of terrane proximity during the late Triassic. CONCLUSIONS 1. A late Triassic coral-sponge reef fauna from a thick-bedded, cobble-to-boulder conglomerate in the informal upper member of the Lower Jurassic Huntington Formation near Huntington, Oregon, United States, represents the first discovery of reef-building lithofacies and fossils of this age in the Olds Ferry terrane. 2. Corals at the site include a high-growing, dendroid-phaceloid species that acted as either framework or sediment baffles, and a lowgrowing, cerioid, encrusting coral and a sponge that acted as sediment binders. Together, these organisms produced at least a 10–50 cm high reef-like or reefal framework. 3. Framework mineralogy of sandstones and clast types in the conglomerate suggest that the source of these Triassic coral-sponge reef faunas was intrabasinal. 4. The occurrence of the same two coral taxa in the Wallowa and Olds Ferry terranes may support the proximity of these two regions in the late Triassic, but the presence of these taxa in other Cordilleran terranes suggests that they are probably cosmopolitan and therefore not good indicators of terrane proximity. ACKNOWLEDGMENTS Funding was provided by grants to T.A.L. from the Weimer fund of SEPM (The Society for Sedimentary Geology), the Geological Society of America, Sigma Xi, AAPG (American Association of Petroleum Geologists), and the Baldwin Fellowship at the University of Oregon. Assistance with fossil collection was provided by T. Sieber. G.D.S. acknowledges support by the National Science Foundation (EAR0229795). We thank Editor Edith L. Taylor, Associate Editor Wolfgang Kiessling, reviewer M. Bernecker, and an anonymous reviewer for improving the readability and broader applicability of the manuscript. 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