Evolution of a Permo-Triassic sedimentary mélange, Grindstone terrane, east-central Oregon

CHARLES D. BLOME U.S. Geological Survey, M.S. 919, Federal Center, Box 25046, Denver, Colorado 80225 MERLYND K. NESTELL Department of , University of Texas at Arlington, Arlington, Texas 76019

ABSTRACT coherent stratigraphic succession consisting of both formal and informal lithostratigraphic units. Dickinson and Thayer (1978) reinterpreted the The Grindstone terrane in east-central Oregon is one of the few Grindstone terrane as a tectonic mélange of dismembered oceanic crust areas in western where large blocks of unmetamor- and associated strata. New paleontological and sedimentological data indi- phosed Devonian, Mississippian, and Permian limestones are inter- cate that the Grindstone exposures represent a sedimentary mélange mixed with Permian and Lower Triassic radiolarian chert and (Raymond, 1984) composed !of redeposited Paleozoic limestone blocks Pennsylvanian?, Permian, and Triassic volcaniclastic rocks. Although intermixed with Permian and Triassic clastic rocks in a forearc-basin set- originally described as parts of a coherent succession, we interpret the ting. The Paleozoic Grindstone rocks are overlain unconformably by Grindstone rocks to be a sedimentary mélange composed of Paleozoic Upper Triassic clastic rocks derived from older rock units and by Lower to limestone slide and slump blocks that became detached from a car- mid- submarine-fan sequences. bonate shelf fringing a volcanic knoll or edifice in Late Permian to Various terrane names have been proposed for the Blue Mountains Middle Triassic time and were intermixed with Permian and Triassic inliers (Vallier and others, 1977; Brooks and Vallier, 1978; Dickinson and slope to basinal clastic and volcaniclastic rocks in a forearc basin Thayer, 1978; Dickinson, 1979; Brooks, 1979). The study area was first setting. Paleogeographic affinities of the Grindstone limestone faunas named the "Paleozoic shelf terrane" by Vallier and others (1977) on the and volcaniclastic debris in the limestone and clastic rocks all indicate basis of shallow-water Devonian rocks in its western part. It was also deposition in proximity to an island-arc system near the North Ameri- named the "mélange terrane" by Dickinson and Thayer (1978), the can craton. The Grindstone terrane deposits are unconformably over- southwesternmost part of the "dismembered oceanic terrane" by Brooks lain by Upper Triassic to Middle Jurassic sequences of the I zee and Vallier (1978), the "central mélange terrane" by Dickinson (1979), terrane. Although (ittiologie and faunal differences indicate that the the "oceanic/mélange terrane" by Mullen-Morris and Sarewitz (1983), Grindstone and Izee terranes together represent a tectonic block sepa- and the "Grindstone terrane" (Fig. 1) by Silberling and others (1984, rate from the adjacent Baker terrane, all three terranes were 1987). juxtaposed by Late Triassic or Early Jurassic time. Dickinson and Thayer (1978) and Dickinson (1979) considered the We recommend reduction to informal status for the Coffee Creek Miller Mountain, Frenchy Butte, and Grindstone/Twelvemile mélange (Mississippian), Spotted Ridge (Pennsylvanian?), and Coyote Butte areas (Fig. 2) to be parts of their "mélange terrane." Silberling and others (Permian) formations because (1) they cannot be mapped or traced (1984,1987) later placed the Miller Mountain and Frenchy Butte areas in beyond limited areas, and (2) these older rocks are chaotically inter- the Baker terrane. We adhere to Silberling and others' (1984, 1987) ter- mixed with younger chert and volcaniclastic rocks. New biostrati- rane nomenclature for all Blue Mountains province terranes, which are, graphic data indicate that the bulk of the Spotted Ridge volcaniclastic from southwest to northeast, the Grindstone, Izee, Baker, Olds Ferry, and rocks represent a part of the Triassic Vester Formation of the Izee Wallowa terranes (Fig. 1). terrane. Previous Studies INTRODUCTION McKitrick (1934) constructed the first geologic map of the Suplee The Blue Mountains province of northeastern Oregon and western- area and suggested that the structure was anticlinal based upon the oppos- most Idaho contains Devonian to Cretaceous rocks exposed in numerous ing dips of the Paleozoic strata, the presence of younger Mesozoic strata on erosional inliers surrounded by Tertiary volcanic and sedimentary rocks the flanks of the older Paleozoic rocks, and the opposing dips in the (Brooks and Vallier, 1978). The Grindstone terrane, located in the south- younger strata. Merriam and Berthiaume (1943) described undifferen- westernmost part of the province (Fig. 1), includes some of the few Pa- tiated clastic rocks as interbedded with their Coffee Creek, Spotted Ridge, leozoic limestone and chert exposures between northern Nevada and and Coyote Butte Formations. They also recorded unconformable contacts northeastern Washington and is unique in possessing unmetamorphosed with the unnamed Triassic volcaniclastic rocks and noted that the sand- eugeosynclinal Paleozoic rocks bearing well-preserved Devonian, Missis- stone exposures are generally float and that angular discordances separate sippian, and Permian faunas. Merriam and Berthiaume (1943) and others the clastic and nearby limestone exposures. Cooper (1957) also observed have interpreted the Grindstone carbonate and clastic rocks as a relatively discordant relations between the Grindstone limestones and surrounding

Additional material for this article, including locality descriptions and figures, can be obtained free of charge by requesting Supplementary Data 9121 from the GSA Documents Secretary.

Geological Society of America Bulletin, v. 103, p. 1280-1296,7 figs., October 1991.


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Figure 1. Distribution of pre-Tertiary rocks with generalized terrane boundaries for the southwestern part of the Blue Mountains province: GS = Grindstone terrane; IZ = Izee terrane; BA = Baker terrane; OF = Olds Ferry terrane; and WA = Wallowa terrane (terminology after Silberling and others, 1984,1987).

rocks and postulated that the limestones are lenticular bodies in the sandy pieces missing" (p. 131). He also suggested that regional east-west shorten- and conglomeratic . An unpublished map of the Suplee area by J. W. ing produced west-dipping thrust faults and that the resulting slices Harbaugh and T. H. Hughes (unpub. map, 1957) shows the Paleozoic had broken into blocks. units as large northeast-trending bands, but it differs from previous maps Vallier and others (1977) placed the Paleozoic rocks south of Suplee by illustrating the margins of individual exposures within each strati- in their "Paleozoic shelf terrane" because the terrane contains mainly graphic unit. shallow-water carbonate and coarse-grained clastic rocks tectonically Dickinson and Vigrass (1965) included only the northeasternmost mixed with finer-grained clastic rocks and chert. Dickinson and Thayer part of the Grindstone terrane in their study and lumped all of the Paleo- (1978; their Grindstone-Twelvernile mélange area) were the first to apply zoic sedimentary rocks into one unit. Jurassic sedimentary rocks were the mélange concept of individual limestone, graywacke, and volcanic designated as formal members of the Snowshoe Formation, some of which blocks in a tectonic matrix of deformed ocean-floor sediments. They also are found near Suplee (Fig. 2). They noted the tectonic complexity of the assigned the conglomerate along the periphery of the mélange to the Vester Suplee rocks, stated that original stratigraphic thicknesses could not be Formation based on its similarities to Begg Member (Vester Formation) estimated with confidence, and interpreted the contact between Paleozoic conglomerate to the east. According to Dickinson and Thayer (1978, and Triassic rocks to the east as a ("Camp Creek fault"). p. 152), all of the major contacts are faulted, and no amount of work short Buddenhagen (1967) briefly discussed some of the lithostratigraphic of wholesale excavation could produce a really satisfactory geologic map, units in the John Day Uplift and stated that "deciphering the geology of given the high degree of structural complexity and the lack of exposure. the Paleozoic area is akin to working a jigsaw puzzle with many of the Wardlaw and others (1982) questioned the "mélange concept" of

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EXPLANATION West of Poison Creek Fault East of Poison Creek Fault Terrestrial sedimentary and Terrestrial sedimentary and volcanic rocks (Cenozoic) volcanic rocks (Cenozoic) Unconformity Unconformity r,c op,c'i 0 o Bernard Formation n n n n o n n (Cretaceous) Unconformity

Volcaniclastic and carbonate Volcaniclastic and carbonate rocks (Upper Jurassic to rocks (Upper Jurassic to Unconformity Lower Jurassic) Unconformity Lower Jurassic)

Vester Formation Aldrich Mountains Group (Upper Triassic) (Lower Jurassic and Upper Triassic) Unconformity Unconformity

Melange terrane Melange terrane (Upper Triassic to Paleozoic) vY (Upper Triassic to Paleozoic)-As mapped, includes the ophiolitic Upper Permian Canyon Mountain Complex

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recommend that these well-established formational names be retained as Figure 2. Generalized geologic map of the Izee and Grindstone the informal names: Coffee Creek limestone, Spotted Ridge clastic rocks, terranes, showing the surrounding mélange areas (modified from and Coyote Butte limestone. Dickinson and Thayer, 1978). Frenchy Butte and Miller Mountain mélange areas now included within the Baker terrane, Grindstone- Devonian Limestone Twelvemile mélange area considered the Grindstone terrane, and other rocks between Suplee and John Day placed within the Izee Lithology and Depositional Setting. Some of the oldest Paleozoic terrane according to Silberling and others (1984,1987). rocks in Oregon are represented by two widely Spaced limestone and associated clastic exposures in the north and south parts of the Grindstone terrane (unit "Dl" in Fig. 3). Kleweno and Jeffords (1961) dated these blocks as Middle Devonian based on megafossil data and described the larger northern outcrop (Fig. 4A) as -100 ft (30 m) of highly folded, Dickinson and Thayer (1978) on the basis of their paleontologie study of massive, cherty limestone with associated cherty breccia and sandstone three Coyote Butte exposures, and they suggested that the similarity among overlain by chert, argillite, and associated sandstone and siltstone. J. W. outcrops meant that the mélange was not as chaotic as originally proposed. Harbaugh and T. H. Hughes (unpub. map, 1957) referred to this outcrop They also implied that the Coyote Butte Formation represented either a as their "Berger" unit and described the clastic rocks as being deposition- fragment of a large olistostrome or a number of structural blocks that ally related to the Devonian limestone pods. This outcrop has been infor- maintained stratigraphic integrity. mally referred to as the "Birdsong limestone" by Danner (1977b). The chert and sandstone directly adjacent to the limestone exhibit GRINDSTONE TERRANE ROCK TYPES, FAUNAS, approximately the same strike, dip, and metamorphic grade; they are more AND DEPOSITIONAL SETTINGS altered than other clastic rock exposures. The contact between the lime- stone and chert appears gradational, but the contact with the adjacent The Grindstone terrane contains some of the oldest rock units in the sandstone is sharp and assumed to be unconformable. Blue Mountains province and includes (1) Middle Devonian limestone A smaller Devonian limestone pod is present in the southern part of interstratified with sandstone, chert, and argillite; (2) Mississippian lime- the terrane just northwest of the Berger Ranch house near the Crook and stone surrounded by, and intermixed with, calcareous and conglomeratic Harney County boundary (unit "Dl" in Fig. 3) and was informally re- sandstone (Coffee Creek Formation of Merriam and Berthiaume, 1943); ferred to as the "Berger Ranch limestone" by Danner (1977b). Coeval (3) Pennsylvanian? mudstone, sandstone, and conglomerate containing limestones have been reported from the Shasta Lake and Yreka areas in plant remains and minor limestone (Spotted Ridge Formation of Merriam northern California, Roberts Mountains in north-central Nevada, and and Berthiaume, 1943); (4) Lower Permian, partly fusulinacean-, northeastern Washington (Kleweno and Jeffords, 1961; Danner, 1967, brachiopod-, and bryozoan-bearing, volcaniclastic and dolomitic lime- 1977a, 1977b). stone (Coyote Butte Formation of Merriam and Berthiaume, 1943); The Middle Devonian limestone formed in an intra-arc basinal pa- (5) Permian and Lower Triassic, radiolarian-bearing, multicolored chert leoenvironment (Danner, 1967; Poole and others, 1977) relatively near and dark mudstone; and (6) Upper Permian and Triassic, volcaniclastic the North American continental margin (Boucot and Potter, 1977). Poole sandstone and siltstone, limestone breccia, and pebble to boulder con- and others (1977) suggested that the Devonian intra-arc basin was contin- glomerate (clasts containing Lower Permian fusulinaceans and Permian uous with the continental shelf but was deeper and rimmed with volcanic and Lower Triassic radiolarians). arcs fringed with reefs. Other correlative arc-related sequences include the Rocks immediately adjacent to the Grindstone terrane in the Izee Kennett Formation in northern California (Watkins and Flory, 1986), part terrane (Fig. 1) include (1) chert-pebble conglomerate assigned to the Begg of the Orcas Group in northwestern Washington, and the Garlock Forma- Member of the Vester Formation; (2) minor unnamed Lower Jurassic tion (of formal usage) in southern California (Danner, 1977b). limestone and associated siltstone; and (3) Middle Jurassic mudstone, Biostratigraphy. The megafossil fauna from the two Devonian lime- siltstone, and minor sandstone (Weberg, Warm Springs, and Basey stone blocks includes Middle Devonian corals, stromatoporoids, and members of the Snowshoe Formation; Dickinson and Vigrass, 1965). brachiopods (Kleweno and Jeffords, 1961; Danner, 1967; Sorauf, 1972; Poole and others, 1977). Additional brachiopod genera (Schizoporia and Validity of Formations Emanuella) and a conodont fauna of Middle Devonian (Givetian) age were found in the northern limestone block (Johnson and Klapper, 1978). The stratigraphic terminology proposed by Merriam and Berthiaume Savage and Admundson (1979) noted that conodonts from that locality (1943) has been cited in a large number of geologic studies, even after the possess a conodont color alteration index (CAI) of 3, which corresponds introduction of plate and the "terrane" concept (Irwin, 1972). to a temperature range of 110-200 °C (Epstein and others, 1977). More than 30 paleontologie studies have dealt with a single isolated ex- The southernmost limestone block yielded Middle Devonian (proba- posure or, in some instances, several exposures that were assigned to bly Givetian) corals, including Heliolites cf. H. relectus, Thamnopora sp., Merriam and Berthiaume's formations. and Grypophyllum sp. (William Oliver, 1987, written commun.). The Biostratigraphic and sedimentologie data presented in this study sug- Oregon Devonian coral faunas have affinities with faunas in the Kennett gest that (1) some of the Spotted Ridge volcaniclastic rocks are a part of Formation, eastern of northern California (Watkins the Permian and Triassic sedimentary sequence, and (2) the Coffee Creek and Flory, 1986), and in England, Germany, the Canadian Arctic, New and Coyote Butte limestone exposures do not represent formations as South Wales, and northern Queensland. originally defined by Merriam and Berthiaume (1943). Recognition of A Triassic? limestone pod that crops out very near the southern their general lack of mappability and traceability negates their formational Devonian exposure (Danner, 1977b) was assigned a Triassic age by John- status (International Subcommission on Stratigraphic Classification, 1976; son and Klapper (1978). The only other Devonian fossils from eastern North American Commission on Stratigraphic Nomenclature, 1983). We Oregon are Middle to Late Devonian conodonts (Polygnathus spp.) from

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/10/1280/3380881/i0016-7606-103-10-1280.pdf by guest on 24 September 2021 Figure 3. Map showing the general distribution of Grindstone Coyote Butte limestone and unnamed chert exposures within the Grindstone- Twelvemile mélange area shown in Figure 2. DI = Middle Devonian limestone; CC = Coffee Creek limestone (type area of Coffee Creek Formation of Merriam and Berthiaume, 1943); J1 = unnamed Lower Jurassic limestone; filled areas = chert exposures and float; outlined areas denote Coyote Butte Permian limestones.

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c D Figure 4. (A) Devonian limestone exposure (Dl in Fig. 3) on west side of Trout Creek in northern part of the Grindstone terrane. Darker chert-grain sandstone exposed on flank (right side in photo) of limestone and on ridge across Trout Creek to the east. (B) Trend of Coyote Butte dolomitic limestone blocks (loc. 83, see footnote 1) along east side of south-flowing drainage to Grindstone Creek. Darker Spotted Ridge chert-pebble conglomerate exposed near base of slope in foreground. (C) Typical exposures of fusulinacean-bearing and dolomitic Coyote Butte limestone and unnamed chert/tuff exposures along south side of Grindstone Creek, central part of Grindstone terrane. (D) One of the rare exposures (loc. 19, see footnote 1) of volcaniclastic sandstone surrounded by softer, less resistant mudstone. Divisions on hammer = 10 cm (4 in.).

a limestone exposure in the Baker terrane (Fig. 1) to the northeast Biostratigraphy. Merriam and Berthiaume (1943, p. 151) listed cor- (Mullen-Morris and Wardlaw, 1986). als, brachiopods, small loxonemoid gastropods, and lithistid sponge spic- ules in limestone ~45 ft (14 m) below the top of their Coffee Creek Coffee Creek Limestone Formation. They also stated that the Coffee Creek sandstones are no older than early Carboniferous based on the presence of the brachiopod Striatif- Lithology and Depositional Setting. Limestone exposed on Coffee era and that the Gigantella horizon is approximately Mississippian Creek, a drainage that enters Grindstone Creek south of Wade Butte, was (Visean) in age. named the "Coffee Creek Formation" by Merriam and Berthiaume The Coffee Creek was assigned a Late Mississippian (middle and late (1943). The type section is in the west-central part of the terrane ("CC" in Meramecian and Chesterian) age by Poole and Sandberg (1977). Skinner Fig. 3; USGS Twelvemile Reservoir 7.5' quad., T. 18 S„ R. 25 E„ SEW, and Wilde (1965) thought that the Coffee Creek contained fusulinacean NW/4, sec. 30). According to Merriam and Berthiaume, typical Coffee faunas of Early Pennsylvanian age, but fusulinaceans (Eostaffella) and Creek rock types include well-bedded, carbonaceous limestone, muddy to corals (Hexaphyllia) collected from near the type section (loc. 47 in Data sandy limestone, and calcareous sandstone; calcareous sandstone accounts Repository1) indicate a Late Mississippian (Chesterian) age (Sada and for a large part of the unit. Dutro (1987) interpreted the Coffee Creek Danner, 1973). Correlative Eostaffella species have been described from limestone as being deposited in a warm, shallow-marine paleoenviron- Chesterian sequences in Japan, China, and the Soviet Union and are ment near island arcs not far from the North American craton. thought to be restricted to shallow-water shelf sequences. Occurrences of Buddenhagen (1967) stated that he had difficulty in establishing the lower and upper limits of the Coffee Creek Formation and in estimating formational thickness. Our study indicates that, with the exception of the type exposure, Coffee Creek exposures are less than 20 ft (6.1 m) thick and 'Detailed locality descriptions and four tables containing corresponding fauna! data have been placed in the GSA Data Repository. This information may be are generally restricted to the west-central part of the Grindstone terrane. obtained free of charge by requesting Supplementary Data 9121 from the GSA Small blocks of Coffee Creek float are scattered throughout (CC, Fig. 5). Documents Secretary.

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Volcaniclastic sandstone cobbles from the type area and near the Figure 5. Distribution of mappable limestone, chert/tuff, con- Coffee Creek type section (north flank) contain coral, bryozoan, brachio- glomerate, and sandstone exposures in and along the border of section pod, and mollusc debris. One volcaniclastic-rich cobble also contained the 10, located ~2 mi (33 km) directly west of the Robertson Ranch fusulinacean Nankinella cf. N. plummeri in its carbonate-cemented matrix shown in Figure 3. Note the northeast trend of Coyote Butte limestone (Fig. 6A). This fusulinacean species is Early Pennsylvanian in age and has and chert/tuff exposures, and the random distribution of Coffee Creek been reported from sequences in southern British Columbia, northwestern limestone (CC), Spotted Ridge clastic rocks (SR), and Jurassic clastic Washington, and Japan by Sada and Danner (1974). Limestone float with rocks (Jc). Lower Permian fusulinaceans is also common at the type area. Several red chert cobbles from Spotted Ridge conglomerate in the central part of the terrane (loc. 15, see footnote 1) contain Early Permian (late Wolfcampian/early Leonardian) radiolarians similar to those from Hexaphyllia in North America are confined to the Pacific Northwest (Nel- the Grindstone bedded cherts (Figs. 2a and 2b in Data Repository, see son, 1982). footnote 1). We believe that much of the Spotted Ridge conglomerate is Late Permian and younger and represents a part of the Vester Formation Spotted Ridge Clastic Rocks based on Lower Permian fusulinaceans and radiolarians in limestone and chert clasts, respectively. Lithology and Depositional Setting. Mudstone, siltstone, and sand- stone to boulder conglomerate exposed on the west flank of Spotted Ridge Coyote Butte Limestone (USGS Delintment Lake 15' quad., T. 18 S., R. 25 E., central part of sec. 20) were named the "Spotted Ridge Formation" by Merriam and Ber- Lithology and Depositional Setting. The Coyote Butte Formation thiaume (1943). Small blocks of mudstone containing plant debris and was named by Merriam and Berthiaume (1943) for a long, prominent carbonaceous material are scattered throughout the terrane (Fig. 5), but limestone ridge that constitutes most of Coyote Butte (also called Three large mudstone exposures are confined to the type locality. The badly Buttes) in the southern part of the terrane (Fig. 3; USGS Twelvemile weathered plant-rich mudstone at the type locality is interpreted to be a Reservoir 7.5' quad., T. 19 S., R. 25 E., east-central part of sec. 18). The large block (or several blocks), the contacts of which are obscured by limestone exposures are lithologically consistent throughout much of the sedimentary cover. terrane in being composed of light gray, massive crinoidal, fusulinacean- Typical Spotted Ridge clastic exposures are small and nonresistant and bryozoan-bearing packstone and grainstone which grade upward into with the exception of chert-pebble conglomerate (Fig. 4B). Volcaniclastic finer-grained packstone and darker gray, brachiopod-bearing wackestone. conglomerate float is common along the Coffee Creek limestone-bearing Ketner (1967) indicated that the upper part of the Coyote Butte Formation slopes. Euhedral-zoned plagioclase; rhyolitic, welded tuff; and andesitic/ was overlain by as much as 900 ft (274 m) of chert. Abundant chert float dacitic rock fragments (Fig. 6A) in volcaniclastic sandstone cobbles from and small pods of chert and siliceous mudstone surround Coyote Butte near the Coffee Creek type section (loc. 85, see footnote 1) indicate (Fig. 3) but are not in depositional contact with the limestone. deposition near a volcanic island source. Rich (1977) suggested that Other large Permian limestone exposures are west and southwest of Spotted Ridge conglomerate deposition occurred in an intra-arc basin. Coyote Butte. Small blocks are exposed in the central and northern parts Merriam and Berthiaume (1943) assigned most of the chert in the of the terrane and on the tops and flanks of topographic highs (Figs. 4B Grindstone terrane to the Spotted Ridge Formation and stated that the and 4C). chert could represent more than one stratigraphic interval. Buddenhagen Many of the limestone blocks, particularly those in the central part of (1967) assigned the Grindstone cherts to his "Birdsong beds," clastic sedi- the terrane, are dolomitic (Fig. 4C). Isolated, fine-grainedooliti c limestone mentary rocks exposed in the hills west of the Weberg and Robertson blocks and rare limestone conglomerate and breccia exposures are gener- ranches (Fig. 3). ally confined to the northern part of the terrane. Biostratigraphy. Read and Merriam (1940) recorded several plant Limestone in the southern part of the Grindstone terrane contains genera from Spotted Ridge mudstones and suggested an Early Pennsylva- minor volcaniclastic debris (loc. 10, see footnote 1), including rhyolitic and nian age, although a Late Pennsylvanian age was questioned. Merriam and welded tuff rock fragments. Volcaniclastic debris (andesitic, dacitic, and Berthiaume (1943) also supported an Early Pennsylvanian age for the unit. welded tuff rock fragments) is also found in fusulinacean- and bryozoan- Arnold (1953) described two new plant species and stated that the flora bearing carbonate rocks (Fig. 6B) in the northern part (loc. 62, see foot- most likely was Early Pennsylvanian. Mamay and Read (1956) also de- note 1). Zeolites replacing fossil debris are common in many of the scribed new flora taxa and concluded that there is just as much evidence to volcaniclastic limestone exposures. support a Late Pennsylvanian age. The limestone outcrops trend northeast in the northern part of the A fossil assemblage from mudstone clasts in the type area contains terrane; this trend changes to northwest in the central part and reverts to the Early Pennsylvanian (Morrowan) ammonoid genus Cancelleroceras the northeast in the southern part (Fig. 3). Individual beds within each (Gordon, 1979). This genus is known from uppermost Namurian beds in exposure generally dip steeply (to 75°). Some limestone blocks appear northwest Europe and from the upper part of the Hale Formation in rotated, whereas others contain reversed stratigraphy, and some exhibit Arkansas. disturbed and deformed bedding. Mullen-Morris and Wardlaw (1986) reported that sandstone blocks Chert replacement of limestone is common throughout as generally containing minor limestone yielded Early Pennsylvanian plants, cono- unfossiliferous, gray to black, translucent irregular patches, pinch-and- donts, and fusulinaceans. Sandy crinoidal limestone collected along the swell beds, or thin amorphous interbeds that alternate with thicker primary southern flank of White Butte (loc. 66, see footnote 1) yielded poorly chert beds. Chert replacement is indicated by the presence of rare, poorly preserved conodonts of probable Pennsylvanian age (Bruce Wardlaw, preserved, silicified fossils and irregular and/or gradational contacts be- 1987, written commun.). tween chert and limestone.

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C D Figure 6. (A) Photomicrograph of carbonate-cemented volcaniclastic sandstone from the Spotted Ridge type area and near the Coffee Creek type section showing the Early Pennsylvanian fusulinacean Nankinella cf. N. plummeri in a matrix of euhedral feldspar and andesitic/ dacitic rock fragments. Magnification = 45"; maximum dimensions of all photos = 3.4 mm. (B) Photomicrograph of coarsely grained crinoidal/ fusulinacean-bearing Coyote Butte grainstone (loc. 62; see footnote 1). Thin section contains about 15% volcaniclastic rock fragments, including abundant andesitic-dacitic and scarce tuffaceous debris. Oasts are well rounded, suggesting moderate distance transport from volcanic source. Magnification = 5x. (C) Photomicrograph of red radiolarian- and sponge spicule-rich red chert (loc. 4, see footnote 1). Dark areas are unfossiliferous, fine-grained siliceous mudstone. Outline of cone-shaped Pseudoalbaillella visible near bottom center of photo. Magnification = 30x. (D) Photomicrograph (uncrossed polars) of volcaniclastic sandstone (loc. 19, see footnote 1) in the Grindstone terrane. Note the poor sorting, high angularity of quartz grains, and the abundance of opaques. Magnification = 25x.

The presence of Early Permian (late Wolfcampanian and Leonard- tuff, andesitic-dacitic, and rhyolitic rock fragments in many Grindstone ian) colonial coral and fusulinacean faunas, and grainstones and pack- limestones, substantiates an island-arc source. The lack of quartzite in stones in many Coyote Butte limestones indicates limestone deposition in association with the shelf carbonates indicates that the terrane was not a high-energy, shallow-water carbonate environments. Slightly younger segment of the Paleozoic continental margin (Dickinson and Thayer, (Leonardian) brachiopod faunas in limestones with a high clastic compo- 1978). Approximately coeval Permian volcaniclastic units, possibly depos- nent closely correlate with deep- and/or cold-water Euro-Russian faunas ited within the same volcanic island-arc province, include the Quinn River (Cooper, 1957). Crossing exposure, northern Nevada (Ketner and Wardlaw, 1981), and Stevens (1977) concluded that the Coyote Butte limestones formed in the Nosoni and Dekkas Formations (Miller and Wright, 1987) in the a volcanic arc province. The presence of volcanic debris, such as welded- eastern Klamath Mountains.

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Biostratigraphy. Brachiopod, conodont, coral, and fusulinacean fau- present in small metamorphosed limestone pods in the west-central part of nas from the Coyote Butte limestone indicate Early Permian (late Wolf- the Baker terrane (Fig. 1) near the town of Sumpter (western Elkhorn campian to Leonardian) ages. The colonial corals include several species of Mountains), and in the southern part of the Greenhorn Mountains Heritschioides, Petalaxisoccidentalis, and Thysanophyllum! sp. (Merriam, (Mullen-Morris and Wardlaw, 1986). Coeval fusulinacean genera of 1942; Stevens and Rycerski, 1983). Some of Merriam's taxa have been Tethyan affinity occur in the Baker terrane east of the Elkhorn Mountains recovered from the Lower Permian McCloud Limestone in northern Cali- and near John Day along the northern edge of the Canyon Mountain fornia (Wilson, 1982), from lower Leonardian strata in northeastern Ophiolite complex (Nestell, 1983). The fusulinacean faunas near Mitchell, Nevada (Stevens, 1977), and from various Permian localities in the Pacific Sumpter, and John Day, and in the Greenhorn Mountains are found in northwest (Stevens and Rycerski, 1983). rocks which have been assigned by Silberling (1984, 1987) to the Baker The Coyote Butte colonial coral fauna includes genera known in the terrane. central Great Basin subprovince, which suggests that the Oregon faunas Pseudofusulinella, a fusulinacean genus common in Coyote Butte were a part of the cratonal Thysanophyllum coral belt (Stevens and Ry- faunas (Table 2 in Data Repository, see footnote 1), northern Californian cerski, 1983). This fauna also has similarities with faunas from several McCloud Limestone faunas, and other faunas from the Pacific Northwest, suspect terranes (Stikine and eastern Klamath), which had an origin out- Canadian and Soviet Arctic, Urals, and Japan is also present in late board of the continental margin during Early Permian time (Stevens, Carboniferous and Permian cratonal faunas (Ozawa, 1967). 1989). The Early Permian Coyote Butte fusulinacean assemblages have af- Brachiopod faunas described by Cooper (1957) from stratigraphi- finities with those from Sonomia (Speed, 1979), a terrane accreted to the cally higher parts of the limestone are no older than latest Leonardian and North American craton in latest Permian or Early Triassic time. Ross and may be as young as early Guadalupian. Cooper correlated the Oregon Ross (1983) discussed and compared Sonomian fusulinacean faunas with brachiopod faunas with faunas from the Glass Mountains, southwestern those from other Pacific Northwest accreted terranes (Quesnellia, Stikinia, Texas, with faunas from the Cache Creek Group of British Columbia, and Northern Cascades) and suggested that Sonomia formed in an arc or and with middle or upper Artinskian faunas from the eastern Soviet back-arc setting off the coast of southwestern California. Union. Several large limestone exposures (Triangulation Hill, Coyote Butte, Siliceous Rocks and Tuckers Butte) were sampled for conodonts and fusulinaceans by Wardlaw and others (1982). Their fusulinacean data suggested, at least in Lithology and Depositional Setting. Siliceous rocks include abun- part, a Leonardian age, and the conodont faunas indicated a Leonardian (= dant blue-black, green, and red radiolarian chert, siliceous mudstone, and Artinskian; see Furnish, 1973) age for the exposures. They also concluded fine-grained tuff. Even though the chert exposures exhibit some lateral that the Grindstone faunas are remarkably similar to those from near coherence, the unit as a whole was never assigned a formational name. Quinn River Crossing, Nevada. Bedded chert in the northern part of the terrane was informally named the In the central part of the terrane, just north of Grindstone Creek, "Birdsong beds" by Buddenhagen (1967) and was included as part of the dolomitic and crinoidal limestones containing limestone breccia and re- "Blanchard" chert in an unpublished map by J. W. Harbaugh and T. H. placement chert crop out over several kilometers in a north-northeast trend Hughes (1957). Most of the Grindstone cherts exhibit well-developed (Figs. 3 and 4B). One limestone pod (loc. 83, see footnote 1) yielded bedding that contrasts with many of the metacherts in the Baker terrane poorly preserved Early Permian conodonts (Sweetognathus), silicified (Fig. 1). Multicolored, bedded chert has not been found in the adjacent gastropods (Tapinotomarial), and poorly preserved dolomitized fusulina- Izee terrane (Blome, 1984; Blome and others, 1986). ceans (probably Schwagerina). A dolomitic crinoidal limestone to the Chert exposures are most abundant in the northern part of the ter- north near the top of White Butte (loc. 84, see footnote 1) contains broken rane, and many parallel the trend of Permian limestone (Figs. 3 and 5). specimens of a primitive form of the Early Permian conodont Neogondo- The chert exposures are typically nonresistant, red and black, and thickly lella idahoensis. Both conodont assemblages contain elements with a CAI bedded in the north near the North Fork of Trout Creek. Thin intrabeds of of 2 (60-140 °C). A limestone sample collected ~ 1.5 mi (2.8 km) west of dark, red to black mudstone and shale represent a minor fraction of the Coyote Butte (loc. 76, see footnote 1) yielded a rich, early Leonardian siliceous rocks. Cherty breccia, tuff, and recrystallized light-colored chert conodont fauna with Neogondolella cf. N. idahoensis, Hindeotus sp., form more prominent exposures than the less altered red and green chert. Sweetina sp., and Neostreptognathodus sp. Chert exposures between Grindstone and Twelvemile Creeks are Merriam and Berthiaume (1943) reported earliest Permian fusulina- generally smaller, more recrystallized, and less continuous. Thinly bedded, ceans from stratigraphically lower parts of the Coyote Butte limestone. dark red, siliceous mudstone crops out ~0.5 mi south of Coyote Butte; it is Skinner and Wilde (1966) also described Early Permian (late Wolfcamp- well laminated, lacks many of the small-scale sedimentary features anian or early Leonardian) fusulinaceans from several limestone blocks common in the dark colored cherts, and contains a smaller microfossil north of the Grindstone-Izee terrane boundary (Iocs. 49-50 and 62-63, see component, with the radiolarian skeletons poorly preserved and footnote 1) and from a limestone pod near Grindstone Creek (loc. 61, see fragmentary. footnote 1). Radiolarians and sponge spicules constitute a substantial part of the Limestones collected from more than 40 localities contain similar red and green chert and are equally concentrated in both lighter colored fusulinacean faunas of late Wolfcampian to early Leonardian age. The laminae and alternating dark, clay-rich and iron-stained laminae (Fig. 6C). major Coyote Butte fusulinacean taxa are listed in Figure 3 of the Data Many of the spicules and cone-shaped radiolarians exhibit preferred orien- Repository (see footnote 1). The Grindstone fusulinacean faunas have tations, which suggests current transportation and reworking (Imoto, affinities with those described from the middle part of the McCloud Lime- 1983). Small-scale sedimentary structures, such as normal graded bedding stone (Zones G and H) in the Shasta Lake area, northern California (both vertical and lateral), minor cross-bedding and cut-and-fill structures (Skinner and Wilde, 1965,1966). disrupting laminae, suggest that the cherts accumulated in a slope paleoen- Another McCloud-related fauna in central Oregon includes poorly vironment dominated by turbidity currents charged with siliceous skeletal preserved fusulinaceans from small, highly altered siliceous limestone pods debris (Nisbet and Price, 1974). in Meyers Canyon, west of the Grindstone terrane and north of Mitchell, One explanation for deposition of the Grindstone chert and siliceous Oregon (Oles and Enlows, 1971). McCloud-related fusulinaceans are mudstone is that the siliceous biogenic material (radiolarians and sponge

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spicules) were deposited at a slow but constant rate, but the clay was According to Merriam and Berthiaume (1943), they underlie Jurassic deposited rapidly and intermittently to form the mudstone interbeds in a strata near Wade Butte (Fig. 2) and overlie the Coffee Creek and Coyote base-of-slope to basinal depositional paleoenvironment (Iijima and others, Butte limestones. Triassic conglomerate on the eastern and western mar- 1978, ¡979). The rapid deposition of the mudstone partings probably gins of the terrane was assigned to the Vester Formation by Dickinson arid resulted from distal turbidity currents or bottom currents at intervals of a Thayer (1978), but volcaniclastic rocks and conglomerate of unknown age few thousand to tens of thousands of years (Iijima and Utada, 1983; also are found between Grindstone and Twelvemile Creeks. The conglom- Matsumoto and Iijima, 1983). Jenkyns arid Winterer (1982) concluded erate and sandstone exhibit wide variations in grain size, texture, clast that fluctuations in radiolarian chert/clay ratios were a result of the near- color, and composition. surface radiolarian productivity coupled with turbidity-current, and par- The siltstone and sandstone exposures are generally nonresistant, ticularly bottom-current, activity. dark colored (gray to green), volcaniclastic, locally chert-grain rich, and Biostratigraphy. "Grindstone chert exposures were considered by exposed only in drainages and road cuts (Fig. 4D; loc. 19, see footnote 1). Merriam and Berthiaume (1943) to be Carboniferous on the basis of their Dark gray sandstone surrounds black limestone and green and black chert placement in the Spotted Ridge Formation. Reported fossils include Early just south of Wade Butte (loc. 9, see footnote 1). Merriam and Berthiaume Triassic conodonts (Neospatkodus pakistanensis and Ellisonia sp.) and (1943) reported that the sandstones are slightly calcareous and contain possibly Carboniferous radiolarians (Dickinson and Thayer, 1978; Ward- angular chert and quartz grains, abundant feldspar, and rare igneous rock law and Jones, 1980). According to Wardlaw and others (1982), all of the fragments. Pétrographie analyses indicate a tuffaceous composition with radiolarian faunas recovered from the Grindstone cherts indicate Mesozoic angular to subangular quartz grains (Fig. 6D), some of which contain ages. glass-infilled inclusions, sparse feldspar (plagioclase), rhyolite, rare carbon- Blome and others (1986) showed that Grindstone chert contains ate and mafic rock fragments, abundant zeolites, and ash (originally Permian (late Wolfcampian to late Guadalupian) radiolarian faunas. Ad- pumice). ditional chert collections from more than 40 localities suggest nearly con- Biostratigraphy. Conglomerate and sandstone in the west-central tinuous Grindstone chèrt deposition from Early Permian through Early part of the terrane were assigned a Triassic age by Merriam and Ber- Triassic time, with the exception of the early Wolfcampian and late thiaume (1943) based on (1) their unconformable relationship to other Djulfian. • Paleozoic units arid (2) the fact that many of the boulders and clasts in the The Grindstone radiolarian faunas are similar to those described from conglomerate contain typical Mississippian (Coffee Creek) arid Permian northern California (Blome and Irwin, 1983), west Texas and the Ural (Coyote Butte) fossils. They also stated that there was no direct fossil Mountains of the Soviet Union (Nazarov and Ormiston, 1985; Ormiston evidence to establish a Triassic age for any of the Grindstone and Babcock, 1979), and Japan (Caridroit and De Wever, 1984,1986; De conglomerates. Wever and Caridroit, 1984; Ishiga, 1984, 1985; Ishiga and Imoto, 1980, Limestone cobble- and boulder-conglomeratë in the northern part of 1982; Ishiga and others, 1982, 1984, 1986; Nishimurà and Ishiga, 1987; thé terrane (loc. 52, see footnote 1) and near volcaniclastic sandstone and Sashida and Tonishi, 1985,1986). Radiolarian taxa from the Grind- exposures (loc. 19, see footnote 1) contains numerous cobbles possessing stone bedded chert are listed in Figures 2a and 2b of the Data Repository typical Coffee Creek and Coyote Butte fusulinaceans, crinoidal textures, (see footnote 1). and volcaniclastic debris. Chert cobbles from conglomerate (loc. 15, see All of the Permian radiolarian faunas can be assigned to radiolarian footnote 1) originally mapped as Spotted Ridge conglomerate also yield Assemblage Zones proposed by Ishiga (1986a, 1986b). The oldest Per- Early Permian radiolarians. Faunal data indicate that most, if not all, of the mian (mid- to late Wolfcampian) faunas correlate with Ishiga's Pseudoal- conglomeratic rocks scattered throughout the Grindstone terrane are as- baillella lomentaria and Ps. scalprata morphotype rhombothoracata Zones signable to the Late Triassic Vester Formation discussed below. and are from cherts collected in the northern part of the terrane (Iocs. 3,5, arid 9, see footnote 1). Definite Leonardian faunas correlate with the IZEE TERRANE ROCK TYPES, FAUNAS, AND Albaillella sinuata Zone and overlying Pseudoalbaillella sp. C Zone and DEPOSITIONAL SETTINGS are from cherts collected from both the north and south parts of thè terrane (Iocs. 6, 36, see footnote 1). Faunas assignable to the late Leoriardian to Vester Formation early. Guadalupian Pseudoalbaillella globosa Zone are from cherts scat- tered throughout (Iocs. 2,20,24,36, and 45, see footnote 1). Late Permian Lithology and Depositional Setting. The chèrt-pebble conglomer- (early Guadalupian) faunas correlate with the Follicucullus monacanthus ate just west and north of the Grindstone terrane near Wade Butte was said Zone and are from widespread localities (Iocs. 5, 14, 26, 30, 31, and 34, to be Triassic deposits by Merriam and Berthiaume (1943), who estimated see footnote 1). Late Guadalupian faunas that correlate with Ishiga's Folli- their thickness at -4,000 ft (1,220 m). Chert-pebble conglomerate ex- cucullus scholasticus Zone, however, are restricted to cherts in the south- posed along the terrane's eastern periphery was initially mapped as the ern part of the terrane near Twelvemile Creek (Iocs. 7,14,23,25,26,27, Begg and Brisbois Formations by Dickinson and Vigrass (1965). These 29,30, and 32, see footnote 1). Latest Permian (Djulfian) faunas correlate formations were treated as formal members of the Vester Formation by with Ishiga's NeoalbaiÙella optima Zone and are from cherts in the central Brown and Thayer (1977), and by Dickinson and Thayer (1978, Fig. 2) and southern parts of the terrane (Iocs. 4, 7, and 14, see footnote 1). because they are, in part, facies equivalents. Dickinson and Thayer inter- Chert (Iocs. 28 and 33, see footnote 1) in the riorthern and southern preted the Begg conglomerate near Wade Butte as unconformable on parts of the terrane contain Early Triassic (Scythian) radiolarians possess- mélange, overthrust by mélange along Camp Creek, and incorporated in ing simple, rod-like spines and entactinid internal structures similar to mélange in other areas. Early Triassic faunas described by Sashida (1983) from Japan. These The Vester Formation is the oldest unit in the Izee terrane (Fig. 2) forms have been recovered from carbonate concretions in strata containing and includes about 3,750 m of clastic strata with lesser volcaniclastic Early Triassic (Smithian) conodonts and ammonites in Owens Valley, rocks. The Begg Member is characterized by chert-grain sandstone, chert- southern California (C. D. Blome, unpub. data). pebble conglomerate, volcaniclastic rocks, and sedimentary breccia inter- calated with equal or greater amounts of mudstone and siltstone. The Unnamed Triassic Volcaniclastic Rocks and Conglomerate Brisbois Member consists predominantly of thinly bedded, gray to black Lithology. Volcaniclastic- and chert-fragment-rich siltstone, sand- siliciclastic mudstone and siltstone, with calcareous sandstone and chert- stone, and chert-pebble conglomerate crop out throughout the terrane. grain sandstone.

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Fusulinacean-bearing Begg conglomerate (Iocs. 52 and 71, see foot- described from the Coyote Butte limestone (Skinner and Wilde, 1966), the note 1) outcrop west of the Suplee road near the northeastern edge of the McCloud Limestone, northern California (Skinner and Wilde, 1965), and Grindstone terrane. Fusulinacean-bearing conglomerate, mapped as Bris- limestone near Quinn River Crossing, northwestern Nevada. Some genera bois (Iocs. 46 and 51, see footnote 1) by Dickinson and Vigrass (1965), common in the McCloud Limestone, such as Thompsonella, Klamathina, appear to be restricted to Izee terrane localities east of the road south from and Cuniculinella, are absent at Big Flat, in the Grindstone terrane, and at Suplee (Fig. 3) and to other parts of the Izee terrane. Quinn River Crossing. Big Flat Parafusulina taxa are similar to coeval Olistostromal sedimentary breccias containing blocks derived from taxa described by Skinner and Wilde (1965) from the lower Guadalupian the Grindstone terrane are exposed along the western periphery of the Izee Nosoni Formation, Shasta Lake area, northern California. Many of the terrane (Dickinson, 1979). Deposition of Vester coarse clastic rocks were more common Big Flat fusulinacean species, and even genera (for exam- derived from the uplift and erosion of the Grindstone terrane (Dickinson ple, Pseudofusulina, Pseudoschwagerina, and Polydiexodina) have not and Thayer, 1978; Dickinson, 1979). Paleocurrent indicators (N = 37) been found in any Grindstone limestone or conglomerate. from the Vester turbidites indicate transport toward the east and southeast The Big Flat fusulinacean Polydiexodina oregonensis resembles other away from the Grindstone terrane (Dickinson and Thayer, 1978, p. 155). Polydiexodina species from coeval late Guadalupian cratonal-related rocks The association of lenticular Begg conglomerate-sandstone bodies incased in west Texas and Mexico (Bostwick and Nestell, 1965) in possessing a in mudstone and the presence of coarse turbidite beds thinning upward definite "central tunnel." The presence of a central tunnel-bearing Poly- indicate deposition on the inner or proximal parts of a subsea fan where diexodina taxon in the Big Flat conglomerate suggests that Begg deposition channels were well defined; the finer turbidite beds and mudstones proba- took place near the North American craton. bly represent inter-channel deposits (Dickinson and Thayer, 1978). The poorly sorted, poorly graded, and commonly mud-supported Unnamed Lower Jurassic Limestone pebble to boulder conglomerate could also be a product of debris-flow sedimentation and possibly represent proximal fan feeder channel fills A small exposure of limestone, shale, and siltstone (unit "Jl" in Fig. (Cook, 1983; Cook and Egbert, 1981). The better-sorted pebble conglom- 3) crops out north of Twelvemile Creek along the Grindstone-Izee terrane erate that displays inverse to normal grading represent inner fan-channel boundary. The block was previously referred to as the "Sherman Ranch fill (Walker, 1978,1984). These deposits could have formed as lag depos- limestone" on several unpublished maps. Buddenhagen (1967) reported its in distributary channels, but the common presence of conglomerate that ammonites from this exposure indicate an Early Jurassic (Hettangian) exhibiting inverse grading suggests deposition in the middle and distal parts age. Coeval siltstone/limestone exposures, assigned by Dickinson and Vi- of a feeder channel within a submarine fan fades (Walker, 1984). Varia- grass (1965, p. 29) to the Graylock Formation, outcrop near Morgan tions in lithology between the type Begg in the central part of the Izee Mountain in the adjacent Izee terrane. terrane and the finer-grained conglomerates exposed near Wade Butte could be the result of paleo-depositional changes from upper-slope, coarse, Snowshoe Formation channel fills to finer-grained,lower-slope , fan-fringe deposits. Biostratigraphy. The precise age of the Begg Member is unknown, Lithology and Depositional Setting. The Snowshoe Formation, although it has been questionably assigned (based on the presence of the established by Lupher (1941) for a sequence of well-bedded siltstone and nautiloid Proclydonautilus) to the Carnian Stage below the Tropites sub- mudstone with minor sandstone, conformably overlies the Hyde Forma- bullatus Zone of Smith (1927); the basal part of the member could extend tion and underlies the Trowbridge Formation along the South Fork of the down into the Middle Triassic (Dickinson and Vigrass, 1965). Spiriferid John Day River near the town of Izee (shown as undifferentiated Jurassic brachiopods and coelenterates from the Begg Member are comparable to volcaniclastic rocks in Fig. 2). Here the Snowshoe Formation was divided those from the overlying Brisbois Member (Dickinson and Vigrass, 1965). into three unnamed members by Dickinson and Vigrass (1965). The lower Resedimented limestone blocks in olistostromal carbonate breccias con- member is characterized by dark gray to black, thin-bedded mudstone, tain Carnian molluscs (Dickinson, 1979). shale, and siltstone and contains ammonite casts and the pelecypod Posi- A black chert clast from Begg chert-pebble conglomerate along the donia on bedding partings, as well as lenses of silty limestone and dark southeast limb of Little Bear (loc. 1, see footnote 1) was assigned gray carbonate concretions. The middle member contains dark gray to a pre-Permian age by Blome and others (1986) based on poorly preserved black shale and mudstone intercalated with gray to green volcaniclastic radiolarians assignable to Latentiflstula spp. Re-examination of this fauna siltstone and fine-grained sandstone. The upper member is typified by suggests an undifferentiated Permian age. thin-bedded mudstone and siltstone with thick intercalations of gray cal- All ammonite collections from the Brisbois Member are indicative of careous sandstone. Dickinson (1979) interpreted the volcaniclastic se- the Tropites subbullatus Zone (Dickinson and Vibrass, 1965). Pectenacid quences as mainly turbidites, although some shelf deposits are related to bivalves (Halobia ornatissima) from the Brisbois Member (loc. 51, see transgressive unconformities. footnote 1; Dickinson and Vigrass' loc. 177) are of late Carnian age Imlay (1973) noted that the lower member of the Snowshoe Forma- (Blome, 1984). tion lithologically resembled the Warm Springs Member in the Suplee Well-rounded limestone cobbles from Brisbois conglomerate north of area (now western limit of the Izee terrane). Smith (1980) subsequently the Grindstone terrane (loc. 51, see footnote 1), and to the east at Big Flat applied the names "Warm Springs Member," "Schoolhouse Member," (loc. 46, see footnote 1), contain late Wolfcampian to late Guadalupian and "South Fork Member" to Dickinson and Vigrass' (1965) informal fusulinacean assemblages. Of more than 250 fusulinacean-bearing cobbles members. Just north of the Grindstone terrane, the Snowshoe Formation collected from the Big Flat area, only one yielded the late Guadalupian rests unconformably on Paleozoic rocks (Dickinson and Vigrass, 1965; fusulinacean Polydiexodina oregonensis, four yielded late Leonardian to Dickinson and Thayer, 1978, their Fig. 2b) and is represented by the early Guadalupian species of Parafusulina with well-developed "cuniculi," Weberg, Warm Springs, Basey, and Shaw Members. and the remainder contained a variety of late Wolfcampian to early Leo- The Weberg Member was originally named the Weberg Formation nardian species of Pseudofusulinella, Pseudofusulina, Eoparafusulina, by Lupher (1941). Dickinson and Vigrass (1965) divided it into a lower Schwagerina, Pseudoschwagerina, and Chalaroschwagerina. A few of the calcareous sandstone and sandy pebbly conglomerate and an upper silty cobbles also contained the Late Mississippian Coffee Creek fusulinacean and sandy limestone. The Weberg Member is exposed in the southwestern Eostaffella. part of the Izee terrane (Smith Basin area) and reaches a maximum thick- Most of the Big Hat fusulinacean taxa are similar to coeval forms ness of 100 ft (30 m).

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A large exposure of sandstone, arenaceous limestone, and inter- (lower Bajocian of others) Shirbuirnia trigonalis and Witchellia laevius- calated shale and mudstone is present on the south and east sides of Wade cula Subzones of the Sonninia sowerbyi Zone. Flattened shells of Posido- Butte (Fig. 2) just west of the Grindstone terrane. Buddenhagen (1967) nia are abundant throughout. Carbonate concretions from typical Warm assigned these rocks to an undifferentiated Jurassic unit composed of Springs mudstone and shale southwest of Suplee (loc. 38, see footnote 1) marine volcaniclastic and tuffaceous sedimentary rocks. The thin, basal contain a well-preserved lower Bajocian (Zone IB of Pessagno and others, part of the rock succession at Wade Butte was assigned to the Weberg 1987) radiolarian fauna. The more common radiolarian taxa are listed in Member by Dickinson and Thayer (1978). Figure 4 of the Data Repository (see footnote 1). The Warm Springs Member rests conformably on the Weberg Megafossils (belemnites and pelecypods) collected from basal strata Member and is overlain conformably by the Basey Member. Typical at Wade Butte were assigned to the lower Middle Jurassic Weberg Forma- Warm Springs rock types include gray, silty, calcareous shale and mud- tion (now Weberg Member of the Snowshoe Formation of Dickinson and stone, with lesser amounts of calcareous, volcaniclastic siltstone and sand- Vigrass, 1965) by Lupher (1941). A small carbonate concretion (loc. 40, stone, muddy limestone, and carbonate concretions (loc. 40, see footnote see footnote 1) from the overlying dark gray, platey shale and mudstone 1). The concretion-bearing mudstone beds that conformably overlie basal contains a well-preserved radiolarian fauna (Table 3 in Data Repository, Weberg Member strata at Wade Butte were assigned to the Warm Springs see footnote 1) of Middle Jurassic (Bajocian) age. This fauna correlates Member by Dickinson and Thayer (1978) and Taylor (1982). with Zone IB (earliest Bajocian) of Pessagno and others (1987) and with The Basey Member is represented by -2,500 ft (760 m) of massive the lower Bajocian Hyperlioceras discites, Witchellia laeviuscula, and volcaniclastic rocks, including marine tuff that grades into tuffaceous vol- most of the Otoites sauzei European Standard Ammonite Zones (Imlay, caniclastic (andesitic) sandstone. Thinner-bedded volcaniclastic siltstone 1973). and mudstone are intercalated between the sandstone layers. Andesitic Imlay (1973) noted that the lower 200 ft (61 m) of his informal lower flows that grade into flow breccia are restricted to the southwestern part of member (equivalent to the Warm Springs Member of Smith, 1980) near the Izee terrane (Dickinson and Vigrass, 1965; Dickinson and Thayer, Izee (Fig. 2) contains late Toarcian and early Bajocian (Aalenian) ammo- 1978). nite faunas. According to Smith (1980), the Warm Springs strata contain Dickinson and Vigrass (1965) indicated that the Shaw Member of lower Bajocian ammonites that correlate with the standard European Hy- the Snowshoe Formation, a sequence of gray shale with minor limestone perlioceras discites, Witchellia laeviuscula, Otoites sauzei, and Stepha- and sandstone lenses, is present near Suplee (Fig. 2; their "Camp Creek" noceras humphriesianum European Standard Zones. Radiolarians and area = Smith Basin of Dickinson and Thayer, 1978). We did not observe ammonites from Schoolhouse Gulch immediately north of Izee (Fig. 2; Shaw Member rock types in this area, but small pods of typical Shaw Pessagno and others, 1987) indicate that the lower part of the Warm rocks could have been overlooked. Springs Member is assignable to the middle and upper Toarcian and that The sedimentary structures in the coarser-grained Snowshoe volcani- the remainder of the member is Aalenian (lower Bajocian of Imlay, 1973) clastic rocks indicate deposition in middle-fan or supra-fan lobes in slope and lower Bajocian (= middle Bajocian of Imlay, 1973). to base-of-slope depositional settings. The siltstone and sandstone com- monly exhibit parallel laminae, and ripple and cross-bedding structures DISCUSSION (Bouma's Tb-Td units, 1962). These small-scale sedimentary structures indicate deposition on the outer parts of a suprafan lobe, in finer-grained Depositional Models for Grindstone and Izee Terrane Rocks facies within braided channels in the middle part of the fan, or on the fringes of the distal part of the fan by turbidity currents (Cook and Mullins, One reason for the varied depositional models proposed for the 1983; Walker, 1978, 1984). The sandstone could also represent deposits Grindstone terrane (see section on Previous Studies; Buddenhagen, 1967; formed in the uppermost, more dilute turbulent parts of a debris flow Dickinson and Thayer, 1978; Wardlaw and others, 1982) is the terrane's (Cook and others, 1972; Krause and Oldershaw, 1979). scarcity and disarray of outcrops. For example, the Devonian and Missis- The presence of abundant and diverse radiolarians in concretions in sippian Coffee Creek limestone blocks are widely separated from one the Wade Butte and Snowshoe mudstone indicate distal fan or basin plain another, yet the southernmost Devonian exposure is almost in contact with depositional settings. This interpretation directly contradicts the shallow- a Triassic limestone pod (Fig. 3). Several of the limestone blocks exhibit marine invertebrate depth model proposed by Taylor (1982) for the random strike/dip orientations, and some have reversed, distorted, or Warm Springs Member of the Snowshoe Formation. incomplete litho- and biostratigraphy. Many of the cherts partly enwrap Biostratigraphy. Ammonites from the lower part of the Weberg the individual limestone exposures (for example, at Coyote Butte). Member just north of the Grindstone terrane near Suplee correlate with Dickinson and Thayer (1978) and Dickinson (1979) implied that the the European Graphoceras concavum Zone (uppermost lower Bajocian or Grindstone terrane represents a mélange belt of dismembered oceanic crust Aalenian), and others from the middle and upper parts correlate mostly and associated strata, which include island-arc volcanic rocks, graywacke, with the Hyperlioceras discites Subzone at the base of the Sonninia sower- and limestone in a tectonic matrix of deformed oceanic-floor chert and byi Zone (lowermost middle Bajocian; Imlay, 1973). Pelecypods, includ- argillite. They infer the severe structural disruption to be the result of ing Ostrea and fragments of Pinna, are also abundant in the lower parts of long-term that lasted through mid-Triassic time. They also the member, along with rhynchonellid brachiopods and belemnite frag- interpreted the presence of volcaniclastic and chert-grain detritus in the ments. Casts of pelecypods, rhynchonellid and terebratulid brachiopods, calcarenites to suggest that the limestone formed on volcanic edifices and and belemnite fragments are abundant in the upper parts (Dickinson and partly on uplifted areas of mélange composed of deformed chert and Vigrass, 1965). argillite within an arc-trench gap. According to Dickinson (1979), the Warm Springs ammonite faunas from near Suplee (Fig. 2) correlate presence of both Tethyan and American fusulinacean faunas in his "cen- approximately with the middle and upper parts of the European Sonninia tral mélange" terrane indicates tectonic juxtaposition of stratal components sowerbyi and Otoites sauzei Zones of middle Bajocian (= early Bajocian of depositional sites from far apart in the Paleopacific. Smith, 1980; and Pessagno and others, 1987) age (Imlay, 1973). Faunas Examination of aerial photos shows somewhat continuous bedding in from the lower part of the member correlate with the middle Bajocian the volcaniclastic rocks between the various limestone and chert expo-

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sures. These volcaniclastic rocks also exhibit bedding that is oblique to, (Silberling, 1984,1987). Furthermore, the Grindstone limestone and chert and distorted and folded near, individual limestone- and chert-block exposures lack or other deformational fabrics at or near their bound- boundaries. Dickinson (1977) suggested that slicing of semi-coherent sec- aries with adjacent volcaniclastic rocks, and much of the chert exhibits tions of trench-floor and ocean-floor sequences into relatively undeformed sedimentary structures indicative of slope to base-of-slope paleo- lenticular blocks bounded by shear surfaces could result from subduction environments. tectonics. Jacobi (1984), however, indicated that large tracts of sediments An alternative depositional model for Grindstone terrane rocks is that very similar to those in tectonic mélange terranes can be formed by subma- the Devonian, Coffee Creek, and Coyote Butte limestones represent grav- rine sediment sliding. ity slide and slump blocks that became detached from a carbonate shelf On the basis of several lines of evidence, we do not believe that the fringing a volcanic knoll(s) or edifice in Late Permian or Early Triassic Grindstone siliceous rocks represent subducted ocean-floor sediments as time. These blocks were redeposited and intermixed with uppermost Per- suggested by Dickinson and Thayer (1978) and Dickinson (1979). Typical mian? and Triassic slope to base-of-slope volcaniclastic rocks and Permian ocean-floor rocks, such as basalt, are missing from the Grindstone rocks to Lower Triassic base-of-slope to basinal chert and siliceous mudstone in and are restricted to the Baker terrane to the northeast. Dickinson and a forearc basin (Fig. 7A). The eroded carbonate shelf was situated on a Seely (1979, p. 6), however, did propose a hypothetical "constructed structural high along the trench flank of the forearc basin (Dickinson and basin" model wherein forearc-basin sediments rest unconformably upon Seely, 1979) or fringed the arc massif itself. Partially coeval and younger arc massif and subduction complex material, and no oceanic material is Upper Triassic to Middle Jurassic submarine-fan deposits, represented by trapped beneath forearc sediments. The only Tethyan faunas within Dick- the Begg Member of the Vester Formation, undifferentiated Lower Juras- inson's mélange are in rocks in the Miller Mountain area (Fig. 2; see sic clastic unit, and Snowshoe Formation, subsequently covered the Grind- Nestell, 1983), an area now considered to be part of the Baker terrane stone deposits (Fig. 7B).

Limestone Ifóiii Megabreccia Shale/Siltstone (concretions) Pelagic Sedimentation

Sandy Limestone Conglomerate X-bedded Clastlcs

Chert Sandstone/Siltstone lOI Sediment Flow Direction

Figure 7. (A) Cartoon of proposed base-of-slope apron model for Late Permian to Early Triassic Grindstone terrane deposition. Erosion and gravity slumping and sliding of Devonian, Mississippian (Coffee Creek), and Permian (Coyote Butte) limestone blocks into inner and outer slope fades containing fine- to coarse-grained volcaniclastics (Spotted Ridge and unnamed Triassic volcaniclastics, now considered part of the Vester Formation). Chert deposition in base-of-slope and basinal settings was relatively continuous from Early Permian to Early Triassic time. (B) Proposed submarine-fan model for Late Triassic to Middle Jurassic I zee terrane deposition. Begg conglomerate (Late Triassic) deposition took place in proximal or inner fan feeder channels. Late Triassic (Begg Member), unnamed Early Jurassic, and Middle Jurassic (Snowshoe Formation) sandstone and siltstone represent deposition in middle-fan or supra-fan lobes. Note carbonate concretion formation in distal-fan and basin plain settings.

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The isolated Pennsylvanian Spotted Ridge mudstone, closely asso- 1987) was based on the absence of conformable contacts between Grind- ciated with the Grindstone Begg volcaniclastic rocks, represents individual stone and Izee rock units and the Izee terrane's lack of Paleozoic litholo- slides or slumps redeposited from shelf mud facies. The slope angle that gies, except for Paleozoic limestone clasts in the Triassic Begg permits gravity sliding of the limestone blocks and clastic rocks need not conglomerate. The presence of Begg conglomerate in both terranes indi- have been high. Large debris flowscontainin g megaliths can be initiated in cates that the Grindstone terrane formed at least part of the for areas of low depositional relief and transported long distances across slope Izee deposition by Late Triassic time. The lack of conformable contacts angles of less than one degree (Cook and others, 1972). between all Grindstone and Izee exposures examined, however, prevent us A similar arc-basin model was proposed by Watkins (1986) for the from reducing the two terranes to subterrane status. Devonian to Carboniferous Kennett Formation in the eastern Klamath We agree that uplift and erosion of Grindstone terrane lithologies Mountains, California. Watkins interpreted the Kennett Formation clastic provided detritus for Izee terrane deposition (Dickinson and Thayer, rocks as volcaniclastic turbidites (some with plant debris) of near-shore 1978). The Grindstone conglomerate is lithologically similar to Izee ter- and slope facies, which grade into siliceous mudstones of basin-floor rane Begg conglomerate near Wade Butte but differs from Begg conglom- origin. He also inferred that the shallow-water carbonates, from which the erate in the central parts of the Izee terrane by containing common Coffee Kennett carbonate debris-apron deposits were derived, are no longer pres- Creek limestone detritus and a somewhat different Permian fusulinacean ent. Mitchell (1970) described a similar case for Miocene reefal units in fauna (for example, Pseudoschwagerina and Polydiexodina), and by lack- which the reef environment itself is missing. The Kennett Formation is ing Late Triassic fossils. These contrasts between Grindstone and Izee overlain by the Bragdon Formation (Watkins and Flory, 1986), a thick conglomerate faunas suggest that (1) the Begg conglomerate had several submarine-fan complex derived from the uplift of the Kennett Formation. provenances or (2) they could be the result of an older Grindstone con- The tectonic setting and direction of subduction for the Grindstone glomerate depositional phase, wherein deposition of the younger and more and other eastern Oregon terranes are problematic. Miller (1987) indi- extensive Izee terrane Begg conglomerate continued through the Late Tri- cated that (1) the Grindstone terrane and other parts of the McCloud assic. Other Permian faunas from conglomerate in both terranes indicate island-arc system were developed above an east-dipping, late Paleozoic penecontemporaneous sources during Begg deposition. subduction complex (Burchfiel and Davis, 1981; Miller and Wright, The Grindstone terrane contains Middle Devonian, Upper Mississip- 1987); (2) there is little evidence to suggest the closure of a major (> 103 pian, Pennsylvanian, and Permian (upper Wolfcampian to Leonardian) km) ocean basin or long periods of westward-dipping subduction; rocks on the basis of floral and faunal (brachiopod, conodont, coral, (3) complex marginal and foreland basins separated the arc from the fusulinacean, and radiolarian) evidence. continental craton; and (4) the McCloud island system occupied a back- The Grindstone rock assemblages are of low metamorphic (zeolite) arc position from Devonian to Permian time (Miller, 1989). The marked grade; fresh zeolites are present in some of the limestone and volcaniclastic contrasts between McCloud and Grindstone limestone faunas indicate that rocks and conodonts have CAI's of 3 or less. Furthermore, much of the the Grindstone terrane was not a part of the McCloud island-arc system. limestone is unaltered. The fusulinacean faunas are of McCloud Limestone Dickinson (1979) suggested that the Paleozoic Grindstone rocks rep- (North American) affinity and do not contain Tethyan verbeekinids. resent uplifted ridges of mélange (between trench and forearc basin) Devonian, Pennsylvanian, and Permian faunas from limestone and produced by east-dipping subduction in an arc-trench gap. The thick suc- chert are present in the Baker terrane, but pre-Late Permian faunas are cession of Izee terrane clastic rocks infilled the forearc basin from Late very rare (Mullin-Morris and Wardlaw, 1986). The Baker terrane lime- Triassic to Late Jurassic time. The presence of sedimentary mélange and stone and chert exhibit tectonic shear fabrics, possess greenschist or higher forearc basin rocks in the Grindstone and Izee terranes, respectively, sup- regional metamorphic grades, contain conodonts with CAI's of 5 to 6, and port an east-dipping subduction model. In this model, the Grindstone are commonly altered to marble and metachert. They also contain two limestone sedimentary mélange would have formed from erosion of car- types of fusulinacean faunas: those containing Tethyan verbeekinids and bonate shelfal rocks fringing volcanic knoll(s) or edifices on uplifted struc- those related to the McCloud Limestone (Nestell, 1983; Nestell and tural highs between trench and forearc basin (Fig. 7 A). Paleomagnetic Blome, 1988; Miller, 1987). data for the "Blue Mountains " (Pessagno and Blome, 1986; Scarce fusulinacean assemblages from small, metamorphosed (green- Vallier and Brooks, 1986), however, indicate that it has rotated 60° schist-grade) limestone pods in the west-central part of the Baker terrane clockwise since the Late Jurassic and(or) Early Cretaceous (Wilson and (east of Elkhorn Ridge) are coeval with, and nearly identical to, the Cox, 1980; Hillhouse and others, 1982). Grindstone Coyote Butte faunas. Exact timing of insertion of these lime- The adjacent Baker terrene to the northeast is a mélange belt of stone outliers into the Baker terrane is difficult to ascertain because, in dismembered oceanic crust (for example, the Canyon Mountain ophiolite some places, Permian fusulinacean-bearing limestone is juxtaposed with complex; Thayer, 1978) and highly altered limestone, chert, and argillite coeval or Late Triassic (Carnian/Norian) radiolarian chert blocks (Nestell (Bostwick and Koch, 1962; Vallier and others, 1977). The disruption of and Macleod, 1984; Blome and others, 1986; and Nestell and Blome, these tectonized fragments reflects deformation through subduction (Dick- 1988). Chert in the Grindstone terrane contains both Permian (late Leo- inson, 1979; Nestell and Blome, 1988). Both Tethyan and American fusu- nardian to Djulfian) and Early Triassic radiolarian and conodont faunas. linacean and coral faunas are found in the Baker terrane limestones. The presence of Coyote Butte detritus in Grindstone and Izee Triassic If rotational data for the Grindstone, Izee, and Baker terranes are conglomerates and the insertion of Coyote Butte limestone outliers into the applicable, counterclockwise rotation back to its original position would western part of the Baker terrane by latest Triassic time indicate that all place the Baker oceanic crust and mélange rocks outboard (northwest) of three terranes were juxtaposed by the Late Triassic or Early Jurassic. Izee and Grindstone forearc basin rocks in an east-dipping (southeast) subduction system. In this model, the Grindstone limestone sedimentary CONCLUSIONS mélange would have formed from erosion of carbonate shelfal rocks fring- ing volcanic knoll(s) on the arc side of the forearc basin with redeposition The Grindstone terrane contains Middle Devonian, Upper Missis- of the shelfal rocks to the west or northwest. sippian (Coffee Creek), and Lower Permian (Coyote Butte) limestones Comparisons of Grindstone, Izee, and Baker Terrane Rocks. intermixed with Pennsylvanian? and Triassic volcaniclastic rocks and Separation of Izee and Grindstone terranes by Silberling and others (1984, conglomerate (Spotted Ridge and unnamed clastic rocks), as well as

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Permian and Lower Triassic radiolarian chert and siliceous mudstone. authors take full responsibility for the interpretations presented in the final These deposits are unconformably overlain by Upper Triassic (Vester version of the manuscript. We are ever grateful to Lawrence and Bill Formation), undifferentiated Lower Jurassic, and Middle Jurassic (Snow- Weberg and family (Weberg Ranch) and Earl McConnell (Grindstone shoe Formation) volcaniclastic rocks. Livestock Co.) for access, logistics, and their hospitality. Mary Beth Cast, Most of the Grindstone exposures were originally assigned to the Margaret Liniecki, Paula Noble, and Leta Smith were outstanding field Coffee Creek (Mississippian), Spotted Ridge (Pennsylvanian), and Coyote assistants during various stages of this study. We also thank John Har- Butte (Permian) Formations of Mérriam and Berthiaume (1943). The baugh for graciously allowing us to use his preliminary geologic map of the plant-bearing Spotted Ridge mudstone exposures represent the only Penn- Paleozoic rocks of the Suplee area, James Baichtal (U.S. National Forest sylvanian clastic deposits in the terrane. We reassign other Spotted Ridge Service) for field and logistical help, John Wolff for aiding in the identifi- clastic rocks to the Upper Triassic Begg Member of the Vester Formation cation of the volcaniclastic rock fragments in thin section, and Jim Vigil based on the présence'of Early Permian fusulinaceans, and Early Permian for processing many of the radiolarian cherts. and Early Triassic radiolarians in limestone and chert clasts, respectively. The general lack of mappability of Merriam and Berthiaume's Coffee Creek, Spotted Ridge, and Coyote Butte Formations and their chaotic REFERENCES CITED

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L., Murchey, B. L., and Liniecki, M-, 1986, Geologic implications of radiolarian-bearing Paleozoic leogeographic affinities of Grindstone limestone faunas also indicate and Mesozoic rocks from the Blue Mountains province, eastern Oregon, in Vallier, T. L., and Brooks, H. C., eds.. shallow-water carbonate-shelf paleoenvironments around volcanic island Geology of the Blue Mountains region of Oregon, Idaho, and Washington; paleontology and biostratigraphy: U.S. Geological Survey Professional Paper 1435, p. 79-93. arcs near the North American craton. This conclusion is based on the Bostwick, D. A., and Koch, G. S., 1962, Permian and Triassic rocks of northeastern Oregon: Geological Society of America Bulletin, v. 73, p. 419-422. following criteria: (1) the Coyote Butte fusulinacean faunas have strong Bostwick, D. A., and Nestell, M. 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