Eastern Klamath Terrane Research Articles

Downslope re-sedimentation from a short-living carbonate platform: Record from the Upper Triassic Hosselkus limestone (Northern California)

Despite their discontinuous occurrence and poor preservation, knowledge about Triassic carbonates from North America has increased considerably during recent years. Their characterization represents a unique way to better assess evolution and recovery of the biosphere after the major Permo-Triassic biological crisis in the Panthalassa Ocean. The Eastern Klamath terrane, located in Northern California, is a key terrane due to its geographic position. It is placed halfway between the terranes of the Canadian Cordillera and the Northern Mexico counterparts, both extensively studied and characterized in recent decades, leaving a gap in knowledge along the Pacific coast of the United States. A few kilometers north-east of Redding, Shasta County, California, Upper Triassic carbonates (i.e., the Hosselkus limestone) crop out as a narrow north–south belt about 20 km long, near the artificial reservoir of Lake Shasta. All the accessible localities in this region have been extensively sampled for microfacies and micropaleontological analysis, leading to new insights about the depositional condition and age of the Hosselkus limestone. A depositional model has been proposed for the first time, corresponding to a steep slope system subjected to platform progradation and collapse, recording shallow water facies and associated fauna in the form of calcareous breccia. Numerous conodont specimens have dated the whole succession as Upper Carnian. Identification of shallow water organisms, associated to a reliable stratigraphic interval, allowed comparison of the Hosselkus limestone with other Upper Triassic carbonates from the Panthalassan domain. Despite the faunal affinities, especially with buildups developed at middle-paleolatitudes, the Hosselkus limestone is among the oldest of the terrane-based carbonates in Eastern Panthalassa. Thanks to peculiar geodynamical and bathymetrical conditions, allowing carbonate deposition slightly earlier than in other terranes, the Hosselkus limestone probably acted like a pioneer reef and may have had a great influence in the further expansion of carbonate buildups in the eastern part of the Panthalassa Ocean.

Fasciculate Kleopatrinid corals from the Bashkirian (late Carboniferous) of Sardar Formation (Ozbak-Kuh Mountains, East-Central Iran)

In the East-Central Iran, the Sardar Formation (upper Visean–Moscovian) consists of shallow-water limestone with intercalations of shale containing rugose corals, tabulate corals and brachiopods. Ten sections were sampled in the Ozbak-kuh Mountains, from north to south. Among the rugose corals, an assemblage of fasciculate Kleopatrinidae has been collected. The latter contains the species: Paraheritschioides antoni antoni, P. antoni minor, P. gracilis and two new species for the genera Fomichevella and Heintzella. Heintzella is described from Iran for the first time. However, its age, as determined by conodonts and foraminifers, is early to middle Bashkirian (early late Carboniferous). The most similar, time-equivalent faunal associations are that of the Ellesmere Island, Sverdrup Basin in Arctic Canada, Alexander terrane and Brooks Range in southeastern Alaska and eastern Klamath terrane in northern California, where similar tropical warm water conditions have been identified during the Bashkirian in the northern hemisphere. During these times central Iran block and Northern provinces, characterized by a dominant carbonate facies and more diversified colonial coral faunas.

Detrital zircon provenance of Pennsylvanian to Permian sandstones from the Wyoming craton and Wood River Basin, Idaho, U.S.A.

Pennsylvanian rocks of the northern U.S. Rocky Mountains are mature quartzose sandstones. This paper uses detrital zircon geochronology on seven samples from the Wood River Formation, Tensleep Sandstone, and Weber Sandstone to determine if these sandstones have a common provenance, representing eastern Laurentian and Appalachian sand reworked within shallow-marine and eolian environments from the Wyoming craton westward to the Pioneer thrust plate of south-central Idaho. Our work suggests that this continental sand blanket was mixed with local sources on the south in the Yavapai-Mazatzal provinces of the Ancestral Rocky Mountains and in samples from the western Cordilleran thrust belt in south-central Idaho. In total, these Pennsylvanian sandstones contain a broad spectrum of detrital zircon U-Pb ages including, from old to young: A) minor Archean-age (3300–2550 Ma) populations; B) Paleoproterozoic (2000–1600 Ma), Mesoproterozoic (1470–1350 Ma), and major “Grenvillian” (1250–950 Ma) populations; and C) Cryogenian- to Ediacaran-age (665–565 Ma) and minor Paleozoic (495–410 Ma) populations. We interpret these detrital zircon ages to represent provenance mainly from the Appalachian mountain belt of eastern North America; however, central Appalachian versus northern Appalachian derivation is not clearly distinguished. The Weber Sandstone from the north flank of the Uinta Mountains in northeast Utah contains a strong 1700–1640 Ma age population derived from the Yavapai-Mazatzal provinces in the adjacent Ancestral Rocky Mountains. The shallow-marine Hailey Member of the Wood River Formation in south-central Idaho yields a population of >1800 Ma detrital zircons reworked from the uplifted Mississippian Copper Basin Formation. Both the Hailey and Wilson Creek Members of the Wood River Formation contain unique 640–490 Ma grains that may represent provenance from the Big Creek-Beaverhead plutonic belt of east-central Idaho and/or eastern Klamath terrane in the Klamath Mountains of northwest California and southwest Oregon. These new data support published models for Pennsylvanian–Permian transport of siliciclastic sediment with sources mainly from the North American craton, north of the Ancestral Rocky Mountains, into continental margin basins.

Late Carboniferous colonial Rugosa (Anthozoa) from Alaska

Late Carboniferous colonial corals from the Moscovian Saginaw Bay Formation and the underlying Bashkirian crinoidal limestone exposed on northeastern Kuiu Island and a nearby islet, part of the Alexander terrane in southeastern Alaska, are described and illustrated for the first time, and are supplemented by revision, re-description and re-illustration of most Atokan specimens from Brooks Range, northern Alaska, first described by Armstrong (1972). New taxa from the Kuiu Island area include the new species Paraheritschioides katvalae and the new genus and species Arctistrotion variabilis, as well as the new Subfamily Arctistrotioninae. The corals Corwenia jagoensis and Lithostrotionella wahooensis of Armstrong (1972) also are redefined and redescribed. Paraheritschioides jagoensis is based on the holotype of ‘C’. jagoensis. P. compositus sp. nov. is based on a “paratype” of ‘C.’ jagoensis. In addition to a redefinition and redescription of ‘L.’ wahooensis as Arctistrotion wahooense, one “paratype” of that species is described as A. simplex sp. nov. The phylogeny and suspected relationships of some fasciculate Carboniferous Rugosa also are discussed. Based on relationships and similarities within the Late Carboniferous colonial Rugosa from the Brooks Range, Kuiu Island and the eastern Klamath terrane, we conclude that all three areas were geographically close enough at that time so that larvae were occasionally dispersed by oceanic currents. Distances between these areas, however, may have been so great and/or isolation so long that individual speciation occurred in all of the various locations. That hypothetical situation is reflected by a common generic, but not a specific, content of the particular faunas.

Distribution and Diversity of Carboniferous and Permian Colonial Rugose Coral Faunas in Western North America: Clues for Placement of Allochthonous Terranes

Colonial rugose corals are common in western cratonal North America and in some of the allochthonous terranes, now amalgamated against its western margin. Throughout the Late Paleozoic, the coral faunas in these two different settings were significantly different. Comparisons of these faunas suggest that during the Mississippian the Alexander terrane probably was southwest of Arctic Alaska and the Stikine terrane probably lay west of the southern part of the North American craton. The Cache Creek terrane lay far out in the Paleopacific Ocean. The Pennsylvanian faunas suggest that the Quesnellia and Eastern Klamath terranes were situated southwest of Arctic Alaska and the Alexander terrane was somewhat farther southwest and farther from cratonal North America. The Stikine terrane continued to be positioned west of the southern part of the North American craton. During the Early Permian, terranes with a cratonal faunal aspect may have lain 2000–3000 km west of cratonal North America and latitudinally generally southwest of their present positions. In the Middle Permian these terranes were carried southward relative to the North American craton. Simultaneously the Tethyan Realm expanded eastward.

Baltica in the Cordillera?

U-Pb ages of detrital zircon suites from Paleozoic strata in the Arctic Alaska–Chukotka terrane (AAC), Alexander terrane, northern Sierra terrane, and eastern Klamath terrane of the North American Cordillera suggest an exotic Gondwana or Baltic origin. We evaluate these hypotheses with U-Pb ages of detrital zircon suites from Cambrian–Devonian strata of northern Baltica. Precambrian zircon populations (ca. 0.8–3.0 Ga) from Baltica compare well with similar age detritus in the AAC and Cordilleran terranes, but the amount and age of younger Neoproterozoic and Ordovician–Silurian components are variable. The AAC shares its stratigraphy with Baltica and has the most similar detrital zircon suites. Closing the Arctic places the AAC against the Lomonosov Ridge and the edge of Baltica in pre-Cretaceous time. After the Caledonian orogeny and before the Ural Mountains formed, the Baltica, AAC, and Cordilleran margins shared a Devonian–Carboniferous rift history and became along-strike portions of a Carboniferous–Permian continental margin. This rifting event might have been responsible for the initial separation of Baltica and Caledonian affinity terranes from this margin.

Early Mesozoic paleogeography and tectonic evolution of the western United States: Insights from detrital zircon U-Pb geochronology, Blue Mountains Province, northeastern Oregon

This study assesses early Mesozoic provenance linkages and paleogeographic tectonic models for the western United States based on new petrographic and detrital zircon data from Triassic and Jurassic sandstones of the Izee and Olds Ferry terranes of the Blue Mountains Province, northeastern Oregon. Triassic sediments were likely derived from the Baker terrane offshore accretionary subduction complex and are dominated by Late Archean (ca. 2.7–2.5 Ga), Late Paleoproterozoic (ca. 2.2–1.6 Ga), and Paleozoic (ca. 380–255 Ma) detrital zircon grains. These detrital ages suggest that portions of the Baker terrane have a genetic affinity with other Cordilleran accretionary subduction complexes of the western United States, including those in the Northern Sierra and Eastern Klamath terranes. The abundance of Precambrian grains in detritus derived from an offshore complex highlights the importance of sediment reworking. Jurassic sediments are dominated by Mesozoic detrital ages (ca. 230–160 Ma), contain significant amounts of Paleozoic (ca. 290, 380–350, 480–415 Ma), Neoproterozoic (ca. 675–575 Ma), and Mesoproterozoic grains (ca. 1.4–1.0 Ga), and have lesser quantities of Late Paleoproterozoic grains (ca. 2.1–1.7 Ga). Detrital zircon ages in Jurassic sediments closely resemble well-documented age distributions in transcontinental sands of Ouachita-Appalachian provenance that were transported across the southwestern United States and modified by input from cratonal, miogeoclinal, and Cordilleran-arc sources during Triassic and Jurassic time. Jurassic sediments likely were derived from the Cordilleran arc and an orogenic highland in Nevada that yielded recycled sand from uplifted Triassic backarc basin deposits. Our data suggest that numerous Jurassic Cordilleran basins formed close to the Cordilleran margin and support a model for moderate post-Jurassic translation (∼400 km) of the Blue Mountains Province.

Detrital zircon geochronology of the western Ellesmerian clastic wedge, northwestern Canada: Insights on Arctic tectonics and the evolution of the northern Cordilleran miogeocline

Detrital zircon provenance investigations of mid-Paleozoic sandstone from the western Ellesmerian clastic wedge and Cordilleran miogeocline in northern Yukon and Northwest Territories, northwestern Canada, provide critical new data on the source of foreland basin sedimentation attributed to terrane accretion and plate convergence along the ancestral Arctic margin of North America. Late Devonian and early Mississippian clastic wedge strata yield “exotic” ca. 360–390, 430–460, 530–680, and 1500–1600 Ma detrital zircon populations that are consistent with source rocks that originated near the Caledonian and Timanian orogenic belts. Specifically, the Pearya and Arctic Alaska–Chukotka terranes, the landmass of Crockerland, and Caledonian rocks in eastern Greenland are the inferred sources for exotic detrital zircons in clastic wedge strata. Progressive recycling of Ellesmerian foreland basin sediments into the continental margin environment along northwestern Laurentia is indicated by the presence of ca. 360–430 Ma and 1500–1600 Ma detrital zircons in post-tectonic, middle to late Mississippian miogeoclinal strata in Yukon. Provenance data from these Mississippian samples record a dramatic shift in the source of the Cordilleran miogeocline, since Caledonian and Baltican (Timanide) detrital zircon signatures are not recognized in pre–Late Devonian sedimentary rocks in western Canada. Devonian strata of the Alexander terrane and Yreka subterrane (eastern Klamath terrane) have Caledonian and Baltican detrital zircon age signatures similar to Ellesmerian clastic wedge sandstones, implying that several Cordilleran terranes originated in the paleo-Arctic realm. Speculative correlations suggest that the Arctic Alaska–Chukotka terrane was located to the west of Crockerland and the Canadian Arctic Islands in pre-Cretaceous time, prior to opening of the Amerasian basin. Rifting models for the western Arctic Ocean featuring counterclockwise rotation of the Arctic Alaska–Chukotka terrane away from the Canadian Arctic Islands may need reevaluation.

Taxonomic affinities and paleogeography of Stromatomorpha californica Smith, a distinctive Upper Triassic reef-adapted demosponge

Stromatomorpha californica Smith is a massive, calcified, tropical to subtropical organism of the Late Triassic that produced small biostromes and contributed in building some reefs. It comes from the displaced terranes of Cordilleran North America (Eastern Klamath terrane, Alexander terrane, and Wrangellia). This shallow-water organism formed small laminar masses and sometimes patch reefs. It was first referred to the order Spongiomorphidae but was considered to be a coral. Other affinities that have been proposed include hydrozoan, stomatoporoid, sclerosponge, and chambered sponge. Part of the problem was diagenesis that resulted in dissolution of the siliceous spicules and/or replaced them with calcite. Well-preserved dendroclone spicules found during study of newly discovered specimens necessitate an assignment of Stromatomorpha californica to the demosponge order Orchocladina Rauff. Restudy of examples from the Northern Calcareous Alps extends the distribution of this species to the Tethys, where it was an important secondary framework builder in Upper Triassic (Norian-Rhaetian) reef complexes. Revisions of Stromatomorpha californica produce much wider pantropical distribution, mirroring paleogeographic patterns revealed for other tropical Triassic taxa. Review of Liassic material from the Jurassic of Morocco, previously assigned to Stromatomorpha californica Smith var. columnaris Le Maitre, cannot be sustained. Species previously included in Stromatomorpha are: S. stylifera Frech (type species, Rhaetian), S. actinostromoides Boiko (Norian), S. californica Smith (Norian), S. concescui Balters (Ladinian-Carnian), S. pamirica Boiko (Norian), S. rhaetica Kühn (Rhaetian), S. stromatoporoides Frech, and S. tenuiramosa Boiko (Norian). Stromatomorpha rhaetica Kühn described from the Rhaetian of Vorarlberg, Austria shows no major difference from S. californica. An example described as S. oncescui Balters from the Ladinian-Carnian of the Rarau Mountains, Romania, is very similar to S. californica in exhibiting similar spicule types. However, because of the greater distance between individual pillars, horizontal layers, and the older age, S. oncescui is retained as a separate species. The net-like and regular skeleton of Spongiomorpha sanpozanensis Yabe and Sugiyama, from the Upper Triassic of Sambosan (Tosa, Japan), suggests a closer alliance with Stromatomorpha, and this taxon possibly could be the same as S. californica.

Terranes of the Western Sierra Nevada Foothills Metamorphic Belt, California: A Critical Review

Previous classifications of the western Sierra Nevada Foothills belt have been modified into five geologic packages: the Northern Sierra terrane, Feather River terrane, Calaveras Complex, Jura-Triassic arc belt, and Middle—Late Jurassic arc sequence. The Northern Sierra terrane comprises the Shoo Fly Complex and an overlying Paleozoic succession of arc volcanics. The Feather River terrane is predominantly serpentinized ultramafics containing tectonic blocks of amphibolite, plagiogranite, and mafic schists. The Permian-Late Triassic Calaveras Complex is a subduction mélange comprising psuedostratigraphic sequences of both chert and argillite with incorporated blocks of limestone, amphibolite, greenschist, phyllite, and basalt. The Red Ant schist is also included in this terrane even though it is of higher metamorphic grade. The Jura-Triassic arc belt consists of a Paleozoic basement of disrupted ophiolite, serpentinite mélange, and ultramafic rocks overlain by uppermost Triassic—Early Jurassic arc volcanics and coeval 200 Ma intrusive rocks. This belt may comprise several small terranes. The Middle—Late Jurassic arc sequence comprises 165-155 Ma volcanic arc rocks, greenstones, and metasedimentary rocks of the Mariposa Formation, and rocks of the Smartville Complex. Coeval intrusive rocks are included within this sequence because they are probably comagmatic with the arc volcanics. The Northern Sierra terrane and Feather River terrane are bounded by pre-Nevadan structures that may represent original sutures or subduction zones and have geologic histories that are relatively decoupled from adjacent rocks; they are therefore designated as terranes. The Calaveras Complex formed either adjacent to the Cordilleran margin as a result of east-dipping subduction, adjacent to arc rocks of the Jura-Triassic arc belt from west-dipping subduction, or a combination thereof. Therefore, the Calaveras Complex has a common geologic history with adjacent rocks and is not designated as a terrane. The Jura-Triassic arc belt comprises several ophiolitic microterranes, which may have been either exotic or fringing relative to North America, and are therefore grouped as a belt instead of individual terranes. The Middle-Late Jurassic arc sequence unconformably overlies rocks of the Jura-Triassic arc belt and is therefore a cover sequence instead of a separate terrane. The accretionary history of the Mesozoic Cordilleran margin is complex. After emplacement of the Northern Sierra terrane and Feather River terrane, the system was dominated by arc volcanism and accretion. The entire Sierra Nevada Foothills metamorphic belt was likely accreted to the margin by the Late Jurassic. The Sierra Nevada Foothills comprise units that appear to be correlative with those in the Klamath Mountains. Possible correlations are drawn between the Northern Sierra terrane and Eastern Klamath terrane, Calaveras Complex + Red Ant Schist and Stuart Fork + Eastern Hayfork terranes, Jura-Triassic arc belt and Rattlesnake Creek terrane, and Middle-Late Jurassic arc sequence and Western Hayfork terrane + coeval intrusives.

Early Permian location of western North American terranes based on brachiopod, fusulinid, and coral biogeography

Brachiopod, rugose coral, and fusulinid faunas present in Early Permian rocks along northern and western margins of North America, in both cratonal localities and accreted terranes, have been compared statistically, allowing refinement in placement of these terranes relative to the North American continental margin at that time. Statistical tests, including conventional and probabilistic indices of similarity, as well as multivariate analysis, show that the faunas of Wrangellia-Alexander are most similar to those of Stikinia and Quesnellia, and to the Yukon–Canadian Rocky Mountains part of the continental margin. They also show that faunas of the Eastern Klamath terrane are most similar to those of Stikinia, Quesnellia, and the central cordilleran part of the continental margin. These results suggest that during the Early Permian Wrangellia-Alexander was the northernmost of these terranes, lying west of the Yukon–Canadian Rocky Mountains region, and the Eastern Klamath terrane was the southernmost, lying west of the central Cordillera. Stikinia and Quesnellia were in intermediate positions. These relative latitudes are compatible with latitudinal determinations based on paleomagnetic data. Faunal diversity in the Eastern Klamath and Stikine terranes is similar to that at similar latitudes on the craton, whereas diversity in the Wrangellia-Alexander terrane is considerably lower than that of the latitudinally similar Yukon–Canadian Rocky Mountains area. As diversity is, in part, a function of temperature, this may suggest water around the Wrangellia-Alexander terrane was cooler than that along the continental margin. Therefore, we suggest that warm-water currents bathed the southern terranes and the southern and central parts of coastal North America, whereas cool-water currents influenced the northernmost terrane (Wrangellia-Alexander). Revised Otsuka similarity coefficients for corals show higher similarities between western North American terranes and the western continental margin than previously published, but they still are relatively low. This and the overall patterns of similarity and limits on distribution of Tethyan corals and fusulinids in the eastern Panthalassa suggest that Wrangellia-Alexander, Stikinia, and the Eastern Klamath terranes were at approximately the same distance (estimated at 2000–3000 km) from their latitudinally equivalent segments of the North American craton.

Upper Paleozoic biostromes in island-arc carbonates of the eastern Klamath terrane, California

Upper Paleozoic biostromes in island-arc carbonates of the eastern Klamath terrane, California

Upper Triassic reef fauna from the Quesnel terrane, central British Columbia, Canada

Massive Upper Triassic (Norian) reef limestone at Eaglenest Mountain, Takla Group, British Columbia, contains a wide variety of shallow-water fossils in two different carbonate units. A sponge-coral facies contains the spongesFanthalamia astoma(Seilacher, 1962),Fanthalamia multicanalisnew species,Cinnabaria expansa(Seilacher, 1962), andCinnabaria? sp.Cinnabaria expansais a widely distributed North American terrane species which, along withF. astoma,was previously known from the Luning Formation of Nevada. Also included is the “disjectoporoid,”Pamiropora sonorensisStanley, 1994, and a massive spongiomorph,Spongiomorpha tenuisSmith, 1927, previously endemic to the Eastern Klamath terrane of California. Colonial corals include:Retiophyllia quesneliananew species,Chondrocoenia waltheri(Frech, 1890),Crassistellacf.juvavica(Frech, 1890),Distichomeandracf.austriaca(Frech, 1890), andAlpinophyllia flexuosaRoniewicz, 1989. A limestone conglomerate overlying these beds is dominated almost exclusively by the planktonic hydrozoan,Heterastridium conglobatumReuss, 1865. A problematic taxonLovceniporacf.chaetetiformisVinassa de Regny, 1915, is reported for the first time outside Timor and the Tethys. The faunas provide a first glimpse into the reef biota of the Quesnel terrane. They contain taxa previously known from the distant Tethys but also include endemics from other inboard terranes.

Remnants of the Northern Sierra Nevada Paleozoic Island Arc in Western Nevada?

Allochthonous upper Paleozoic volcanic island-arc suites of the U.S. Cordillera have previously been interpreted as parts of a single island arc. New lithologic, age, structural, biogeographic, and geochemical data indicate the presence at least of two arcs, one built on a basement with continental crustal affinities including that of the Northern Sierra terrane, and the other built on an oceanic basement including that of the Eastern Klamath terrane. In the Garfield Hills, western Nevada, the Lower Permian Black Dike Formation appears to be a remnant of the Northern Sierra Paleozoic island arc. It consists of calc-alkaline rocks with low-to-negative ratios. Volcanic rocks share similar ages, magmatic affinities, and ratios with lavas of the Goodhue Formation in the Northern Sierra terrane. Our new data suggest that these rocks are part of the Northern Sierra terrane, and we therefore infer that part of western Nevada was originally underlain by a basement with continental crustal affinities.

Far‐travelled Permian chert of the North Fork terrane, Klamath Mountains, California

Permian chert in the North Fork terrane and correlative rocks of the Klamath Mountains province has a remanent magnetization that is prefolding and presumably primary. Paleomagnetic results indicate that the chert formed at a paleolatitude of 8.6° ± 2.5° but in which hemisphere remains uncertain. This finding requires that these rocks have undergone at least 8.6° ± 4.4° of northward transport relative to Permian North America since their deposition. Paleontological evidence suggests that the Permian limestone of the Eastern Klamath terrane originated thousands of kilometers distant from North America. The limestone of the North Fork terrane may have formed at a similar or even greater distance as suggested by its faunal affinity to the Eastern Klamath terrane and more westerly position. Available evidence indicates that convergence of the North Fork and composite Central Metamorphic‐Eastern Klamath terranes occurred during Triassic or Early Jurassic time and that their joining together was a Middle Jurassic event. Primary and secondary magnetizations indicate that the new composite terrane containing these and other rocks of the Western Paleozoic and Triassic belt behaved as a single rigid block that has been latitudinally concordant with the North American craton since Middle Jurassic time.

U‐Pb geochronology of detrital zircon from Upper Jurassic synorogenic turbidites, Galice Formation, and related rocks, western Klamath Mountains: Correlation and Klamath Mountains provenance

Synorogenic turbidites of the Upper Jurassic Galice Formation overlie a variety of basement terranes within the western Klamath Mountains along the Oregon‐California border, including the early Late Jurassic ophiolite assemblages, ensimatic arc deposits, and sedimentary terranes. U‐Pb analyses of 68 multiple grain fractions from 11 samples of detrital zircon support the correlation of Galice Formation on these various basement terranes, although some new complexities in provenance are revealed. With one exception, upper intercept ages range from 1509−3+3 to 1675−8+8 Ma. Least squares regression of all fractions yields an upper intercept age of 1583±1 Ma, indicating the importance of an ultimately continental, recycled, and generally well‐mixed sedimentary source. Early Mesozoic lower intercept ages range between 183−2+2 and 263−3+4 and average 215±1 Ma. Results from Galice cover on sedimentary basement show significantly older 2.1 Ga Precambrian component, however, that may be locally derived from pre‐Late Jurassic basement rocks that are rich in recycled sedimentary debris. Existing isotopic data from older, zircon‐bearing Klamath units further indicate that Galice detritus was derived from immediate source terranes within the Klamath Mountains. Reworking of fragile limestone clasts from the biogeographically distinctive eastern Klamath terrane (McCloud Limestone) into Galice Formation substrate also supports early paleogeographic ties between terranes. Thus the tectonic setting of the Late Jurassic Nevadan orogeny in the Klamath Mountains is tightly constrained by original paleogeographic ties between subterranes of the western belt and by provenance ties to terranes to the east. Ultimately continent‐derived clastic debris and other distinctive tracers were recycled within this long‐lived ensimatic convergent margin system.

Radiolarian Biostratigraphy of the Quinn River Formation, Black Rock Terrane, North-Central Nevada: Correlations with Eastern Klamath Terrane Geology

The Quinn River Formation, Black Rock terrane, Quinn River Crossing, is one of the few Nevadan sections of Permian and Triassic strata that are unaffected by Sonoman deformation. The formation consists of: (1) a basal tuff overlain by limestone and ferruginous dolomite, (2) interbedded radiolarian-bearing chert and argillite, (3) siltstone and carbonaceous shale, and (4) partly volcaniclastic rocks that include siltstone, shale, and minor sandstone and radiolarian-bearing argillite. Disconformities separate the dolomite from the radiolarian chert and the chert from the siltstone and shale. Abrupt lithologic and faunal changes indicate that the partly volcaniclastic unit is faulted. All but the uppermost (barren) chert samples contain Late Permian (Abadehian and Djulfian) radiolarian taxa belonging to Albaillella, Deflandrella, Ishigaum, Neoalbaillella, and Triplanospongos. These radiolarians suggest that early Wordian conodonts reported from near the top of the chert and argillite unit are reworked. Poorly preserved Early(?) or Middle Triassic radiolarians and Middle Triassic ammonites and pectenacid bivalves from the middle part of the volcaniclastic unit indicate that Early Triassic deposition cannot be documented at the Quinn River locality. Late Triassic (early to middle Carnian) radiolarians assignable to the Triassocampe nova Assemblage Zone of Yao occur about 21 meters below the top of the Quinn River section; diagnostic genera include Castrum, Corum, Poulpus, Pseudostylosphaera, Triassocampe, and Xipha. The ages of the Quinn River brachiopod, conodont, and radiolarian faunas resemble those of the Dekkas and Pit Formations, eastern Klamath terrane, northern California. The Early Triassic age for the lower part of the Pit Formation is questioned because the unit contains only unidentifiable primitive radiolarians and long-ranging (Late Permian and Early Triassic) neogondolellid conodonts. The analogous Quinn River and eastern Klamath rock types and faunal ages, as well as similar hiatuses in their stratigraphic records, suggest that they may be lateral equivalents that formed in the same island-arc sedimentary basin.

Upper Triassic Invertebrates from the Antimonio Formation, Sonora, Mexico

A diverse Upper Triassic tropical marine fauna from northwestern Sonora, Mexico, includes 31 taxa of tropical invertebrates including scleractinian corals, spongiomorphs, disjectoporoids, “hydrozoans,” thalamid and nonthalamid sponges, spiriferid and terebratulid brachiopods, gastropods, bivalves, coleoids, and anomuran microcoprolites. They occur within the late Karnian to Norian part of the Antimonio Formation (Antimonio terrane), which is juxtaposed against a fragmented portion of the North American craton. Most of the fauna is also known from the Tethys region. Sixteen Sonoran taxa co-occur in the western Tethys and five have never been known outside this region. Four additional taxa (one identified only at genus level) are geographically widespread. Some taxa occur in displaced terranes of North America, especially in west-central Nevada (Luning Formation). A weak link exists with the California Eastern Klamath terrane but stronger ties exist with Peru. Among Sonoran sponges,Nevadathalamia polystomawas previously recognized only from the Luning Formation, western Nevada. SpongesCinnabaria expansa, Nevadathalamia cylindrica, and a coral,Astraeomorpha sonorensisn. sp., are also known from Nevada. The coralsDistichomeandra austriaca, Chondrocoenia waltheri, Pamiroseris rectilamellosa, andAlpinophyllia flexuosaco-occur in central Europe. Two new taxa, a spongiomorph hydrozoan,Stromatoporidium lamellatumn. sp., and a disjectoporoid,Pamiropora sonorensisn. sp., have distinct affinities with the Tethys. The geographically widespread North American brachiopod,Spondylospira lewesensis, andPseudorhaetina antimoniensisn. gen. and sp. are among the Sonoran fauna. The Sonoran coleoid (aulacocerid)Dictyoconites(Dictyoconites) cf.D. reticulatumoccurs in the Tethys realm andCalliconitescf.C. drakeiis comparable with a species from the Eastern Klamath terrane.Calliconites millerin. sp. is the first occurrence of the genus outside Sicily. The bivalvesMyophorigonia jaworskii, M. salasi, andPalaeocardita peruvianaare known from Sonora and Peru. Eight gastropod taxa includeGuidoniacf.G. intermediaandG.cf.G. parvula, both previously known from Peru, andEucycloscala subbisertusfrom the western Tethys. The gastropods are unlike those already known from other North American terranes.

Permian longitudes of Wrangellia, Stikinia, and Eastern Klamath terranes based on coral biogeography

Trend-surface analysis of biogeographic data and probabilistic estimates of diversity and similarity provide a new approach to understanding the origin of North American suspect terranes. Results from Permian corals indicate that (1) the eastern boundary of the Tethyan coral province was about 2000 km west of the North American craton; (2) Eastern Klamath and Stikinia were close to one another and were up to 6700 km west of North America during the Early Permian; (3) Wrangellia was situated to the southeast of Stikinia, as much as 5000 km west of the craton; (4) the Late Permian location of the Eastern Klamath terrane was 3000-5800 km west of the craton and between 11° and 21°N; and (5) the Eastern Klamath terrane moved westward during the Permian, possibly as a result of back-arc spreading.

Eruption-Controlled Epiclastic Sedimentation in a Devonian Trench-Slope Basin: Evidence from Sandstone Petrofacies, Klamath Mountains, California

ABSTRACT The Devonian Gazelle Formation comprises sparsely fossiliferous shale, siltstone, siliceous mudstone, volcaniclastic sandstone, and conglomerate whose cumulative thickness is at least 1.25 km. Two end-member sand compositions combined locally to form a third petrofacies. The volcaniclastic petrofacies was derived from an undissected magmatic arc, whereas the chert-mudrock petrofacies reflects derivation from melangee of the underlying accretionary prism. The stratigraphically restricted mixed petrofacies is compositionally discrete and records thorough mixing of these two compositional end members. Data from sandstone petrography are consistent with independent geologic evidence indicating that the Gazelle Formation represents the fill of a Devonian trench-slope basin that for ed above an east-dipping subduction zone. Our interpretation of the Balaklala Rhyolite as the source of the volcaniclastic petrofacies requires proximity of the Yreka and Eastern Klamath terranes during the Early Devonian, and indicates that the eastern Klamath province has behaved as a single crustal block (sensu lato) ever since. Field study and petrographic analysis indicate that the delivery of coarse terrigenous detritus to the basin was controlled principally by episodic eruptions of rhyolitic tephra in the arc source and also by one discernible episode of change in relative sea level. This study indicates that caution must be used when invoking changes in relative sea level to explain the stratigraphic distribution of epiclastic turbidites in island-arc settings. Identification of compositionally and stratigraphically discrete mixed petrofacies in other ancient orogens may permit similar inferences regarding controls on stratigraphic development that have operated on poorly fossiliferous, immature convergent margins.