Synopsis of late Palaeozoic and Mesozoic terrane accretion within the Cordillera of western North America

1990 ◽  
Vol 331 (1620) ◽  
pp. 479-486 ◽  
Keyword(s):  
North America ◽  
Western North America ◽  
Island Arcs ◽  
Multidisciplinary Research ◽  
The West ◽  
Marginal Sea ◽  
Faunal Diversity ◽  
Cordilleran Margin ◽  
Terrane Accretion ◽  
Faunal Studies

Establishing the paleogeographic origin of most of the terranes within the Cordillera remains an ellusive goal; despite more than 10 years of multidisciplinary research, the home port of any major terrane has not been identified unequivocally. Even most continental fragments that show affinities to North America cannot be repositioned confidently along the Cordilleran margin, and some continental fragments (e.g. Chulita) probably are not North American in origin. Cordilleran oceanic terranes, including island arcs, seamounts, off-ridge islands, and scraps of ocean basins, are especially difficult to reposition because Panthalassa has been destroyed. Faunal studies with emphasis on palaeobiogeographic affinities are the most useful, particularly when coupled with analyses of faunal diversity and endemism. Such studies suggest that some terranes previously thought to have formed near the Cordillerran margin were situated thousands of kilometres to the west, and were separated from the continent by broad ocean basins, rather than by a narrow marginal sea.

The Lower Jurassic phosphorites of southeastern British Columbia and terrane accretion to western North America

1989 ◽  
Vol 26 (8) ◽  
pp. 1612-1616 ◽  
Author(s):  
T. P. Poulton ◽  
J. D. Aitken
Keyword(s):  
British Columbia ◽  
North America ◽  
Oceanic Crust ◽  
West Coast ◽  
Cold Water ◽  
Lower Jurassic ◽  
Depositional Model ◽  
Western North America ◽  
The West ◽  
Terrane Accretion

Sinemurian phosphorites in southeastern British Columbia and southwestern Alberta conform with the "West Coast type" phosphorite depositional model. The model indicates that they were deposited on or near the Early Jurassic western cratonic margin, next to a sea or trough from which cold water upwelled. This suggests that the allochthonous terrane Quesnellia lay well offshore in Sinemurian time. The sea separating Quesnellia from North America was partly floored by oceanic crust ("Eastern Terrane") and partly by a thick sequence of rifted, continental terrace wedge rocks comprising the Purcell Supergroup and overlying Paleozoic sequence. This sequence must have been depressed sufficiently that access of upwelling deep currents to the phosphorite depositional area was not impeded.

The Pseudoomphalina kalchbrenneri complex in North America

Botany ◽  
2020 ◽  
Vol 98 (2) ◽  
pp. 91-101
Author(s):  
Andrus Voitk ◽  
Irja Saar ◽  
Renée Lebeuf ◽  
Peter Kennedy
Keyword(s):  
New Species ◽  
North America ◽  
North American ◽  
Western North America ◽  
The West ◽  
Ancestral Species ◽  
Eurasian Species ◽  
One New Species

Pseudoomphalina kalchbrenneri is a Eurasian species. In North America the Pso. kalchbrenneri complex is represented by Pseudoomphalina anticostica sp. nov. and Pso. compressipes in the east and Pso. intermedia in the west. Pseudoomphalina farinacea and Pso. felleoides are later synonyms for Pso. compressipes. The somewhat similar Pseudolaccaria pachyphylla occupies a temperate band through Eurasia, confirmed by sequencing in both eastern and western North America. It differs from species of the Pso. kalchbrenneri complex by smaller size, finely granular pileus, non-decurrent gills, and lack of hymenial cystidia. All species of the Pso. kalchbrenneri complex are uncommon, and macroscopically similar. Pseudoomphalina kalchbrenneri and Pso. intermedia can be identified by their distribution (Europe and western North America, respectively) and lack of cystidia. The cystidiate eastern North American Pso. anticostica and Pso. compressipes can be differentiated by the smaller spores of the latter. Pseudoomphalina cokeri is the most ancestral species on the Pseudoomphalina lineage, while Clitocybe thujana and Agaricus apertus (Clitocybe/Clitocybula aperta) fall outside Pseudoomphalina and Pseudolaccaria. We add 21 new sequences to GenBank, including six types (Agaricus compressipes, Clitocybe felleoides, C. farinacea, C. intermedia, C. thujana, Agaricus apertus), and one new species (Pso. anticostica).

scholarly journals Early Paleozoic post-breakup magmatism along the Cordilleran margin of western North America: New zircon U-Pb age and whole-rock Nd- and Hf-isotope and lithogeochemical results from the Kechika group, Yukon, Canada

Geosphere ◽  
2019 ◽  
Vol 15 (4) ◽  
pp. 1262-1290 ◽  
Author(s):  
Roderick W. Campbell ◽  
Luke P. Beranek ◽  
Stephen J. Piercey ◽  
Richard Friedman
Keyword(s):  
North America ◽  
Continental Shelf ◽  
Mantle Source ◽  
Tectonic Setting ◽  
Plate Boundary ◽  
Hf Isotope ◽  
Passive Margin ◽  
Western North America ◽  
South Central ◽  
Cordilleran Margin

AbstractPost-breakup magmatic rocks are recognized features of modern and ancient passive margin successions around the globe, but their timing and significance to non-plume-related rift evolution is generally uncertain. Along the Cordilleran margin of western North America, several competing rift models have been proposed to explain the origins of post-breakup igneous rocks that crop out from Yukon to Nevada. New zircon U-Pb age and whole-rock geochemical studies were conducted on the lower Paleozoic Kechika group, south-central Yukon, to test these rift models and constrain the timing, mantle source, and tectonic setting of post-breakup magmatism in the Canadian Cordillera. The Kechika group contains vent-proximal facies and sediment-sill complexes within the Cassiar platform, a linear paleogeographic high that developed outboard of continental shelf and trough basins. Chemical abrasion (CA-TIMS) U-Pb dates indicate that Kechika group mafic rocks were generated during the late Cambrian (488–483 Ma) and Early Ordovician (473 Ma). Whole-rock trace-element and Nd- and Hf-isotope results are consistent with the low-degree partial melting of an enriched lithospheric mantle source during margin-scale extension. Equivalent continental shelf and trough rocks along western North America are spatially associated with transfer-transform zones and faults that were episodically reactivated during Cordilleran rift evolution. Post-breakup rocks emplaced along the magma-poor North Atlantic margins, including those near the Orphan Knoll and Galicia Bank continental ribbons, are proposed modern analogues for the Kechika group. This scenario calls for the release of in-plane tensile stresses and off-axis, post-breakup magmatism along the nascent plate boundary prior to the onset of seafloor spreading.

Middle Devonian conodonts from the Wadleigh Limestone, southeastern Alaska

1995 ◽  
Vol 69 (3) ◽  
pp. 540-555 ◽  
Author(s):  
Norman M. Savage
Keyword(s):  
North America ◽  
Middle Devonian ◽  
Western North America ◽  
The West ◽  
Beta Form ◽  
Western Shore

Conodonts from two localities on the western shore of Alberto Island, southeastern Alaska, includePolygnathus alexanderensisn. sp.,P. angustipennatus, P. borealisn. sp.,P. praetrigonicusn. sp.,P. robusticostatus, P. pseudofoliatus, P. linguiformis linguiformisgamma form of Bultynck,P. parawebbibeta form of Chatterton,P. angusticostatus, P. costatus costatus, Polygnathussp. B of Savage, 1977,Tortodus kockelianus australis, andT. kockelianus kockelianus.The faunas are considered to be of middle to late Eifelian (kockelianusZone) age. On Prince of Wales Island, just north of Staney Creek, exposures of Wadleigh Limestone include the conodontsPolygnathus trigonicus, P. kennettensis, P. alexanderensis, P. angustipennatus, P. parawebbibeta form,P. eiflius, P. linguiformis linguiformisgamma form,P. borealis, P. angusticostatus, P. robusticostatus, P. costatus costatus, P. pseudofoliatus, Tortodus kockelianus australis, andT. kockelianus kockelianus, also suggesting a middle to late Eifelian (kockelianusZone) age. Conodonts from the west end of the easternmost of the Alberto Islands includePolygnathus linguiformis linguiformisgamma form,P. parawebbibeta form,P. xylus ensensis, andOzarkodina brevis, indicating a late Eifelian to early Givetian (ensensistovarcusZones) age. The presence ofPolygnathus kennettensis, P. parawebbibeta form, andP. borealissuggests a biogeographic affinity with other parts of western North America during Eifelian time.

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