scholarly journals Calcareous Nannofossils From the Late Triassic - Early Jurassic of the Queen Charlotte Islands, British Columbia

1991 ◽  
Author(s):  
P R Bown
Keyword(s):  
British Columbia ◽  
Early Jurassic ◽  
Late Triassic ◽  
Calcareous Nannofossils ◽  
Queen Charlotte Islands

scholarly journals Late Triassic-Early Jurassic Calcareous Nannofossils of the Queen Charlotte Islands, British Columbia

1992 ◽  
Vol 11 (2) ◽  
pp. 177-188 ◽  
Author(s):  
Paul R. Bown
Keyword(s):  
British Columbia ◽  
North America ◽  
Mediterranean Area ◽  
Lower Jurassic ◽  
Late Triassic ◽  
Time Interval ◽  
Calcareous Nannofossils ◽  
Low Latitude ◽  
Queen Charlotte Islands ◽  
Northwest Europe

Abstract. Sediments of the Kunga and Maude groups (Early Norian-Aalenian) from the Queen Charlotte Islands, British Columbia, have yielded the first records of early Mesozoic calcareous nannofossils in North America. These occurrences are the only record of Triassic nannofossils away from the recent discoveries in the Tethyan area (Austria, Indonesia, and the northwestern Australian margin). The nannofossil assemblages from the Queen Charlotte Islands are generally poor to moderately preserved, with species diversities typical for this time interval (2–10 species). The assemblages are comparable to those from northwest Europe, for the Lower Jurassic, and to those from Austria, Indonesia, and the Australian margin, for the Upper Triassic. They show compatible stratigraphical ranges, allowing the application of existing biostratigraphical zonations. Palaeobiogeographical interpretations are inconclusive and fail to positively confirm a low latitude (Tethyan) position for the Queen Charlotte Islands, as indicated by macrofossil data. However, Triassic nannofossil assemblages have yet to be described from high palaeolatitude locations. In addition, certain features of the Lower Jurassic assemblages may indicate Tethyan affinities but also distinguish these assemblages from those which have been previously documented. These features include the absence of Schizosphaerella punctulata, which occurs abundantly in the circum-Mediterranean region and was previously thought to be “cosmopolitan” in distribution; and the absence of Mitrolithus jansae which characterizes “Tethyan” assemblages in the circum-Mediterranean area. The Queen Charlotte Islands results are compared with new nannofossil data from Argentina, Timor and North America.

Atypical diagenetic effects on strontium-isotope composition of Early Jurassic belemnites, Queen Charlotte Islands, British Columbia, Canada

2007 ◽  
Vol 44 (2) ◽  
pp. 181-197 ◽  
Author(s):  
Darren R Gröcke ◽  
Stephen P Hesselbo ◽  
Duncan J Findlay
Keyword(s):  
British Columbia ◽  
Isotope Composition ◽  
Early Jurassic ◽  
Striking Similarity ◽  
Geochemical Data ◽  
Screening Methods ◽  
Element Abundances ◽  
Queen Charlotte Islands ◽  
Diagenetic Alteration ◽  
Carbon And Oxygen Isotope

In this study, strontium-, carbon- and oxygen-isotope data are reported from Early Jurassic belemnites from Yakoun River, Queen Charlotte Islands (QCI), British Columbia. Assuming that the established ammonite correlations between Canada and Europe are accurate, the seawater 87Sr/86Sr curve between Europe and QCI should be similar. However, the Rarenodia planulata and Phymatoceras crassicosta ammonite biozones from Yakoun River record 87Sr/86Sr values that are lower than expected. This shift is interpreted to be a result of diagenetic alteration by later hydrothermal fluid (87Sr-depleted). In general, the diagenetic samples have more negative δ13Cbel and δ18Obel values, and higher Mn concentrations, but show no difference in Fe concentration. A δ13Cbel curve from diagenetically screened samples exhibits only slightly depleted values with respect to a similar curve generated from Europe. A similar curve for δ18Obel shows a striking similarity with that generated from Europe. This study illustrates that diagenetic effects on Sr-isotope composition can lower values from the expected seawater 87Sr/86Sr curve, thus potentially producing erroneous correlations between ammonite biostratigraphic schemes. Traditional screening methods for diagenesis, such as cathodoluminescence and trace-element abundances, were inadequate for evaluating diagenesis in the Yakoun River sections. Other such studies must also consider alternative and (or) a combination of methods in evaluating geochemical data from belemnites.

scholarly journals Late Triassic (Early to Middle Norian) radiolarians from the Antalya Nappes, Antalya, SW Turkey

2003 ◽  
Vol 22 (2) ◽  
pp. 147-162 ◽  
Author(s):  
Ugur Kagan Tekin ◽  
Tugrul Sukru Yurtsever
Keyword(s):  
British Columbia ◽  
Late Triassic ◽  
Associated Fauna ◽  
The West ◽  
Queen Charlotte Islands ◽  
Sw Turkey ◽  
Age Range

Abstract. The Gökdere Formation of the Alakircay Nappe (Antalya Nappes) mainly consists of cherty limestone and limestone with calciturbidite intercalations. Moderately to well-preserved radiolarians were obtained from the Gökcam section of the Gökdere Formation located to the west of Antalya City, southwestern Turkey. The radiolarians of the Gökdere Formation obtained in this study are comparable to the faunas described from the Queen Charlotte Islands, British Columbia and the Antalya Nappes, southwestern Turkey. The age range of the radiolarians is late Early Norian to early Middle Norian based on the co-occurrence of Capnodoce serisa, Harsa siscwaiensis, Xiphosphaera fistulata and an associated fauna. Three species (Nodocapnuchosphaera altineri, Renzium whalenae and Enoplocampe(?) norica) and one subspecies (Kinyrosphaera helicata goekcamensis) are defined as new.

Carmacks Copper Cu-Au-Ag Deposit: Mineralization and Postore Migmatization of a Stikine Arc Porphyry Copper System in Yukon, Canada

2020 ◽  
Vol 115 (7) ◽  
pp. 1413-1442
Author(s):  
Nikolett Kovacs ◽  
Murray M. Allan ◽  
James L. Crowley ◽  
Maurice Colpron ◽  
Craig J.R. Hart ◽  
...  
Keyword(s):  
British Columbia ◽  
Porphyry Copper ◽  
Copper Deposit ◽  
Early Jurassic ◽  
Amphibolite Facies ◽  
Late Triassic ◽  
Ionization Mass ◽  
Sulfide Mineralization ◽  
Porphyry Cu ◽  
South Central

Abstract Late Triassic to Early Jurassic porphyry Cu mineralization is common in British Columbia, yet there are few age-equivalent porphyry occurrences in Yukon. This study presents new data for the enigmatic Carmacks Copper Cu-Au-Ag deposit in south-central Yukon, Canada, which is hosted in amphibolite facies metamorphic inliers within the Early Jurassic Granite Mountain batholith. Sulfide mineralization occurs mainly as net-textured bornite and chalcopyrite in leucosome, and as chalcopyrite ± pyrite blebs and disseminations in amphibolite and quartz-plagioclase-biotite schist. Several studies suggest that the Carmacks Copper deposit and the nearby Minto deposit are related to porphyry belts in British Columbia, but constraining the timing of alteration, mineralization, and metamorphism has been difficult. This study establishes a geologic and high-precision geochronologic framework for sulfide mineralization and its host rocks at the Carmacks Copper deposit, using Re-Os dating of molybdenite, and chemical abrasion-thermal ionization mass spectrometry (CA-TIMS) analysis of both whole zircon grains and laser-cut fragments of complexly zoned zircon grains. Our data indicate that the igneous protolith of the metamorphic inliers formed at 217.53 ± 0.16 Ma, followed by peak metamorphism at amphibolite facies at 205.82 ± 0.23 Ma, which occurred prior to Granite Mountain batholith emplacement but subsequent to Cu-Au-Ag mineralization of the protolith. An early phase of the Granite Mountain batholith was emplaced at 199.84 ± 0.14 Ma, followed by the main phase at 195 to 194 Ma. A second generation of metamorphic zircon in migmatite at 196.01 ± 0.12 Ma represents a partial melting event associated with Granite Mountain batholith emplacement. Two petrographically distinct populations of molybdenite are present in unstrained, net-textured copper sulfides. A sample dominated by strained molybdenite yielded an 187Re/187Os age of 212.5 ± 1.0 Ma, which represents the minimum mineralization age of the protolith. A sample dominated by euhedral grains yielded an 187Re/187Os age of 198.5 ± 0.9 Ma, constraining the maximum age of sulfide remobilization. These results indicate that primary mineralization is >212.5 Ma and potentially coeval with the ~217.5 Ma generation of Late Triassic magmatism. The mineralized protolith, best interpreted as the potassic alteration zone of a Late Triassic (~217–213 Ma) porphyry Cu-Au system, was metamorphosed to amphibolite facies at ~206 Ma, and subsequently migmatized during 200 to 194 Ma intrusion of the Granite Mountain batholith. The chalcopyrite-bornite-dominant assemblage in neosome precipitated from an immiscible Cu-Fe-S melt phase that partly consumed xenocrystic molybdenite and reprecipitated new molybdenite grains. The Carmacks Copper deposit and the related Minto deposit are remnants of a Late Triassic porphyry belt, where a significant fraction of the original metal endowment was likely lost through digestion of mineralized rocks by midcrustal magma in the Early Jurassic. These Yukon deposits are rare examples of metamorphosed porphyry Cu systems in the global geologic record, where rapid tectonic burial following mineralization was the principal factor in their preservation.

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