Geochronometry of the Eagle Plutonic Complex and the Coquihalla area, southwestern British Columbia

1992 ◽  
Vol 29 (4) ◽  
pp. 812-829 ◽  
Author(s):  
C. J. Greig ◽  
R. L. Armstrong ◽  
J. E. Harakal ◽  
D. Runkle ◽  
P. van der Heyden
Keyword(s):  
British Columbia ◽  
Late Jurassic ◽  
Middle Eocene ◽  
Timing Constraints ◽  
Early Eocene ◽  
East Side ◽  
Eastern Margin ◽  
Plutonic Complex ◽  
Southwestern Margin

New U–Pb, K–Ar, and Rb–Sr dates from the Eagle Plutonic Complex and adjacent map units place timing constraints on intrusive and deformational events along the southwestern margin of the Intermontane Belt. U–Pb zircon minimum dates for Eagle tonalite and gneiss (148 ± 6, 156 ± 4, and 157 ± 4 Ma) document previously unrecognized Middle to Late Jurassic magmatism and syn-intrusive deformation along the eastern margin of the Eagle Plutonic Complex and the southwestern margin of the Intermontane terrane. Widespread mid-Cretaceous (Albian–Cenomanian) resetting of K–Ar and Rb–Sr isotopic systematics in Jurassic and older rocks is coeval and cogenetic with emplacement of plutons of the Fallslake Plutonic Suite (110.5 ± 2 Ma, U–Pb) which crosscut Jurassic plutons and structures but were themselves ductilely deformed along the Pasayten fault during sinistral, east-side-up, reverse displacement. K–Ar and Rb–Sr cooling dates for the Fallslake Suite of ca. 100 Ma, including dates from mylonites along the Pasayten fault, suggest that uplift, cooling, and unroofing of the Eagle Plutonic Complex occurred in mid-Cretaceous time along the Pasayten fault. Regional geologic evidence suggests that this thermal and unroofing event affected much of the southwest margin of the Intermontane Belt. Initial 87Sr/86Sr ratios and U–Pb geochronometry for the Fallslake Plutonic Suite suggest that it was derived, in part, from preexisting and relatively nonradiogenic Paleozoic to Mesozoic crust. K–Ar dating of several stocks demonstrates widespread Early Eocene plutonism in the Coquihalla area, and dating of the Needle Peak pluton indicates plutonism continued into Middle Eocene time.

Jurassic and Cretaceous plutonic and structural styles of the Eagle Plutonic Complex, southwestern British Columbia, and their regional significance

1992 ◽  
Vol 29 (4) ◽  
pp. 793-811 ◽  
Author(s):  
Charles J. Greig
Keyword(s):  
Late Jurassic ◽  
High Strain ◽  
Middle Eocene ◽  
Ductile Deformation ◽  
Brittle Deformation ◽  
East Side ◽  
The West ◽  
The North ◽  
Plutonic Complex ◽  
Southwestern Margin

The Eagle Plutonic Complex is an elongate north-northwest-trending body of deformed Middle to Late Jurassic and middle Cretaceous rocks which underlies the southwestern margin of the Intermontane terrane. New mapping of the complex and its country rocks, in concert with geochronometry, has defined episodes of contractional, ductile deformation in the Middle to Late Jurassic and middle Cretaceous, as well as brittle deformation in Tertiary time. Synkinematic Middle to Late Jurassic Eagle tonalite at the eastern margin of the Eagle Complex intrudes mylonitic Nicola Group rocks and structurally overlies them along a southwest-dipping belt of high strain (Eagle shear zone) with a structural thickness of > 1 km and a strike length of > 100 km. In the central and western Eagle Complex, Eagle tonalite grades into tonalite orthogneiss (Eagle gneiss), and both are crosscut by mid-Cretaceous, muscovite-bearing plutons of the Fallslake Plutonic Suite. Fallslake Suite rocks are themselves ductilely deformed along the Pasayten fault, which bounds the Eagle Complex on the west and was active mainly in the mid-Cretaceous (ductile deformation with sinistral, east-side-up, reverse displacement). The Jurassic and Cretaceous episodes of deformation may reflect the respective initial and final stages of the accretion of the Insular terrane to the North American margin. West of the Pasayten fault, Middle to Late Jurassic and older(?) rocks of the Zoa Complex are structurally overlain, in part, by deformed Middle Eocene and middle Cretaceous sedimentary rocks. In the north, the Middle Eocene rocks are intruded on their west side by the Middle Eocene Needle Peak pluton.

Biochronology of selected Bowser Basin strata; tectonic significance

1988 ◽  
Vol 25 (10) ◽  
pp. 1571-1578 ◽  
Author(s):  
I. W. Moffat ◽  
R. M. Bustin ◽  
G. E. Rouse
Keyword(s):  
British Columbia ◽  
Late Jurassic ◽  
Plant Succession ◽  
Fossil Plant ◽  
North Central ◽  
Eastern Margin ◽  
Time Period ◽  
Tectonic Significance ◽  
Age Range ◽  
Recent Evaluation

Recent evaluation and reinterpretation of fossil floral and faunal data more clearly define the ages of strata exposed in the Groundhog Coalfield and the surrounding Bowser Basin of north-central British Columbia. In the Groundhog Coalfield, Bowser Lake Group strata consist of an overall coarsening-upwards cycle divisible into four informal stratigraphic units, which are, from oldest to youngest, the Jackson, Currier, McEvoy, and Devils Claw units. The section has an unconformable relationship with underlying Bajocian Spatsizi marine shales, volcanics, and arenaceous sediments. Marine macrofossils indicate a Callovian to Oxfordian age for the Jackson unit. The fossil plant succession present in the overlying Currier unit indicates Late Jurassic affinities. Recent unpublished palynologic data from lower McEvoy rocks in the northern Groundhog Coalfield suggest a Barremian age. The palynoassemblage present in the lower Devils Claw unit in the central part of the Groundhog Coalfield suggests a late middle Albian age.Rocks of the Sustut Group have an angular unconformable relationship with underlying Bowser Lake Group strata near the eastern margin of the Bowser Basin. The palynoassemblage present in Sustut Group rocks from the southern Sustut Basin suggests a Campanian to Maastrichtian age range, in contrast to a probable late Albian to Campanian age range for the northern Sustut Basin and a middle to late Albian age from Sustut Group outliers present within the northern Bowser Basin. Within the Groundhog Coalfield, Devils Claw strata have a conformable or paraconformable relationship with underlying Bowser Lake Group strata.Regional discrepancy in the age and geometry of the sub-Sustut unconformity is attributed to a time-transgressive unconformity that resulted from cratonward advance of an isostatically induced peripheral bulge. Age and contact relationships suggest that deformation in the Bowser Basin and surrounding Sustut Basin must have spanned the time period that corresponds to a second uplift pulse of the Columbian orogen (Aptian to early Cenomanian) and the uplift pulse related to the Laramide orogen (Campanian to Maastrichtian).

Additions to the Eocene Perissodactyla of the Margaret Formation, Eureka Sound Group, Ellesmere Island, Arctic Canada

2015 ◽  
Vol 52 (2) ◽  
pp. 123-133 ◽  
Author(s):  
Jaelyn J. Eberle ◽  
David A. Eberth
Keyword(s):  
United States ◽  
British Columbia ◽  
Middle Eocene ◽  
The United States ◽  
Geographic Range ◽  
Ellesmere Island ◽  
Early Eocene ◽  
Arctic Canada ◽  
Fossil Assemblages ◽  
Freezing Temperatures

We describe early Eocene (Wasatchian) occurrences of the isectolophid Homogalax, tapiroids Heptodon posticus, Heptodon cf. H. posticus, and Heptodon sp., as well as early middle Eocene (Bridgerian) fossils of the brontothere Palaeosyops from localities in the Margaret Formation of the Eureka Sound Group on Ellesmere Island, Nunavut, Arctic Canada. Their occurrence on Ellesmere Island considerably extends the geographic range of these taxa, previously known from mid-latitude localities in British Columbia (only Heptodon), the Western Interior of the United States, and Asia (Homogalax, Heptodon, and Palaeosyops). We also place the fossil localities near Bay Fiord on central Ellesmere Island into a refined lithostratigraphic framework based upon data from three measured stratigraphic sections. Our stratigraphic data confirm the presence of two, stratigraphically distinct fossil assemblages — a late Wasatchian-aged lower assemblage and a Bridgerian-aged upper assemblage that were previously hypothesized by others based on faunal differences — that are separated by a 478 m thick stratigraphic gap that appears to lack fossil vertebrates. From a paleoenvironmental perspective, occurrence of the tapiroid Heptodon in the Eocene Arctic corroborates an hypothesis put forward by others that tapiroids are proxies for densely forested habitats, although they were adapted to a range of temperatures including near (or at) freezing temperatures of Eocene Arctic winters. Further, Arctic occurrences of tapiroids and brontotheres imply that these typical mid-latitude ungulate mammals were adapted to Arctic environments, thereby increasing the probability of Trans-Beringian dispersal during early and middle Eocene time.

Interpretation of isotopic ages and 87Sr/86Sr initial ratios for plutonic rocks in the Whitehorse map area, Yukon

1979 ◽  
Vol 16 (10) ◽  
pp. 1988-1997 ◽  
Author(s):  
Gregg W. Morrison ◽  
Colin I. Godwin ◽  
Richard L. Armstrong
Keyword(s):  
British Columbia ◽  
Oceanic Crust ◽  
Late Cretaceous ◽  
Canadian Cordillera ◽  
Initial Ratio ◽  
Eastern Margin ◽  
The North ◽  
Plutonic Complex ◽  
Coast Plutonic Complex ◽  
North American Craton

Sixteen new K–Ar dates and four new Rb–Sr isochrons help define four plutonic suites in the Whitehorse map area, Yukon. The Triassic(?) suite, defined on stratigraphic evidence, is the southern extension of the Yukon Crystalline Terrane and is correlative with plutonic suites in the Intermontane Belt in British Columbia. The mid-Cretaceous (~100 Ma) suite in the Intermontane Belt in the Whitehorse map area is time equivalent to plutonic suites in the Omineca Crystalline Belt to the east. Late Cretaceous (~70 Ma) and Eocene (~55 Ma) suites include volcanic and subvolcanic as well as plutonic phases and are correlative with continental volcano–plutonic suites near the eastern margin of the Coast Plutonic Complex. The predominance of the mid-Cretaceous suite in the Intermontane Belt in Whitehorse and adjacent map areas in Yukon and northern British Columbia suggests that this area has undergone posttectonic magmatism more characteristic of the Omineca Crystalline Belt than of the Intermontane Belt elsewhere in the Canadian Cordillera.87Sr/86Sr initial ratio determinations suggest that the southern extension of the Yukon Crystalline Terrane in the western part of the Whitehorse map area and in northern British Columbia includes Precambrian crust separated from the North American craton by Paleozoic oceanic crust of the Intermontane Belt.

U–Pb and K–Ar dates related to the timing of magmatism and deformation in the Cache Creek terrane and Quesnellia, southern British Columbia

1990 ◽  
Vol 27 (1) ◽  
pp. 117-123 ◽  
Author(s):  
N. Mortimer ◽  
P. van der Heyden ◽  
R. L. Armstrong ◽  
J. Harakal
Keyword(s):  
British Columbia ◽  
Early Cretaceous ◽  
North American ◽  
Late Jurassic ◽  
Early Jurassic ◽  
Early Permian ◽  
Magmatic Arc ◽  
Plutonic Complex ◽  
Minimum Age ◽  
Coast Plutonic Complex

U–Pb dating of zircon from the Guichon Creek batholith indicates an emplacement age of 210 ± 3 Ma. Comparison with previously published K–Ar (211–188 Ma) and Rb–Sr (205 and 196 Ma) dates reveals that intrusion, mineralization, cooling, and uplift of the batholith took some 20 Ma, spanning the Triassic–Jurassic boundary on the Decade of North American Geology (DNAG) time scale.The Mount Martley pluton and Tiffin Creek stock yield Late Jurassic dates of 155 ± 2 Ma (U–Pb, zircon) and 152 ± 5 Ma (K–Ar, hornblende), respectively, and provide a reliable minimum age (Kimmeridgian) for penetrative deformation in the Cache Creek terrane. K–Ar whole-rock dates from Cache Creek terrane and Ashcroft Formation argillites range from Early Permian (266 ± 8 Ma) and Early Jurassic (194 ± 6 Ma) to Late Jurassic, Kimmeridgian (154 ± 5 Ma). We interpret the younger dates as recording Middle–Late Jurassic tectonism and the older ones as possible relics from earlier deformation episodes.An Early Cretaceous K–Ar date (129 ± 5 Ma) for a lamprophyre dike that cuts the Nicola Group suggests that the Early Cretaceous magmatic arc of the Coast Plutonic Complex had an eastern alkalic fringe in the Intermontane Belt.

Upper limit of docking time for Stikinia and Terrane I: paleomagnetic evidence from the Eocene Ootsa Lake Group, British Columbia

1990 ◽  
Vol 27 (2) ◽  
pp. 212-218 ◽  
Author(s):  
T. A. Vandall ◽  
H. C. Palmer
Keyword(s):  
British Columbia ◽  
North America ◽  
Large Scale ◽  
Middle Eocene ◽  
Pole Position ◽  
Upper Limit ◽  
Plutonic Complex ◽  
Coast Plutonic Complex ◽  
The Mean ◽  
Reversed Polarity

The Middle Eocene Ootsa Lake Group is exposed in the central portion of the Stikine Terrane, where it was sampled along the shoreline of Tahtsa Reach and Whitesail Reach. The group consists of dominantly subaerial flows, which range in composition from basalt to rhyolite, that unconformably overly the Jurassic Hazelton Group. Detailed alternating-field and thermal stepwise demagnetizations were done on all specimens from the 21 sites collected. The presence of a normal- and reversed-polarity remanence, a positive fold test, and high coercivities and unblocking temperatures indicate that a prefolding primary remanence has been isolated. The mean tilt-corrected direction of D = 002.2°, I = 69.2 °(α95 = 7.4°) from 13 sites for which paleohorizontal is well known yields a pole position at 354.6°E, 88.0°N (A95 = 11.5°), which is statistically indistinguishable from published 50 Ma reference poles for cratonic North America. This evidence demonstrates that the proposed large-scale northward displacement of Stikinia since mid-Cretaceous was completed by at least Middle Eocene time. This result is consistent with other paleomagnetic results from Stikinia, Quesnellia, and the Coast Plutonic Complex indicating that much of the allochthonous Cordillera had assembled and docked with cratonic North America by the Middle Eocene.

Vegetative Growth of Eorhiza arnoldii Robison and Person from the Middle Eocene Princeton Chert Locality of British Columbia

1994 ◽  
Vol 155 (5) ◽  
pp. 606-616 ◽  
Author(s):  
Ruth A. Stockey ◽  
Kathleen B. Pigg
Keyword(s):  
British Columbia ◽  
Vegetative Growth ◽  
Middle Eocene

Further observations on Paleorosa similkameenensis (Rosaceae) from the Middle Eocene Princeton chert of British Columbia, Canada

1993 ◽  
Vol 78 (3-4) ◽  
pp. 277-291 ◽  
Author(s):  
Sergio R.S. Cevallos-Ferriz ◽  
Diane M. Erwin ◽  
Ruth A. Stockey
Keyword(s):  
British Columbia ◽  
Middle Eocene

Fossil Mosses from the Bisaccate Zone of the Mid-Eocene Allenby Formation, British Columbia

1974 ◽  
Vol 11 (3) ◽  
pp. 409-421 ◽  
Author(s):  
Marian Kuc
Keyword(s):  
British Columbia ◽  
Middle Eocene ◽  
Plant Tissues ◽  
Plant Remains ◽  
Lake Bottom ◽  
White Colour

New fossil taxa (Ditrichites fylesi, Muscites maycocki, M. ritchiei, Palaeohypnum jovet-asti and P. steerei); unnamed moss and moss-like fossils, detrital fragments of various plant tissues, and paleobotanical evidence of the bisaccate zone are described from the Middle Eocene Allenby Formation near Princeton, British Columbia. These remains occur in laminated, tuffaceous, silty and pyroclastic shale, deposited under lacustrine conditions.Detailed examination of the various laminae indicates that beds of white colour and composed of coarser silt grains are poor in fossils and could be related to periods of decreasing bioproduction; less silty and darker coloured beds are rich in macro- and microfossils and could be related to periods of extensive bioproduction. The rock features, lamination, and distribution of macrofossils indicate the slow and undisturbed accumulation of plant remains on a lake bottom.

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