Lower to Middle Jurassic (Pliensbachian to Bajocian) stratigraphy of the northern Spatsizi area, north-central British Columbia

1986 ◽  
Vol 23 (12) ◽  
pp. 1963-1973 ◽  
Author(s):  
Robert C. Thomson ◽  
Paul L. Smith ◽  
Howard W. Tipper
Keyword(s):  
British Columbia ◽  
Grain Size ◽  
Middle Jurassic ◽  
Water Environment ◽  
Upper Jurassic ◽  
Calc Alkaline ◽  
Volcanic Arc ◽  
North Central ◽  
Area North ◽  
Southern Flank

The Lower to Middle Jurassic (Pliensbachian to lower Bajocian) Spatsizi Group in the northern Spatsizi area of north-central British Columbia is formally defined and subdivided into the Joan, Wolf Den, Melisson, Abou, and Quock formations. Each formation reflects deposition in a different, dominantly fine-clastic environment with a varying input of volcanic (epiclastic or pyroclastic) detritus. The Spatsizi Group represents the basinward sedimentary equivalent of the coeval Cold Fish Volcanics, a group of calc-alkaline flows and breccias that accumulated in a volcanic arc along the southern flank of the Stikine Arch. Arc-to basin-facies trends are best developed in the Joan and Wolf Den formations and are characterized by a decrease in the volcaniclastic component of the sediments, an overall reduction in grain size, and a progressively deeper water environment of deposition, as inferred from both sedimentological and faunal evidence.In the study area, the Spatsizi Group underlies with a slight angular discordance the Middle to Upper Jurassic Bowser Lake Group. Bowser lake sediments were deposited in the Bowser Basin, the largest Mesozoic successor basin in British Columbia. Based on evidence from the Spatsizi area and from other areas to the south at Diagonal Mountain and the Oweegee Mountains, the Spatsizi Group is interpreted as passing laterally into shales that underlie most of the Bowser Basin.

Jura-Cretaceous (Oxfordian to Cenomanian) stratigraphy of the north-central Bowser Basin, northern British Columbia

1989 ◽  
Vol 26 (5) ◽  
pp. 1001-1012 ◽  
Author(s):  
H. O. Cookenboo ◽  
R. M. Bustin
Keyword(s):  
British Columbia ◽  
Lower Cretaceous ◽  
Middle Jurassic ◽  
Late Jurassic ◽  
Upper Jurassic ◽  
Thick Section ◽  
North Central ◽  
The North

Three new formations of Late Jurassic and Early to mid-Cretaceous age are defined for a 2000 m thick section of Jura-Cretaceous rocks exposed in the north-central Bowser Basin. The Currier Formation (Oxfordian to Kimmeridgian or Tithonian) consists of 350–600 m of interbedded shales, siltstones, sandstones, coals, and carbonates. The McEvoy Formation (Barremian to as young as Albian) consists of 400–800 m of siltstones and shales with minor sandstones, thin coals, limestones, and conglomerates. The Devils Claw Formation (in part mid-Albian to Cenomanian) consists of 300–600 m of strata characterized by thick pebble and cobble conglomerates, with associated coarse sandstones and minor siltstones and shales.Two successive coarsening-upward sequences are identified in the study area. The first begins with Middle Jurassic marine shales of the Jackson unit grading upwards to coarser Upper Jurassic facies of the Currier Formation. The Currier Formation is conformably or unconformably overlain by siltstones and shales of the Lower Cretaceous McEvoy Formation, which forms the base of a second coarsening-upward sequence. Conglomerates appear with increasing frequency in the upper McEvoy and are the dominant lithology of the overlying Devils Claw Formation. The contact between the McEvoy and Devils Claw formations is gradational. The Devils Claw Formation forms the top of the second coarsening-upward sequence.The Currier Formation (Late Jurassic) is equivalent to the upper units of the Bowser Lake Group. The McEvoy and the Devils Claw formations (Barremian to Cenomanian) are coeval with the Skeena Group (Hauterivian? to Cenomanian). A probable unconformity separating the Upper Jurassic Currier Formation from the Lower Cretaceous McEvoy Formation correlates with a hiatus in the southern Bowser Basin and probably represents a regional unconformity.

Geology of the Cadwallader Group and the Intermontane–Insular superterrane boundary, southwestern British Columbia

1987 ◽  
Vol 24 (11) ◽  
pp. 2279-2291 ◽  
Author(s):  
Margaret E. Rusmore
Keyword(s):  
British Columbia ◽  
Middle Jurassic ◽  
Tectonic Evolution ◽  
Middle Triassic ◽  
Upper Triassic ◽  
Tectonic Block ◽  
Volcanic Arc ◽  
Arc Volcanism ◽  
Clastic Rocks ◽  
Tectonic Settings

Several lower Mesozoic, fault-bounded units separate the Intermontane and Insular superterranes in southwestern British Columbia. Detailed study of one of these Mesozoic units, the Cadwallader Group, helps clarify the boundary between the superterranes and establish the tectonic evolution of southwestern British Columbia. The Cadwallader Group is the oldest unit in an Upper Triassic through Middle Jurassic volcanic and sedimentary tectono-stratigraphic terrane. Two formations, the Pioneer and the Hurley, compose the Cadwallader Group; the previously recognized Noel Formation is no longer considered valid. The Pioneer Formation contains pillow basalt, flows, and basalt breccia. Siltstone, sandstone, conglomerate, and minor amounts of limestone megabreccia and basalt belonging to the Hurley Formation conformably overlie the Pioneer. The Hurley spans latest Carnian or earliest Norian to middle Norian time. Two episodes of deformation affected the Cadwallader, and a thrust fault separates the group from slightly younger clastic rocks of the Tyaughton Group. Similarities in clastic rocks indicate the Tyaughton was deposited on the Cadwallader; together the units form the Cadwallader terrane. Basalts and clastic rocks in the terrane record deposition in or near a Carnian to earliest Norian volcanic arc. Volcanism waned later in the Norian, but presence of the arc is preserved in the clastic rocks.Oceanic rocks of the Middle Triassic to Middle Jurassic Bridge River terrane became juxtaposed with the Cadwallader terrane in Middle Jurassic time, after which the terranes functioned as a single tectonic block. Contrasting volcanic histories suggest that the Cadwallader terrane was not accreted to the Intermontane superterrane until Middle Jurassic or Early Cretaceous time, although the similar tectonic settings of Stikinia and the Cadwallader terrane allow a common earlier history. The Cadwallader terrane is not part of either the Alexander terrane or Wrangellia, and so the inboard margin of the Insular superterrane must lie west of the Cadwallader terrane.

scholarly journals Potential for Volcanogenic Massive Sulfide Mineralization at the A6 Anomaly, North-West British Columbia, Canada: Stratigraphy, Lithogeochemistry, and Alteration Mineralogy and Chemistry

Minerals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 867
Author(s):  
Stefanie M. Brueckner ◽  
Gregory Johnson ◽  
Stephanie Wafforn ◽  
Harold Gibson ◽  
Ross Sherlock ◽  
...  
Keyword(s):  
British Columbia ◽  
Middle Jurassic ◽  
Isotope Composition ◽  
Massive Sulfide ◽  
Igneous Rocks ◽  
Calc Alkaline ◽  
Volcanogenic Massive Sulfide ◽  
North West ◽  
Group A ◽  
Group B

The Middle Jurassic A6 Anomaly is located 30 km southeast of Eskay Creek, north-central British Columbia and consists of thick, altered felsic igneous rocks overlain by a mafic volcano-sedimentary package. Lithogeochemistry on igneous rocks, x-ray diffraction on altered felsic units, and electron probe microanalysis and secondary ion mass spectrometry on illite and quartz were applied to explore the volcanogenic massive sulfide (VMS) potential, characterize alteration, and determine fluid conditions at the A6 Anomaly. Lithogeochemistry revealed calc-alkaline rhyodacite to trachyte of predominantly FII type, tholeiitic basalts with Nb/Yb < 1.6 (i.e., Group A), and transitional to calc-alkaline basalts and andesites with Nb/Yb > 2.2 (i.e., Group B). The felsic units showed weakly to moderately phyllic alteration (quartz–illite with minor orthoclase and trace chlorite–pyrite–calcite–barite–rutile). Illite ranged in composition from illite/smectite (K = 0.5–0.69 apfu) to almost endmember illite (K = 0.69–0.8 apfu), and formed from feldspar destruction by mildly acidic, relatively low temperature, oxidized hydrothermal fluids. The average δ18O composition was 10.7 ± 3.0‰ and 13.4 ± 1.3‰ relative to Vienna Standard Mean Ocean Water for illite and quartz, respectively. Geothermometry involving illite composition and oxygen isotope composition on illite and quartz yielded average fluid temperatures of predominantly 200–250 °C. Lithogeochemical results showed that the A6 Anomaly occurred in a late-Early to Middle Jurassic evolving back-arc basin, further east then previously recognized and in which transitional to calc-alkaline units formed by crustal assimilation to enriched Mid-Ocean Ridge Basalt (EMORB) (i.e., felsic units, Group B), followed by thinning of the crust resulting in tholeiitic normalized MORB basalts (i.e., Group A) with a minor crustal component. The alteration assemblage is representative of distal footwall alteration, and metal transport in this zone was limited despite favorable temperature, pH, and redox state, indicating a metal depleted source (i.e., felsic units).

Evolution of a Middle Jurassic volcanic arc: stratigraphic, isotopic, and geochemical characteristics of the Harrison Lake Formation, southwestern British Columbia

1995 ◽  
Vol 32 (10) ◽  
pp. 1759-1776 ◽  
Author(s):  
J. Brian Mahoney ◽  
Richard M. Friedman ◽  
Sean D. McKinley
Keyword(s):  
British Columbia ◽  
Middle Jurassic ◽  
Volcanic Rocks ◽  
Explosive Volcanism ◽  
Eastern Coast ◽  
Geochemical Data ◽  
Isotopic Data ◽  
Volcanic Arc ◽  
Fine Grained ◽  
Lake Formation

The Harrison Lake Formation is an Early to Middle Jurassic volcanic-arc assemblage unconformably overlying Triassic oceanic basement in the eastern Coast Belt of southwestern British Columbia. The formation is subdivided into four members including, in ascending order, the Celia Cove Member (conglomerate), the Francis Lake Member (fine-grained strata), the Weaver Lake Member (flows and breccias), and the Echo Island Member (pyroclastic and epiclastic strata). New biostratigraphic constraints pinpoint the initiation of volcanism to late early Toarcian. U–Pb geochronology demonstrates the arc was active until at least late Bajocian–early Bathonian time (166.0 ± 0.4 Ma), and that the timing of arc volcanism strongly overlaps emplacement of both hypabyssal intrusions (Hemlock Valley stock) and deep-seated plutons (Mount Jasper pluton) within and adjacent to the arc. Geochemical data indicate the arc is of medium- to high-K calc-alkaline affinity, and is strongly light rare earth element enriched (LaN/YbN = 1.5 – 2.5). Nd and Sr isotopic data from primary volcanic rocks demonstrate the juvenile nature of the magmatic system, but isotopic data from associated fine-grained sedimentary rocks suggest temporally controlled variations in isotopic composition interpreted to represent two-component mixing between juvenile volcanic detritus and a more evolved detrital component. The succession of facies in the Harrison Lake Formation records initial basin subsidence in the Early Jurassic, initiation of explosive volcanism in the late early Toarcian, a change to effusive volcanism in the early Aalenian, and late-stage explosive volcanism in the late Bajocian. The Harrison Lake Formation contains mesoscopic folds and overturned bedding that are absent in the overlying Callovian Mysterious Creek Formation, strongly suggesting the existence of a regional Bathonian deformational event in the southern Coast Belt.

Late Paleozoic and Mesozoic terrane interactions in north-central British Columbia

1991 ◽  
Vol 28 (6) ◽  
pp. 947-957 ◽  
Author(s):  
Hubert Gabrielse
Keyword(s):  
British Columbia ◽  
North America ◽  
Middle Jurassic ◽  
Subsequent Development ◽  
Structural Data ◽  
Strike Slip ◽  
Granitic Rocks ◽  
Late Triassic ◽  
North Central ◽  
Dextral Strike Slip

Five clearly defined terranes, comprising from northeast to southwest, Ancestral North America, Slide Mountain, Quesnellia, Cache Creek, and Stikinia, are the dominant tectonic elements of north-central British Columbia. Stratigraphic, sedimentological, plutonic, metamorphic, and structural data show that the Slide Mountain Terrane evolved as a subduction, accretion, and island-arc complex during Permian time. Sedimentological data hint at the demise of the Slide Mountain and Cache Creek oceanic environments in the Permian or Early Triassic and Late Triassic, respectively. Subduction led to the development of volcanic–plutonic island arcs on Stikinia, Quesnellia, and locally on the Cache Creek Terrane in Late Triassic to Middle Jurassic time. Marked inter- and intra-terrane contraction in the Middle Jurassic resulted in the south westward thrusting of the Cache Creek Terrane onto Stikinia, the subsequent development of the Bowser Basin on Stikinia, and possible coeval culmination of the emplacement of Quesnellia and the Slide Mountain Terrane onto Ancestral North America. Deformation, metamorphism, and plutonism along the western margin of Ancestral North America closely followed these events. Contraction was succeeded by a dextral strike-slip regime during the mid-Cretaceous accompanied by the intrusion of voluminous potassic, silica-rich granitic rocks in Ancestral North America. The emplacement of Early to mid-Cretaceous plutons postdated the development of broad, open, regional anticlinoria and synclinoria, perhaps during Early Cretaceous time. The plutonic episode coincided approximately with initiation of the Sustut Basin. Dextral strike-slip faulting further disrupted Ancestral North America until post-Eocene time.

scholarly journals ON THE OCCURRENCE OF A VOLCANIC ASH LAYER IN THE XYLOKASTRO AREA, NORTH PELOPONNESUS, GREECE: MINERALOGY AND GEOCHEMISTRY

2017 ◽  
Vol 43 (5) ◽  
pp. 2773 ◽  
Author(s):  
Ch. Vasilatos ◽  
M. Vlachou-Tsipoura ◽  
M.G. Stamatakis
Keyword(s):  
Volcanic Ash ◽  
Crustal Contamination ◽  
Geochemical Characteristics ◽  
Calc Alkaline ◽  
Volcanic Arc ◽  
Lacustrine Deposits ◽  
Ash Layer ◽  
Area North ◽  
Reported Data ◽  
First Time

This paper reports, for the first time, the occurrence of an ash layer intercalated within the Plio-Pleistocene lacustrine deposits near Xylokastro area, North Peloponnesus, Greece. Petrographic and geochemical characteristics of the ash layer are the basis of this study. An attempt was made to correlate the present findings to the reported data from other ash deposits. The composition of the ash bed showed a dacitic to rhyolitic calc alkaline suit. The geochemistry of the volcanic ash indicates high crustal contamination of the lava and points to an origin from the northwest part of the Aegean volcanic arc.

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