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.

Stratigraphy and tectonic setting of the upper part of the Cadwallader terrane, southwestern British Columbia

1990 ◽  
Vol 27 (5) ◽  
pp. 702-711 ◽  
Author(s):  
Paul J. Umhoefer
Keyword(s):  
British Columbia ◽  
Middle Jurassic ◽  
Tectonic Setting ◽  
Source Region ◽  
Upper Triassic ◽  
Magmatic Arc ◽  
Clastic Rocks ◽  
Coast Plutonic Complex ◽  
A Minor ◽  
Depositional Setting

The Upper Triassic to Middle Jurassic Cadwallader terrane lies on the northeastern edge of the Coast Plutonic Complex in southwestern British Columbia. Previous work on the Cadwallader Group, the basal unit of the terrane, suggested it was an Upper Triassic (Carnian to middle Norian) volcanic arc and related clastic rocks. Volcanism ceased in early Norian time. A detailed study of the upper part of the Cadwallader terrane (Tyaughton Group and overlying Last Creek formation) shows that it is a sedimentary sequence deposited on the fringe of the inactive Cadwallader magmatic arc. The Upper Triassic (middle to upper Norian) Tyaughton Group consists of nonmarine to shallow-marine clastic rocks and limestones that show sudden changes in depositional setting. The Lower to Middle Jurassic Last Creek formation, a transgressive sequence of clastic rocks, disconformably overlies the Tyaughton Group. The clastic rocks in the two units were derived from a mixed volcanic and plutonic source region that also included a minor metamorphic component and local lower Norian limestones. The stratigraphy of the upper part of the Cadwallader terrane records long-term thermal subsidence of the basin caused by cooling of the magmatic arc after volcanism ceased in the early Norian. The detailed stratigraphy of the upper Cadwallader terrane supports correlation of the Cadwallader with the Stikine terrane, along which it is currently structurally juxtaposed.

The southern Coast Mountains, British Columbia: New interpretations from geological, seismic reflection, and gravity data

2013 ◽  
Vol 50 (10) ◽  
pp. 1033-1050 ◽  
Author(s):  
Amanda M.M. Bustin ◽  
Ron M. Clowes ◽  
James W.H. Monger ◽  
J. Murray Journeay
Keyword(s):  
British Columbia ◽  
Early Cretaceous ◽  
Middle Jurassic ◽  
Gravity Data ◽  
Normal Faults ◽  
Southern Coast ◽  
Seismic Profiles ◽  
Coast Mountains ◽  
Clastic Rocks ◽  
Coast Plutonic Complex

The southern Coast Mountains of British Columbia are characterized by voluminous plutonic and gneissic rocks of mainly Middle Jurassic to Eocene age (the Coast Plutonic Complex), as well as metamorphic rocks, folds, and thrust and reverse faults that mostly diverge eastward and westward from an axis within the present mountains, and by more localized Eocene and younger normal faults. In the southeastern Coast Mountains, mid-Cretaceous and younger plutons intrude Bridge River, Cadwallader, and Methow terranes and overlap Middle Jurassic through Early Cretaceous marine clastic rocks of the Tyaughton–Methow basin. The combination of geological data with new or reanalyzed geophysical data originating from Lithoprobe and related studies enables revised structural interpretations to be made to 20 km depth. Five seismic profiles show very cut-up and chaotic reflectivity that probably represents slices and segments of different deformed and rearranged rock assemblages. Surface geology, seismic interpretations, physical properties, and gravity data are combined in two profiles across the Coast Mountains to generate two new 2-D density models that are interpreted in terms of the geological units. The western part of the southern Coast Mountains consists primarily of Jurassic to mid-Cretaceous plutons to depths of 20 km with slices of Wrangellia (in the west) and Early Cretaceous volcanic and sedimentary rocks (Gambier group) in the upper 10 km. The eastern part, east of the Owl Creek fault, consists of slices of Cadwallader and Bridge River terranes and Tyaughton–Methow basin strata with limited slices of plutonic rocks at depths less than 10 km. Below that, Eocene and Late Cretaceous plutons dominate for another 10 km.

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.

Relay Mountain Group, Tyaughton–Methow basin, southwest British Columbia: a major Middle Jurassic to Early Cretaceous terrane overlap assemblage

2002 ◽  
Vol 39 (7) ◽  
pp. 1143-1167 ◽  
Author(s):  
Paul J Umhoefer ◽  
Paul Schiarizza ◽  
Matt Robinson
Keyword(s):  
British Columbia ◽  
Lower Cretaceous ◽  
Middle Jurassic ◽  
The West ◽  
Shallow Marine ◽  
Clastic Rocks ◽  
Marine Facies ◽  
Oblique Convergent ◽  
Back Arc ◽  
Middle Unit

The upper Middle Jurassic to Lower Cretaceous Relay Mountain Group is the lower part of the northern Tyaughton–Methow basin, southwestern British Columbia. The Relay Mountain Group consists of ~2700–3400 m of clastic rocks that we subdivide into three formal formations. The Callovian and lower Oxfordian Tyoax Pass Formation is marine shale and sandstone turbidites. The Teepee Mountain Formation consists of upper Oxfordian to Valanginian shallow marine clastic rocks with common Buchia and fluvial and marginal marine facies in the upper part of the unit in the northwest. These rocks overlie the lower formation across an abrupt conformable to disconformable contact. The Hauterivian (and Barremian?) Potato Range Formation consists of clastic rocks that are marine in the southeast, mainly nonmarine to the northwest, and derived from the west. This unit displays an abrupt conformable to disconformable contact with the middle formation and locally rests above the lower formation across an angular unconformity. The Relay Mountain Group and correlative strata of the southeastern Coast Belt form an overlap assemblage above the Bridge River and Cadwallader (including Methow) terranes and link them by late Middle Jurassic time. The early Relay Mountain Group appears to have been a fore-arc basin, possibly along an oblique–convergent margin in the middle unit. The upper unit indicates major changes to a back-arc basin linked to the Ottarasko, and possibly Gambier, arc to the west. This is the oldest probable link (~130 Ma) between the southeastern and southwestern Coast belts.

A remarkable small ichthyosaur from the Upper Triassic of British Columbia, representing a new genus and species

1995 ◽  
Vol 32 (3) ◽  
pp. 292-303 ◽  
Author(s):  
C. McGowan
Keyword(s):  
British Columbia ◽  
New Genus ◽  
Middle Triassic ◽  
Lower Jurassic ◽  
Upper Triassic ◽  
New Taxon ◽  
New Genus And Species

A small, nearly complete ichthyosaur skeleton is described from the Upper Triassic of Williston Lake, in northeastern British Columbia. The age of the material, based on conodonts, is early Norian. Although the length of the entire skeleton would probably not have exceeded 1 m, there is no evidence of immaturity–quite the contrary. Named Hudsonelpidia brevirostris, the new taxon shares some features with Triassic taxa, as exemplified by Mixosaurus from the European Middle Triassic, and with post-Triassic ichthyosaurs like Ichthyosaurus, from the English Lower Jurassic. Mixosaurian characters include an elongate tibia with emarginated pre- and postaxial margins, and phalanges in the hindfin with pre- and postaxial notches. Like Ichthyosaurus, the humérus is elongate rather than broad, so too is the pubis and ischium. Mixosaurus is unusual among Triassic ichthyosaurs for having a relatively large orbit, but the orbit is even more prominent in Hudsonelpidia, probably because of the shortness of the snout. Hudsonelpidia has an unusually large femur that approaches the length of the humérus, dwarfing the rest of the hindfin. The rostrum is unique in being perforated by foramina, but this could possibly be an abnormality.

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.

Paleomagnetism of the Triassic Guichon Batholith and Rotation in the Interior Plateau, British Columbia

1971 ◽  
Vol 8 (11) ◽  
pp. 1388-1396 ◽  
Author(s):  
D. T. A. Symons
Keyword(s):  
British Columbia ◽  
Pole Position ◽  
Upper Triassic ◽  
Late Triassic ◽  
Ratio Analysis ◽  
Tectonic Block ◽  
Clockwise Rotation ◽  
The North ◽  
South Central ◽  
Intrusive Rocks

The Guichon Batholith, located near the south end of the Interior Plateau in south–central British Columbia, is composed of unmetamorphosed massive felsic intrusive rocks in several distinct phases (Northcote 1969). Stratigraphic and radiometric evidence indicate that the batholith was emplaced during the Late Triassic (198 ± 8 m.y.) and unroofed by Early Jurassic. Analysis of the remanence of 92 cores (184 specimens) from 19 representative sites led to the isolation of a stable primary remanent magnetism at 15 sites after alternating-field demagnetization. Variance ratio analysis of the remanence directions indicates that the phases cannot be distinguished by the paleomagnetic method. This supports the evidence from contact relationships and K–Ar isotopic dating of biotites that the phases cooled nearly contemporaneously. The pole position determined for the Guichon Batholith (12.9° E, 65.6° N) is discordant with other Upper Triassic pole positions determined for North American formations. The discordance may be explained by a clockwise rotation 40° ± 10° of the batholith and surrounding rocks in the southern end of the Interior Plateau, with most of the Plateau to the north acting as a stable non-rotated tectonic block. Other evidence is cited which is consistent with this hypothesis.

scholarly journals The Mesozoic megafossil genus Linguifolium Arber 1917

2015 ◽  
Vol 55 (2) ◽  
pp. 123-147 ◽  
Author(s):  
Gary A. Pattemore ◽  
John F. Rigby ◽  
Geoffrey Playford
Keyword(s):  
South Africa ◽  
Middle Jurassic ◽  
Leaf Morphology ◽  
Middle Triassic ◽  
Upper Triassic ◽  
Late Triassic ◽  
New Material ◽  
Stratigraphic Ranges ◽  
First Time

Abstract The plant megafossil genus Linguifolium Arber 1917 is chiefly known from the Middle and Upper Triassic of Gondwana. The range of Linguifolium extended beyond Gondwana by the Late Triassic, persisting there through the earliest Jurassic (Hettangian). The parent plants probably grew in a well-watered, canopied environment. Diagnoses of the genus and four of its species - Linguifolium tenison-woodsii (Shirley 1898) Retallack 1980, L. waitakiense Bell in Bell et al. 1956, L. parvum Holmes & Anderson in Holmes et al. 2010, and L. steinmannii (Solms-Laubach 1899) Arber 1917 - are emended with particular reference to venation and leaf morphology; consequently, the stratigraphic ranges of the species have been more precisely defined. Coalescent venation has previously been reported in some species of Linguifolium and is identified in new material described herein. Although the vast majority of specimens assigned to the genus are from the Upper Triassic, none shows coalescent venation. This character is entirely restricted to the Middle Triassic, in particular to two species: L. waitakiense and L. parvum. Linguifolium tenison-woodsii is restricted to the Carnian-lowermost Norian of Australia and South Africa and is recorded here for the first time from the Tarong Basin (upper Carnian), Queensland. Confusion regarding assignment of specimens to this species from the Middle Jurassic of Queensland is resolved.

Sign in / Sign up

Export Citation Format

Share Document