Permian and Triassic radiolarian ages from the Cache Creek Complex, Dog Creek and Alkali Lake areas, southwestern British Columbia

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Permian and Triassic radiolarian ages from the Cache Creek Complex, Dog Creek and Alkali Lake areas,

southwestern British Columbia

F. Cordey, Peter Read

To cite this version:

F. Cordey, Peter Read. Permian and Triassic radiolarian ages from the Cache Creek Complex, Dog

Creek and Alkali Lake areas, southwestern British Columbia. Current Research, Part E/Recherches

En Cours, Partie E, Geological Survey of Canada, 1992, pp.41-51. �hal-03274267�

GEOLOGICAL SURVEY OF CANADA COMMISSION GEOLOGIQUE DU CANADA

PAPER/ETUDE 92-1E

CURRENT RESEARCH, PART E RECHERCHES EN COURS, PARTIE E

1992

THE ENERGY OF OUR RESOURCES· THE POWER OF OUR IDEAS

Permian and Triassic radiolarian ages from the Cache Creek Complex, Dog Creek and Alkali Lake

areas, southwestern British Columbia!

Fabrice Cordey and Peter B. Read

Cordilleran Division, Vancouver

Cordey, F. and Read, PB., 1992: Permian and Triassic radiolarian ages from the Cache Creek Complex, Dog Creek and Alkali Lake areas, southwestern British Columbia;

in.

Abstract

Ten radiolarian chert localities from the Cache Creek Complex on both sides of the Fraser Fault in Dog Creek and Alkali Lake areas range in age from Early Permian (late Asselian-late Sakmarian) through Middle Triassic (late Anisian-early Ladinian) to Late Triassic (Early Carnian, Early-Middle Norian, Late Norian). This age range is similar to that of the Cache Creek cherts in their type locality, 150 km to the south. The newly discovered localities come from one or more slices of the complex which were thrust northeastward over Early Jurassic rocks. Chert-bearing units underlie undated clastic rocks that may represent a regional(? ) overlap assemblage.

Resume

Les associations de radiolaires provenant de dix loealites de radiolarites dans Ie complexe de Cache Creek de part et d' autre de la faille Fraser, zones de Dog Creek et d' Alkali Lake, ont un age qui s' etend du Permien precoce (fin de l' Asselien

a

a

a

I Contribution to the Frontier Geoscience Program Chilcotin-Nechako Hydrocarbon Province

2 Geotex Consultants Limited, #1200 - 100 West Pender Street, Vancouver, British Columbia V6B 1 R8

INTRODUCTION

This paper gives the faunal associations, ages and structural setting of major areas of ribbon chelt in the Riske Creek (920/15) and Alkali Lake (920/16) map areas. The results are part of the continuing study of Jurassic and older rocks which underlie the northeast comer of the Taseko Lakes map area (920)(Hickson et ai., 1991; Read, 1992). The discovery of moderately to well preserved radiolaria in the ribbon cherts of this area, which straddles the major dextral strike-slip Fraser Fault, provides critical support for the correlation of the Cache Creek Complex across the fault. Both authors sampled the chert-rich successions of units shown in Figures 1 and 2, but Cordey is responsible for the paleontology and Read, the geological mapping.

West of the fault, Early Permian to Late Triassic grey to green ribbon chert, siliceous phyllite and phyllite of unit PTcctp dated by radiolarians are part of the Cache Creek Complex. South of Ross Gulch (Fig. 2) a light to medium grey, locally bedded limestone (PTccc) up to 140 m thick outlines an isoclinal fold in the upper part of the ribbon chert succession. These rocks structurally overlie unnamed Early Jurassic flows and tuffs (IJv) which range from dacite to andesite and aphanitic to porphyritic. Grey siltstone and poorly bedded dacite lapilli tuffform layers and lenses of unit IJvs and a few medium grey limestone lenses up to 5 m thick of unit IJc are scattered through the volcanics. In the absence of fossils and radiometric dating, the rocks are tentatively correlated with dated Early Jurassic (late Toarcian) rocks 12 km southwest of Ross Gulch (Fig. 1) based on the presence of dacite tuffs and the good preservation of primary textures.

The contact between the Cache Creek Complex and underlying rocks is poorly exposed. At the head of Ross Gulch, knobs of dark grey ribbon chert (tp), grey limestone (c) and greenstone (v) dot the meadows, and in a few creeks outcrops of slickensided black serpentinite (us) form extensive banks.

This area of fault-bounded blocks in a serpentinite matrix exposes the melange unit PTccmx that forms between thrust slices of the complex west of Fraser Fault.

The metadiorite (JKdi) is part of Farwell Pluton, which immediately south of the map area (Fig. 1), intrudes the Early Jurassic volcanics on the west bank of the Fraser River.

Although a mid-Permian zircon age of 258±5 Ma for the pluton (Friedman and van der Heyden, 1992) would require the intruded volcanics to be pre-mid-Permian, a lithologically similar pluton exposed 12 km to the south in Word Creek yields radiometric ages of 135.5±1.6 Ma and 161.1±2.6 Ma from hornblende for integrated 4oAr-³⁹Ar and K-Ar respectively (unpublished data) and would permit intruded wall rocks of Early Jurassic age. On the basis of two radiometric dates, Farwell Pluton may be composite as presently named and include rocks of Permian and Jura-Cretaceous ages.

East of Fraser Fault, the Cache Creek Complex encompasses rocks of mid-Pennsylvanian to Middle(?) Jurassic age (Monger, 1989). In the northeast comer of Taseko Lakes, the massive limestone of the Marble Canyon Formation forms the eastern edge of the area. West of it, and probably structurally higher, lies a tightly folded but upright

succession of marble, grey phyllite, ribbon chert and basic metavolcanic rocks of Permo-Triassic age. Parts of this consist of fault-slivered marble, grey phyllite, ribbon chert, metabasalt flows of unit PTccrnx (Fig. 2). Structurally above this unit is a thick sequence (PTccpw) of poorly bedded grey siltstone, with less shale and lithic greywacke, and no chert (Fig. 1,2). The unit is locally tuffaceous.

RADIOLARIAN ASSOCIATIONS AND AGES

Permian

Early Permian radiolarians were obtained from a disrupted grey radiolarian chert sequence (Ioc. 1, Fig. 1, Table 1).

Although the preservation of the siliceous skeletons is moderate to poor, the association (Table 2) reliably correlates with the Pseudoalbaillella lomentaria Assemblage zone of Japan (Ishiga, 1990) in the interval late Asselian to late Sakmarian (Tables 2, 3).

Middle Triassic

The radiolarian association (Table 2) found at loc. 6 (Fig. 2;

Table 1) is correlative with the Triassocampe deweveri Assemblage zone of Yao (1982), Middle Triassic in age (Tables 2, 3) previously reported in many different part ofthe world, including North America (Cordey, 1986; Blome et aI., 1988), Japan (Yao, 1982; Matsuda and Isozaki, 1982; Kido, 1982), and Europe (Dumitrica et aI., 1980; De Wever, 1979;

Gorican and Buser, 1990). The closest faunal resemblance with our association is obtained from chert of the Mino belt of southwest Japan (Yao et aI., 1982) which includes Triassocampe sp. G. (pI. 1, fig. 16-18), Eptingium sp. cf.

manfredi Dumitrica 1978 sensu Yao 1982 similar to our Eptingium (?) sp. A. (pI. 1, fig. 20). In the present knowledge of Middle Triassic radiolarian faunas in the world, it is premature to assess if this similarity is due to similar paleogeographic distribution factors or if they represent coeval stratigraphic levels. However, our association also contain taxa reported in the Tethyan realm as in the chert/limestone sequence of Zaklanec, Bohinj, and Vojsko, Slovenia (Gorican and Buser, 1990) including Pseudostylosphaera longispinosa (De Wever) 1979 (pI. 1, fig. 7), PS. tenuis (Nakaseko and Nishimura) 1979 (pI. 1, fig. 9), Sepsagon? robustus Lahm 1984 and Silicarmiger sp.

(pI. 1, fig. 12).

Poor radiolarian preservation prevented dating of four chert localities more precisely than Ladinian-Carnian (loc. 2, 3, and 7; Tables 2, 3) and Ladinian-Early Carnian (loc. 8).

Late Triassic

Carnian

Locality 5 (Fig. 2; Table 1) released an Early Carnian radiolarian association (Table 2), including Pseudostylosphaera nazarovi Kozur and Mostler 1979 which occurs also in the Middle Triassic of the Harrison Lake

. .--....

_----

o 5 \0

15' . -

1 . . '

---..&' _____

k

m .

'-£v }

Geological contact {approximate ... ..

{assumed ... ,,- _ _ ...

Geological contact btried beneath Tertiary rocks ••••••• "".",

Thrust fault {approximate •••••••••••••••••• ~

(teeth on upper plate) {assumed ... .4 ",,4 IV

Strike-slip fault ... .

Fault btried beneath Neogene rocks ••••••••••••••••••• . ' "~' ... . Melange consisting of blocks in a serpentinite matrix •••• ~ AxiaJ trace of folds {northeast overturned anticline ••• ~ ⁱ ~

(upright syncline ••••••••••••••• ~

Fossil locality ...

CIY

Radiometric date lOCality ... <D

Eruptive centre ... .. .. .. • .. .. .. .. .. .. • .. • • • .. • • .. • • • Limit of mapping (I 99 I) ... .

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Figure 1. Preliminary geological map of parts of Riske Creek (920/15) and Alkali Lake (920/16) map areas showing radiolarian-bearing ribbon chert localities 1, 2 (west of Fraser Fault) and 3 (east of Fraser Fault), and emplacement of Figure 2.

Juras~ic or Cretaceous

PALEOZOIC AND MESOZOIC Permian to Jurassic

Lower Permian to Middle(?) Jurassic Middle Jurassic or Early Cretaceous

IJKdil Chloriti7.~d and locally foliated

~ meladlOrlte and metagranodlOrlte

metadioritej minor quartz CACHE CREEK COMPLEX (PJccpw 10 Plccm.) IpJ ccpwlGrey siltstone, shale; minor grey lithic wacke

Jurassic I Plicctp IGrey to green ribbon chert, siliceous phyllite and phyllite

lower Jurassic

'IJI

§;]

~ cite ami (plagioclase) andesite flows and tulls

r;T;~ Tectonic(?) lenses of greenstone, limestone and chert in a

~serrentinite (m) or grey phyllite (gp) matrix. The matrix is

IjJ;,I ^Gr~y nuncalcareous siltstone and coarsely bedded dacite lapilii

L~~ _ _ l tulf

~ Medium grey unbedded limestone

hachured and the litholo~y of the blocks is given by c : lime- stone, Ip = grey phyllite and ribbon chert, v : greenstone.

Figure 2. Geological setting of the radiolarian-bearing ribbon chert localities 4-1 0 on both sides of the Fraser Fault south of Ross Gulch.

CENOZOIC

Quaternary and Tertiary Pleistocene

LEGEND Figure 2

CHlLCOTINGROUP (-Pvb to Ms)

~ Grey olivine- and/or plagioc!ase-phyric subaerial basalt flows Tertiary

Pliocene

~ Grey olivine- ao%r plagioclase-phyric subaerial basalt flows ID.Ip Unconsolidated fluviatile sandstone and pebble to boulder conglom-

~erate Miocene

~ Grey olivine- and/or plagioclase-phyric subaerial basalt (Jows r;-;-:---,M Unconsolidated fluviatile sediments; minor rhyolite ash and diatoma-

~ ceous earth

Eocene

~ Conglomerate, sandstonej minor siltstone and bentonitic shalej rare

~coaJ

MESOZOIC Jurassic

Homblende-piagioclase-phyric dacite and homblende-biotite-quartz- phyric rhyolite flows ard tuff; rare basalt

Middle to Upper Jurassic

I mJcgl South of Bald Mountain: Red sparsely pJagiocJase-phyric volcanic conglomerate overlying nonbedded quartz-bearing feldspathic sand- stone

!

I

IJ==I

~ gabbro. Hypabyssal dacite and felsite intrusions occur marginally

~ Olloritized hornblende diorite and quartz diorite Lower Jurassic

IIJ=I_p ~rey noncalcareous siltstone with thin sandstone laminae; minor thin

~ limestone

~ Grey-green and locally maroon porphyritic (plagioclase, quartz) dacite

~ and rhyolite flows and tuffs, felsite- and quartz-feldspar porphyry- bearing tuff; minor green metabasalt flows

Tr lassic

Middle to Upper Tr iassie

~ Grey nonlimy siltstone and minor interbedded thin calcareous sand-

~ stone

~ Nonbedded light to medium grey micritic limestolle PALF.OZOIC

Permian Late Permian

~ FARWELl. PLUTON

~ Chtoritizeci and locally foliated metadioritej I'ninor quartz metadioritc and metagranooiorite

Permian to Jurassic

Lower Permian to Middle(?) JUrassic

~ CACHE CREEK COMPLEX (PJccpw to Pccvbl

~ Western BeLt: Grey siltstone, shale; minor grey lithic wacke

I

I

I PJcctpc] Western Bel.t: Tecto~ic(?) lenses of greenstone, limestone and chert in a grey phyllite matrIx

~PJ Western Belt: Grey phyllite, siliceous phyllite, and grey to green

~ ribbon chert

~ Marble Canyon Formation

~ Grey unbedded micritic limestone Permian to Triassic

~ Green and grey-green aphanitiC basic metatuff and minor flows

I Picctp! Grey, grey-green and minor light green chert, rii)bon chert and phrllite

I

I

Lower Permian and(?) older

[ Pccvb

I

W ....J

o o

~

Ladinian

? - ? - ? Anisian

Top of Section

I I I I I

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(D

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~ §§

~ §§

~ §§

~ ~

~ _~~

~ ~

~ !§§

~ ~

~-==@b IJv?

355m

180 130 'u

u u

0

....

~

Q) C 0

288 -;;;

Q)

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CU VI

0

720 ..D

E 865

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.

Figure 3. A "stratigraphic column" showing the positions of the fossil localities relative to the base of limestone (PTccc) on the right side of the column and to the age of each locality (Table 3) given on the left side of the column. The limestone unit is at present undated.

package (Cordey et aI., 1988). At locality 10, the association is Late Carnian or Early Norian in age; it contains Capnodoce anapetes De Wever 1979 and C apnuchosphaera theloides De Wever 1979, described in the western Tethyan realm but reported also in Japan and North America by numerous workers.

Norian

Early-Middle Norian radiolarians were found at locality 4 (Fig. 2; Tables 1, 2), including taxa of Xipha striata and Latium paucum subzones of Blome (1984).

The first Late Norian cl1m of British Columbia found so far at locality 9 contains Gen. nov. C (in Carter, 1990) previously reported in the Queen Charlotte Islands and possibly in "Rhaetian" strata of eastern fonner-USSR (in Bragin, 1991: "Hagiastrum sp.", broken specimen, pI. 7, fig.

2). Our association is possibly correlative with Assemblage 3 of Carter (1990), the youngest of the Late Norian.

DISCUSSION

Stratigraphic and structural significance

On the west side of Fraser Fault, the ribbon chert sequences range from Early Permian to latest Triassic. Five of the localities (5-9) are in an area south of Ross Gulch (Fig. 2) and come from a 2100 m "thick" sequence of grey-green ribbon chert with a 140 m thick limestone immediately beneath loco 9 (Fig. 2, 3). This steep easterly dipping sequence spans time from the late Anisian or early Ladinian (Ioc. 6) to Late Norian (loc. 9), and based on the distribution of the dated samples, the sequence is upright. The "thickness" of nearly 2100 m for the sequence probably results from intense folding and faulting replicating the section but still retaining its overall original facing. A folded thrust forms the base of the section and sets it over structurally deeper Jurassic(?) rocks.

A 2.5 km wide belt of ribbon chert outcrops along the lower parts of Word and McEwen creeks and locally in the intervening area (Fig. 1). Although several collections from it were extensively recrystallized, localities I and 2 show that the sequence ranges in age from Early Permian to Middle or Late Triassic. The Early Permian locality (1) lies near the western edge of the belt close to the metavolcanic rocks of unit PTvb, and the Ladinian or Carnian locality (2) is near the eastern margin of the belt adjacent to Fraser Fault.

Because these intensely deformed rocks likely dip and face easterly, the metavolcanic rocks west of the belt probably stratigraphically underlie the ribbon chert sequence.

The combined stratigraphy from these two areas west of the Fraser Fault indicates that ribbon chert was the dominant sediment deposited from Early Permian to Late Norian time.

The absence of Late Permian and Early Triassic dates may reflect the degree of recrystallization of the radiolarians and difficulties of sampling rather than the absence of rocks of this in terv al.

West of the Fraser Fault, the Cache Creek Complex and Jurassic rocks form three or more northeasterly directed thrust slices (Fig. 1). Between the Chilcotin River and Bald Mountain, the slices from bottom to top are: (a) Wineglass Slice composed of dated but unnamed Early Jurassic stratified rocks and younger intrusions, all of which may be autochtonous, (b) Farwell Slice containing Farwell Pluton and probably the metavolcanics and dated ribbon cherts of the Cache Creek Complex; (c) Bald Mountain Slice consisting of Middle to Late Triassic limestone of the Cache Creek Complex and unnamed Middle to Late Jurassic sediments; and (d) Thaddeus Slice made of undated volcanics. The ribbon cherts south of Ross Gulch and along McEwen Creek belong either to Farwell Slice or a new unnamed slice. Because the complex west of Fraser Fault is a collage of slices, it provides an explanation as to why the deposition of Permo-Triassic ribbon chert along Ross Gulch and McEwen

Table 1. Radiolarian localities in the study area. 1-10 correspond to localities in Figures 1 and 2

TEXT GSC SAMPLE No.

UTM

LOC. LOC. COLLECTOR

E. N. Lat. Long.

1. C-1n598 FC91-CHIL6 540930 572n50 51°42'02" 1~24'25" Elev. 3340', 3.5 km at 273° light green

F. Cordey from the mouth of McEwen Ck ribbon chert

2. C-177597 FC91-CHIL3 541800 5728250 51°42'20" 122°23'40" Elev. 2900', 2.8 km at 283° light grey

F. Cordey from the mouth of McEwen Ck ribbon chert

3. C-081597 C91-3F 554970 5737800 51°47'25" 1~12'11" Elev. 2650', 1.2 km at 081 ° grey and green

P.B. Read from Patrick & Alkali Ck junct. ribbon chert

4. C-176161 C91-15F 541710 5740860 51 °49'08" 122°23'42" Elev. 1600', 6.65 km at 1n° grey and green

P.B. Read from the mouth of Riske Creek ribbon chert

5. C-081571 C91-34F 539250 5742080 51 °49'48" 122°25'50" Elev. 3075', 5.8 km at 201 ° light green

P.B. Read from the mouth of Riske Creek ribbon chert

6. C-081570 C91-33F 538730 5742350 51 °49'57" 122°26'17" Elev. 3200', 5.75 km at 207° light green

P.B. Read from the mouth of Riske Creek ribbon chert

7. C-081572 C91-35F 538880 5742930 51 °50'16" 122°26'08" Elev. 3375', 5.2 km at 209° light green

P.B. Read from the mouth of Riske Creek ribbon chert

8. C-081574 C91-37F 537700 5743000 51 °50'18" 1~27'10" Elev. 3450', 5.75 km at 219° red to grey-

P.B. Read from the mouth of Riske Creek green r.c.

9. C-081573 C91-36F 539250 5744000 51 °50'50" 1~25'49" Elev. 3425', 4.07 km at 210° light green

P.B. Read from the mouth of Riske Creek ribbon chert

10. C-176164 C91-18F 543170 5745550 51 °51'40" 1~22'40" Elev., 2150', 2.8 km at 135° grey and green

P.B. Read from the mouth of Riske Creek ribbon chert

Table 2. Radiolarian determinations and age assignments

TEXT GSC FAUNA AGE

LOC. LOC.

1.

C-177598 Pseudoalbaillella sakmarensis

1981 Early Permian, Ps. sp. ct. longicornis Ishiga

Imoto 1980 late Asselian to late Ps. sp. ct. scalprata m. sca/prata Holdsworth

Jones 1980 Sakmarian

Ps. sp. ct. sca/prata m. postsca/prata Ishiga

2. C-177597 Pseudosty/osphaera sp. Middle or Late Triassic,

Triassocampe sp. e.Ladinian to L.Carnian

3. C-081597 ?Pseudostylosphaera sp. Triassic,

Oertlispongid-related spines possibly early Ladinian

Conical nassellarian shells to Late Carnian

4. C-176161 Capnodoce extenta Blome 1984 Late Triassic,

Capnuchosphaera de we veri Kozur

Mostler 1979 Early or Middle Norian Corum sp. ct. regium Blome 1984

Lotta sp.

Napora sp. cf. robusta Nakaseko

Nishimura 1979 Palaeosaturnalis vigrassi (Blome) 1984

5. C-081 571 Capnuchosphaera sp. Late Triassic,

Platkerium sp. Early Carnian

Pseudosty/osphaera hellenica (De Wever) 1979 Ps. nazarovi (Kozur

Mostler) 1979

Ps. sp. cf. compacta (Nakaseko

Nishimura) 1979

? Vinassaspongus subsphaericus Kozur

Mostler 1979

6. C-081 570 Plafkerium sp. Middle Triassic,

Pseudostylosphaera longispinosa Kozur

Mostler 1981 late Anisian or early Ps. tenuis (Nakaseko

Nishimura) 1979 Ladinian

Ps. sp. aff. tenuis (Nakaseko

Nishimura) 1979 Ps. sp. A

Sepsagon? robustus Lahm 1984 Silicarmiger sp.

Triassocampe sp. G

Yeharaia sp. aff. elegans Nakaseko

Nishimura 1979

7. C-081 572 ? Eptingium manfredi Dumitrica 1978 Triassic,

Pseudostylosphaera compacta (l\Jakaseko

Nishim.) 1979 Ladinian-Carnian

? Staurodoras variabilis Nakaseko

Nishimura 1979 Triassocampe sp.

8. C-081 574 Eptingium manfredi Dumitrica 1978 Triassic,

Pseudostylosphaera japonica (Nakaseko

Nishim.) 1979 early Ladinian to Early Ps. spinulosa (Nakaseko

Nishimura) 1979 Carnian

9. C-081573 Betraccium sp. Late Triassic,

Cantalum sp. ct.inornatum Blome 1984 Late l\Jorian Podocapsa sp.

Gen. nov. C sp. 1 Carter 1990

10.

C-176164 Canesium len tum Blome 1984 Late Triassic,

Capnodoce anapetes De Wever 1979 Late Carnian or Early

Capnuchosphaera theloides De Wever 1979 Norian

Creek in the Farwell or an unnamed slice is absent from the several hundred metre thick Bald Mountain limestone of Middle to Late Triassic age only 12 km away, in the Bald Mountain

~. Apparently the collage consists of stratigraphic elements which were formerly widely separated.

East of the Fraser Fault, ribbon chert combined with basic metavolcanics, grey phyllite and limestone to form two zones each up to a few hundred metres in thickness. The western of these two zones first appears north of Dog Creek and outcrops sporadically within a few kilometres of the fault trace for 31 km northward to and beyond locality 10 where an eastward dipping ribbon chert yields a Late Carnian or Early Norian radiolarian age. Exposures around the locality show that the rock units are extensively faulted along their boundaries. Here the zone is treated as a melange rather than a stratigraphic succession, but farther south exposures are insufficient to allow an interpretation.

The eastern zone dips gently westerly and crosses Alkali Creek at the Alkali Lake Indian Reservation. The limestones and some of the metavolcanics are lenticular, the ribbon chert

is intensely crumpled, and the phyllite has a good sheen on the foliation. These characteristics contrast to the unfolded, bedded siltstone and shale of the overlying and upward-facing rocks of unit PJccpw which separate the eastern and western ribbon chert zones and fill the core of a northerly trending syncline. Although the Ladinian or Carnian age of the poorly preserved fauna of locality 3 on the eastern limb of the syncline is less precise than the Late Carnian or Early Norian range from locality 10 on the western limb, the ranges allow a correlation of the limbs in a sequence which may have been partly dismembered.

Correlation with other chert-bearing units in the region

The ten new radiolarian ages (Table 3) substantiate earlier correlations of the ribbon chert-greenstone assemblages on the west side of Fraser Fault to the Cache Creek Complex on the east side (Hickson et a!., 1991; Read, 1992). In particular, cherts in the eastern belt of the complex also range from Early Permian (Pseudoalbaillella scalp rata Assemblage zone of

Table 3. Ages of radiolarian associations at localities 1 to 10. Each vertical bar shows the age interval for one radiolarian association in one sample (isotopic ages for stage boundary based on DNAG time scale; Palmer, 1983)

1. 2. 3. 4. 5. 6. 7. 8. 9. 10

208 I

Norian ma LATE

223

Carnian

TRIAS. 228 I

Ladinian

I

MID.

232 I

Anisian

EARLY Scythian 236

Tatarian 245

LATE Kazanian 253

Ufinian

PERM. Kungurian 262

Artinskian 267

EARLY

275

Sakmarian Asselian

286

Ishiga, 1990) near Carquile (Cordey, 1986) to the Late Triassic (Orchard, 1984; Cordey, 1986, Capnodoce Zone of Blome, 1984, in the matrix of the melange zone). Although Late Norian is absent in the type locality, it does occur in the Northern Cache Creek Complex in southern Yukon (Cordey et aI., 1991). In contrast to the Cache Creek Complex, the Bridge River Complex contains not only Permian and Triassic, but also Mississippian, Early Jurassic, lower Middle and late Middle Jurassic radiolarian cherts (Cordey and Schiarizza, in prep.). The apparent sparsity of Jurassic rocks in the study area may result from a lack of Jurassic ribbon cherts, not a lack of Jurassic rocks. For example, in the Cache Creek Complex east of Fraser Fault and near Alkali Lake, the structurally highest rocks within the map area are grey shale-siltstone-greywacke turbidites of unit PJccpw, which are devoid of chert, undated, upward-facing, and probably younger than the radiolarian chert dated Ladinian or Carnian (loc. 3) to Late Carnian or Early Norian (Ioc. 10) that they overlie. These rocks could be correlative with the Early or Middle Jurassic radiolarian-bearing clastic rocks from the western belt of the Cache Creek Complex near Kelly Lake (Cordey et aI., 1987). East of Alkali Lake, the abrupt upward passage from a grey siliceous phyllite and ribbon chert sequence containing lenses (tectonic ?) of limestone and greenstone into a thick succession of grey slate and siltstone with no chert across a few hundred metre wide gap in outcrop parallels the transition described by Journeay and Northcote (1992) from the eastern Bridge River Complex into the overlying but undated grey turbidites of the Cayoosh Assemblage. If the dating of unit PJccpw and the Cayoosh Assemblage were to substantiate such a correlation, it could suggest that they fonn a regional overlap assemblage across the eastern Bridge River and the Cache Creek complexes.

ACKNOWLEDGMENTS

Funding by the Geological Survey of Canada project 810028, a post-doctoral fellowship administrated by the National Sciences and Engineering Research Council of Canada to Cordey, and C.J. Hickson's financial support through the Chilcotin-Nechako Hydrocarbon Province Project under contract #232S4-1-01-0146/01-XSB to Read pennitted the unravelling of a small area of the Cache Creek Complex along lines that may be more widely applicable. We are grateful to Susan Cannon and Hillary Tay~r~o picked a large part of the samples residues. Special thanks to Steve Irwin, Peter Krauss, Jim Monger and Mike Orchard for their support for radiolarian dating. Bev Vanlier and Jim Monger edited and improved the manuscript.

REFERENCES

Blome,C.D.

1984: Upper Triassic Radiolaria and radiolarian zonation from western North America; Bulletin of American Paleontology, v. 85, n' 318, 88 p.

Blome, C.D., Reed, K.M., and Tailleur, I.L.

1988: Radiolarian biostratigraphy of the Otuk Formation in and near the national petroleum reserve in Alaska; United States Geological Survey, Professional Paper 1399, p. 725-774.

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1991: Radiolaria and Lower Mesozoic units of the USSR east regions;

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Geological Survey of Canada Project 810028

Plate 1

Scanning electron micrographs of Permian (fig. 1-4) and Triassic (fig. 5-22) radiolarians from the Cache Creek Complex, Dog Creek and Alkali Lake map area, southwestern British Columbia. The following are indicated for each figure: identification, locality (cf. text-Fig. 1,2), GSC locality no., field sample no., GSC specimen no., and magnification.

fig. l. Pseudoalbaillella sakmarensis (Kozur) 1981, Loc. I, GSC C-I77598, FC91-CHIL6, GSC 101453, x 170.

fig. 2. Pseudoalbaillella sp., Loc. I, GSC C-I77598, FC91- CIDL6, GSC 101454, x 170.

fig. 3. Ps. sp. cf. scalprata m. postscalprata Ishiga 1983, Loc. I, GSC C-I77598, FC91-CIDL6, GSC 101455, x 130.

fig. 4. Ps. sp. cf. longicornis Ishiga & Imoto 1980, Loc. 1, GSC C-I77598, FC91-CHIL6, GSC 101456, x 250.

fig. 5, 6. Pseudostylosphaera sp. A, Loc. 6, GSC C-081570, C91-33F, 5: GSC 101457, x 130,6: GSC 101458, x 130.

fig. 7. Pseudostylosphaera longispinosa Kozur & MostIer 1981, Loc. 6, GSC C-081570, C91-33F, GSC 101459, x 110.

fig. 8. Ps. sp. aff. tenuis (Nakaseko & Nishimura) 1979, Loc. 6, GSC C-081570, C91-33F, GSC 101460, x 105. fig. 9. Ps. tenuis (Nakaseko & Nishimura) 1979, Loc. 6, GSC

C-081570, C91-33F, GSC 101461, x 115.

fig. 10. Ps. nazarovi (Kozur & Mostler) 1979, Loc. 5, GSC C-081571, C91-34F, GSC 101462, x 110.

fig. 11. Plafkerium sp. , Loc. 6., GSC C-081570, C91-33F, GSC 101463, x 130.

fig. 12. Silicarmiger sp., Loc. 6., GSC C-081570, C91-33F, GSC 10 1464, x 190.

fig. 13. Yeharaia sp. aff. elegans Nakaseko & Nishimura 1979, Loc. 6., GSC C-081570, C91-33F, GSC 101465, x 215.

fig. 14. Yeharaia sp., Loc. 6, GSC C-081570, C91-33F, GSC 101466, x 200.

fig. 15. Triassocampe sp., Loc. 6, GSC C-081570, C91-33F, GSC 101467, x 200.

fig. 16,17,18: Triassocampe sp. G, Loc. 6, GSC C-081570, C91-33F, 16: GSC 101468, x 200. 17: GSC 101469, x 200, 18: x 500 (enlargement of fig. 17 outlining shape of cephalo-thorax).

fig. 19. gen. sp. indet, Loc. 6, GSC C-081570, C91-33F, GSC 101470, x 170.

fig. 20. Eptingium (?) sp. A, Loc. 6, GSC C-081570, C91-33F, GSC 101471, x 150.

fig. 2l. Capnodoce extenta Blome 1984, Loc. 4, GSC C-17616I, C91-15F, GSC 101472, x 140.

fig. 22. Palaeosaturnalis vigrassi (Blome) 1984 , Loc. 4, GSC C-176161, C91-15F, GSC 101473, x 150.