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Systematics and Biostratigraphy o f Lower Cambrian Trilobites o f W estern Laurentia
by
Lisa Lynn Bohach B.Sc. U niversity o f Alberta, 1991
A Dissertation Subm itted in Partial Fulfillm ent o f the Requirem ents for the D egree o f
DOCTOR OF PHILOSOPHY
in the School o f Earth and O cean Sciences
We accept this dissertation as con form ing to the required standard
Dr. R. Ludvigsen, Supervisor (School o f Earth and O cean Sciences)
Dr. C.Rv BarnesTDepartmental M ember (School o f Earth an d O cean Sciences)
Dr. E. Van der Flier-Keller, Departmental M ember (School o f Earth and O cean S ciences)
Dr. V ifJu'nnicliffe, O u 6 d e Member j^Depa rtmen t of Biology)
Dr. A.R. Palmer, External Éxaminer (Institute for Cambrian Studies)
© Lisa Lynn Bohach, 1997 U niversity of Victoria
All rights reserved. This dissertation m ay not be reproduced in w h o le or in part, by p hotocop yin g or other m eans, w ith ou t the p erm ission o f the au th or.
S u p er v iso r Dr. Rolf Ludvigsen
Abstract
M edial L ow er Cambrian strata from continental sh elf deposits o f w estern Laurentia yield abundant, lo w diversity trilobite faunas. N ew faunas from the Cranbrook and Eager form ations (southeastern British Columbia) and the upper C am pito, Poleta, H arkless and S alin e Valley form ations (southw estern Great Basin, California and Nevada) have yielded: 33 sp ecies o f O lenellina (20 new); 2 n ew sp ecies o f Edelsteinaspidae (Redlichiina); 13 species o f
C orynexochida (5 new); 4 sp ecies o f Ptychopariina (1 new); 1 new species of Eodiscina; 1 species o f O ryctocephalidae; 1 n ew species o f Protypidae; and 1 possible species o f
C heiruroideidae. One new gen u s, Wannerelliis, is established and tentatively a ssign ed to the W anneriidae.
System atic stu d ies em phasize the importance o f early ontogenetic features and ventral m orp h ology in determ ining supraspecific relationships. Major changes are m ade to the suprageneric classification o f the Olenelloidea: the W anneriidae is recognized as a fam ily separate from the Olenellidae; the Laudoniinae and Cabriellinae are abandoned an d their type genera a ssig n ed to the W anneriidae; the M esonacinae is characterized as a peram orphic subfam ily o f the Olenellidae; and the Bristoliinae is synonym ized with the Biceratopsinae (O lenellidae). The Corynexochidae is also changed in membership to include the D orypygin ae (= O g yg op sid ae). Heterochrony is a major pattern o f evolutionary change in Lower Cambrian trilobites.
Biostratigraphic division of the medial lower Cambrian comprises 10 n ew su b zon es o f 4 zon es and is the first species-based trilobite zonation for Laurentia. It replaces previous gen u s-b ased zon ation s that are imprecise and questionable in recognition. In ascending order, the zonation includes: the Nevadia weeksi and Nevadia palmeri su b zon es of the Nevadia Zone; the Nevadella parvoconica an d Nevadella eiicharis subzones of the Nevadella Zone; the Elliptocephala stewarti, Gabriellus poletensis and Wannerellus alcatrazensis su b zon es of the Elliptocephala Zone; and the Wanneria logani, Wanneria dunnae and Proliostracus buelnaensis subzones o f the Olenelliis transitans Z one. T h ese zo n es and subzones can be correlated w ith other successions in w estern and eastern Laurentia.
Biofacies differentiation of restricted shelf d eposits is poorly developed in the Nevadella though Elliptocephala Z ones. For this interval, the Nevadella and Wanneriid biofacies are su ccessiv e
biofacies o f restricted sh elf deposits and the Labradoria and Ekwipagetia biofacies are successive biofacies o f open sh elf deposits. Biofacies differentiation is w ell d ev elo p ed in the Olenelliis transitans Zone, w ith an Olenelliis Biofacies in elastics; a W anneriid Biofacies in silty and oolitic carbonates; a Bonnia Biofacies in pure carbonates; and an Ogygopsis Biofacies in op en shelf d ep osits.
Examiners:
Dr. R. Ludvigsen, Supervisor (School o f Earth and O cean Sciences)
Dr. C.R.^BapaÊSrDëpartmental Member (School o f Earth and O cean Sciences)
Dr. E. Van der Flier-Keller, Departmental M ember (School o f Earth and Ocean Sciences)
Dr. V.J. T unnidiffe, O utsid|é^î^m ber (D epartm ent o f Biology)
IV
Table of Contents
A b stract... ii
Table o f C o n te n ts ... iv
List o f T a b l e s ... xi
List o f T e x t-fig u r e s ... xiii
A c k n o w le d g m e n ts ... xvii
D ed ica tio n ...xviii
C hapter 1. I n tr o d u c tio n ... 1
Chapter 2. C et)l o g y ... 5
The C am brian S y s t e m ...5
Base o f the C am brian... 7
The Lower - M id dle Cambrian B o u n d a ry ... 8
Regional Tectonic and D epositional S e ttin g ... 9
Proterozoic P r e lu d e ...9
L ow er Cambrian D eposition and Tectonic Setting... U) G eo lo g y and Historical Paleontolog) of the Study A r e a s... 11
S outheastern British C olu m b ia... 11
Cranbrook F orm ation ... 11
Eager F orm ation ... 15
S outhw estern Great B a sin ... 17
W ym an through Cam pito form ations...19
Poleta F o rm atio n ...21
H arkless Form ation... 22
Saline V alley F orm ation ...22
Post-Saline V alley Form ations...23
C hapter 3. L ow er Cam brian B iostratigraphy... 25
H istorical CK'erview...26
Zonal Biostratigraphy... 44
Chapter 4. Trilobite T erm in ology... 55
General Features...55 C e p h a lo n ... 55 Thorax... 59 P y g id iu m ... 61 Ventral M o r p h o lo g y ... 61 O n to g en y ... 63
Chapter 5. Systematic P h ilo so p h y ... 65
Ventral M o r p h o lo g y ... 67
O n to g en y ... 69
H ete ro ch ro n y ... 72
H eterochrony in Lower Cambrian T rilob ites... 73
Cladistic A n a ly sis...80
R e su lts ... 83
Chapter 6. System atics...88
C lass Trilobita Walch, 1771 ... 88
O rder Redlichiida Richter, 1933 ...88
Suborder O lenellina Walcott, 1890 ...88
Superfamily Fallotaspidoidea Hupe, 1953a... 95
Family Archaeaspididae Repina, 1979... 96
G en us Brad]/fallotaspis Fritz, 1972... 97
Bradyfallotaspis repim e n. sp... 98
Family N evad iid ae H upé, 1953a... 101
G en u s Nevadia Walcott, 1910b... 104
Nevadia weeksi Walcott, 1910b... 105
Nevadia palmeri n. sp ... 107
G en us Nevadella Raw, 1936 ... 109
Nevadella eucharis (Walcott, 1913)... I l l Nevadella parvoconica (Fritz, 1 9 9 2 )... 112
Nrvadella gracile (Walcott, 1910b)... 116
G en us Cirquella Fritz, 1993...118
Superfam ily O len elloid ea Walcott, 189Üa...12Ü
Family H olm iidae Hupé, 1953a...120
G enus Esmeraldina Resserand Howell, 1938... 121
Esm eraldim arpenta (Walcott, 1910b)...124
Family W anneriidae Hupé, 1953a... 126
G enus Wanneria Walcott, 1910b... 128
Wanneria walcottana (Wanner, 1901)...131
Wanneria logani (Walcott, 1910b)... 135
Wanneria dunnae n. sp... 138
Wanneria zvatsonensis n. sp ... 141
G enus Elliptocephala Emmons, 1844... 142
Elliptocej.ihala asaphoides Emmons, 1844...145
Elliptoce].!liala parentalis n. sp ...148
Elliptoceidiala nelsoni n. sp ...151
Elliptocephala stcivarti n. sp ...152
Elliptocqduila trueitiani? (Walcott, 1913)... 154
G enus Luidonia Harrinj^ton, 19 5 6 ... 156
Laudonm prima (Lochman, 1952)... 158
Luidonia harringtoiu n. sp ... 160
G enus M/()«;tws7)/s Fritz, 1992... 163
Mtintmaeipià albersi n. sp ... 164
G enus Cabriellits Fritz, 1992... 165
Cahriellii> poleten^L n. sp ...167
Cabriellus sp. 1 ... 169
G enus Mesolenellus Palmer and Repina, 1993... 169
Mesolenellus guthi n. sp...170
Mesolenelltts moorei n. sp ... 173
G enus Wannerellus n. gen ... 175
Wannerellus alcatrazensis n. gen., n. sp ... 176
Family O len ellid ae Walcott, 1890b... 177
Subfam ily O lenellinae Walcott, 1890...179
G enus Olenelliis Hall, 1861... 180
Olenelliis thompsoni (Hall, 1859)... 188
Olenelliis cf. thompsoni... 192
Olenelliis transitans (Walcott, 1910b)...192
v i i
Olenelliis ricei n. s p ...199
C e n u s Bolbolenellus Pal.ner and Repina, 1993... 233
Subfam ily Biceratopsinae Pack and Gayle, 1971 ... 2Ü4 G en us Peachella W alcott, 1910b...205
G enus Ne^ihrolenellits Palmer and Repina, 1 99 3... 206
G enus Bristolia Harrington, 1956...206
Subfam ily M esonacinae Walcott, 1890...208
G enus Mesonacis Walcott, 1885...209
Mesonacis eagerensis (Best, 1952)... 211
Mesonacis graingerensis n. sp ...213
Mesonacis? Schofieldi (Best, 1952)... 215
aff. Mesonacis leechi n. sp ... 217
G enus Olenelloides Peach, 1894...218
G enus Fremontella Harrington, 1956... 220
Freinontella halli (Walcott, 1910b)...223
Fremontella canipbcllae n. sp ...225
Fremontella aslitoni n. sp ...226
Suborder Redlichiina Harrington in Mix;re, 1959... 228
Superfam ilv Paradoxidacea H aw le and Corda, 1847...228
Fam ily Edelsteinaspidae H upé, 1953b...228
G enus Polliaxis Palmer, 1968...229
Polliaxis miiralensis n. sp ... 230
Polliaxis sp. 1 ... 231
G enus Labradoria Resser, 1936...231
Libradoria lochmanae n. sp ... 233
Order C orynexochida Kobayashi, 1935 ... 235
Fam ily D olichom etopidae Walcott, 1916b...240
G enus Wenkcliemnia Rasetti, 1951... 243
Wenkchemnia? sp. 1 ... 245
Fam ily C orynexochidae Angelin, 1854 ... 245
Subfam ily Corynexochinae Angelin, 1854 ... 247
G enus Bonnaspis Resser, 1936...248
Bonnaspis fieldensis (Walcott, 1916b)... 251
Subfam ily Dor\'pyginae Kobayashi, 1935...254
G enus Bonnia Walcott, 1916b... 257
Bonnia laterispina Fritz, 1972 ... 265 Bonnm fritzi n. sp ... 268 Bonnia grandis n. sp ... 270 Bonnia ornata n. sp ... 274 Bonnia drysdalea n. sp ...276 Bonnui payinasterensis n. sp ...279 Bonnia sp. 1...281
G enus Ogi/i^ops/s Walcott, 1889... 282
Ogygopsis batis (Walcott, 1916b)... 285
Ogygopsis tifincalis (Resser, 1939)...287
Ogygopsis inarcoui (Whitfield, 1884)... 289
?Order Corynexochida Kobayashi, 1935... 292
Family Zacanthoididae Swinnerton, 1915...292
G enus Zacanthopsis Resser, 1938 ... 294
Zacantliopsis contractus Palmer, 1 9 6 4 ... 295
Order Pt\'chopariida Swinnerton, 1915... 296
Suborder Pt\'chopariina Richter, 1933... 297
Superfam ily Ptychopariacea Matthew, 1887 ... 297
Family Ptychopariidae M attliew, 1887 ... 297
G enus Proliostracus Poulsen, 1932... 300
Proliostracus I'lu’lnacnsis (Lochman, 1952)... 305
Proliostracus sp. 1 ... 307
Proliostracus sp. 2 ... 308
Family U n a ssign etl... 309
G enus Gdascne Palmer, 1968 ... 309
Gdasenc aureum n. sp ...310
Suborder Eodiscina Kobayashi, 1939 ...311
Family Eodiscidae Raym ond, 1913 (em end. Jell, 197 5)... 311
G enus Elavipagetia Fritz, 1973... 312
Ekiuipagetia rasettii n. sp ... 313
Order U n assign ed ...315
Family O ryctocephalidae Beecher, 1 8 9 7 ...315
Subfam ily O ryctocephalinae Beecher, 1897... 316
G enus Lancastria Kobayashi, 1935 ... 316
Lancastria roddyi (Walcott, 1912a)...317
G enus Cheiniroides Kobayashi, 1935... 319
Cheiruroiiies? sp. 1 ...319
Family Prot\'pidae... 32U G enus Protypus W alcott, IS.S6...32U Protxjinis injhitiis n. sp ... 322
Chapter 7. C on clu sion s...323
Literature C ited ... 325
A p p en dix A. Localit\' Information and Collection D a ta ... 347
Part 1 Measured Stratigraphie S ectio n s...348
British C olu m b ia...348
MG3 - M ount Grainger M easured S ectio n ...348
MGl - M ount W atson Measured Section 1...352
MG2 - M ount W atson Measured Section 11... 355
RC4 - Ram Creek Measured S e c tio n ... 359
Great Basin - N evada and California... 363
Esmeralda C ounty, N ev a d a ... 363
PC - Pavm aster Canyon Measured S ectio n ... 363
GF - C old field Measured S ectio n ... 367
GP - Gold Point Measured S e c tio n ...372
Northern Inyo Count}', C alifornia... 378
CF - Cedar Flat Measured S ectio n ...378
NH - N ecklace Flill Measured S e c t io n ... 383
WM - W aucoba Mountain M easured S ection ... 387
Part 11 Localities w ithout M easured S e c tio n s... 390
British C olu m b ia...390
1. Mt. Kerkeslin Local it}' (CSC locality 57672)... 390
2. Grainger Range Local it}' (CSC locality 23916)...390
3. H ughes R ange Locality (CSC locality 23851)...391
4. St. Eugene M ission Localit}'... 391
5. Cranbrook Rifle Range L o cality...391
6. M arysville L ocality...392
7. H ellroaring Creek L ocality... 392
E>rrw?raida C ou n ty, N e v a d a ...393
.S. Miller M ountain Locality (LACMIP locality 24411)... 393
9. VVeepah Hills Locality (LACMIP locality 2bH77)...393
U). Goat Island Lixzality... 394
11. Alcatraz Island Locality # l (LACMIP locality 2 6 8 7 2 )...394
12. Alcatraz Island Localit}' #2 (LACMIP locality 26873)... 395
13. Alcatraz Island Locality #3 (LACMIP locality 26 8 6 8 )...395
14. C oyote Road Localit}' (LACMIP locality 27 29 7)...395
15. M oniozum a Ridge Locality (LACMIP localit\' 2677U)...396
16. M ontezum a Peak H orizon 1 ... 396
17. M ontezum a Peak H orizon 2 ... 396
18. C old field Localit}'... 397
19. M agruder M ountain Locality (LACMIP locality' 26854)... 397
20. Mt. D u n fee Locality (LACMIP locality 26 142 )...397
Northern Invo Count}', C aliforn ia... 398
21. Payson Canyon Locality (LACMIP locality 2 6 7 8 6 )... 398
22. Cedar Flat G ully L ocality... 398
23. Deep S p iin g Lake Localities (L,4CM1P localities 26S55, 26858)...399
24. W aucoba Wash Lixzalit}' 1 (LACMIP localit}' 2 6 8 3 3 )... 399
25. W aucoba Wash Localit}' 2 (LACMIP locality 2 6 8 3 4 )... 399
2h. W aucoba Wash Localit}- 3 (L.AC.MIP localit\ 2 6 7 8 4 )...400
27 W aucoba Wash Locality 4 (LACMIP locality 2 6 S 3 8 )... 400
28. W aucoba Wash Lixzalit}' 5 (LACMIP locality 2 6 8 7 8 )...400
29. W aucoba Wash 6 (LACMIP locality 26896)...4(X) A ppendix B C ladistic Data... 402
Characters for cladistic an alysis of the W anneriidae and O len ellid a e... 402
Taxa and Material used in C ladistic A n a ly s is ...407
List of Tables
Table 1. Zonal biostratigraphy o f the Lower Cambrian after W alcott (1910b)... 27
Table 2. Zonal biostratigraphy of the Lower Cambrian after Resser (1938) and H ow ell
et al. (1944)... 28
Table 3. Zonal biostratigraphic sch em e developed by Rasetti ( 1966, 1967) for the
Taconic Region... 3U
Table 4. Zonal biostratigraphy o f the Lower Cambrian portion o f th e Pioche
Formation, after Palmer (in Merriam, 1964)...31
Table 5. Zonal biostratigraphy o f the Lower Cambrian portion o f tlie Cararra Formation, California and Nevada, sum m arized from P alm er and Hailey
(1979)...31
Table o. Zonal biostratigraphv o f the Lower Cambrian o f Laurentia a s proposed bv
Fritz (1972)... 33
Table 7. C om parison of the relabve stratigraphie positions of p rev io u s autlior's biostratigraphic schem es w ith the zonal biostratigraphy p ro p o sed here for
L iuren tia... 51
Fable S. C o rre la tio n of selectevi Low er Cam brian form ations of L i u r e n t i a based on
trilobite biostratigraphv... 54
Table 9. Proposed classification o f the suborder O len ellin a... 91)
Table ID. Palmer and Repina's (1993) taxonomic sch em e for the su b ord er O lenellina... 91
Table 11. Exam ples illustrated herein o f genal lines ob served on O len ello id ea for com parison to hom ologous structures described for the Fallotaspididae
(Geyer, 1996)... 92
Table 12. Evaluation o f Fritz' (1995) proposed differences between Esmeraldina and
Palmettaspis...123
T able 14. Laurentia-centric classification of the Corynexochida h ere propose*.!... 239
T able 15. C om parison o f the general holaspid morphologx in Corx n exoch ida and
Ptychopariida...241
T able 16. List o f possible C orynexochida sp ecies with illustrated o n to g e n ie s... 242
T able 17. List o f Laurentian sp ecies assigned to Proliostracus w ith k now n thoraxes... 3Ü4
List o f Text-figures
Text-fig. 1. Reconstruction o f tiie Late Proterozoic s'. percontinent Rodinia at
approxim ately 70Ü m illion years ago (after Hoffman, 1991)... 6
Text-fig. 2. Reconstruction o f Early Cambrian continental positions (after McKerrow e ta l., 1992)...6
Text-fig. 3. G eneral locality m ap w ith study areas in southeastern British Columbia and the sou th w estern Great Basin indicated... 12
Text-fig. 4. Locality map o f stu d y area in southeastern British C olu m b ia...13
Text-fig. 5. C om p osite Upper Proterozoic to M id d le/U p p er Cambrian stratigraphie su ccession in southeastern British C olum bia... 14
Text-fig. 6. Locality map o f stu d y area in southw estern Great Basin... 18
Text-fig. 7. Upper Proterozoic and Lower Cambrian stratigraphie succession of tlie sou th w estern G reat Basin (after Signor and Mount, 1986)... 20
Text-fig. 8. Typical distribution o f trilobite taxa o f tlie NcMiiella Biofacies...37
Text-fig. 9. Tvpical distribution of trilobite taxa o f the Wanneriid Biofacies...37
Text-fig. 10. Typical distribution o f trilobite taxa of tlie Libradoria B iofacies... 37
Text-fig. 11. Typical distribution o f trilobite taxa o f tlie EkwipagetUi Biofacies...39
Text-fig. 12. Typical distribution o f trilobite taxa of tlie Olenelliis B iofacies... 39
Text-fig. 13. T ypical distribution o f trilobite taxa o f tlie Proliostracus Biofacies... 39
Text-fig. 14. T ypical distribution o f trilobite taxa o f tiie Bonnia Biofacies...41
Text-fig. 15. Typical distribution o f trilobite taxa o f tine Ogygops/s Biofacies... 41
Text-fig. 16. Relationship b etw een lithofacies, biofacies and biostratigraphic zones exp ressed in Lower Cambrian strata, southeastern British C olum bia...42
Text-fig. 17. Relationship betw een iithofacies, biofacies and biostratigraphic zo n es
expressed in Lower Cambrian strata, s o u t'w e ste r n Great Basin... 43
Text-fig. 18. C om posite Lower Cambrian stratigraphie su ccession and zonal biostratigraphy in southeastern British C olu m b ia...45
Text-fig. 19. C om posite Lower Cambrian stratigraphie su ccession and zonal biostratigraphv in southw estern Great Basin... 47
Text-fig. 20. M orphology o f the O lenellina... 56
Text-fig. 21. M orphology of the Corynexochida...58
Text-fig. 22. M orphology o f the Eodiscina... 60
Text-fig. 23. Ventral trilobite m orphology...62
Text-fig. 24. Com parative ontogenies of the W anneriidae and O len ellid ae... 71
Text-fig. 25. Com parison of tiie ontogenetic pattern of Olciicllus traiifttans (W alcott) (left) and Mesonacis graingerensis n. sp. (right)...76
Text-fig. 26. C om parison of tlie ontogenies of Wanneria dunnae n. sp. (top) and ElliptOLLfduila asapiicuies Emmons (bottom )... 77
Text-fig. 27. O ntogenv o f Liudonia pnma (Lochm an)... 78
Text-fig. 28. Evolution via paedom orphosis in the C orynexoch id a... 79
Text-fig. 29. Cladogram o f species within the W anneriidae and O lenellidae p rod ucin g a consen su s tree (50% majority rule) from 51 trees o f equal length u sin g two taxa as outgroups...84
Text-fig. 30. O ptim ized character distribution for 50% majority rule con sen su s tree generated using PAUP's "show apomorphies" o p tio n ...85
Text-fig. 31. A. C onsensus tree (strict) from 6 trees o f equal len gth using tw o taxa as outgroups and excluding FretwonfeZ/fl/w//i. B. C ladogram from A d raw n w ith branch lengths proportional to number o f character changes on branch... 87
T ext-fig. 32. BraLÜjfallcttisiJis rq.nnae n. sp. A. clique B m eraspid B. clique G h o la s p id ... 99
T ext-fig. 33. Neviuim inihticri n. sp ... IÜ<S T ext-fig. 34. Nevadeila eticluiris (W alcott)... 108
Text-fig. 35. O ntogeny o f Ntxnuiella parooconica (Fritz)...113
T ext-fig. 36. Esmeraldina ar;^enta (W alcott)...125
T ext-fig. 37. Wanneria luakottana (W anner)...132
Text-fig. 38. Hijpostomes o f Elliptocepltala parentalis n. sp ... 149
T ext-fig. 39. Liiidonia luirrin^toni n. sp ... 161
Text-fig. 40. O ntogeny o f Mesolenellus ^iith i n. sp ... 171
T ext-fig. 41. Standard com parative o n to g en y for the O len ellin a ...186
Text-fig. 42. O ntogeny o f Olenelliis ricei n. s p ...2LK) Text-fig. 43. O ntogeny o f Mesonacis ea;^erensts ( Best)... 212
Text-fig. 44. A. Bonnaspis fu'hkasis {W alcott) B. Bonnasfiis coliiinbensis {Resser)... 252
Text-fig. 45. A. Bonnia parciiLi {BilUr\p,s) B. Bonnia ornata n. s p ...263
T ext-fig. 46. A. Bonnia fr itz i n. sp. B. Bonnia laterispina E ritz... 266
T ext-fig. 47. O ntogeny o f Bonnia ;^randis n. sp ...271
T ext-fig. 48. O ntogeny o f Bonnia drysdalea n. s p ...277
T ext-fig. 49. Bonnia payinasterensis n. s p ...280
T ext-fig. 50. A. Ogygopsis batis (Walcott) B. Ogygopsis inarcoui (W hitfield) C. Ogygopsis typical is (Resser)... 286
T ext-fig. 51. Location m ap for measured section s of the C an al Flats area...349
T ext-fig. 52. Stratigraphy and species ranges for the M ount G rainger m easured section (MG3)...350
Text-tig. 53. Stratigraphy and species ranges tor the .Mount W atson measure,4 section I
(M G l)... 353
Text-fig. 54. Stratigraphy and species ranges for the Mount W atson measured section II
(M G 2)... 356
Text-fig. 55. Location map for the Ram Creek measured section (RC4)...360
Text-fig. 56. Stratigraphy and species ranges for the Ram C reek m easured section
(RC4)...361
Text-fig. 57. Location map for the Paymaster Canyon m easured section (PC)...364
Text-fig. 58. Stratigraphy and species ranges o f the Paym aster C anyon measured
section (PC)... 365
Text-fig. 59. Location map for the Coldfield measurevi section (G F)... 368
Text-fig. 60. Stratigraphy and species ranges for the C oldfield m easured section (GF)
and C oldfield localitx' (IS) (com posite section)...369
Text-fig. 61. Location map for the Gold Point measured section (G P)... 373
Text-fig. 62. Stratigraphy and species ranges for the Gold Point m easured section
(G P)... 374
Text-fig. 63. Location map for measured sections of the C edar Flat area...379
Text-fig. 64. Stratigraphy and species ranges for the Cedar Flat m easured section (CF)...380
Text-fig. 65. Stratigraphy and species ranges for the N ecklace H ill m easured section
(N H ) w ith locality 22 collections tied into sectio n ... 384
Text-fig. 66. Location map for the Waucoba Mountain m easured section (WM)...388
Text-fig. 67. Stratigraphy and species ranges for the Waucoba M ountain measured
A cknow ledgm ents
Funding tor this project w as provided in part by an NSERC grant to R. Ludvigsen as well as by NSERC Postgraduate Scholarships A and B and a White M ountain Research Station Fellowship to the author. Research facilities were kindly provided by C.R. Games and photolab facilities bv the B iology Department, Universitv' of Victoria. .A. Brandenburg assisted with field work in the Great Basin.
This project w ould not have been possible w itliout the inspiration o f Rolf L udvigsen, who
challenged m e and ensured that this thesis w as the best that it cou ld be. Clem N elson generously provided num erous collections for this stu d y and shared his exp ertise on the g eo log}' and fossil localities o f the Great Basin. Pete Palmer provided collections and information on system atics of Cambrian trilobites as w ell as useful d iscussion s on many aspects o f tills work. M y com mittee m em bers, Chris Barnes, Verena T unnidiffe and Eileen Van der Flier Keller, all read this massive diK um ent and provided useful com m ents. Ed Bousfield w as unable to com plete his term as a com m ittee member, but also provided useful com m ents and challenged me to kxik at trilobites as part o f the larger biological picture.
My friends, .Annalisa Ferretti, Margaret C a m p b e ll a n d Ruby Littlepage, gave s ta u n c h
en c o u ra g e m e n t th ro u g h o u t this w ork a n d participated in useful discussions. C h ristia n Gronau w as an e n h e a rte n in g presence with his c o n sta n t strea m of p h o to g r a p h s and u illingness to discuss lid iuui>ùnn minutia of the Olenellina. M anv a m a te u r paleontologists, professional collectors a n d field geologists m ade trilobite collections that w e re accessed in this s tu d y . 1 wish to recognize the role that these non-professional paleontologists h a v e played a n d the importance of c o m m u n itv ’ involvem ent in paleontology .
Special thanks are due to my family and friends, John and Joyce Bohach, Todd A shton, Margaret Cam pbell and Terry Russell, w h o gen erously volunteered as unpaid field assistants. My parents have a lw ay s encouraged and stood behind me, even when m y endeavors puzzled them. Last but never least, 1 w ish to thank m y husband, T odd Ashton, for his lo v in g support, en d urin g patience and unfailing belief in me.
XVIII Dedication
For Clem and Pete,
Chapter 1. Introduction
The L ow er Cam brian is a critical tim e in earth histor\' that m arks the eariv ev o lu tio n of the M etazoa. T his is the time o f the Cambrian explosion: the abrupt ap pearan ce and
d iv ersifica tion o f most of the major marine invertebrate phyla. The sp ectacu lar soft-bodied faunas from Cambrian lagers fatten have received much attention, h ow ev er, trilobites are a m ore co m m o n ly preserved Cambrian fossil. It is trilobite zon ation s that form the basis for relative d a tin g and correlation o f younger Lower Cambrian strata in Laurentia. Revision of m edial L ow er Cambrian trilobite system atics and zonal biostratigraphv are th e goals of this project.
W hile h u n d red s o f species o f Lower Cambrian trilobites have been d escrib ed , suprageneric cla ssifica tion s h ave either fluctuated from author to author (i.e. the O len ellin a ) or have been inad eq u ately investigated (i.e. tlie Corvnexochida). Little u se has been m ad e o f earlv
on to gen etic information or ventral morphologv' in svstem atic stu d ies o f Lower Cambrian trilobites, y e t these are excellen t features to u se in resolving higher taxon om ic relationships. Som e o f the key trilobite genera, such as Olenelliis and Bonnia, h ave such a broad attributed m orp h o log y that the genera can n ot be precisely defined or d ia g n o sed . They h a v e acted as w astebask et taxa for Lower Cambrian species that share som e general m orphological features. In ad dition , many sp ecies have been oversplit as preservational and ontogenetic differences h a \ e not been d istin gu ished from actual taxonom ic d ifferences. .All o f these problem s h a v e serious im plications w hen an unstable, poorly defin ed taxonomx is used in b io str a tig r a p h v .
Lower C am brian trilobite faunas of Laurentia are largely en d em ic, ex cep t for th ose of deep w ater or o u ter sh elf to slope d ep osits. The majority of species b elon g to the O lenellina and an O len ellian Fauna I Realm w as described by K obayashi (1972) and T heokritoff (1979) that in clu d es Laurentia, Avalonia and Baltica. In contrast, a Redlichian Faunal Realm was d esign ated in G ondw ana, in clu siv e o f China, Australia and Antarctica. T hese faunal realms are not m u tu a lly exclusive: in Morocco and Siberia, both O lenellina and R edlichacean trilobites are found and a M ixed Realm is recognized. These strong faunal d ifferen ces make w o r ld -w id e correlation problem atic as alm ost no species and few gen era are shared between faunal realm s. Endem ism is pronounced even w ithin faunal realm s, for ex am p le, both
Laurentia a n d Avalonia are part o f the O lenellian Faunal Realm , y et n o gen era o f O lenellina are com m on to both. An additional problem is that strata d esignated as Lower Cambrian in so m e parts o f the world, correlate to strata designated as M iddle Cam brian in oth er areas
(G eyer and Palm er, 1995). Since the base of the M iddle Cambrian has not yet been d esignated , this problem ca n n o t be resolved.
Palm er (1977) p ro vid ed a sum m ary o f Cambrian biostratigraphic d iv isio n s applied in various areas o f the w o r ld . Laurentian sch em es have focused on trilobites, alth ough the sm all shelly fossil Salterella has been described as indicative o f the medial L ow er Cambrian (Fritz and Y ochelson, 1988). The biostratigraphic schem e currently in use for Laurentia w as d ev elo p ed b y Fritz (1972) o n faunas of the S ek w i Formation o f the Mackenzie M ountains. There are m any problem s w ith this zonal biostratigraphy: first, it is a genus-based zon ation . Genera are long- ranging and con seq u en tly cannot be used for precise correlation or relative dating. There are a lso problem s w ith the current taxonom ic definitions of many genera. Second, m ost o f the zon al boundaries have not been d efin ed . It m ight be assumed that the zon es are gen u s-ran ge zo n e s, but it h as n ot been exp licitly stated. If they are genus-range zon es, then the Fallotasyis Z o n e is particularly problematic sin ce no species o f Fallotaspis h a v e y et been described from Laurentia. T hird, the zones h a v e n o t been adequately characterized. For exam ple, the
B o nnia-O lenellus Z one represents a thick stratigraphie interval, yet Fritz (1972) listed o n ly a
few genera that are supposed to characterize the upper part of that zo n e. Fourth, there is no attem p t m ade to account for biofacies restrictions and to integrate the spatial com p o n en t of biostratigraphy w ith the time com ponent. All o f these factors contribute to a Lower Cambrian biostratigraphy for Laurentia that is im precise and difficult to a p p ly . What is n eed ed is a species-based zon ation .
D evelop m en t o f a species-based zon al biostratigraphy requires three things: a con sisten t and d efen sib le tax on o m y, docum entation o f biofacies and detailed stratigraphie inform ation on sp ecies ranges. To facilitate this investigation, tw o study areas w ere identified. T he first area, in southeastern British C olum bia, was collected from in the fall o f 1991 and the sp rin g of 1992. It com prises tw o fossiliferous Lower Cambrian units: the C ranbrook and Eager
form ations. Representation o f faunas from the m id dle carbonate belt is go od w h ile
representation o f faunas from the inner detrital belt is fair. These faunas, how ever, represent o n ly a portion o f the Lower Cambrian trilobite succession. An ad dition al study area n eed ed to b e identified a n d other fossiliferous Lower Cambrian strata in British C olum bia w e r e either alread y under investigation by oth er researchers, or were inaccessible w ithout h elicop ter support. N earb y d ep osits in W ashington and Idaho were inappropriate for investigation as their Lower C am brian trilobite faunas are rare and of poor quality. T he Great Basin o f the w estern U nited States was targeted next as a potential study area and A.R. Palmer o f the Institute for C am brian Studies w a s contacted to determ ine w hat areas w ere available for
3 stu d y . Palm er invited the author o n a tour of the southw estern Great Basin in A u g u st o f 1992 and p ro vid ed an introduction to the geo lo gy and faunas. At that tim e, C.A. N e ls o n , a retired g e o lo g is t w ith extensive, u ndescribed collections from the W hite-lnyo M ountains, California, and Esm eralda County, N evad a, w a s introduced to the author. It w as agreed that th ese co llectio n s be m ad e available for this study and that the southw estern Great Basin b ecom e a second stu d y area for the project. The Poleta, H arkless and Saline Valley form ation s w ere identified as the main fossiliferous formations and designated as the stratigraphie u nits for in vestigation . Faunas from th ese strata provided goo d coverage o f both inner d etrital and m id d le carbonate belt d ep o sits w h ile faunas from outer shelf facies h ave lim ited
representation. Som e collections from the M ontenegro Member o f the Cam pito Form ation were later a d d ed w h en necessary for taxonom ic com pleteness. The stratigraphie su cce ssio n of the Great Basin is the correlative o f the British Colum bia succession, but represents a m ore co m p r eh en siv e stratigraphie and fossil record.
Field w o rk in the southw estern Great Basin was d o n e in the spring o f 1993. All field w ork in this stu d y em ph asized m aking stratigraphie collections from m easured sections an d obtaining large sam p les. A total o f 10 sections w ere measured and collected: four in sou th eastern British C olum bia and six in the so u th w estem Great Basin. These have been su p p lem en ted bv
collection s from 29 spot localities (7 in British Colum bia; 22 in the Great Basin) that co u ld be tied into the stratigraphie su ccession . All collections are of crack-out lim estone an d shale m aterial that required exten siv e splitting in the field to make collections. In the lab, m aterial w a s sp lit further and sp ecim ens were prepared using a sm all chisel and electric engraver. The best specim ens w ere prepared further and photographed. All sta g e s o f the photographic process were d o n e by the author.
G oals o f the preparatory and system atic work w ere to discover and describe as m u ch as p o ssib le o f the w h ole body m orp h ology (particularly ventral features) and the o n to g en etic d ev elo p m en t o f each species. O f the 55 species recognized from the stu d y areas (44 o f w hich are reasonably w ell-know n), h y p o sto m es are illustrated for 26 and ontogenetic sta g e s for 36. Major o n togen etic patterns and hypos to mal m orphologies can be recognized and u sed to d ia g n o se fam ilies and genera. Recognition of ontogenetic patterns further perm its d escrip tion o f h eteroch ron y in the evolu tion o f Lower Cambrian trilobites.
O nce a revised and defensible taxonom y is produced, d evelopm ent o f a zonal biostratigraphy can p roceed . Biofacies an a lysis is the first step to determ ine the spatial restrictions o n trilobite distributions. Specim en counts were m ade o f all trilobite collections an d biofacies
4 d efin ed based o n th e predom inant gen era. Since collection s are a.I o f relatively low taxon om ic d iversity, sim p le in sp ection and p rod u ction o f pie diagram s w ere sufficient to identify and d o cu m en t biofacies patterns. B iofacies are w ell-d ev elo p ed in the y ou n ger strata exam ined, but O lenellina trilobites are found in m o st shelf d ep o sits and a single zonation schem e is su fficien t for d e p o s its o f the continental shelf. The species-based zonal biostratigraphy d ev elo p ed here can be related to m ost sh elf sequences described for Laurentia.
Chapter 2. G eology
The Cambrian S y stem
T he C am brian S ystem w as on e of the last chronostratic u n its to be acceptably defined by 19th cen tu ry stratigraphers. A d am Sedgwick first proposed the nam e in 1835 for a package o f rocks in N orth W ales. The n am e Cambrian, w as coined from the Latin nam e for W ales, Cambria. A t the sam e tim e as S ed gw ick announced the Cambrian S ystem , Roderick M urchison d efin ed h is S ilurian S ystem . W hen later field work d em on strated that the u p p er strata of the C am brian S ystem and the low er strata o f the Silurian S y stem w ere the sa m e stratigraphie p ack age, d efin ition o f both system s became u nresolved . T his created a bitter conflict b etw een M u rchison and S ed gw ick , as neither system had priority o v er the other, an d neither g e o lo g ist w o u ld agree to redefine the sequence o f rocks assigned to h is system . T he conflict w as not reso lv ed until after the d eath o f both parties, w hen Lapw orth in 1879 p rop osed the O rd o v icia n S ystem for the disputed strata (Secord, 1986).
Strata u n d erlyin g the Cam brian System are com m on ly referred to as Precambrian and s u b d iv id e d into an older Archean Eon and a younger Proterozoic Eon (H arland et al.. 199Ü). T he term Proterozoic w ill be used here to refer to the strata and the tim e interval preceding th e C am brian.
T he term Cam brian System did not come into general u se in North America until the 1880s w ith the w ork o f H un t (1883, 1884) and Walcott (1883). It replaced, in part, the term Taconic S y stem (E m m ons, 1844), and similarly the "Primordial Fauna " of various authors (i.e.
Barrande, 1861) becam e, in part, Cambrian. Parts o f both th e Taconic S y stem and the Prim ordial Fauna represent strata and fossils n o w a ssig n e d to the O rdovician and Silurian. W alcott (1886) w a s the first to attempt to su bd ivide the N orth Am erican Cambrian rocks into series. W alcott (1886, 1890) initially used the nam e G eorgian Series for the Lower Cam brian, w h ic h h e later (1912b) replaced with the name W aucoban Series w h en h e d ecid ed that it w a s in bad form to u se a form adonal name (i.e. the Georgia sla te o f Franklin C ounty, Vermont) as a series nam e.
Fritz (1991b, 1995) restricted the Waucoban Series to the u p p er portion o f the Lower Cam brian in Laurentia, and ap p lied the name Placentian Series for th e low er portion. Recognition and u s e o f the term Placentian for Laurentian strata is here con sid ered problem atic since it w a s d e fin e d b y L anding (1989) for rocks and fossils in the A valon ian portion o f N ew fou n d lan d , w h ic h w a s a d ifferen t continent from Laurentia in the ea rly Cambrian (T ext-fig. 2). The b ase
Au
EA
OQ'
VVA
Text-fi^. l. Reconstruction ot the Late Proterozoic supercontinent Rodinia at approximately 700 million years av;o ta ter Hotïman, IWl). A=Amazonia, Au=Australia, B=Baltica,
C=Congo, EA=East Antarctica, L= Laurentia, S=Siberia, WA=West Africa
Text-fig. 2. Reconstuction of Early Cambrian continental positions (after McKerrow
o f th e Placentian Series a n d the base o f the Cam brian System in A vaionia is defin ed a t the base of the Phycodes pedum z o n e (trace fossil). The top of the Placentian Series equ ates to the base of the Callavia Z o n e (trilobite). The fossils, and consequently the faunal zones, are different on A vaionia a n d Laurentia a n d correlation is speculative a t best. Fritz (1991b) defined the b o u n d a ry betw een the Placentian and W aucoban series in L aurentia as the b o u n d a ry betw een his (Fritz, 1972) Fallotaspis and Nevadella zones, based o n ten tativ e co rrelatio n b etw een th e Callavia a n d Nevadella zones (Fritz, 1972). N o trilo b ite species o r genera are shared betw een these tw o zones and, accordingly, the tw o successions cannot be c o rre la te d .
Base of the C am brian
The base of the C am b rian has been placed at different, w idely-spaced levels since the m iddle o f the last century, eith er at the unconform ity in most shelf sequences of P recam brian to
C am brian rocks, o r a t the first app earan ce of a particular gro u p of skeletal fossils. S tarting in 1972, the Precam brian-C am brian B oundary W orking G roup began searching for the m ost a p p ro p ria te stra to ty p e section and the best interval at w hich to define the b o u n d a ry (i.e. see C ow ie a n d Brasier, 1989). In 1992, th e controversy was finally resolved w hen the
International U nion of Geological Sciences ratified placem ent of the Low er C am brian
b o u n d a ry at the base of the Phycodes pedum Zone, at a strato ty p e section of d e e p -w a te r strata a t Fortune Head, N ew foundland (L anding, 1994). This boundary placem ent w as a radical decision in that it used trace fossil rath e r than body fossil zonation and included in the C am brian System a thick series of poorly fossiliferous rocks that m any a u th o rs previously had considered Proterozoic. This b o u n d a ry is located well below the first a p p e ara n ce of trilobites, but only a sh o rt stratigraphie distance below the first sm all shelly fossils. Only rare a n d problem atic tu b u lar shelly fossils such as Cloudina (see M cM enam in an d M cM enam in, 1990) a n d Wyattia (see Taylor, 1966) occur elsewhere in Proterozoic rocks. An ag e of
approxim ately 544 m illion years for the boundary has been determ in ed by radiom etric dating u sing uranium -lead zircon data (Bowring e ta l., 1993), w hich is co n siderably less than
p revious estim ates o f 570 to 590 m illion years (i.e. H arland et al., 1990).
In the sh o rt tim e since the Phycodes pedum Zone has been chosen as the basal C am b rian zone, there has been little docum entation in w estem Laurentia of the P recam brian-C am brian boundary. An unconform ity has long been recognized at the b oundary in m any places, especially so u th e rn B ritish C olum bia (i.e. W alcott, 1910a; Aitken, 1969), a n d it is unlikely th at strata of this a g e will be found. In northern Canada, Brasier a n d C ow ie (1989) recorded
w hile Fritz et al. (1983) reco rd ed P. pedum fro m an unnam ed m ap unit im m e d ia te ly below the V am pire Form ation. Fritz (1984) also recordeo Phycodti, sp. in the Boya F o rm a tio n of the Om ineca M ountains. In m y s tu d y area w ith in the Great Basin, C rim es (1989) recorded
Phycodes a n d o th er com plex, typically C am b rian trace fossils from the D eep S p rin g Form ation. Recognition of th e genus gives little age control on the strata as C rim e s (1992) indicated th at the range o f Phycodes extends to the Silurian, b u t it can be tak e n as an indication th a t the strata a re a t least C am brian as opposed to Proterozoic in a g e (Crim es, 1989).
The Lower - M iddle C am b rian Boundary
A global stratotype section fo r the base of the M iddle Cam brian is c u rre n tly un d efin ed (i.e. see Geyer a n d Landing, 1995). W alcott (1891) considered the Low er C am b rian to be
synonym ous w ith the "Olenellus Zone": in m o d e m terms, this placed W alco tt’s b o u ndary at the last occurrence of the O lenellina. Many subsequent trilobite w orkers d id n o t follow
W alcott’s definition a n d R esser (1938), H ow ell et al. (1944) an d L ochm an (1947) all recognized a variably defined post-O lenellina Lower C am b rian zone.
Rasetti (1951) recom m ended a provisional re tu rn to W alcott’s b o u n d a ry d e fin itio n , although he recognized the com plications of an unconform ity at this interval for m ost continental shelf deposits and that the d isa p p e a ra n c e of a g ro u p w as not likely to be sy n c h ro n o u s in all places. Fritz (1991b) accepted W alcott’s definition of th e boundarv w ithout c o m m en t a n d Palmer (1979) suggested that this faunal change m ig h t be a biomere b o u n d ary ^ . T h e stratigraphie code guidelines state that th e top of a stratig rap h ie interval is by the base o f th e overlying unit. Accordingly, the Low er - M iddle C am brian boundary sh o u ld be d e fin e d by the lowest fossil zone characteristic of th e M iddle C am brian.
W ithin the stu d y area in B ritish Colum bia, M iddle Cam brian strata are n o t p rese rv ed and Fritz (1991b) recorded the U p p e r Cam brian Jubilee Formation u n conform ably ov erly in g the Lower C am brian Eager Form ation. In the G re a t Basin, the presence of a u n c o n fo rm ity in the basal M iddle C am brian is controversial.
^ A biom ere, according to P alm er (1979, p. 33) is a "regional biostratigraphic u n it, bounded by abrupt, non-evolutionary chan g es in the d o m in a n t elements of a single p h y lu m , w hich were not related to physical disco n tin u ities in the sed im en tary record". T he bio m ere c o n c ep t is
controversial. Ludvigsen a n d W es trop (1985) discounted the attrib u ted u n iq u e n e ss of a biom ere and, instead, proposed th at U p p er Cam brian biom ere boundaries are sta d ia l boundaries.
Regional Tectonic and D epositional Setting Proterozoic Prelude
T he existence of the m id-Proterozoic supercontinent R odinia h a s gained w id e acceptance (H offm an, 1992). The consensus for distribution of the c o n tin en ts is that Laurentia occupied a central position w ithin the supercontinent (Text-fig. 1; H offm an, 1991) w ith Siberia adjoining the cu rre n t north w est Laurentian m argin (Condie and Rosen, 1994; Pelechaty, 1996), A ustralia th e central w estem m argin (Young, 1992; Idnurm and G id d in g s, 1995) a n d east Antarctica the so u th w e ste m m argin (Moores, 1991; Dalziel, 1991). Tim ing o f the breakup o f R odinia has been vario u sly constrained using evidence from paleom agnetism (Pow ell et al., 1993), regional stra tig rap h y (Lickorish and Simony, 1995; Pelechaty, 1996) a n d tectonic sub sid en ce curves (Bond et al., 1984; Levy and Christie-Blick, 1991). M ultiple rifting events w ere likely involved beginning around 7(X) million years ago and c u lm in a tin g w ith final continental se p ara tio n a n d initiation of the Paleozoic phase of passive m arg in subsidence near the Precam brian-C am brian boundary (Bond eta l., 1985; Devlin a n d Bond, 1988; Ross, 1991). L ow er C am b rian strata record the final phase of rifting a n d the initiation of m iogeoclinal sedim entation o n a passive margin.
Ross et al. (1989), Aitken and McMechan (1991) and G abrielse and C am pbell (1991) provided o verview s of Proterozoic sedim entation in eastern British C olum bia. M iddle Proterozoic rocks consist of the Purcell Supergroup in the southern region w hich is interpreted to have been d ep o sited in an intracratonic setting as rifting of Rodinia com m enced (G abrielse and Yorath, 1991). A period of deform ation and uplift followed, p receding deposition of the Upper Proterozoic rocks of the W inderm ere Supergroup. W inderm ere strata, w hich include glacial d ep o sits, have been tentatively interpreted (Ross, 1991) as a rift to passive m argin sequence w h ich p red a tes the rift event associated w ith initiation o f th e C am b rian p assiv e m argin subsidence.
S tew art (1991) p ro vided an excellent overview of Proterozoic to C am brian sedim entation in the w e stem U nited States. He docum ented a late Proterozoic glacial an d volcanic succession follow ed by a clastic sequence extending through to the C am brian. In the so u th w estem G reat Basin just south o f the thesis area, the m id-Proterozoic P a h ru m p G roup, a n intracra tonic rift sequence, is unconform ably overlain by the N oonday F orm ation that m arks a transition to th erm ally d riv e n subsidence (Levy a n d Christie-Blick, 1991). O verlying elastics w ere in terp reted as a possible extensional sequence w ith subsidence curves in d icating final co n tinental separation an d initiation of passive m argin d e p o sitio n occu rrin g in this interval.
Low er C am b rian Deposition and Tectonic Setting
M any reconstructions of continental positions have been pro p o sed over th e years fo. the Early C am brian. O n e of the m ost recent is show n in Text-fig. 2. L atitudinal positions of continents a re c o n strain ed by paleo m agnetism , b u t longitudinal positions are less exact, based largely on faunal sim ilarities betw een continents. All reconstructions sh o w Laurentia to be an isolated continent located a t low latitudes and oriented approxim ately 90° clockw ise com pared to the present. T his o rien tatio n is significant as it m eans that no large scale la titu d in a l variations in clim ate w o u ld have influenced faunal distributions of w e stem Laurentia. Baltica and Siberia w ere also isolated continents positioned between Laurentia and G o n d w a n a.
N o rth (1971) a n d Fritz (1991b) have both provided excellent overview s of C am b rian geology o f eastern B ritish C olum bia. The sedim entary record of the Proterozoic-C am brian boundary is v ariously p rese rv ed . Colpron and Price (1995) suggested th a t the pericratonic Kootenay T errane w as depositionally linked to a n d is continuous w ith typical L aurentian era tonic deposits. T h e up p erm o st Proterozoic to Lower Cam brian H am ill G roup of this region records the extensional tectonism to passive m argin subsidence near the Precam brian-C am brian b o u n d a ry (D evlin and Bond, 1988; Devlin, 1989). Another record of this late rifting event is the G og G ro u p of the Rocky M ountain main ranges (Lickorish an d Simony, 1995). In the so u th e rn m o st portion of the province, C am brian sedim entation w as influenced by M ontania (i.e. Deiss, 1941; N orth, 1971), a tectonically positive area, responsible for a sub-M iddle C am brian unconform ity (Norris and Price, 1966; Ross et al., 1989; Colpron a n d Price, 1995). W ithin the s tu d y area in British C olum bia, the Lower C am brian C ranbrook Form ation unconform ably overlies M iddle Proterozoic strata of the Purcell S upergroup. In the Great Basin, strata o f the Proterozoic to Cam brian boundary contain only localized evidence tor the C am brian rift e v e n t indicated by the presence of a small a m o u n t of volcanic rocks and a m inor
u n co n fo rm ity (Levi and Christie-Blick, 1991).
Initial d e p o sits on the new ly rifted passive m argin of w estem Laurentia co n sist m ainly of thick s a n d sto n e a n d quartzite sequences w ith m inor conglom erates (G abrielse an d Yorath, 1991). T he C ra n b ro o k Form ation of southeastern British C olum bia is an excellent example. T he Deep S p rin g Form ation of the southeastern Great Basin has a m ore m ixed lithology of a b u n d a n t co arse elastics w ith lim estones.
Lithofacies d istrib u tio n s for Low er C am brian strata a re sim ilar to those described by Palm er (1960) for U pper C am brian rocks. Three depositional belts can be recognized: a near sh o re in n er d e trita l belt, continental shelf m iddle carbonate belt and o ffshore o u te r detrital
belt. These facies belts interfinger as they m igrated laterally in response to changes in sea level, subsid en ce rate and sedim entation. A itken (1966) recognized th at the pattern of
sed im en tatio n w as cyclic w ith large scale alteratio n s of p red o m in an tly clastic sed im en tatio n follow ed by p red o m in an tly carbonate sedim entation th at he called g ran d cycles. This con cep t has been a p p lie d to Lower (Cambrian strata of th e C ordillera by Palm er and Hailey (1979), Fritz (1975), M o u n t a n d Row land (1981) and M ount et al. (1991).
G eology a n d Historical Paleontology of the S tudy Areas
Tw o stu d y a re a s a re targeted in this thesis (Text-fig. 3): one in southeastern British C olum bia, the o th e r in the so u th w estem G reat Basin.
S ou th eastern B ritish C olum bia
The stu d y are a in British C olum bia is centered in the C ranbrook to Canal Flats regions (Text- fig. 4) a n d focuses on the C ranbrook and Eager form ations. The generalized stratigraphy for the region is o u tlin ed in Text-fig. 5). Early geological exploration of the region was d one by Daly (1913), Schofield (1914, 1915, 1922) and W alcott (1924). W alcott (1924, p. 29-3U) nam ed M ount G rainger an d published a m easured section, including a list of fossils collected and previously rep o rted by Schofield (1922, p. 14). Schofield (1921) also anno u n ced discovery of Lower C am brian trilobites near C ranbrook, from w h a t is now know n as the Rifle Range locality. D etailed m apping of the C ranbrook region was done by Rice (1937) and Leech (1958a) and m a p p in g of the C anal Flats region by Leech (1954, 1958b)
C ranbrook Form ation
As is typical o f the lowest Low er Cam brian form ations in the south-central C ordillera, the C ranbrook F orm ation is a coarse clastic deposit sep arated from underlying M iddle Proterozoic strata by an unconform ity. The a n g u la r unconform ity at this contact is graphically
dem o n strated by th e variety of Proterozoic form ations of differen t ages (i.e. Siyeh, G atew ay , Purcell intru siv es) th at underlie the C ranbrook F orm ation in different localities. Basal deposits of the C ranbrook consist of conglom erates containing clasts of the sam e lithology as und erly in g s tra ta . Schofield (1922) first designated the C ranbrook Form ation for a series o f light coloured q u a rtz ite s near the city of Cranbrook. The form ation has since been recognized in the Purcell M ountains betw een St. Mary Lake a n d C reston (Rice, 1941), the Stanford R ange of the Rocky M ountains near Fort Steele (Rice, 1937; Leech, 1958a) and n o rth to the area aro u n d Canal Flats (Leech, 1954, 1958b).
Northwest Territi . les Yukon British Alberta C olum bia Saskatchewan Montana Washington Idaho ~ f ---1 --- 1 Nevada ' Utah ■— [
J--- '
\ N ew Arizona I / I Mexico CaliforniaText-fig. 3. General locality m ap w ith studies areas in southeastern British Columbia and the southw estern G reat Basin indicated.
13
rairmont Hot Springs
MC3#L Mt. Grainger M C I ? \ M G 2 Mt. Watson Whiteswan Lake Canal Flats Ram Skookumchuck Premier Lake
@ 9
Kimberlv St. Marv Lake 4 # 5 ^ 6 # Wvcliff 7 # Cranbrook M oyie Range Wardner 6 km JaffrayText-fig. 4. Locality map o f study area in southeastern British Columbia. Locality numbers correspond to those listed in Appendix A.
14 Text-fig. 5. Composite Upper Proterozoic to M iddle/Upper Cambrian stratigraphie succession in
southeastern British Columbia.
Jubilee 400 Formation M, U C Eager Formatii-'n Cranbrook Formation 300 ZOO 100 LC Purcell Supergroup „ ,T ~rr. U I 1 1 X IX T . 1 1 1 1 1 O 'X L l I
in
X L r i T i 11u r n 1
Vplo/Sj,'Rice (1937) a n d Leech (1954) have b o th described the general character of the C ranbrook q u a n tité s a n d reco rd ed local variations. The quartzites are distinctly b e d d e d w ith bed thickness ranging from 30 to 180 cm. M ost beds are m assive. Interbedded pebble conglom erates a n d g rits w ere also reported by Leech (1954) as well as a less-cem ented interval of yellow - w eathering sa n d sto n e s tow ards the top of the form ation. Shale interbeds becom e com m on ap p ro ach in g th e u p p e r boundary. Schofield recorded a thickness of 180 m in the C ranbrook region. Leech (1954) a thickness of 240 m in the Hughes ^u^d G rainger ranges an d 75 m a t M ount D eSm et (north o f M ount Grainger).
O nly a single fossil locality is know n from the C ranbrook quartzites. G.B. Leech m ade a large collection of trilobites (see locality 3, A ppendix A) from this locality in th e H ughes Range, R am C reek area. T he present a u th o r w as unable to relocate this locality o r to find a n y o th e r fossiliferous C ra n b ro o k strata.
E ager Form ation
T he Eager F orm ation is a shale and siltstone, to shale an d lim estone sequence. Leech (1954) a n d Schofield (1922) both reported th a t the lower b o u n d a ry with the C ra n b ro o k Form ation is conform able, w h ile Rice (1937) suggested a minor disconform ity. C o n sid erin g the age
d isp a rity betw een fossils of the u p p e r C ranbrook Form ation and those of the low er Eager Form ation, a d isco n fo rm ity is probably present. Both Leech (1954) a n d Fritz (1991b) re p o rt a disconform ity betw een the Eager Form ation and overlying Upper C am b rian Jubilee Form ation.
Schofield (1922), Rice (1937, 1941) a n d Leech (1954% 1958a, 1958b) h a v e described and
delim ited the E ager Form ation. In th e type area near C ranbrook, the E ager Form ation consists m ain ly of a shale a n d siltstone sequence w ith minor g rit layers (< 1 cm thick) an d rare sm all calcareous lenses. Rice (1937) recorded that the u p p er Eager Form ation strata near W ycliff c o n sist of c rystalline lim estone. The shales are generally grayish on fresh surfaces but w e a th e r to a v a rie ty of red and oran g e hues. Silts tones are generally pink. In the type area, o n ly th e basal sh ales of the form ation have yielded fossils. Rice (1937) estim a ted the total thickness of the E ager Form ation as o v e r 1800 m. O ver 600 m of strata w e re m easured by th e a u th o r in an incom plete section in th e type area along the highw ay in te rch a n g e for
C ranbrook, F em ie a n d Fort Steele.
^ In Leech's (1954) prelim inary account of the Canal Flats region, h e referred to these stra ta s im p ly as "post-C ranbrook Lower C am b rian strata", th o u g h he recognized th at they are the lateral eq u iv alen t of the Eager an d M ount Whyte form ations. W hen Leech (1958b) later pub lish ed the geological m ap for the region, he designated these rocks as Eager Form ation s t r a t a .
The lithology of the Eager Formation in the H ughes a n d G rainger ran g es n ear Canal Flats is differen t from the type area near C ranbrook in th at it consists of in te rb e d d e d lim estone a n d shale. T he shales are generally cleaved and have not yielded bod y fossils. One heavily bio tu rb ated shale interval was noted on M ount W atson. The lim estones ran g e from m arls to p u re lim estones. The latter tend to be thick-bedded (> 1 m) and in clu d e oolites and m u dstones. W ackestones, packs tones and marls tend to be thin bedded w ith sh a ly partings. M any of the lim estone beds are lenticular and of a lim ited extent. Leech (1954) in clu d ed interbedded san d stones, conglom erates and shales in the low er p a rt of the form ation, how ever, the sandstones an d conglom erates should be assigned to the C ranbrook Form ation to be consistent w ith form ational designations in the type area (Rice, 1937; Schofield, 1922). The contact betw een the C ranbrook an d Eager form ations has never been form ally d efin ed . Here it is pro p o sed th at the base of the Eager Form ation be placed at the top of the highest s a n d sto n e or q u a rtz ite bed. A pproxim ately 130 m of Eager Form ation were m easu red by the author on M ount W atson, and about 50 m in the Ram Creek area. The base of the Jubilee Form ation is taken a t the base of the lowest bed of dolostone.
The difference in carbonate content in the Eager Form ation strata o f the C ranbrook and C anal Flats areas m ay possibly be attributed to the latter being more offshore deposits. The
shoreline d u rin g the Early C am brian w as to the east, near the p rese n t d a y British C olum bia- Alberta b o rd er (Lochman Balk, 1968), but the southern deposits n e a r C ranbrook w ould h a v e also been u n d e r the influence of an additional land m ass, M ontania . W hether the elastics w ere tran sp o rted from the south (M ontania) or the east (craton) has yet to be determ ined, but the form er seem s likely considering the abundance of inner d etrital d e p o sits at C ranbrook versu s the m ixed in n er detrital and carbonate platform deposits n e a r C anal Flats.
T he only previous taxonom ic study on trilobites from the Eager F orm ation is that of Best (1952) on trilobites from the Cranbrook region. Hu (1985) presented an ontogenetic study on one of these species an d an o th er on species from m aterial collected near R adium , north of the stu d y area. T he strata near Radium may be the Eager Form ation, o r a t least th e laterally
eq u iv alen t. T he non-trilobite arth ro p o d s Anotnalocaris and Tuzoia h a v e also been d escrib ed from the Eager Form ation near C ranbrook (Resser, 1929; C opeland, 1993).
