The most intensively studied Cambrian stadial suites are those of Australia, southern China, Kazakhstan, Siberia, and North America, shown in Fig. 11.1, and Baltica.
AU S T R A L I A N C A M B R I A N S TAG E S
Australian stages are summarized by Shergold (1995) and Young and Laurie (1996), on which the following outline is based. They are described as “biochronological” units and are defined in terms of their contained fauna (Shergold, 1995). Boundary stratotypes are therefore not designated. Ordian apart, the stages discussed below have all been erected in the Georgina Basin of western Queensland.
Pre-Ordian Stages have not yet been designated for most of the Lower Cambrian of Australia. Archaeocyathans, small shelly fossils, and trilobite correlations indicate that the Adta- banian to Toyonian Stages of the Siberian Platform and the Altay–Sayan Foldbelt of Russia can be recognized through- out southern and central Australia. Ichnocoenoses in southern Australia are thought, possibly, to represent the Tommotian
and Nemakit–Daldynian (Bengtson et al., 1990; Shergold in Young and Laurie, 1996).
Ordian–Lower Templetonian An Ordian Stage was originally proposed by ¨Opik (1968) as a time and time-rock division of the Cambrian scale characterized by the occurrence of the Redlichia chinensis faunal assemblage. The Templetonian Stage, “a liberal interpretation of Whitehouse’s [1936] Templetonian series” ( ¨Opik, 1968), was originally conceived by ¨Opik as containing the Xystridura templetonensis assemblage of western Queens- land overlain by fauna of the Triplagnostus gibbus Zone. In prac- tice, it is difficult to distinguish the Redlichia and Xystridura fauna because four species of Xystridura, similar eodiscoid and ptychoparioid trilobites, some bradoriid ostracodes, and chan- celloriids occur in rocks of both Ordian and early Templetonian ages. Accordingly, Shergold (1995) regarded the Ordian–early Templetonian as a single stadial unit. It is retained as the earliest Middle Cambrian Stage in Australia even though it apparently correlates with the Longwangmiaoan Stage of China (Chang, 1998) and Toyonian Stage of the Siberian Platform (Zhuravlev, 1995), which are traditionally regarded as terminal Early Cambrian.
Upper Templetonian–Floran As originally defined ( ¨Opik, 1979), the Floran Stage contained the agnostoid trilobite zones of Acidusus atavus and Euagnostus opimus. This concept was re- vised by Shergold (1995) to include the late Templetonian zone of Triplagnostus gibbus, arguing on grounds of sequence stratig- raphy (Southgate and Shergold, 1991) and faunal continuity as suggested by the overlap of A. atavus and T. gibbus in western Queensland. We maintain the late Templetonian–Floran as a single unified stage. Having a global distribution, this stage is a very important datum, because, besides agnostoid trilobites, it contains oryctocephalid trilobites (Shergold, 1969) which are also significant for international correlation.
Undillan The Undillan Stage, defined by ¨Opik in 1979, is unrevised, and is based on the fauna of two agnostoid zones, the Ptychagnostus punctuosus Zone below, overlain by the Goni- agnostus nathorsti Zone above. A third zone, based on Doryag- nostus notalibrae, containing the overlap of 15 bizonal agnostoid species, including P. punctuosus and G. nathorsti, was recognized by ¨Opik (1979) in the Undilla region of the Georgina Basin. The agnostoid fauna of the Undillan Stage have cosmopolitan distribution. Agnostoids apart, other trilobites include pty- choparioids, anomocarids, mapaniids and damesellids, cono- coryphids, corynexochids, nepeiids, and dolichometopids, all of widespread distribution.
Boomerangian The Boomerangian Stage ( ¨Opik, 1979) is es- sentially the Lejopyge laevigata Zone divided into three. A Pty- chagnostus cassis Zone at the base is overlain by zones defined by the non-agnostoid trilobites Proampyx agra and Holteria arepo. Boomerangian agnostoids are accompanied by a range of poly- meroid trilobites including species of Centropleura, dolichome- topids, olenids, mapaniids, corynexochids, and damesellids. A Zone of Passage, characterized by the occurrence of Damesella torosa and Ascionepea janitrix, was interposed by ¨Opik (1966, 1967) between the Boomerangian (latest Middle Cambrian) and Mindyallan (considered at that time to mark the begin- ning of the Upper Cambrian) Stages. Subsequently, Daily and Jago (1975) restricted this zone to the Middle Cambrian, and placed the Middle–Upper Cambrian boundary within the early Mindyallan.
Mindyallan Originally ( ¨Opik, 1963), the Mindyallan Stage was considered to be represented by a Glyptagnostus stolido- tus Zone (above) and a “pre-stolidotus” Zone (below). Sub- sequently ( ¨Opik, 1966, 1967), the former was maintained in the late Mindyallan but the latter was divided into an ini- tial Mindyallan Erediaspis eretes Zone and an overlying Ac- marhachis (Cyclagnostus) quasivespa Zone. The E. eretes Zone contains 45 trilobites, including 18 agnostoid genera. The polymeroid trilobites belong to a wide variety of families: anomocarid, asaphiscid, catillicephalid, damesellid, leioste- gid?, lonchocephalid, menomoniid, nepeiid, norwoodiid, rhys- sometopid, and tricrepicephalid. The A. quasivespa Zone has 18 species of trilobites confined to it, but many other species range from earlier zones. Daily and Jago (1975) proposed to subdivide the A. quasivespa Zone into two assemblages based on the occurrence of Leiopyge cos ¨Opik and Blackwelderia sab- ulosa. Since they regarded L. cos to be synonymous with L. l. armata Westerg˚ard, a late Middle Cambrian taxon, they drew the Middle–Late Cambrian boundary between these two as- semblages. Only eight species range from ¨Opik’s A. quasivespa Zone into the overlying Glyptagnostus stolidotus Zone, which contains 75 species with partly American (asaphiscid, aurita- mid, catillicephalid, norwoodiid, and raymondinid) and partly Chinese (damesellid and liostracinid) relationships.
Idamean The Idamean Stage was introduced by ¨Opik in 1963, originally conceived as representing five successive assemblage-zones: Glytagnostus reticulatus with Olenus ogilviei, Glypagnostus reticulatus with Proceratopyge nectans, Corynex- ochus plumula, Erixanium sentum, and Irvingella tropica with Agnostotes inconstans. This biostratigraphic scheme was criti- cized by Henderson (1976, 1977) who proposed an alternative
tum Zone was subdivided into a zone of E. sentum followed by a zone of Stigmatoa diloma. The Irvingella tropica–Agnostotes in- constans Zone is abbreviated to Irvingella tropica Zone. Hender- son’s scheme was adopted by Shergold (1982) and is followed here with the exception that the Irvingella tropica Zone be ex- cluded from the Idamean Stage and be recognized as the initial zone of the succeeding Iverian Stage (see Shergold, 1982, for justification; Shergold, 1993).
There is a major faunal crisis at the beginning of the Idamean where no Mindyallan species survive the stadial pas- sage ( ¨Opik, 1966), and very few genera persist into the early Idamean. There is also a major re-organization of trilobite families as outer shelf communities dominated by agnostoids, olenids, pterocephaliids, leiostegiids, eulomids, and ceratopy- gids abruptly replace those of the shallow shelf Mindyallan biota. Shergold (1982) recorded a total of 69 Idamean taxa, which permit a highly resolved biochronology capable of yield- ing very accurate international correlations.
Iverian The Iverian Stage (Shergold, 1993) was proposed for the concept of a post-Idamean–pre-Payntonian interval in the eastern Georgina Basin, western Queensland, the only region where a probable complete sequence has so far been described (Shergold, 1972, 1975, 1980, 1982, 1993). Paleontologically, the Iverian Stage is clearly distinguished. On the basis of trilo- bites, it is characterized by: the occurrence of the cosmopoli- tan genus Irvingella in Australia; the diversification of the agnostoid subfamily Pseudagnostinae during which Pseudag- nostus, Rhaptagnostus, and Neoagnostus separate, and become biostratigraphically important; diversification of the Leioste- gioidea, especially the families Kaolishaniidae and Pagodiidae; the first occurrence of the Dikelocephaloidea, Remopleuri- doidea, and Shumardiidae; and the separation of the true asaphids from ceratopygids. As a result, ten trilobite assem- blage zones have been recognized based on successive species of Irvingella, Peichiashania, Hapsidocare, and Lophosaukia (Sher- gold, 1993). Over 160 trilobite taxa occur in the type area of the Iverian Stage.
Payntonian As defined by Jones et al. (1971), the Paynto- nian Stage is recognized on the basis of its trilobite assem- blages (Shergold, 1975), its base lying at the point, in its type section (Black Mountain, western Queensland), where the co- mingled American–Asian assemblages of the Iverian are re- placed by others of total Asian affinity. These are dominated
suggested by Nicoll and Shergold (1992), Shergold and Nicoll (1992), and Shergold (1993). In ascending order, these zones are based on Sinosaukia impages, Neoagnostus quasibilobus with Shergoldia nomas, and Mictosaukia perplexa. These zones are fully calibrated by a comprehensive conodont biostratigraphy (Nicoll, 1990, 1991; Shergold and Nicoll, 1992). The Paynto- nian Stage contains a total of 30 trilobite taxa.
Datsonian The concept of the Datsonian Stage remains as defined by Jones et al. (1971) with its base located at the first appearance datum of the conodont Cordylodus proavus. Only rare trilobites, Onychopyge and leiostegiids, occur and these are insufficient for the establishment of a trilobite biostratigraphy. Accordingly, the Datsonian Stage is defined solely on the basis of conodonts (see discussion in Section 11.2.4 below).
N O RT H A M E R I C A N C A M B R I A N S TAG E S
The development of a stadial nomenclature for Laurentia has until recently (Palmer, 1998) been complicated by the con- cept of the biomere (“segment of life”) introduced by Palmer (1965a) and subsequently reviewed by him (1979, 1984), Stitt (1975), and Taylor (1997) among others. As originally defined, a biomere is a regional biostratigraphic unit bounded by abrupt extinction events on the shallow cratonic shelf. At these times existing evolving community complexes are replaced by low- diversity trilobite fauna dominated by simple ptychoparioid trilobites invading from the outer shelf or shelf break, which in turn rapidly evolve. Six such events have been suggested by Hollingsworth (1997), but the lower two are as yet undefined. In ascending order they are the “Olenellid,” “Corynexochid,” Marjumid, Pteropcephaliid, Ptychaspid, and Symphysurinid biomeres.
Ludvigsen and Westrop (1985) emphatically considered biomeres to be stages since they were based on an aggregate of trilobite zones and subzones. Palmer (1998) currently con- siders biomeres can be retained as subtly different units based on his (1979) modified concepts, and has subsequently (1998) proposed a sequence of stages for the Laurentian Cambrian based on trilobites, as follows. The pre-trilobite Cambrian still lacks defined stages.
Montezuman The Montezuman Stage (Palmer, 1998) is named from the Montezuma Range, Nevada. Its base is de- fined by characteristic fallotaspid trilobites, as in Morocco and
Siberia, which are followed by nevadiids and holmiines, and is distinguished by at least three families of Olenellina, which are different from ollenellids of the succeeding stage (see generic range charts in Palmer and Repina, 1993). The Montezuman Stage also contains the oldest Laurentian archaeocyathans.
Dyeran The Dyeran Stage (Palmer, 1998) is named from the town of Dyer, Nevada, and covers the biostratigraphic interval previously assigned to the Olenellus Zone, currently regarded as tripartite (Palmer and Repina, 1993). The base of the stage coincides with a major change in the olenelloid fauna following the nevadiid bearing late Montezuman. A similar change has been documented by Fritz (1992) in British Columbia. Olenel- lidae are characteristic.
Delamaran The Delamaran Stage (Palmer, 1998) has a boundary stratotype in the Delamar Mountains, Nevada, at the Oak Spring Summit section. The stage embraces the “Corynexochus” biomere and the Plagiura–Poliella, Al- bertella, and Glossopleura Zones in restricted shelf environ- ments. It is characterized by ptychoparoid, corynexochid, zacanthoidid, dolichometopid, and oryctocephalid trilobites. The biostratigraphic status quo has been presented by Palmer and Halley (1979) and, in part, by Eddy and McCollum (1998).
Marjuman The Marjuman Stage (Ludvigsen and Westrop, 1985; emended Palmer, 1998) is named from Marjum Pass in the House Range, Utah. Ludvigsen and Westrop (1985) orig- inally defined the base of the Marjuman Stage at the base of the Acidusus atavus Zone, but this is not a major extinction event according to Palmer (1998). Ludvigsen and Westrop (op. cit.) equated the Marjuman Stage with the Marjumiid biomere (Palmer, 1981), but this event occurs earlier on the in- ner shelf at the major change from trilobites of the Glossopleura Zone to those of the Ehmaniella Zone (Proehmaniella subzone), which has been documented by Sundberg (1994). On the open shelf this event is correlated to the base of the Bathyuriscus– Elrathina and Bolaspidella Zones, whose fauna characterize the early Marjuman.
The late Marjuman is characterized on the open shelf by cedariid trilobites, four zones of which are documented by Pratt (1992), distributed among the Cedaria and Kingstonia biofacies, regarded as bathymetrically related communities. Cedariid and crepicephalid trilobites characterize the inner shelf. The Mar- juman Stage embraces agnostoid zones from Pentagnostus prae- currens to Glyptagnostus stolidotus.
Steptoean The Steptoean Stage (Ludvigsen and Westrop, 1985) was named from Steptoe Valley, in the Duck Creek Range, near McGill, eastern Nevada. The base of the stage is defined at the base of the Aphelaspis Zone, which also cor- responds to the base of the Pterocephaliid Biomere (Palmer, 1965b). The Aphelaspis Zone contains Glyptagnostus reticulatus (Angelin), a very important species for international correla- tion of the Steptoean Stage. Above the Aphelaspis Zone, the Steptoean Stage embraces the Dicanthopyge, Prehousia, Dun- derbergia, and lower part of the Elvinia Zones in restricted-shelf environments, and the Glyptagnostus reticulatus, Olenaspella regularis, O. evansi Zones and the Parabolinoides calvilimbata and Proceratopyge rectispinata fauna, documented by Pratt (1992), in open-shelf environments.
Late Steptoean trilobites from the Elvinia Zone in SE British Columbia have recently been described by Chatterton and Ludvigsen (1998). The Steptoean Stage also embraces the significant Sauk II–III discontinuity event which is widespread across Laurentia (Palmer, 1981). Palmer (1998) has sug- gested a parastratotype section in the Desert Range, Nevada, where the extinction event at the Marjuman–Steptoean boundary is defined at the base of the Coosella perplexa Zone.
Sunwaptan This stage (Ludvigsen and Westrop, 1985) is named from Sunwapta Creek, Wilcox Peak, Jasper National Park, southern Alberta. The base of the Sunwaptan Stage is taken at the Irvingella major subzone of the Elvinia Zone, which Chatterton and Ludvigsen (1998) argue should be regarded as a separate zone. This is succeeded by the Taenicephalus Zone, Stigmatocephalus oweni fauna, and Ellipsocephaloides Zone in the early Sunwaptan, and the Illaenurus Zone and most of the Saukia Zone in the late Sunwaptan. More than 130 trilo- bite taxa of Sunwaptan age have been documented in Al- berta by Westrop (1986), and from the District of Mackenzie, North Western Territories, Canada, by Westrop (1995). Char- acteristic are dikelocephalid, ptychaspidid, parabolinoidid, saukiid, ellipsocephaloidid, illaenurid, and elviniid trilobites. The Sunwaptan Stage corresponds to the Ptychaspid Biomere (Longacre, 1970; Stitt, 1975).
Skullrockian The Skullrockian Stage (Ross et al., 1997) was named from Skull Rock Pass in the House Range, Utah. It was conceived as the earliest stage of the Ibexian Series. The base of the Skullrockian is defined by conodonts at the base of the Hirsutodontus hirsutus Subzone of the Cordylodus proavus Zone. On the trilobite zonal scale this level corresponds to the base of the Eurekia apopsis Subzone of the Saukia Zone
correlation is conodonts. The upper part of the Skullrockian Stage is Ordovician.
1 1 . 2 C A M B R I A N S T R AT I G R A P H Y 11.2.1 Faunal provinces
The Cambrian Period is of particular biological interest in that it marks the appearance of multicellular phyla that have popu- lated the Earth since.
Faunal provincialism was strongly developed and bios- tratigraphic zonal schemes generally cannot be applied be- yond their provincial boundaries. This is most marked in the Early Cambrian where two major trilobite faunal provinces were developed, one characterized by Redlichi- ina (Redlichian Province), composed of endemic redlichi- ids and pandemic Ellipsocephaloidea and eodiscid fauna, the other by Olenellina (Olenellian Province), composed of en- demic olenellids and pandemic ellipsocephaloids and eodiscid fauna (Chang, 1989, 1998; Palmer, 1973; Palmer and Repina, 1993).
Debrenne (1992) suggests that three archaeocyathid faunal provinces existed in the Early Cambrian: an Afro–European Province, which possibly extends to China, characterized by Anthomorphidae; an Australo–Antarctica Province character- ized by Flindersicyathidae, Metacyathidae, and Syringocne- midae; and a Siberian Province characterized by all of these genera. Kruse and Shi (2000), on the other hand, applying so- phisticated statistical analysis to the distribution of archaeocy- athans, recognizes five provinces based on Siberia–Mongolia, Europe–Morocco, Central–East Asia, Australia–Antarctica, and North America–Koryakia. During the Middle and Late Cambrian, Chang (1989) recognizes Pacific Provinces, based on Centropleuridae, Xystriduridae, and Olenidae, respectively; and Atlantic Provinces, based on Paradoxidae and Olenidae, respectively.
Jell (1974) recognized three trilobite provinces: Colum- ban in North and South America; Viking in Europe, maritime North America and NW Africa; and Tollchuticook in Asia, Australia, and Antarctica. Thus the trilobite fauna of Aus- tralia, China, and Kazakhstan have many elements in common, but differ markedly from those of North America (Jell, 1974; Palmer, 1973). In the latest Cambrian, conodonts provide fine biostratigraphic subdivision and substantially aid global cor- relation.
pods. They enable fine stratigraphic subdivision and good cor- relation reliability in deposits of the continental shelf and plat- form within faunal provinces (for general statements on the occurrence of trilobites see Whittington, 1992, and Kaesler, 1997).
In the Late Cambrian, trilobite diversification and evolu- tionary turnover was extreme and fine zonations are estab- lished on the major paleocontinents (Jago and Haines, 1998). Through the late Middle and Late Cambrian, an interval of 18 myr (Fig. 11.2), there are 26 fossil zones, averaging 700 000 years each in duration. One group of trilobites, the agnostids, were pelagic and pandemic and enable global correlation of the Middle and Late Cambrian (Westerg˚ard, 1946; ¨Opik, 1979; Shergold and Laurie, 1997).
Australia, China, Russia, Scandinavia, and North America have the most complete Cambrian trilobite zonal successions. Those of Australasia and North America are shown in Fig. 11.1. Differing biostratigraphic philosophies, developed since the late eighteenth century, have resulted in different concepts of trilobite zones. In North America, for example, the concept of a zone is based on the range of a characteristic genus, which is subdivided into subzones by species or associations of species (interval-zones, Robison, 1994). A dual biostratigraphy (zones and biofacies) currently operates in Canada (Ludvigsen et al., 1986). In Australia, species-zones or assemblage-zones have been most commonly applied (index fossil biostratigraphy), as in Scandinavia, Russia, and China. In Scandinavia, the Late Cambrian is minutely divided into 32 subzones on the basis of successive species of olenid trilobites (Henningsmoen, 1957).