Palaeogeographical Controls on the Cambrian Trilobite Immigration and Evolutionary Patterns Reported in the Western Gondwana Margin

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Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35 www.elsevier.com/locate/palaeo

Palaeogeographical controls on the Cambrian trilobite immigration and evolutionary patterns reported in the western Gondwana margin

J. Javier AŁ lvaro a;Ã, Olaf Elicki b, Gerd Geyer c, Adrian W.A. Rushton d, John H. Shergold e

a UMA 8014 CNRS, Universite¤ de Sciences et Technologies de Lille, Sciences de la Terre, 59655 Villeneuve d’Ascq Cedex, France b Institut fu«r Geologie, TU Bergakademie Freiberg, Bernhard-von-Cotta-Str. 2, 09596Freiberg/Sachsen, Germany c Institut fu«r Pala«ontologie, Universita«tWu«rzburg, Pleicherwall 1, 97070 Wu«rzburg, Germany d Palaeontological Department, The Natural History Museum, London SW7 5BD, UK e La Freunie, Benayes, 19510 Masseret, France

Received 12 April 2002; received in revised form 18 July 2002; accepted 25 January 2003

Abstract

Southward drifting of the western Gondwanan margin during the Cambrian has been demonstrated by means of both palaeomagnetic methods and lithological indicators of climate (such as carbonates and evaporites). Recent improvements in biostratigraphical correlations permit an enhanced understanding of the climatic and palaeobiogeographical constraints that controlled the distribution of Cambrian benthic communities. Palaeogeo- graphical and biogeographical reconstructions based on trilobites are reported in this paper in order to test interaction between migration, speciation and extinction rates. The variability of the documented biogeographical patterns is directly related to species diversity, in which wider distribution coincides with transgressive trends and subsequent connection of neighbouring platforms. Early Cambrian trilobite faunas show a high degree of both substrate control and endemicity, although transgressions led to parallel shifts in faunal compositions. By contrast, Mid-Cambrian trilobite faunas are relatively uniform across western Gondwana, and latest Mid- and Late Cambrian associations document influence of an increased similarity with Asian trilobite faunas. ß 2003 Elsevier Science B.V. All rights reserved.

Keywords: biogeography; palaeogeography; extinction; trilobites; western Gondwana; Cambrian

1. Introduction

* Corresponding author. Tel.: +33-3-2033-6392; Four disciplines are the main sources for pa- Fax: +33-3-2043-6900. laeogeographical reconstruction: palaeomagne- E-mail addresses: [email protected] tism, sedimentology, palaeoclimatology, and bio- (J. Javier AŁ lvaro), [email protected] (O. Elicki), [email protected] (G. Geyer), geography. The boundaries of the postulated [email protected] (A.W.A. Rushton), plates and terranes (commonly discussed from [email protected] (J.H. Shergold). the viewpoints of geophysics, tectonophysics and

PALAEO 3071 9-5-03 6 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35 structural geologists) do not always match the cally the reproductive communication of trilobites biogeographical boundaries worked out by palae- was maintained by means of larvae, the Cambrian ontologists and biostratigraphers. However, do trilobite-based biogeographical patterns of the the biogeographical boundaries that prevented re- western Gondwanan margin, as it drifted towards productive communication necessarily coincide the South Cambrian pole, are not homogeneous, with those of the tectonic plates? In some cases and the changes in patterns of dispersal and evo- they do; many plate and terrane boundaries, how- lution of some trilobite families remain uncertain. ever, do not correspond with biogeographical bar- This paper o¡ers an examination of the biogeo- riers and, on the contrary, a single continental graphical patterns displayed by the Cambrian tri- margin can display barriers, particularly during lobites on the western margin of Gondwana, as a regressive conditions, which separate di¡erent method of testing the established palaeogeograph- groups of organisms that are signi¢cant biogeo- ical models. graphically. As a result, a biogeographical unit contains similar biotas, but may or may not show physical continuity. 2. Basins and platforms: a nomenclatural approach One of the main projects of the International Subcommission on Cambrian Stratigraphy (ISCS) The Moroccan and European Hercynian (or is the proposal of a global chronostratigraphical Variscan) massifs, the latter located south of the chart useful for international correlation (see Rheno^Hercynian zone and north of the Alpine Geyer and Shergold, 2000, for a recent statement realm (Fig. 1), contain a mosaic of Cambrian suc- of the problem). One of the major di⁄culties is cessions assigned to the western Gondwanan mar- the resolution of the drastic provincialism exhib- gin, namely Morocco, the Iberian and Armorican ited by the benthic fauna, such as the trilobites massifs, Montagne Noire, Sardinia, Saxo^Thurin- (Palmer, 1998). From the earliest occurrences of gia and Bohemia. Associated with the same mar- trilobite faunas there is clear evidence of biogeo- gin are other small cratonic domains recognised in graphical di¡erentiation into two main provinces: the southern British Isles; some of their bound- the olenellid province, comprising much of Bal- aries are less well-de¢ned (Cocks et al., 1997). tica, Laurentia, and Siberia, and the redlichiid province of Gondwana (Palmer, 1972). Subse- 2.1. Morocco quently, an overlapping bigotinid province was distinguished (Pillola, 1991a). For the Mid- and The Neoproterozoic(?)^Cambrian successions Late Cambrian, Palmer (1972) reported a more of the Moroccan Atlas are located in the Anti- complicated scheme involving four provinces for Atlas and central High Atlas mountains, although the continental seas, and three other ones for ex- some disconnected outcrops occur in the Jbilet posed shorelines. In addition, conodont distribu- and Rehamna regions, and the Meseta plateau. tion in the Late Cambrian indicates the presence The axis of the Late Proterozoic to Early Pa- of two faunal realms (Bergstro«m, 1990), a tropical laeozoic Souss Basin (Geyer, 1989) roughly coin- Midcontinent region and a cool Atlantic region. cides with the modern trend of the Anti-Atlas One geographical area where the biostrati- (SW^NE). Common west-to-east facies changes graphical correlations are still strongly debated throughout the Cambrian successions re£ect the is the western Gondwana margin, which includes eastern setting of proximal areas (Destombes et the Mediterranean area and much of western and al., 1985; Geyer and Landing, 1995; Geyer et central Europe. Geophysical data that would in- al., 1995). dicate Cambrian plate boundaries are scarce within this area. However, biogeographical disparities 2.2. The Iberian Massif based on detailed and extensive trilobite studies re£ect major palaeogeographical di¡erences and The Cambrian tectonosedimentary outcrops of relative sea-level £uctuations. Although theoreti- the Iberian Massif were subdivided by Lotze

PALAEO 3071 9-5-03 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35 7

TR ANS - EUROPE

- POLISH FA AN ULT CANTABRIAN WEST CALEDONIDE ZONE RTH - GERM ASTURIAN- NO LEONESE ZONE ARMORICAN S MASSIF RHENO-HERCYNIAN

SAXO-THURINGIA ANU MOLD ? CENTRAL- ? -BIAN IBERIAN DEMANDA TEPLA- ZONE MOUNTAINS BARRANDIAN SOUTH CENTRAL PORTUGUESE MASSIF ZONE PYRENEES ALPINE REALM OSSA-MORENA ZONE IBERIAN MONTAGNE NOIRE CHAINS Western Plateau

High Atlas SW SARDINIA Anti-Atlas

Pre-Hercynian outcrops of western and central Europe, and Morocco

Fig. 1. Main tectonostratigraphical units of the Variscan Belt (modi¢ed after Franke, 2000), and northwestern Africa.

(1961) into zones, viz. the Cantabrian (CZ), West- other hypothesis considers the Iberian Massif as a ern Asturian^Leonese (WALZ), Central Iberian complex tectonic mosaic constructed from two (CIZ) and Ossa^Morena (OMZ) zones. Their evo- distinct plates that collided during the Early De- lution has been interpreted in terms of two dis- vonian (Acadian orogeny; Mart|¤nez-Garc|¤a and tinct troughs: the CantabroÎberian and the An- Rolet, 1991). Because of this discussion, and the dalusian basins, the latter including the OMZ. displacement of the OMZ from NW to SE along The CantabroÎberian Basin comprises the CZ, the Badajoz^Co¤rdoba shear zone during the Her- WALZ, northern CIZ, and their eastern prolon- cynian orogeny, we will illustrate the OMZ as a gation into the Demanda Mountains (DM) and neighbouring basin of the western Gondwanan the Iberian Chains (IC). It was limited to the margin. NE by the CantabroÊbroan Land area, which constituted the main source of sediments for 2.3. The southern British Isles (‘eastern Avalonia’) both the CantabroÎberian and the Pyrenean basins (Carls, 1983), and in the SW by some uplifted The main structural elements are the Midland areas (or median highs; Lotze, 1961), which epi- Platform, bounded to the NW and NE by depo- sodically supplied sediments (Aramburu et al., sitional troughs, and truncated to the south by the 1992). Hercynian front. The trough to the NE is the The geodynamic a⁄nity of the OMZ is still concealed ‘Eastern England Caledonide Belt’, in controversial. One hypothesis supposes its accre- which Cambrian rocks of the Tornquist Sea may tion to the Iberian Autochthon (which would be present, but have not been proven. To the NW include the rest of northern zones) during the of the Midland Platform lies the Welsh Trough, Cadomian orogeny (Quesada, 1991), whereas an- an elongated ensialic basin that experienced sub-

PALAEO 3071 9-5-03 8 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35 sidence throughout much of the Cambrian Period. area, a mosaic of platforms is represented in the The Welsh Trough is limited to the NW by the Cambrian outcrops of the Pyrenees and Mon- tectonically active Monian Terranes that behaved tagne Noire. The Cambrian stratigraphical and as a positive area through the Cambrian, and biogeographical patterns of southwestern Sardinia which separate the Welsh Trough from the Lein- reveal a close similarity to the Montagne Noire so ster Basin of SE Ireland (Blucket al., in Cope et that this platform can be considered neighbouring al., 1992); the latter contains Cambrian rocks but the Montagne Noire segment at that time. has not yielded any trilobites. To the north, the Cambrian of Scotland is part of Laurentia, and is 2.6. Saxo^Thuringia and Bohemia not discussed further here. The Cambrian of England and Wales is devel- According to Havl|¤c›eket al. (1994) , both the oped in three main facies: (1) basinal clastic de- German and Barrandian (an area situated in the posits of the Welsh Trough, exposed in two main central part of the Bohemian Massif) Cambrian areas in northern Wales (Harlech Dome and Ar- deposits belong to the ‘Perunica terrane’. This fon) and two in the south (St. David’s and Llan- crustal segment was de¢ned as a separate micro- gynog areas); (2) outer-shelf clastics on the Mid- plate occupying ‘the major part of the Bohemian land Platform (Nuneaton); and (3) shallow-water Massif, and involving the Moldanubian, Barran- clastics with very local limestones in the Welsh dian and Saxothuringian (Saxothuringian^Lu- Borderland (Comley and Rushton areas), on the gian) Zones’ (Havl|¤c›eket al., 1994) . This interpre- margin of the Midland Platform. The geology of tation was based on biogeographical a⁄nities of these areas was reviewed by Rushton (1974) and benthic faunas with those of Baltica and a north- Rushton et al. (1999), and the palaeogeography ward drift of Perunica from high (57.9‡S for the was summarised by Brasier et al. (in Cope et al., Lower Cambrian Paseky Shale) to lower latitudes 1992). McKerrow et al. (1992) showed eastern (31.1‡S for Middle Cambrian sediments and Avalonia located close to Morocco at a latitude 28.6‡S for Upper Cambrian andesites; Krs et of about 40‡S in the Early Cambrian, drifting al., 1987; Vra¤na and Sítefldra¤, 1997). By contrast, south to about 60‡S in the Late Cambrian Kukal (1971) assumed a semi-arid, rather warm (L.R.M. Cocks, pers. commun., 2002). climate of continental type for the Lower Cam- brian. The Barrandian palaeolatitude setting has 2.4. The Armorican Massif been widely debated. Recently, Linnemann et al. (2000) revised the concept of Perunica, eliminat- The Cambrian of the Armorican Massif con- ing the Saxo^Thuringia area; they distinguished sists dominantly of siliciclastic deposits. The facies the Brittany^Normandy, Perunica and Saxo^ strongly depends on the local position on the shelf Thuringia terranes, which would form the so- and includes locally Lower Cambrian carbonates called ‘Armorican Terrane collage’. Discussion deposited in nearshore environments. Its apparent about the existence of these microplates is beyond polar wander path can be superimposed across the aims of this paper. Nonetheless, two tectono- the NeoproterozoicÊarly Palaeozoic interval on stratigraphical areas are considered here: the Bar- the Gondwana path. A counter-clockwise rotation randian and Saxo^Thuringian areas. The latter of the massif has been proposed for Early Palaeo- comprises a fault-bounded crustal fragment that zoic times (Young, 1990), based on sedimentolog- contains Cambrian outcrops in the Doberlug Syn- ical and palaeogeographical similarities with some cline, Thuringia and the Franconian Forest area. Portuguese outcrops. The palaeogeographical a⁄nity of the Go«rlitz Syncline o¡ers some uncertainties but is here con- 2.5. The Montagne Noire and southwestern sidered as a relic of an overlapping succession on Sardinia the Cadomian basement of Saxo^Thuringia. In the Barrandian area, a distinct Cambrian To the north of the CantabroÊbroan Land sedimentary trough, the Pr›¤|bram^Jince Basin, is

PALAEO 3071 9-5-03 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35 9 commonly recognised. It contains a thickLower bination of the Cambrian Moroccan and Iberian Cambrian continental succession covered by Mid- scales for the Lower Cambrian, and the Iberian^ dle Cambrian, transgressive marine fossiliferous Montagne Noire scale for the Middle Cambrian. shales (the Jince Formation), and Upper Cambri- The sparse Upper Cambrian faunas are related to an volcaniclastic complexes. Laterally, the Jince the Australian succession, though in Britain there Formation crops out in the Skryje^Tyr›ovice area. are su⁄cient olenid trilobites to correlate with the In the biogeographical discussions expressed be- Scandinavian succession. For Britain, the strati- low, the trilobites of the Skryje^Tyr›ovice area graphical classi¢cation used in Cowie et al. will be reported with those of the Pr›¤|bram^Jince (1972) is employed because it supplies a single Basin. standard for England and Wales and facilitates reference to Rushton’s (1974) stratigraphical summary. It is recognised that the lower two of the 3. Cambrian palaeogeographical evolution: British regional series divisions ^ Comley and St. an overview David’s series ^ do not correspond precisely with the usage of Lower and Middle Cambrian in use Lackof uniformity in the successions of faunas elsewhere, the inter-series boundary lying rather and depositional environments in the western higher than the Lower^Middle Cambrian bound- Gondwanan margin has led to the development ary in Morocco (Geyer, 1990a). The base of the of di¡erent regional biostratigraphies (Fig. 2). In Merioneth Series corresponds closely to that of order to avoid nomenclatural confusion in chro- the Upper Cambrian as generally understood nostratigraphical correlations, we here use a com- and its top lies very close to the internationally

Fig. 2. Chronostratigraphic correlation of regional charts (based on Thomas et al., 1984; Geyer, 1990a; AŁ lvaro and Vizca|«no, 1998; Sdzuy et al., 1999; Geyer and Shergold, 2000).

PALAEO 3071 9-5-03 10 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35

Fig. 3. Palaeogeographical evolution interpreted in the Cambrian basins and platforms of the western Gondwanan margin across eight intervals (not to scale).

PALAEO 3071 9-5-03 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35 11

Fig. 3 (Continued).

PALAEO 3071 9-5-03 12 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35 agreed base of the Ordovician (Landing et al., tions). The late Late Cambrian is unknown from 2000). Fig. 3A,B provides graphic representation the Moroccan Atlas but appears in part to be of the changing palaeoenvironmental relation- characterised by some 115 m of shallow-marine ships discussed on the following pages. ¢ne-grained siliciclastics (Dar Bou Azza Forma- tion) in the Moroccan Meseta (Mergl et al., 1998). 3.1. Morocco In this area this unit overlies a signi¢cant unit of 100 to 200 m of sandstones representing another The Late Proterozoic (‘Panafrican’) orogeny in important regressive unit of apparently earliest Morocco and northwestern Africa was followed Late Cambrian shoreline deposits, the El Hank by deposition of a Neoproterozoic(?)^Cambrian Formation. cover succession that illustrates a long-term transition in lithofacies associations, and includes a 3.2. The Iberian Massif thickinterval (locally more than 2000 m) of carbonate-dominated rocks followed by siliciclastic- The Cambrian rocks rest unconformably on dominated rocks higher in the Cambrian in the Neoproterozoic rocks in the whole massif except western Anti-Atlas. The Neoproterozoic(?)^Cam- in the CIZ, where the Vendian^Cambrian transi- brian transition in this region, viz the Adoudou, tion is tentatively located in the Pusa Shales Lie de vin, and Igoudine Formations, is dominat- (Brasier et al., 1979). The transition contains mega- ed by restricted marine platform limestones and breccias, conglomerates, quartzites, limestones dolostones, and is overlain by a long-term shale^ and anoxic sediments deposited in a mixed shelf carbonate cycle in the Lower Cambrian, the and slope apron (Valladares, 1995). The Cambri- AmouslekFormation. Uppermost Lower Cam- an commences with a dominantly terrigenous suc- brian units include up to 200 m of ¢ne-grained cession (or lower lithosome): the Herrer|¤a Forma- siliciclastics with relatively minor nodular and tion, 900^1700 m thick, in the CZ, representing bedded limestones (Issafen Formation), overlain deltaic deposits with £uvial and intertidal episodes by the higher energy, shallow-marine, sandstone- (Rodr|¤guez Ferna¤ndez et al., 1991); the Ca¤ndana dominated facies of the Asrir and Tazlaft Forma- Group, up to 2500 m, in the WALZ with shallow- tions, which characterises the Lower^Middle water marine and continental facies (Crimes et al., Cambrian transition. This period re£ects a signi¢- 1977); the Tamames^Azorejo Formations in the cant change in sedimentation, related to an im- CIZ, 500^600 m thick; the Torrea¤rboles Forma- portant phase of relative sea-level £uctuation tion, 0^350 m thick, in the OMZ with shallow which caused a major regression followed by an subtidal and intertidal deposits; and the Ba¤mbola immediate transgressive event (Geyer, 1989; and Embid Formations, 500^900 m thick, in the Geyer and Landing, 1995). IC, interpreted as progradational deltaic systems Limited carbonates also characterise the lower and storm- and wave-dominated nearshore set- Middle Cambrian. Fossil-hash limestone beds are tings passing upward into tidally in£uenced sub- regularly encountered only in the ‘Bre'che a' Mic- tidal and intertidal environments. During Early macca’ Member (lower part of the Jbel Wawrmast Cambrian times, the OMZ displayed the setting Formation, up to 300 m thick). Progressively of rifting processes (Vegas, 1978; Mata and stronger, higher-latitude in£uences are shown by Munha¤, 1990). the thickshallow-marine deposits that accumu- The second lithosome re£ects the diachronous lated during most of the Mid- and Late Cambri- establishment of mixed carbonate^siliciclastic an; they are a monotonous succession, up to 700 platforms, ranging from Ovetian to early Mid- m thick, of siliciclastic sediments representing Cambrian times: the lower member of the La¤n- sandy shoals and tidal-£at environments as well cara Formation (150^225 m thick) in the CZ, as £uvial to deltaic environments prograding on and the Vegadeo Formation (50^500 m) in the distal muddy substrates (Jbel Afraou, Rich Khli- WALZ, displaying peritidal to shallow-water fa, Bailiella, Azlag, and Jbel Lmgaysmat Forma- deposits with isolated microbial^archaeocyathan

PALAEO 3071 9-5-03 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35 13 buildups (Zamarren‹o, 1972; Russo and Bech- representing storm-dominated o¡shore, prograd- sta«dt, 1994; AŁ lvaro et al., 2000b). Mixed plat- ing sandy shoals, and tidal-£at environments (AŁ l- forms were established across the late Ovetian^ varo and Vennin, 2001). Marianian interval in the IC (the Jalo¤n, Ribota and Hue¤rmeda Formations; 300^500 m thick), 3.3. The southern British Isles Los Navalucillos and Tamames Limestones in the CIZ (120^600 m thick), and the Pedroche In the southern British Isles, Cambrian rocks and Alconera Formations in the OMZ (350^900 occur in England and Wales in scattered inliers, m thick). These contain stromatolitic and archae- the largest of which are: (1) the Harlech Dome ocyathan-microbial buildups, sandstones and var- (and the St. Tudwal’s Peninsula), and the Arfon iegated shales deposited in shallow subtidal to in- area of northern Wales; (2) Pembrokeshire in tertidal and supratidal environments; locally they south Wales; (3) a number of small outcrops in bear anhydrite or gypsum pseudomorphs (see AŁ l- Shropshire; (4) the Malvern Hills; and (5) the varo et al., 2000a, and references therein). By con- Nuneaton area in Warwickshire, British Mid- trast, the mixed sedimentation of the second lith- lands. osome was interrupted in the IC, CIZ and OMZ The lithostratigraphical successions of these by early Bilbilian regressive siliciclastic sediments areas di¡er greatly. The relatively thickand com- related to the Daroca regression (AŁ lvaro and Ven- paratively complete succession of northern Wales nin, 1998), lithostratigraphically recognised as the includes Lower Cambrian deposits consisting of Daroca (IC), Los Cortijos^Endrinal (CIZ) and s 450 m of deltaic sandstones (Dolwen Grits) Castellar (OMZ) Formations (50^150 m thick). overlain by up to 200 m of prodeltaic shales An early Bilbilian prograding shoreline is postu- (Llanbedr Slates), and a formation of up to 800 lated in these areas, in which coastal and shoal m of proximal turbiditic sandstones with shale complexes grew and migrated seawards during intercalations (Rhinog Grits). Middle Cambrian times of rapid sediment in£ux and regressive con- deposits are generally basinal turbiditic sand- ditions. stones and shales, together about 700 m thick, The Lower^Middle Cambrian transition is capped by 100 m of darkfossiliferous shales. characterised by a signi¢cant change in the style Manganese-bearing rocks occur close to the base of sedimentation, related primarily to an impor- of the Middle Cambrian. The Upper Cambrian tant phase of tectonic activity. As a result, an consists of 2000 m of ¢ne-grained shales (or irregular topography was widely developed on slates) and feldspathic £ags, capped by a con- the platforms, which were di¡erentiated into a densed unit of blackmudstone, the Dolgellau mosaic of horsts and grabens. In situ carbonate Formation, about 100 m thick. The lower Upper production on relative topographic highs gave rise Cambrian (Maentwrog Formation) is basinal, but to the ‘griotte’ facies of the upper member of the the Festiniog and Dolgellau are open-shelf depos- La¤ncara (CZ) and Mansilla (IC) Formations. its. The third lithosome re£ects the disappearance The successions in Pembrokeshire show a com- of carbonate deposition in the whole Iberian Mas- parable depositional sequence, commencing with sif; it is interpreted as shallow platform deposits the Lower Cambrian Caerfai Group, about 300 m of intertidal and braid-plain deltaic environments thick, consisting of sandstones and shales overly- in the Oville Formation (80^800 m) and the lower ing a transgressive basal conglomerate deposited part of the Barrios Formation (300^400 m thick) in a shallow-marine, continuously subsiding ba- in the CZ (Aramburu et al., 1992; Aramburu and sin. A depositional breaktesti¢es a regressive Garc|¤a-Ramos, 1993), the shallow-marine depos- trend near the top of the group. The lower Middle its of the Cabos Series (up to 4000 m thick; Bald- Cambrian Solva Group consists of roughly 500 m win, 1977; Marcos and Pe¤rez Estau¤n, 1981), and of sandstones and shales deposited in relatively the Murero Formation, Aco¤n Group and Valcon- high-energy waters, whereas the upper Middle cha¤n Formation in the IC (600^1400 m thick) Cambrian, about 250 m of pyritous mudstones,

PALAEO 3071 9-5-03 14 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35 termed the Menevian Group, suggests quiet, oxy- Carteret Formation, ca. 1000 m, consisting of lit- gen-depleted environments. The Upper Cambrian toral alternations of shales and silty sandstones ‘Lingula Flags’ (more than 600 m thick) are shal- rich in microfossils and ichnofossils of Cordubian low-water storm-in£uenced deposits of a rapidly age; and (3) the Saint-Jean-de-la-Rivie're Forma- subsiding marine basin. tion, ca. 200 m thick, made up of peritidal alter- The shelf deposits in the English Midlands nations of limestones and siltstones, containing commence with Early Cambrian sandstones, the salt pseudomorphs, microbial^archaeocyathan Hartshill Formation (260 m thick), which shows buildups and oolitic shoals. Other Lower Cambri- progressive deepening from a basal shoreface an successions are known in central and southern sand. There follow 600 m of outer-shelf mud- Normandy and Maine, and comprise small shelly stone, the Stockingford Shales, which extend fossils, brachiopods and ichnofossils. A post-oro- from the higher Lower Cambrian to the top of genic volcanism tookplace along two volcano^ the Upper Cambrian. The upper Middle Cambri- tectonic structures: ignimbrite sequences underly- an and the uppermost Upper Cambrian show ing Lower Cambrian sediments, and the Maine strong lithological and palaeontological similar- graben interbedded with Lower Cambrian to ities to the correlative rocks in Wales, though Arenig? sediments. Other Cambrian fossiliferous the formations are thinner. The upper Middle rocks are incompletely known, such as a Middle Cambrian to Tremadoc succession is relatively Cambrian trilobite assemblage from the north- complete. The successions in Shropshire, on the eastern Vende¤an Massif and a suspected Late margin of the Midlands Platform, partly depos- Cambrian brachiopod assemblage from the Chan- ited in fault-bounded depocentres (Smith and tonnay synclinorium. Rushton, 1993), suggest the in£uence of shallow water almost throughout. At the top of the Com- 3.5. The Montagne Noire and southwestern ley Series are the condensed Comley Limestones Sardinia that represent shallow-marine carbonates containing the best preserved and most important late Both areas display the same three-fold litho- Early Cambrian (in the traditional British sense) some subdivision as that reported in the CZ trilobite faunas of the British Isles. and WALZ for Early to Mid-Cambrian times. In summary, the lowest Cambrian deposits The Neoproterozoic^Cambrian transition is not were deposited unconformably on a variegated clearly identi¢ed in the former, where the lower volcanic basement in both Wales and England, terrigenously dominated lithosome begins with whereas younger Cambrian sediments in Wales the Marcory (more than 1000 m thick) and Ma- formed in a subsiding ensialic basin, while their toppa (300^600 m) Formations. The second, Ove- English equivalents formed on the subsiding Mid- tian^Bilbilian, lithosome represents the establish- land Platform. ment of carbonate platforms; in the southern Montagne Noire these are subdivided into the 3.4. The Armorican Massif Pardailhan, Lastours and Pont de Poussarou For- mations (100^500 m thick), and in Sardinia the The Cambrian rocks of the Armorican Massif Punta Manna, Santa Barbara, Planu^Sartu and unconformably overlie the Cadomian basement. San Giovanni Formations (600^1200 m thick). The most representative and complete Lower These platforms were widely colonised by build- Cambrian succession is that of the North Conten- ups of microbial-archaeoyathan communities, as- tin Syncline. A SW^NE-trending trough was ¢lled sociated in Sardinia with a tensional tectonic ac- by a succession ranging from 590 to 2100 m in tivity re£ecting the establishment of an isolated thickness (Dore¤, 1994) with, from bottom to top: carbonate platform (see a summary in Perejo¤net (1) the Couville Formation, up to 400 m thick, al., 2000). In both areas the Lower^Middle Cam- composed of conglomerates and sandstones inter- brian transition displays the tectonic instability bedded with a volcanoclastic complex; (2) the already reported in the CZ and the IC, with de-

PALAEO 3071 9-5-03 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35 15 velopment of palaeotopographies and deposition deposited on an open siliciclastic platform. The of the ‘griotte’ facies (La Tanque and Campo Pi- Middle Cambrian of the Franconian Forest con- sano Formations; up to 80 m thick). After drown- sists of isolated outcrops that represent at least ing of the platforms and burial of the palaeoto- ¢ve di¡erent formations, in ascending order the pography by o¡shore shaly sediments (Coulouma Galgenberg, Wildenstein, Triebenreuth, Lipperts- and lower Cabitza Formations; 30^80 m thick), gru«n and Bergleshof Formations, of unknown the evolution in both areas di¡ered drastically. thickness, all characterised by signi¢cant trilobite The southern Montagne Noire exhibits the pro- faunas. gradation of sandy shoals (Ferrals Formation; The Early Cambrian of the Go«rlitz Syncline is 130^200 m thick) and tidally induced systems very incomplete, but has yielded important trilo- (La Gardie Formation; 0^500 m thick), followed bites. The Charlottenhof Formation is a fragment by important carbonate developments leading to of a carbonate platform and represents the tran- deposition of new mixed carbonate^siliciclastic sition from rather shallow to deep subtidal con- sediments on intra-shelf ramps (Val d’Homs For- ditions (Ludwigsdorf Member) and subsequently mation; 60^200 m thick). This episodic carbonate to deeper platform environments (Lusatiops Mem- sedimentation is unique across the whole western ber). The age of the formation is late Marianian Gondwanan margin for Late Cambrian times. By or late Banian (Elicki, 1994; Geyer and Elicki, contrast, southwestern Sardinia shows a Middle^ 1995). Finally, the Cambrian (s.l.) of Thuringia Upper Cambrian shale-dominated deposition (Berga Anticline) is known only from two bore- (Cabitza Formation), distinctly condensed and re- holes: it is a slightly metamorphosed carbonate markably uniform (ca. 190 m thick; Loi et al., succession that has yielded a poorly preserved mi- 1995), which gradually passes into the Tremado- crofauna, with siliciclastic deposits at the base cian. (Elicki, 1997).

3.6. Saxo^Thuringia 3.7. Bohemia

Lower and Middle Cambrian successions occur The Pr›¤|bram^Jince Basin of the Barrandian in the Doberlug^Delitzsch and Go«rlitz synclines, area contains about 2000 m of Lower Cambrian the Franconian Forest and Thuringia (Berga An- continental conglomerates and sandstones, punc- ticline). Early Cambrian relationships between tuated by the deposition of sediments in a brack- them are controversial because they are of di¡er- ish environment (the Paseky Shale) containing en- ent ages and the limited occurrence of fossils. demic merostome(?) arthropods and possibly Upper Cambrian successions are generally not phyllocarids (Chlupa¤c›, 1995). Deposition of Mid- preserved, as a result of uplift combined with de- dle Cambrian transgressive marine fossiliferous nudation and weathering (Linnemann and Busch- shales was accompanied by two major palaeogeo- mann, 1995). The incomplete Early Cambrian graphical changes: (1) an eastward shift of the succession of the Doberlug Syncline represents a area of maximum subsidence, and (2) a change carbonate ramp with archaeocyathan-microbial in orientation of the main structural directions buildups (Zwethau Formation, more than 700 m and longitudinal basin axis from a NE^SW to a thick) developed during early Ovetian times on NW^SE trend (Havl|¤c›ek, in Chlupa¤c› et al., 1998). the Cadomian basement of Saxo^Thuringia (Eli- The Jince Formation (up to 400 m thick) consists cki, 1999). The Lower^Middle Cambrian transi- of shales and ¢ne-grained sandstones containing a tion is unknown because of the scarcity of out- rich and diverse fossil fauna of trilobites, brachio- crops and structural di⁄culties. The Middle pods and echinoderms. The unfossiliferous Upper Cambrian of the Doberlug area (Tro«bitz and Cambrian deposits consist of volcanic complexes Delitzsch Formations, ca. 600 m thick), early with rhyolitic e¡usions and pyroclastic layers. In Leonian^Caesaraugustian in age, is relatively the Skryje^Tyr›ovice area, the Cambrian succes- fossiliferous (Sdzuy, 1972). The sediments were sion consists only of the lower part of the Jince

PALAEO 3071 9-5-03 16 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35

Formation, which rests unconformably on Upper western Australian Current (parallel to the west- Proterozoic rocks. These outcrops re£ect a Mid- ern face of Australia) that disappeared with the dle Cambrian deposition in a ‘channel-like’ Eocene opening of a gap between both continents. trough a¡ected by synsedimentary deformation Apparently a similar western Gondwanan SW^ and partly eroded during Upper Cambrian regres- NE current rising in latitude from polar areas sive conditions. The thickness of the Middle Cam- operated during Cambrian times, which obviously brian decreases from about 200 m in Skryje to a¡ected faunal migrations and the palaeoclimates. several tens of metres towards the northeast. The lackof extensive carbonate deposition across the Precambrian^Cambrian transition in the western Gondwanan margin, except the 4. Palaeooceanographic and palaeoclimatic Adoudou and Lie-de-vin Formations in Morocco, constraints can be explained by a combination of active Ca- domian orogenic phases, and active source re- The western Gondwanan margin during the gions, which supplied coarse-grained siliciclastics Cambrian is commonly portrayed as oriented ap- and inhibited carbonate production. Much of our proximately SW^NE in a position on the South- understanding of the Lower Cambrian palaeocli- ern Hemisphere (McKerrow et al., 1992). As a mate evolution on the western Gondwanan mar- consequence of this orientation, the shape of the gin comes exclusively from lithological indicators tropical zones was a¡ected by the course of major of climate, such as limestone (mainly reefal) and ocean currents transporting cool waters towards evaporite precipitation (AŁ lvaro et al., 2000a). the tropics (Fig. 4). This would have caused the Lower Cambrian salinities seem to have been epi- tropics to occupy a narrower latitudinal area on sodically and locally high enough to generate this western margin compared with the eastern widespread deposition of evaporates, suggesting margins (Briggs, 1995). This inferred palaeogeo- a generally subtropical arid climate. Although graphical situation may be compared with that of an Early Cambrian warm period has been the western Australian margin during the Eocene claimed, global warming does not necessarily im- (McGowran et al., 1997), when Australia and ply a poleward shifting of isotherms but might Antarctica were close enough to prevent the de- re£ect their spacing when thermal gradients be- velopment of a circum-Antarctica circulation. As came £atter. a result, two main surface circulation patterns During Early and earliest Mid-Cambrian times, tookplace: a South Equatorial Current £owing the western Gondwanan margin was rimmed by (up to the Recent) as a low-salinity surface com- enormously extensive shallow-water subtropical ponent of the global thermocline system, and a platforms, where carbonate deposition was some-

Fig. 4. Global Cambrian palaeogeography (modi¢ed after McKerrow et al., 1992) and proposal of palaeocurrents discussed in the text.

PALAEO 3071 9-5-03 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35 17 times outpaced by local, craton-derived terrige- disappearance of bioclastic carbonates. On the nous clastic sediments. As a result, the proportion other hand, the development of Late Cambrian of carbonate and siliciclastic rocks varies both isolated carbonate platforms within temperate- regionally and stratigraphically. Incursions of water settings of the southern Montagne Noire shale onto the platforms is commonly related to (Val d’Homs Formation) signals short-lived warm- sea-level rises, when the remobilisation and trans- ing episodes in meridional parts of the western port seaward of ¢ne-grained siliciclastic sediments Gondwana margin extending into Tremadocian outpaced carbonate production. By contrast, re- times. gressive trends are represented by basinward shifts of peritidal deposits in carbonate and mixed platforms, and deltaic and coastal plain dilution re- 5. Biogeographical patterns lated to terrigenous in£ux on platforms close to continental sources. For instance, the siliciclastic 5.1. Lower Cambrian deposition related to the Daroca regression during the earliest Tissa¢nian or early Bilbilian age, af- The Lower Cambrian has for a long time been fected the Souss Basin, the OMZ, CIZ and IC based on the concept of being characterised by platforms, but was absent in the CIZ, WALZ, the earliest Phanerozoic fossils. Bro«gger (1886) Montagne Noire and southwestern Sardinia plat- and subsequently Walcott (1891) developed the forms. idea of a Lower^Middle Cambrian boundary Despite the lackof lithological indicators for based on the ¢rst appearance of the trilobite ge- the climate during the Mid- to Late Cambrian, nus Paradoxides (s.l.) in Baltica and the disap- a transition from carbonate-dominated rimmed pearance of Olenellus (s.l.) in Laurentia. The low- platforms to siliciclastic temperate- to cool-water er boundary of the Cambrian was not ¢xed with platforms is attributed to changing oceanographic any precision but in early days was assumed to conditions across the Lower^Middle Cambrian coincide roughly with the ¢rst appearance of transition. The southward-moving warm tropical trilobites. Since 1974 workby the International waters of western Gondwana progressively in- Subcommission on Cambrian Stratigraphy has vaded cold seas; as a result, Middle Cambrian changed this concept. Incorporation of strata sediments re£ect a transition to temperate-water with ‘primitive’ Metazoan sclerites of uncertain platform sediments. In a study of the Cambrian systematic a⁄nities (the so-called small shelly fos- Iberian platform (IC), AŁ lvaro and Vennin (2001) sils) pushed down the level of the Cambrian lower described a succession of benthic communities in- boundary considerably. In the present concept, terpreted to have developed during a cooling pe- the earliest Cambrian strata are characterised by riod. This cooling trend, from subtropical to tem- rocks with the ¢rst diversi¢ed trace fossil assem- perate waters, was marked by the successive blages that underly strata with small shelly fossils. decline and disappearance of: (1) ooids, evaporite As a result, the Lower Cambrian was extended relics and microbial carbonates; (2) eocrinoid- dramatically and the trilobite-bearing strata rep- sponge meadows; (3) hydrodynamic bioclastic resent less than half of Early Cambrian time as carbonates related to the contraction of carbonate presently understood (Landing, 1994; Landing et factories into increasingly narrow belts (‘griotte’ al., 1998). facies); and there are trends to (4) an increase In the Lower Cambrian, the ideal of a global of trilobite-dominant communities on muddy bot- biostratigraphy and palaeobiogeography su¡ers toms; and (5) to decreasingly fossiliferous com- from both a relatively limited diversity of trilo- munities, then dominated by linguliform brachio- bites and their pronounced endemism. Further- pods in sandy shoals. The Languedocian^Late more, the distribution of trilobites is, from the Cambrian interval seems to markthe culmination earliest times, strongly controlled by facies, so of the cooling trend as shown by the pervasive that even a precise interregional correlation is dif- decrease in diversity, associated with the drastic ¢cult. The most complete Early Cambrian trilo-

PALAEO 3071 9-5-03 18 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35

PALAEO 3071 9-5-03 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35 19 bite succession of western Gondwana, with rela- sia, Pararedlichia, and Resserops) are also typical tively diverse trilobite faunas from various biofa- in ¢ne-grained siliciclastics. They share characters cies, comes from the Moroccan Atlas ranges (Fig. with genera from other Cambrian regions such as 5A), with more than 200 trilobite species de- the South China (or Yangtze) Platform (Nan- scribed from Lower and lowermost Middle Cam- gaoian Stage) and are sometimes erroneously syn- brian strata. This area clearly is the key for our onynised with Eoredlichia because of the limited understanding of the Lower Cambrian palaeobio- set of characters. geography of western Gondwana and the neigh- Lemdadella and bigotinid trilobites are typical bouring regions. Historically, this is the region of well-bedded platform carbonates. They may be where the ¢rst elaborate Lower Cambrian biozo- helpful for future correlations but are still imper- nation was developed (Hupe¤, 1952). The Lower fectly known because the past research concen- Cambrian to lowermost Middle Cambrian bio- trated largely on shale faunas. Similar bigotinids stratigraphy of Morocco now comprises ten bio- are known from the Lower Cambrian of the Ar- zones assigned to three stages (Fig. 2), which are morican Massif and the Co¤rdoba platform of the all characterised by signi¢cant trilobite faunas and OMZ (Bigotina) but also from the Lower Cam- separated by faunal turnovers (Geyer, 1990a; brian Pagetiellus anabarus Zone (middle Atdaba- Geyer and Landing, 1995). nian) of the Siberian Platform, in both areas also Recent correlations suggest that the earliest tri- in platform carbonates. Finally, Lemdadella has lobites from the lowermost Issendalenian Stage been reported from the Lower Cambrian of the pre-date other trilobite occurrences in western OMZ (Lin‹a¤n and Sdzuy, 1978) and Antarctica Gondwana and are among the ¢rst trilobites (Palmer and Rowell, 1995). known so far on a global scale (Sdzuy and Geyer, In summary, the Issendalenian shows a moder- 1988; Geyer and Landing, 1995). These faunas of ate diversi¢cation of trilobite faunas with high the Eofallotaspis Zone include several species of preference for ¢ne-grained siliciclastics and periti- the fallotaspidid genus Eofallotaspis and the big- dal carbonate muds. Most species and the major- otinid genera Hupetina and Bigotinops, all of ity of the genera are endemic, which is probably which are endemic, as are most trilobites of the due to a lackof knowledge of coeval faunas from overlying Fallotaspis tazemmourtensis, Choubertel- other western Gondwanan areas. la and Daguinaspis Zones. The entire Issendale- The Issendalenian^Banian transition in Moroc- nian is characterised by fallotaspidid, redlichiid co is marked by a dramatic decrease of the fallo- and bigotinid trilobites. Fallotaspidids (the genera taspidids, whereas primordial ellipsocephaloids Choubertella, Daguinaspis, Eofallotaspis, and Fal- (the antatlasiids) arise and increase impressively lotaspis) appear to have preferred ¢ne-grained sil- in number and diversity to form the most charac- iciclastic substrates and are now found almost ex- teristic faunal element in the Banian. Fallotaspi- clusively in shales; deposition tookplace on a dids are replaced by neltneriids. The ¢rst eodis- slightly restricted carbonate platform with archae- coids (Delgadella, Hebediscus) occur in the lower ocyathan-microbial buildups, apparently with lim- Banian. All trilobites apparently have noticeable ited connections to the open sea. Elsewhere fallo- preferences for distinct lithofacies, but the frame- taspidids (in a broad sense) occur with certainty workis more complicated than the simple distinc- in the Lower Cambrian of the White^Inyo Moun- tion between shale and carbonate facies in the tains, California, adjacent Nevada, and Siberia. Issendalenian. Banian rocks are dominated by Redlichiid^saukiandid trilobites (such as Marsai- ¢ne-grained siliciclastics with relatively minor

Fig. 5. Global distribution chart illustrating presence (black) and absence (white) of Lower Cambrian trilobite genera reported in the western Gondwanan margin (A), biodiversity patterns (B), and analysis of hierarchical Phi^Pearson similarity (C). Some of the reported genera could occur in Fig. 6 as Middle Cambrian trilobites according to the considered horizon of the Lower^Mid- dle Cambrian boundary.

PALAEO 3071 9-5-03 20 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35 nodular and bedded limestones deposited in a Charlottenhof Formation of the Go«rlitz area, low-energy middle to upper platform environ- Saxo^Thuringia (S. silesius). The German and ment. Spanish Marianian assemblages also share the During the Banian, for the ¢rst time, strong genera Ferralsia and Lusatiops. Ferralsia is known similarities of trilobite faunas can be detected be- from the OMZ, but was originally described from tween the Moroccan Atlas region and the OMZ. the uppermost(?) Lower Cambrian of the Mon- Delgadella is found in the lower, middle and even tagne Noire. An Acanthomicmacca, although dif- in the upper part of the Banian (A. hollardi, A. ¢cult to judge in terms of precise ontogeny, is also guttapluviae and Sectigena Zones) and is also a known from the Charlottenhof Formation. A frequent faunal element in the earliest assemblag- probable species of Holmia is also identi¢ed es of the OMZ. The Sectigena Zone of Morocco from the Charlottenhof Formation, and species shares a number of genera and even species with tentatively assigned to Holmia and Kjerul¢a were the lower two assemblages of the OMZ, such as described from the lower? Sectigena Zone of the Andalusiana cornuta, Gigantopygus, Rinconia, Sau- Anti-Atlas. Both genera are distinctive of the Hol- kianda andalusiae, Termierella and Triangulaspis. mia kjerul¢ Zone of Baltica. This distinctive zone is represented in Morocco by The faunas of the Moroccan Sectigena Zone several quite di¡erent local assemblages that por- and the coeval assemblages from Iberia, Saxo^ tray a variety of coeval biofacies. Stratigraphical Thuringia, the southern British Isles, southeastern successions dominated by low-energy shales in- Newfoundland and other areas are characterised clude the Ossa^Morena-type Saukianda^Termier- by an assemblage that include relatively wide- ella assemblage. Shales to ¢ne-grained sandstones spread eodiscoids. Typical species of this assem- deposited in more agitated shallow-marine envi- blage include Calodiscus helena, C. lobatus (in ronments tend to yield a Berabichia^Delgadella^ strict sense), C. schucherti, Hebediscus (or Dipha- Pentagonalia fauna. Limestones and marls yield rus) attleborensis, Serrodiscus bellimarginatus, S. an assemblage with Hebediscus and Sectigena. silesius, S. speciosus, Triangulaspis annio, T. vigi- Other trilobites are facies-independent and occur lans, and other species of Triangulaspis (Fletcher, in di¡erent types of rocks. Issafeniella has been 1972; Robison et al., 1977; Geyer, 1990b; Geyer identi¢ed from the Marianian of the OMZ, which and Palmer, 1995). Most of these species are rel- also shares a ¢rst and simple species Acanthomic- atively endemic, but their ranges show some macca) with the Moroccan Sectigena Zone. Secti- regional overlap and associated taxa permit a gena itself, Berabichia and Issafeniella, have their subglobal recognition, for example in Baltica counterparts, and obviously close relatives, in the (Sweden), Avalonia (southeastern Newfoundland, Siberian genera Charaulaspis and Chorbusulina. New Brunswick, Welsh Borderlands), western Both occur in the latest Atdabanian and early Gondwana (Spain, Morocco), Siberia, the Al- Botoman of the northern Siberian Platform, tay^Sayan Mountains, and Kazakhstan. In west- where they are accompanied by Hebediscus spp. ern Gondwana, Triangulaspis zirarii of Morocco and Triangulaspis. Two additional species of has its counterpart in the extremely similar Trian- Chorbusulina were described from the Lower gulaspis fusca from the OMZ, which is associated Cambrian of Antarctica, but in fact could belong with Calodiscus schucherti, a species that also oc- to Berabichia. curs in the Moroccan Sectigena Zone. An important genus that has its ¢rst appear- Such assemblages are the earliest to show clear ance in the Sectigena Zone is Serrodiscus. This faunal relationships between Avalonia and west- genus has a long stratigraphical range, but it is ern Gondwana. The top of the Callavia broeggeri remarkable that the same type of red shales of the Zone in southeastern Newfoundland (regarded as Issafen Formation, in which Serrodiscus ¢rst oc- a distinct Serrodiscus bellimarginatus Zone by curs in the Anti-Atlas, also contains the ¢rst Ser- Fletcher, 1972) includes not only Serrodiscus bel- rodiscus species (S. silesius and other species) in limarginatus and Hebediscus attleborensis, but also the Marianian of the CIZ and OMZ, and in the Acanthomicmacca species typical of the Sectigena

PALAEO 3071 9-5-03 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35 21

Zone, the Marianian of the IC, and the Charlot- Pillola’s (1991a) revision partly a¡ected the no- tenhof Formation in Saxo^Thuringia. It also in- menclature of trilobites from the Lower Cambrian cludes Mallagnostus (formerly Ladadiscus; see of the Montagne Noire. Galloredlichia noiri was Whittington et al., 1997) llarenai, a species ¢rst assigned to the ‘Yangtze’ genus Eoredlichia, a ge- described from the OMZ. Very similar trilobites, nus that occurs in relatively early trilobite assem- including Acanthomicmacca, Calodiscus lobatus, blages on the South China Platform such as the Hebediscus attleborensis, Serrodiscus bellimargina- famous Chengjiang Fauna. This assemblage can tus, and Triangulaspis annio, are known from var- be correlated with the Uper Issendalenian and ious levels in the Comley Limestones in the Welsh Upper Ovetian. In the Montagne Noire, Gallored- Borderlands of England. Some eodiscoids, such as lichia occurs together with Granolenus midi, a spe- Calodiscus, Hebediscus, Serrodiscus, and Triangu- cies also known from the Upper Ovetian of the laspis, are shared with assemblages from the top CIZ. of the Judomia and B. micmacciformis^Erbiella A Banian^Tissa¢nian faunal turnover is Zones on the Siberian Platform. marked by a relatively sharp change in the com- The Lower Cambrian of southwestern Sardinia position of benthic communities, exempli¢ed by: has yielded a relatively diverse trilobite fauna with (1) the appearance and massive increase of proto- a pre-Sectigena age. Most of the species and even lenine trilobites, (2) the sudden but apparently genera are endemic, probably because they are stacked appearance of other new trilobite groups, largely from lithologies incompletely studied in and (3) the relatively abrupt disappearance of el- supposedly coeval successions from other parts lipsocephaloid lineages. These strata with Lower^ of western Gondwana. Particularly well known Middle Banian faunas are traditionally termed the are the genera Dolerolenus, Giordanella, and ‘Protolenus Zone’ and regarded as of Early Cam- Metadoxides. The few eodiscoids in these assem- brian age. blages are of little help for either biostratigraph- Early Cambrian (Comley Series) trilobites are ical or biogeographical correlations because they known from Comley and the Rushton area in are also endemic. Another so-called Dolerolenus the Welsh Borderland and at Nuneaton on the fauna has been described from the Ovetian of Midland Platform, together with a very few, in- the IC (Sdzuy, 1987), an assemblage representing cluding Hamatolenus and Pseudatops, from north- the oldest diverse trilobite fauna known from ern Wales. There has been little recent revision of Spain. However, the trilobites are mostly de- British Early Cambrian trilobites, and in view of scribed under open nomenclature because of their signi¢cant recent workin Morocco, Spain and poor preservation. Nevertheless, the taxonomic Germany, the generic placement of certain British a⁄nities are su⁄cient to recognise that both areas taxa, particularly of ellipsocephaloids, is now share a similar trilobite fauna and obviously were open to question. Thomas et al. (1984) listed biogeographically connected. Both may be re- some 36 taxa from the Comley Series. If we ac- garded as faunas particularly adapted to relatively cept the names currently applied, their a⁄nities lie isolated, probably rimmed, carbonate platforms. most strongly with trilobites from elsewhere in In a monographic reappraisal of the Sardinian Avalonia. About 12 species are common to west- trilobites, Pillola (1991a) described a number of ern Avalonia, including some eight of eodiscoids new, endemic species and revised older species, and species of Protolenus, Strenuella and possibly mainly redlichioids. He assigned many of them of Callavia; and a further 12 represent genera to genera known almost exclusively from the known from Avalonia and the Taconic Belt of South China Platform and proposed a strong pa- New York. In contrast, only two species and three laeobiogeographical connection to that Cambrian or four genera can be compared with Baltic fau- continent. However, trilobite faunas of similar age nas. The a⁄nities with marginal Gondwana ap- and from similar facies are unknown from the pear to be restricted to three species known from platforms supposed to have been situated between the OMZ ^ Calodiscus schucherti, Mallagnostus those regions during the Lower Cambrian. llarenai and possibly Serrodiscus serratus ^ and

PALAEO 3071 9-5-03 22 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35

Fig. 6. Global distribution chart illustrating presence (black) and absence (white) of Middle Cambrian trilobite genera reported in the western Gondwanan margin (A), biodiversity patterns (B), and analysis of hierarchical Phi^Pearson similarity (C). there are another 12 genera in common. The Brit- Strenuella (Comluella)), Condylopyge amitina, El- ish representatives of these genera are: Callavia lipsocephalus (or Ourikaia?) heyi (see Geyer, callavei and other species, Cobboldites comleyen- 1990b), Hamatolenus douglasi, Hebediscus attle- sis, Comluella platycephala (Morris, 1988, has borensis, Latoucheia latouchei, Micmacca spp.,

PALAEO 3071 9-5-03 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35 23

Protolenus paradoxoides, Serrodiscus bellimargina- sive episodes and representing new migratory in- tus and other spp., and Triangulaspis annio.Ac- puts of recurrent trilobite genera. Both episodes cording to Sdzuy (1961), possibly Andalusiana? were punctuated by distinct faunal turnovers. (or Kjerul¢a?) granulata should also be included. Several lines of evidence have been put forward The greatest resemblance is shown by faunas from that imply extinction events towards the end of the ‘Bre'che a' Micmacca’ in the basal Middle the Early Cambrian. They point to the concept Cambrian in Morocco. Geyer and Malinky (1997) of a widespread latest Early Cambrian biocrisis, correlated this unit with the Protolenus Lime- as the culmination of a worldwide decline of tri- stone of Comley, Shropshire (Cobbold’s unit lobites and other taxa that commenced earlier in Ac5; see Rushton et al., 1999), which in Britain the Early Cambrian and led to a global diachro- was treated hitherto as late Early Cambrian. nous extinction (Debrenne, 1991; Brasier, 1995; Zhuravlev, 1995; AŁ lvaro et al., 1999). The termi- 5.2. Middle Cambrian nal Lower Cambrian strata display a succession of extinction events related to the disappearance As discussed above for the Lower Cambrian in the western Gondwana margin of microbial^ trilobites of the western Gondwana margin, the archaeocyathan buildups and the establishment database from which the following analysis is of regressive conditions. A local event has been made is heterogeneous. This is due to the exis- identi¢ed in the IC at the end of this tendency, tence of barren intervals, across the Leonian in termed the ‘Valdemiedes event’. Data from the the Montagne Noire and the Middle^Late Lan- trilobites do not necessarily support a catastroph- guedocian in Morocco and the OMZ, which pre- ic extinction at this horizon, their record being vent complete correlations (Fig. 6A). The Lower^ imperfect on account of barren intervals prior to Middle Cambrian boundary is not uniform over that event. The event represents the end of the the whole area, because it has been characterised relatively endemic, inner-platform survivors of by di¡erent bioevents based on trilobite and acri- the area, followed by an inshore migration of tarch appearances. The Lower^Middle Cambrian more pandemic, outer-platform faunas. transition contains numerous barren stratigraphi- It should be noted that during the Lower^Mid- cal intervals and unconformities, so that the tran- dle Cambrian transition the Moroccan succession sition (and not its boundary) will be described shows a di¡erent pattern from that portrayed by below in two key areas with continuous sedimen- southwestern Europe. In the Atlas ranges, the ter- tation and fossil wealth: Morocco and the IC. In minal Lower Cambrian^basal Middle Cambrian the present state of knowledge, two di¡erent bio- regressive^transgressive trends are represented by diversity patterns are recognised during Mid- a marked coarse clastic input, regionally over- Cambrian times: (1) a progressive decrease in di- printed by volcanoclastic deposits. Two distinct versity in Morocco, and (2) a composite increase^ unconformities exist, one within the sandstone^ decrease trend in the whole of southwestern Eu- volcanoclastic unit (which is accordingly divided rope. Consequently, during Early to Middle Cam- into the Tazlaft and Tatelt Formations), and an- brian times, the area of maximum diversity mi- other one at its top. The fossil record, however, is grated northeastwards; a result that may be rich across both formations and suggests that a related to the southwestward drifting of the west- punctuated extinction did not take place. Al- ern Gondwana margin. though the faunal turnover reported across the In general, two Middle Cambrian trilobite di- Banian^Tissa¢nian transition signals a strongly versi¢cations are recognised (Fig. 6B): (1) a major depauperate fauna in the basal Tissa¢nian Hupeo- migratory radiation of trilobites during the Tissa- lenus Zone, some species range across the bound- ¢nian/Upper Bilbilian to Caesaraugustian when ary; this turnover pre-dates the ‘Valdemiedes most families appeared without obvious ancestors event’ of the IC, which roughly coincides with in the fossil record; and (2) a Late Languedocian the base of the Cephalopyge notabilis Zone. The trilobite diversi¢cation connected with transgres- fossil poverty of the Hupeolenus Zone fauna can

PALAEO 3071 9-5-03 24 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35 largely be attributed to unfavourable living con- from Newfoundland and Rhode Island to Turkey ditions during the pronounced input of terrig- (e.g. Badulesia tenera). There were no physical enous clastics and volcanogenic components. By barriers preventing trilobite dispersal, which was contrast, the C. notabilis Zone includes one of the favoured by uniform sea£oor conditions (open- most diverse trilobite assemblages in the world platform, muddy o¡shore substrates), and low known from this time. Its base is regionally placed temperature-gradients. Diversity increased and within the clastic blanket so that the diversi¢ca- species proliferated during Caesaraugustian times. tion can be proved to be a true radiation rather The acme is associated with transgressive condi- than merely created by a favourable diversity of tions and subsequent connection of platforms, ecological niches. Nevertheless, the peakdiversity and represents the peakin diversity of trilobite was not reached until the establishment of a num- families, genera and species during the Middle ber of diverse facies conditions on the basal Mid- Cambrian. dle Cambrian platforms. As noted above, the A major reduction in the number of trilobite strata with Lower^Middle Banian faunas are cor- genera occurred across the Caesaraugustian^Lan- related with the ‘Protolenus Zone’ in areas such as guedocian transition, at a time of widespread eastern Avalonia (England and Wales), western coarse-grained terrigenous input associated with Avalonia (southeastern Newfoundland and New a well-documented regressive trend. The disap- Brunswick) and Baltica, and are regarded as of pearance of trilobite taxa is related to the dis- Early Cambrian age. appearance of their habitats. This diachronous The earliest Mid-Cambrian faunal recovery can decline was catastrophic for some previously be regarded as an adaptative radiation of an im- successful trilobites, such as the solenopleuropsi- migrant trilobite community that progressively in- nae (except the genus Sao). This biocrisis is not a vaded the western Gondwanan margin from deep- major extinction at familial level for trilobites, but er-water environments. The Tissa¢nian/Leonian represents a signi¢cant generic turnover. The fau- immigration is characterised by the stepwise ap- nal turnover coincides with a rapid prograding pearance of relatively cosmopolitan trilobites, and shoaling that produced widespread areas of such as the acrocephalitids, agraulids, corynexo- coarse-grained sandstones and, therefore, seems chids, conocoryphids, paradoxidids, solenopleur- to re£ect geographically extensive environmental ids and agnostoids (condylopygids, phalacromids changes. In Baltica there is a regression at the and spinagnostids). The observed pattern of di- level of the late Middle Cambrian Andrarum versi¢cation was not facies-controlled because tri- Limestone (Nielsen, 1996), and this is recognised lobites appeared in a wide diversity of facies and in the southern British Isles and Newfoundland as environments. Some trilobite families crossed the an ‘Andrarum Limestone regression’, with the lae- Lower^Middle Cambrian transition, although de- vigata Zone above. It is unlikely that the last Lan- creasing sharply in diversity, such as the ellipso- guedocian fauna is as young as the L. laevigata cephaline and protolenine trilobites. Subsequent- Zone (see Fig. 2); paradoxidids appear to be ex- ly, the western Mediterranean area apparently tinct by then in Baltica and a new fauna occurs operated as a centre of evolutionary radiation with trilobites of Upper Cambrian aspect, such as (or a site of speciation), from which the species Agnostus, Andrarina, and Proceratopyge. were able to spread outward into adjacent plat- The Late Languedocian trilobite diversi¢cation forms, in some cases by sympatric speciation (AŁ l- is well documented in the southern Montagne varo and Vizca|«no, 2001). As a result, a relative Noire, Sardinia, and Saxo^Thuringia, where it is biogeographical concordance of evolutionary pat- characterised by an abrupt increase in genera and terns is virtually complete for some trilobite fam- families. The appearance of this new assemblage ilies, and there are no apparent extrinsic barriers of trilobites represents an immigration event re- separating the sibling species. Some Caesaraugus- lated to transgressive pulses. Episodically, o¡- tian benthic species evolved in this area and platform trilobite taxa migrated towards the inner proved capable of migrating to colonise areas platform, leading to a strict facies control on the

PALAEO 3071 9-5-03 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35 25 lithofacies di¡erentiation, and coinciding with the ans, L.? pugnax (Clarella in Morris, 1988) and establishment of suitable muddy o¡shore sub- Paradoxides abenacus. The faunas are most strates. However, the diversity of the new groups closely related to those of Baltica, with which 40 is less than in the previous radiation. Dispersal species are in common, and a further 14 at generic tookplace to some extent, but the presence of level, and with western Avalonia (mainly New- some provincialism suggests that species exchange foundland), with which 34 species are in common was selective, and that the oceanic areas may have and a further fourteen at the generic level. Resem- served as partial barriers to migration. Late Lan- blance with the Gondwanan margin is consider- guedocian trilobites include typical genera of the ably lower: there are eight species in common Leonian^Caesaraugustian diversi¢cation (such as with Bohemia and Saxo^Thuringia, namely Con- the conocoryphids and paradoxidids) and new dylopyge rex, Eccaparadoxides pusillus, Luhops Asian invaders, such as the genera Abharella, expectans, Peronopsis integra(?), Phalacroma bi- Chelidonocephalus, Derikaspis and Dorypyge (see bullatum, Phalagnostus nudus, Pleuroctenium gra- AŁ lvaro et al., 1999, and references therein). This nulatum granulatum, and Plutonides (Hydrocepha- in£uence illustrates the immigration of faunas lus) hicksii. Further genera in common appear to from the northern Gondwanan margin, which include Acadoparadoxides, Agraulos, Ctenocepha- went on during Late Cambrian times (see below). lus, Dawsonia? (if Metadiscus is a synonym), Ho- However, the percentage of pandemic species de- locephalina, Hypagnostus, Paradoxides, Ptychag- creased across the Languedocian, and geographic nostus, and Ptychoparia? There are about six distribution also decreased because of successive species in common with the Iberian Peninsula, regressive pulses. namely Agraulos longicephalus, Condylopyge cari- The Middle Cambrian of the British Isles (St. nata, C. rex, Paradoxides davidis?, Peronopsis fal- David’s Series) is in the lower part generally de- lax?, Plutonides hicksii, and, from Sardinia, Ano- veloped as arenaceous clastic deposits, and in polenus henrici?(Loi et al., 1995). The only British Shropshire (and possibly elsewhere also, though member of the important peri-Gondwanan family the evidence is not so clear) they overlie a break Solenopleuropsidae is Solenopleuropsis (Manuble- in the succession. These deposits contain a re- sia) variolaris, which occurs in the punctuosus stricted fauna of agnostoids, paradoxidids and a Zone. This assessment shows once again that the few other taxa such as Bailiella. Higher up, dark agnostoid trilobites are the most widely dispersed mudstones (the classical ‘Menevian Beds’) are of taxa, with Condylopyge rex being recorded widespread. They contain a richer fauna of agnos- from each of the regions considered here. The toids, paradoxidids and various polymerid trilo- resemblance of the British (eastern Avalonia), bites, commonly including blind genera. These Newfoundland (western Avalonia) and Baltic fau- darkbeds are overlain by a hiatus that in most nas rests largely on the similarity of their agnos- places is evinced by erosion during the marine toids, and doubtless the relative paucity of peri- low-stand corresponding to the Solenopleura Gondwanan agnostoids is a hindrance to inter- (now Erratojincella) brachymetopa Zone (Rush- regional correlation. Avalonia and Baltica show ton, 1978; Nielsen, 1996). Thomas et al. (1984) agnostid faunas intermediate between those of listed 106 named St. David’s taxa, and more re- Laurentia and parts of the Gondwanan margin cent workhas added a few more: in St. Tudwal’s (Conway Morris and Rushton, 1988). Some spe- Peninsula, northern Wales, Young et al. (1994) cies of paradoxidids are also relatively widely dis- ¢gured forms derived from the brachymetopa tributed, although their larger size and commonly Zone, namely Bailiaspis glabrata (as a senior syn- fragmentary preservation sometimes makes for onym of B. nicholasi), Dolichometopus cf. svecicus, di⁄culties in collection and identi¢cation. The Linguagnostus aristatus, and fragments of Acro- polymerid trilobites such as conocoryphids and cephalites, Dorypyge and Centropleura, whilst ptychopariids appear much more frequently to Bridge et al. (1998) have ¢gured Luhops expect- be endemic.

PALAEO 3071 9-5-03 26 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35

5.3. Upper Cambrian and olenid fragments now thought to represent a species of Jujuyaspis that would indicate an ear- Upper Cambrian trilobites are very rare in the liest Ordovician age. It is possible that the occur- western Gondwanan margin, compared with the rence of P. (Wittekindtia) in the DM is also of this wealth recorded in the Lower and Middle Cam- age. Both there and in the IC, this subgenus is brian, and occur in a variety of lithofacies associ- associated with the echinoderm-like Oryctoconus ations ranging from inner platform sandstones lobatus Colchen and Ubaghs, 1969. By virtue of and shales to outer platform and slope carbon- the aphelaspidoid morphologies in the IC, and ates. Temperate-water faunas were less diverse Maladioidella in the DM, the trilobites of north- and more impoverished than Lower^Middle Cam- ern Spain are considered to have an Iverian age brian ones. In contrast, British faunas contain according to the Australian standard and a Sun- around 100 taxa that represent the whole Upper waptan age on the Laurentian timescale. Cambrian. 5.3.2. Montagne Noire 5.3.1. The Iberian Massif Late Cambrian trilobites occur in the Val Late Cambrian trilobites occur in the WALZ, d’Homs Formation (Ferrals-les-Montagnes). DM and IC. The occurrence of Late Cambrian They were ¢rst described by Feist and Courtessole trilobites in the DM was ¢rst reported by Colchen (1984), who recognised two species referred to (1967) who determined the presence of Chuangia Prochuangia gallica and Bergeronites latifalcatus. and Prochuangia in the lower member of the Na- Subsequent collecting from a limestone lens close jerilla Formation. These trilobites were subse- to the base of the formation has revealed the pres- quently described and revised by Shergold et al. ence of further taxa (Shergold et al., 2000): (1983), who recognised two trilobite associations: Abharella sp., Ammagnostus (A.) a¡. sinensis, Kor- (1) an oldest one comprising four taxa (aphelas- magnostus? sp., Olentella cf. africana, Palaeadotes pidine, leiostegiid?, Maladioidella colcheni, and latefalcata, Paraacidaspis ultima, Proceratopyge Langyashania felixi); and (2) a younger assem- (P.) spp., Prochuangia gallica, Shengia cf. spinosa, blage, from the second member of the Najerilla and Stigmatoa courtessolei. The age of this fauna Formation, containing only two taxa (pagodiine is judged to be similar to, but slightly older than, and a solenopleuroidean? a¡. Lajishanaspis). that characterised by Maladioidella in the DM. These determinations support Colchen’s conten- Many of its elements have a widespread distributions of an Asian in£uence, e.g. Maladioidella tion along the Gondwanan margin (Shergold et has a distribution that extends from Spain to al., 2000), and the agnostoids and Proceratopyge northern China (Rushton and Hughes, 1996; extend even to Laurentia. However, the Ferrals Jago, in Brocket al., 2000 ). association shows greatest relationship with In the IC, the ¢rst Late Cambrian trilobites southern and central China, Australia and Ant- were determined by Sdzuy (in Josopait, 1972), arctica. and subsequently described by Shergold and Elsewhere in the Montagne Noire, an assem- Sdzuy (1991). These occur both in the middle blage containing species of Maladioidella, On- part of the Valtorres Formation and the lower chonotellus, Probilacunaspis, Proceratopyge, Pro- part of the overlying Valconcha¤n Formation. chuangia, and a pseudagnostinid occurs in The faunal association includes agnostoid, aphe- carbonates of the Val d’Homs Formation to the laspidine a¡. Aphelaspis rara (OrIowski) sensu Zç y- southwest of Coulouma. Once more, its composi- lin¤ska (2001), Elegantaspis cf. beta, Parachangsha- tion is dominated by Chinese genera. This assem- nia sp., Pseudagnostus sp., Punctaspis? schmitzi, blage is the youngest Cambrian fauna found so solenopleuroidean, and Valtorresia volkeri.The far in the Montagne Noire. The earliest Ordovi- Upper Cambrian assemblage is overlain in the cian is marked traditionally by the appearance of uppermost Valconcha¤n Formation by a sandstone Proteuloma geinitzi described by Sdzuy (1958) bed containing Pagodia (Wittekindtia) alarbaensis from reddish limestones just below the base of

PALAEO 3071 9-5-03 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35 27 the La Dentelle Quartzite in the vicinity of of Olenus. The higher Merioneth is developed Combes de Barroubio. everywhere as blackmudstones related to the olenid biofacies and contains a considerable variety 5.3.3. Sardinia of olenids, admixed with a small number of ag- Although they have not been systematically nostoid and other non-olenid genera. A number documented, Late Cambrian trilobites have been of new records have appeared since the publica- noted and illustrated in the upper part of the tion of Thomas et al. (1984): Allen and Jackson Cabitza Formation in the Cabitza area and north (1985) recorded the presence of Niobella homfrayi of Domusnova (Loi et al., 1995, 1996). They oc- preciosa, Parabolina acanthura, P. cf. angusta, and cur in ¢ne sandstones and siltstones probably rep- Parabolinella contracta; Hughes and Rushton resenting a tide-dominated deltaic environment. (1990) transferred ‘Dikelocephalus’ discoidalis to Illustrated trilobites (Loi et al., 1995, 1996) are the ceratopygid genus Cermatops; Cope and from faunal assemblage CAB 5b, which contains Rushton (1992) described previously unknown Macropyge sp., Maladioidella cf. colcheni, Micrag- faunas from Llangynog, south Wales, that include nostus cf. haudei, Niobella cf. primaeva, Onchono- Ctenopyge (C.) linnarssoni; Howells and Smith tellus? amsassensis, Proceratopyge sp., a leioste- (1997) recorded the presence of Loganellus sp., giid a¡. Pagodia, a eulomid, and a calymenid. Maladioidella abdita (‘Conokephalina’inMorris, At Monte Cani this assemblage is succeeded by 1988), Olenus cf. solitarius, Parabolina a¡. mober- green siltstones containing (CAB 6) Rhabdinopora gi and P. (Neoparabolina) lobata praecurrens; £abelliformis (Pillola and Gutie¤rrez-Marco, 1988; Bridge et al. (1998) noted Ctenopyge (C.) pecten Pillola and Leone, 1993), Proteuloma geinitzi (Pil- tenuis from a borehole. lola, 1991b) and Oryctoconus cf. lobatus. The Of these trilobites, the olenids are widely dis- younger assemblage is clearly of earliest Trema- tributed where the appropriate dysaerobic facies is docian age. present, and some others, such as agnostoids (es- pecially Glyptagnostus reticulatus), Proceratopyge 5.3.4. Morocco and other ceratopygoids, Irvingella and Maladioi- Two Late Cambrian trilobite taxa have been della (Rushton and Hughes, 1996) are widely dis- documented from the upper member of the Jbel tributed in a variety of shelf environments. In Lmgaysmat Formation, in the Foum Zguid re- Britain other rare non-olenid, non-agnostoid gion (Destombes and Feist, 1987). Olentella afri- taxa include species of Acanthopleurella, Aphelas- cana and Seletella latigena represent the ¢rst pis (Zç ylin¤ska, 2001), Araiopleura, Conophrys, Cy- Upper Cambrian occurrence in North Africa. clolorenzella, Eoasaphus, Loganellus, Modocia, Both genera occur in the Sakian, Aphelaspis^Ku- Niobella, Parabolinoides, Proteuloma, Richardso- jandaspis Zone, in central Kazakhstan (Ivshin, nella, and Schmalenseeia. 1955, 1956, 1962). Olentella cf. africana has also Thomas et al. (1984) listed 86 named taxa and been described from Ferrals-les-Montagnes in the the above-mentioned works added nine more. Of Montagne Noire (Shergold et al., 2000). The fos- these, 61 are identi¢ed with, or compared with, siliferous Upper Cambrian is overlain by a dis- species from Baltica, and a further 10 are compa- cordance followed by shales containing Rhabdino- rable at the generic level. The Upper Cambrian pora £abelliformis. faunas of western Avalonia appear to be less fully known, but, out of a total of about 20 species 5.3.5. British Isles recorded by Martin and Dean (1988), there are The Late Cambrian (Merioneth Series) trilo- 13 species in common with British faunas and bites have been found in England and Wales four or ¢ve additional shared genera. wherever rocks of that age are exposed, and all The Upper Cambrian in the peri-Gondwanan the main zones are proved. In the lower Merio- region contains a number of faunas (discussed neth Series there are commonly muddy, silty and above), but, presumably because the proli¢c ole- sandy beds with Homagnostus and a few species nid biofacies is not well developed, there are rel-

PALAEO 3071 9-5-03 28 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35 atively few taxa in common with Britain. For ex- noted to occur in the Sardinian CAB 6 fauna, ample, there is nothing in British faunas to match though not illustrated). Micragnostus, Niobella the oriental genera recorded from the Montagne and Parakoldiniodia, for example, are related to Noire, and with the transfer of Olentella rara of taxa described from the Acerocare Zone (Rush- Rushton (in Allen and Jackson, 1985)toAphelas- ton, 1982), which Landing et al. (1978) regard pis (Zç ylin¤ska, 2001), there is no genus in common as correlatable with the Cordylodus proavus con- with the Moroccan fauna. Upper Cambrian out- odont Zone. Given the current acceptance of the crops from Spain (Shergold et al., 1983) have only position of the CambrianÔrdovician boundary yielded Maladioidella, and possibly an undeter- (Cooper and Nowlan, 1999) at the ¢rst appear- mined aphelaspidine that can be compared with ance of the conodont Iapetognathus £uctivagus taxa in British faunas, while a fauna from Sardi- Nicoll et al., 1999, associations correlated with nia only has a few more comparable taxa, namely the C. proavus Zone are terminal Cambrian age, Maladioidella, Proceratopyge, an early form of or Datsonian in the Australian standard (see also Niobella and some unspeci¢ed olenids (Loi et the discussion of the Sardinian CAB 6 assemblage al., 1995). by Loi et al., 1995; and the correlations proposed by Geyer and Shergold, 2000). Accordingly, it 5.3.6. Turkey may be necessary to reassess the Sultan Dagfl Late Cambrian trilobites have been recorded ‘Tremadocian’. from the Taurus and Amanos Mountains in Finally, in southeastern Turkey, Late Cambrian south^central Turkey. In the northeast, they oc- trilobites have been reported by Dean et al. (1981) cur in the Seydis°ehir Formation of the Sultan Dagfl and Dean and Monod (1997) from the Seydis°ehir (Shergold and Sdzuy, 1984; Dean et al., 1993), on Formation of the Samur Dagfl area, on the Yayla the Tu«lu«ce Tepe section. Trilobites described by Tepe section. Trilobites reported from here in- Shergold and Sdzuy (1984) include Homagnostus? clude species of Chuangia, Drepanura, and Pro- sp., Maladioidella kelteri, Pseudagnostus cf. cyclo- chuangia, overlain by younger assemblages char- pyge, Pseudagnostus sp., and undetermined pty- acterised by Alborsella, Niobella, Pagodia (Witte- choparioids and solenopleuroideans. Dean et al. kindtia), and Saukia, all indicating a⁄nities with (1993) also illustrated specimens of Homagnostus northern Iran. and M. kelteri. All these assemblages are Late Cambrian in age, which may well correlate with the Maladioidella-bearing horizons of Sardinia, 6. Biogeographical cluster analyses Montagne Noire, and northeastern Spain. In the Sultan Dagfl, this fauna is succeeded by a A matrix tabulating all genera and species younger association (Shergold and Sdzuy, 1984) known from the Lower and Middle Cambrian containing Koldinioidia (K.) cf. sulcata, Macro- of Morocco, Ossa^Morena, the CantabroÎberian pyge cf. taurina, Micragnostus haudei, Niobella Basin, Montagne Noire, Sardinia, Saxo^Thurin- cf. primaeva, Onchonotellus a¡. amsassensis, Para- gia, the Barrandian area and Turkey (the latter koldinioidia cf. gibbosa, Proteuloma cf. geinitzi, only for the Middle Cambrian) has provided sig- and Rhaptagnostus? sp. This was assumed by ni¢cant information (Figs. 5C and 6C). Phyloge- Shergold and Sdzuy (1984) to indicate an Early netic biogeography (Lieberman, 2002) is not Tremadocian age since elements of the association available for the Cambrian trilobites of the west- are traditionally considered to be of this age and ern Gondwanan margin due to the scarcity of have a wide distribution in the Franconian Forest cladistic analyses. However, the data reported area (Germany), the Montagne Noire, the Czech here (114 genera and 249 species for the Lower Republic, southern Kazakhstan, southern Siberia, Cambrian, and 113 genera and 442 species for the and the Xinjiang Province in China. However, all Middle Cambrian) were analysed using a stan- of the generic taxa have latest Cambrian origins, dard method of linkage cluster analysis, namely except perhaps Macropyge (although the genus is analysis of hierarchical Phi^Pearson similarity,

PALAEO 3071 9-5-03 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35 29 which produces dichotomising patterns that are illustrated in palaeogeographical maps. Trilobite easier to interpret than multivariate analyses. Per- faunas show a marked change in distribution pat- centage similarity in a single linkage cluster anal- terns across the Lower^Middle Cambrian transi- ysis provides an approximate key to robustness of tion; this is attributed to a major palaeogeograph- branching nodes within the constraints of para- ical reorganisation, in which the endemic patterns metric analysis. Trilobite faunas from the di¡erent displayed by the Lower Cambrian trilobite fauna basins and platforms are associated in terms of ended diachronously and were followed by a pe- their shared genera and species. The analysis of riod of relative sedimentary homogeneity, with an similarity produces bifurcating dendrograms read- open connection of platforms that allowed immi- ily interpreted in terms of biogeography. The dis- gration of trilobites. advantage of this method is that biofacies patterns are not considered, and that the total 6.2. Middle Cambrian diversity of each platform strongly a¡ects the percentage of shared taxa. Endemic taxa were elimi- Trilobite similarity shows two main clusters nated from the database before they were entered (Fig. 6C): (1) Balticaêastern Avalonia, and (2) in the data matrix because they may represent the rest of the basins discussed here. This also local ecological conditions, lackof marine con- shows strong support for the presence of two nections to neighbouring platforms, or sampling Mid-Cambrian biogeographical entities within biases. Further research might extend the known the Mediterranean subprovince of Sdzuy (1972), biogeographical distribution of some taxa but it distinctly di¡erentiated from eastern Avalonia seems unlikely that such new data would seriously and Baltica. Therefore the relative Baltic a⁄nity modify the basic patterns discussed in this paper. of the Middle Cambrian faunas from the Pr›¤|bram^Jince Basin (Havl|¤c›ek, 1999) does not 6.1. Lower Cambrian support di¡erentiation of a Middle Cambrian Pe- runica terrane. Another important biogeographi- The Lower Cambrian shallow subtropical ma- cal relationship with Bohemia is indicated by a rine biota exhibits the greatest diversity patterns Middle Cambrian trilobite assemblage found in in the whole Cambrian. One of the most interest- the Ptychagnostus atavus Zone of the Carolina ing features of the Lower Cambrian is the wide- Slate belt (eastern United States). The latter is spread development of endemic species. The Low- considered as an exotic terrane likely accreted to er Cambrian palaeogeographical complexities of North America during the Early or Middle Pa- the carbonate and mixed platforms, episodically laeozoic, although an alternative possibility has related to the development of microbialârchaeo- been proposed placing this fauna in cool-water cyathan reefal complexes, o¡ered various oppor- environments along the periphery of Laurentia tunities for the isolation of populations and sub- (Samson et al., 1990). sequent allopatric speciation. Many subtropical The variability of the biogeographical distribu- endemic trilobites assemblages are essentially re- tion documented in the studied populations is di- lated to reef communities. Trilobite similarity ex- rectly related to species diversity. Decreasing pro- hibits two major clusters (Fig. 5C): (1) the south- vinciality of trilobites during the Caesaraugustian ern British Isles, Morocco, and the OMZ; and (2) appears to have been accompanied by an increase Saxo^Thuringia, Montagne Noire, the CIZ, the in total diversity. The development of regional CantabroÎberian Basin, and Sardinia. The close regressions induced habitat di¡erences on a local relationship of the OMZ with the entity ‘eastern and regional scale favouring ‘microallopatric’ spe- Avalonia^Morocco’ is signi¢cant because it could ciation. re£ect easier reproductive communication in the Regarding the British Cambrian faunas, they southwesternmost part of the area studied due to have their closest a⁄nity to those of the Gond- open oceanographic conditions and a possible set- wanan margin at the end of the Early Cambrian ting of the OMZ closer to Morocco than that (or earliest Mid-Cambrian in Morocco) and this

PALAEO 3071 9-5-03 30 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35 a⁄nity declines through the Middle and Late an: the cooling associated with the southwestward Cambrian. Through the same period the British drift of the continental margin. Diverse Lower Cambrian faunas retain considerable similarities Cambrian trilobite assemblages are found in the with western Avalonian faunas (those of east mar- shallow waters of subtropical areas, as studied in itime Canada and eastern United States, e.g. Mas- the Souss Basin of Morocco. The progressive sachusetts, New Brunswick, Newfoundland, etc.) change from relatively endemic to cosmopolitan and become progressively more similar to Baltic trilobite assemblages across the Lower^Middle faunas. Cambrian transition can be related to three main events: (1) the disappearance of microbial^ 6.3. Upper Cambrian archaeocyathan buildups and neighbouring peri- reefal environments, (2) the relative uniformity of A cluster analysis of the Upper Cambrian tri- muddy o¡shore substrates related to a regional lobite faunas is not signi¢cant because of their (eustatic?) early Mid-Cambrian transgression, low diversity patterns in areas other than Britain. and (3) the disappearance of signi¢cant temper- In addition, trilobite biofacies possibly occur at ature gradients on the Southern Hemisphere. only three stratigraphical levels: (1) the Idamean The peakof Middle Cambrian trilobite diversity or Steptoean (IC, Montagne Noire, Morocco), progressively migrated from Morocco to south- characterised by aphelaspidoid morphologies; (2) western Europe (Cantabro^Iberian, Montagne the Iverian or Sunwaptan (DM, Montagne Noire, Noire, Saxo^Thuringia and Barrandian areas), Sardinia, western Turkey), characterised by the although these subtropical- to temperate-water occurrence of Maladioidella; and (3) the Datso- platforms did not reach the richness reported in nian, of Cordylodus proavus Zone age. If the age the Lower Cambrian of the Souss Basin. Finally, of strata with Niobella, Macropyge, Pagodia (Wit- Upper Cambrian temperate-water faunas are dra- tekindtia), and Parakoldinioidia can be ¢rmly es- matically impoverished compared with the pre- tablished as of Cordylodus proavus Zone age, then vious wealth, except in the southern British Isles, that biofacies becomes the third of latest Cambri- where the proli¢c olenid biofacies developed, ex- an age. Some support for this assumption comes hibiting a strong biogeographical relationship from conodonts recovered by Oº zgu«l and Gedik with Baltica. (1973) from the Seydis°ehir Formation in the cen- Ocean currents played a signi¢cant role in the tral Taurus Mountains, which by Australian stan- regional distribution of benthic communities. Two dards are terminal Cambrian. Strata with Orycto- Cambrian unidirectional circulation trends seem conus also support this assignment, since they to have been in operation: (1) in the Early to occur in association with the Acerocare Regressive Mid^Cambrian, a western peri-Gondwanan cur- Event (Erdtmann, 1986; Nicoll et al., 1992; Loi et rent with a SW^NE trend extended from polar al., 1995, 1996), a global sea-level £uctuation areas to lower latitudes and favoured interchange close to the currently adopted Cambrian^Ordovi- with benthic communities of Baltic a⁄nity; (2) in cian boundary. Most of the Upper Cambrian fau- the Late Cambrian a NE^SW longshore current nas described from western Gondwana contain £owed towards higher latitudes and seem to have elements interpreted as of central and southeast- involved organisms of Asian a⁄nity. However, it ern Asian provenance. remains a question whether the dispersal of subtropical, Australo^Sinian trilobites into temperate or cold seas of the Southern Hemisphere can be 7. Conclusions and further questions attributed to transport of southward-drifting currents? Or did the migration take place in a direc- One process can be considered primarily re- tion opposite to that of the main northeastward sponsible for the northeastward migration of the £ow of surface waters? biodiversity centre (based on trilobites) on the Numerous questions are still open for future western Gondwanan margin during the Cambri- discussion that will bene¢t from a multidiscipli-

PALAEO 3071 9-5-03 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35 31 nary approach. This paper constitutes only one Aramburu, C., Garc|¤a-Ramos, C., 1993. La sedimentacio¤n new step in the establishment of Cambrian palaeo- cambro-ordov|¤cica en la Zona Canta¤brica (NO de Espan‹a). Trab. Geol. Univ. Oviedo 19, 45^73. biogeographical models. The palaeogeographical Aramburu, C., Truyols, J., Arbizu, M., Me¤ndez-Bedia, I., Za- maps and biogeographical interpretations ex- marren‹o, I., Garc|¤a-Ramos, J.C., Sua¤rez de Centi, C., Va- pressed here are intended to stimulate critical re- lenzuela, M., 1992. El Paleozoico Inferior de la Zona Can- marks from specialists of other fossil groups and ta¤brica. In: Gutie¤rrez-Marco, J.C., Saavedra, J., Ra¤bano, I. geological disciplines, and to be tested further in (Eds.), Paleozoico Inferior de Ibero^Ame¤rica. UNEX Press, Me¤rida, pp. 397^422. the light of new data. Baldwin, C.T., 1977. The stratigraphy and facies associations of trace fossils in some Cambrian and Ordovician rocks of northwestern Spain. In: Crimes, T.P., Harper, J.C. (Eds.), Acknowledgements Trace Fossils 2. Geol. J., Spec. Issue 9, 9^40. Bergstro«m, S.M., 1990. Relations between conodont provincialism and the changing paleogeography during the early Pa- The authors thankwarmly the proposals and leozoic. In: McKerrow, W.S., Scotese, C.R. (Eds.), Palaeo- discussions of Per Ahlberg (Lund), Pete Palmer zoic Palaeogeographies and Biogeographies. Geol. Soc. (Boulder), and the editing workof Alain Blieck London Mem. 12, pp. 163^174. (Lille), which have helped to complete and im- Brasier, M.D., 1995. The basal Cambrian transition and Cam- prove a previous manuscript. This paper is a con- brian bio-events. In: Walliser, O.H. (Ed.), Global Events and Event Stratigraphy in the Phanerozoic. Springer, Berlin, tribution to Project ATI 15-52. pp. 113^118. Brasier, M.D., Perejo¤n, A., San Jose¤, M.A., 1979. Discovery of an important fossiliferous Precambrian^Cambrian sequence References in Spain. Estud. Geol. 35, 379^383. Bridge, D.McC., Carney, J.N., Lawley, R.S., Rushton, Allen, P.M., Jackson, A.A., 1985. Geology of the country A.W.A., 1998. The geology of the country around Coventry around Harlech. Mem. Brit. Geol. Surv., Sheet 135 with and Nuneaton. Mem. Brit. Geol. Surv., Sheet 169 (England part of 149 (England and Wales), H.M.S.O., London, and Wales). The Stationery O⁄ce, London, x+185 pp. xii+111 pp. Briggs, J.C., 1995. Global Biogeography. Develop. Palaeontol. AŁ lvaro, J.J., Vennin, E., 1998. Stratigraphic signature of a Strat. 14, 1^454. terminal Early Cambrian regressive event in the Iberian Pen- Brock, G.A., Engelbretsen, M.J., Jago, J.B., Kruse, P.D., insula. Can. J. Earth Sci. 35, 402^411. Laurie, J.R., Shergold, J.H., Shi, G.R., Sorauf, J.E., 2000. AŁ lvaro, J.J., Vennin, E., 2001. Benthic marine communities Palaeobiogeographic a⁄nities of Australian Cambrian fau- recorded in the Cambrian Iberian platform, NE Spain. Pa- nas. Mem. Assoc. Aust. Palaeontol. 23, 1^61. laeontographica A 262, 1^23. Bro«gger, W.C., 1886. Om alderen af Olenelluszonen i Nord- AŁ lvaro, J.J., Vizca|«no, D., 1998. Re¤vision biostratigraphique amerika. Geol. Fo«ren. Stockholm Fo«rhandl. 101, 182^213. du Cambrien moyen du versant me¤ridional de la Montagne Carls, P., 1983. La Zona Asturoccidental^Leonesa en Arago¤n Noire (Languedoc, France). Bull. Soc. ge¤ol. Fr. 169, 233^ y el macizo del Ebro como prolongacio¤n del Macizo Can- 242. ta¤brico. In: Comba, J. (Coord.), Contribuciones sobre temas AŁ lvaro, J.J., Vizca|«no, D., 2001. Evolutionary trends in the generales. IGME, Libro Jubilar J.M. R|¤os 3, pp. 11^32. ornamentation of Cambrian solenopleuropsine trilobites. Chlupa¤c›, I., 1995. Lower Cambrian arthropods from the Pa- Palaeontology 44, 131^141. seky Shale (Barrandian area, Czech Republic). J. Czech AŁ lvaro, J.J., Vizca|«no, D., Vennin, E., 1999. Trilobite diversity Geol. Soc. 40, 9^36. patterns in the Middle Cambrian of southwestern Europe: a Chlupa¤c›, I., Havl|¤c›ek, V.J., Kr›¤|z›, J., Kukal, Z., Sítorch, P., comparative study. Palaeogeogr. Palaeoclimatol. Palaeoecol. 1998. Paleozoic of the Barrandian (Cambrian to Devonian). 151, 241^254. Czech Geol. Surv. Publ., Prague, 183 pp. AŁ lvaro, J.J., Rouchy, J.M., Bechsta«dt, T., Boucot, A., Boyer, Cocks, L.R.M., McKerrow, W.S., van Staal, C.R., 1997. The F., Debrenne, F., Moreno-Eiris, E., Perejo¤n, A., Vennin, E., margins of Avalonia. Geol. Mag. 134, 456^460. 2000a. Evaporitic constraints on the southward drifting of Colchen, M., 1967. Sur la pre¤sence du Cambrien supe¤rieur a' the western Gondwana margin during Early Cambrian Prochuangia et a' Chuangia dans la Sierra de la Demanda times. Palaeogeogr. Palaeoclimatol. Palaeoecol. 160, 105^ (Logron‹o), Espagne. C.R. Acad. Sci. 264, 1687^1690. 122. Colchen, M., Ubaghs, G.P., 1969. Sur les restes d’Echino- AŁ lvaro, J.J., Vennin, E., Moreno-Eiris, E., Perejo¤n, A., Bech- dermes (?) du Cambro^Ordovicien de la Sierra de la Deman- sta«dt, T., 2000b. Sedimentary patterns across the Lower^ da (Burgos^Logron‹o, Espagne). Bull. Soc. ge¤ol. Fr. Se¤r. 7 Middle Cambrian transition in the Esla nappe (Cantabrian 11, 649^654. Mountains, northern Spain). Sediment. Geol. 137, 43^61. Conway Morris, S., Rushton, A.W.A., 1988. Precambrian to

PALAEO 3071 9-5-03 32 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35

Tremadoc biotas in the Caledonides. In: Harris, A.L., their bearing on punctuations in early nematophorid (planc- Fettes, D.J. (Eds.), The CaledonianÂppalachian Orogen. tic) graptolite evolution. In: Walliser, O.H. (Ed.), Global Geol. Soc. London Spec. Publ. 38, pp. 93^109. Bio-Events. Lecture Notes in Earth Sciences 8, Springer, Cooper, R.A., Nowlan, G.S., 1999. Proposed global stratotype Berlin, pp. 139^152. and point for base of the Ordovician System. Acta Univ. Feist, R., Courtessole, R., 1984. De¤couverte de Cambrien Carolinae Geol. 43, 61^63. supe¤rieur a' trilobites de type est-asiatique dans la Montagne Cope, J.C.W., Rushton, A.W.A., 1992. Cambrian and early Noire (France me¤ridionale). C.R. Acad. Sci. se¤r. 2 298, 177^ Tremadoc rocks of the Llangynog Inlier, Dyfed, South 182. Wales. Geol. Mag. 129, 543^552. Fletcher, T.P., 1972. Geology and Lower to Middle Cambrian Cope, J.C.W., Ingham, J.K., Rawson, P.F. (Eds.), 1992. Atlas Trilobite Faunas of Southwestern Avalon, Newfoundland. of Palaeogeography and Lithofacies. Mem. Geol. Soc. Part Two. Unpubl. Ph.D. Thesis, Univ. of Cambridge, 295 Lond. 13, xiii+153 pp. pp. Cowie, J.W., Rushton, A.W.A., Stubble¢eld, C.J., 1972. A Franke, W., 2000. The mid-European segment of the Varis- correlation of Cambrian rocks in the British Isles. Spec. cides: tectonostratigraphic units, terrane boundaries and Rep. Geol. Soc. London 2, 1^42. plate tectonic evolution. In: Franke, W., Haak, V., Oncken, Crimes, T.P., Legg, I., Marcos, A., Arboleya, M.L., 1977. O., Tanner, D. (Eds.), Orogenic Processes: Quanti¢cation ?Late Precambrian^low Lower Cambrian trace fossils from and Modelling in the Variscan Belt. Geol. Soc. London Spain. In: Crimes, T.P., Harper, J.E. (Eds.), Trace Fossils. Spec. Publ. 179, pp. 35^61. Geol. J. Spec. Issue 9, pp. 91^138. Geyer, G., 1989. Late Precambrian to early Middle Cambrian Dean, W.T., Monod, O., 1997. Cambrian development of the lithostratigraphy of southern Morocco. Beringeria 1, 115^ Gondwanaland margin in Southeastern Turkey. Turk. As- 143. soc. Petrol. Geol. Spec. Publ. 3, 61^74. Geyer, G., 1990a. Revised Lower to lower Middle Cambrian Dean, W.T., Monod, O., Perinc°ek, D., 1981. Correlation of biostratigraphy of Morocco. Newslett. Stratigr. 22, 53^70. the Cambrian and Ordovician rocks in southeastern Turkey. Geyer, G., 1990b. Die marokkanischen Ellipsocephalidae (Tri- Petroleum activities at the 100th year (100 Yilda Petrol Faa- lobita: Redlichiida). Beringeria 3, 1^363. liyeti). T.C. Petrol Içsleri Genel Mu«du«rlu«gflu« Dergisi 25, An- Geyer, G., Elicki, O., 1995. Lower Cambrian trilobites from kara, pp. 269^300. the Go«rlitz Synclinorium (Germany) ^ review and new re- Dean, W.T., Martin, F., Monod, O., Gu«l, M.A., Bozdogflan, sults. Pala«ontol. Z. 69, 87^119. N., Oº zgu«l, N., 1993. Early Palaeozoic evolution of the Geyer, G., Landing, E., 1995. The Cambrian of the Moroccan Gondwanaland margin in the western and central Taurids, Atlas regions. Beringeria 2, 7^46. Turkey. In: Turgut, S. (Ed.), Tectonics and Hydrocarbon Geyer, G., Malinky, J.M., 1997. Middle Cambrian fossils from Potential of Anatolia and Surrounding Regions. Ozan Sun- Tizi N’Tichka, the High Atlas, Morocco. Part 1. Introduc- gflurlu Symposium Proceedings, November 1991, Ankara, pp. tion and trilobites. J. Paleontol. 71, 620^637. 262^272. Geyer, G., Palmer, A.R., 1995. Neltneriidae and Holmiidae Debrenne, F., 1991. Extinction of the Archaeocyatha. Hist. (Trilobita) from Morocco and the problem of Early Cam- Biol. 5, 95^106. brian intercontinental correlation. J. Paleontol. 69, 459^474. Destombes, J., Feist, R., 1987. De¤couverte du Cambrien supe¤r- Geyer, G., Shergold, J.H., 2000. The quest for internationally ieur en Afrique (Anti-Atlas, Central Maroc). C.R. Acad. Sci. recognized divisions of Cambrian time. Episodes 23, 188^ se¤r. 2 304, 719^724. 195. Destombes, J., Hollard, H., Willefert, S., 1985. Lower Palaeo- Geyer, G., Landing, E., Heldmaier, W., 1995. Faunas and zoic rocks of Morocco. In: Hollard, C.H. (Ed.), Lower Pa- depositional environments of the Cambrian of the Moroc- laeozoic Rocks of the World, vol. 4. Lower Palaeozoic of can Atlas region. Beringeria 2, 47^120. North-Western and West Central Africa. Wiley, Chichester, Havl|¤c›ek, V., 1999. Perunica microplate: relation to Ukranian pp. 157^184. Shield, mid-Bohemian rift, and hypothetic large-scale Dore¤, F., 1994. Cambrian of the Armorican Massif. In: Kep- overthrusts in central Bohemia. Veflst. Cí esk. Geol. u¤st. 74, pie, J.D. (Ed.), Pre-Mesozoic Geology in France and Re- 75^81. lated Areas. Springer, Berlin, pp. 136^141. Havl|¤c›ek, V., Vanek, J., Fatka, O., 1994. Perunica microcon- Elicki, O., 1994. Lower Cambrian carbonates from eastern tinent in the Ordovician (its position within the Mediterra- Germany: palaeontology, stratigraphy and palaeogeogra- nean province, series division, bentic and pelagic associa- phy. N. Jb. Geol. Palao«nt. Abh. 191, 69^93. tions). Sbor. geol. Vefld, Geol. 46, 23^56. Elicki, O., 1997. Biostratigraphic data of the German Cambri- Howells, M.F., Smith, M., 1997. Geology of the Country an ^ present state of knowledge. Freiberger Forsch.-H. C around Snowdon. Mem. British Geol. Surv., Sheet 119 466, 155^165. (England and Wales), H.M.S.O., London, x+104 pp. Elicki, O., 1999. Palaeoecological signi¢cance of calcimicrobial Hughes, N.C., Rushton, A.W.A., 1990. Computer-aided resto- communities during ramp evolution: an example from the ration of a late Cambrian ceratopygid trilobite from Wales, Lower Cambrian of Germany. Facies 41, 27^40. and its phylogenetic implications. Palaeontology 33, 429^ Erdtmann, B.D., 1986. Early Ordovician eustatic cycles and 445.

PALAEO 3071 9-5-03 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35 33

Hupe¤, P., 1952. Sur les zones de Trilobites du Cambrien infe¤- Gondwana in the light of single zircon geochronology and rieur marocain. C.R. Acad. Sci. 235, 480^481. basin development (Central European Variscides, Germany). Ivshin, N.K., 1955. Vosem’novykh rodov trilobitov iz verkh- In: Franke, W., Haak, V., Oncken, O., Tanner, D. (Eds.), nego kembriya tsentral’nogo Kazakhstana. Izvestiya Akade- Orogenic Processes: Quanti¢cation and Modelling in the miya Nauk Kazakhskoy SSR, Syr’ya Geologiya 21, 106^ Variscan Belt. Geol. Soc. London Spec. Publ. 179, pp. 131^ 123. 153. Ivshin, N.K., 1956. Verkhnekembriskie trilobity Kazakhstana, Loi, A., Pillola, G.L., Leone, F., 1995. The Cambrian and Chast 1. Kuyandinskiy faunisticheskiy gorizont mezhdure- Early Ordovician of southwestern Sardinia. In: Cherchi, chiya Olenty^Shiderty. Izdatel’stvo Institut Geologicheskikh A. (Ed.), Sardinia 95, 6th Paleobenthos International Sym- Nauk, Akademiya Nauk Kazakhskoy SSR, Alma-Ata, pp. posium, Guide-book. Rend. Sem. Fac. Sci. Univ. Cagliari, 1^98. Suppl. vol. 65, pp. 63^81. Ivshin, N.K., 1962. Verkhnekembriskie trilobity Kazakhstana, Loi, A., Pillola, G.L., Leone, F., 1996. La limite Cambrien^ Chast 2. Seletinskiy gorizont Kuyandinskogo yarusa tsen- Ordovicien dans le SW de la Sardaigne: relations avec des tral’nogo Kazakhstana. Izdatel’stvo Institut Geologiche- e¤ve¤nements eustatiques globaux. C.R. Acad. Sci. se¤r. 2 323, skikh Nauk, Akademiya Nauk Kazakhskoy SSR, Alma 881^888. Ata, pp. 1^412. Lotze, F., 1961. Das Kambrium Spaniens. Teil 1: Stratigra- Josopait, V., 1972. Das Kambrium und das Tremadoc von phie. Abh. Math. Naturwiss. Kl. 1961, 1^498. Ateca (westliche Iberischen Ketten, NE-Spanien). Mu«nst. Marcos, A., Pe¤rez Estau¤n, A., 1981. La estratigraf|¤a de la Serie Forsch. Geol. Pala«ontol. 23, 1^121. de los Cabos en la Zona de Vegadeo (Zona AsturÔcciden- Krs, M., Krsova¤, M., Pruner, P., Chvojka, R., Havl|¤c›ek, V., tal Leonesa, NW de Espan‹a). Trab. Geol. Univ. Oviedo 11, 1987. Palaeomagnetism, palaeogeography and the multicom- 89^94. ponent analysis of Middle and Upper Cambrian rocks of the Martin, F., Dean, W.T., 1988. Middle and Upper Cambrian Barrandian in the Bohemian Massif. Tectonophysics 139, acritarch and trilobite zonation at Manuels River and Ran- 1^20. dom Island, eastern Newfoundland. Geol. Surv. Can. 381, Kukal, Z., 1971. Sedimentology of Cambrian deposits of the 1^91. Barrandian area (Central Bohemia). Sbor. Geol. Vefld. Geol. Mart|¤nez-Garc|¤a, E., Rolet, J., 1991. Correlations between the 20, 53^100. Palaeozoic orogens of Spain and France. New data from the Landing, E., 1994. Precambrian^Cambrian boundary global Iberian, Armorican and Aquitanian Massifs. Project 233 stratotype rati¢ed and a new perspective of Cambrian TCAPO, Terranes in the Arctic Caledonides, Tromso, Nor- time. Geology 22, 179^184. way, Abstr. vol. 4. Landing, E., Taylor, M.E., Erdtmann, B.D., 1978. Correlation Mata, J., Munha¤, J., 1990. Magmatoge¤nese de Metavulcanitos of the CambrianÔrdovician boundary between the Acado^ Ca“mbricos do Nordeste Alentejano: os esta¤dios iniciais de Baltic and North American faunal provinces. Geology 6, ‘rifting’ continental. Comun. Serv. Geol. Port. 76, 61^89. 75^78. McGowran, B., Li, Q., Moss, G., 1997. The Cenozoic neritic Landing, E., Bowring, S.A., Davidek, K.L., Westrop, S.R., record in southern Australia: the biogeohistorical frame- Geyer, G., Heldmaier, W., 1998. Duration of the Early work. In: James, N.P., Clarke, A.D. (Eds.), Cool-Water Cambrian; U^Pb ages of volcanic ashes from Avalon and Carbonates. SEPM, Spec. Publ. 56, pp. 185^203. Gondwana. Can. J. Earth Sci. 35, 329^338. McKerrow, W.S., Scotese, C.R., Brasier, M.D., 1992. Early Landing, E., Bowring, S.A., Davidek, K.L., Rushton, A.W.A., Cambrian continental reconstructions. J. Geol. Soc. London Fortey, R.A., Wimbledon, W.A.P., 2000. CambrianÔrdo- 149, 599^606. vician boundary age and duration of the lowest Ordovician Mergl, M., Geyer, G., El-Attari, A., 1998. The billingsellid Tremadoc Series based on U^Pb zircon dates from Avalo- genus Saccogonum (Brachiopoda) from the Moroccan Cam- nian Wales. Geol. Mag. 137, 485^494. brian and its signi¢cance for the regional geology and stra- Lieberman, B.S., 2002. Phylogenetic biogeography with and tigraphy. N. Jb. Geol. Pala«ontol. Abh. 209, 273^293. without the fossil record: gauging the e¡ects of extinction Morris, S.F., 1988. A Review of British Trilobites, Including a and paleontological incompleteness. Palaeogeogr. Palaeocli- Synoptic Revision of Salter’s Monograph. Monogr. Palae- matol. Palaeoecol. 2726, 1^14. ontogr. Soc. London Publ. 574, 316 pp. Lin‹a¤n, E., Sdzuy, K., 1978. A trilobite from the Lower Cam- Nicoll, R.S., Miller, J.F., Nowlan, G.S., Repetski, J.E., brian of Co¤rdoba (Spain), and its stratigraphical signi¢- Ethington, R.L., 1999. Iapetonudus (new genus) and Iapetog- cance. Senckenb. lethaea. 59, 387^399. nathus Landing, unusual earliest Ordovician multielement Linnemann, U., Buschmann, B., 1995. Die cadomische Diskor- conodont taxa and their utility for biostratigraphy. Brigham danz im Saxothuringikum (oberkambrisch^tremadocische Young Univ. Geol. Stud. 4, 27^101. Overlap-Sequenzen). Z. geol. Wiss. 23, 707^727. Nicoll, R.S., Nielsen, A.T., Laurie, J.R., Shergold, J.H., 1992. Linnemann, U., Gehmlich, M., Tichomirowa, M., Busch- Preliminary correlation of latest Cambrian to Early Ordovi- mann, B., Nasdala, L., Jonas, P., Lu«tzner, H., Bombach, cian sea level events. In: Webby, B.D., Laurie, J.R. (Eds.), K., 2000. From Cadomian subduction to Early Palaeozoic Global Perspectives on Ordovician Geology. Balkema, Rot- rifting: the evolution of Saxo^Thuringia at the margin of terdam, pp. 381^394.

PALAEO 3071 9-5-03 34 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35

Nielsen, A.T., 1996. Iltsvind, sort slam og trilobiter. Varv for tions. National Museum of Wales, Cardi¡, Geol. Ser. 3, pp. 1996 (1), pp. 3^39. 41^59. Oº zgu«l, N., Gedik, I., 1973. New data on the stratigraphy and Rushton, A.W.A., Hughes, N.C., 1996. Biometry, systematics conodont faunas of the C°altepe Limestone and Seydis°ehir and biogeography of the Late Cambrian trilobite Maladioi- Formation lower Paleozoic of the central Taurus Range. della abdita. Trans. R. Soc. Edinb. Earth Sci. 86, 247^256. Bull. Geol. Soc. Turk. 16, 39^52. Rushton, A.W.A., Owen, A.W., Owens, R.M., Prigmore, J.K., Palmer, A.R., 1972. Cambrian trilobites. In: Hallam, A. (Ed.), 1999 (2000). British Cambrian to Ordovician Stratigraphy. Atlas of Palaeobiogeography. Elsevier, Amsterdam, pp. 3^ GCR Series 18, Joint Nature Conservation Committee, Pe- 11. terborough, xxi+435 pp. Palmer, A.R., 1998. Why is the intercontinental correlation Russo, A., Bechsta«dt, T., 1994. Evolucio¤n sedimentolo¤gica y within the Lower Cambrian so di⁄cult? Rev. Esp. Paleon- paleogeogra¤¢ca de la formacio¤n Vegadeo (Ca¤mbrico Inferi- tol., 17^21. or^Medio) en la zona entre Visun‹a y Piedra¢ta do Caurel Palmer, A.R., Rowell, A.J., 1995. Early Cambrian trilobites (Lugo, NO de Espan‹a). Rev. Geol. Esp. 7, 299^310. from the Shackleton Limestone of the Central Transantarc- Samson, S., Palmer, A.R., Robison, R.A., Secor, D.T.Jr., tic Mountains. J. Paleontol. 45, 1^28. 1990. Biogeographical signi¢cance of Cambrian trilobites Perejo¤n, A., Moreno-Eiris, E., Fro«hler, M., Bechsta«dt, T., from the Carolina slate belt. Geol. Soc. Am. Bull. 102, Boni, M., 2000. Archaeocyathan assemblages from the Gon- 1459^1470. nesa Group, Lower Cambrian (Sardinia, Italy) and their Sdzuy, K., 1958. Fossilien aus dem Tremadoc der Montagne sedimentologic context. Boll. Soc. Paleontol. Ital. 39, 257^ Noire. Senckenb. lethaea 39, 235^253. 291. Sdzuy, K., 1961. Das Kambrium Spaniens. Teil II: Trilobiten, Pillola, G.L., 1991a. Trilobites du Cambrien infe¤rieur du SW 1. Abschnitt. Akad. Wiss. Lit. (Mainz). Abh. Math.-Natur- de la Sardaigne, Italie. Palaeontographia Ital. 78, 1^174. wiss. Kl., for 1961, 7, pp. 499^594 (217^312). Pillola, G.L., 1991b. Occurrence of Proteuloma (Trilobita) in Sdzuy, K., 1972. Das Kambrium der acadobaltischen Faunen- the Cabitza Formation (Cambro^Tremadoc, SW Sardinia, provinz ^ Gegenwa«rtiger Kenntnisstand und Probleme. Italy): palaeobiogeographic implications. In: Geologia del Zent. Geol. Pala«ontol. II 1972, 1^91. Basemento Italiano. Convegno in memoria di Tommaso Co- Sdzuy, K., 1987. Trilobites de la base de la Formacio¤n Jalo¤n cozza, Siena, 21^22 Marzo 1991, pp. 59^61. (Ca¤mbrico Inferior) de Arago¤n. Rev. Esp. Paleontol. 2, 3^8. Pillola, G.L., Gutie¤rrez-Marco, J.C., 1988. Graptolites du Sdzuy, K., Geyer, G., 1988. The base of the Cambrian in Tremadoc du sud-ouest de la Sardaigne (Italie): pale¤oe¤colo- Morocco. In: Jacobshagen, V.H. (Ed.), The Atlas System gie et contexte tectono^se¤dimentaire. Ge¤obios 21, 553^ of Morocco. Studies on its Geodynamic Evolution. Lecture 565. Notes in Earth Sciences 15, pp. 91^106. Pillola, G.L., Leone, F., 1993. Biostratigraphical and sedimen- Sdzuy, K., Lin‹a¤n, E., Gozalo, R., 1999. The Leonian stage tological data from the Cabitza Formation (Middle Cambri- (early Middle Cambrian): a unit for Cambrian correlation an^Tremadoc, SW Sardinia, Italy): palaeogeography and in the Mediterranean subprovince. Geol. Mag. 136, 39^48. CambrianÔrdovician boundary. IGCP 319, Liverpool, Ab- Shergold, J.H., Sdzuy, K., 1984. Cambrian and early Trema- stracts, p. 22. docian trilobites from Sultan Dagfl, central Turkey. Senck- Quesada, C., 1991. Geological constraints on the Paleozoic enb. lethaea 65, 51^135. tectonic evolution of tectonostratigraphic terranes in the Shergold, J.H., Sdzuy, K., 1991. Late Cambrian trilobites from Iberian Massif. Tectonophysics 185, 225^245. the Iberian Mountains, Zaragoza Province, Spain. Beringe- Robison, R.A., Rosova, A.V., Rowell, A.J., Fletcher, T.P., ria 4, 193^235. 1977. Cambrian boundaries and divisions. Lethaia 10, Shergold, J.H., Lin‹a¤n, E., Palacios, T., 1983. Late Cambrian 257^262. trilobites from the Najerilla Formation, north-eastern Spain. Rodr|¤guez Ferna¤ndez, L.R., Barba, P., Bardaj|¤, T., Silva, P.G., Palaeontology 26, 71^92. Sua¤rez Rodr|¤guez, P.L., Heredia, N., Gallastegui, G., Pan- Shergold, J.H., Feist, R., Vizca|«no, D., 2000. Early Late Cam- iagua, A., Gala¤n, L., 1991. Mapa Geolo¤gico de Espan‹a, E. brian trilobites of Australo^Sinian aspect from the Mon- 1/50.000, 2a serie, 102 (Los Barrios de Luna). ITGE Press, tagne Noire, southern France. Palaeontology 43, 599^632. Madrid, pp. 1^130. Smith, N.J.P., Rushton, A.W.A., 1993. Cambrian and Ordo- Rushton, A.W.A., 1974. The Cambrian of Wales and England. vician stratigraphy related to structure and seismic pro¢les In: Holland, C.H. (Ed.), Cambrian of the British Isles, Nor- in the western part of the English Midlands. Geol. Mag. den and Spitsbergen. Wiley, London, pp. 42^122. 130, 665^671. Rushton, A.W.A., 1978. Fossils from the MiddleÛpper Cam- Thomas, A.T., Owens, R.M., Rushton, A.W.A., 1984. Trilo- brian transition in the Nuneaton District. Palaeontology 21, bites in British stratigraphy. Geol. Soc. London Spec. Rep. 245^283. 16, 1^78. Rushton, A.W.A., 1982. The biostratigraphy and correlation Valladares, M.I., 1995. Siliciclastic^carbonate slope apron in of the Merioneth^Tremadoc boundary in North Wales. In: an immature tensional margin (Upper Precambrian^Lower Bassett, M.G., Dean, W.T. (Eds.), The CambrianÔrdovi- Cambrian), Central Iberian Zone, Salamanca, Spain. Sedi- cian Boundary: Sections, Fossil Distributions, and Correla- ment. Geol. 94, 165^186.

PALAEO 3071 9-5-03 J. Javier AŁ lvaro et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 195 (2003) 5^35 35

Vegas, R., 1978. Sedimentation and tectonism in the Iberian Young, T.P., 1990. Ordovician sedimentary facies and faunas massif prior to the Hercynian deformation (late Precambri- of southwest Europe: palaeogeographic and tectonic impli- an times). Cuad. Sem. Est. Cera¤m. Sargadelos 27, 271^ cations. In: McKerrow, W.S., Scotese, C.R. (Eds.), Palaeo- 286. zoic Palaeogeography and Biogeography. Geol. Soc. Mem. Vra¤na, S., Síteﬂdra¤, V., 1997. Geological model of Western Bo- 12, pp. 421^430. hemia related to the KTB borehole in Germany. Sbor. Geol. Young, T., Martin, F., Dean, W.T., Rushton, A.W.A., 1994. Veﬂd. Geol. 47, 1^240. Cambrian stratigraphy of St Tudwal’s Peninsula, Gwynedd, Walcott, C.D., 1891. The Fauna of the Lower Cambrian or northwest Wales. Geol. Mag. 131, 335^360. Olenellus Zone. Tenth Ann. Rep. U.S. Geol. Surv., Part 1, Zamarren‹o, I., 1972. Las litofacies carbonatadas del Ca¤mbrico pp. 509^774. de la Zona Canta¤brica (NW Espan‹a) y su distribucio¤n pa- Whittington, H.B., Chatterton, B.D.E., Speyer, S.E., Fortey, leogeogra¤¢ca. Trab. Geol. Univ. Oviedo 5, 1^118. R.A., Owens, R.M., Chang, W.T., Dean, W.T., Jell, P.A., Zhuravlev, A.Yu., 1995. Reef ecosystem recovery after the Laurie, J.R., Palmer, A.R., Repina, L.N., Rushton, A.W.A., Early Cambrian extinction. In: Hart, M.B. (Ed.), Biotic Re- Shergold, J H., Clarkson, E.N.K., Wilmot, N.V., Kelly, covery from Mass Extinction Events. Geol. Soc. Spec. Publ. S.R.A., 1997. Trilobita. Introduction, Order Agnostida, Or- 102, pp. 79^96. der Redlichiida. Treatise on Invertebrate Paleontology, Part Zç ylin¤ska, A., 2001. Late Cambrian trilobites from the Holy O, revised, vol. 1. University of Kansas and Geological So- Cross Mountains, central Poland. Acta Geol. Pol. 51, 333^ ciety of America, xxiv+530 pp. 383.

PALAEO 3071 9-5-03