Cambrian and Ordovician biogeography of the South American margin of Gondwana and accreted terranes

Geological Society, London, Special Publications

doi: 10.1144/SP325.11p201-232.

2009, v.325;Geological Society, London, Special Publications and R. D. FogliaJ. L. Benedetto, N. E. Vaccari, B. G. Waisfeld, T. M. Sánchez American margin of Gondwana and accreted terranesCambrian and Ordovician biogeography of the South

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Cambrian and Ordovician biogeography of the South American

margin of Gondwana and accreted terranes

J. L. BENEDETTO*, N. E. VACCARI, B. G. WAISFELD, T. M. SANCHEZ & R. D. FOGLIA

CICTERRA-CONICET, Centro de Investigaciones Paleobiologicas, Facultad de Ciencias

Exactas, Fısicas y Naturales, Universidad Nacional de Cordoba, Av. Velez Sarsfield 299,

X5000JJC Cordoba, Argentina

*Corresponding author (e-mail: [email protected])

Abstract: Three main geological units were involved in the Early Palaeozoic history of SouthAmerica: (1) autochthonous intracratonic and pericratonic basins developed around the Gondwanabasement (e.g. the Central Andean basin, CAB); (2) volcano-sedimentary basins marginal to Gond-wana (e.g. Famatina and Puna volcanic belts); (3) crustal fragments accreted to the Andean marginthrough the Palaeozoic (e.g. Precordillera terrane). Knowledge of brachiopods, trilobites andbivalves has increased substantially over recent years, leading to the assembly of a more completedataset. Furongian–Tremadocian trilobites from Famatina, western Puna and the CAB are mostlywidespread forms (Olenid Fauna); however, the record of Amzasskiella and Onychopyge suggests aconnection with East Gondwana, Siberia and Kazakhstan. At that time, the Central Andean bra-chiopods and bivalves show links with Iberia, Bohemia and North Africa. Floian trilobites fromthese regions show a complex array of endemic and peri-Gondwanan forms, indicative of relativelyfree migration for some taxa around Gondwana. Coeval brachiopods from Famatina and westernPuna volcaniclastic rocks are of Celtic type, having some taxa in common with coeval faunas fromsouth Peru, which would support the existence of a long and nearly continuous volcanic arc mar-ginal to the Iapetus Ocean. Cambrian to Middle Ordovician platform carbonate rocks are confinedto the Precordillera basin. Trilobites from the Lower and Upper Cambrian limestones of the Pre-cordillera include key genera indicating Laurentian affinities (Arcuolenellus, Madarocephalus,Plethopeltis). Associated rhynchonelliformean brachiopods (e.g. Nisusia, Wimanella) are alsotypical of low-latitude palaeocontinents. Trilobites from the upper Tremadocian–Floian sequencesof the Precordillera match those of the Bathyurid Fauna, whereas associated brachiopods include ahigh percentage of Laurentian taxa. From the Floian, a biotic exchange with Gondwana and Balticabecomes evident in the Precordilleran trilobite faunas. By Darriwilian times, Precordilleran bra-chiopods form a well-defined low-latitude realm, but numerous Celtic and Baltic taxa immigratedinto the basin. By the Sandbian, affinities of Precordilleran brachiopods shift to West Gondwanan(North Africa, Armorica, Perunica and central Andes), probably reflecting the accretion of the Pre-cordillera (Cuyania) terrane to the proto-Andean margin, although some mixed faunas persist. Thelow-richness CAB brachiopod, bivalve and trilobite assemblages display stronger ‘Mediterranean’affinities than those from the Precordillera. In summary, there are abundant palaeontological datasupporting the view that the Precordillera is a Laurentian-derived far-travelled microcontinentaccreted to Gondwana during the Early Palaeozoic. A new early Middle Ordovician reconstructionof the southern and central proto-Andean margin is based on recently published geological data aswell as the new palaeontological evidence summarized in this paper.

The geodynamic history and developing palaeogeo-graphy of the southern proto-Andean margin ofGondwana, which today forms the Andean and Sub-andean ranges of Argentina, Chile, Bolivia andPeru, have been fully addressed in the collectionsof papers edited by Pankhurst & Rapela (1998),Ramos & Keppie (1999) and Vujovich et al.(2004), among others. There is general agreementthat three main geological units were involved inthe early Palaeozoic history of South America(Fig. 1): (1) autochthonous intracratonic andpericratonic basins developed on and aroundthe Gondwana basement; (2) early Palaeozoic

subduction-related volcanic arcs and associatedvolcano-sedimentary basins marginal to Gondwana;(3) crustal fragments accreted to the Andean marginof Gondwana through the Palaeozoic (Precordillera,Chilenia). Palaeogeographical evolution of thenorthern segment of the Andes (Ecuador, Colombia,Venezuela) is less well known, but at least twoterranes (Merida and Chibcha) have been recog-nized (Toussaint & Restrepo 1989; Bellizzia1992; Bellizzia & Pimentel 1994). The autochtho-nous ‘Caparo Block’ is located on the easternflank of the Venezuelan Andes, adjacent to theMerida terrane.

From: BASSETT, M. G. (ed.) Early Palaeozoic Peri-Gondwana Terranes: New Insights from Tectonics andBiogeography. Geological Society, London, Special Publications, 325, 201–232.DOI: 10.1144/SP325.11 0305-8719/09/$15.00 # The Geological Society of London 2009.

at University of Southern California on April 10, 2014http://sp.lyellcollection.org/Downloaded from



The biogeographical signature of Cambrian andOrdovician faunas has been useful to discriminatethe boundaries between such geotectonic units andalso for determining the probable origin, trajectory

and timing of accretion of the Precordillera (orCuyania) terrane, which constitutes a major com-ponent of the southern proto-Andean margin andis a focal point for understanding the early history

Fig. 1. Map of central–western South America showing main geological units and Cambro-Ordovician sedimentarybasins. 1, El Baul Massif (Venezuela); 2, Merida Andes, Rıo Caparo area (Venezuela); 3, Sierra de la Macarena(Colombia); 4, Sierra de Araracuara (Colombia); 5, Contaya (Peru); 6, Solimoes basin (Brazil); 7, Cordillera Oriental andSierras Subandinas (Bolivia and NW Argentina); 8, Puna region (northern Chile, Bolivia and NW Argentina); 9, Sierra deFamatina (western Argentina); 10, Precordillera (western Argentina); 11, Pampean Ranges (central Argentina); TB,Transbrazilian lineament. (Modified from Benedetto & Sanchez 1996; Ramos & Aleman 2000; Ramos 2008.)

J. L. BENEDETTO ET AL.202




of this Gondwana portion (Benedetto 1993, 1998a,2004; Astini et al. 1995; Thomas & Astini 1996).As is well known, biogeographical affinitiesof the Cambrian trilobite faunas (Vaccari 1994,and references therein) are the keystone of thehypothesis supporting the Laurentian derivationof the Precordillera terrane (Astini et al. 1995;Benedetto 2004).

By the Ordovician, brachiopods and trilobites,and to a lesser extent bivalves, were commoncomponents of carbonate and clastic platforms,and also of volcaniclastic areas surrounding volca-nic edifices (Waisfeld et al. 2003), and they havebeen critical in understanding the complex palaeo-geography of the South Iapetus Ocean during theearly Palaeozoic (Benedetto 1993, 1998a, 2004;Astini et al. 1995; Benedetto & Sanchez 1996;Waisfeld 1995; Vaccari 1995, 1996; Benedettoet al. 1999; Vaccari et al. 2006). Other groups,such as sponges and ostracodes, are relatively abun-dant in the Precordillera basin but they are scarce orpoorly known in other South American basins, sothey will not be addressed in detail in this synthesis.Biogeography of Ordovician sponges has been ana-lysed by Carrera & Rigby (1999) and Carrera(2003), and ostracodes were addressed by Salas(2002a, b) and Williams et al. (2003).

The main purpose of this contribution is to reas-sess the biogeographical affinities of the SouthAmerican benthic faunas in the light of new discov-eries and recent advances in the taxonomy oftrilobites, brachiopods and bivalves. Within thisframework, we discuss in some detail the recentpaper by Finney (2007), who argued that availableevidence is also compatible with a parautochtho-nous (SW Gondwana) origin of the Precordilleraterrane. Palaeontological data presented in thisreview are no longer consistent with such a prove-nance and indicate that the most likely place oforigin is Laurentia.

Faunas from each of the above-mentioned geo-logical units are compared with coeval assemblagesfrom Gondwana and other palaeocontinents andmicroplates. Information is examined for EarlyCambrian, Late Cambrian, Furongian–early Tre-madocian, late Tremadocian–Floian, Dapingian–Darriwilian, Sandbian–Katian and Hirnantiantime intervals.

Cambrian–Ordovician basins of

South America

Cambrian–Ordovician biotas are preserved in awide variety of deposits along the western part ofthe present-day South American plate (Benedetto& Sanchez 1996, and references therein) (Fig. 1).Lower Palaeozoic fossiliferous rocks in Venezuela

form small exposures in the El Baul Massif andthe Merida Andes (Caparo Block). In the formerlocality there are Upper Cambrian black shalesreferred to the Mireles Formation. The Caparo For-mation is composed of green siltstone and fine-grained sandstone bearing graptolites, brachiopodsand trilobites of Sandbian age (Arnold & Smith1964). In the Sierra de la Macarena and theeastern slope of the Cordillera Oriental of SEColombia the Guejar Group consists of calcareoussandstones and limestones of Cambrian age, andsandstones interbedded with dark grey fossiliferousshales that have been correlated with the widespreadOrdovician clastic succession lying in the subsur-face of the Colombian and Venezuelan pre-Andeanplains (‘Llanos Orientales’) (Ulloa et al. 1982;Mojica & Villarroel 1988; Pimentel de Bellizia1992). In the Central Cordillera of Colombia,Ordovician rocks are represented by the CristalinaFormation in the north and the El Hıgado Formationin the south. The latter consists of sandstones, bio-clastic lenses and fossiliferous dark shales bearinggraptolites and trilobites. The Middle Ordovician(Darriwilian) age of these rocks has been well estab-lished recently by conodonts (Gutierrez-Marco et al.2007, and references therein), but the presence ofreworked conodonts of Tremadocian age indicatesdeposition of older rocks in the area. At the Sierrade Araracuara, near the Guyana shield border, inthe SE corner of Colombia, reddish violet conglom-erates, sandstones and siltstones yielded Cruziana,linguliform brachiopods and acritarchs of EarlyOrdovician age (Thery et al. 1984).

The Lower Palaeozoic succession of Ecuador isalmost completely unknown. In the westernmostpart of the Amazonas basin of Brazil (Solimoesdepocentre) shales and sandstones have beendetected in the subsurface, lacking shelly faunasbut dated as Early Ordovician by mean of palyno-morphs. The Contaya Formation in east–centralPeru consists of sandstones and dark shalesbearing graptolites, brachiopods and trilobites ofMid-Ordovician age (Hughes et al. 1980).

Most palaeontological information from theLower Palaeozoic sequences of South Americacomes from the up to 6000 m thick sedimentary suc-cessions that are exposed superbly in the CordilleraOriental (Eastern Ranges) and Sierras Subandinas(Subandean Ranges) of southern Peru, Bolivia andNW Argentina, forming the vast Central Andeanbasin (Fig. 1). Stratigraphical nomenclature ofthe Cambro-Ordovician units in this basin variesaccording to the countries, mountain belts and geo-tectonic provinces, and their correlation is often dif-ficult in the absence of adequate biostratigraphicalmarkers and accurate palaeontological studies.Some preliminary data from the San Jose Formation(Lower Ordovician) of the Cordillera Oriental of SE

BIOGEOGRAPHY OF SOUTH AMERICAN BENTHIC FAUNAS 203




Peru were published by Chacaltana et al. (2004) andGutierrez-Marco et al. (2004), and brachiopodswere described by Gutierrez-Marco & Villas(2007). Of particular interest for palaeogeographicalreconstruction is the volcaniclastic succession thatunderlies the San Jose Formation, named the Ollan-taytambo Formation, and the correlative Umachiribeds that crop out in the Peruvian altiplano. TheOllantaytambo Formation is a succession of darkshales, quartz-rich graded sandstones and ignim-brites of calc-alkaline basaltic to andesitic compo-sition; this geochemical signature indicates thatthese rocks formed in a volcanic arc setting. Onthis evidence, Bahlburg et al. (2006) concludedthat these volcanogenic deposits were connectedto the westward-lying Ordovician granitoids on theArequipa Massif, and also that this magmatic arcmay represent the northward continuation of theFamatina–Puna magmatic arc of northern Chileand NW Argentina.

In the Cordillera Oriental of NW Argentina, theCambro-Ordovician succession starts with shallow-water, Skolithos-rich reddish sandstones and silt-stones (Meson Group) of inferred Early–MiddleCambrian age. Apart from trace fossils, thistidal-dominated succession yielded only scatteredlinguliformean brachiopods. The Meson Group isoverlain by the Santa Victoria Group, whichincludes the Santa Rosita Formation (Furongian–Tremadocian), the Acoite Formation (upperTremadocian–Floian), and the Alto del Condor For-mation (Dapingian–lower Darriwilian?). However,a varied set of formations has been established toaccount for the strong lithofacial changes throughthe Cordillera Oriental and Sierras Subandinas(see stratigraphical chart by Astini 2003). A basin-wide transgressive surface separates this sequencefrom the overlying open platform deposits of latestDarriwilian–Sandbian age (Capillas or Santa Ger-trudis formations). Comparable siliciclastic rockscan be traced northwards into southern Bolivia,where the Cambrian–Lower Ordovician successionis represented by the Sama, Iscayachi, Cieneguillas,Obispo, Agua y Toro, and Pircancha or Sellaformations, and the Middle Ordovician by theAnzaldo and San Benito formations. A lithostrati-graphical and biostratigraphical scheme of Bolivianunits was provided by Suarez Soruco (2000), andbasin evolution of southern Bolivia was discussedby Erdtmann & Suarez Soruco (1999) and Egenhoffet al. (2004), among others. The Ordoviciansuccession culminates with glacigenic deposits ofHirnantian age, named the Zapla Formation inNW Argentina and Cancaniri Formation in Bolivia.

The Puna region of NW Argentina and northernChile is characterized by a lower volcanosedimen-tary succession of Furongian–Early Ordovicianage bearing graptolites and scarce trilobites and

brachiopods (Las Vicunas and Aguada de laPerdiz formations). These units are overlain by theup to 3500 m thick ‘Puna Turbidite Complex’,dated essentially as Middle Ordovician (Bahlburget al. 1990). South of Salar in the Atacama of north-ern Chile, the volcanosedimentary Cordon de LilaComplex is overlain unconformably by a transgres-sive, c. 1000 m thick marine succession namedthe Quebrada Grande Formation, containingbrachiopods and graptolites (Niemeyer et al. 2007;Benedetto et al. 2008). Approximately equivalentvolcaniclastic rocks (Umachiri beds) are exposedin the southern Peruvian altiplano (Bahlburg et al.2006).

Stratigraphy of the Sierra de Famatina wasreviewed by Astini & Benedetto (1996), Mangano& Buatois (1996, 1997), Astini (1999a, 2003) andAstini & Davila (2002). The oldest sedimentaryrocks, named the Volcancito Formation, of Furon-gian–Tremadocian age, consist of calcarenites,marls and laminated dark siltstones deposited on astorm-influenced marine platform (Albanesi et al.2005). The Bordo Atravesado Formation consistsof deep-water black shales of late Tremadocianage. The overlying volcaniclastic succession,c. 2000 m thick, starts with the Suri Formation,composed of silicified black shales, tuffs, biotur-bated siltstones bearing calcareous nodules, andfine-grained green sandstones, and culminates withthe Molles Formation, which consists of reddishpurple sandstones and siltstones, pyroclastic brec-cias and tuffaceous dark mudstones. The overallsuccession displays a shallowing upward trend,evolving from starved-basin graptolitic blackshales to storm and tidally influenced shallow-watersandstones. Muddy and silty intervals of both theSuri and Molles formations are rich in brachiopods,bivalves and trilobites. The Floian–Dapingian ageof this succession is well constrained by graptolitesand conodonts (Albanesi & Vaccari 1994; Lehnertet al. 1997; Toro & Brussa 1997).

The Precordillera basin of western Argentinacontrasts strongly with other South Americangeological provinces in the development of ac. 2500 m thick succession of Cambrian to MiddleOrdovician shallow-water platform carbonates. Itsstratigraphy, lithofacies, biostratigraphy, palaeocol-ogy, and fossil content have been the target ofnumerous studies in the last 25 years (summarizedby Benedetto 2003a). The Cambrian succession isrepresented, in ascending order, by the CerroTotora, La Laja and Zonda or La Flecha formations.The Ordovician carbonate units are the La Sillaand San Juan Formations (Keller et al. 1994;Canas 1999, 2002). The evaporites, dolomites andreddish clastic deposits of the Cerro Totora For-mation have been interpreted by Astini & Vaccari(1996) as recording synrift graben-filling deposits





related to the rifting of the Precordillera terranefrom Laurentia. These rocks grade upwards into apassive-margin carbonate succession, which rep-resents, according to this model, the rift–drifttransition. Along the western Precordilleran belt(‘western tectofacies’, Astini 2003) Cambrianrocks are preserved as limestone boulders and largeolistoliths, including deep-water platy limestoneand lime-shale strata, embedded within Ordovicianshales. This olistostromic unit, named the Los Som-breros Formation, records deposition in a deep-waterslope setting. The San Juan Formation is a wide-spread, 300–380 m thick carbonate unit dominatedby richly fossiliferous limestones deposited on topof an unrimmed shelf, which by the Darriwilianevolved into an homoclinal ramp with a depocentrelocated to the north of the basin (Canas 1999).Outer ramp and basinal facies are represented bymixed carbonate–clastic facies and graptoliticblack shales, respectively (Gualcamayo Formation).The Middle and Upper Ordovician successions aredominantly clastic and were deposited in a variedset of environments (fan deltas, marine platformand slope, glacigenic) displaying abrupt lithofacieschanges and hiatuses, attesting to a strong dep-ositional instability (Astini 2003). According toBenedetto & Astini (1993) and Astini et al. (1995),these phenomena may reflect the docking of thePrecordillera terrane against the Gondwana marginand subsequent post-collisional extension.

The Pampean Ranges (Pampia terrane) of centralArgentina are a series of mountainous ridgesuplifted during the Tertiary Andean orogeny, com-posed largely of polymetamorphic rocks and grani-toid plutons of Mesoproterozoic to early Palaeozoicage (Pankhurst & Rapela 1998, and referencestherein). The first shelly fossils, of Early Ordovicianage, were discovered recently in amphibolite-grademetasedimentary rocks (Verdecchia et al. 2007).

Data and methods

The brachiopod database for this study includes 117Ordovician genera and 166 species from variouslocalities of western Argentina. Of these, 80 generaand 97 species come from upper Tremadocian toHirnantian successions of the Precordillera terrane.The Lower Ordovician assemblages from the Fama-tina and Puna volcaniclastic rocks are composed of30 genera and 34 species. The Central Andean silici-clastic rocks of the Cordillera Oriental have yielded35 species and 29 genera of Cambrian to Sandbianage. Ordovician brachiopods from Chile, Boliviaand Peru are still poorly known, and consequentlythey are under-represented in our statistical analyses.This should, however, not be relevant to the resultsbecause the large Central Andean basin extendsinto NW Argentina (Salta and Jujuy provinces),

where fossil faunas are adequately known(Benedetto 1998b). It seems, therefore, that the bio-geographical signature of these faunas should notchange substantially with new findings.

Multivariate analyses of faunal data were per-formed using the program PAST, version 1.28(Hammer & Harper 2004). Cluster analysis wascarried out only for brachiopods and bivalves, ofwhich reasonably complete databases are available,whereas principal coordinates analysis (PCO) wasapplied only for brachiopods. In the cluster analysis,the Dice similarity index by unweighted pair grouplinkage was used to compare associations. As withother similarity indices, the Dice index ranges fromzero (no similarity) to one (identity). Principal coor-dinates analysis is an ordination method that finds theeigenvalues and eigenvectors of a matrix containingthe distances between all data points. It can be used tointerpret large multivariate datasets including pres-ence or absence data. The eigenvalues are given forthe first and second eigenvectors, and these valuesare plotted in a coordinate system, graphicallyshowing relationships (affinity) between datapoints (faunal assemblages). To enhance palaeobio-geographical affinities, both endemic and cosmopo-litan taxa were excluded from statistical analyses.

Biogeographical affinities of Ordovician bi-valves were evaluated previously by Sanchez &Babin (2003) using the Jaccard index. In thepresent paper, associations from 12 localities wereclustered by using the Dice similarity index. Ofthe nearly 150 bivalve genera reported globally forthe Ordovician Period, only 48 non-endemic taxahave been analysed statistically for two temporalintervals: Tremadocian–early Darriwilian, andSandbian–Hirnantian.

Early Cambrian

Brachiopods

Rhynchonelliformean brachiopods in the Precordil-lera terrane are rare and still poorly known. A pre-liminary survey of the Lower Cambrian carbonatebeds indicates the presence of Nisusia (probably anew species), Wimanella (close to W. simplexWalcott), some undetermined obolellids, and prob-able protorthids and eoorthids (Benedetto 2003b)(Fig. 2). Nisusia and Wimanella are confined toplates located within the equatorial belt (e.g. Laur-entia, Siberia, Altay–Sayan, South China), support-ing the low-latitudinal position of the Precordilleraterrane at that time.

Agmatan

Discovery of the cone-shaped agmatan Salterellamacculochi (Murchison) in a Lower Cambrian





olistolith within the Los Sombreros Formation ofthe Precordillera is significant, as this species isrestricted to North America, Greenland, Scotlandand Spitsbergen, and it has never been found any-where in Gondwana (Astini et al. 2004) (Fig. 2).

Trilobites

Borrello (1963) described the first Early Cambriantrilobite from the Precordillera and referred it toFremontella inopinata Borrello. This species isbased on poorly preserved material from the ElEstero Member of the La Laja Formation (Sierrade Villicum). Later, Borrello assigned to thisspecies an additional specimen from the locality ofZonda (Borrello 1964). Despite the poor preser-vation of this material it is possible to concludethat it is not conspecific with F. inopinata. In theLower Cambrian units of the Precordillera (Sierrade Villicum) Borrello (1971) identified Laudonia,Olenellus, Zacanthopsis, Eoptychoparia and Koote-nia, and later Bordonaro (1986) described speciesof Olenellus, Bristolia, Bonnia and Antagmus.This material is poorly preserved and many diag-nostic features are obscured, precluding reliable

identifications. Palmer & Repina (1993) mentionedthe occurrence of Olenellus (Mesolenellus) and Fre-montella in the La Laja Formation. New extensivetrilobite collections from this unit are now understudy by one of us (R.F.) and representativesof the Olenellidae, Biceratopsidae, Dorypygidae,Zacanthoididae and Ptychopariidae have beenrecognized. Initial results (Foglia & Vaccari 2006)indicate the presence of a new species of BonnimaFritz and Zacanthopsis (previously reported byBorrello 1971, p. 405). Additionally, followingthe revision by Lieberman (1999, p. 193), aspecies of Bolbolenellus (Palmer & Repina 1993)close to B. groenlandicus (Poulsen 1927) has beenrecognized. Although the material is still scarce itmay prove to be conspecific with B. groenlandicus,to which may belong the specimens described byBorrello (1963). So far, Arcuolenellus megafron-talis (Vaccari 1988) from the Cerro Totora Forma-tion (Guandacol, La Rioja) is the best documentedspecies from the Lower Cambrian sequencesof the Precordillera. It is associated with threeadditional species of Olenelloidea and a Ptychopar-iidae. The Lower Cambrian boulders from theLos Sombreros Formation at Rio Ancaucha have

Fig. 2. Selected Cambrian trilobites and brachiopods from the Precordillera terrane. (a) Arcuolenellus megafrontalis(Vaccari), Cerro Totora Formation, Lower Cambrian; (b) Bonnima sp., La Laja Formation, Lower Cambrian; (c)Salterella maccullochi (Murchison), Ancaucha olistolith, Lower Cambrian; (d) Nisusia sp., Ancaucha olistolith, LowerCambrian; (e, f) Wimanella sp., La Laja Formation, Middle Cambrian; (g) Glossopleura walcotti Poulsen, La LajaFormation, Middle Cambrian; (h) Madarocephalus laetus Resser, La Flecha Formation, Marjuman; (i, j) Crepicephalusiowensis (Owen), La Flecha Formation, Marjuman; (k, l) Cheilocephalus brachyops Palmer, La Flecha Formation,Furongian.





yielded at least four species associated with theagmatan Salterella maccullochi, two of whichbelong to Arcuolenellus and a third can be referredto Elliptocephala Emmons. The fourth speciesis fragmentary but may belong to Olenellus (Paude-mias). Olistoliths in the Los Tuneles section containSombrerella argentina Vaccari & Bordonaro andfragmentary olenelloidea referred to Olenellus? sp.(Vaccari & Bordonaro 1993). Palaeogeographi-cally, it is worth noting that both Arcuolenellusand Bolbolebellus belong to a clade recorded sofar only in Laurentia.

Middle–Late Cambrian

Brachiopods

Some assemblages of lingulate brachiopods fromPrecordillera were described by Holmer et al.(1999). The fauna, composed mainly of acrotretids,comes from Middle Cambrian limestone olistolithswithin Ordovician slope deposits named the LosSombreros Formation. Other samples are from theMiddle Cambrian Cerro Pelado Formation and theEl Relincho olistolith of Marjuman age. All ofthe nine genera identified and two of the species areknown elsewhere from Laurentia, and Curticia rep-resents the first record outside that palaeocontinent.Picnotreta is a widespread genus recorded fromAustralia, Greenland, Kazakhstan and North Tien-Shan (Kirgizia). According to Holmer et al. (1999,p. 230), the Cambrian lingulate faunas of the Precor-dillera demonstrate a consistent similarity to thecontemporaneous assemblages of North America.Moreover, they stressed their affinities with Siberianassemblages (e.g. both Neotreta and Hadrotretahave been recorded from southeastern Siberia).

Trilobites

Middle Cambrian trilobites are under revision;consequently they are not considered herein. LateCambrian faunas from the Precordillera arederived largely from the La Flecha Formation(Marjuman–Sunwaptan) that crops out in the Guan-dacol area (La Rioja province) in the north to theCerro Pedernal (San Juan province) in the south.This unit has been interpreted as a peritidal carbon-ate shelf by Canas (1999). Other Late Cambrian fos-siliferous localities contain resedimented bouldersof the Empozada and Los Sombreros formations inMendoza and San Juan (Bordonaro et al. 1993).

Vaccari (1994, 1995, 1996) recognized in the LaFlecha Formation the Crepicephalus, Aphelaspisand Saukia zones. Trilobites from the Crepicepha-lus Zone include species of Crepicephalus,Cosella, Pemphigaspis, Madarocephalus, Welleras-pis, Lonchocephalus, Kingstonia and Komaspidella.

So far, only Dytremacephalus and Cheilocephalushave been reported from the Aphelaspis Zone. Anassociation belonging to the Saukia Zone is domi-nated by plethopeltids, represented by species ofPletopelthis and Stenopilus, recovered from theuppermost levels of the La Flecha Formation atGualcamayo, La Silla and La Flecha localities.Boulders of the Empozada and Los Sombrerosformations have yielded trilobites of the Cedaria,Crepicephalus, Elvinia and Saukia zones (Borrello1971; Shergold et al. 1995; Bordonaro 2003).Reported taxa include widely distributed forms(e.g. agnostids and Irvingella), along with thegeographically more restricted Tricrepicephalus,Elvinia and Hungaia.

Genera documented in the peritidal carbonatesof the La Flecha Formation are overall exclusiveto Laurentia (Fig. 2). Moreover, it is remarkablethat the occurrence of several Late Cambrianspecies is shared by Laurentia and the Precordillera,such as Crepicephalus iowensis (Owen), Tricre-picephalus texanus (Shumard), Komaspidellalaevis Rasetti, Madarocephalus laetus Resser,Cheilocephalus brachyops Palmer and Elviniaroemeri (Shumard), along with the pelagic trilobiteIrvingella major Ulrich & Resser. Some ofthese species (e.g. T. texanus, C. brachyops andE. roemeri) are widely represented in NorthAmerica (Palmer 1965; Westrop 1986; Pratt 1992;Chatterton & Ludvigsen 1998, among others),whereas others are more restricted. Among them,M. laetus was reported from Alabama, Tennesseeand Quebec (Rasetti 1946, 1965), and K. laevisfrom Virginia, Missouri and Newfoundland(Rasetti 1961; Lochman 1968; Westrop 1992).Accordingly, Later Cambrian trilobite faunas fromthe Precordillera belong to the biogeographical pro-vince of Laurentia; the greatest affinities are evidentwith the eastern part of this palaeocontinent. Theserecords strongly support the view that during theLate Cambrian there were no barriers to faunalexchange between the Precordillera and Laurentia.

Furongian–early Tremadocian

Brachiopods

The earliest rhynchonelliformean brachiopod so farpublished from the Central Andean basin is Proto-rthisina simplex Benedetto, from Furongian darkgrey mudstones (Lampazar Formation) of the Cor-dillera Oriental of NW Argentina and Bolivia. Mor-phological and stratigraphical evidence suggeststhat this species is the stem group of both nanorthidand euorthisinid clades and that it gave origin to thegenus Kvania, which is represented by at least threespecies in the lower Tremadocian strata of theCordillera Oriental and western Puna (Benedetto





2007a) (Fig. 3). Kvania is known elsewhere from theupper Tremadocian of Bohemia (where the typematerial come from; Mergl 1984) and NE Bavaria,Germany (Villas, in Sdzuy et al. 2001). This recordof Kvania suggests a migratory route linking theCentral Andean basin with north Gondwana, prob-ably along the clastic platforms fringing the NorthAfrican and Brazilian shields. Accompanyingforms are Apheoorthis? Ulrich & Cooper andFinkelnburgia (Benedetto 2003a, plate 21, fig. 13).

In the revised version of the brachiopod Treatisethe genus Orusia Walcott is mentioned as occurringin the Cambrian of Argentina (Williams & Harper2000). It should be noted, however, that the presenceof this genus in the Central Andean basin has notbeen confirmed. Orthis saltensis Kayser, whichwas reassigned to Orusia by Kobayashi (1937),was referred subsequently to Nanorthis by Ulrich& Cooper (1938). Orusia putilliformis Kobayashi(1937), of early Tremadocian age, was reassignedto Nanorthis by Castellaro (1963), but owing tothe very limited material on which this specieswas erected and the lack of types designated, ithas been considered a nomen nudum (Benedetto2007a). Finally, the mention in the Treatise ofOtusia Walcott for the Upper Cambrian ofArgentina is also erroneous.

The Furongian–Tremadocian brachiopods fromthe Famatina basin are poorly known. Harrington(1938) referred some external moulds from theVolcancito Formation to Finkelnburgia samensisKobayashi. In ornament, these specimens resembleKvania? primigenia Benedetto, but because internalfeatures are unknown their systematic positionremains uncertain.

The uppermost Furongian–lower Tremadocianassemblages from Andean Gondwana cannot beincluded easily neither in the Billingsella Associ-ation nor in the Huenella Association recognizedby Bassett et al. (2002) because of the absence of syn-trophioidean pentamerides. Billingsellidines, on theother hand, are represented by a new genus thatbelongs to a lineage that probably branched off atthe base of this clade (Benedetto, unpublished). Adistinctive feature of the Andean assemblages,besides their low diversity, is the occurrence of theearliest representatives of the nanorthid clade,which during the late Tremadocian and Floiandiversified in shallow shelf environments.

Trilobites

The only trilobite from the uppermost Cambrianrestricted carbonate facies (La Silla Formation, Pre-cordillera) is Plethopeltis obtusus (Vaccari 1995), atypical Laurentian form. Furongian trilobites areconfined to the Neoparabolina frequens argentinaZone, both in the Central Andean basin (LampazarFormation, Casa Colorada Member of the SantaRosita Formation) and the Famatina Range (Vol-cancito Formation) (Fig. 3). They have beenincluded traditionally in the ‘olenid fauna’ knownelsewhere from several broadly similar environ-mental settings in biogeographically disparateregions such as Baltica, Avalonia, Laurentia andSiberia. Olenids are associated with several wide-spread agnostid taxa. The widespread Asaphellusand Conophrys are common forms in NWArgentina. Hapalopleurids (e.g. Hapalopleura,Rhadinopleura) are also common (Waisfeld &

Fig. 3. Selected Upper Cambrian–lower Tremadocian trilobites and brachiopods from the Central Andean basin (CA),western Puna (WP) and Precordillera (P). (a, b) Plethopeltis obtusus (Rasetti), La Silla Formation, Furongian (P);(c) Amzasskiella n. sp., Las Vicunas Formation, Furongian, lower Tremadocian (WP); (d) Neoparabolina frequensargentina (Kayser), Lampazar Formation, Furongian (CA); (e) Onychopyge sp., Lampazar Formation, Furongian (CA);(f) Protorthisina simplex Benedetto, Lampazar Formation, Furongian (CA); (g) Kvania? primigenia, LampazarFormation, Furongian (CA).





Vaccari 2003); however, considerable generic split-ting of the group and the lack of recent taxonomicrevisions makes it difficult to assess their biogeogra-phical significance.

Vaccari et al. (2006) noted that some lowerTremadocian taxa documented in the CordilleraOriental suggest East Gondwana connections.Onychopyge occurs in the Furongian VolcancitoFormation and Furongian and Lower Tremadocianstrata of Cordillera Oriental (Harrington & Leanza1957; Tortello & Esteban 1999). This genus isknown from several species in the Furongian ofNE China (Lu et al. 1986), and it is more widely dis-tributed in the early or middle Tremadocian, withrecords in Australia, New Zealand, North andSouth China, and Mexico. The occurrence of theleiostegiid Brackebuschia in the lower Tremadocianof the Cordillera Oriental is also remarkable.Although the genus ranges into the early Sandbian(Ludvigsen 1980; Ebbestad 1999; Adrain, in Jell &Adrain 2003), the earliest records are so far restrictedto the upper Tremadocian of Scandinavia (Tjernvik1956; Ebbestad 1999) and the Cordillera Oriental.

Leiostegium, recorded from the lower Tremado-cian of the Cordillera Oriental (Harrington &Leanza 1957; Waisfeld & Vaccari 2003) is knownelsewhere from Laurentia, the Precordillera, Chinaand Australia. Australoharpes occurs in the lowerTremadocian of the Cordillera Oriental (Harrington& Leanza 1957), and it was also reported fromVictoria (Australia). Jell (1985) pointed out the affi-nities of the Victoria and NW Argentina faunas, andWebby et al. (2000) also discussed the affinities ofthe Australian fauna and emphasized the records ofAustraloharpes and Onychopyge as good indicatorsof these connections. The occurrence of Amzass-kiella in the lower Tremadocian of the CordilleraOriental reported by Vaccari et al. (2006) is also sig-nificant because it occurs in East Gondwana (China,Australia and New Zealand), as well as in Siberia andKazakhstan. Hence, lower Tremadocian trilobitesexhibiting restricted geographical distributionssupport faunal affinities with warm-water settings.Some of these forms are also present in the lower Tre-madocian Las Vicunas Formation (western Puna),where the occurrence of Amzasskiella, Leiostegiumand Onychopyge (Vaccari & Waisfeld 2000, 2008)also reveals exchange with low-latitude areas.

Late Tremadocian–Floian

Brachiopods

The Precordilleran assemblages recovered from thelowermost part of the San Juan Formation lime-stones, of late Tremadocian–Floian age (P. delti-fer/O. evae conodont zones) are moderatelydiverse and include Archaeorthis, Paralenorthis,

Orthidium, Ranorthis, Nothorthis, Nanorthis,Hesperonomiella, Hesperonomia, Tritoechia, Syn-trophia, Parallelostrophia, Huacoella and Leptella(Leptella) (Benedetto 2001a, 2002; Benedetto et al.2003a) (Fig. 4). With the exception of Ranorthis,which occurs in Baltica, and the endemics Hua-coella and Parallelostrophia, most of these taxahave also been recorded from Laurentia and SouthChina (Zhan & Rong 2003).

In general, brachiopod assemblages recoveredfrom inner to mid-carbonate-ramp settings of thePrecordillera terrane may be ascribed to thelow-latitude Clarkella Fauna (Bassett et al. 2002),typified by the co-occurrence of pentamerides, fin-kelnburgiids, eoorthids and tritoechiids. However,in contrast to the typical assemblages from Lauren-tia and Central Asian terranes, eoorthiids andfinkelnburgiids are absent in the Precordillera,whereas ranorthids and orthidiellids are relativelyabundant, as in Baltica (Egerquist 1999, 2004) andnorthern Gondwana (North Africa, Bohemia;Havlıcek 1971, 1977). This is consistent with themixed Laurentian–Baltic–Gondwanan signatureof the Precordilleran benthic faunas noted byHerrera & Benedetto (1991) and supports thehypothesis that the Precordillera terrane waslocated at that time in an almost equidistant positionbetween Laurentia and Gondwana (Benedetto et al.1999). It should be noted that the Clarkella Faunais unknown from coeval clastic cold–temperateplatforms of the Andean region of Gondwana.

The Central Andean assemblages are differentfrom the low-latitude faunas. A distinctive featureof these Andean faunas is the occurrence of theendemic euorthisinids Notorthisina Havlıcek &Branisa (1980) and Lesserorthis Benedetto(2007a), and the earliest known enteletacean Lipa-northis Benedetto (Harper et al. 2004) (Fig. 5).Also notable is the absence of tritoechiids, whichwere dominant in the north Gondwanan ‘Tritoe-chia–Protambonites Association’ (Bassett et al.2002). The occurrence of Astraborthis Williams inupper Tremadocian beds of NW Argentina(Benedetto & Carrasco 2002) is biogeographicallysignificant as it is known elsewhere only from theWelsh Borderland of Britain, although in slightlyyounger rocks (Williams 1974). The record ofEuorthisina in Peru (Gutierrez-Marco & Villas2009), Bolivia, NW Argentina, Avalonia andSouth China (Zhan et al. 2006) points to a faunalconnection along the Gondwana periphery, fromintermediate to high latitudes. As noted previously(Benedetto & Sanchez 2003; Sanchez & Benedetto2004; Benedetto 2007a), the autochthonous Andeanshelves were the site of the early diversification ofeuorthisinids, nanorthids and primitive endopunc-tate orthides, and such a diversification pattern isin striking contrast to that seen in the low-latitude





Laurentian carbonate platforms (Patzkowsky 1995).It is now apparent that the first ‘articulate’ brachio-pod radiation on temperate to cold-water Gondwanashelves was not delayed with respect to other conti-nents (e.g. Baltica, Laurentia) but it started beforeand involved different clades (see Harper 2005).

Bivalves

The lower Floian Precordilleran strata have yieldedonly two poorly preserved species of bivalves, amodiolopsid (Modiolopsis? sp.) and an undeter-mined ambonychiid. As ancestors of ambonychiidsare unknown in Laurentia, and considering that theearliest known member of this family is from thePrecordillera, the origin of this group may lie inthat terrane. By the Late Ordovician ambonychiidsdiversified in Laurentia, becoming a characteristiccomponent of its faunas.

In the Central Andean basin of NW Argentinaand Bolivia several Gondwanan genera have beenrecorded (e.g. Redonia, Coxiconchia, Babinka,Hemiprionodonta; Fig. 5), supporting closestpalaeogeographical relationships with southEurope (Sanchez & Babin 2005). The dendrogram

in Figure 6a shows a well-defined Gondwanagroup embracing Iberia, Armorica and Morocco.By the late Tremadocian–early Floian bivalvesunderwent a remarkable radiation in the Andeanbasins of Gondwana including origination of newclades, such as goniophorinids, ucumariids (prob-ably ancestral to the Anomalodesmata), redoniidsand cycloconchids (Sanchez & Vaccari 2003;Sanchez 2005, 2006). Some of them dispersed sub-sequently along the Gondwanan shelves, whereasothers became extinct before the end of the Ordovi-cian. It seems likely that the coxiconchins, recentlyrecognized as a clade within the Family Babinkidae(Sanchez 2008), and babinkids, evolved from thelate Tremadocian Coxiconchia babini Sanchezfrom northwestern Argentina. Babinkids (includingcoxiconchins) are typical of Gondwanan andperi-Gondwanan terranes.

Bivalve faunas from Famatina are highlyendemic (four of the seven Floian genera areendemic), leading to an inference of some kind ofisolation from other basins and/or peculiar environ-mental conditions (e.g. narrow and unstable plat-forms peripheral to volcanoes). The FamatinanColpomya is recorded elsewhere from younger

Fig. 4. Selected upper Tremadocian–Floian brachiopods and trilobites from the Precordillera terrane (San JuanFormation) and Sierra de Famatina. (a, b) Peltabellia n. sp., San Juan Formation, upper Tremadocian; (c, g) Benedettianiquivilensis (Harrington & Leanza), San Juan Formation, Floian; (d) Annamitella harringtoni Vaccari, San JuanFormation, Floian; (e, f) Pliomera tmetophrys Harrington & Leanza, Suri Formation, Floian (Sierra de Famatina); (h)Syntrophia sanjuanina Benedetto, San Juan Formation, upper Tremadocian; (i) Leptella (L.) alata Benedetto & Herrera,San Juan Formation, Floian; (j) Huacoella radiata Benedetto & Herrera, San Juan Formation, Floian; (k) Tritoechiaprima Benedetto, San Juan Formation, Floian; (l) Orthidium prominens Benedetto, San Juan Formation, upperTremadocian–lower Floian.





Fig. 5. Selected upper Tremadocian–Floian brachiopods, bivalves and trilobites from Sierra de Famatina (F) andCentral Andean basin (CA). (a) Merlinia megacantha (Harrington & Leanza), Suri Formation, Floian (F);(b) Famatinolithus jujuyensis Benedetto & Malanca, Acoite Formation, Floian (CA); (c, f) Neseuretus (N.) lipanensisWaisfeld, Acoite Formation, Floian (CA); (d) Carolinites sp., Acoite Formation, Floian (CA); (e) Hungioidesintermedius (Harington & Leanza), Suri Formation, Floian (F); (g, h) Kayseraspis asaphelloides Harrington, SanBernardo Formation, Floian (CA); (i, j) Pytine wirayasqa Vaccari, Waisfeld, Chatterton & Edgecombe, AcoiteFormation, Floian (CA); (k, m) Colpocoryphe perforata Waisfeld, Acoite Formation, Floian (CA); (l) Branisaspisn. sp., Acoite Formation, Floian (CA); (n) Astraborthis quebradensis Benedetto, Coquena Formation, upperTremadocian (CA); (o) Incorthis sp., Acoite Formation, upper Floian (CA); (p) Euorthisina sp., Acoite Formation,upper Floian (CA); (q) Lipanorthis santalaurae Benedetto, Floresta Formation, lower upper Tremadocian (CA);(r) Ucumaris conradoi Sanchez, Floresta Formation, lower upper Tremadocian (CA); (s) Babinka notia Sanchez,Santa Victoria Group, upper Tremadocian–lower Floian (CA); (t) Suria ovalis Sanchez, Suri Formation, Floian (F);(u) Coxiconcha sellaensis Sanchez & Babin, Sepulturas Formation, Floian.





rocks of Laurentia, Redonia from the CentralAndean basin and south Europe, and Goniophorinafrom younger strata of China. Suria, a typical Fama-tinan genus, was reported recently by Gutierrez-Marco et al. (2004) from the Ordovician of southernPeru (Fig. 5).

Trilobites

Records from Famatina (Bordo AtravesadoFormation, upper Tremadocian) are restricted todeep-water environments, and hence are of littlebiogeographical meaning. Tortello & Esteban(2003) described an ‘atheloptic assemblage’ (seeFortey & Owens 1987) from this unit, composedof widespread forms as well as cyclopygids charac-teristic of peripheral sites marginal to Gondwana.No equivalent assemblage has been reported so farform the Cordillera Oriental.

Late Tremadocian faunas from the CordilleraOriental include widespread elements (Conophrys,Asaphellus, Apatokephalus, Parabolinella, Lepto-plastides, Bienvillia), some endemic asaphids(Notopeltis, Doloreasaphus, Mekynophrys), aswell as some forms that are in need of taxonomicrevision. Latest Tremadocian to early Floian low-diversity trilobite associations are included in theThysanopyge Fauna (Harrington & Leanza 1957;Waisfeld et al. 1999). This fauna exhibited arather narrow intraregional distribution and devel-oped in relatively restricted, locally oxygen-deficient prodeltaic settings (Waisfeld & Astini2003; Waisfeld & Vaccari 2008). Several endemictrilobites such as Thysanopyge itself, Australopyge,Sanbernardaspis, Niobides, Zuninaspis andprobably ‘Colpocoryphoides’, are associated withwidespread forms (Asaphellus, Megistaspis (Eker-aspis), Ogygiocaris, Conophrys, Hypermecaspis,Bienvilllia). Kayserapsis is otherwise known fromthe upper Tremadocian of North China (Zhou &

Fortey 1986), and lower Floian of Korea (Choi1998), Australia (Laurie & Shergold 1996) andKazakhstan (Lisogor 1961). The raphiophoridRhombampyx has been recorded in Spitsbergen,Baltica and South China (Nielsen 1995), and theolenid Psilocara is so far known from the lowerFloian of Spitsbergen. Although biogeographicallysensitive elements are scarce, the records ofKayseraspis, Psilocara and Rhombampyx suggestexchange with warm-water areas. Recently,Waisfeld & Vaccari (2008) interpreted the peculiarbiogeographical signature of the Thysanopyge faunaas a result of ecological or environmental factorscoupled with a particular geodynamic context.Accordingly, restricted circulation and limited con-nections to oceanic waters might have been linked tothe development of a shallow seaway related to anactive volcanic arc to the west. In this setting, het-erogeneous dysoxic or anoxic conditions, variablein intensity and duration, promoted the establish-ment of a distinctive trilobite fauna having onlyweak connections with other peri-Gondwananregions.

By late early Floian–late Floian times, deposi-tional patterns in the Central Andean basinchanged, associated with a remarkable coastal pro-gradation bringing about a complete shift in thearray of trilobites. These associations, mostlyreferred to the Famatinolithus Fauna, displayhigher diversity than earlier Floian counterpartsand also include a suite of endemics (Famatino-lithus, Pliomeridius, Branisaspis, Hoekaspis), aswell as widespread forms (Hypermecaspis, Porter-fieldia). In inshore environments the widespreadperi-Gondwanan genera Neseuretus and Ogyginusoccur (Fortey & Cocks 1988, 2003). Neseuretusranges into mid-shelf environments (Waisfeld1995, 1997), where it is associated with Colpo-coryphe and raphiophorids resembling Britishrepresentatives of the group (see Fortey & Owens

Fig. 6. Dice similarity index dendrograms for (a) Early Ordovician bivalves and (b) Late Ordovician bivalves.





1987), accounting for a west Gondwanan signature.Interestingly, these forms are associated with Caro-linites, an epipelagic taxon distributed between308N and 308S (McCormick & Fortey 1999), andPsilocara and Pytine, recently reported from thelower Floian of the Cordillera Oriental (Vaccariet al. 2006; Fig. 5). Pytine occurs elsewhere inSpitsbergen, Australia, North and South China,and probably Baltica.

Some members of the Famatinolithus Faunahave also been reported from Bolivia (e.g. SellaFormation and equivalents units) by Branisa(1965), Pribyl & Vanek (1980) and Acenolazaet al. (1999), and recently Neseuretus, Anebolithusand Branisaspis were recorded in the lower part ofthe San Jose Formation, southern Peru, byGutierrez-Marco et al. (2004). Branisaspis is anendemic asaphid hitherto known from the CordilleraOriental of Argentina and Bolivia, and Neseuretus isa peri-Gondwanan form, extensively represented inthe Cordillera Oriental of Argentina and Bolivia,and also in Famatina.

Unlike the Thysanopyge fauna, the Famatino-lithus fauna has been recorded in widely separateareas of the Cordillera Oriental, and representativesof this fauna were also documented in the CordilleraOriental of Bolivia (Branisa 1965; Pribyl & Vanek1980; Acenolaza et al. 1999), accounting for theregionally widespread nature of this assemblage inthe South American proto-Andean margin(Waisfeld 1998). From a biogeographical view-point, the Floian trilobite fauna reveals a complexpattern, which is consistent with the position ofthe South American margin at intermediate latitudes(see Fortey & Cocks 2003). Endemism, mainly inasaphids, supports a certain degree of isolation;meanwhile, provincially significant elementsexhibit a mixture of affinities either with warm-water areas or with West Gondwana.

Coeval early and late Floian trilobite faunas fromthe volcaniclastic successions of Famatina show amixture of East and West Gondwanan forms(Vaccari 1995; Waisfeld 1998; Fig. 5). Famatinashares with Precordillera mostly widely distributedtaxa, and with the Cordillera Oriental, apart fromwidespread taxa, the endemic genera Famatino-lithus and Pliomeridius. The Neseuretus biofacieshas been recognized in inshore settings (Vaccariet al. 1993). Neseuretus is associated with Merlinia,otherwise known from the British Floian–Darriwil-lian (Fortey & Owens 1978; Rushton & Hughes1981), and Annamitella. High-diversity middle-shelf faunas account for an interesting mixing ofMerlinia and Salterocoryphe, of clear West Gond-wana affinities, Hungioides, widely distributed indisparate peri-Gondwanan areas, and Pliomera,Gogoella and Pliomerina, showing connectionswith warm-water settings (East Gondwana and

Baltica). The occurrence of the epipelagic Caroli-nites and Oopsites (Vaccari & Waisfeld 1994) alsoreinforces these connections. Low-diversity distalshelf faunas are composed of agnostids andolenids (Porterfieldia, Hypermecaspis).

Affinities of Ordovician trilobites from the Pre-cordillera are particularly interesting as they docu-ment a progressive latitudinal change from atropical position in the Tremadocian to high lati-tudes in the Hirnantian. A shallow-water assem-blage dominated by bathyurids (e.g. Peltabelliaand Uromystrum) and Leiostegium occurs at thebase of the overlying San Juan Formation (upperTremadocian) (Fig. 4). In the early Floian(P. elegans Zone) the endemic pliomerid Benedettia,which is closely linked to the Australian Cannin-gella, has been recorded. Annamitella, Illaenus,Platillaenus, Benedettia and a new bathyuridspecies very close to Petigurus are present in theO. evae Zone. The bathyurid biofacies is character-istic of inshore settings of Laurentian and Siberiancarbonate platforms (Fortey 1975; Fortey & Peel1983). Species of Peltabellia occur in Laurentiaand Siberia, whereas Uromystrum is so far restrictedto Laurentia. Leiostegium, Annamitella and Illaenusexhibit a wide geographical distribution. Theabsence of Annamitella in the carbonate platformof North America and Siberia has been interpretedas a result of facies controls (Fortey & Shergold1984; Webby & Edgecombe in Webby et al.2000). Fortey & Cocks (2003) suggested that Anna-mitella is absent not only in the carbonate succes-sions of Laurentia and Siberia, but also in thesiliciclastic platforms of Europe. This pattern isonly partially endorsed in Argentine basins. Annami-tella is lacking in siliciclastic successions of the Cor-dillera Oriental of Bolivia and Argentina, and it iscommon in volcaniclastic settings of Famatina andPuna. However, Annamitella is the most widespreadtrilobite in the Floian to Darriwilian carbonate suc-cessions of the Precordillera (Vaccari et al. 2006),demonstrating that its distribution was not controlledby facies.

Trilobites from volcanosedimentary successionsof western Puna (at Vega Pinato, partially equi-valent to Aguada de La Perdiz Formation) exhibitinteresting biogeographical affinities (Vaccari2003). Relevant taxa include Hystricurus (s.l.), aform displaying a pan-Equatorial distribution,Protostygina, recorded in Kazakhstan, Bohemia,Spitsbergen and western Ireland, and Gogoella, sofar known from Australia and Famatina. Therecord of a dikelokephalinid is also significant.Although representatives of this family exhibit alargely peri-Gondwanan distribution, earlierOrdovician species are restricted to East Gondwana.Illaenus and Annamitella are widely distributedforms, but in Argentina they are confined to the





carbonate and volcaniclastic successions of the Pre-cordillera, Famatina and Puna, and are lacking in thesiliciclastic deposits of the Cordillera Oriental. Insummary, trilobite faunas from western Punaexhibit a notable influence of East Gondwanaelements, showing close affinities with the Famatinaassemblages and a sharp contrast to those of the Cor-dillera Oriental.

Dapingian–Darriwilian

Brachiopods

The time interval analysed here ranges essentiallyfrom the O. triangularis to E. suecicus conodontzones. However, to analyse the affinities of theFamatina and Cordillera Oriental those assemblagesfrom the late Floian O. evae have also beenincluded. The dendrogram of Figure 7a showsthree main clusters, which coincide largely withthe biogeographical units recognized by Williams(1973): (1) low-latitude brachiopod faunas devel-oped on a heterogeneous set of palaeocontinentsand microplates; (2) mid- to high-latitude volcano-sedimentary Iapetus Ocean-related settings (theCeltic Realm sensu Neuman 1984); (3) mid- to high-latitude Gondwanan and peri-Gondwanan assem-blages. It should be noted that the mid-latitude,highly endemic Baltic faunas cluster among thesecond group because endemic taxa have not beenconsidered. This grouping does not differ substan-tially from the dendrogram produced by Harper(2005). Perhaps the main difference lies in that inHarper’s analysis the Central Andean brachiopodscluster within the Celtic Realm, but this is nolonger consistent with the absence of Celtic taxain the Central Andes of Bolivia and Argentina.Also comparable is the dendrograma produced by

Rong et al. (2005) in which Celtic, Gondwananand low-latitude assemblages are clearly separated.

The Precordilleran faunas form a well-definedcluster together with the Laurentian (not differen-tiated here in ‘marginal’ and ‘intra-plate’ faunas)and Irish faunas (Tourmakeady Limestone;Williams & Curry 1985), which in turn are linkedwith the peri-equatorial carbonate-platform assem-blages from South China, Kazakhstan and Altay–Sayan (marginal to the Siberia plate). This ensembleis roughly equivalent to the Toquima–Table HeadRealm of Ross & Ingham (1970), redefined laterby Neuman & Harper (1992). By Darriwilian time,several Celtic and Baltic genera migrated into thePrecordillera basin, giving a mixed ‘Laurentian–Baltic–Celtic’ signature to these assemblages(Herrera & Benedetto 1991). In the correspondenceanalysis performed by Neuman & Harper (1992,fig. 2), the Precordillera plots near to the Celticlocalities, although closer to the Laurentian faunasthan any other Celtic assemblage. The samepattern is shown in the PCO diagram of Figure 8.By the Dapingian–early Darriwilian (B. navis–L.variabilis zones) typical Celtic Realm elementssuch as Monorthis, Ffynnonia, Rugostrophia, Pro-ductorthis, Ahtiella and Inversella (Reinversella)suddenly appear towards the top of the San JuanFormation, where they constitute up to 40% ofthe genera (Fig. 9). Except for Inversella, all thesegenera also occur in the Famatina basin, but inslightly older rocks. Increasing similarity betweenFamatinan and Precordilleran brachiopods can beinterpreted as resulting from the final approximationof the Precordillera terrane to the Gondwanamargin. It is believed that in such a palaeogeo-graphical configuration, most brachiopods inhab-iting the Famatina basin moved into the narrowseaway separating the two crustal blocks and then

Fig. 7. (a) Dice similarity index dendrogram for the late Floian–early Darriwilian rhynchonelliform brachiopods(all orders included); (b) similar dendrogram for Order Orthida only.





reached the Precordilleran carbonate ramp(Benedetto 2004; Benedetto & Cech 2006). Simi-larity between the brachiopods from the upper partof the volcanosedimentary succession of Famatina(Molles and Cerro Morado Formations) and theupper San Juan Formation of the Precordillera isparticularly strong. The two units share similarspecies of Ahtiella and Skenidioides, suggestingthat by Darriwilian time the Precordillera lay rela-tively close to the Famatina volcanic arc (Benedettoet al. 2003b).

Rhynchonelliformean brachiopods from Fama-tina, Wales, Central Newfoundland–New Bruns-wick and western Puna form a statisticallysignificant cluster, supporting the distinctivenessof the Celtic faunas (Neuman & Bates 1978;Neuman 1984; Bruton & Harper 1985; Neuman &Harper 1992; Harper et al. 1996). The Celtic signa-ture of the Famatinan brachiopods was confirmedby Benedetto (2003c, fig. 3) by using multivariatecluster analysis. In the present analysis, brachio-pods from the western Puna volcaniclastic rocks(Benedetto 2001b) were included in the datamatrix. As dendrograms (Fig. 7) and the PCOdiagram (Fig. 8) show, the Puna assemblage clusters

close to Famatina. Besides the endemic Pinatoto-echia and Trigonostrophia, these regions shareHesperonomia, Tritoechia and Rugostrophia. Therecent discovery of Monorthis transversa Bene-detto, a typical Famatinan taxon, in the Puna highplateau of northern Chile (Atacama region)(Niemeyer et al. 2007), and of Ffynnonia in thePampean Ranges, almost 200 km east of the Fama-tina Range (Verdecchia et al. 2007) (Fig. 10) con-firms the wide geographical distribution of thesetaxa, supporting the existence of a more or less con-tinuous chain of emergent volcanic islands separ-ated by shallow seas along the Andean margin(Benedetto 1998a). Strikingly, the Puna brachio-pods contrast markedly with those of the neighbour-ing Cordillera Oriental (Benedetto 1998b), whichdisplay affinities with the Welsh Borderland,Shelve District brachiopods (Williams 1974). Thissuggests the existence of a geographical barrier sep-arating the Puna and Central Andean faunas. Itappears that the barrier was the deep-water exten-sional back-arc basin developed behind the volcanicarc, which is well documented by thick turbiditedeposits associated with submarine bimodal volcan-ism (Bahlburg 1990; Coira et al. 1999).

Fig. 8. PCO analysis (Dice similarity index) for the late Floian–early Darriwilian time interval (all rhynchonelliformorders included).





The Central Andean faunas form, together withthe NW African, Avalonian and Perunican faunas,a Gondwana cluster (Fig. 7b), although all theseregions share only a few taxa. The genus Incorthis

(Fig. 5), perhaps one of the most distinctive brachio-pods of the temperate to cold-water Gondwananshelves, has been recorded in Floian strata of NWArgentina, Bolivia and NW Africa (Morocco), but

Fig. 9. Selected Dapingian–Sandbian brachiopods, trilobites and rostroconchs from the Precordillera terrane. (a)Productorthis cienagaensis Herrera & Benedetto, upper San Juan Formation, lower Darriwilian; (b) Orthidiumgeniculatum Herrera & Benedetto, upper San Juan Formation, lower Darriwilian; (c) Porambonites sp., upper San JuanFormation, lower Darriwilian; (d) Taffia anomala Benedetto & Herrera, upper San Juan Formation, lower Darriwilian;(e) Monorthis cumillangoensis Benedetto, San Juan Formation, Dapingian; (f) Ahtiella argentina Benedetto & Herrera,upper San Juan Formation, lower Darriwilian; (g, i) Petroria rugosa Wilson, San Juan Formation, Dapingian–Darriwilian; (h) Inversella (Reinversella) arancibiani Herrera & Benedetto, upper San Juan Formation, lowerDarriwilian; (j) Martellia talacastoensis (Benedetto), upper San Juan Formation, lower Darriwilian; (k) Idiostrophiasp., upper San Juan Formation, lower Darriwilian; (l) Ffynnonia spondyliformis Benedetto, San Juan Formation,Dapingian–Darriwilian; (m, n) Waisfeldaspis beatrizae Vaccari, upper San Juan Formation, Darriwilian; (o) Lehnertiawawisapa Vaccari, Waisfeld, Chatterton & Edgecombe, Las Chacritas Formation, Darriwilian; (p) Stenoblepharumastinii Edgecombe, Chatterton, Vaccari & Waisfeld, Las Aguaditas Formation, Sandbian; (q, r) Ceratocara argentinaChatterton, Edgecombe, Vaccari & Waisfeld, Las Aguaditas Formation, Sandbian; (s) Prosopiscus sp., Las AguaditasFormation, Darriwilian; (t) Talacastella herrerai Sanchez, San Juan Formation, lower Darriwilian.





also in lower Dapingian volcaniclastic rocks ofFamatina, indicating a certain degree of admixturebetween the Famatina back-arc basin and clasticshelves surrounding Gondwanan shields. Therecent discovery of Ahtiella in the San Jose For-mation (Floian) of Peru (Gutierrez-Marco & Villas2007) indicates that faunas of ‘Famatinan’ signaturecan be traced far to the north. Other typical Gondwa-nan genera, but not necessarily restricted to thispalaeocontinent, are Euorthisina, Tissintia andprobably Tarfaya. The presence of the last,however, needs to be confirmed by further studies(see Villas & Herrera 2004; Benedetto 2007a).

The statistical study performed by Tychsen &Harper (2004) was based exclusively on orthides.To compare their and our results, a new datamatrix including solely orthid genera was con-structed; the resulting Dice index dendrogram isshown in Figure 7a. It is worth noting that it doesnot differ substantially from the dendrogramdepicted in Figure 7b. In the Early Ordovician den-drogram produced by Tychsen & Harper (2004, fig.3), the Precordillera appears closest to Siberia, andLaurentia groups with ‘South America’ (probablythe Central Andean basin), and by the ‘Llanvirn’the Precordillera terrane groups with the

Avalonia–South America–North Africa cluster,whereas Laurentia forms a separate cluster withBaltica. This is no longer consistent with the highlatitude of NW Gondwana and the low to intermedi-ate latitude of the Precordillera terrane at that time,as extensive carbonate platform demonstrate.

Rostroconchs

In South America, rostroconchs are scarce andalmost restricted to the Upper Cambrian and LowerOrdovician successions. The Upper Cambrianand Lower Ordovician genera from the CentralAndean basin are widespread forms. It is interestingto note that Ribeiria spinosa Babin & Branisaoccurs both in the Central Andean basin (SellaFormation of Bolivia and Acoite Formation ofArgentina) and Famatina basin (Fig. 10). In thePrecordillera terrane Ribeiria is represented by aspecies close to R. compressa Whitfield, which isknown otherwise from the Lower Ordovician ofNew York and Vermont. The endemic rostroconchTalacastella is restricted to the upper San Juan For-mation (lower Darriwilian) (Fig. 9). Although itsphylogenetic relationships are unclear, it seems to

Fig. 10. Selected Floian–Dapingian brachiopods, trilobites, bivalves and rostroconchs from Famatina (F), NW Chile,and Pampean Ranges (P). (a) Productorthis angulensis Benedetto, Molles Formation, lower Dapingian (F); (b)Famatinorthis turneri Levy & Nullo, Molles Formation, Dapingian (F); (c) Skenidioides kayseri Benedetto, MollesFormation, Dapingian (F); (d) Ffynnonia famatinensis Benedetto, Suri Formation, upper Floian (F); (e) Monorthis aff.cumillangoensis Benedetto, Quebrada Grande Formation, Dapingian, NW Chile; (f) Tritoechia (T.) mollesensisBenedetto, Molles Formation, Dapingian (F); (g) Ahtiella cf. argentina Benedetto & Herrera, Molles Formation,Dapingian (F); (h) Ffynnonia sp., La Cebila Formation, Dapingian–Darriwilian, Pampean Ranges; (i) Ribeira spinosaBabin & Branisa, Suri Formation, Floian; (j) Catamarcaia chaschuilensis (Acenolaza & Toselli), Chaschuil,Dapingian; (k) Redonia suriensis Sanchez & Babin, Suri Formation, upper Floian; (l) Neseuretus (N.) chaschuilensisVaccari & Waisfeld, Chaschuil, Dapingian.





be related to Tremadocian genera of Manchuria andLaurentia (Sanchez 1986).

Trilobites

Diversity of trilobites from the Precordillera basinincreases significantly during the Dapingian–Darriwillian, associated with the record of silicifiedfaunas in the San Juan, Gualcamayo and LasAguaditas formations. So far, Annamitella, Illaenus,Waisfeldaspis, Prosopiscus, Macrogrammus, Pater-aspis, Pliomerina, Carolinites, Telephina, Chom-atopyge, Basilicus (Basiliella), Nileus, Ampyx,Mendolaspis, Lehnertia, Protoincaia, Bancrofto-lithus, Kweichowilla, Changchowilla, Nieszkowskia,Platycalymene, Frencrinuroides, Lasaguaditas,Lasarchopyge, Stenoblepharum, Ceratocara andPorterfieldia have been recognized. Among them,Annamitella, Illaenus, Nieszkowskia, Platycaly-mene, Carolinites, Telephina, Stenoblepharum,Basilicus (Basiliella), Nileus, Ampyx, Mendolaspisand Porterfieldia are widespread taxa. According toEdgecombe et al. (1999), trilobites from the LasAguaditas Formation exhibit two broadly contrast-ing biogeographical patterns: Laurentian andperi-Gondwanan. Laurentian affinities are phylogen-etically supported by the presence of sister speciesof Ceratocara (Chatterton et al. 1997), Stenoble-pharum (Edgecombe et al. 1997) and Frencrinur-oides (Edgecombe et al. 1998) in the east of NorthAmerica. On the other hand, peri-Gondwananaffinities are upheld by key taxa from this paleocon-tinent, such as Prosopiscus, Pliomerina, Pateraspis,Lehnertia, Kweichowilla and Changchowilla(Fig. 9). The presence of endemic forms (Waisfeldas-pis, Protoincaia, Bancroftholithus, Lasaguaditasand Lasarchopyge) is also remarkable. The samepattern of mixed Laurentian and peri-Gondwanantaxa persists in the Sandbian.

Darriwilian trilobites have been reported else-where from Eastern Peru by Hughes et al. (1980).The association is composed of Anebolithus,Ogygiocaris (¼Ogygiocarella) and Porterfieldia.These are widespread forms, except for Anebo-lithus, so far known from the Floian or Dapingianof Wales (Hughes & Wright 1970) and SouthernPeru (Gutierrez-Marco et al. 2004).

Sandbian

Brachiopods

No shelly faunas of this age have been encounteredeither in the Famatina Range or in the western Punaregion. In the former there is a stratigraphical gapspanning the Late Ordovician–Late Devonian,whereas in the Puna basin shallow-water volcani-clastic deposition evolved in post-Dapingian time

to deep-water turbidites lacking shelly faunas(Bahlburg 1990). In contrast, Sandbian brachiopodsare well documented in the Precordillera terrane andthe Central Andean basin. Precordilleran brachio-pods come from the Las Plantas Formation, amixed carbonate–clastic succession (Benedetto1995), and from the almost coeval bioclastic sand-stones named La Pola Formation (Benedetto1998c, 2003d). The biogeographical signal ofthese faunas is not conclusive, but could be takenas indicating predominantly Gondwanan affinities.Some components, such as Tissintia, Aegiromena,Drabovia? and Howellites cf. macrostomaBarrande, are members of the Mediterranean Aegir-omena–Drabovia Fauna (Havlıcek 1989) (Fig. 11).These taxa are associated with the pan-tropicalgenera Atelelasma and Anoptambonites, theformer having numerous species in Laurentia andthe latter in Kazakhstan, Siberia, Australia, Scotlandand North America. The fauna from the Las PlantasFormation includes a species of Campylorthis(Benedetto 1995) which, until its recognition inthe Precordillera basin, was thought to have beenan endemic Scoto-Appalachian genus, and Oandu-porella, known elsewhere from the East Baltic(Hints 1975) and Ireland (Harper et al. 1985) (thematerial illustrated by Havlıcek & Branisa 1980,from Bolivia, seems to be closer to Nocturniellathan Oanduporella). Destombesium, which occursin the Precordilleran Trapiche Formation of Katianage, has been recorded elsewhere from Boliviaand Morocco (Benedetto 1999a).

A dendrogram resulting from a data matrix of112 genera (Fig. 12) shows three well-definedclusters. The first encompasses the North African,Bohemian (Perunican) and Armorican brachiopodassemblages, which in turn are linked with theCentral Andean and Precordilleran faunas. Thisgrouping is significant because for the first time affi-nities of the Precordilleran brachiopods shift fromLaurentian to Gondwanan, reflecting, in ouropinion, the final approximation and docking ofthe Precordillera terrane against the proto-Andeanmargin (Benedetto 2004).

The low-diversity upper Darriwilian–Sandbianbrachiopods from the Central Andes are almostexclusively of Mediterranean type. Havlıcek &Branisa (1980) first reported from Bolivia Destom-besium, Drabovinella, Eorhipidomella (probablysynonymous with Crozonorthis) and Aegiromena.The finding of Heterorthis alternata (Sowerby)(Havlıcek 1990) stressed the similarities to Mediter-ranean assemblages. New sampling from the Boli-vian San Benito Formation cropping out in theCochabamba area yielded Drabovinella cf. erratica(Davidson) (Suarez Soruco & Benedetto 1996) anda species closely related to Rafinesquina pseudo-loricata (Barrande) (unpublished). Drabovinella





mojotoroensis Benedetto also forms monospecificassemblages in the Cordillera Oriental of northwes-tern Argentina (Benedetto 1999b). The sole brachio-pod described from the upper Darriwilian ContayaFormation of eastern Peru is Tissintia (Hugheset al. 1980), which is a common taxa in Bohemia,Spain, Morocco and England, but also in the Precor-dillera terrane (Las Plantas Formation). The secondcluster embraces the Baltic and ‘Anglo-Welsh’faunas, reflecting the progressive separation of Ava-lonia from Gondwana through the Ordovician as theRheic Ocean enlarged, and its drifting towardsBaltica as the Tornquist Ocean became narrower(Cocks 2000). The third cluster is formed by theclosely related North American and Scottishfaunas (the ‘Scoto-Appalachian’ province ofWilliams 1973). They are weakly linked to the NE

Chinese and the Kazakhstanian faunas; the former,according to Cocks & Zhan (1998), show someaffinity with those from the Sibumasu terrane, notincluded in our analysis. The Australian (Percival1991) and Tasmanian (Laurie 1991) brachiopodsform an independent pair having low affinity withLaurentia–NE China–Kazakhstan, which form alarge low-latitude cluster. The PCO diagram(Fig. 13) also shows a well-defined groupingformed by the Central Andes, Morocco, Bohemiaand Armorica, which reaches the highest values onthe first eigenvector. This cluster is well separatedfrom the low-latitude faunas, which have muchlower scores on the first eigenvector. BothAustralia–Tasmania and Avalonia–Baltica are sep-arate from these clusters whereas the Precordilleraterrane plots at an intermediate position between

Fig. 11. Selected Sandbian, Katian and Hirnantian brachiopods, bivalves and trilobites. (a) Incaia deormacheai Baldis& Cabaleri, Las Aguaditas Formation, Sandbian (Precordillera); (b) Tissintia robusta Benedetto, Las Plantas Formation,Sandbian (Precordillera); (c) Campylorthis gualcamayensis Benedetto, Las Plantas Formation, Sandbian(Precordillera); (d) Destombesium argentinum Benedetto, Trapiche Formation, Katian (Precordillera); (e) Drabovinellasp., San Benito Formation, Katian (Bolivia); (f) Aegiromena glacialis Benedetto, boulder of Sandbian age fromHirnantian glacigenic diamictite (Precordillera); (g, h) Huemacaspis gallinatoensis Waisfeld & Henry, Santa GertrudisFormation, Sandbian (Central Andean basin); (i) Cadomia typa de Tromelin, Santa Gertrudis Formation, Sandbian(Central Andean basin); (j, k) Mucronaspis sudamericana (Baldis & Blasco), Don Braulio Formation, Hirnantian(Precordillera); (l) Hirnantia sigittifera (M’Coy), Don Braulio Formation, Hirnantian (Precordillera); (m)Paromalomena polonica (Temple), Don Braulio Formation, Hirnantian (Precordillera); (n, o) Eohomalonotusvillicumensis (Baldis & Blasco), Don Braulio Formation, Hirnantian (Precordillera).





the two main clusters. This is due to theco-occurrence of Mediterranean (the most abun-dant), Scoto-Appalachian, Baltic and pan-tropicalgenera, which may be interpreted as evidence of

some geographical separation of the Precordilleraterrane from Gondwana or, alternatively, as theresult of the marginal location of the Precordillerabasin with respect to the Gondwana plate. Depo-sition in the Precordillera of a thick successionof graptolitic black shales punctuated bybrachiopod-rich carbonate lenses reflects a majortransgressive event that can be correlated with thewidespread late Darriwilian–Sandbian FurudalHighstand (Nielsen 2003). Thus, the input of cosmo-politan or widespread brachiopods seems to beclosely related to global sea-level fluctuations, thehighstand events enhancing dispersal of larvaeacross tectonic arches (Stigall Rode & Lieberman2005). As a result, the sea penetrated profoundlyinto the Gondwana plate where shallow-watersandy deposits (e.g. San Benito Formation ofBolivia; Capillas Formation of Subandean Rangesof NW Argentina) are characterized by nearlypure, low-diversity Gondwanan assemblages.

Bivalves

The Sandbian bivalves so far recorded from theCentral Andean basin are the glyptarcoid ZaplaellaSanchez, and the palaeotaxodonts Cardiolaria andCadomia (Fig. 11). All of them show clear affinitieswith cold to temperate areas of Gondwana (Sanchez1986, 2003; Sanchez et al. 2003). The species

Fig. 13. PCO analysis (Dice similarity index) for Sandbian brachiopod assemblages.

Fig. 12. Dice similarity index dendrogram for Sandbianbrachiopod assemblages.





Cadomia typa de Tromelin, recorded in the SantaGertrudis Formation, was described from Iberiaand the Armorican Massif, whereas glyptarcoidsare typical of peri-Gondwanan shelves. Cardiolariahas been recorded from Morocco, Spain, the Armor-ican Massif and Wales. The genus Lyrodesma,recorded in the Bolivian San Benito Formation(Sanchez & Suarez Soruco 1996), is a widespreadgenus lacking biogeographical significance.

The Sandbian bivalve fauna recovered fromboulders within the Hirnantian glacigenic diamictite(Don Braulio Formation) consists of 10 genera,eight of which are endemic. Strong endemism wasinterpreted as the result of a local, short-term radi-ation event followed by extinction, linked to alocal climatic warming (Sanchez 1999a, b). Thetwo non-endemic genera are Praenucula, a wide-spread form, and Concavodonta, restricted to Gond-wana. The cluster of Figure 6b shows two maingroups, a ‘Gondwana group’, to which the CentralAndean bivalves belong, and a ‘Northern group’,which includes Ireland, North America and otherareas from the northern hemisphere.

Trilobites

Sandbian trilobite faunas from the Cordillera Orien-tal are of low diversity and sparse. The lower Sand-bian association reported by Waisfeld (1996) andWaisfeld & Henry (2003) from the Santa GertrudisFormation is composed of Neseuretus, the endemicasaphid Hoekaspis, Huemacaspis (the only repre-sentative of the Kerfornellinae outside southerncentral Europe and northern Africa) and Eohomalo-notus?, also reported from the last mentionedregions (Fig. 11). Similar associations are documen-ted in Bolivia (Pribyl & Vanek 1980). Thus, avail-able data suggest faunal connections with WestGondwana during Sandbian times.

Katian and Hirnantian

Brachiopods

Katian brachiopods are rare in the Andean basins.They are restricted to the upper part of the TrapicheFormation in the northern Precordillera, which con-tains Trucizetina, Hotedahlina? and Cyphomena?(Benedetto 1999a). No representatives of the deep-water Foliomena Fauna have yet been discovered inSouth America. Typical elements of the HirnantiaFauna are well documented in the Don Braulio For-mation of the central Precordillera (Benedetto 1986,1990; Astini & Benedetto 1992), including most ofthe taxa that characterize the Kosov Provincedefined by Rong & Harper (1988) (Fig. 11). Theirassociation with glacigenic rocks indicates con-ditions of grounded glaciers, and a near shore

floating ice shelf supports the high-latitude (c.608S) location of the Precordillera by the HirnantianStage (Astini 1999b). A deep-water Hirnantianfauna dominated by Anisopleurella and small speci-mens of Reuschella has also been recorded.

Bivalves

Hirnantian bivalves are represented by the wide-spread genus Modiolopsis, which is associatedwith the shallow-water Hirnantia fauna in the DonBraulio Formation, and Whiteavesia, from coevaldeep-water mudstones. The latter genus has beenrecorded elsewhere from Laurentia and Siberia(Sanchez et al. 1991).

Trilobites

In the Hirnantian successions of the Precordillera alow-diversity trilobite association including Mucro-naspis and Eohomalonotus (Fig. 11) has beenreported, both forms having displayed a widegeographical distribution.

The Precordillera terrane: Laurentian or

Gondwanan?

Trilobite evidence through the entire Cambrian suc-cessions of the Precordillera points to a strongfaunal identity with Laurentia, and denotes theabsence of faunal exchange with areas of EastGondwana. Essential for paleogeographical inter-pretation is the fact that Precordilleran trilobitesare mostly from shallow-water environmental set-tings. It is widely accepted that such ‘inshore biofa-cies’ tend to be confined to a single palaeocontinent(Fortey & Owens 1978) and, hence, these associ-ations are among the best biogeographicalmarkers. In the parautochthonous model proposedby Acenolaza et al. (2002), and recently reviewedby Finney (2007), the Precordillera terrane (orCuyania) in the Cambrian is placed adjacent to theGondwanan margin, close to Antarctica. In such areconstruction Australia, Antarctica and Cuyaniaare in a similar latitudinal position, with carbonateplatforms developed in continuity in the threeareas, without separation by oceanic barriers.Despite such a geographical proximity, no faunalelements of the Redlichiid Realm, which character-izes the Cambrian trilobites of Antarctica andAustralia, have been recorded in the Precordilleraterrane. On the other hand, in the parautochthonousreconstruction by Finney (2007, fig. 5) a fluid bidir-ectional faunal exchange between the Precordilleraand Antarctica–Australia should be expected.Finney (2007, p. 149) argued that the westwarddirection of equatorial oceanic currents is





responsible for the lack of tropical Gondwananelements in the Precordillera. However, as statedabove, during the Furongian–Tremadocian intervalactive larval dispersion into the Andean platformsfrom Australia, New Zealand and South China iswell documented by the occurrence of characteristicforms such as Onychopyge, Amzasskiella and Aus-traloharpes, among others (Vaccari et al. 2006;Vaccari & Waisfeld 2008). If Cuyania was adjacentto Gondwana, the question that arises is: why arefaunal affinities of the Precordillera exclusivelyLaurentian until the Tremadocian? On the otherhand, if Laurentian faunas were carried into the Pre-cordillera by ‘west’-flooding equatorial currents(Finney 2007, fig. 10) it is hard to explain whythey did not reach the East Gondwanan carbonateplatforms. Clearly, the more parsimonious biogeo-graphical interpretation is to place the Precordilleraterrane close to Laurentia.

With respect to the questioning of the biogeogra-phical value of olenelloids (Finney 2007, p. 145)and the role of oceanic currents in their dispersal,it is interesting to note that, in the exhaustivestudy of Lower Cambrian trilobites by Lieberman(2003, and references therein) he found that geodis-persal had little influence in radiation and distri-bution of the olenellids. Instead, observed patternsappear to be mediated mainly by vicariance eventsassociated with continental fragmentation.

The upper Tremadocian–Floian trilobites of thePrecordillera belong to the bathyurid fauna, indicat-ing unequivocal affinities with Laurentia (seeCocks & Torsvik 2002, fig. 3), which is what canbe expected in the light of the Laurentian signatureof the Cambrian trilobites. Most rhynchonelliformbrachiopods from this interval are present inLaurentia, but they are also known from other low-latitude continents (pan-tropical taxa). The presencein the Floian–Dapingian of two genera in commonwith Baltica (Nothorthis, Ranorthis), together withthe appearance of Celtic forms (e.g. Monorthis,Ffynnonia), strongly suggests a trans-Iapetus trajec-tory for the Precordillera as depicted by Benedetto(1998a) and Cocks & Torsvik (2006), and not adisplacement from the southern margin of WestGondwana as Finney (2007, fig. 5a, b) showed inhis parautochthonous model.

At that time, the autochthonous Andean shelveswere the site of early diversification of euorthisinids,nanorthids and primitive endopunctuate orthides.However, no Gondwanan taxa belonging to theselineages have been discovered in the Precordilleraterrane. The Gondwanan diversification patterncontrasts strongly with that seen in the low-latitudeLaurentian platforms (summarized by Patzkowsky1995) and demonstrates that at that time the Precor-dillera terrane was not attached to Gondwana.Bivalves also underwent a significant radiation in

the Andean clastic platforms with the appearanceof endemic taxa, but non-endemic forms indicateclosest palaeogeographical relationships withIberia, Armorica and Morocco. No bivalves of suchlineages have been recorded in Cuyania, as wouldbe expected in the parautochthonous interpretation.

Although by the Darriwilian the number of taxa(not the percentage) shared by the Precordilleraterrane and Laurentia is higher than in previouslevels, as Finney (2007) noted, it is important topoint out that (1) most of them, if not all, are verywidespread taxa, thus having limited biogeographi-cal significance, and (2) the number of taxa sharedwith Laurentia reached a maximum at that time(Ahtiella argentina Zone) because communitieswere by far the richest of the Ordovician carbonateplatform. This does not mean that ‘dispersalbetween Laurentia and Cuyania was far easier andmore efficient’ (Finney 2007, p. 141) at that time,but rather denotes a change in ecological conditions(Benedetto 2007b). More significant for palaeobio-geographical interpretation is the progressiveincrease of non-Laurentian taxa throughout theOrdovician until the Silurian. This is the reasonwhy we have used in our analyses ‘percentage’rather than ‘total number’ of taxa. We still considerthat the best explanation for this change in the bio-geographical signal is the drifting of the Precordil-lera terrane away from Laurentia and itsapproximation to Gondwana, as proposed pre-viously (see Benedetto et al. 1999). The translationof the Precordillera terrane along the Gondwanamargin does not account for such an evolvingbiogeographical pattern.

By the Dapingian–Darriwilian, a well-definedcluster embracing Famatina, western Puna, Wales,Central Newfoundland and New Brunswick assem-blages had emerged, supporting the distinctivenessof the Celtic brachiopod realm. Precordilleranfaunas are characterized by a sudden increase ofCeltic components. Notable also is the presence ofspecies in common with Famatina, suggesting thatCuyania had been located at that time relativelyclose to the Famatina magmatic arc. The mixedLaurentian–peri-Gondwanan signature of trilobitesalso indicates approximation of the Precordilleramicrocontinent to Gondwana. A major incongru-ence in Finney’s (2007) model is the arrival of theCuyania terrane at its present position during LateSilurian–Devonian time. According to this recon-struction the Precordillera was located by theEarly Ordovician at the corner formed by southernSouth Africa (Kalahari Craton) and southern SouthAmerica. However, as Benedetto (2004) statedpreviously, it is well known that both the Capefold belt and the Malvinas–Patagonia basins lackCambro-Ordovician carbonates; their first linkagewith the Precordillera does not become evident





Fig. 14. Palaeogeography of the proto-Andean margin of Central and southern South America showing the volcanicarcs and back-arc basins discussed in the text, and the distribution of key rhynchonelliform brachiopods in Dapingian–early Darriwilian times (compiled from maps by Benedetto 2004 and Ramos 2008; platform system and Rio de laPlata–Amazonas craton boundaries after Astini 2003).





until the Early Devonian, with the appearance ofMalvinokaffric Realm faunas in all these regions.

By the late Darriwilian and Sandbian–Katian theGondwanan signature was stronger than in the pre-ceding faunas, especially in ostracodes, trilobitesand brachiopods, marking the onset of the so-called‘pre-accretion stage’ (Benedetto et al. 1999). TheSandbian scenario was one of more generalizedcollision, involving the progressive closure of theremnant seaway separating Cuyania from Gond-wana. In shallow-water environments highlyendemic bivalves and ostracodes flourished, butendemism is also evident in trilobites and, to alesser extent, in brachiopods.

The precise timing of collision of the Precordil-lera is still a matter of debate. On the basis of faunalaffinities, facies distribution and tectonic data,Benedetto (2004) proposed an oblique sinistraldocking against Gondwana that may have begunin the Darriwilian, although sustained collisionleading to a climax of deformation, the so-called‘hard collision’, may have continued through thelate Ordovician and probably the early Silurian,until the remnant ocean between the Precordilleraand Gondwana was completely destroyed. Weprovide here (Fig. 14) a new reconstruction of thesouthern and central proto-Andean margin duringthe Middle Ordovician, including new geologicaldata by Bahlburg et al. (2006), Rapela et al.(2007) and Ramos (2008), as well as the newpalaeontological evidence summarized above.

Conclusions

(1) The Early Palaeozoic proto-Andean margin ispart of the Terra Australis orogen, which developedalong the ‘Pacific’ margin of Gondwana, fromAustralia to South America (Cawood 2005). Thecomplex geodynamic history of the Andeansegment of this orogen included extension, riftingand subsequent reaccretion of Gondwanan frag-ments, opening of back-arc basins, development ofsubduction-related volcanic arcs, accretion ofexotic terranes and several phases of deformationand metamorphism. Evidence from differentgroups of benthic fossils taken together is a power-ful tool for determining the origin, trajectoryand timing of docking of terranes, and also for arbi-trating between contrasting palaeogeographicalmodels.

(2) Palaeontological data from South Americaare not uniform; the majority of publishedCambro-Ordovician fossils are from Argentina andBolivia; available information from Venezuela,Colombia and northern Peru is still very limited.

(3) Tremadocian–Floian faunas from the auto-chthonous siliciclastic platforms developed along

the periphery of the Brazilian craton include deep-water, widespread trilobites (agnostids, olenids, shu-mardiids) and inshore faunas displaying Gondwananaffinities. However, the biogeographical signal fromthe brachiopods and bivalves is not identical to thatfrom the trilobites. Rhynchonelliformean brachio-pods and bivalves include typical Ibero-Armorican,Perunican and North African genera, but some trilo-bites show affinities with warm-water Australasianfaunas, which indicates relatively free migrationfor some taxa around Gondwana. By the late Trema-docian and Floian, a suite of endemic trilobites(mainly asaphids) flourished in the Central Andeanbasin. Endemism is also remarkable among thebivalves and, to a lesser extent, among the brachio-pods. The very low degree of faunal exchangebetween epicontinental platforms and continental-margin volcanic arcs indicates some kind of barriersto the migration, which would have been the poorlyoxygenated, deep-water marginal seas locatedbehind the arc (Fig. 14).

(4) The Ordovician volcanoes and relatedback-arc basins located outboard from the pericra-tonic platforms were a major component of theproto-Andean margin from western Argentina tosouthern Peru. In general, Tremadocian and Floiantrilobites inhabiting volcanic settings displaymixed West and East Gondwanan affinities. Theperi-Gondwanan Neseuretus biofacies has beenrecognized in the inshore settings of both clasticplatforms and back-arc basins. Similarity betweenthe Early–Mid-Ordovician brachiopods fromwestern Puna–Famatina, southern Peru andCentral Newfoundland–Wales would support theexistence of a system of volcanic chains up to2500 km long and/or microplates marginal to theIapetus Ocean, which might have played a role inthe migrations (Fig. 14). As can be expected insuch volcanic settings, endemism was relativelyhigh, in particular among bivalves. As pointed outpreviously (Benedetto & Sanchez 2003), the mid-latitude volcanic arcs fringing West Gondwananshelves were the sites of origination and rapid diver-sification of several clades.

(5) Cambrian to Middle Ordovician platformcarbonate rocks are confined to the Precordillerabasin. There are abundant geological, palaeomag-netic, palaeoclimatic and palaeontological data toindicate that the Precordillera is a Laurentian-derived far-travelled microcontinent that accretedto Gondwana during the Early Palaeozoic.

We acknowledge continuous support for research on EarlyPalaeozoic shelly faunas of western Argentina by theConsejo Nacional de Investigaciones Cientıficas y Tecni-cas (CONICET) and the Agencia Nacional de PromocionCientıfica y Tecnologica of Argentina. Current researchis supported by Grants PIP 5599 and 6348, and PICT21857.





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Cambrian and Ordovician biogeography of the South American margin of Gondwana and accreted terranes