Sponge Fauna and Spicule Assemblages from the Ordovician of Argentina: A Review

Matilde S. BERESI1 and Susana B. ESTEBAN2

Abstract. SPONGE FAUNA AND SPICULE ASSEMBLAGES FROM THE ORDOVICIAN OF ARGENTINA: A REVIEW. Ordovician sponges and sponge spicules assemblages were described from many localities of Precordillera; Famatina and Puna, north of Argentina. The most diverse and well-preserved faunas are from the San Juan Formation (Arenig-Lower Llanvirn, Precordillera terrane, western Argentina). Precordilleran sponge faunas are dominated by orchoclad lithistid demosponge genera, whereas hexactinellids are represented by loose spicules and root tufts, and calcareous heteractinid sponges are known from isolated octactine spicules and a single genus. In addition, spicules assemblages were reported from diverse localities of the Precordillera, a hexactinellid sponge genus was described from the Tremadocian of the Puna area, and hexactinellid spicule assemblages were reported from the lower Tremadocian black shales of the Famatina System. A discussion on the paleoecological and paleoambiental implications of these faunas is given.

Resumen. LA FAUNA DE ESPONJAS Y ASOCIACIONES DE ESPÍCULAS DEL ORDOVÍCICO DE ARGENTINA: UNA REVISIÓN. Las esponjas y las asociaciones de espículas mencionadas en este trabajo fueron coleccionadas en diversas localidades de Precordillera, Sistema de Famatina y Puna, en el norte de Argentina. La fauna de esponjas más diversa y mejor preservada del Ordovícico de Argentina proviene de la Formación San Juan (Arenigiano-Llanvirniano inferior, terreno de Precordillera, oeste de Argentina). La fauna de esponjas precordilleranas está dominada por géneros de demospongeas lithístidas del Suborden Orchocladina, aunque hexactinéllidas son conocidas mediante espículas sueltas y penachos de raíces. Esponjas heteractínidas calcáreas están representadas por un sólo género y por espículas octactinas aisladas. Asociaciones de espículas fueron registradas de diversas localidades de Precordillera. Un género de esponja hexactinéllida fue descripto de las sedimentitas volcaniclásticas tremadocianas de la Puna, en tanto que asociaciones de espículas hexactinéllidas fueron colectadas en las lutitas negras del Tremadociano inferior del Sistema de Famatina. Se presenta un resumen de las consideraciones paleoecológicas y paleoambientales.

Key words: Ordovician. Sponges. Puna. Famatina. Precordillera.

Palabras clave: Ordovícico. Esponjas. Puna. Famatina. Precordillera.

Introduction

Sponges are the most primitively organized multicellular animals. Specialized cells of most sponges secrete a mineral skeleton (spicules) which provides a firm basis for classification.

The Ordovician sponges from Argentina are mostly represented in the Precordillera terrane (western Argentina). Well-preserved and diverse faunas occur in the carbonate platform of the San Juan Formation (Arenig-Lower Llanvirn) in the San Juan Province, constituting the most extensive record of Ordovician sponges from South America.

In addition, fragmentary remains of Ordovician spicules have been reported in the Famatina System and the Puna area (northwestern Argentina): isolated hexactinellid spicules were mentioned from the Chaschuil area (Catamarca Province) (Aceñolaza and Toselli, 1977), fragments of hexactinellid reticulated nets were described from the shales of the Volcancito Formation (Esteban and Rigby, 1998), and a single hexactinellid sponge was found in the Puna area (Carrera, 1998).

Kayser (1925) found sponges at quebrada de Talacasto, San Juan Precordillera, but they were only mentioned as undetermined “spongiae”. The first sponge spicules assemblage from the lower Ordovician of the San Juan Precordillera was fully described by Gnolli and Serpagli (1980). Micritic beds with Archaeoscyphia in growth position from the upper part of the San Juan Formation at quebrada de Talacasto were first interpreted as “buildups” by Beresi (1986). Sponges in situ also occur at Cerro San Roque (Jáchal) and quebrada Las Lajas (sierra Chica de Zonda). These Lower- Middle Ordovician buildups were later on described as reef-mound structures by Keller and Bordonaro (1993) and included in the Archaeoscyphia-Calathium association (Cañas and Carrera, 1993) and the presence of stromatoporoid-like organism (zondarella Keller and Flügel, 1996) The Precordilleran sponge faunas have been intensely studied in the last decades (Beresi, 1985, 1986, 1990; Beresi and Rigby, 1993; Carrera 1985, 1994a, 1994b, 1996). The distribution pattern of these sponges has been recently analyzed by Carrera and Rigby (1999) and Carrera (2000, 2001). In addition, Mehl and Lehnert (1997) reported Cambro-Ordovician sponge spicules assemblages from diverse localities of the Precordillera, and Beresi and Heredia (2000) have described sponge spicules assemblages from Lower and Middle Ordovician strata of the Sierra Pintada, southern Mendoza Province.

The purpose of this paper is to summarize all published data on the occurrence of Ordovician sponges from Argentina. It should be pointed out that the descriptions and interpretations offered simply transcribe the authors’ opinions in the original papers.

Geographic distribution of taxa

The best-know Ordovician sponges come from threegeographic basins: Puna, Famatina System and Precordillera, from levels that range from Tremadocian to Llanvirn.

I. Puna

A single specimen of a complete hexactinellid sponge is the first Ordovician sponge discovered from the Puna region. It has been collected from volcaniclastic rocks of the Las Vicuñas Formation (Tremadocian) in quebrada Lari (southwest of the Salar del Rincon area, Salta Province) (Locality 1 of Figure 1). This specimen was assigned to Larispongia magdalenae, constituting the first representative of the Family Pelicaspongiidae in western Gondwana (Carrera, 1998). It is characterized by an irregular, thick-walled skeleton and large, smooth hexactines on the dermal and gastral surfaces, which are not arranged into a quadrate pattern. The associated fauna is represented by trilobites and brachiopods of Tremadocian age.

II. Famatina System

1. Catamarca Province

The only discovery of Ordovician sponges in this province corresponds to isolated hexactinellid spicules described by Aceñolaza and Toselli (1977) from the Chaschuil region (Locality 2 of Figure 1). The material appears dispersed in carbonate concretions of the Suri Formation (Arenig).

2. La Rioja Province

The sponge material came from black siliceous graptolitic shales of the upper part of the Volcancito Formation (= upper member of Turner, 1964) at Peña Negra locality (río Achavil, Sierra de Famatina) (Locality 3 of Figure 1). The sponges are associated with planktic graptolites (Rhabdinopora and Anisograptus) and remains of dendroid graptolites. Based on the graptolitic fauna, these levels were assigned to the Lower Tremadocian (Esteban and Gutierrez-Marco, 1997). The sponges from the Volcancito Formation were studied by Esteban and Rigby (1998), who recognized fragments of reticulated skeletal nets of the hexactinellid sponge Protospongia. Because of incomplete preservation, specific identification was not possible.

III. Precordillera of San Juan Province San Juan Formation: Upper Tremadocian - Early Llanvirn

1. Villicum Range

The limestone section of quebrada Don Braulio is exposed on the eastern flank of the Sierra de Villicum (Locality 10 of Figure 1) about 40 km northeast of San Juan City. The San Juan Formation is 250 m thick at the Sierra de Villicum. In quebrada Don Braulio, the sponge beds are in the Amorphognathus variabilis-Eoplacognathus suecicus Zone (Sarmiento, 1985), indicating that they are Lower Llanvirn in age. These beds are in the upper part of the San Juan Formation at quebrada Don Braulio. The shaly limestone member is 10 m thick. It consists of fossiliferous, fine-grained limestones and calcipelitic beds.

The sponge fauna from the Sierra de Villicum locality includes Hudsonospongia cyclostoma Raymond and Okulitch 1940, Calycocoelia perforata, Aulocopium sanjuanensis, and Psarodictyum magna. These orchocladine demosponges occur with hexactine spicules, extensive hexactinellid root tufts, and an additional single isolated octactine spicule that documents the presence of the Heteractinida (Beresi and Rigby, 1993).

A shelly fauna composed by orthocean brachiopods, trilobites, and crinoids is common in the fine limestones. The lithistid sponges are associated with the other fossils, but root tufts do not occur associated with other sponges at the quebrada Don Braulio locality.

2. Huaco area

a. Buenaventura Luna section

The section studied crops out on the eastern flank of the core of the Huaco anticline, along the sulphurous quebrada Agua Hedionda. There, the San Juan Formation is about 170 m thick (Locality 5 of Figure 1).

Sponges occur principally in the shaly limestone member at the top of the limestone sequence, in association with conodont faunas of early Upper Arenig age (Baltoniodus navis Zone, Lemos, 1981).

Protachilleum kayseri Zittel 1877 and Archeoscyphia nana Beresi and Rigby 1993, are the only sponges known at present from the Buenaventura Luna section, in the Huaco locality. They occur with monactine and hexactine spicules in the dark limestone member, associated with articulate brachiopods, trilobites, bryozoans, crinoids and microalgae in marly limestones. Sponges represent only 10 percent of the fossils in this locality.

b. Cerro Viejo section

In the Cerro Viejo section (Locality 5 of Figure 1) nodular limestones and marls of the San Juan Formation contain a diverse sponge fauna. The conodont fauna is assignable to the Eoplacognathus suecicus Zone of early Llanvirn age (Hünicken and Ortega, 1987). The sponges are partly or wholly embedded in irregular lenses surrounded by dark grey micrite from the mudstone and wackestone layers of the San Juan Formation.

Lithistid demosponges Archaeoscyphia, Calycocoelia and Hudsonspongia (Carrera 1985), Archaeoscyphia tenuis and root tufts were recognized (Carrera, 1994a). A new megamorinid genus Rugospongia viejoensis of the Family Saccospongidae was described from this section (Carrera, 1996b).

3. Cerro La Silla, Niquivil

The carbonate sequence consists of skeletal wackestones alternating with biolithoclastic grainstones (Locality 7 of Figure 1). The sponge fauna is associated with conodonts assignable to the Oepikodus evae Zone (Hünicken, 1985) of early Arenig age.

In this section Eospongia and Nexospongia sillaensis, which is included in the Family Nexospongia, were described by Carrera (1996b). According to this author, Nexospongia sillaensis is composed of irregularly distributed heloclones and monaxons as principal spicules.

4. Cerro La Chilca

In the Cerro La Chilca section (south Jáchal) (Locality 8 of Figure 1), sponges were collected from skeletal wackestones and packstones alternating with thin layers of bioclastics grainstones and rudstones. In this limestones section two new genera and species were described: the calcareous heteractinid Chilcaia bimuralis (Carrera, 1994a) and a lithistid species Incrassospongia ramis (Carrera, 1996a) from the upper levels of the San Juan Formation (early Llanvirn; Eoplacognathus variabilis-E. suecicus Zones).

Other common sponge genera recognized are Archaeoscyphia, Patellispongia cf. P. occulata Bassler 1927, as well as root tufts in life position (Carrera, 1994b).

5. Quebrada de Talacasto

Quebrada de Talacasto is situated in San Juan province, about 89 km northwest of San Juan City in the Precordillera Central (Locality 9 of Figure 1). The San Juan Formation section is 350 m thick.

Sponge faunas occur in the calcareous shaly limestone member, in the lower part of the formation, and in the fossiliferous member (mudstones and skeletal wackestones) at the top of the calcareous sequences. The lowest conodont faunas correspond to the Oepikodus evae Zone (Hünicken, 1985).

The Pygodus serra Zone occurs in the upper section. The age of the San Juan Formation at Quebrada de Talacasto ranges from late Lower Arenig to the Lower Llanvirn.

Quebrada de Talacasto is the most productive Ordovician sponge locality yet known from Argentina. The sponge fauna is one of the most characteristic features in the Ordovician limestones of the San Juan Formation.

The species from the Talacasto section include: Archaeoscyphia annulata Cullison 1944 (Beresi, 1985), Archaeoscyphia sp., Patellispongia sp., Calycocoelia sp. and Nevadocoelia sp. (Beresi, 1986). The species Archaeoscyphia minganensis (Billings 1859) and Rhopalocoelia clarkii Raymond and Okulitch 1940 were reported by Beresi and Rigby (1993).

The new genus and species Talacastonia chela are described from this locality. The new species from the Talacasto section include: Anthaspidella inornata, Anthaspidella annulata, Anthaspidella alveola, Archaeoscyphia nana, Aulocopium sanjuanensis, Hudsonospongia talacastensis, Patellispongia robusta, and Rhopalocoelia rama (Beresi and Rigby, 1993).

Root tufts and isolated hexactine spicules are the only known representatives of the Hexactinellida and a single loose octactine spicule is the only evidence of the Heteractinida at this locality.

Patellispongia argentina, Patellispongia cf P. occulata Bassler 1927, Archaeoscyphia tenuis and scarce root tufts were also described from this section (Carrera, 1994a).

6. Las Chacritas and Las Tunas sections

Data on the occurrence of sponge faunas from the carbonate and siliciclastic sequences overlaying the San Juan Formation are scarce. Sponges have only been described from two sections of the central Precordillera of San Juan.

In the Las Chacritas river and the Las Tunas sections (Sierra La Trampa) (Locality 6 of Figure 1), a late Arenig-early Llanvirn carbonate unite is recognised, bearing conodonts of the Lenodus variabilis Zone. Such unite named Las Chacritas Formation (Peralta et al., 1999) 70 m in thickness, is composed mainly of carbonate deposits, overlaying in stratigraphic discontinuity (paraconformity) the limestones of the San Juan Formation, which is Arenig in age.

The collected material comes from the upper part of the carbonate sequence in Las Chacritas and Las Tunas sections (Carrera, 1997). The sponge association is mainly composed of two species of the genus Archaeoscyphia: A. pulchra Bassler and A. minganensis Billings reaching up to 76 % of the sponge biovolume. Other less represented taxa are: Rhopalocoelia clarkii Raymond and Okulitch, Hudsonospongia sp., Calycocoelia sp., “root-tufts” and domical to discoidal sponges.

Sponge spicule assemblages

The oldest spicules assemblage from the Lower Ordovician limestones (O. intermedius Zone) of the San Juan Formation was documented by Gnoli and Serpagli (1980) in the Pachaco section, San Juan Precordillera. The sponge spicules were recovered from acetic acid-etched residues for the recovery of conodonts. The five basic types of spicules found are: undistorted hexactines, desmas (dencroclones and rhizoclones), octactines and monaxones.

Well preserved silicified sponge spicule assemblages were described from residues of conodont samples by Mehl and Lehnert (1997). The Ordovician spicules were recovered from San Juan, Gualcamayo and Las Aguaditas Formations. The spicule assemblage includes Polyactinellidae, Heteractinellidae (Calcarea) and hexactinellid and demospongid spicules.

In the San Juan Formation the assemblages are related to reef-mound horizons and biostromes with sponges, stromatoporoids, receptaculitids and some autrotrophic organisms. The genera Dodecaactinella oncera, Sardospongia cynodonta, Praephobetractinia sp. and Eiffelia sp. were reported from Arenig strata of the San Juan Formation (Mehl and Lehnert, 1997). From the Gualcamayo and the upper part of the Las Aguaditas Formations, only hexactine spicules were documented.

Isolated sponge spicules were recovered from dilute acetic-acid residues of conodonts of clear

Plate I

1. Psarodictyum magna Beresi and Rigby, 1994, holotype, nature of the coarse skeletal net of trabs interrupted by limited canals of the palmate or frond-like species, San Juan Formation, Villicúm Range, Ianigla PI VI- 44.

2. Aulocopium sanjuanensis Beresi and Rigby, 1994, oblique side view shows the general obconical form of the species, Ianigla PI VI-13.

3. Patellispongia robusta Beresi and Rigby, 1994, side view of obconical, moderately thin-walled, paratype shows the nature of the skeletal net, San Juan Formation, Talacasto Gulch section, Ianigla PI T-1/15.

4. Calycocoelia perforata Beresi and Rigby, 1994, paratype shows the smooth dermal surface of the subcylindrical species, San Juan Formation, Villicum Range, Ianigla PI VI-2.

5. Archaeoscyphia minganensis (Billings, 1859). moderately robust specimen showing irregularity in annulations, San Juan Formation at Talacasto Gulch, Ianigla PI T-47.

6. Anthaspidella annulata Beresi and Rigby, 1994, holotype dermal surface showing annulate nature of the sponge, Talacasto Gulch section. Ianigla PI T-49.

7. Hudsonospongia cyclostoma Raymond and Okulitch, 1940, from the Villicum Range section, showing the general growth form of the species and the moderately coarse trab-based anthaspidellid skeleton, Ianigla PI VI-2.

gray limestone and black argillaceous limestone of the Ponón Trehue section, Sierra Pintada (Locality 12 of Figure 1), southern Mendoza Province, Argentina. Poriferan taxa include heteractinida spicules as well as hexactinellid hexactines and non-lithistid demospongiid triaene and oxeas with some doubt.

The heteractinid spicules were collected from Arenig allochthonous megaconglomerates of the Oepikodus evae Zone, on the Quebrada Ponón Trehue. Hexactinellid hexactines and non-lithistid demospongiid triaene and oxeas were described from Llanvirn autochthonous limestone and carbonate sandstone with the Pygodus serra Zone and the P. anserinus Zone (Heredia, 1996; 2001) in the La Tortuga section (southern Quebrada Ponón Trehue).

The Precordilleran sponge fauna: Paleogeographic and paleoecologic considerations

The Ordovician sponge faunas from the Precordillera are most similar to assemblages from North America, particularly to those from the northern Appalachian region (Beresi and Rigby, 1993; Carrera and Rigby, 1999) and the Great Basin area.

The lithistid Ordovician sponges are well known from North America, Australia, Europe, Asia and South America. Generalized genera, such as Archaeoscyphia, Patellispongia, Aulocopium, Hudsonospongia, and Calycocoelia occur widely in the Middle Ordovician. Most other genera, however, show some provincialism. In the Precordillera, endemic genera such as Protachilleum, Talacastonia, Rugospongia and Chilcaia were reported from the San Juan Formation. In this way, based on the distribution of endemic and restricted genera in the Middle Ordovician, the sponge associations from the Precordillera are included in the “eastern North American Laurentian faunas” (Carrera and Rigby, 1999).

Some kinds of sponges (such as Archaeoscyphia) are common reef formers. The characteristic association Archaeoscyphia, Calathium and stromatoporoid-like organisms occurs in a broad belt along the southern and western margins in eastern North America, the Argentina Precordillera and China. The presence of these reef-mound structures, was interpreted as a characteristic world wide episode in the early Ordovician apparently restricted to tropical or subtropical areas without any other paleogeographic significance (Carrera and Rigby, 1999).

The evolution of the Ordovician sponge fauna from the Precordillera involves notorious changes from algal-sponge (reef ecosystems) in the early Arenig to stromatoporid associations in the Middle Arenig to anthaspidellid demosponge dominated associations in the Upper Arenig to Lower Llanvirn.

From the Llanvirn up to the Upper Ordovician, effect of diverse abiotic factors such as volcanigenic activity, sea level fluctuations and finally the global climatic cooling could have been contributed to the decrease of the sponges.

Distribution patterns of the sponges of the Argentine Precordillera were first analyzed by Beresi and Rigby (1993) and recently by Carrera and Rigby (1999) and Carrera, 2000. These patterns suggest that distributions of sponges were strongly influenced by depth, current intensity on the carbonate platform and by continental convergence and latitudinal climatic gradients.

The diverse San Juan sponge faunas of siliceous lithistid demosponges and hexactinellids thrived in an open subtidal environment, but were not successful in shallower, possibly more turbid waters. They are associated with a well preserved biota of brachiopods, bryozoans, nautiloids, gastropods, ostracods, trilobites, crinoids, and algae. The sediments and diversity and abundance of other elements of the biota, in addition to the sponges, suggest good water circulation in an open shelf, a mainly subtidal environment of carbonate deposition, and waters of normal salinity in

Plate II

1. Protospongia sp. B Esteban and Rigby, 1998, specimen PIL 14.193 from Volcancito Formation, Famatina region, photomicrograph showing spicules and quadrules in the fragment of a reticulate net.

2. Protospongia sp. A Esteban and Rigby, 1998, specimen PIL 14.192 from Volcancito Formation, Famatina region, photomicrograph of skeletal structure showing relief features on hexactines in the well-ordered skeleton net.

3. Larispongia magdalenae Carrera, 1998, holotype CEGH-UNC 17365 from Lari Creek, Puna region, vertical view of the complete specimen showing open spongocoel and part of the external surface.

4. Detail of the same specimen showing dermal hexactines surrounding major gaps.

5. Incrassospongia ramis Carrera, 1996, holotype CEGH-UNC 9308, lateral view of a complete specimen from San Juan Formation, Cerro La Chilca, San Juan Precordillera.

6. Nexospongia sillaensis Carrera, 1996, upper surface of the holotype from San Juan Formation, Cerro La Chilca, San Juan Precordillera CEGH-UNC 3613.

7. Chilcaia bimuralis Carrera, 1996, photomicrograph showing the homogeneous arrangement of the sexiradiates in one side of the paratype CEGH-UNC 9336. San Juan Formation, Cerro La Chilca, San Juan Precordillera.

8. Rugospongia viejoensis Carrera, 1996. Side view of the holotype CEGH-UNC 9252, San Juan Formation, CerroViejo, San Juan Precordillera.

which there was an adequate nutrient supply. Preservation of associated algae indicates that rocks in which they occur accumulated in the photic zone.

The siliceous hexactins occur together with conodont faunas of the Pygodus–periodon community typical for deeper slope environments around Laurentia (Mehl and Lehnert, 1997) and the Precordillera.

Because of their relatively plastic morphology, shapes of the sponges may be indicative of their environments and are considered as good paleoenvironmental indicators. For example, columnar or tubular forms as for example Archaeoscyphia, occur where currents were moderately strong. The tubular form aids in “sucking” water through the system, like effluents up and out a chimney (Rigby, 1983).

Beresi and Rigby (1993) described four general morphotypes of sponges present in the Precordillera assemblages: 1) columnar, cylindrical-shaped forms, 2) cup-vase and funnel-shaped forms, 3) discoid to flattened, saucer-shaped forms, and 4) pear- or hemispherical-shaped forms.

Three distinct sponge biofacies zones have been distinguished in the Cambro-Ordovician of the Argentine Precordillera by Mehl and Lehnert (1997):

1. Slope facies with Hexactinellida.

2. Outer or deeper platform with lithistid demosponges (Orthocladina) and subordinate hexactinellid and octactinellid spicules.

3. Reef and reef-mound of the eastern Precordillera: sponge-algal mound with lithistids (e.g. Archaeoschypia); octactinellid spicules from strata within the reef horizons; assemblages of polyactinellid and heteractinellid Calcarea and soft demosponges (inter-reef basins or in tidal channels).

Similar conclusions were obtained from the carbonate-clastic sequence of the Ponón Trehue section, southern Mendoza Province (Beresi and Heredia, 2000). There, associations of exclusively heteractinellid spicules (Eiffeliidae) are restricted to allochthonous blocks of the shallow platform of the San Juan Formation. In the outer platform and slope, autochthonous calcarenites and dark limestones only contain hexactin spicules. The heteractinid sponges and isolated octactine-based spicules, show a general restriction to the middle (biohermal and biostromal horizons) and upper parts of the San Juan Formation platform and with highly diverse faunas (Keller and Flugel, 1996) in the interval Arenig/early Llanvirn. Besides, isolated octactine-based spicules have been registered in allochthonous blocks derived of this platform, at the Ponón Trehué section (Beresi and Heredia, 2000).

Recently, Carrera (2001) has recognized seven main biofacies in the San Juan Formation: 1) Archeoscyphia-Calathium-Girvanella biofacies 2) Archaeorthis biofacies 3) Leptellinid biofacies 4) stromatoporoid biofacies 5) Petroria-Paralenorthis biofacies 6) Demosponge biofacies and 7) Nileid biofacies. In biofacies 1 and 6, sponges dominate the assemblages.

According to this author, this pattern of highly variable biozone content and the absence of recurrent biofacies may imply the absence of refuge areas possibly related to the isolation of the Argentine Precordillera terrane during its drifting away from Laurentia.

A clear change in biofacies framework is verified since the late Arenig with the development of stromatoporids (Carrera, 1997).

Final remarks

The Argentine Ordovician sponge faunas are found in three different settings: 1) carbonate platform, 2) volcaniclastic sequence and 3) black shales facies.

1) The Ordovician lithistid demosponge faunas from the Precordillera occur in limestone deposited in open subtidal environments, on a stable carbonate platform environment. A diverse, well preserved associated fauna is mainly composed of brachiopods, gastropods, trilobites, nautiloids, bryozoans, crinoids, bivalves and diverse algae.

On the other hand, hexactinellid sponges are much less common and diverse in the Ordovician Precordillera, although isolated hexactin spicules have been recognized in deeper environments from slope sequences.

Calcareous heteractinida have a limited record. Heteractinid calcareous sponges are represented by Chilcaia bimuralis Carrera and by the genera Dodecactinella, Sardospongia and Eiffelia. The heteractinid sponges and isolated octactine-based spicules, show a general restriction to the middle (biohermal and biostromal horizons) and upper parts of the San Juan Formation in the interval Arenig/early Llanvirn. Besides, isolated octactine-based spicules have been recorded in allochthonous blocks at the Ponón Trehué section, Sierra Pintada.

2) The single hexactinellid sponge (Pelicaspongiidae) from the Puna region, western margin of Gondwana, was found in fossiliferous sandstones of the Tremadocian volcaniclastic sequence of the Las Vicuñas Formation. The associated fauna is represented by trilobites and brachiopods.

3) The material from the Famatina System is associated with deep environments. The sponge material from the Lower Ordovician Volcancito Formation is preserved in thinly laminated black siltstones and is associated with dendroids graptolites. This black shales facies represents sedimentation from suspension fall-out in very low-energy settings below storm wave base. The hexactinellid sponges of the Famatina region occur in less favorable conditions that those of shelf depositional environments. The sediments in which the sponges occurr suggest restricted water circulation on the shelf, with oxygen depletion in the sea floor (Esteban and Rigby, 1998). These protosponges document the occurrence of such relatively primitive haxactinellid sponge in Paleozoic black-shale facies at margins of the continents (Rigby et al., 1996; Esteban and Rigby, 1998).

Taxonomic list of the new genera and species described from the Ordovician of Argentina

DEMOSPONGEA

- Familia Anthaspidellidae Miller, 1889

Anthaspidella alveola Beresi and Rigby, 1993

Anthaspidella annulata Beresi and Rigby, 1993

Anthaspidella inornata Beresi and Rigby, 1993

Archaeoscyphia nana Beresi and Rigby, 1993

Aulocopium sanjuanensis Beresi and Rigby, 1993

Calycocoelia perforata Beresi and Rigby, 1993

Hudsonospongia talacastensis Beresi and Rigby, 1993

Incrassospongia ramis Carrera, 1996

Nexospongia sillaensis Carrera, 1996

Patellispongia argentina Carrera, 1994

Patellispongia inornata Beresi and Rigby, 1993

Patellispongia robusta Beresi and Rigby, 1993

Psarodictyum magna Beresi and Rigby, 1993

Rhopalocoelia rama Beresi and Rigby, 1993

Rhopalocoelia tenuis Carrera 1997

Rugospongia viejoensis Carrera, 1996

Talacastonia chela Beresi and Rigby, 1993

CALCAREA

- Familia Astraeospongiidae Miller, 1889

Chilcaia bimuralis Carrera, 1994

HEXACTINELLIDA

- Familia Pelicaspongiidae Rigby, 1970

Larispongia magdalenae Carrera, 1998

- Familia Protospongiidae Hinde, 1887

Protospongia sp. A Rigby and Esteban, 1998

Protospongia sp. B. Rigby and Esteban, 1998

Table 1. Distribution of Ordovician sponges into Argentine basins. Fossiliferous localities: Huaco (1), Cerro La Silla (2), Cerro La Chilca (3), Las Chacritas-Tunas sections (4), Talacasto Gulch (5), Villicum Range (6). Present +

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Recibido: 4 de Septiembre de 2002