7thISS - Book - Porifera Research.pdf - Porifera Brasil - UFRJ

16The greatest generic and specific diversity of lithistidsponges occurs during the Lower Llanvirnian (Darriwilian)in the upper most part of the San Juan Formation. A total of15 demospongiid genera and 20 species are described. Thisfauna shows a variety of external morphologies and bodyplan.Many new Ordovician species were described for the SanJuan Formation by Beresi and Rigby (1993): Anthaspidellainornata, A. annulata (Fig. 3C), and A. alveola,Archaeoscyphia nana, Aulocopium sanjuanensis (Fig.3K), Calycocoelia perforata (Fig. 3D), Hudsonospongiatalacastensis (Fig. 3G), H. cyclostoma (Fig. 3F),Patellispongia robusta, Psarodictyum magna, Rhopalocoeliarama, among other species. The new species Talacastoniachela (Fig. 3A-B) was described from the classicalOrdovician Talacasto section, Central Precordillera (Fig.1B). Root tufts of hexactinellids also occur (see Table 1).New megamorinid genera as Rugospongia viejoensis(family Saccospongidae) (Carrera, 1996a) and thetricranocladine sponge Eoscheiella concave (FamilyHindiidae Rauff, 1893) have been recovered from the top ofthe San Juan Formation in the Cerro Viejo, Huaco (Carrera2007). Nexospongia sillaensis (family NexospongiidaeCarrera, 1996a) was described from the Cerro La Silla,Niquivil Range, Eastern Precordillera.In the upper levels of the San Juan Formation from theEarly Llanvirnian, at the Cerro La Chilca section, thecalcareous heteractinid Chilcaia bimuralis (Carrera, 1994)and a lithistid species Incrassospongia ramis (Carrera,1996a) were described (Fig. 3I).Endemic genera such as Protachileum and TalacastoniaBeresi and Rigby, 1993, from the Talacasto Gulch andRugospongia Carrera, 1996 and Chilcaia from differentlocalities of the San Juan Formation occur in thePrecordillera.Ordovician sponges from the Precordillera show changesfrom algal-sponge (reef ecosystems) in the Early Arenigto stromatoporid associations in the Middle Arenig toanthaspidellid demosponge dominated associations in theUpper Arenig to Lower Llanvirn. From the Llanvirn up tothe Upper Ordovician, the effects of diverse abiotic factorssuch as volcanic activity, sea level fluctuations and finallythe global climatic cooling, could have contributed to thedecrease of the sponges diversity.The diversification of the orchoclad demosponges in theLower Ordovician carbonate platform of the Precordillerawas similar to worldwide radiation pattern (Carrera andRigby 1999).Ordovician sponge spiculesPrecordillera of San Juan ProvinceThe oldest spicule assemblage comes from the LowerOrdovician limestones (Oepikodus intermedius Zone) ofthe San Juan Formation. The Arenigian silicified spiculeassemblages were documented by Gnoli and Serpagli (1980)in the Pachaco section, western Precordillera.Calcarean and demosponge spicules assemblagesrecovered from residues of conodont samples of severalLower to Middle Ordovician sections of the San JuanPrecordillera were described by Mehl and Lehnert (1997). Thewell preserved silicified spicules include: Polyactinellidae,Heteractinellidae (Calcarea) and hexactinellid anddemosponge spicules. The species Dodecaactinella onceraMehl and Lehnert, 1997, Sardospongia cynodonta Mehl andLehnert, 1997, Praephobetractinia sp. and Eiffelia sp. werereported from Lower Ordovician (Arenig) strata of the SanJuan Formation (Fig. 4A-E).These spicule assemblages were collected from reef-moundhorizons and biostromes with sponges, stromatoporoidsand receptaculitids of the San Juan Formation (LowerArenig-Lower Llanvirn) and from the Gualcamayo and LasAguaditas formations (Lower Llanvirn to Caradocian).San Rafael BlockSponge spicules are derived from residues of conodontsamples from Middle Ordovician strata, in the geologicalprovince of the San Rafael Block, southern MendozaProvince, Argentina (Fig. 1C-D). Spicules (Fig. 4F-Q) havebeen recovered from the Ponón Trehué Formation, a clasticcarbonatesequence. Poriferan taxa (Beresi and Heredia2000) include two spicule assemblages: 1) associations ofexclusively heteractinellid spicules (sexiradiates) restricted toArenigian allochthonous blocks of the Oepikodus evae Zone(Heredia 2001) from the shallow platform of the San JuanFormation; and 2) associations of hexactinelliid spicules,calcarean triaene and monaxons, from Upper Llanvirnianautochthonous limestones and carbonate sandstones of thePigodus serra Zone and the P. anserinus Zone (Heredia2001) from the outer platform and slope.The spicule associations of the Ponón Trehué Formationrepresent the most austral Ordovician assemblage describedin the context of the Precordillera (Cuyania) Terrane.Jurassic sponges from the Neuquén BasinA late Jurasic (Oxfordian) carbonate complex wasdeveloped on the foreland side of the Neuquén Basin (Fig.1B), west- central Argentina and form part of the CordilleraPrincipal. Shelf carbonates facies are exposed throughoutMendoza and Neuquén provinces.One of these facies consists of small siliceous spongebuildups of the La Manga Formation (Plicatilis Zone), welldeveloped at the Río Poti Malal section, in southern MendozaProvince. The siliceous sponges with moderate diversityare fossilized in their original shape and exhibit calcareouspreservation.Sponge fauna is dominated by hexactinellids(Hexactinosida and Lyssacinosida, 95%) and lithistiddemosponges (5%). Up to now, approximately 20% of thematerial has been preliminary determinated (Beresi 2003b).