The Lower Ordovician Sponges of San Juan, Argentina

BERESI, M.S.; RIGBY, J.K.

BYU GEOLOGY STUDIES

Brigham Young University

Lugar: Provo, UTAH; Año: 1993 vol. 39 p. 1 - 63

0068-1016

ABSTRACT The most diverse sponge faunas known from the Ordovician of South America are described here from the Arenigian San Juan Formation, from the Precordillera region of San Juan Province, western Argentina. Faunas described were collected from Talacasto Gulch, about 90 km northwest of San Juan City; from Huaco along Agua Hedionda Creek, 165 km north of San Juan City; and from Don Braulio Gulch in the Villicum Range, approximately 40 km northeast of San Juan City. Faunas are dominated by orchoclad lithistid demosponge genera, although hexactinellids are known from loose spicules and root tufts, and heteractinids are known from isolated octactine spicules. The new genus and species Talacastonia chela are reported from the San Juan Formation at Talacasto, in addition to the previously described species Archaeoscyphia minganensis (Billings 1859) and Rhopalocoelia clarkii Raymond and Okulitch, 1940. The new species from the Talacasto section include Archaeoscyphia nana, Rhopalocoelia rama, Hudsonospon­gia talacastensis, Calycocoelia perforata, Aulocopium sanjuanensis, Patellispongia robusta, Anthaspidella inornata, Anthaspidella annulata, and Anthaspidella alveola. 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 Talacasto Gulch. Talacasto Gulch is the most productive Ordovician sponge locality yet known from South America.      The sponge fauna from the Villicum Range locality includes Hudsonospongia cyclostoma Raymond and Okulitch, 1940, and the new species 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. The previously described Protachilleum kayseri Zittel, 1877, and the new species Archaeoscyphia nana are the only sponges known at present from the Huaco locality. The Argentine Ordovician sponge faunas show the most similarity to assemblages from North America, particularly to those from the northern Appalachian region and the Great Basin area. The sponges occur in limestone deposited in open subtidal environments on a stable carbonate platform environment along the western margin of Gondwana. They are associated with a well-preserved biota of brachiopods, bryozoans, nautiloids, gastropods, ostracodes, trilobites, crinoids, and algae.