Early Ordovician (Arenig) brachiopods from volcaniclastic rocks of the Famatina Range, northwest Argentina

Abstract

This paper constitutes the first monographical study of the rich brachiopod faunas from the Early Ordovician Suri and Molles Formations of the central Famatina Range, which form a nearly continuous, more than 2,000 m thick succession of fossiliferous clastic and volcaniclastic rocks. Conodonts from the brachiopod-rich levels of the upper third of the Suri Formation and Los Molles Formation indicate the upper part of the Oepikodus evae Biozone (mid-Arenig). The systematic study of brachiopod faunas reveals the presence of 22 species belonging to 19 genera, three of which are new. The new genera recognized are the orthid Suriorthis, the hesperonomiid Mollesella, and the rectostrophiid Trigonostrophia. The following 12 new species and subspecies are described and illustrated: the clitambonitoidean Tritoechia mollesensis; the skenidioideans Crossiskenidium? stelzneri and Skenidioides kayseri; the orthoideans Paralenorthis suriensis, Paralenorthis riojanus brevis, Panderina? ambigua, Productorthis angulensis, Hesperonomiella arcuata, and Monorthis transversa; the plectorthoideans Ffynnonia famatinensis and Desmorthis? bifurcata; and the porambonitoidean Rugostrophia protoandina. Associated forms are Tritoechia sp., Pinatotoechia acantha Benedetto, 2001b; Protoskenidioides cf. revelata Williams, 1974; Hesperonomia orientalis Benedetto, 1998a; Paralenorthis riojanus (Levy and Nullo, 1973), Famatinorthis turneri (Levy and Nullo, 1973); and Camerella sp. Brachiopods from the Famatina Range display strong affinities with Welsh and Central Newfoundland, Maine and New Brunswick volcanic assemblages forming with them a statistically well defined Celtic cluster. Faunal evidence suggests that the Famatina volcanic belt continues northward into the western Puna belt.