Sponge spicule assemblages from the Middle Ordovician of Ponón Trehue, Southern Mendoza, Argentina

Abstract

Sponge spicule assemblages are described from residues of conodont samples from Ordovician strata in the Sierra Pintada, southern Mendoza Province. Argentina. Spicules have been recovered from the Arenigian allochthonous megaconglomerates and from autochthonous limestones and carbonates sandstones of the Ponón Trehué Formation. This formation is a clastic-carbonate sequence representing olistostromic and turbidite facies. Conodonts in this formation are Llandeillan in age. The spicules are calcified and moderately preserved. The material shows a low diversity. Poriferan taxa found in this formation include heteractinid spicules as well as hexactinellid hexactines and non-Iithistid demospongiid triaene and oxeas with so me doubt. Associations of exclusively heteractinid spicules are restricted to allochthonous blocks of the shallow carbonate platform of the San Juan Formation (Arenig). In the outer platform and slope. autochthonous calcarenites and dark limestones contain hexactine spicules. These spicules evidence the existence of sponges in the Ordovician of the Ponón Trehué area, as a part of the Precordillera terrane.