Late triassic hexactinellid sponges from the Pongo de Lorocache limestones, Peru: New evidence for siliceous sponge dominance on shallow carbonate platforms

Abstract

We hereby report the finding of Upper Triassic hexactinellid sponges in Pongo de Lorocache limestones, in the south edge of the Santiago basin, Peru (Fig. 1). The sponges were found in the uppermost levels of the Chambará Formation. This unit exhibits sequences of the Upper Norian to Lower Rhaetian showing an unconformable contact with Jurassic sequences (Aramachay Formation). A great number of complete sponge body fossils occur in life position and show gregarious habits forming biostrome-type accumulations including bivalves and ammonoids. Previous reports of isolated sponge spicules in Peru (Ritterbush et al., 2015) show the great abundance and dominance of this group in the Triassic–Jurassic transition, with other examples occurring in Nevada (USA), Morocco, Austria and France (Neuweiler et al., 2001; Delecat et al., 2011; Ritterbush et al., 2014; Corsetti et al., 2015). The internal characteristics of the sponges are not well preserved, thus preventing a precise identification. However, the abundance and significance of these siliceous sponges in a key biotic interval, such as that of just before the end of the Triassic–early Jurassic event, represent a valuable finding.