Resumen de Taphonomy of the Oxfordian-Lowermost Kimmeridgian Siliceous Sponges of the Prebetic Zone (Southern Iberia)
The siliceous sponges in the Oxfordian-lowermost Kimmeridgian deposits of the Prebetic were important rock-forming organisms, and the most important in the spongiolithic lithofacies group. The siliceous sponges were in several cases the main component in macroinvertebrate assemblages. This taphonomic analysis shows the sequence of processes that occur in the fossilization of siliceous sponges. As soon as the sponge is dead, the fixation to the substrate is weakened and currents or organisms can tilt and overturn the sponge. The decay of soft tissue led to the precipitation of automicrites (possibly influenced by sulphate-reducing bacteria); at the same time skeletal silica dissolves where, later, the calcitic cementation is produced. Afterwards, the sponge remains were bored by lithophagous bivalves and colonized in the upward surfaces by benthic microbial communities and nubeculariids, and secondarily other foraminifera, whereas downward surfaces were encrusted by annelids (serpulids and terebellids), sessile foraminifera (Tolypammina, Subdelloidina, and Bullopora among others) and bryozoans. Local fragmentation of sponges and their encrustations formed the tuberoids, which behave like an intraclast subjected to transport and encrustation.
