the oldest reefs consist of small (ca. 5mm) sponges
encrusting thin bivalve shell layers, which probably facilitated
their settlement and enhanced their preservation. Although
these sponges are preserved in life position, their initial essentially
globular shape now seems compacted. The sponges are associated with small serpulids within a very abundant micritic matrix, and with common echinoderm plates (probably crinoids) locally reworked as bioclastic accumulations in storm-induced deposits. These biostromes, tens of centimetres thick, are formed by alternating gregarious settling and hydraulic reworking. The latter leads to multiple short-term events of hard-part concentrations in a low to moderate energy mid ramp environment.
Isolated sponges are also found within overlying beds, identified
only by sparse bundles of spicules. Sponges occur a few metres
higher in recurrent large (ca. 50 m of lateral exposure) lenticular ca. 5-
cm-thick layers, throughout a ca. 20 m-thick stratigraphic interval. These sponges are preserved in situ as lenticular reefs composed of small coalesced spheres (ca. 1 cm in diameter) that resemble lyssacine hexactinellids bound by submillimetre-scale biofilms. Within the lowermost Spathian PR beds, serpulids form small millimetre to centimetre-consortia with abundant ostracods, brachiopods and rare gastropods, alternating
with tempestite deposits