The observations made on these bioclasts bring us to comment on the reasons, the effects and the consequences of degradation of the shells. These lead us to closely interpret the fossil record. The interference of sulfur-reducing bacteria in parts of the shell rich in organic materials leads to the formation of framboidal pyrite. Manifestations of this phenomenon can be done early or later as well as the siliceous epigenization, or the interplay of dissolution-recristallization in borders of architectural elements of the shell.