Early Smithian reef deposits are characterized by more diverse sponge morphologies. The oldest sponges are embedded within
microbialites forming reefs, tens of centimetres thick, distributed
throughout a massive (up to 10m high) microbial carbonate unit.
These microbialites are composed of centimetre-scale stromatolitic
domes and thrombolites sealed off by micrite. Complete cup- to
flat-shape and dendroid centimetre-scale sponges are preserved,
resting on micrite matrix or encrusting microbialitic crusts. They
show an internal re-crystallized spiculitic network and are often partially to completely dissolved and replaced by calcite-cemented
cavities.