Lower Cambrian archaeocyathan bioconstructions

Archaeocyatha are now confidently considered as a Class within the phylum Porifera. Regulares and Irregulares are no longer a systematic division, but have only ecological significance. Topographic relief, biogenic framework and a wave-resistant capability are in favour of the reefal nature of archaeocyathan bioconstructions. Several types of boundstones are recognized, based on the relative proportion of the different framework builders. The same basic plan, characterized by component domains occupied by an association of lime mud, archaeocyaths calcimicrobes, growth cavities, shows little changes throughout the Early Cambrian. A four-stage ecological succession can be inferred, according to some documented cases of distinct biological zonation in archaeocyathan reefs. There is no consensus about the question of photosynthesis in those reefs. They follow the transgression of carbonate facies in sub-tropical areas during the Early Cambrian.