CAMBRIAN SKELETAL BIOMINERALIZATION AND ITS BIOGEOCHEMICAL CONSEQUENCES

In phylogenetic, physiological and functional terms, most innovations in animal skeletons trace to the Cambrian Period. Despite this, petrographic examination of multiple stratigraphic successions indicates that recognizable skeletons form only a limited proportion of Cambrian carbonates. Most carbonates in Cambrian successions reflect physical and microbial controls, much as they did in Proterozoic oceans. Both ecological (predation pressure) and physical (carbonate saturation state) hypotheses have been advanced to explain the Ordovician radiation of heavy calcifiers in multiple clades, and, as they are not mutually exclusive, both classes of explanation may have merit. Similarly, while radiolarians, siliceous sponges and other (minor) silica biomineralizers radiated in Cambrian oceans, physical controls on silica deposition did not disappear until the succeeding Ordovician Period. Further innovations in both silica and carbonate biomineralization ensued during Mesozoic ecosystem change, especially among microplankton. Geobiological data, therefore, add to the growing perception of the Cambrian Period as biologically, biogeochemically, and environmentally intermediate between preceding Proterozoic and later Phanerozoic states of the Earth system.