Our samples from Late Triassic, Early Jurassic and Early Cretaceous limestones in southern UK show that B-CIC calcite occurs in both marine and non-marine sediments, therefore ocean processes are not mandatory for its formation. There is no proof that fibrous calcite was formed before lithification, but our Early Jurassic samples do prove fibrous calcite formed after compaction, thus interpretation of crystal growth in unconsolidated sediment is problematic. Furthermore, B-CIC crystals mostly grew both upwards and downwards equally, contradicting the interpretation of the novel carbonate factory that they grew preferentially upwards in soft sediment. Finally, Early Jurassic and Early Cretaceous examples are not associated with mass extinction.
Three further key points derived from the literature include: (1) B-CIC calcite is widespread geographically and stratigraphically, not clustered around mass extinctions or the Paleocene–Eocene Thermal Maximum (PETM) event; (2) isotope signatures suggest B-CIC calcite formed under high pressure in burial at 70–120 °C, incompatible with interpretation of formation of B-CIC calcite at the redox boundary below the ocean floor; and (3) B-CIC calcite reported in P/T boundary microbialites in one site in Iran is the only occurrence known despite extensive published studies of similar shallow marine settings, demonstrating its formation is localized to the Iran site.
Based on the above evidence, our opinion is that B-CIC calcite is best explained as a later diagenetic feature unrelated to rapid Earth-surface environmental change associated with mass extinctions; thus a novel carbonate factory is highly unlikely.