Spatio-temporal distribution of the Cambrian maceriate reefs across the North China Platform

Maceriate reefs, characterized by centimeter- to decimeter-scale branching structures, flourished during the Cambrian to Early Ordovician on Laurentia, and Gondwana (the North China Platform). Dendritic and columnar maceriate reefs were newly discovered from the northwestern and central parts of the North China Platform. The maceria structures are composed of sponges (e.g., keratosans and lithistids) and microbial components, including Girvanella, Renalcis, and Tarthinia, whereas the interstitial material consists of lime mud with bioclasts and intraclasts. The first appearance of maceriate reefs was diachronous across the North China Platform, younging from the northwest (Drumian Age, Miaolingian) to the southeast (Jiangshanian Age, Furongian). In general, thrombolites and dendrolites were dominant in the microbialite-dominated reefs of the Miaolingian and microbe–sponge maceriate reefs were dominant in the Furongian. This dramatic shift to microbe–metazoan reef assemblages resulted from a combination of factors associated with the Miaolingian–Furongian boundary interval, including global transgression and a shift from widespread anoxia of the SPICE event to more oxygenated post-SPICE conditions. The North China examples suggest that sea level and paleoenvironmental conditions may have played a major role in this transition and its timing.