LAUSR

The Cambrian Series 3 thrombolites from the Changhia Formation, at the Jiulongshan section in Shandong Province, northern China, provide an excellent example for studying the development of calcimicrobial structures. Thrombolites constructed by calcimicrobes have particular stacking patterns, which are controlled by their environments and are reflected in the relationships between micro-, meso- and macroscopic structures, requiring an approach we term “multiscopic”. Under high-energy conditions, Epiphyton A (with dense micritic bifurcating thalli) grew sporadically and adapted to the environment by taking a bushy-lateral form, because the bushy-upward form is more likely to be broken by waves or currents. Epiphyton A was fused with each other to form spotted frameworks at the mesoscopic level. The weak baffling of spotted frameworks led to the formation of low-relief tabular/lentoid macrostructures via preferential lateral accretion. In low-energy, deep-subtidal settings, Epiphyton A and Epiphyton B (with microsparry segments in the bifurcating thalli) coexisted with Hedstroemia A (with a wide terminal) and B (with a narrow terminal). These calcimicrobes grew abundantly in both the vertical and lateral directions, fusing together to form meshed frameworks, or dendritic frameworks if vertical fusion of bushy-upward calcimicrobes was predominant. The preferential vertical stacking of meshed and dendritic mesostructures highlights the ability of these frameworks to actively baffle lime mud, and ultimately to form large-domed macrostructures. Stacking patterns in these multiscopic structures help to inform environmental interpretations of thrombolites. The thrombolitic growth model we present here provides important insights into the environmental interpretations of thrombolites in other cases, especially the calcimicrobe-dominated early and middle Palaeozoic thrombolites.