Abstract:
The Great Ordovician Biodiversification Event (GOBE) ranks among the most significant bioradiation events in geological history. Algal evolution played a pivotal role in this radiation, extending beyond atmospheric and oceanic oxygenation to encompass critical functions in maintaining ecological stability. However, research on the role of algal changes during the early stages of this event remains relatively scarce. As primary producers within ecosystems, algae exhibit diverse response mechanisms to the onset of the GOBE and serve as robust indicators of paleoenvironmental shifts. To investigate the role of algae in the early stages of the GOBE, this study examines three sections in South China: the Jiangjunling section, deposited in a mixed shelf environment; and the Guanyinqiao and Huanghuachang sections, both formed in shallow-water settings. Through biomass comparisons, algal taxonomic identification, and sedimentary environment analysis, we confirm the relative consistency of algal radiation across different environments in South China. A total of three phyla and five genera of algae are identified, including Cyanophyta (Girvanella, Nuia, and Botomaella), Chlorophyta (Halimeda), and Rhodophyta (Petrophyton). The evolutionary succession of these algal groups indicates a sustained decrease in temperature and a gradual increase in oceanic oxygen levels from the Tremadocian to the Floian, consistent with findings from previous studies. Comparisons among sections reveal that algae underwent radiation prior to other taxa following oceanic oxygenation. Once reaching a critical abundance threshold, they established a sufficient material and energy foundation, thereby driving the rapid diversification of other organisms. Analysis of biomass trends of the Huanghuachang section—including trilobites, bivalves, brachiopods, bryozoans, and algae—demonstrates that interspecific equilibrium was achieved, and that the ecosystem as a whole became structurally complete by the end of the Floian. This milestone marks the culmination of the first episode of the GOBE. The results offer a novel methodological approach: statistics of biomass of diverse taxa, combined with analyses of interspecific balance, can serve as a reliable basis for subdividing biological events.
