Benthic Pleurocapsales (Cyanobacteria) Blooms Catalyzing Carbonate Precipitation and Dolomitization Following the End‐Permian Mass Extinction

• Published in: Geophysical research letters Vol. 49; no. 24
• Main Authors: Wu, Siqi, Chen, Zhong‐Qiang, Fang, Yuheng, Pei, Yu, Foster, William J.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28.12.2022
• Subjects: Benthos; Blooms; Calcification; Calcium; Capacity; Carbonate minerals; Carbonates; Cyanobacteria; Dolomitization; Extinction; Fossils; Geologists; Juveniles; Life cycle; Life cycles; Magnesium; Major constituents; mass extinction; Mass extinctions; Microbial activity; microbialite; Microorganisms; Mineralization; Minerals; Morphology; Permian; Permian‐Triassic boundary; Pleurocapsales; Raman spectroscopy; Ratios; Species extinction; Spectrum analysis; Triassic
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2022GL100819

The widespread development of Permian/Triassic boundary microbialites is a key biosedimentary response to the mass extinction event. The microbial communities that precipitated these structures remain, however, poorly resolved. Here, we report abundant columnar microfossils from five Permian‐Triassic successions in South China. Four phases of the microfossil life cycle are recorded: baeocytes, juvenile column, mature column, and baeocyte‐splitting, which are interpreted as Pleurocapsales (cyanobacterial clade that reproduces by multiple fission). The great thickness (up to 13 m) of these microbial deposits and Raman spectrum analysis indicate a strong calcification capacity of the Pleurocapsales. Pronounced peaks of Mg/(Mg + Ca) ratios from microbialite and distinct Mg‐enrichment in microfossils indicate that Pleurocapsales blooms may also have facilitated dolomitization of the microbialites. Common occurrence, strong biomineralization capacity, baffling framework, and the close association with carbonate minerals suggest that Pleurocapsales were key constructors of post‐extinction microbialites. Plain Language Summary As a biosedimentary response to the end‐Permian mass extinction, the widespread occurrence of microbialites has attracted increasing levels of interests from geologists worldwide. However, the major constituents of microbial communities that constructed the microbialites have long been disputed. Our new study describes morphological features, growth direction and reproduction characteristic of columnar microfossils obtained from the microbialites, and all characteristics indicate that these microfossils are assignable to a type of photosynthesizing bacteria, known as Pleurocapsales cyanobacteria. Both biomineralization and dolomitization of these Pleurocapsales are evaluated based on in‐situ observations and geochemical analyses. The new results show that the cluster‐branching morphologies, together with common occurrence and strong calcification capacity indicate that Pleurocapsales were key constructors of the microbialites. High Mg/(Mg + Ca) ratios coinciding with the microbialites and Mg‐enrichment in the microfossils suggest that the Pleurocapsales may have catalyzed dolomitization of the microbialites after the end‐Permian mass extinction. Key Points Four phases of a microbe life cycle are recognized from fossils within microbialites reflecting Pleurocapsales asexual reproduction Common occurrence and baffling framework indicate that Pleurocapsales cyanobacteria are important in constructing microbialites Pleurocapsales cyanobacteria were an important component of microbialite calcification and magnesium enrichment