Выпуск: 11 , Том: 66 , Год издания: 2025

Remains of calcareous cyanobacteria of the genera Garwoodia Wood, 1941, ortonella Garwood, 1914 and hedstroemia Rothpletz, 1913 (Garwoodiaceae family) were first identified in the late Darriwilian deposits of the Moyero River section (Eastern Siberia). ortonella and Garwoodia were previously found on the Siberian Platform only in Silurian deposits, making this the earliest discovery of representatives of these genera in the region. ortonella and Garwoodia dominate, whereas hedstroemia occupy a subordinate position in stromatoporoidcyanobacterial bioherms. Only ortonella was found in biostromes and shell interlayers of the bivalve banks. The sediments in question accumulated in the shallow-water lagoonal environment. The latter determined the failure of skeletal metazoan organisms to become the main frame builders of biostromes and bioherms, despite the global increase in biodiversity during the Great Ordovician Biodiversification Event (GOBE). Their role was taken over by cyanobacterial communities, which proved more resistant to such environmental conditions. The increase in phosphorus content in bottom sediments apparently triggered the development of cyanobacteria; which probably caused a local paleoecological crisis of the benthic fauna in this part of the paleobasin. The latter is confirmed by the depleted ostracod assemblage in the Moyero River section (in contrast to coeval deposits of the Lena, Podkamennaya Tunguska, and Kulyumbe river sections). The decline in biodiversity of benthic fauna and, particularly, of skeletal metazoan frame builders during cyanobacterial "blooms" may be explained by the impact of cyanotoxins, which are destructive to marine life. The data obtained demonstrate that even in the age of global biotic expansion of the Ordovician period, local conditions could limit the contribution of skeletal metazoans to reef construction, maintaining the dominance of microbial communities.