STRUCTURE AND DIVERSITY OF OLDEST SPONGE-MICROBE REEFS - LOWER CAMBRIAN, ALDAN RIVER, SIBERIA

The oldest sponge reef is a small Early Cambrian bioherm at the base o f the Tommotian Stage (similar to 535-540 Ma) in southeast Siberia. Th e mainly archaeocyath construction may be a response to turbid conditi ons. Cambrocyathellus bowls fused to create a rigid cavernous frame co lonized by cryptic Archaeolynthus and calcified microbes (Renalcis). I n addition to these constructors and binders, other reef guilds are pr esent: bafflers (other archaeocyaths, spiculate sponges, and hyoliths) and dwellers (hyoliths, mollusks, and many others). This is the oldes t known reef possessing an open skeletal frame structure built by anim als and a mixed animal-autotroph composition. It provides a blueprint for younger Phanerozoic reefs.