The World’s Oldest-Known Bryozoan Reefs: Late Tremadocian, mid-Early Ordovician; Yichang, Central China

The world’s earliest-known bryozoan-built reef-mounds are in mid-Lower Ordovician (upper Tremadocian) strata near Yichang, Hubei Province, central China. Their framework, a globstone, was built by abundant rounded zoaria of the trepostome Nekhorosheviella semisphaerica. That framework further baffled micrite immediately around the colonies, more broadly surrounded regionally by bioclastic calcarenites (Fenxiang Formation). Fragments of delicate branching Orbiramus normalis occur rarely in the bryohermal micrite.