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Why were coral mound reefs common during the Silurian Period?

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Silurian paleogeography — Silurian Period Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the middle part of the Silurian Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.

During the Silurian Period, coral mound reefs (or bioherms) became common primarily due to significant environmental changes following the Late Ordovician ice age. As extensive glaciers melted, global sea levels rose dramatically, flooding large expanses of continental shelves with shallow seas. These warm, shallow-water environments provided ideal conditions for the proliferation of diverse marine life, including corals, brachiopods, gastropods, crinoids, and trilobites.12

The development of these reefs reached a climax during the Wenlock Epoch. While these mound-type reefs were widespread, they were distinct from flat-layered (biostromal) accumulations of tabulate corals and stromatoporoids that also inhabited shallow seafloors during this time. The widespread flooding of continental interiors created vast, stable habitats that allowed these complex, organically constructed reef systems to flourish across various paleocontinents.21