Reefs died in the Great Lakes region near the end of the Silurian because of local environmental change. The sea shallowed to become a tidal flat, and sediments were exposed to the air during low tide. These tidal-flat deposits buried the reefs. The salinity of this sea also increased and salt deposits formed. These conditions could not be tolerated by stromatoporoids, corals, and many other organisms, and reef growth ended.
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