Abstract

Pinnacle reefs of the Niagara Group in northern Michigan are located on a paleotopographic ramp basinward of a massive shelf-edge reef complex. The reefs increase in height from 90 m near the shelf to 180 m at the basinward limit. The more basinward pinnacles initiated in deep water as carbonate mud mounds. Pinnacles closer to the shelf started growth in shallower water as coral-stromatoporoid reefs. As the basinward mud mounds grew upward to wave base, coral-stromatoporoid reefs were initiated and deposition of this facies in all pinnacles accompanied a uniformly rising sea level. Near the end of the Niagara deposition, an increase in salinity of the basin resulted in a restricted marine facies being deposited over all the reefs. The upper part of this facies on the reef crests contains supratidal features, which indicate that reef growth terminated near sea level.

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