Chazy Formation

The reef structure was formed largely by cryptostome and trepostome bryozoa, some of the oldest known bryozoans, but corals made an early appearance, and stromatoporoids.

[2] The reef extends from Tennessee to Quebec[3] and Newfoundland, but its most easily studied outcropping is at Goodsell Ridge, Isle La Motte, the northernmost island in Lake Champlain; there, gentle uplift has tilted the sediments: the bedding planes now dip slightly to the north, revealing sequences of horizons in exposed rock.

[6] The system formed in warm tropical waters of the Iapetus Ocean, in low latitudes of the Southern Hemisphere.

The time was some 480-450 Ma (million years ago), at a period when global paleoclimate was so warm that the planet was all but ice-free.

The Chazy Reef Formation, which built up vertically from a muddy base catching fine dark silt as it grew, began as mounds deposited by bryozoans that stabilized a muddy bottom, then built up into the water column to such an extent that the connected mounds modified their surrounding environment (Mehrtens).