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Earth and Space Sciences · 术语表

什么是 Reef, carbonate platform, ooid？

又称： reef · carbonate platform · ooid

Definition 22.3 University Earth and Space Sciences — Year 1 · 第 22 章 — Carbonate, Siliceous and Evaporite Sediments

A reef is a carbonate build-up whose framework of organisms, corals, algae or others, grown in place and bound and cemented together, stands above the surrounding sea floor and resists the waves. A carbonate platform is a thick body of shallow-water carbonate whose flat top lies close to sea level and which is bounded by a slope down to deeper water. An ooid is a round grain of sand size made of concentric layers of calcium carbonate grown around a nucleus as it rolled in agitated water; a rock made of ooids is an oolite.

Left: the three kinds of coral reef in cross-section (schematic, vertical scale much exaggerated), drawn as Darwin explained them: (a) a reef fringing a volcanic island; (b) the island has sunk and the reef, growing upward, has become a barrier separated from the shore by a lagoon; (c) the island has sunk out of sight and the reef is an atoll around a lagoon floored with carbonate sediment. Right: Bora Bora, a volcanic island in a lagoon enclosed by a barrier reef with low islands on it, photographed by an astronaut from the International Space Station on 19 March 2003 (NASA, public domain, via Wikimedia Commons).
Left: the three kinds of coral reef in cross-section (schematic, vertical scale much exaggerated), drawn as Darwin explained them: (a) a reef fringing a volcanic island; (b) the island has sunk and the reef, growing upward, has become a barrier separated from the shore by a lagoon; (c) the island has sunk out of sight and the reef is an atoll around a lagoon floored with carbonate sediment. Right: Bora Bora, a volcanic island in a lagoon enclosed by a barrier reef with low islands on it, photographed by an astronaut from the International Space Station on 19 March 2003 (NASA, public domain, via Wikimedia Commons).
The two shapes of carbonate platform (schematic, slopes much exaggerated). (a) A rimmed shelf: a rim of reefs and ooid shoals breaks the waves, a quiet lagoon of lime mud lies behind it, and debris shed from the rim falls down the slope to the basin. (b) A ramp slopes gently from the shore to the basin, its sediments sorted by the depth the waves reach.
The two shapes of carbonate platform (schematic, slopes much exaggerated). (a) A rimmed shelf: a rim of reefs and ooid shoals breaks the waves, a quiet lagoon of lime mud lies behind it, and debris shed from the rim falls down the slope to the basin. (b) A ramp slopes gently from the shore to the basin, its sediments sorted by the depth the waves reach.
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