Calcite sea
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A calcite sea is a sea in which low-magnesium calcite is the primary inorganic marine calcium carbonate precipitate. An aragonite sea is the alternate seawater chemistry in which aragonite and high-ma
The alternation of calcite and aragonite seas through geologic time
Jurassic hardground with encrusting oysters and borings
Table showing the conditions for calcite and aragonite seas
Tectonic mechanism for changing Mg/Ca ratios in seawater
Ordovician
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The Ordovician is a geologic period and system, the second of six periods of the Paleozoic Era, and the second of twelve periods of the Phanerozoic Eon. The Ordovician spans 43.75 million years from t
Calcite sea
…and the contemporaneous dissolution of aragonite shells in shallow warm seas. Hardgrounds were very common, for example, in the calcite seas of the Ordovician and Jurassic, but virtually absent from the aragonite seas of the Permian. Fossils of invertebrate organisms found in calcite sea deposits are usually…
External mold of the Ordovician bivalve Anomalodonta gigantea showing that the original aragonite shell dissolved on the sea floor, leaving a cemented mold for biological encrustation (Waynesville Formation of Franklin County, Indiana).
A diorama depicting Ordovician flora and fauna
Fossiliferous limestone slab from the Liberty Formation (Upper Ordovician) of Caesar Creek State Park near Waynesville, Ohio.
The trilobite Isotelus from Wisconsin