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The Calymmian (from Greek calymma, "cover") is the first geologic period in the Mesoproterozoic Era and lasted from 1600 Ma to 1400 Ma (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.
The period is characterised by expansion of existing platform covers, or by new platforms on recently cratonized basements.
The supercontinent Columbia broke up during the Calymmian some 1500 Ma.
* "Calymmian Period". GeoWhen Database. http://www.stratigraphy.org/geowhen/stages/Calymmian.html. Retrieved January 5, 2006.