Calymmian

The Calymmian is the first geologic period in the Mesoproterozoic Era, lasting from to million years ago and spanning 200 million years. It follows the Statherian Period from the Paleoproterozoic Era, and precedes the Ectasian Period. Instead of being based on stratigraphy, these dates are defined chronometrically.
The period is characterised by the expansion of existing platform covers, and by new platforms forming on basements that were recently cratonized.
The supercontinent of Columbia started to break up during the Calymmian some 1500 Mya. The Volyn biota have also been dated to 1500 Mya.
File:Grandilingulata qianxiensis.png|180px|thumb|A reconstruction of Grandilingulata qianxiensis, a macrofossil from the Calymmian Gaoyuzhuang Formation