Calymmian

The Calymmian Period (from Greek κάλυμμα (kálymma), meaning "cover") is the first geologic period in the Mesoproterozoic Era and lasted from 1600 Mya to 1400 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.

The period is characterized by expansion of existing platform covers, or by new platforms on recently cratonized  basements.

The supercontinent Columbia broke up during the Calymmian some 1500 Mya.