| Calymmian | |
| Color: | Calymmian |
| Top Bar: | all time |
| Time Start: | 1600 |
| Time End: | 1400 |
| Caption Map: | Paleoglobe of the Earth at the start of the Calymmian, c. 1590 Ma |
| Timeline: | Calymmian |
| Name Formality: | Formal |
| Celestial Body: | earth |
| Usage: | Global (ICS) |
| Timescales Used: | ICS Time Scale |
| Chrono Unit: | Period |
| Strat Unit: | System |
| Timespan Formality: | Formal |
| Lower Boundary Def: | Defined chronometrically |
| Lower Gssa Accept Date: | 1991[1] |
| Upper Boundary Def: | Defined chronometrically |
| Upper Gssa Accept Date: | 1991 |
The Calymmian Period (from grc|κάλυμμα|kálymma, meaning "cover") is the first geologic period in the Mesoproterozoic Era and lasted from Mya to Mya (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 started to break up during the Calymmian some 1500 Mya.
The Volyn biota have been dated to 1500 Mya.