Calymmian

Calymmian
Paleoglobe of the Earth at the start of the Calymmian, c. 1590 Mya
Chronology
Etymology
Name formality	Formal
Usage information
Celestial body	Earth
Regional usage	Global (ICS)
Time scale(s) used	ICS Time Scale
Definition
Chronological unit	Period
Stratigraphic unit	System
Time span formality	Formal
Lower boundary definition	Defined chronometrically
Lower GSSA ratified	1990
Upper boundary definition	Defined chronometrically
Upper GSSA ratified	1990

The Calymmian Period (from Ancient Greek: κάλυμμα, romanized: kálymma, meaning 'cover') is the first geologic period in the Mesoproterozoic Era and lasted from 1600 to 1400 Mya (million years ago). 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.

A reconstruction of Grandilingulata qianxiensis, a macrofossil from the Calymmian Gaoyuzhuang Formation

See also

• Boring Billion – Earth history, 1.8 to 0.8 billion years ago
• Jotnian – Oldest known sediments in the Baltic area that have not been subject to metamorphism

Further reading

• "Calymmian Period". GeoWhen Database. Archived from the original on May 12, 2006. Retrieved January 5, 2006.
• James G. Ogg (2004). "Status on Divisions of the International Geologic Time Scale". Lethaia. 37 (2): 183–199. doi:10.1080/00241160410006492.