Calymmian

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.

Calymmian
1600 – 1400 Ma Pha. Proterozoic Archean Had.
Paleoglobe of the Earth at the start of the Calymmian, c. 1590 Mya[citation needed]
Chronology
−1620 — – −1600 — – −1580 — – −1560 — – −1540 — – −1520 — – −1500 — – −1480 — – −1460 — – −1440 — – −1420 — – −1400 — – −1380 — Pa Mesoproterozoic Statherian Calymmian Ectasian ← Breakup of the supercontinent Columbia ← “Gaoyuzhuang biota” emerges, earliest Archaeplastida? Events of the Calymmian Period. Vertical axis scale: Millions of years ago
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	1991[1]
Upper boundary definition	Defined chronometrically
Upper GSSA ratified	1991[1]

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