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The Calymmian Period (from , meaning "cover") is the first geologic period in the 
Mesoproterozoic
The Mesoproterozoic Era is a geologic era that occurred from . The Mesoproterozoic was the first era of Earth's history for which a fairly definitive geological record survives. Continents existed during the preceding era (the Paleoproterozoic ...
Era and lasted from Mya to Mya (million years ago). Instead of being based on stratigraphy
Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks.
Stratigraphy has three related subfields: lithost ...
, these dates are defined chronometrically.
The period is characterised by expansion of existing platform covers, or by new platforms on recently craton
A craton ( , , or ; from "strength") is an old and stable part of the continental lithosphere, which consists of Earth's two topmost layers, the crust and the uppermost mantle. Having often survived cycles of merging and rifting of contine ...
ized basement
A basement is any Storey, floor of a building that is not above the grade plane. Especially in residential buildings, it often is used as a utility space for a building, where such items as the Furnace (house heating), furnace, water heating, ...
s.
The supercontinent
In geology, a supercontinent is the assembly of most or all of Earth's continent, continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", ...
Columbia started to break up during the Calymmian some 1500 Mya.
The Volyn biota have been dated to 1500 Mya.
See also
* *References
* * Mesoproterozoic Geological periods Proterozoic geochronology {{geochronology-stub