The Calymmian Period (from Ancient Greek : κάλυμμα , romanized : 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 .
2-453: 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. This geochronology article is a stub . You can help Misplaced Pages by expanding it . Platform cover In geology,
4-405: A platform is a continental area covered by relatively flat or gently tilted, mainly sedimentary strata , which overlie a basement of consolidated igneous or metamorphic rocks of an earlier deformation. Platforms, shields and the basement rocks together constitute cratons . Platform sediments can be classified into the following groups: a "protoplatform" of metamorphosed sediments at
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