盖层纪（Calymmian，符号MP₁）是地质时代中的一个纪，开始于同位素年龄1600±0百万年(Ma)，结束于1400±0Ma。

盖层纪期间蓝藻、褐藻发育，出现大型宏观藻类。

盖层纪属于前寒武纪元古宙中元古代；盖层纪的上一纪为固结纪，下一纪为延展纪。

The Calymmian (from Greek calymma, "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.

The period is characterised by expansion of existing platform covers, or by new platforms on recently cratonized basements.