Nonconformity

A nonconformity is a specific type of unconformity characterized by much older igneous or metamorphic rocks below, overlain by younger sedimentary rocks above an unconformity surface. The older igneous or metamorphic rocks indicate active igneous and/or tectonic period, followed by uplift and erosion. The overlying sedimentary rocks indicate a time of relative subsidence and deposition of sedimentary layers in a basin.

 

This photograph from the Bou  Azzer region in Morocco illustrates a nonconformity. The dark gray rocks in the lower right are Late Proterozoic (~650 Ma) metavolcanic rocks. The overlying light brown layers to the upper left are Lower Cambrian limestone rocks of the Ouarzazate Formation (~540 Ma). 

Photograph by Kevin Hefferan

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