In geology, relating to a stage of the Carboniferous period, named after the French town of Autun.
From Autun (a town in France) + -ian (suffix forming adjectives). Geological term established in the 19th century to classify rock strata from this ancient period.
The Autunian stage represents when ancient swamps were being buried to eventually become the coal we burn today—the rocks beneath France tell the story of energy we'd use 300 million years later.
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