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How did the Tell Atlas form during the Paleogene and Neogene periods?

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Map showing the Atlas Mountains across Morocco, Algeria, and Tunisia in North Africa, with color shading to indicate elevation changes. Major mountain ranges, cities, rivers, and physical features such as the High Atlas, Anti-Atlas, Saharan Atlas, and surrounding deserts are labeled. An inset locator map highlights the region's position in northern Africa. — Atlas Mountains The Atlas Mountains.

The Tell Atlas formed through a complex, lengthy mountain-building process during the Paleogene and Neogene periods (approximately 65 to 2.6 million years ago).1

The range originated from a sediment-filled basin bordered to the north by a marginal rim. Key developments during this formation included:1

Initial Folding: The first major folding of the range occurred during the Oligocene Epoch.2
Uplift and Deformation: The mountains were elevated through a series of upheavals. During the Miocene, extensive layers of flysch—deposits composed largely of sandstone and clay—were pushed from the north over the top of the marginal rim.12
Ongoing Activity: The Tell Atlas is considered a young, folded mountain range that remains in the process of formation, as evidenced by the earth tremors that continue to affect the region.1

This geological activity distinguishes the Tell Atlas from the Saharan Atlas, which is associated with the ancient base rock of the African continent.1