The mountains around Chebika are composed of fossilised seabed from the Cretaceous period, when this part of North Africa lay under a shallow tropical ocean. The rock is full of shell impressions, sea urchin tests, and the occasional ammonite, pressed into the pale limestone and sandstone of the cliff faces.
You do not need to look hard — the fossils are visible in rock faces throughout the oasis gorge and on the hillsides above the abandoned village. The local guides and stall vendors will point them out, and some of the souvenirs for sale are genuine fossil specimens (though the quality varies considerably). The juxtaposition of ancient ocean floor and current desert is one of the more thought-provoking features of the Saharan landscapes in this part of Tunisia.