Paleodolina

A doline (a word of Slovenian origin meaning ‘valley’ or ‘depression’) refers to a specific type of geological depression characteristic of karst landscapes....

In the Sierras Subbéticas there are impressive karst formations known as dolines or sinkholes. These are circular hollows in the mountains that have been formed by the dissolution of limestone over hundreds of thousands of years. These processes are not only taking place today, but also occurred in the Subbética millions of years ago. Near Fuenfría, on the signposted Río Bailón trail, there is an example of a very ancient doline. The oolitic limestones, so abundant in the Sierra de Cabra, originated in the waters of the ancient Tethys Sea some 165 million years ago (Middle Jurassic). Following a relative drop in sea level, these rocks emerged, forming islands, and began to be eroded, in much the same way as they are eroded today, creating valleys, sinkholes, lapiaz, rock shelters, etc. After some time, the waters once again covered the oolitic limestones, leaving the irregular relief beneath the sea. Subsequently, more recent sediments accumulated in the lowest-lying areas. A palaeodoline is an ancient doline that has been covered by later sediments; in other words, a ‘fossilised doline’. As it is buried by Cretaceous sediments, dating back some 140 million years, we know that it formed before that time.