The geological story of southern Spain
Chapter 2
the Jurassic / Cretaceous palaeogeography of southern Spain
As Pangea began its break-up, the 'palaeogeography' (the ancient geographic environment) of southern Spain changed from the arid continental setting of the Triassic to a marine environment, as seas started to flood over the fragmenting supercontinent.
At the beginning of the break up, in the Jurassic, southern Spain was at a latitude about that of the modern day Bahamas, and a similar palaeo-environment developed - warm, shallow tropical seas with extensive carbonate platforms including reefs, lagoons, and tidal flats. The type of sediments accumulating were dominated by eroded fragments of marine creatures - coral, shells, carapaces and other detritus - material dominantly composed of the mineral calcium carbonate. When these sediments are subsequently buried, compacted and cemented together, they eventually form limestone rock (See Background section on Rocks). Like modern-day carbonate settings, there were also areas of deeper water where finer mud-sized material settled ('marl'), or where coarse sediments were swept in from nearby shallower areas via 'turbidity currents' during, for example, severe storms or earthquakes. These marine, carbonate-rich, environments developed around remnant land masses, not just in southern Spain but also on the northern edge of the Africa continent, and indeed across other parts of Europe (see map opposite). In southern Spain, the local coastline would have been further north than it is today, with the warm, shallow seas blanketing the current coastal areas. It would have been a great place to have gone snorkelling if you could have avoided the larger marine life around at the time, including ichthyosaurs, pliosaurs and plesiosaurs. The massive amounts of limestone deposited during this period, today make up some of the most striking features along the coast - e.g. the Rock of Gibraltar and El Torcal. The Cretaceous was a somewhat less romantic (and less understood period). As the new Atlantic Ocean grew, and the presence of the approaching collision between Africa and Eurasia began to make itself felt, the carbonate platforms of the Jurassic were disrupted. Some shallow carbonate sedimentation continued, but progressively there were longer periods when areas were uplifted above sea-level for a while, and when debris flows deposited chaotic material into deepwater environments - material eroded from the closing continents on either side. All-in-all, it was a time presaging the collision to come. [Next: Chapter 3 - Collision] |