Depositional and diagenetic evolution of late Jurassic coral reefs in northern Iberian Ranges (north Spain)

Abstract

The studied reefs are situated around the Cameros Basin (Late Jurassic-Early Cretaceous; North Spain) in a nm of marine Jurassic outcrops. The last marine Jurassic sediments in the area are characterized by the development of coral reefs which correspond to the Kimmeridgian. These reefs were situated in an epicontinental seaway which lay between the Iberian and Ebro massives. This sequences is best exposed near Torrecilla en Cameros where a fringing reef has been identified. In each buildup of this reef complex, the reef-core, with a fore-reef and long-shore carbonate sand bars can be distinguished. The reef complex in Soria has a different geometry for vertical growth dominates, although some progradation occurs and a back reef grainstone facies prograded over the core reef facies. Many diagenetic processes have affected these reefs although cementation is particularly important because it has provided a clear paragenetic sequence related to the diagenetic evolution of these limestones. The most common sequence evolves from submarine cements (only present in primary cavities) to cements precipitated under active fresh-water phreatic conditions, stagnant phreatic afterwards, and finally under burial conditions. This sequence represents progressive burial of these reefs when a very thick series of essentially continental sediments was deposited. Another less common sequence is present in some dissolution cavities generated in the subsurface. This sequence evolved from cements precipitated in a reduced burial environment to shallower oxidizing ones precipitated under telodiagenetic conditions.