Origin of Late Cretaceous dolomites at the southern margin of the Central System, Madrid Province, Spain

This study focuses on the Late Cretaceous dolomitic units situated at the southern margin of the Central System in Spain. Dolomites were petrographically studied ( transmited light, cathodoluminescence and scanning electron microscopy) and geochemically characterized (Mg/Ca ratio, delta C-13, delta O-18, Sr-87/Sr-86) to interpret the diagenetic environment in which they precipitated and to infer the possible mechanisms for dolomitization. Our data suggest that units of the lower and middle part of the section ( Caballar, Castrojimeno and Burgo de Osma Fms.), although deposited in different sedimentary environments, were simultaneously dolomitized during the initial stages of burial, via the reflux of brines derived from the overlying Valle de Tabladillo Fm. This formation consists of interbedded evaporites and dolomicrites and/or collapsed breccias and was deposited in a coastal sabkha environment, where the unit was dolomitized during the initial stages of diagenesis.