[EN] 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, ä13C, ä18O, 87Sr/86Sr) 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 refl ux 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.
[ES] Este trabajo ha consistido en la caracterizacion petrografi ca y geoquimica de las unidades dolomiticas del Cretacico Superior que
se encuentran en el borde Sur del Sistema Central, en la interpretacion del ambiente diagenetico de precipitacion de las dolomias y
en la defi nicion del modelo de dolomitizacion para cada una de las unidades. El estudio petrografi co, realizado mediante microscopia
convencional, catodoluminiscencia y microscopia electronica, y el estudio geoquimico elemental (relacion Mg/Ca) e isotopico
(ƒÂ13C, ƒÂ18O y 87Sr/86Sr) de las dolomias sugieren que las unidades que se encuentran en la parte inferior y media de la serie (formaciones
Caballar, Castrojimeno y Burgo de Osma), aunque se depositaron en ambientes sedimentarios distintos, se dolomitizaron a
la vez, durante las primeras etapas del enterramiento, mediante el refl ujo de salmueras procedentes de la unidad suprayacente, la
Fm. Valle de Tabladillo. La Fm. Valle de Tabladillo, por su parte, esta formada una alternancia de evaporitas y dolomias o bien por
brechas de colapso y su dolomitizacion tuvo lugar durante las etapas mas tempranas de la diagenesis de acuerdo con el modelo de "gsabkha".
Funds for this study were provided by a postdoctoral
fellowship to the fi rst author by the Comunidad de Madrid
and the European Union and by the Ministerio de
Educación y Cultura of Spanish government (projects
No. PB97-0298, BTE2001-026 and BTE2002-04453-
C02-02). The authors would like to thank L. Wingate, G. Herrero, B. Moral, A. Fernández, and I. Sevillano for
their technical support. We also thank Kyger C. Lohmann,
Agustín Martín-Algarra and Alfonso Yébenes for
their reviews, which have improved this paper.
Peer reviewed