We propose to investigate the massive dolomitization of an Upper Miocene reef complex cropping out in excellent three- dimensional exposures near Nijar, southeastern Spain. This proposal is a renewal for an ongoing project focussing on regional dolomitization of Upper Miocene reefs in Spain, previous work having studied reefs in Mallorca (Balearic Islands). Work in Mallorca has narrowly constrained age of dolomitization, and field, petrographic, geochemical modelling approaches have yielded a model which invokes dolomitization of Messinian reefs by evaporitic basinal brines that formed as a result of the late Messinian "salinity crisis". A prime objective of the Nijar project is to test the regional applicability of this model, by mapping dolomite and dolomite type distributions within the context of the sequence stratigraphy, and by applying petrographic, geochemical (C, O, Sr isotopes; Ca, Mg, Na, Cl, SO4, Sr, Fe, Mn, Al, K abundances), and quantitative modelling approaches. Preliminary field and petrographic work at Nijar has shown similarities in sequence stratigraphy and dolomite fabrics to those in Las Negras (about 20kms away), and in Mallorca. The Nijar project will also test other dolomitization models involving meteoric and normal seawater.
