Massive dolomites in the Messinian evaporitic sequence (Sicily, Italy): multi-analytical characterization and implications for the dolomitization processes

Abstract

A combined geochemical, mineralogical, petrographic and geological approach has allowed to constrain the dolomitization process responsible for the formation of massive dolomitic body within the Messinian evaporitic series. We focused our investigations on an example of massive dolomite body, outcropping over the marginal area of the evaporitic basin in the Peloritani Mountains (NE area of Sicily region, Italy). Field observations allowed recognizing several sedimentary structures, such as erosion surfaces, lenses of conglomerates and ripples highlighting a clastic origin. The petrographic study revealed fine-grained and massive structure, scarce porosity, light to pink color and absence of micro-fossils. The chondrite-normalized trace element pattern shows a general enrichment in LREE and depletion in HREE. The isotopic signatures of the studied dolomites (δ18O = – 4.38–1.24‰, V-PDB; δ13C = – 1.48–1.94‰, V-PDB) are comparable with those of type-3 “Calcare di Base” which is the common reference to record the Messinian salinity crisis. The positive co-variant relationship between the δ18O and δ13C values suggests a dolomitization process in the seawater/freshwater mixing zone. The occurrence of the studied dolomites in the evaporitic sequence coupled with the results we gained point towards an origin from “early diagenetic” processes. As a consequence, a model explaining the genetic mechanism for the studied dolomitic rocks can be essentially summarized as: (1) the massive dolostones were originally deposited as evaporitic limestones under rather high-salinity conditions; (2) the dolomitization process occurred in the seawater/freshwater mixing zone that provided Mg-rich fluids over uplifted submarine masses.