Giovanni Barbera

Petrology and Geochemistry of Cretaceous Sedimentary Rocks of the Monte Soro Unit (Sicily, Italy): Constraints on Weathering, Diagenesis, and Provenance

The mineralogy and chemical compositions of shale and sandstone alternations of Cretaceous age of the Monte Soro Unit, Sicily, have been determined. The clay minerals in the shales are mostly illite and I-rich mixed-layer I/S reflected by enrichment in Al2O3, K2O, and chemically similar elements. The sandstones are subarkose to quartz arenite. The shales and sandstones have upper-crustal rare earth element patterns, and except for K2O, they are depleted in alkaline and alkaline-earth elements as a result of intense weathering. The sandstone and shale mineralogy suggests a diagenetic history in which the sediments were subjected to temperatures in excess of 100°C, during which interaction between some minerals in the shales and sandstones took place. Thus, diagenetic quartz cementation and feldspar alteration in the sandstones and smectite illitization in the shales occurred together with the shales being a sink for potassium and the sandstones a sink for silicon. Negative europium anomalies ( between 0.45 and 0.87), (Gd/Yb)ch ratios (<2, except for sample C1), and Sc/Cr versus La/Y and La-Th Sc diagrams suggest that the sedimentary rocks were derived from post-Archean granitoid-like rocks in a tectonically stable area. In addition, the foliated fabrics of polycrystalline quartz grains and the abundant phyllite rock fragments indicate a provenance from metamorphic rocks. The study of several trace element ratios (Ti/Zr, Cr/Zr, Y/Ni, Cr/V, Zr/Th, La/Th, La/Th, Cr/Th, Zr/Hf, Zr/Yb, Yb/Hf, V/La, La/Yb) strongly supports a local derivation from the European paleomargin.

A multi-technique approach for the determination of the porous structure of building stone

The complete knowledge of the porous structure of rocks is necessarily requested for the prediction of the damages induced by salt crystallization. Nevertheless, the geometric description of the porous structure is usually very difficult because of the variability of the size distribution of voids, ranging from nanometers to millimeters, which generally is not accessible by a single methodology. For this reason, a multi-technique approach was used here: the investigation at sub-micrometric dimensional scale (> 0.004 μm) was carried out by Hg intrusion porosimetry (MIP), whereas the study at the nanoscale required Small Angle Neutron Scattering (SANS) analysis. All the results were interpreted in the framework of a fractal model. The analyses were performed on limestones of different geological formations, cropping out in south-eastern Sicily and largely used as building stones in Baroque monuments of the Noto Valley (belonging to the UNESCO Heritage List).

Mineralogy and Geochemistry of the Numidian Formation (Central-Northern Sicily): intra-formation variability and provenance evaluation

Mudrocks and sandstones of Numidian Formation in Sicily have been analysed for mineralogical, petrographic, major element and selected trace element compositions to constrain the intraformational variability and the sediment provenance. The mudrocks are characterized by a kaolinite-rich signature while the sandstones have a quartz-arenitic composition. The high Chemical Index of Alteration and Plagioclase Index of Alteration strongly suggest that recycling processes have been responsible for the present compositions. The mudrocks geochemical data suggested a compositional variability function of the paleogeographic depositional environments. In particular, the Numidian Formation of the more external Serra Del Bosco Unit is affected by the terrigenous contribution of epicontinental-type sediments. With regard to provenance, the geochemical data indicate a derivation from post-Archean sedimentary siliciclastic rocks. The contribution of African cratonic sediments was confirmed by the trace elements ratios and by the end-member modelling processed on mudrocks compositional data. In particular the suitability of the Nubian sediments as one of the sources of sediment supply is also attested.