Stable isotope compositions of host rock and calcite cements in the Calcari a Briozoi e Litotamni Formation, Central Italy

Stable carbon and oxygen isotope data from host rocks and veins were used to constrain the geochemical environment of precipitation and possible sources of fluids. A total of 12 powders were prepared from samples of Guadagnolo CBZ by using a dentist’s drill. Due to the very small thickness of cement around and within clasts, it was not possible to separate the cement from the clasts in the CBZ wall rock. Powdered samples were analyzed with an Elementar IRMS mass spectrometer at the Centro Interdipartimentale Grandi Strumenti of the University of Modena and Reggio Emilia. The δ¹³C and δ¹⁸O values are expressed referring to the international standard VPDB (Vienna Pee Dee Belemnite). Isotope determination analytical precision was 0.10 ‰ and 0.15 ‰ VPDB for carbon and oxygen, respectively. The δ13C and δ18O ranges of bulk CBZ host rocks fall within, or very close to, the range of compositions of marine carbonates of Burdigalian age in the Mediterranean. C1v calcites are indistinguishable from the host rock. C2v calcite falls instead out of the host rock range, with a pronounced enrichment in light oxygen. Lowering of the δ18O ratio associated with a constant δ13C in carbonates is coherent with the interaction with meteoric water in rock-buffered conditions (low water/rock ratio).