Carbon and oxygen isotopic analyses have been carried out on carbonates from laves, ejectites and sedimentary formations in the region of the Alban Hills.
The calcite occurring in the laves, both in veins and cavities and dispersed in the groundmass shows within each flow a fairly uniform isotopic composition not different from that normally observed in sedimentary carbonates, except in the case of one particular flow, where unusually low ~ laC values were recorded. The latter are discussed in terms of a possible contribution of organic carbon or of isotopically light carbonates, the presence of which in the Alban Hills area had been previously recorded.
The ejeetites examined comprise both limestone and dolostone blocks of various degree of metamorphism and materials of uncertain origin, some of which containing carbon and oxygen of isotopic composition wholly different from that of all carbonates analysed in this work, approaching the range observed in some carbonatites. The isotopic data and the geochemical features of the latter materials are discussed in terms of thermal metamorphism of limestones and of a possible syntexis of evaporite materials.
The ~ 1sO and 6 laC values of certain marine limestones from major Mesozoic sedimentary formations in the region are also reported.