The petrographic, cathodoluminescence (CL), stable isotope, and micmthermometry investigation of inner platform facies of the pervasively dolomitized carbonate platform of the Norian (Upper Triassic) Dolomia Principale (Southern Alps, N Italy) identified two major dolomite phases. An early replacement fabric-retentive dolomite (D1 and D2, respectively replacing the sedimentary facies - from fenestral mudstone/wackestone to bioclastic packstone and mudstone and stmmatolites- and early marine cements) is followed by a later, vug- and fracture-filling dolomite cement phase (D3, planar-s texture). The fabric-retentive dolomitized carbonates (<4 mu m 30 mu m, D1) and marine fibrous cements (30 mu m 250 mu m, D2) exhibit dull luminescence under CL whereas the burial dolomite cement (200 mu m 500 mu m, D3) exhibits zoned luminescence. Microthermometric measurements of the primary two-phase fluid inclusions in D3 yielded a mean homogenization temperature of 112.4 +/- 8.2 degrees C. Supposing a surface seawater temperature of at least 20-25 degrees C and a geothermal gradient of about 40 degrees C/km during the Early Jurassic rifting that led to the opening of the Alpine Tethys, such temperature might be reached at reasonable burial depth ranging from 2.0 km to about 2.5 km. According to the subsidence curve this depth, compatible with the temperature recorded by the fluid inclusions, was reached during the Early Jurassic, with D3 cement precipitation causing a significant reduction of the porosity. The delta C-13 values of the investigated dolomites (D1, D2, and D3) show a narrow range of variation (2.0-3.1%o VPDB), pointing toward a fluid-buffered system. Differently, the delta O-18 values largely varies, ranging from 12.8 to +1.9 parts per thousand VPDB. In this range, D3 values cluster distinctively between 6.0 to 12.8 parts per thousand VPDB with respect to D1 and D2, which cluster from about 4 to +1.9 parts per thousand VPDB. The estimated oxygen isotope composition of the parent fluid of D1 and D2 (similar to 0 to -5 parts per thousand VSMOW) suggests possible contributions from marine to slightly evaporated seawater, which is consistent with the arid climate and some basin restrictions suggested by earlier studies, whereas that of D3 (+1 to +5 parts per thousand VSMOW) is consistent with burial fluids. The followed integrated approach highlights the possibility to better characterize the occurrence of multiple diagenetic events in time and space, as well as their feedback effects on the porosity evolution of dolomitized carbonate reservoirs, framing the diagenetic events at regional scale.
