Stable-isotope and fluid inclusion constraints on the timing of diagenetic events in the dolomitized Dolomia Principale inner platform (Norian, Southern Alps of Italy)

Abstract The petrographic, cathodoluminescence (CL), stable isotope, and microthermometry 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 stromatolites- 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 ( The δ13C values of the investigated dolomites (D1, D2, and D3) show a narrow range of variation (2.0–3.1‰ VPDB), pointing toward a fluid-buffered system. Differently, the δ18O values largely varies, ranging from −12.8 to +1.9‰ VPDB. In this range, D3 values cluster distinctively between −6.0 to −12.8‰ VPDB with respect to D1 and D2, which cluster from about −4 to +1.9‰ VPDB. The estimated oxygen isotope composition of the parent fluid of D1 and D2 (∼0 to −5‰ 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‰ 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.