Permian–Triassic sedimentary and diagenetic reconstruction of the southern Adriatic area

Three cores coming from the Permian–Triassic interval of the Puglia 1 well were studied. Core 1 (5.048–5.056 m – Triassic) is characterized by laminated dolomudstones with thinly microbial laminae alternated to lenticular/ tabular shaped anhydrite crystal levels, suggesting an intertidal/sabkha-type environment. Core 2 (6.067–6.075 m – Triassic), shows coarse-grained crystalline massive dolomite with remnants of oolites and shell fragments, defining a marginal shallow-water setting. Core 3 (6.372–6.379 m – Permian) includes quartzolithic sandstone with iron oxides, clay (illite, kaolinite+chlorite) and dolomite, ankerite, calcite cements, indicating a continental setting. Dolomitization is ubiquitous and occurred early after the deposition through the circulation of high saline dolomitizing fluids under reducing conditions. The early-dolomitization preserved the dolomites from major burial diagenetic transformations, permitting only the ordering and the development of xenotopic textures in the dolomite crystals (aging). Primary anhydrite crystals were lately affected at least by one burial hydration–dehydration cycle, whereas fracture-filling anhydrite is a later-stage diagenetic product of circulating sulphate-rich fluids. The integration of other six wells and a seismic line allowed the reconstruction of the Permian–Triassic sedimentary evolution of the Southern Adriatic area. During Permian continental/coastal lagoon settings developed, while in the Ladinian, after a generalized subaerial exposure and an erosional phase, the extensional tectonic inputs linked to Tethys rifting brought to a relative sea-level rise and to the formation of carbonate shelves in NW–SE oriented tectonic depressions. During Carnian–early Norian a further extensional tectonic pulse coupled with a relative sea-level drop, led to the formation of NW–SE elongated intrashelf basin with a consequent enhancement of salinity and settlement of evaporative conditions. This triggered a massive evaporite deposition during the Norian, that filled the intrashelf basinal areas. Lastly, in the late Norian– Rhaetian a marked relative sea-level rise, restored the connections with open-sea and shifted the evaporite deposition up to the shallowest parts that previously remained under subaerial conditions.