Late Permian-Triassic sedimentary evolution of the Southern Adriatic area based on wells and cores analysis

Abstract

Rock samples from two cores within the Triassic interval of the Puglia 1 well, were studied to reveal the sedimentary facies and diagenesis. The Core 1 (5.048–5.056 m deep) is characterized by laminated dolomudstones with thinly microbial laminae alternated to lenticular/tabular shaped anhydrite crystal levels, suggesting an intertidal/sabkha-type environment. The Core 2 (6.067–6.075 m deep), shows coarse-grained crystalline massive dolomite with remnants of oolites and shell fragments, suggesting a marginal shallow-water setting. Dolomitization is ubiquitous and occurred early after the deposition through the circulation of high saline dolomitizing fluids under general 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. Moreover, the integration of Puglia 1 well data with other six exploration wells and a seismic line allowed a possible 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 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 of the basins that previously remained under subaerial conditions.