THE "GERMANIC" TRIASSIC OF SARDINIA (ITALY): A STRATIGRAPHIC, DEPOSITIONAL AND PALAEOGEOGRAPHIC REVIEW

Abstract

The collection of new lithostratigraphical and sedimentological data has allowed to re-examine the Triassic sedimentation cycle in Sardinia The most important outcrops have been revisited and their general setting reinterpreted. A detailed and homogeneous depositional, palaeoenvironmental and stratigraphic picture is proposed, pointing to the analogies with both the typical Germanic Triassic of Central Europe, and the Middle Triassic Sephardic domain of Western Europe and North Africa. The lower, essentially siliciclastic, lithostratigraphic units, resting discordantly on the Hercynian Palaeozoic basement, resemble the "Buntsandstein" facies association. They are generally of Anisian age. Their depositional environments range from high-energy continental to transitional environments to the floodplain, where a shallow, epicontinental sea gradually transgressed. Overlaying these are the carbonate units of the "Muschelkalk" facies association. They are generally dolomitic at the bottom passing to calcareous at the top. These deposits, generally of Ladinian age, formed in the various subenvironments of a carbonate ramp. The few Upper Triassic successions in Sardinia point to the existence, during this period, of diverse depositional conditions in the North (Nurra) and South (Sulcis) of the island. In southern Sardinia, lagoon to shallow sea carbonate shelf deposition predominates, with minor amounts of evaporites and siliciclastics. By contrast, in Northern Sardinia mixed evaporitic-siliciclastic-carbonate facies of paralic-continental (mudflat), locally restricted lagoonal environments, were deposited. The latter are very similar to the classic Germanic "Keuper" facies. These data suggest that the Upper Triassic successions in Southern Sardinia can be set in a transitional environmental context between the open Alpine-Tethyan domain and the Germanic Triassic proper. An attempt has been made to correlate these successions with the Middle to Late Triassic eustatic cycles.