Alluvial, aeolian and tidal deposits in the Lower to Middle Triassic Buntsandstein of NW Sardinia (Italy): a new interpretation of the Neo-Tethys transgression

In NW Sardinia, investigations of the Lower(?) to early Middle Triassic Verrucano Sardo Fm of the Buntsandstein Group evidenced that this unit was deposited in rapidly evolving variable continental to transitional-shallow marine environments under a prevalently arid to sub-arid climate. The Verrucano Sardo Fm is composed of two lithofacies separated by an erosive surface that is probably referable to a ravinement. The lower Conglomerato del Porticciolo Lithofacies may be mainly referred to a wadi braided system with limited aeolian sediments close to the coastline. The wadi system passes upwards to a narrow sandy aeolian coastal system with frequent ephemeral marine ingressions reworking the aeolian deposits. The upper Arenarie di Cala Viola Lithofacies represents the start of the Triassic marine transgression, advancing over mainly aeolian deposits through a progressively flooded tidal fl at with an increasing degree of energy; the tidal cycle is repeated twice before the transition to the Muschelkalk carbonate shelf. The early tidal influence on this Buntsandstein, which is different from other similar contexts of the European mainland, may be due to the Sardinia location, posed during Early to Middle Triassic times close to the developing Western Neo-Tethys European margin. Affinities with some coeval European successions are also briefly discussed herein.