Biostratigraphic evidence of the middle Liassic hiatus in the Foza Section. (Eastern sector of the Trento Platform, Calcari Grigi Formation, Venetian Prealps)

•The section studied is located at the eastern border of the Asiago plateaux close to the village of Foza. In this area, the Calcari Grigi are noticeably different from the classic succession subdivided into three members and characterizing the formation westwards. The whole Calcari Grigi formation of the Foza section is composed of a monotonous succession, mainly micritic, showing the typical facies of the Lower Member. This micritic unit fades upwards into a granular body, mainly composed of ooids and peloids, whose interpretation, owing to the absence of detailed biostratigraphic studies, has been long debated. Some authors considered this grainy body as equivalent to the late Liassic San Vigilio Oolite or, more recently, as a coeval to the Rotzo Member. An alternative hypothesis, whose demonstration is one of the aims of this paper, considers the granular unit at the top of the Foza section as the base of the Middle Oolitic Member and postulates the absence of middle Liassic deposits in the eastern sector of the Trento Platform. A detailed micropaleontological study, focused to different taxa of algae (particularly dasyclads) and forams, confirms that the youngest platform preserved deposits at the top of the Foza section are referable to the upper Sinemurian.