The Rhaetian facies of the Lombardian Basin (Southern Alps) are syn-rift deposits characterized by a high rate of deposition, considerable variation of thickness and a cyclic deposition of limestone-shale/marl alternations in which the limestone beds mostly show a thickening-upward trend. Each thickening-upward asymmetric cycle represents a relatively minor shallowing which in most cases is reflected by changes in the microfacies types. The superposition of these minor cycles resulted in an overall shallowing of the sedimentation and thus two major shallowing-upward cycles were distinguished. This paper shows the interrelationship between facies patterns and the evolution of a shallow basin, describes the cyclicity of the sedimentation and discusses possible causes. A comprehensive microfacies analysis of the Calcare di Zu is presented. Fourteen microfacies that vary from shallow basinal facies to intertidal/supratidal facies are identified. Almost all the major biotic constituents described from the Rhaetian deposits of the Tethys are present, but their diversity is rather low. The fauna and flora of the Calcare di Zu include corals, sponges, calcareous algae, microproblematica, ‘tabulozoa’, ‘hydrozoa’, bivalves, brachiopods, echinoderms, gastropods, serpulids and very rare ammonites. All the Upper Triassic foraminifers seem to be present. Compared to the foraminifers in the Northern Calcareous Alps some marked differences in their distibution patterns can be observed.Triasina hantkeniMajzon is present in the algal foraminiferal facies, algal laminated bindstone facies, oncoidal facies, bioclastic grainstones and in the biolithite facies.Agathammina austroalpinaKristan-Tollmann & Tollmann is not restricted to the terrigenous mud facies, but is found in the peloidal bioclastic packstone/grainstone facies and in the lumachelle facies. In places oolitic grainstones are rich in foraminifers. Some of the oolitic grainstones yield ooids whose nuclei are almost entirely composed of foraminifers. Miliolids (Galeanella sp.,Ophthalmidium sp.) characteristic of the biolithite facies are very rare,Sigmoilina sp. is lacking. The distribution pattern of foraminifers is not strictly facies controlled.