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A detailed geochemical analysis was performed on the upper part of the Maiolica Formation in the Breggia (southern Switzerland) and Capriolo sections (northern Italy). The analysed sediments consist of well-bedded, partly siliceous, pelagic carbonate, which lodges numerous thin, dark and organic-rich layers. Stable-isotope, phosphorus, organic-carbon and a suite of redox-sensitive trace-element contents (RSTE: Mo, U, Co, V and As) were measured. The RSTE pattern and Corg:Ptot ratios indicate that most organic-rich layers were deposited under dysaerobic rather than anaerobic conditions and that latter conditions were likely restricted to short intervals in the latest Hauterivian, the early Barremian and the pre-Selli early Aptian. Correlations are both possible with organic-rich intervals in central Italy (the Gorgo a Cerbara section) and the Boreal Lower Saxony Basin, as well as with the facies and drowning pattern in the Helvetic segment of the northern Tethyan carbonate platform. Our data and correlations suggest that the latest Hauterivian witnessed the progressive installation of dysaerobic conditions in the Tethys, which went along with the onset in sediment condensation, phosphogenesis and platform drowning on the northern Tethyan margin, and which culminated in the Faraoni anoxic episode. This episode is followed by further episodes of dysaerobic conditions in the Tethys and the Lower Saxony Basin, which became more frequent and progressively stronger in the late early Barremian. Platform drowning persisted and did not halt before the latest early Barremian. The late Barremian witnessed diminishing frequencies and intensities in dysaerobic conditions, which went along with the progressive installation of the Urgonian carbonate platform. Near the Barremian-Aptian boundary, the increasing density in dysaerobic episodes in the Tethyan and Lower Saxony Basins is paralleled by a change towards heterozoan carbonate production on the northern Tethyan shelf. The following return to more oxygenated conditions is correlated with the second phase of Urgonian platform growth and the period immediately preceding and corresponding to the Selli anoxic episode is characterised by renewed platform drowning and the change to heterozoan carbonate production. Changes towards more humid climate conditions were the likely cause for the repetitive installation of dys- to anaerobic conditions in the Tethyan and Boreal basins and the accompanying changes in the evolution of the carbonate platform towards heterozoan carbonate-producing ecosystems and platform drowning.

Alternations of marine and meteoric diagenetic conditions, most probably caused by relative sea level fluctuations, are recorded in an Upper Triassic (Rhaetian) patch reef in the Calcare di Zu Formation, Lombardian Basin. Three main types of cements have been distinguished: 1)isopachous fibrous calcite cement, partially to completely filling mostly secondary solution cavities; 2) radial-fibrous calcite cement in which strongly turbid relics of precursor fibrous cements suggesting a neomorphic origin can be observed, and 3) equant spar calcite found both as a last cement occluding the remaining void space after the cementation by the fibrous cements and as a neomorphic product in corals. Both marine and non-marine internal sediments are present in the patch reef. The marine internal sediments are composed of fecal pellets, peloids, micrite and bioclasts. They could be precedent, successive or contemporaneous to the isopachous marine cement and could have a geopetal disposition or may completely fill cavities. The observations made indicate that a "peloidal texture" (a nucleus of anhedral HMC crystals from which fibrous crystals radiate) could result from the introduction of peloids/fine-grained micritic intraclasts into fibrous marine cements during their growth. This texture has not been observed in geopetal infill peloids. Non marine internal sediments are composed of crystal silts and their deposition was preceded by the partial dissolution of the isopachous fibrous cements., Rivista Italiana di Paleontologia e Stratigrafia (Research In Paleontology and Stratigraphy), V. 100, N. 1