Incipient and final carbonate platform drowning phases of Early Cretaceous age have been recognized throughout the Tethyan realm. The resulting drowning unconformities represent often multiphase and very complex surfaces, which were formed in an interplay of physical, chemical and biological erosion, and cementation by calcite, dolomite, phosphate, glauconite, quartz and iron oxyhydroxides. They result from a multitude of processes, such as sea-level rise, sea-surface water cooling or warming, increased detrital and nutrient input, and sea surface water acidification. Sedimentological, (bio)stratigraphical and geochemical studies have been performed on the drowning surfaces. A thorough and modern study on diagenetic features of the top of these drowned carbonate platforms using optical, mineralogical and geochemical tools is however still lacking. It is therefore the aim of this project to complement our detailed knowledge on the age and sedimentology of these drowning phases with a detailed diagenetic study on a selection of well-known drowning unconformities of Valanginian, Hauterivian and Aptian age in the Jura Mountains (Eclépens) and Helvetic Alps (Pilatus, Lopper and Col de la Plaine Morte). Further areas outside the Alps will be investigated for reasons of comparison (e.g., Vercors, Bauges, SE France). The ultimate goal is to unravel the detailed history of each of these drowning phases, in order to better understand the combination of paleoenviron-mental and paleoceanographic factors leading to these drowning phases. A second goal is to trace mechanisms akin to the Early Cretaceous drowning phases, which also may play a role in the present-day widespread demise of coral reefs and carbonate platforms.