The Betlis Limestone and the Diphyoides Limestone, Lower Cretaceous (Valanginian) formations of the Helvetic nappes, have been studied in central and eastern Switzerland. The Betlis Limestone (mostly bio-pelsparites and biomicrites) represents a shallow water environment on a shelf platform reaching occasionaly into the supratidal level. The Diphyoides Limestone (spiculitic biomicrites) was deposited in deeper water on the upper and lower shelf slope. The morphology of the shelf was conditioned by synsedimentary faulting, which caused differential subsidence of individual blocks. There is evidence for phreatic fresh-water diagenesis in the Betlis Limestone. Betlis Limestone and Diphyoides Limestone are part of a cyclic sequence. The underlying formation, consisting of alternating limestone-marl beds, was deposited during high influxes of clay and fine quartz sands. After this detrital supply was terminated, the predominantly biogenic Betlis and Diphyoides Limestones formed on the shelf platform and slope, until the Hauterivian transgression interrupted the sedimentation. A hardground developed on top of the Betlis Limestone and marked the end of this major cycle. The cause for this cyclicity, which is typical for the Helvetic Lower Cretaceous, is seen in a complex interrelationship of tectonic movements, climatic changes and eustatic sea-level fluctuations.