Abstract

The depositional cycle is a simple model for interpreting the stratigraphic record. The idealized, wedge-shaped, unconformity-bounded carbonate cycle of transgression and regression differs from similar clastic cycles in lacking continental deposits and in having a flatter basal surface. The sequence of rock types for such an idealized carbonate cycle from offshore landward is planktonic-micritic limestone, coralgal limestone, oolite, molluscan-micritic limestone, pellet-micritic limestone, laminated-algal limestone, and dolomite and anhydrite. Ancient cyclic models differ from the modern owing to extinction of mainly organically controlled depositional facies through evolution.

The cyclic model is limited because of insufficient documentation, peculiarities of the Recent transgression, the effect of evolution, and the combined effects of topography and physical and biological forces on sedimentation. The facies model serves better as a base for explaining sedimentary patterns, but it does not account for rock sequences. A more complete approach to evaluating rock sequences is to combine the facies model and the recurrent cycles of transgression and regression. This approach can be extended to include aspects of diagenesis and lithification.

The irregularity and randomness of sequential events resulting from the interplay of physical and biological forces on an inherited topographic base seem to negate the strictly cyclic nature of sedimentation and to reduce the usefulness of the cyclic model.