FACIES SUCCESSIONS IN PERITIDAL CARBONATE SEQUENCES

High-frequency stratigraphic order in epicratonic sections is increasi ngly attributed to the widespread influence of Milankovitch-band clima te forcing and attendant eustatic sealevel change on patterns of limes tone and dolostone accumulation throughout much of the Proterozoic and Phanerozoic record. However, the actual existence of upward-shallowin g lithofacies associations has rarely been explicitly demonstrated and , in contrast to such perceptions of periodic and global accumulation, many carbonate sequences can just as readily be interpreted as largel y constituting unordered assemblages of various peritidal lithologies. Examination of published data from several long epicratonic sequences indicates that their division into shallowing cycles is a rather subj ective exercise. Inference of repeated shoaling has commonly relied mo re heavily on the stratigraphic recurrence of particular units interpr eted as representing extremely shallow to exposure conditions than on any documented tendency for groups of lithofacies to actually constitu te upward-shallowing associations. Moreover, cycle definition via such picking of cycle ''tops'' results not only in a varied assemblage of overlying substitutable ''base'' and mid-cycle lithologies, but also l eads to the designation of cycles that contain a relatively small numb er of stratal elements; most reported peritidal cycles contain only tw o stratal elements (mean = 2.25 lithofacies/shallowing cycle; n = 627) and thus are indistinguishable from sequences of randomly stacked per itidal units. Comparison of data on thicknesses and numbers of stratal elements in real-world ''cyclic'' and model chaotic sequences demonst rates that most Proterozoic and Phanerozoic sections exhibit little mo re meter-scale ordering of component units than would commonly be pres ent in sequences of randomly associated peritidal lithofacies. On the basis of these considerations, we conclude that meter-scale cyclicity in many if not most epicratonic sequences is more apparent than real, that perceptions of repeated and eustatically driven platform flooding are largely incorrect, and that a substantial component of presumed m eter-scale stratigraphic order in peritidal carbonates reflects little more than the random migration of various sedimentary subenvironments over specific platform localities during long-term accumulation of pe ritidal carbonate.