STRATAL ORDER IN PERITIDAL CARBONATE SEQUENCES

Speculation on the depositional origins and geological significance of meter-scale cycles in peritidal carbonates is becoming an increasingl y prominent facet of sequence stratigraphic theory, the understanding of which bears directly on their appropriateness as chronostratigraphi c entities as well as their usefulness as records of periodic extrabas inal forcing during sediment accumulation, In spite of the generally w ide acceptance of the stratigraphic importance and interpretational si gnificance of meter-scale parasequences, little has been done to quant itatively document the stratigraphic nature of regularly recurring lit hologic associations or to verify the predominance of such cyclicity i n shallow-water limestone/dolostone sequences. In order to determine t he statistical extents and stratigraphic scales of stratal order in su ch sequences, we have examined several long sections of peritidal carb onate both with respect to the presence or absence of Markovian lithol ogic transitions and with respect to the ''upward-shallowing'' charact er of lithofacies associations, In contrast to common wisdom, these me asures of stratal order suggest that lithologic manifestation of meter scale cyclicity is relatively uncommon, AU of the several sequences d eemed ''cyclic'' via qualitative inspection in fact contain relatively few intervals of demonstrable lithologic order, and even fewer exhibi t any tendency for contained units to shallow upsection, In reality, m ost parts of most shallow-mater carbonate sequences exhibit Little mor e stratal order than would be apparent in random sequences of peritida l lithologies. On the basis of these considerations, we suggest that d iscrimination of meter-scale cyclicity in epicratonic carbonates is pe rhaps more perceptional artifact than stratigraphic reality, Imminent and future efforts intended to fruitfully evaluate the importance of i ntrabasinal versus extrabasinal processes of sedimentation in shallow low-latitude settings should perhaps eschew more generic perceptions o f periodic paleoclimatic forcing in favor of a less regimented view to ward the importance of stochastic processes of carbonate accumulation.