Print this pageThe long-term organization exhibited by peritidal sections occurs on a scale of 10s to 100s of meters; yet, the question persists, what specific stratigraphic characteristics are responsible for these changes? Two end-member hypotheses present themselves. First, thickness variation within peritidal sections could occur across all facies types, wherein regions of a stratigraphic section are generally thicker or thinner bedded than the long-term average. Such cross-lithologic thickness variation could be driven by gradual changes in long-term rates of accommodation space creation. Alternatively, a second hypothesis suggests that there exist thickness-frequency relationships unique to specific lithologies. Vertical variation in the abundance of these different facies would then result in variation about the average bed thickness. Long-term variation in bed-thickness as driven by lithology-specific thickness relationships could be the result of shifting facies mosaics across the depositional surface, or to more strictly allogenic changes in facies abundance in an updip or down-dip direction driven by eustasy or tectonism. Preliminary analysis of the Ordovician Kindblade and West Spring Creek Formations of southern Oklahoma supports the hypothesis of lithology-specific thickness variation. Algal boundstone facies average 0.78 m while mud and grain-rich particulate carbonate beds while more abundant, average only 0.25 m in thickness. Stratigraphic distribution of boundstone within the sequence strongly correlates with the shape of the Fischer plot constructed for this sequence. Elementary forward models of carbonate deposition tend to support the notion of lithology-specific thickness variation as being the dominant factor in controlling large-scale stratal architecture within peritidal sequences.
AAPG Search and Discovery Article #90926©1999 AAPG Eastern Section Meeting, Indianapolis, Indiana