Abstract: Porosity-Permeability Development Below Parasequence Surfaces in Upper Cambrian-Lower Ordovician (Sauk) Platform Carbonates of the Northern Appalachian Passive Margin

Gerald M. Friedman

Sauk platform carbonates of the northern Appalachian passive (Gondwana) margin are composed of high-frequency stacking patterns containing fifth-order (ca. 1-5 m thick; 50-100 k.y. duration) depositional cycles. These cycles, termed parasequences in this study, display upward-shoaling patterns, commonly terminating in emergence. Parasequences surfaces are unconformities resulting from this emergence which created karst features, especially solution-collapse breccia. Whereas the carbonates, mostly fine to medium-crystalline and locally vuggy dolostones, are generally of low permeability, solution-collapse breccias increase their permeability through fractures. In addition to solution-collapse breccias, emergence generated terra-rossa soil, now lithified, as well as silcrete, now chert, and caused the dedolomitization of dolostones. Fifth-order parasequences may be the result of extraterrestrial forcing or tectonic events that involved rapid eustatic sea level changes. Hence, porosity-permeability development must likewise relate to these changes.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994