Comparative Cycle Stratigraphy of Cordilleran and Appalachian Late Cambrian Passive Margins: Field and Computer-Modeling Study: ABSTRACT

Abstract

Superimposed scales of cyclicity can be recognized within the Upper Cambrian carbonate sequences of the early Paleozoic Appalachian and Cordilleran passive margins. Fifth-order (10,000-100,000 years) small-scale (1-10 m) shoaling-upward cycles are evident throughout both miogeoclinal sequences. The Upper Cambrian of the Appalachians is dominated by peritidal cycles consisting of a grainstone lag overlain by cryptalgal bioherms and ribbon rocks capped by laminated dolomites. The flat-topped platform that developed behind the rimmed shelf margin favored the development of broad tidal flats that rapidly responded to even small fluctuations in sea level. Subsidence modeling has revealed synchronous deviations from model cooling curves for both passive margin sequences which suggests a eustatic control on the development of third-order (1-10 m.y.) cycles. Third-order sea level events, ranging from 2 to 8 m.y., correlate well between the geographically separate localities, further supporting a eustatic origin. Two-dimensional computer modeling of third-order cyclic sequences allows for an estimation of the probable parameters involved in their development. The model incorporates tectonic and rotational subsidence, platform flexure, isostatic compensation for sediment and water loading, linearly interpolated water depth-dependent sedimentation rates, platform slope and width, and complex superimposed scales of sea level fluctuations to generate synthetic sequences similar to themore » actual sequences in the field.« less