Questioning the Role of Eustasy in Sequence Stratigraphy: Linear vs. Nonlinear Models

Abstract

ABSTRACT Oxygen isotope results indicate that glacio-eustasy cannot be the main driving mechanism for the apparent 1-2 Myr. (third order) cyclicity observed in Gulf Coast sediments. It is possible that some unknown mechanism is driving eustasy at the appropriate frequency or that eustasy does not fluctuate at the required third order periodicity. Such considerations lead us to examine more closely the models we use when doing sequence stratigraphy. The standard sequence stratigraphic approach assumes the sediment record is controlled by three parameters: sediment flux, tectonic subsidence, and eustasy. Because no feedback mechanism is invoked, only linear models can be used to describe the interaction of these three parameters. Alternatively we can allow for feedback mechanisms thereby creating non-linear relationships. Such models suggest that sediment profiles may oscillate between apparent highstands and lowstands without eustatic forcing. Oxygen isotope results suggest that age correlations based on biostratigraphy are not precise enough to address the question of the importance of eustasy in sequence stratigraphy. This is because the dominant frequencies forcing eustasy appear to be 40-100 Kyrs. Our work indicates we do not yet fully understand the relationship of rapidly varying eustasy to sediment flux and subsidence and the complex system response seen in the rock record.